Patent Grant
12168943
The present disclosure relates to thermal energy storage and utilization systems. More particularly, the present disclosure relates to an energy storage system that stores electrical energy in the form of thermal energy, which can be used for the continuous supply of hot air, carbon dioxide (CO2), steam or other heated fluids, for various applications including the supply of heat to industrial processes and/or electrical power generation.
A. Variable Renewable Electricity
The combustion of fossil fuels has been used as a heat source in thermal electrical power generation to provide heat and steam for uses such as industrial process heat. The use of fossil fuels has various problems and disadvantages, however, including global warming and pollution. Accordingly, there is a need to switch from fossil fuels to clean and sustainable energy.
Variable renewable electricity (VRE) sources such as solar power and wind power have grown rapidly, as their costs have reduced as the world moves towards lower carbon emissions to mitigate climate change. But a major challenge relating to the use of VRE is, as its name suggests, its variability. The variable and intermittent nature of wind and solar power does not make these types of energy sources natural candidates to supply the continuous energy demands of electrical grids, industrial processes, etc. Accordingly, there is an unmet need for storing VRE to be able to efficiently and flexibly deliver energy at different times. Moreover, the International Energy Agency has reported that the use of energy by industry comprises the largest portion of world energy use, and that three-quarters of industrial energy is used in the form of heat, rather than electricity. Thus, there is an unmet need for lower-cost energy storage systems and technologies that utilize VRE to provide industrial process energy, which may expand VRE and reduce fossil fuel combustion.
B. Electrochemical Energy Storage Systems
Electrochemical energy storage systems such as lithium-ion batteries and other forms of electrochemistry are commonly used for storing electricity and delivering it upon demand, or “dispatch.” Electrochemical storage of energy can advantageously respond rapidly to changes in supply and demand. The high cost of this form of energy, however, has limited its wide adoption. These financial barriers pose hurdles to the wider use of electrochemical storage of energy.
C. Storage of Energy as Heat
Thermal energy in industrial, commercial, and residential applications may be collected during one time period, stored in a storage device, and released for the intended use during another period. Examples include the storage of energy as sensible heat in tanks of liquid, including water, oils, and molten salts; sensible heat in solid media, including rock, sand, concrete and refractory materials; latent heat in the change of phase between gaseous, liquid, and solid phases of metals, waxes, salts and water; and thermochemical heat in reversible chemical reactions which may absorb and release heat across many repeated cycles; and media that may combine these effects, such as phase-changing materials embedded or integrated with materials which store energy as sensible heat. Thermal energy may be stored in bulk underground, in the form of temperature or phase changes of subsurface materials, in contained media such as liquids or particulate solids, or in self-supporting solid materials.
Electrical energy storage devices such as batteries typically transfer energy mediated by a flowing electrical current. Some thermal energy storage devices similarly transfer energy into and out of storage using a single heat transfer approach, such as convective transfer via a flowing liquid or gas heat transfer medium. Notable thermal energy storage devices include heat recuperation devices such as Cowper stoves in steel blast furnaces and “regenerators” in glass melting furnaces, which absorb heat from exiting gases and return heat by preheating inlet gases. Such devices use “refractory” materials, which are resistant to high temperatures, as their energy storage media. Examples of these materials include firebrick and checkerbrick. These materials may be arranged in configurations that allow the passage of air and combustion gases through large amounts of material.
Some thermal energy systems may, at their system boundary, absorb energy in one form, such as incoming solar radiation or incoming electric power, and deliver output energy in a different form, such as heat being carried by a liquid or gas. But thermal energy storage systems must also be able to deliver storage economically. For sensible heat storage, the range of temperatures across which the bulk storage material—the “storage medium”—can be heated and cooled is an important determinant of the amount of energy that can be stored per unit of material. Thermal storage materials are limited in their usable temperatures by factors such as freezing, boiling, or thermally driven decomposition or deterioration, including chemical and mechanical effects.
Further, different uses of thermal energy-different heating processes or industrial processes-require energy at different temperatures. Electrical energy storage devices, for example, can store and return electrical energy at any convenient voltage and efficiently convert that voltage up or down with active devices. On the other hand, the conversion of lower-temperature heat to higher temperatures is intrinsically costly and inefficient. Accordingly, a challenge in thermal energy storage devices is the cost-effective delivery of thermal energy with heat content and at a temperature sufficient to meet a given application.
Some thermal energy storage systems store heat in a liquid that flows from a “cold tank” through a heat exchange device to a “hot tank” during charging, and then from the hot tank to the cold tank during discharge, delivering relatively isothermal conditions at the system outlet during discharge. Systems and methods to maintain sufficient outlet temperature while using lower-cost solid media are needed.
Thermal energy storage systems generally have costs that are primarily related to their total energy storage capacity (how many MWh of energy are contained within the system) and to their energy transfer rates (the MW of instantaneous power flowing into or out of the energy storage unit at any given moment). Within an energy storage unit, energy is transferred from an inlet into storage media, and then transferred at another time from storage media to an outlet. The rate of heat transfer into and out of storage media is limited by factors including the heat conductivity and capacity of the media, the surface area across which heat is transferring, and the temperature difference across that surface area. High rates of charging are enabled by high temperature differences between the heat source and the storage medium, high surface areas, and storage media with high heat capacity and/or high thermal conductivity.
But each of these factors can add significant cost to an energy storage device. For example, larger heat exchange surfaces commonly require 1) larger volumes of heat transfer fluids, and 2) larger surface areas in heat exchangers, both of which are often costly. Higher temperature differences require heat sources operating at relatively higher temperatures, which may cause efficiency losses (e.g. radiation or conductive cooling to the environment, or lower coefficient of performance in heat pumps) and cost increases (such as the selection and use of materials that are durable at higher temperatures). Media with higher thermal conductivity and heat capacity may also require selection of costly higher-performance materials or aggregates.
Another challenge of systems storing energy from VRE sources relates to rates of charging. A VRE source, on a given day, may provide only a small percentage of its full capacity, due to prevailing conditions. For an energy storage system that is coupled to a VRE source and that is designed to deliver continuous output, all the delivered energy must be absorbed during the period when incoming VRE is available. As a result, the peak charging rate may be some multiple of the discharge rates (e.g., 3-5×), for instance, in the case of a solar energy system, if the discharge period (overnight) is significantly longer than the charge period (during daylight). In this respect, the challenge of VRE storage is different from, for example, that of heat recuperation devices, which typically absorb and release heat at similar rates. For VRE storage systems, the design of units that can effectively charge at high rates is important, and may be a higher determinant of total system cost than the discharge rate.
1. Cowper Stoves
Examples of solid-media storage designs that achieve relatively higher isothermal conditions during discharge include Cowper stoves, which arrange a long gas path through successive portions of thermal storage material, and which reverse the flow of heat transfer gases between charging and discharging.
2. Siemens Electric Thermal Energy Storage (ETES)
This system stores energy as heat in a solid medium such as rocks or rubble that form air passages. The material is heated convectively by a heat transfer fluid that is heated externally to the storage system. European Patent 3 245 388 76 discloses such an approach at
Further, during operation of a system according to Siemens/ETES, like any system employing packed beds of loose/unstructured solids (whether rocks, gravel, manufactured spheres, or other shapes and methods), the storage media can be expected to expand and contract repeatedly, and repeatedly exert high forces during expansion on the outer container holding the media, and to settle during cooling and shrinking, causing the media and rubble to settle and potentially be crushed into small fragments or powder, diminishing their heat capacity. In addition, the expansion due to heating of bulk, unstructured material as in Siemens can be expected to exert stress on the container for the bulk material, and thus require the use of expensive insulation and container walls.
3. Conlon
Other approaches have described possible thermal energy storage systems in the abstract, without enabled designs described or referred to. US Patent Application US2018/0245485A illustrates using solar thermal energy to heat a liquid storage medium (i.e., molten salt) and refers to the possibilities of storing heat in solids at [0038] and [0039]. However, this approach does not recognize or resolve the problems and disadvantages, or provide enabling disclosure of the solutions necessary to enable such storage of VRE in solid media.
4. Stack
Still other approaches have described VRE storage systems with rapid charging. For example, Stack, in “Performance of firebrick resistance-heated energy storage for industrial heat applications and round-trip electricity storage,” describes design concepts using electrical energy as the source energy to heat and store energy in refractory solids (bricks) (https://doi.org/10.1016/j.apenergy.2019.03.100). Stack discloses a primary heating method that includes metallic resistive heating elements embedded within an array of refractory materials that are heated (charged) by radiative heat transfer from such resistive heating elements to surfaces immediately adjacent to the heating elements, and cooled (discharged) primarily by convective heat discharge using flowing air as the heat transfer fluid, and discloses the optional use of resistive heating of conductive refractory materials and heating by means of passing electrical currents through such conductive refractory materials. As discussed below, Stack's primary heating method disclosure has significant disadvantages versus the present inventions, as the proposed designs have high vulnerability to even small nonuniformities in properties of heaters and bricks; high thermal gradients due to reliance on conductive heat transfer and nonuniform heating of surfaces; and high consequences of occurrences of brick failures, including the well-known cracking and spalling modes. Because the heater wires are exposed to a small amount of brick area and heat transfer is by conduction, nonuniformity in the heating of the refractory material and potential thermal stress in that material may result, which would be exacerbated in case of failure of individual heater elements, and because internal cracking changes conductive heat transfer, any cracked areas result in substantially higher surface temperatures near such cracks, which may result in significantly higher local temperatures of heating elements, causing either early-life heater temperatures or significant limits in the practical operating temperatures of such heaters, or both. The present innovations overcome these challenges with both structural and operational features that allow the reliable operation of storage media and heaters at high temperatures and long life by intrinsically assuring more uniformity of temperatures throughout the storage media, even in the presence of nonuniformities of heaters and bricks and cracking and spalling of brick.
5. Others
United States patent application US20180179955A1 is directed to baffled thermoclines in thermodynamic cycle systems. Solid state thermoclines are used in place of heat exchangers in an energy storage system. However, this teaches limiting the conductive and/or radiative transfer of heat within different zones defined by the baffle structure.
United States patent U.S. Pat. No. 9,370,044B2 (McDonald) is directed to a thermal storage device controller that load-balances requirements of a user to manage heating, and discloses the use of bricks with heating elements disposed in the bricks. Controllers are disclosed that can have plural operating modes, each operating mode being associated with a default core temperature, such as a first operating mode and a standby operating mode. The operating modes may be set based on a season. The McDonald design may also include a controller that receives information associated with forecasted climatic conditions, and set operational temperatures based on the forecasted climatic conditions. However, this approach does not address the above problems and disadvantages with respect to the charging and discharging of the brick.
The above-described approaches have various problems and disadvantages. Earlier systems do not take into account several critical phenomena in the design, construction, and operation of thermal energy storage systems, and thus does not facilitate such systems being built and efficiently operated. More specifically, current designs fail to address “thermal runaway” and element failure due to non-uniformities in thermal energy charging and discharging across an array of solid materials, including the design of charging, discharging, and unit controls to attain and restore balances in temperature across large arrays of thermal storage material.
Thermal energy storage systems with embedded radiative charging and convective discharging are in principle vulnerable to “thermal runaway” or “heat runaway” effects. The phenomenon may arise from imbalances, even small imbalances, in local heating by heating elements and in cooling by heat transfer fluid flow. The variations in heating rate and cooling rate, unless managed and mitigated, may lead to runaway temperatures that cause failures of heaters and/or deterioration of refractory materials. Overheating causes early failures of heating elements and shortened system life. In Stack, for example, the bricks closest to the heating wire are heated more than the bricks that are further away from the heating wire. As a result, the failure rate for the wire is likely to be increased, reducing heater lifetime.
One effect that further exacerbates thermal runaway is the thermal expansion of air flowing in the air conduits. Hotter air expands more, causing a higher outlet velocity for a given inlet flow, and thus a higher hydraulic pressure drop across the conduit, which may contribute to a further reduction of flow and reduced cooling during discharge. Thus, in successive heating and cooling cycles, progressively less local cooling can occur, resulting in still greater local overheating.
The effective operation of heat supply from thermal energy storage relies upon continuous discharge, which is a particular challenge in systems that rely upon VRE sources to charge the system. Solutions are needed that can capture and store that VRE energy in an efficient manner and provide the stored energy as required to a variety of uses, including a range of industrial applications, reliably and without interruption.
Previous systems do not adequately address problems associated with VRE energy sources, including variations arising from challenging weather patterns such as storms, and longer-term supply variations arising from seasonal variations in VRE generation. In this regard, there is an unmet need in the art to provide efficient control of energy storage system charging and discharging in smart storage management. Current designs do not adequately provide storage management that considers a variety of factors, including medium-term through short-term weather forecasts, VRE generation forecasts, and time-varying demand for energy, which may be determined in whole or in part by considerations such as industrial process demand, grid energy demand, real-time electricity prices, wholesale electricity market capacity prices, utility resource adequacy value, and carbon intensity of displaced energy supplies. A system is needed that can provide stored energy to various demands that prioritizes by taking into these factors, maximizing practical utility and economic efficiencies.
There are a variety of unmet needs relating generally to energy, and more specifically, to thermal energy. Generally, there is a need to switch from fossil fuels to clean and sustainable energy. There is also a need to store VRE to deliver energy at different times in order to help meet society's energy needs. There is also a need for lower-cost energy storage systems and technologies that allow VRE to provide energy for industrial processes, which may expand the use of VRE and thus reduce fossil fuel combustion. There is also a need to maintain sufficient outlet temperature while using lower-cost solid media.
Still further, there is a need to design VRE units that can be rapidly charged at low cost, supply dispatchable, continuous energy as required by various industrial applications despite variations in VRE supply, and that facilitate efficient control of charging and discharging of the energy storage system.
The example implementations advance the art of thermal energy storage and enable the practical construction and operation of high-temperature thermal energy storage systems which are charged by VRE, store energy in solid media, and deliver high-temperature heat.
Aspects of the example implementations relate to a system for thermal energy storage, including an input, (e.g., electricity from a variable renewable electricity (VRE) source), a container having sides, a roof and a lower platform, a plurality of vertically oriented thermal storage units (TSUs), inside the container, the TSUs each including a plurality of stacks of bricks and heaters attached thereto, each of the heaters being connected to the input electricity via switching circuitry, an insulative layer interposed between the plurality of TSUs, the roof and at least one of the sides, a duct formed between the insulative layer and a boundary formed by the sides, an inner side of the roof and the lower platform of the container, a blower that blows relatively cooler fluid such as air or another gas (e.g. CO2) along the flow path, an output (e.g., hot air at prescribed temperature to industrial application), a controller that controls and co-manages the energy received from the input and the hot air generated at the output based on a forecast associated with an ambient condition (e.g., season or weather) or a condition (e.g., output temperature, energy curve, etc.). The exterior and interior shapes of the container may be rectangular, cylindrical (in which case “sides” refers to the cylinder walls), or other shapes suitable to individual applications.
The terms air, fluid and gas are used interchangeably herein to refer to a fluid heat transfer medium of any suitable type, including various types of gases (air, CO2, oxygen and other gases, alone or in combination), and when one is mentioned it should be understood that the others can equally well be used. Thus, for example, “air” can be any suitable fluid or gas or combinations of fluids or gases.
According to another aspect, with regard to the TSUs as explained above, the bricks are configured in arrays. The bricks have elongate channels or slots through them, which are vertically oriented in the stack and induce turbulent flow for effective heat transfer to the fluid flowing through the stack. The arrays of bricks define radiation chambers, either between bricks or formed within the bricks themselves, or both, which enable efficient distribution and absorption of heat energy through the stack by exposing surfaces of bricks directly or indirectly to heat radiation from the heater elements, heating brick throughout the stack more quickly and uniformly than by conduction or convection alone, particularly at high temperatures. The elongate channels have a long axis and a short axis, and may have curved or rounded corners.
The bricks may be stacked in a 3D alternating (e.g., checkerboard) pattern, with alternating brick-chamber-brick, etc. In each dimension (x, y, z). Vertical air flow paths are formed through channels in at least some of the bricks, then through the next radiation chamber, then through the next channels of a subsequent brick, and so on, from the bottom of the stack to the top. Resistive heaters are positioned in gaps formed between bricks, orthogonal to the channels, to heat the stack using incoming electricity (from an energy source, such as solar, wind, etc.). A blower directs air from the bottom of the stack to the top to discharge the stack and provide hot air for industrial use. In some implementations, the stacks are enclosed in a structure that is designed for seismic isolation to avoid damage during a seismic event such as an earthquake.
The structure is also designed for the circulation of air from the blower through pathways surrounding the core array structure, to provide dynamic insulation between the stacks, the foundation and the structure. One arrangement provides such circulation to an upper portion of the structure, and then down one or more sides of the structure, and then up through the brick array to heat the air to a desired temperature range for discharge to industrial uses.
Thermal energy storage (TES) systems according to the present designs can advantageously be integrated with or coupled to steam generators, including heat recovery steam generators (HRSGs) and once-through steam generators (OTSGs). The terms “steam generator”, “HRSG”, and “OTSG” are used interchangeably herein to refer to a heat exchanger that transfers heat from a first fluid into a second fluid, where the first fluid may be air circulating from the TSU and the second fluid may be water (being heated and/or boiled), oil, salt, air, CO2, or another fluid. In such implementations, the heated first fluid is discharged from a TES unit and provided as input to the steam generator, which extracts heat from the discharged fluid to heat a second fluid, including producing steam, which heated second fluid may be used for any of a variety of purposes (e.g. to drive a turbine to produce shaft work or electricity). After passing through a turbine, the second fluid still contains significant heat energy, which can be used for other processes. Thus, the TES system may drive a cogeneration process. The first fluid, upon exiting the steam generator, can be fed back as input to the TES, thus capturing waste heat to effectively preheat the input fluid. Waste heat from another process may also preheat input fluid to the TES.
According to yet another aspect, an integrated thermal energy storage calciner system is provided. The TES unit delivers a gaseous fluid output connected to a calciner or kiln, wherein the gaseous fluid output provides a first portion of the heat and/or temperature required to drive the calcination process, and an optional second heat source may provide further energy and/or temperature. The TES unit may have a gaseous fluid output directly connected to all or any portion of a material transformation system that includes material drying, preheating or other conditioning, and calcination, wherein the TES provides all or substantially all of the energy required to drive such material transformation processes. The TES unit in some applications has a gaseous fluid output indirectly connected to a calciner/kiln for activation of a material to remove unwanted substances (for example CO2, in a calcination process for cement production), wherein the gaseous fluid output is configured to provide a primary working fluid at a higher temperature that exchanges heat with a secondary working fluid at a lower temperature that in turn heats a solid raw material. The primary working gas is hot gas for convective heat transfer (e.g., at the calcination plant). A feedback system may recirculate the post-process gas to the TES for reheating. Applications may include construction material, biomass and/or food processing.
Additional aspects may include a solid-oxide electrolysis application that includes the TES unit coupled to an electrolysis system. A high-temperature solid oxide electrolyzer converts water into hydrogen and oxygen in a hydrogen generation unit (e.g., for use in a fuel cell). The electrolyzer includes an anode, a cathode and a solid ceramic (oxide) electrolyte, and uses heat (e.g., output of the thermal energy storage (TES)) to decrease the electrical energy needed to be used in the electrolysis process. The heat that flows from the TES stack is received at the solid oxide electrolysis cells (SOEC) as hot air and/or steam, at a rate that is determined by a controller (manual and/or automatic) that sets the flow rate to maintain the SOEC at a desired temperature (e.g., 860° C.). The electricity source may be any of a variety of sources, such as a photovoltaic (PV) cell, an electricity output application associated with the TES, or stored electricity at the SOEC itself. The hydrogen generated by the SOEC by may be used in a wide variety of known applications, including in a hydrogen filling station (e.g., electric vehicle charging station), or other industrial application (e.g., renewable diesel refinery), and the highly oxygenated by-product may also be used for industrial or commercial applications, including power generation. The lower-temperature waste heat released by the SOEC (e.g. at 650° C.) can optionally be directed and optionally supplemented by higher-temperature heat by the TES, and coupled into a steam generator for the use of such heat or used for another industrial process. As an alternative to electrolysis of water to hydrogen, electrolysis of other gases may be performed, such as carbon dioxide to carbon monoxide, either separately or in combination with electrolysis of water.
According to an additional aspect, a DC/DC power conversion system includes an array of galvanically isolated individual converters, each receiving an input from a photovoltaic (PV) array at a primary side, a secondary side of each of the individual converters coupled in series for higher output voltage, and in parallel for higher output current, a combiner coupled to the array and other arrays, and a junction box including a plurality of high voltage switches coupled, by a variable DC line to the combiner, having an output to a thermal storage unit (TSU) or a DC charging system.
According to another aspect, a dynamic insulation system include a container having sides, a roof and a lower platform, a plurality of vertically oriented thermal storage units (TSUs) spaced apart from one another, an insulative layer interposed between the plurality of TSUs, the roof and at least one of the sides and floor, a duct formed between the insulative layer and a boundary formed by the sides, an inner side of the roof and the lower platform of the container, and a blower that blows unheated air along the air flow path, upward from the platform to a highest portion of the upper portion, such that the air path is formed from the highest portion of the roof to the platform, and is heated by the plurality of TSUs, and output from the TES apparatus. The unheated air along the flow path forms an insulated layer and is preheated by absorbing heat from the insulator.
Further aspects include applications associated with a carbon dioxide separator. The separation of carbon dioxide from other gases including ambient air and combustion exhaust gases is often beneficially accomplished by processes that use large amounts of heat to regenerate a chemical that absorbs or reacts with carbon dioxide. Such processes include but are not limited to processes that use a carbonation/calcination reaction cycle, for example using calcium or potassium reactions, or absorption/adsorption/release cycles, for example using liquid or solid materials including zeolites or amines. The provision of heat to serve these capture processes from VRE may be beneficial in further reducing the emissions and costs such of carbon capture processes. For example, a combustion exhaust gas input from an industrial source, or from a direct air capture (DAC) unit, may require heat to drive a solvent “reboiler,” a steam generator or a calcium carbonate calciner, to raise the temperature of a reactant that causes the release separation of carbon dioxide. The combustion exhaust gas is received via a heat exchanger and a stripper tower. A carbon dioxide compressor receives power generated by a steam turbine connected to the TES system, and compresses the selectively separated carbon dioxide. Compressed carbon dioxide may be input to a solid oxide electrolysis cell (SOEC), industrial processes, or geologic sequestration.
The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate example implementations of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
In the drawings, similar components and/or features may have the same reference label.
Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
Aspects of the example implementations, as disclosed herein, relate to systems, methods, materials, compositions, articles, and improvements for a thermal energy storage system for power generation for various industrial applications.
The present disclosure is directed to effectively storing VRE as thermal energy in solid storage media.
While systems such as Cowper stoves store high-temperature energy in solid media, such units are charged and discharged at similar rates, and are heated and cooled primarily by convection, by flowing heat transfer gases. Pressure differences caused by any combination of buoyancy-mediated draft (the “stack effect”) and induced or forced flow (i.e., flow caused by a fluid movement system which may include fans or blowers) moves the heat transfer fluids through the solid media. Approaches such as this use convection for charge and discharge, with the heat transfer fluid being heated externally to the storage media array. But applying this approach to VRE storage disadvantageously requires large surface area and is therefore costly, because such convective heat transfer systems must operate at the much higher rates associated with VRE charging than heat delivery.
Thermal storage systems include various element heaters, storage media, enclosing structures, and heat transfer subsystems, all of which may be affected by temperatures of the storage system and by the rate of change of such temperatures. Excessive temperatures and/or excessive rate of change of temperature can induce failures due to various effects. Some of these effects include material softening, oxide spallation, metal recrystallization, oxidation, and thermal stress-induced cracking and failure.
Rising temperatures within a thermal storage unit cause thermal expansion of the materials that are used for thermal energy storage. Nonuniformities in these temperatures can cause stress in solids. Such temperature nonuniformities may arise during both discharging periods (due to flowing heat transfer fluids that cool the storage media) and charging periods (due to the high heat transfer rate). In general, a heat flux at one surface causes nonuniform temperatures within the solid media; such temperature nonuniformity causes heat to flow by conduction to cooler zones, at a rate determined by the thermal conductivity of the material and the magnitude of the temperature nonuniformity.
Temperature nonuniformities may also be caused by repeated heating and cooling of a thermal storage array that includes heating elements and channels through which the heat transfer fluid flows. These nonuniformities may be amplified in successive cycles of heating and cooling, which in turn causes localized areas of a storage system to become excessively hot or cool during operation. This phenomenon is known as “thermal runaway,” and can lead to early-life failure of thermal storage arrays. Nonuniformities in temperature may be exacerbated when individual heating elements fail, resulting in the zone of a storage unit having the failed heating elements being unheated, while another zone of the storage unit continues to have active heating elements and high temperatures.
Finally, VRE storage systems must operate under an exacting set of standards. They should be able to fully charge during periods that the variable energy is available (e.g., during daylight hours in the case of solar energy, as defined by a solar diurnal cycle that begins with the time of sunrise and ends with the time of sunset; it is understood that the time of sunrise and sunset can vary depending on physical location in terms of latitude and longitude, geography in terms of terrain, date, and season). They need to consistently deliver energy, even though their input energy source is not always predictably available. This means that these systems must sometimes be able to deliver output energy during periods that are longer than the periods of input-energy availability. VRE storage systems need to be able to operate under these conditions daily over decades of use.
The present disclosure relates to the field of thermal energy storage and utilization systems, and addresses the above-noted problems. A thermal energy storage system is disclosed that stores electrical energy in the form of thermal energy in a charging mode, and delivers the stored energy in a discharging mode. The discharging can occur at the same time as charging; i.e., the system may be heated by electrical energy at the same time that it is providing a flow of convectively heated air. The discharged energy is in the form of hot air, hot fluids in general, steam, heated CO2, heated supercritical CO2, and/or electrical power generation, and can be supplied to various applications, including industrial uses. The disclosed implementations include efficiently constructed, long-service-life thermal energy storage systems having materials, fabrication, physical shape, and other properties that mitigate damage and deterioration from repeated temperature cycling.
Optionally, heating of the elements of the storage unit may be optimized, so as to store a maximum amount of heat during the charging cycle. Alternatively, heating of elements may be optimized to maximize heating element life, by means including minimizing time at particular heater temperatures, and/or by adjusting peak charging rates and/or peak heating element temperatures. Still other alternatives may balance these competing interests. Specific operations to achieve these optimizations are discussed further below.
Example implementations employ efficient yet economical thermal insulation. Specifically, a dynamic insulation design may be used either by itself or in combination with static primary thermal insulation. The disclosed dynamic insulation techniques provide a controlled flow of air inside the system to restrict dissipation of thermal energy to the outside environment, which results in higher energy storage efficiency.
In the depicted implementation, thermal energy storage system 10 is coupled to input energy source 2, which may include one or more sources of electrical energy. Source 2 may be renewable, such as photovoltaic (PV) cell or solar, wind, geothermal, etc. Source 2 may also be another source, such as nuclear, natural gas, coal, biomass, or other. Source 2 may also include a combination of renewable and other sources. In this implementation, source 2 is provided to thermal energy storage system 10 via infrastructure 4, which may include one or more electrical conductors, commutation equipment, etc. In some implementations, infrastructure 4 may include circuitry configured to transport electricity over long distances; alternatively, in implementations in which input energy source 2 is located in the immediate vicinity of thermal energy storage system 10, infrastructure 4 may be greatly simplified. Ultimately, infrastructure 4 delivers energy to input 5 of thermal energy storage system 10 in the form of electricity.
The electrical energy delivered by infrastructure 4 is input to thermal storage structure 12 within system 10 through switchgear, protective apparatus and active switches controlled by control system 15. Thermal storage structure 12 includes thermal storage 14, which in turn includes one more assemblages (e.g., 14A, 14B) of solid storage media (e.g., 13A, 13B) configured to store thermal energy.
These assemblages are variously referred to throughout this disclosure as “stacks,” “arrays,” and the like. These terms are intended to be generic and not connote any particular orientation in space, etc. In general, an array can include any material that is suitable for storing thermal energy and can be oriented in any given orientation (e.g., vertically, horizontally, etc.).
Likewise, the solid storage media within the assemblages may variously be referred to as thermal storage blocks, bricks, etc. In implementations with multiple arrays, the arrays may be thermally isolated from one another and are separately controllable, meaning that they are capable of being charged or discharged independently from one another. This arrangement provides maximum flexibility, permitting multiple arrays to be charged at the same time, multiple arrays to be charged at different times or at different rates, one array to be discharged while the other array remains charged, etc.
Thermal storage 14 is configured to receive electrical energy as an input. As will be explained in greater detail below, the received electrical energy may be provided to thermal storage 14 via resistive heating elements that are heated by electrical energy and emit heat, primarily as electromagnetic radiation in the infrared and visible spectrum. During a charging mode of thermal storage 14, the electrical energy is released as heat from the resistive heating elements, transferred principally by radiation emitted both by the heating elements and by hotter solid storage media, and absorbed and stored in solid media within storage 14. When an array within thermal storage 14 is in a discharging mode, the heat is discharged from thermal storage structure 12 as output 20. As will be described, output 20 may take various forms, including a fluid such as hot air. (References to the use of “air” and “gases” within the present disclosure may be understood to refer more generally to a “fluid.”) The hot air may be provided directly to a downstream energy consuming process 22 (e.g., an industrial application), or it may be passed through a steam generator (not shown) to generate steam for process 22. More detail regarding steam generation is provided later in this Section, and more detail regarding various potential downstream processes is provided in Section IV.
Additionally, thermal energy storage system 10 includes a control system 15. Control system 15, in various implementations, is configured to control thermal storage 14, including through setting operational parameters (e.g., discharge rate), controlling fluid flows, controlling the actuation of electromechanical or semiconductor electrical switching devices, etc. The interface 16 between control system 15 and thermal storage structure 12 (and, in particular thermal storage 14) is indicated in
Control system 15 may also interface with various entities outside thermal energy storage system 10. For example, control system 15 may communicate with input energy source 2 via an input communication interface 17B. For example, interface 17B may allow control system 15 to receive information relating to energy generation conditions at input energy source 2. In the implementation in which input energy source 2 is a photovoltaic array, this information may include, for example, current weather conditions at the site of source 2, as well as other information available to any upstream control systems, sensors, etc. Interface 17B may also be used to send information to components or equipment associated with source 2.
Similarly, control system 15 may communicate with infrastructure 4 via an infrastructure communication interface 17A. In a manner similar to that explained above, interface 17A may be used to provide infrastructure information to control system 15, such as current or forecast VRE availability, grid demand, infrastructure conditions, maintenance, emergency information, etc. Conversely, communication interface 17A may also be used by control system 15 to send information to components or equipment within infrastructure 4. For example, the information may include control signals transmitted from the control system 15, that controls valves or other structures in the thermal storage structure 12 to move between an open position and a closed position, or to control electrical or electronic switches connected to heaters in the thermal storage 14. Control system 15 uses information from communication interface 17A in determining control actions, and control actions may adjust closing or firing of switches in a manner to optimize the use of currently available electric power and maintain the voltage and current flows within infrastructure 4 within chosen limits.
Control system 15 may also communicate downstream using interfaces 18A and/or 18B. Interface 18A may be used to communicate information to any output transmission structure (e.g., a steam transmission line), while interface 18B may be used to communicate with downstream process 22. For example, information provided over interfaces 18A and 18B may include temperature, industrial application demand, current or future expected conditions of the output or industrial applications, etc. As will be explained in greater detail below, control system 15 may control the input, heat storage, and output of thermal storage structure based on a variety of information. As with interfaces 17A and 17B, communication over interfaces 18A and 18B may be bidirectional—for example, system 10 may indicate available capacity to downstream process 22.
Still further, control system 15 may also communicate with any other relevant data sources (indicated by reference numeral 21 in
As will be described in detail below, thermal energy storage system 10 is configured to efficiently store thermal energy generated from input energy source 2, and deliver output energy in various forms to a downstream process 22. In various implementations, input energy source 2 may be from renewable energy and downstream process 22 may be an industrial application that requires an input such as steam or hot air.
Through various techniques, including arrays of thermal storage blocks that use radiant heat transfer to efficiently storage energy and a lead-lag discharge paradigm that leads to desirable thermal properties such as the reduction of temperature nonuniformities within thermal storage 14, system 10 may advantageously provide a continuous (or near-continuous) flow of output energy based on an intermittently available source. The use of such a system has the potential to reduce the reliance of industrial applications on fossil fuels.
The electricity generated by source 201 is provided to the thermal storage structure within the thermal energy storage system. In
In the depicted implementation, a blower 213 drives air or other fluid to thermal storage 205 such that the air is eventually received at a lower portion of each of the arrays 209. The air flows upward through the channels and chambers formed by bricks in each of the arrays 209, with flow controlled by louvers (as shown 1611 in
Once the heat has been output in the form of a fluid such as hot air, the fluid may be provided for one or more downstream applications. For example, hot air may be used directly in an industrial process that is configured to receive the hot air, as shown at 217. Further, hot air may be provided as a stream 219 to a heat exchanger 218 of a steam generator 222, and thereby heats a pressurized fluid such as air, water, CO2 or other gas. In the example shown, as the hot air stream 219 passes over a line 221 that provides the water from the pump 223 as an input, the water is heated and steam is generated as an output 225, which may be provided to an industrial application as shown at 227.
Control system 399 may include a variety of sensors/devices, including one or more voltage and current sensors integrated with power conditioning equipment 311 and switching equipment 303, a wind sensor 301, a sky camera 302 that detects passing clouds, and/or solar radiation sensor 303. Control system 399 may also receive data via a network connection from various remote data sources, such as cloud data source 304. Accordingly, control system 399 may access many different forms of information, including, for example, weather forecasts and market conditions such as the availability of electricity, cost of electricity, presence of other energy sources, etc.
Control system 399 is also configured to communicate with input energy sources via power conversion and control devices such as 303, 311, 321, and 341. These controllers may be configured not only to pass data to control system 399, but also to receive commands from control system 399. Control system 399 may be configured in some instances to switch between input power sources in some instances by communicating with these controllers. Accordingly, in one implementation, control system 399 might analyze numerous different external data sources to determine which of several available input energy sources should be utilized, and then communicate with controllers such as 311 and 321 to select an input source. In a similar fashion, control system 399 may also communicate with downstream devices or systems, such as a steam generator 334, a hot air output 335, and an industrial application 336. Control system 399 may use information from such input sensors to determine actions such as selectively activating switches 303-1 through 303-N, controlling heaters within array 330. Such control actions may include rapid-sequence activation of switches 303-1 through 303-N in patterns to present varying total resistive loads in response to varying available power, so as to manage voltage and current levels at controllers 311, 321, and 341 within predetermined ranges.
Information within the thermal storage structure itself may also be used by control system 399. For example, a variety of sensors and communication devices may be positioned within the bricks, arrays, storage units and other locations within the thermal storage structure, as represented as electrical switches, including semiconductor switches, by 303-1 through 303-N. The information may include state of charge, temperature, valve position, and numerous other operating parameters, and the switches may control the operation of the thermal storage system 330, based on a signal received from the control system 399, for example. Such control actions may include activation of switches 303-1 through 303-N so as to manage temperatures and state of charge within array within predetermined ranges.
Control system 399 can communicate with devices such as 303 to perform operations based on received data that may be either internal and/or external to the thermal storage structure. For example, control system 399 may provide commands to heating elements controls, power supply units, discharge blowers pumps, and other components to perform operations such as charging and discharging. Control system 399 may specifically receive data from thermal storage system 330, including from subsections such as 350, and individual bricks or heating elements such as 305-1 through 305-N.
The ability to receive data from numerous locations inside and outside the thermal storage structure permits system 300 to be able to operate in a flexible and efficient manner, which is advantageous given the challenges that arise from attempting to deliver a continuous supply of output energy from a variable source.
A thermal storage structure such as that depicted in
As has been described, thermal storage structure 400 includes outer structure 401 such walls, a roof, as well as thermal storage 403 in a first section of the structure. The OTSG is located in a second section of the structure, which is separated from the first section by thermal barrier 425. During a charging mode, thermal energy is stored in thermal storage 403. During a discharging mode, the thermal energy stored in thermal storage 403 receives a fluid flow (e.g., air) by way of a blower 405. These fluid flows may be generated from fluid entering structure 400 via an inlet valve 419, and include a first fluid flow 412A (which may be directed to a first stack within thermal storage 403) and a second fluid flow 412B (which may be directed to a second stack within thermal storage 403).
As the air or other fluid directed by blower 405 flows through the thermal storage 403 from the lower portion to the upper portion, it is heated and is eventually output at the upper portion of thermal storage 403. The heated air, which may be mixed at some times with a bypass fluid flow 412C that has not passed through thermal storage 402, is passed over a conduit 409 through which flows water or another fluid pumped by the water pump 407. In one implementation, the conduit forms a long path with multiple turns, as discussed further in connection with
As shown in
For applications using water with a higher mineral content, an OTSG may be a better option. One such application is oil extraction, in which feed water for a steam generator may be reclaimed from a water/oil mixture produced by a well. Even after filtering and softening, such water may have condensed solid concentrations on the order of 10,000 ppm or higher. The lack of recirculation in an OTSG enables operation in a mode to reduce mineral deposit formation; however, an OTSG needs to be operated carefully in some implementations to avoid mineral deposits in the OTSG water conduit. For example, having some fraction of water droplets present in the steam as it travels through the OTSG conduit may be required to prevent mineral deposits by retaining the minerals in solution in the water droplets. This consideration suggests that the steam quality (vapor fraction) of steam within the conduit must be maintained below a specified level. On the other hand, a high steam quality at the output of the OTSG may be important for the process employing the steam. Therefore, it is advantageous for a steam generator powered by VRE through TES to maintain close tolerances on outlet steam quality. There is a sensitive interplay among variables such as input water temperature, input water flow rate and heat input, which must be managed to achieve a specified steam quality of output steam while avoiding damage to the OTSG.
Implementations of the thermal energy storage system disclosed herein provide a controlled and specified source of heat to an OTSG. The controlled temperature and flow rate available from the thermal energy storage system allows effective feed-forward and feedback control of the steam quality of the OTSG output. In one implementation, feed-forward control includes using a target steam delivery rate and steam quality value, along with measured water temperature at the input to the water conduit of the OTSG, to determine a heat delivery rate required by the thermal energy storage system for achieving the target values. In this implementation, the control system can provide a control signal to command the thermal storage structure to deliver the flowing gas across the OTSG at the determined rate. In one implementation, a thermal energy storage system integrated with an OTSG includes instrumentation for measurement of the input water temperature to the OTSG.
In one implementation, feedback control includes measuring a steam quality value for the steam produced at the outlet of the OTSG, and a controller using that value to adjust the operation of the system to return the steam quality to a desired value. Obtaining the outlet steam quality value may include separating the steam into its liquid and vapor phases and independently monitoring the heat of the phases to determine the vapor phase fraction. Alternatively, obtaining the outlet steam quality value may include measuring the pressure and velocity of the outlet steam flow and the pressure and velocity of the inlet water flow, and using the relationship between values to calculate an approximation of the steam quality. Based on the steam quality value, a flow rate of the outlet fluid delivered by the thermal storage to the OTSG may be adjusted to achieve or maintain the target steam quality. In one implementation, the flow rate of the outlet fluid is adjusted by providing a feedback signal to a controllable element of the thermal storage system. The controllable element may be an element used in moving fluid through the storage medium, such as a blower or other fluid moving device, a louver, or a valve.
The steam quality measurement of the outlet taken in real time may be used as feedback by the control system to determine the desired rate of heat delivery to the OTSG. To accomplish this, an implementation of a thermal energy storage system integrated with an OTSG may include instruments to measure inlet water velocity and outlet steam flow velocity, and, optionally, a separator along with instruments for providing separate measurements of the liquid and vapor heat values. In some implementations, the tubing in an OTSG is arranged such that the tubing closest to the water inlet is positioned in the lowest temperature portion of the airflow, and that the tubing closest to the steam exit is positioned in the highest temperature portion of the airflow. In some implementations of the present innovations, the OTSG may instead be configured such that the highest steam quality tubes (closest to the steam outlet) are positioned at some point midway through the tubing arrangement, so as to enable higher inlet fluid temperatures from the TSU to the OTSG while mitigating scale formation within the tubes and overheating of the tubes, while maintaining proper steam quality. The specified flow parameters of the heated fluid produced by thermal energy storage systems as disclosed herein may in some implementations allow precise modeling of heat transfer as a function of position along the conduit. Such modeling may allow specific design of conduit geometries to achieve a specified steam quality profile along the conduit.
As shown in
Certain industrial applications may be particularly well-suited for cogeneration. For example, some applications use higher temperature heat in a first system, such as to convert the heat to mechanical motion as in the case of a turbine, and lower-temperature heat discharged by the first system for a second purpose, in a cascading manner; or an inverse temperature cascade may be employed. One example involves a steam generator that makes high-pressure steam to drive a steam turbine that extracts energy from the steam, and low-pressure steam that is used in a process, such as an ethanol refinery, to drive distillation and electric power to run pumps. Still another example involves a thermal energy storage system in which hot gas is output to a turbine, and the heat of the turbine outlet gas is used to preheat inlet water to a boiler for processing heat in another steam generator (e.g., for use in an oilfield industrial application). In one application, cogeneration involves the use of hot gas at e.g. 840° C. to power or co-power hydrogen electrolysis, and the lower temperature output gas of the hydrogen electrolyzer, which may be at about 640° C., is delivered alone or in combination with higher-temperature heat from a TSU to a steam generator or a turbine for a second use. In another application, cogeneration involves the supply of heated gas at a first temperature e.g. 640° C. to enable the operation of a fuel cell, and the waste heat from the fuel cell which may be above 800° C. is delivered to a steam generator or a turbine for a second use, either alone or in combination with other heat supplied from a TSU.
A cogeneration system may include a heat exchange apparatus that receives the discharged output of the thermal storage unit and generates steam. Alternately, the system may heat another fluid such as supercritical carbon dioxide by circulating high-temperature air from the system through a series of pipes carrying a fluid, such as water or CO2, (which transfers heat from the high-temperature air to the pipes and the fluid), and then recirculating the cooled air back as an input to the thermal storage structure. This heat exchange apparatus is an HRSG, and in one implementation is integrated into a section of the housing that is separated from the thermal storage.
The HRSG may be physically contained within the thermal storage structure, or may be packaged in a separate structure with ducts conveying air to and from the HRSG. The HRSG can include a conduit at least partially disposed within the second section of the housing. In one implementation, the conduit can be made of thermally conductive material and be arranged so that fluid flows in a “once-through” configuration in a sequence of tubes, entering as lower-temperature fluid and exiting as higher temperature, possibly partially evaporated, two-phase flow. As noted above, once-through flow is beneficial, for example, in processing feedwater with substantial dissolved mineral contaminants to prevent accumulation and precipitation within the conduits.
In an OTSG implementation, a first end of the conduit can be fluidically coupled to a water source. The system may provide for inflow of the fluids from the water source into a first end of the conduit, and enable outflow of the received fluid or steam from a second end of the conduit. The system can include one or more pumps configured to facilitate inflow and outflow of the fluid through the conduit. The system can include a set of valves configured to facilitate controlled outflow of steam from the second end of the conduit to a second location for one or more industrial applications or electrical power generation. As shown in
The output of the steam generator may be provided for one or more industrial uses. For example, steam may be provided to a turbine generator that outputs electricity for use as retail local power. The control system may receive information associated with local power demands, and determine the amount of steam to provide to the turbine, so that local power demands can be met.
In some implementations, the “hybrid” or joint supply of steam or process heat from a thermal storage unit powered by VRE and a conventional furnace or boiler powered by fossil fuel is beneficial.
A controller 9903 may control or partially control the operation of the fuel-fired heater 9905 and the VRE storage heater 9901, with inputs to the controller including information derived from forecasts of weather 9910, the pricing and availability of electricity 9911, the pricing and availability of fuel 9911, the state of charge of the TSU 9915, the readiness and state of the equipment 9913, and the current and planned energy requirements of the connected load 9914. The controller may schedule and control the operation of TSU charging, fuel combustion, and TSU output in a means to meet the needs of the use at the lowest possible CO2 emissions and/or the lowest total operating cost.
In addition to the generation of electricity, the output of the thermal storage structure may be used for industrial applications as explained below. Some of these applications may include, but are not limited to, electrolyzers, fuel cells, gas generation units such as hydrogen, carbon capture, manufacture of materials such as cement, calcining applications, as well as others. More details of these industrial applications are provided further below.
Further, switchgear or other electrical and electronic equipment may be installed at thermal storage structure 701. This is made possible due to the dynamic insulation, which reduces the heat that is transferred to the outer surface of structure 701, which in turn allows for equipment having a limited temperature operating range to be positioned there. Such equipment may include sensors, telecommunication devices, controllers, or other equipment required to operate structure 701.
Additionally, one or more base isolators 1115 (which may include elastic and/or plastic deformation materials which may act respectively as springs and as energy absorbers) may be provided below the foundation that reduce the peak forces experienced during seismic events. In some implementations, the base isolator may reduce the peak force in an earthquake such that 10% or less of the force from the earthquake is transferred to the structures above the base isolator. The above percentages may vary as a function of relative motion between the ground and base isolator. Just as an example, the thermal energy storage structure may include a space of 45 cm to 60 cm between the ground and the slab to reduce the g-forces transmitted to stack by 90%. By providing the seismic reinforcing structure 1101, the thermal storage structure may be more safely operated in earthquake-prone regions.
It is generally beneficial for a thermal storage structure to minimize its total energy losses via effective insulation, and to minimize its cost of insulation. Some insulation materials are tolerant of higher temperatures than others. Higher-temperature tolerant materials tend to be more costly.
The outer container includes roof 1401, walls 1403, 1407 and a foundation 1409. Within the outer container, a layer of insulation 1411 is provided between the outer container and columns of bricks in the stack 1413, the columns being represented as 1413a, 1413b, 1413c, 1413d and 1413e. The heated fluid that is discharged from the upper portion of the columns of bricks 1413a, 1413b, 1413c, 1413d and 1413e exits by way of an output 1415, which is connected to a duct 1417. The duct 1417 provides the heated fluid as an input to a steam generator 1419. Once the heated fluid has passed through the steam generator 1419, some of its heat is transferred to the water in the steam generator and the stream of fluid is cooler than when exiting the steam generator. Cooler recycled fluid exits a bottom portion 1421 of the steam generator 1419. An air blower 1423 receives the cooler fluid, and provides the cooler fluid, via a passage 1425 defined between the walls 1403 and insulation 1427 positioned adjacent the stack 1413, through an upper air passage 1429 defined between the insulation 1411 and the roof 1401, down through side passages 1431 defined on one or more sides of the stack 1413 and the insulation 1411, and thence down to a passage 1433 directly below the stack 1413.
The air in the passages 1425, 1429, 1431 and 1433 acts as an insulating layer between (a) the insulations 1411 and 1427 surrounding the stack 1413, and (b) the roof 1401, walls 1403, 1407 and foundation 1409. Thus, heat from the stack 1413 is prevented from overheating the roof 1401, walls 1403, 1407 and foundation 1409. At the same time, the air flowing through those passages 1425, 1429, 1431 and 1433 carries by convection heat that may penetrate the insulations 1411 and/or 1417 into air flow passages 1435 of the stack 1413, thus preheating the air, which is then heated by passage through the air flow passages 1435.
The columns of bricks 1413a, 1413b, 1413c, 1413d and 1413e and the air passages 1435 are shown schematically in
In some implementations, to reduce or minimize the total energy loss, the layer of insulation 1411 is a high-temperature primary insulation that surrounds the columns 1413a, 1413b, 1413c, 1413d and 1413e within the housing. Outer layers of lower-cost insulation may also be provided. The primary insulation may be made of thermally insulating materials selected from any combination of refractory bricks, alumina fiber, ceramic fiber, and fiberglass or any other material that might be apparent to a person of ordinary skill in the art. The amount of insulation required to achieve low losses may be large, given the high temperature differences between the storage media and the environment. To reduce energy losses and insulation costs, conduits are arranged to direct returning, cooler fluid from the HRSG along the outside of a primary insulation layer before it flows into the storage core for reheating.
The cooler plenum, including the passages 1425, 1429, 1431 and 1433, is insulated from the outside environment, but total temperature differences between the cooler plenum and the outside environment are reduced, which in turn reduces thermal losses. This technique, known as “dynamic insulation,” uses the cooler returning fluid, as described above, to recapture heat which passes through the primary insulation, preheating the cooler air before it flows into the stacks of the storage unit. This approach further serves to maintain design temperatures within the foundation and supports of the thermal storage structure. Requirements for foundation cooling in existing designs (e.g., for molten salt) involve expensive dedicated blowers and generators—requirements avoided by implementations according to the present teaching.
The materials of construction and the ground below the storage unit may not be able to tolerate high temperatures, and in the present system active cooling—aided by the unassisted flowing heat exchange fluid in the case of power failure—can maintain temperatures within design limits.
A portion of the fluid returning from the HRSG may be directed through conduits such as element 1421 located within the supports and foundation elements, cooling them and delivering the captured heat back to the input of the storage unit stacks as preheated fluid. The dynamic insulation may be provided by arranging the bricks 1413a, 1413b, 1413c, 1413d and 1413e within the housing so that the bricks 1413a, 1413b, 1413c, 1413d and 1413e are not in contact with the outer surface 1401, 1403, 1407 of the housing, and are thus thermally isolated from the housing by the primary insulation formed by the layer of cool fluid. The bricks 1413a, 1413b, 1413c, 1413d and 1413e may be positioned at an elevated height from the bottom of the housing, using a platform made of thermally insulating material.
During unit operation, a controlled flow of relatively cool fluid is provided by the fluid blowing units 1423, to a region (including passages 1425, 1429, 1431 and 1433) between the housing and the primary insulation (which may be located on an interior or exterior of an inner enclosure for one or more thermal storage assemblages), to create the dynamic thermal insulation between the housing and the bricks, which restricts the dissipation of thermal energy being generated by the heating elements and/or stored by the bricks into the outside environment or the housing, and preheats the fluid. As a result, the controlled flow of cold fluid by the fluid blowing units of the system may facilitate controlled transfer of thermal energy from the bricks to the conduit, and also facilitates dynamic thermal insulation, thereby making the system efficient and economical.
In another example implementation, the buoyancy of fluid can enable an unassisted flow of the cold fluid around the bricks between the housing and the primary insulator 1411 such that the cold fluid may provide dynamic insulation passively, even when the fluid blowing units 1423 fail to operate in case of power or mechanical failure, thereby maintaining the temperature of the system within predefined safety limits, to achieve intrinsic safety. The opening of vents, ports, or louvres (not shown) may establish passive buoyancy-driven flow to maintain such flow, including cooling for supports and foundation cooling, during such power outages or unit failures, without the need for active equipment. These features are described in greater detail below in connection with
In the above-described fluid flow, the fluid flows to an upper portion of the unit, down the walls and into the inlet of the stacking, depending on the overall surface area to volume ratio, which is in turn dependent on the overall unit size, the flow path of the dynamic insulation may be changed. For example, in the case of smaller units that have greater surface area as compared with the volume, the amount of fluid flowing through the stack relative to the area may utilize a flow pattern that includes a series of serpentine channels, such that the fluid flows on the outside, moves down the wall, up the wall, and down the wall again before flowing into the inlet. Other channelization patterns may also be used.
Additionally, the pressure difference between the return fluid in the insulation layer and the fluid in the stacks may be maintained such that the dynamic insulation layer has a substantially higher pressure than the pressure in the stacks themselves. Thus, if there is a leak between the stacks and the insulation, the return fluid at the higher pressure may be forced into the leak or the cracks, rather than the fluid within the stacks leaking out into the dynamic insulation layer. Accordingly, in the event of a leak in the stacks, the very hot fluid of the stacks may not escape outside of the unit, but instead the return fluid may push into the stacks, until the pressure between the dynamic insulation layer in the stacks equalizes. Pressure sensors may be located on either side of the blower that provide relative and absolute pressure information. With such a configuration, a pressure drop within the system may be detected, which can be used to locate the leak.
Earlier systems that store high temperature sensible heat in rocks and molten salts have required continuous active means of cooling foundations, and in some implementations continuous active means of heating system elements to prevent damage to the storage system; thus, continuous active power and backup power supply systems are required. A system as described herein does not require an external energy supply to maintain the safety of the unit. Instead, as described below, the present disclosure provides a thermal storage structure that provides for thermally induced flows that passively cools key elements when equipment, power, or water fails. This also reduces the need for fans or other cooling elements inside the thermal storage structure.
The operation of a thermal storage unit as described herein can be optimized based on factors such as the lifetime of the components (heaters, bricks, structure, electronics, fans, etc.), required temperature and duration of output heat, availability of energy source and cost, among other factors. In some instances, the components exposed to high temperature are limited, using dynamic insulation to reduce temperatures of foundation, walls, etc.).
The control system may use feedback from computer models, weather predictions and sensors such as temperature and airflow to optimize long term performance. In particular, rates of heating and cooling as well as duration at peak temperature can have a detrimental effect on the lifetime of heating elements, bricks and other components. As physical properties of the components and airflow patterns, for example, may change as they age, feedback can be used to inform an artificial intelligence (AI) system to continue to provide high performance for years. Examples of such evolving physical properties and data reflecting such changes may include changing resistance of the heater elements, failure of heaters, changes in airflow behavior, and changes in heat transfer in bricks due to cracks or other damage.
An operational mode that reduces exposure to peak temperature can use data from models, weather predictions, sensors and time of year and location information to intelligently tune charging rates and extent. For example, during peak photovoltaic (PV) production days of summer, the days are relatively long and dark hours are relatively short. If the weather prediction expects multiple sunny days in a row, the thermal storage unit does not need to be charged to a high degree in order for the storage to serve the customer's needs during dark hours. In such an example case, reducing the charging extent and peak temperature reduces the stress on the system so that service life is increased.
Example implementations of the present disclosure may include a smart energy storage controller system 300 as described above with respect to
Thermal storage control system 1502 is configured to control a thermal energy storage system such as those that have been disclosed herein, and may be an implementation of control system 15 depicted in
Power source control system 1506 is configured to control aspects of the energy source for the thermal storage system. In one implementation, the energy source is a source of variable renewable electricity such as a field of photovoltaic panels (“solar field”) or a wind turbine farm. Systems 1502 and 1506 are configured to communicate with one another to exchange control information and data, including data relating to the operational status of the thermal energy storage system or energy source, input energy requirements of the thermal energy storage system, predicted future output of the energy source, etc. In one implementation, control system 1506 may be configured to control one or more aspects of the thermal energy storage system relevant to operation of the energy source.
Application control system 1504 is configured to control aspects of a system receiving output energy from the thermal energy storage system controlled by system 1502. Systems 1502 and 1504 are configured to communicate with one another to exchange control information and data, including data relating to the operational status of the thermal energy storage system or application system, amount of energy output from the thermal storage system needed by the application system, predicted future energy output from the thermal storage system, etc. In one implementation, control system 1504 may be configured to control one or more aspects of the thermal energy storage system relevant to operation of the application system.
External analytics system 1508 is configured, in one implementation, to obtain and analyze data relevant to operation of one or more of systems 1502, 1504 and 1506. In one implementation, system 1508 is configured to analyze forecast information such as weather information or energy market information and generate predictions regarding availability or cost of input power to thermal storage control system 1502. System 1508 may then communicate with thermal storage control system 1502 over link 1503 in order to convey information and/or commands, which may then be implemented by system 1502 and/or systems 1506 and 1504.
Two potential types of control are sensor-based control and model-based control. In a sensor-based control paradigm, readings from sensors placed throughout system 1500 may be used to determine real-time values that correspond to actual measurements. Thermal storage structures according to this disclosure may be designed in order to limit the exposure of certain components to high, thereby improving reliability. But the use of sensors, while potentially representing the most accurate possible state of system 1500, may be expensive, and also may be prone to malfunction if sensors fail. A model-based control paradigm, on the other hand, provides the ability to control a large complex system with less expense than that associated with deploying a multitude of sensors, and to minimize safety risks that might be associated with undetected sensor failure. A modeling program 1520 within memory 1512 may thus be used to model and predict behavior of the thermal energy storage system over a range of input parameters and operational modes. Control system 1502 may also be configured to combine model-based and sensor-based control of the thermal energy storage system-which may allow for redundancy as well as flexibility in operation. Other programs may also be stored in memory 1512 in some implementations, such as a user interface program that allows for system administration.
Data storage 1514 can take any suitable form, including semiconductor memory, magnetic or optical disk storage, or solid-state drives. Data storage 1514 is configured to store data used by system 1502 in controlling the operation of the thermal storage system, including system data 1522 and historical data 1524. In one implementation, system data 1522 describes the configuration or composition of elements of the one or more thermal storage arrays being controlled. Examples of possible system data include shape or composition of bricks within a thermal storage assemblage, composition of heating elements integrated with an assemblage, and the number of thermal storage assemblages in the thermal storage system. Historical data 1524 may include data collected over time as the thermal storage system is operated, as well as data from other units in some cases. Data 1524 may include system log data, peak heater temperatures, peak output gas temperatures, discharge rates of a thermal storage assemblage, a number of heating and cooling cycles for an assemblage, etc.
Communications interface 1516 is configured to communicate with other systems and devices, such as by sending and receiving data and signals between system 1502 and control systems 1504 and 1506, or between system 1502 and external analysis system 1508. Interface 1516 is also configured to send control signals to controlled elements of the thermal storage system, and receive sensor signals from sensors for the control system, such as sensors 303-1 through 303-N of
Processor 1530 is a processor configured to execute programs stored in memory 1532, such as supply forecast program 1538, maintenance forecast program 1540, market forecast program 1542 and predictive analytics program 1520. Supply forecast program 1538 includes instructions executable to use weather forecast data and predictive analytics methods to predict power supply availability to the thermal energy storage system. Maintenance forecast program 1540 includes instructions executable to use system data and predictive analytics methods to predict maintenance requirements for the thermal energy storage system. Market forecast program 1542 includes instructions executable to use power market data and predictive analytics methods to predict power pricing values or trends for power used by or produced by the thermal energy storage system. Predictive analytics 1520 includes instructions executable to implement algorithms for analyzing data to make predictions. Algorithms within predictive analytics 1520 are used by programs 1538, 1540 and 1542.
Data storage 1534 stores data including weather data 1546, market data 1548, supply data 1550, thermal storage (TS) data 1552, and application (App.) data 1554. Data stored in data storage 1534 may be used by programs stored in memory 1532. Weather data 1546 may include data collected at the location of the power source for the thermal energy storage system along with broader-area weather information obtained from databases. Market data 1548 includes energy market data received from external data providers. Supply data 1550 includes data associated with the power source controlled by system 1506, and may include, for example, system configuration data and historical operations data. TS data 1552 includes data associated with the thermal energy storage system, and application data 1554 includes data associated with the application system controlled by control system 1504. Communications interface 1536 is configured to send data and messages to and from system 1502 as well as external databases and data sources.
Systems and components shown separately in
In other scenarios, systems 1502 or 1508 may contain fewer program and data types than shown in
As noted above, forecast information such as weather predictions may be used by a control system to reduce wear and degradation of system components. Another goal of forecast-based control is to ensure adequate thermal energy production from the thermal energy storage system to the load or application system. Actions that may be taken in view of forecast information include, for example, adjustments to operating parameters of the thermal energy storage system itself, adjustments to an amount of input energy coming into the thermal energy storage system, and actions or adjustments associated with a load system receiving an output of the thermal energy storage system.
Weather forecasting information can come from one or more of multiple sources. One source is a weather station at a site located with the generation of electrical energy, such as a solar array or photovoltaic array, or wind turbines. The weather station may be integrated with a power generation facility, and may be operationally used for control decisions of that facility, such as for detection of icing on wind turbines. Another source is weather information from sources covering a wider area, such as radar or other weather stations, which may be fed into databases accessible to by the control system of the thermal energy storage system.
Weather information covering a broader geography may be advantageous in providing more advanced notice of changes in condition, as compared to the point source information from a weather station located at the power source. Still another possible source of weather information is virtual or simulated weather forecast information. In general, machine learning methods can be used to train the system, taking into account such data and modifying behavior of the system.
As an example, historical information associated with a power curve of an energy source may be used as a predictive tool, taking into account actual conditions, to provide forecasting of power availability and adjust control of the thermal energy storage system, both as to the amount of energy available to charge the units and the amount of discharge heat output available. For example, the power curve information may be matched with actual data to show that when the power output of a photovoltaic array is decreasing, it may be indicative of a cloud passing over one or more parts of the array, or cloudy weather generally over the region associated with the array.
Forecast-related information is used to improve the storage and generation of heat at the thermal energy storage system in view of changing conditions. For example, a forecast may assist in determining the amount of heat that must be stored and the rate at which heat must be discharged in order to provide a desired output to an industrial application—for instance, in the case of providing heat to a steam generator, to ensure a consistent quality and amount of steam, and to ensure that the steam generator does not have to shut down. The controller may adjust the current and future output of heat in response to current or forecast reductions in the availability of charging electricity, so as to ensure across a period of future time that the state of charge of the storage unit does not reduce so that heat output must be stopped. By adjusting the continuous operation of a steam generator to a lower rate in response to a forecasted reduction of available input energy, the unit may operate continuously. The avoidance of shutdowns and later restarts is an advantageous feature: shutting down and restarting a steam generator is a time-consuming process that is costly and wasteful of energy, and potentially exposes personnel and industrial facilities to safety risks.
The forecast, in some cases, may be indicative of an expected lower electricity input or some other change in electricity input pattern to the thermal energy storage system. Accordingly, the control system may determine, based on the input forecast information, that the amount of energy that would be required by the thermal energy storage system to generate the heat necessary to meet the demands of the steam generator or other industrial application is lower than the amount of energy expected to be available. In one implementation, making this determination involves considering any adjustments to operation of the thermal energy storage system that may increase the amount of heat it can produce. For example, one adjustment that may increase an amount of heat produced by the system is to run the heating elements in a thermal storage assemblage at a higher power than usual during periods of input supply availability, in order to obtain a higher temperature of the assemblage and greater amount of thermal energy stored. Such “overcharging” or “supercharging” of an assemblage, as discussed further below, may in some implementations allow sufficient output heat to be produced through a period of lowered input energy supply. Overcharging may increase stresses on the thermal storage medium and heater elements of the system, thus increasing the need for maintenance and the risk of equipment failure.
As an alternative to operational adjustments for the thermal energy storage system, or in embodiments for which such adjustments are not expected to make up for a forecasted shortfall of input energy, action on either the source side or the load side of the thermal energy storage system may be initiated by the control system. On the input side, for example, the forecast difference between predicted and needed input power may be used to provide a determination, or decision-support, with respect to sourcing input electrical energy from other sources during an upcoming time period, to provide the forecasted difference. For example, if the forecasting system determines that the amount of electrical energy to be provided from a photovoltaic array will be 70% of the expected amount needed over a given period of time, e.g., due to a forecast of cloudy weather, the control system may effectuate connection to an alternative input source of electrical energy, such as wind turbine, natural gas or other source, such that the thermal energy storage system receives 100% of the expected amount of energy. In an implementation of a thermal energy storage system having an electrical grid connection available as an alternate input power source, the control system may effectuate connection to the grid in response to a forecast of an input power shortfall.
In a particular implementation, forecast data may be used to determine desired output rates for a certain number of hours or days ahead, presenting to an operator signals and information relating to expected operational adjustments to achieve those output rates, and providing the operator with a mechanism to implement the output rates as determined by the system, or alternatively to modify or override those output rates. This may be as simple as a “click to accept” feedback option provided to the operator, a dead-man's switch that automatically implements the determined output rates unless overridden, and/or more detailed options of control parameters for the system.
On the output, or load, side of a thermal energy storage unit, various actions may be initiated in response to a forecast-based prediction of an input energy shortfall affecting the output heat to a load.
Another possible action in response to a forecast shortfall of input energy is to supplement the output from the thermal energy storage system with an alternate source of that output. In an implementation for which the heated fluid output from a thermal energy storage system is used to generate steam for an industrial process, for example, an alternate source of steam could be an additional steam generator using an alternate fuel source. The control system may provide signals to effectuate connection of the alternate output source to the load system in some implementations. Alternatively, the control system may send a message, such as an instruction or alert, to an operator or controller associated with the load system to indicate the need for connection to the alternate source.
In addition to ensuring sufficient output production by the thermal energy storage system to a load, forecast information is used to automatically control the thermal energy storage system to ensure its continued stable operation. For example, when a reduced amount of input power is predicted, the controller may in some implementations adjust the fluid flow rate through a thermal storage assemblage to lower the discharge rate from the assemblage so that the assemblage does not discharge to a point where the associated thermal storage unit shuts down.
As another example, the powering of the heater elements may be adjusted to a desired temperature for safety and efficiency, based on the forecast information. For example, if it is expected or forecast that during a future period, the amount of energy from the input source will be less than the expected amount of energy, the system can be configured to “supercharge”, i.e. heat some or all of the bricks in one or more stacks to temperatures higher than normal operation temperatures—for instance, if the normal stack temperature is 1100° C., in case of an expected period of lower energy input, the system can be controlled to heat up to 1300° C. or more for a selected period of time. This can be accomplished by reducing the discharge from certain units and/or by increasing the temperatures of the heater elements.
If the forecast indicates an extended period of reduced energy input, such as due to several days of cloudiness, the lead-lag capability of the system explained below may also be modified, because the issue of hotspots and thermal runaway may be somewhat reduced due to the fact that the system will be operating at a temperature that is below the peak temperature. Additionally, in a thermal energy storage system with multiple thermal storage units, if the system cannot be run at full capacity, the controller may reduce or disable charging or completely shut off one or more of the units based on the forecast, such that only a subset of units are operating at full capacity, rather than have none of the units be able to operate at full capacity.
In contrast to a situation involving a forecast of reduced power, forecast information may show that the expected electricity availability will meet or exceed the expected amount of energy that is input into the thermal energy storage system. In some implementations, responses of a control system to a forecast of excess energy may include one or more of adjusting operation of the thermal energy storage system to improve system reliability, reducing the amount of input power to the thermal storage energy system, or increasing thermal power to the load. Adjusting operation of the thermal energy storage system may include reducing input power to its heater elements when input energy is available for longer periods, so that a corresponding thermal storage assemblage operates at a lower peak temperature while still delivering sufficient thermal energy output. Such reduction in peak temperature may increase reliability and lifetime of the system. Excess input power supply may allow heating elements to remain powered after a thermal storage assemblage has already been charged with thermal energy, allowing the heating elements to directly heated fluid flowing through a thermal storage assemblage without discharging the assemblage, possibly to use provided such heated fluid to another use.
A control system of the thermal energy storage system may cause an amount of energy that is input to the system to be reduced. The energy source or the thermal energy storage system may be coupled to a larger power grid, in which case a reduction in input energy to the thermal energy storage system may be implemented by transferring excess energy to the power grid, e.g., when there is low demand from the system and/or high demand from the power grid to meet other electrical needs. In the absence of a grid connection, a reduction in input energy may be implemented in some implementations by curtailing production from a portion of the energy source infrastructure, such as shutting down certain solar panels in a solar field or wind turbines at a wind farm.
Alternatively or in addition to control of the input power supply or thermal energy storage system operation parameters, a response to a forecast of an excess of input energy may be made at the output side of the thermal energy storage system. In an implementation for which electric power is produced at the output of the system (for example, by feeding heated fluid from a thermal storage unit to a steam generator, then passing the produced steam through a turbine), excess power may be transferred to a larger power grid if a grid connection is available, thus providing energy to the grid instead of storing it as heat in the system. In an implementation for which the output to the load is heated fluid, a property of the output fluid may be changed. For example, a higher temperature and/or flow rate of output fluid may be produced. For an implementation in which steam is produced at the output of the thermal energy storage system, a higher vapor quality of the steam may be provided during periods of increased input energy. In some implementations, altered output properties may provide enhanced cogeneration opportunities, through cogeneration systems and methods described elsewhere in this disclosure. The input and output control described above may be interactively controlled in combination, to advantageously adjust the operation of the system.
Thus, the controller can use inputs from the forecasting system to account for variations in input energy due to factors such as cloudiness in the case of solar energy, variability in wind conditions for wind generated electricity, or other variability in conditions at the power source. For example, the controller may allow for additional heating, or heating at a higher temperature, prior to a decrease in the forecast availability of input of electricity, based on the forecast information.
Additionally, maintenance cycles may be planned based on forecast weather conditions. In situations where the availability of renewable energy is substantially less than the expected energy, such as due to forecast information (e.g., rainy season, several days of low wind cycles, shorten solar day, etc.), maintenance cycles may be planned in advance, to minimize the loss of input energy.
Based on the received information, the control system determines and commands, via signals, charging elements, power supply units, heaters, discharge blowers and pumps for effective and reliable energy storage, charging, and discharging. For example, the command may be given to power source controllers for solar energy, wind energy, and energy from other sources. The control system 399 may also provide instructions to controllers which admit power to the entire heater array or to local groupings of heaters.
The control system may include or be in communication with a forecasting and analytics system to monitor real-time and forecasting data corresponding to one or more meteorological parameters associated with an area of interest (AOI) where the electrical energy sources are being installed. The meteorological parameters can include, without limitation, solar radiation, air temperature, wind speed, precipitation, or humidity. The control system, based on the monitored real-time and forecasting data of the meteorological parameters, may in some implementations switch the electrical connection of the system between VRE sources and other energy sources. For instance, when the weather forecast predicts that the availability of sunlight or wind will be lower than a predefined limit for upcoming days, then the control system may command the system to electrically couple the heating elements of the system to other energy sources to meet the demands of a load system for the upcoming days.
In another example implementation, the control system monitors real-time and forecast data regarding availability of VRE, and selects an energy discharge rate and command the system to operate at such rate, so as to allow the system to continuously produce energy during the forecast lower-input period. Continuous energy supply is beneficial to certain industrial processes, making it is undesirable for a thermal storage unit to completely discharge itself and shut down.
It is also beneficial to certain industrial processes for adjustments in energy supply to be made slowly, and to be made infrequently. Therefore, the control system in some implementations selects a new discharge rate based on a multi-hour or multi-day weather forecast and corresponding VRE production forecast, so as to be able to operate at a fixed rate for (for example) a 24-hour period, or a 48-hour period, or a 72-hour period, given that forecast VRE supply. The control system may additionally and frequently update the information regarding a VRE supply forecast, and may make further adjustments to energy discharge rate so as to meet demand without interruptions, optionally providing signals and interface mechanisms for operator input, adjustment or override as described above. Thus, the behavior of energy delivery is controlled based on the above explained parameters, including forecasting.
In addition to forecasting of an input condition such as the weather, forecasting aspects of the thermal energy storage system may also include forecasting of energy markets and available sources and prices of energy, along with supply and demand of the industrial applications at the output of the thermal energy storage system to tune the operation of system. The control system may use the forecast information to control one or more aspects of the thermal energy system, including input of electrical energy, temperature of various elements of the thermal energy storage system, quantity and quality of the output heat, steam, or fluid (including gas), as well as improving the operation of the associated industrial processes. For example, the input electricity may be received or purchased at a time when the cost of the electricity is lower, in conjunction with forecast information about the conditions at the electricity source, and may be output when the demand or pricing of the output from the thermal energy storage system, or of power produced using that output, is higher.
Additionally, in situations where there is variability across different time periods as to the forecast conditions, the control system may make the adjustments on a corresponding variable basis. For example, if the expected cost of the input electricity is higher on a first day as compared with a second day, the controller may control the various inputs and outputs and parameters of the thermal energy system to account for differences in conditions between the first day and the second day that are based on differences in the initial forecast. In addition to the foregoing aspects, predictive analytics may be used to more effectively plan for equipment maintenance and replacement cycles. For example, predictive analytics may be used in predicting when maintenance will be needed, based on historical data. These analytics may be used in conjunction with one or more of the above forecast aspects to provide for planned downtime, for example, to coincide with times when input power availability or pricing conditions make operation of the system less advantageous.
The foregoing controls may be provided to an operator that makes decisions based on the forecasting information and the operation of the control system. Alternatively, the control system may include some automated routines that provide decision support or make determinations and generate commands, based on the forecast information, in an automated or semi-automated manner.
As explained above, the system can be operated in a charging mode for storing electrical energy as thermal energy while simultaneously generating and supplying steam and/or electrical power for various industrial applications as required. The charging and discharging operations are independent of one another, and may be executed at the same time or at different times, with varying states of overlap as needed, e.g. to respond to actual and forecast energy source availability and to deliver output energy to varying load demands. The system can also be operated in a discharging mode for supplying the stored thermal energy for steam and/or electrical power generation, as well as other industrial applications. Optionally, the system may be used to provide heated gas to an industrial application directly without first producing steam or electricity.
A key innovation in the present disclosure is the charge-discharge operation of the unit in such a means as to prevent thermal runaway, by periodically cooling each element of the storage media well below its operating temperature. In one implementation, this deep-cooling is achieved by operating the storage media through successive charge and discharge cycles in which constant outlet temperature is maintained and each storage element is deep-cooled in alternate discharge cycles. The narrative below refers process flow diagrams 1700a-1700h in
At
As shown at valves 1705 and 1707, the controller 1751 provides a signal for valve 1705 (a fluid flow control louver, damper, or other control device) to close for a first thermal storage array, and also provides a signal to a valve 1707 to be open for a second thermal storage array. Both units are heating, and flow through unit 1727 is providing flow to deliver heat to the steam generator.
With respect to the second unit 1727, the second unit is being charged, and flow is provided, as indicated by the valve 1707 being open. Thus, gas at the input temperature Tlow flows by way of the blower 1721, via the dynamic insulation, through the valve 1707 and through the thermal storage of unit 1727 to the upper fluid conduit. The gas is heated by the stacks of bricks to an output temperature equal to or above the desired fluid outlet temperature Thigh, which may be a value such as 800° C.
A sensor 1742 may provide information to the controller 1751 about the temperature of the gas prior to entering the steam generator. The controller 1751 modulates the setting of valve 1741 to allow cooler air to mix with the air flowing through the stack of bricks to reduce the blended fluid temperature at point 1742 to the specified Thigh value. The hot outlet air continues to flow, including through the steam generator 1709, which is supplied with water 1719 as controlled by pump 1717, and cooled air at temperature Tlow is forced by blower 1721 through the dynamic insulation paths and back to the inlets of valves 1705, 1707 and 1741. Additional sensors may be provided throughout the system, such as at 1713 and 1715. The controller 1751 may also use the same communication and power lines to transmit commands to control elements such as the valves 1705, 1707.
When charging stops, as for example occurs at the end of each solar day or each windy period, discharging continues. In
As each stack discharges, its outlet gas temperature remains roughly constant until approximately ⅔ of the usable heat has been delivered. At this point the outlet temperature from the stack will begin to drop, and continues dropping as discharge continues. The present innovation uses this characteristic to accomplish “deep cooling” as operation continues. The controller 1751 senses a reduction in the temperature at point 1742 and begins closing bypass valve 1741. By the time the outlet temperature from unit 1727 has reached Thigh, valve 1741 reaches the fully closed position, and as temperature further drops it is no longer possible for unit 1727 to deliver heat at temperature Thigh.
As shown at 1700c in
As shown in 1700d in
In some implementations, it is beneficial for controller actions to have chosen a rate of discharge such that when next charging begins—as at the beginning of the next solar day, for instance—the system is not yet fully discharged. 1700e in
At the end of this period of charging (electricity supply is again off), both stacks are fully charged, and discharging continues as in 1700f as shown in
Thus it will be understood that through actions of the controller responding to the measured and/or modeled state of charge of each stack, in successive charge/discharge cycles each stack is cooled to a gas outlet temperature of approximately Thigh in a first cycle and a gas outlet temperature substantially below Thigh in a second cycle. This alternating deep-cool operation effectively prevents thermal runaway. Those skilled in the art will recognize that this technique may be applied in larger systems with more than two independent stacks, for instance by organizing the system into pairs which operate as shown here in parallel or in series with other pairs; or by arranging more than two stacks in a deep-cool operating pattern.
Flow through the one or both of the stacks may be varied, as explained above. To avoid overheating and to control the output temperature, all or a portion of gas may be diverted by one or more baffles or flow control devices to a bypass 1741, controlled by the controller 1751, such that the inlet gas is mixed with the discharge gas of the stacks, to provide the output at a constant temperature or specified, non-constant temperature profile.
As shown, system 1800 may also be required to simultaneously generate some combination of hot gas, supply steam and/or other heated fluid for various industrial applications. This output may be facilitated within second section 1805 within thermal storage structure 1801, which includes a pump 1821 that provides water to a first end 1817 of a conduit 1815. Accordingly, during a discharging mode, blower units 1823 can be actuated to facilitate the flow of a gas such as air from one end to the other of thermal storage 1807 (e.g., from the bottom to the top), and from there into second section 1805 such that the gas passing through the first section can be heated to absorb and transfer the thermal energy emitted by the heating elements 1813 and/or thermal storage. This flow of heated air passes into second section 1805, which allows conduit 1815 to convert the water flowing through the conduit 1815 into steam and facilitate outflow of the generated steam through a second end 1819 of conduit 1815.
Alternatively, during simultaneous charging and discharging, gas flow through thermal storage 1807 may be minimal or none, and all or a portion of gas from blowers 1823 may be diverted by one or more baffles or flow control devices, and may be heated by a separate bypass heater (not shown) to deliver inlet gas, such as inlet air, to the steam generator at a suitable temperature. This bypass mode of operation may be beneficial in achieving predefined temperature distributions in thermal storage and in mitigating the required power dissipation of the heating elements.
In some configurations, the only required output from the thermal storage structure is the output of hot gas (e.g., hot air) to an industrial process. Accordingly, a steam generator may either not be present or not used. In such configurations, a separate conduit connecting to a processing chamber may be provided to facilitate to delivery of the hot gas.
In another implementation, if the available electrical energy being received by the structure 1800 is low, then during charging mode, a smaller number of the total number of available heating elements 1813 receive the limited available electrical energy. Accordingly, only a portion of thermal storage is heated during charging mode. During discharging, gas can be passed largely through only the portion of thermal storage 1807 that has been heated. The heated gas thus continues to transfer the stored thermal energy to the conduit 1815 in order to keep the temperature of the gas at the conduit 1815 sufficiently high to maintain continuous and controlled steam production, thereby preventing any damages or failure in the steam production system.
Implementations discussed above have described the flow of a fluid such as air into a first section of a thermal storage structure that includes the thermal storage material itself, and from there into a second section of the thermal storage structure that includes an output device such as a steam generator.
Other fluid flows within the thermal storage structure are also contemplated. In some implementations, the system is configured to cause a heated air flow to be directed into the second section, without first having flowed through the first section. In such implementations, the system is configured to heat inlet air using a heater that is electrically connected to the electrical energy sources. In this manner, the air may be heated to a same temperature range that would be expected from heated air being output from the thermal storage. This mode may be utilized in charging mode, during which time the energy supply from the electrical energy source is likely to be plentiful, and therefore less costly. A heater powered by the input electrical energy receives inlet air (e.g., which may be ambient air, recirculated air, etc. that is cooler than the peak temperatures of air produced by the thermal storage), heats the inlet air, and directs it to the second section of the thermal storage structure, where it may pass over a conduit of an OTSG, for example. During this operation, the system may allow very little or no air to pass through the thermal storage such that charging is performed efficiently without discharging into the second section before discharging mode is initiated.
In another type of air flow, the thermal storage structure can be configured to facilitate the passive outflow of heated air from the housing due to the buoyancy effect of heated air. This may be used to provide intrinsic safety for people working in areas near the unit and for the equipment itself, without requiring active equipment or standby electric power sources to maintain safe conditions. For example, if pump or blower motors or drives fail, if control systems fail, or if the operating electric power supply fails, the present innovations include features that cause air to flow in such a manner as to provide ongoing cool temperatures at exterior walls, foundation, and connected equipment points. This type of operation can maintain the temperature of all parts of the system within safety limits and prevent any potential harm to people, the environment, other equipment or the components of the system from being thermally damaged.
A blower 1621 takes inlet air from louver 1619 and directs it to thermal storage blocks 1607. Air that has passed through the thermal storage blocks 1607 can then pass into second section 1605 during a discharging mode. As an example of another air flow, release valve 1623 may be controlled to allow for the release of hot air, and inlet valve 1619 may be opened to allow for the intake of ambient air, such as in the event of a need for quick shutdown or emergency. By suitable arrangement of the valve locations and air flow paths, a “chimney effect” or buoyancy-driven air flow may establish suitable air flow through the dynamic insulation and system inlets to maintain cool outer temperatures and isolate the steam generator or other high-temperature process from the storage core temperatures, without active equipment.
Auxiliary heater 1609 is a type of auxiliary heater that can be used to heat a portion of the fluid (such as air) moving through the thermal storage structure. As shown in
These are just two examples of multiple possible fluid flows within system 1600. As has been described, system 1600 is configured to receive inlet fluid at inlet valve 1619. This fluid may variously be directed directly to the dynamic insulation or directly to thermal storage 1607. Optionally, the system can include one or more louvers 1611 positioned at the bottom of the stacks within first section 1603, and are configured such that the flow path of the fluid flowing through each of the storage arrays and thermal storage elements is as uniform as possible such that constant air pressure is maintained across each thermal element for efficient charging and discharging. Still further, inlet fluid may be directed to second section 1605 via auxiliary heater 1609, as controlled by a louver 1611 positioned between the blower 1621 and the auxiliary heater 1609, without passing through the dynamic insulation or thermal storage 1607.
Additionally, fluid flow from the top of the stacks within thermal storage 1607 may be provided to steam generator 1615 via a valve 1613 between first section 1603 and second section 1605. Valve 1613 can separate receive fluid flows produced from each of the stacks in thermal storage 1607. For example, in the case in which two stacks are used, valve 1613 can receive a first fluid flow from a first stack and a second fluid flow from a second stack. Valve 1613 can also receive a bypass fluid flow, which corresponds to fluid (such as from louver 1619) that has not passed through either the first or second stacks. As will be described below in the context of the lead-lag paradigm, valve 1613 is controllable by the control system to variously output no fluid, a combination of the first fluid flow and the bypass fluid flow, a combination of the second fluid flow and the bypass fluid flow, a combination of the first and second fluid flows, etc. In order to achieve an output fluid having a specified temperature profile. Louver 1619 can also be used to release cool fluid from the system instead of recirculating it to thermal storage 1607, in the event that the blower is not operational, for example.
While the foregoing example includes the bypass heater louvers, such as high-temperature louvers, these features are optional. Further, the bypass heater may have an advantage, in that it can reduce the required heater power within the array. In other words, the bypass heater may discharge heat during charging, without passing air through the array during charging.
Note that various other control valves are contemplated, including those described below with reference to
These air flows and associated control structures may provide benefits in terms of safety and temperature regulation, in addition to the benefit of efficient charging and discharging.
The selection of charging and discharging modes may be made by a control system on an automatic schedule based on, for example, measurements of temperature or power distribution. Similarly, other features such as the hot air booster mode described above may also be controlled by the control system based on conditions detected within the thermal storage structure.
Such sensing may include measurements of radiation by cameras, spectrometers, or other devices, and may include remote measurements carried by optical waveguide systems including fiber optic, fixed reflector, and movable reflector systems; measurements of temperature based on measurements of resistance or current flow in heating elements; direct sensing of temperatures within the refractory array, within flow channels exiting the array, or by other sensing means or locations.
Next, the use of a particular type of discharging “deep discharging” is described.
Thermal energy storage systems are vulnerable to “thermal runaway” or “heat runaway” effects. The phenomenon may arise from imbalances in local heating by heating elements and imbalances in local cooling by heat transfer gas flow. Even small imbalances may be problematic, which are amplified across successive charge-discharge cycles. After several cycles, even small imbalances may result in large temperature differences which may be damaging to bricks and/or heaters, and/or severely limit the temperature range within which the system can be safely operated.
Point in time 2050 corresponds to an initial, fully charged state for both arrays 1 and 2. In this state, the conduits are heated to 1000° C. along each section of their lengths. In the case of solar energy input, such a state might to correspond to arrays at the end of a solar day. While the value of 1000° C. is included, this is just an example, and the temperature may be varied depending on factors such as applications or use points. For example, the conduits may be heated within a range of 800° C. to 1600° C., and more specifically, 900° C. to 1300° C., and even more specifically, 800° C. to 1100° C. Other factors that may impact the temperature include temperature impact on heater life, storage capacity, heating patterns, weather conditions, temperature, and heater materials. For example, a ceramic heater may have an upper conduit temperature range as high as 1500° C. to 1600° C., whereas other heaters may have a conduit temperature range of 600° C. to 700° C. The range of conduit temperatures may be varied vertically within the stack by varying the brick materials.
At the beginning of discharge period 2051 (e.g., dusk in the case of solar energy input) of the arrays, cooler heat transfer gas is introduced at the bottom of the arrays and flows upwards. During the charging period that has just concluded, heat has been added by heating elements 2031-2036, which may be oriented transverse to the fluid columns and grouped by horizontal position within the array. Ideally, the same input energy will have been supplied to all heating elements in each group, but in practice, individual heating units vary slightly in their resistance (and thus their power delivery). Similarly, local cooling flow rates will vary between conduits, given that individual channels vary in roughness, brick alignment, or are otherwise mismatched in their resistance to flow.
Here, example 2000 assumes that the flow rate in conduit 2020 is below the flow rate in 2010. Accordingly, portions of array 2 adjacent to conduit 2020 will exhibit higher temperatures than portions of array 1 adjacent to conduit 2020, due to the lower cooling flow. The result at the end of discharge period 2051 is shown in
These variations in heating and cooling rates, unless managed and mitigated, can lead to runaway of mismatched storage element temperatures, and can lead to runaway temperatures that cause failures of heaters and/or deterioration of refractory materials within the array.
At the end of discharge period 2051, the control system determines how much energy to apply to each heating element group during a charging (or recharging) period in order to restore the full state of charge. But the control system may not have information about every temperature nonuniformity within every location within a set of thermal storage arrays. For example, there might be a limited number of sensors available, and thus temperature nonuniformities may be undetected. Sensors may also malfunction. In some implementations, the heating elements may be controlled by a model-based paradigm in which sensors are not used or are used in a limited fashion. The system may also not be configured to vary heating to a fine enough granularity to resolve every area of temperature nonuniformity. In example 2000, it is determined that heating elements 2031 are given enough total energy to raise the surrounding materials by 800° C., while heaters 2036 are given enough energy to raise their surrounding materials by 400° C.
At the end of a charging period 2052 that uses the above-noted heating parameters, the temperature differences at the end of discharge period 2051 remain. This is due to inefficient discharging of conduit 2020 relative to conduit 2010, and conduit 2020's higher residual temperature at the end of discharge period 2051. Accordingly, the amount of input energy received during charging period 2052 overheats conduit 2020 along its length by roughly 300 degrees. Note that over the course of a single discharge and charge cycle, temperatures along conduit 2020 are now 250-300° C. warmer as compared to fully charged state 250. If another cycle were repeated (that is, another discharge period followed by another charge period), the overheating of conduit 2020 would be even more pronounced. (The values shown in
An effect that exacerbates this runaway is the thermal expansion of fluid flowing in the conduits. Hotter gas expands more, causing a higher outlet velocity for a given inlet flow, and thus a higher hydraulic pressure drop across the column. This effect may contribute to a further reduction of flow.
The present disclosure teaches several techniques that may be used to mitigate thermal runaway in a manner that achieves long-term, stable operation of the thermal energy storage system.
First, the height of the storage material stack and the physical measurements of the fluid flow conduits may be chosen in such a manner that the system is “passively balanced.” Low fluid flow rates are selected for system discharge, and flow rates and conduit geometries are designed with a relatively low associated hydraulic pressure drop and long column length. In this configuration, the lower density of hotter gas will create a “stack effect,” a relative buoyancy component to the flow rate, which increases fluid flow in hotter conduits. This mismatched cooling flow provides a balancing force to stabilize and limit temperature differences across the thermal storage array.
Second, a “deep-cool” sequencing is used to rebalance or level temperature differences among conduits. This concept can also be referred to as a deep discharge (also referred to as “deep-discharge”). Generally speaking, deep discharging refers to continuing discharge of one or more arrays until temperature nonuniformities within the array have reduced (such arrays can thus be said to have been “deeply discharged,” which amounts to a thermal reset). The amount of discharge of an array might be measured in several ways, such as by a comparison of the array's total bulk temperature to that of the inlet gas temperature from inlet or bypass air admitted through an inlet valve. A deep discharge of an array may be contrasted with a partial discharge of the array, in that during a deep discharge, gas flows through the array for a longer period of time (and potentially with greater flow volume) than during a partial discharge. In some applications of a deep discharge, an array may be fully discharged to the inlet air temperature, which may also be referred to as bypass temperature. The operations sequence shown in
Consider the effect of deep-discharge period 2054. By discharging arrays 1 and 2 more completely than in discharge period 2051 (e.g., by flowing gas over the arrays for a longer period of time), it can be seen that arrays 1 and 2 discharge more uniformly during deep-discharge period 2054. Temperatures in array 1 range between 300-310° C., while temperatures in array 2 range between 310-480° C. Accordingly, subsequent charging period 2055 results in a temperature distribution within both arrays 1 and 2 that more closely approximates starting point 2050, and thus greatly reduces thermal runaway within the thermal storage.
Deep discharging is thus an effective solution to the problem of thermal runaway within a thermal storage array. But thermal runaway is not the only constraint on the thermal energy storage systems contemplated in this disclosure. As noted, it is desirable for thermal energy storage systems to be able to provide a continuous or near-continuous supply of thermal energy for downstream processes. This requires that at least some media within the storage unit be at temperatures above the required delivery temperature. The present inventors have realized that while deep-discharge is desirable for thermal storage arrays, discharging all arrays in a system every discharge cycle is not possible, as it would create periods when no element within the system has sufficient temperature to meet outlet temperature requirements. Accordingly, the inventors have developed a paradigm of only periodically deep-discharging each thermal storage array in a set of one or more storage arrays. This approach meets the dual objectives of periodically performing a thermal reset of each thermal storage array and maintaining sufficient temperature within the thermal storage to meet outlet temperature specifications.
One specific implementation that is contemplated includes the use of two thermal storage arrays, and is referred to as the “lead-lag” technique. In this technique, the system deep-discharges each of the two thermal storage arrays every other discharge period. For example, array 1 would be discharged in discharge periods 0, 2, 4, etc. and array 2 would be discharged in discharge periods 1, 3, 5, etc.
The process elements for a lead-lag operation are shown in
As shown in chart 2060Aa, temperature is shown along the vertical axis, while time is shown along the horizontal axis. A peak temperature 2061 of the first stack and the second stack are shown, along with bypass temperature 2063, which is the inlet gas temperature. Additionally, at 2065, a delivery temperature of the stream of blended output fluid flow is shown. The horizontal axis shows time, including 24-hour intervals 2067 and 2067a, as well as a solar day at 2069 and 2069a.
The peak temperature of the first stack is indicated by line 2071, while the peak temperature of the second stack is indicated by line 2073. As will be shown, the first stack and the second stack operate together such that the first stack is in a “lead” mode of operation when the second stack is in a “lag” mode of operation, and vice versa. During the first day, the first stack is cooled to a very low temperature relative to both peak temperature 2061 and delivery temperature 2065, while the second stack is cooled to a minimum required temperature to deliver the output at the delivery temperature 2065, which is shown here as a constant. On the second day, the second stack is cooled to the lower temperature while the first stack is cooled to the delivery temperature.
In short, in the case where two stacks are operating together, each stack may be deeply discharged to well below the delivery temperature every other discharge period. Similarly, in those discharge periods in which a given stack is not being deeply discharged, it is discharged from the peak discharge temperature to the delivery temperature (or a temperature approaching the delivery temperature). The cycling between the lead mode and the lag mode for a given stack is accomplished by the control system controlling the flow of fluid in each of the stacks. (In the lead mode, a given stack is deeply discharged, while in the lead mode, the given stack is discharged to a temperature at or above the delivery temperature.) The stack that is being deeply discharged may continue to be heated by having the resistive heating elements receive the electrical energy and emit heat; alternatively, the resistive heating elements may be switched to an off state.
At the leftmost position of the chart 2060Aa, the first stack and the second stack are both at the peak temperature 2061. This starting position may occur outside the solar day such as at midnight. Then, as indicated by line 2071, the first stack begins discharging. As the temperature of the first stack starts to fall and continues to fall to below the output delivery temperature, hot fluid from the second stack is blended as shown at 2073. As the temperature of the first stack continues to fall, the flow through the first stack is reduced and additional heated fluid is blended in from the second stack, in order to maintain delivery temperature 2065.
The first stack continues to discharge until it reaches or approaches a minimum temperature, which, in this example, corresponds to bypass temperature 2063 and represents a fully discharged state of the first stack. This minimum temperature is, in some cases such as in chart 2060A, a temperature that approximates the bypass temperature. The degree to which the minimum temperature approximates the bypass/inlet gas temperature may depend on factors such as the quality of heat transfer out of the bricks, as well as a difference between delivery temperature 2065 and peak temperature 2061. For example, if peak temperature 2061 were 1000° C. and delivery temperature 2065 were 900° Celsius, the amount of cool air that can be blended into the air that is 1000° C. is relatively small. Thus, minimum temperature 2063 to which the stack can be cooled may be higher, such as 800° C. On the other hand, if the delivery temperature 2065 were lower, such as 650° C., then the minimum temperature 2063 to which the stack can be deeply cooled may be lower, such as around 200° C. Thus, the lower delivery temperature 2065 is relative to peak temperature 2061, the lower minimum temperature 2077 can be set relative to bypass temperature 2063. Thus it is not necessarily the case that a stack must be discharged to the bypass temperature in order to achieve deep discharging. Rather, discharging may occur within a range of temperatures (a “deep-discharge temperature region”) that is sufficient to reduce thermal runaway by reducing thermal nonuniformities. In some cases, the range of a deep-discharge temperature region for a particular use case is bounded on the upper end by the delivery temperature and on the lower end by the inlet gas temperature, the bounds including both the delivery temperature and inlet gas temperature (or bypass temperature) in the region. As noted, the bounds for this region for a particular situation will vary, for example based on the peak temperature and delivery temperature, and may be more specifically determined in some cases by monitoring the thermal behavior of the thermal storage arrays. Alternately, a deep-discharge temperature region may be determined via execution of a computer modeling program.
During the deep discharging of the first stack, the bypass valve may be turned off, such as by starting to close the louver on the bottom of the stacks as controlled by the control system, to accelerate the cooling process. At this point, the second stack is being used as the primary source of heated fluid to provide the blended stream at delivery temperature 2065. Further, as explained above, fluid may be flowed through the fluid bypass valve so that the fluid is provided at the inlet temperature to the blended stream. The fluid bypass may be used to bypass fluid directly to the blended fluid flow, in order to bring the temperature down at a time when both of the stacks become too hot, such as towards the end of the solar day.
As the second stack continues to discharge, its discharge temperature starts to approach the delivery temperature 2065, as shown at 2081. The discharge may be buffered, such that the minimum discharge temperature of the second stack is higher than the constant delivery temperature 2065, as shown at 2081z. This temperature of the second stack is the minimum temperature at which the blended stream can be provided at delivery temperature 2065. Here, the temperature of the first stack at 2079 is substantially cooler than the temperature of the second stack at 2081.
At this point, which is at or around the start of the solar day (e.g., dawn), the flow to the first stack is turned off at 2079, and the first stack begins to charge as shown by a broken line 2083 in
Alternatively, as shown in 25, fluid continues to be trickled through the first stack as it increases its discharge temperature. The trickle may account for the possibility that the units are not sealed in such a manner that would permit 0% flow, and that the louvers permit a residual flow, such as 5% or the like. Further details of this approach are explained with respect to
Returning to
At 2087, the roles of the first stack and the second stack are reversed, such that the second stack begins to discharge to a deeply discharged state while the first stack continues to provide the fluid for the blended stream, so as to maintain constant delivery temperature 2065. The remainder of the timeline shown in
At the end of the first 24-hour period cycle 2067 and the start of the second 24-hour period cycle 2067a (i.e., at 2087), the second stack and the first stack are both at peak temperature 2061. As can be seen at 2071a, the second stack begins discharging. As the temperature of the second stack starts to fall and continues to fall to below the delivery temperature, hot fluid from the first stack is blended at 2073a. As the temperature of the second stack continues to fall, the flow through the second stack is reduced and additional heated fluid is blended in from the first stack to maintain delivery temperature 2065.
The second stack continues to discharge, such as until it reaches a minimum temperature at 2077a or other discharge temperature.
During the deep discharging of the second stack, the bypass valve may be turned off, such as by starting to close the louvre on the bottom of the stacks as controlled by the control system, to accelerate the cooling process. At this point, the first stack is being used as the primary source of heated gas to provide the blended stream at delivery temperature 2065.
As the first stack continues to discharge, its discharge temperature starts to approach delivery temperature 2065, as shown at 2081a. The discharge may be buffered, such that the minimum discharge temperature of the second stack is higher than the constant delivery temperature 2065, as shown at 2081za. This temperature of the first stack is the minimum temperature (or approximately the minimum temperature) at which the blended stream can be provided at delivery temperature 2065. Here, the temperature of the second stack at 2079a is substantially cooler than the temperature of the first stack at 2081a.
At 2079a, which is at or around the start of the solar day, the flow to the second stack is turned off, and the second stack charges as shown by broken line 2083a of
Alternatively, as shown in
The first stack continues to provide the hot fluid at the peak discharge temperature while the second stack continues to charge between 2085a and 2087a. On the other hand, louvers of the second stack are fully closed at this point, such that there is essentially no fluid flow through the second stack.
This pattern of having a lead stack and a lag stack repeats (e.g., every 48 hours). Accordingly, the first discharge operation in discharge period of 2067d1 and the second discharge operation in successive discharge period 2067d2 can be repeated, such that the control system alternates between performing the first discharge operation (deep-discharging the first stack but not the second stack) and the second discharge operation (deep-discharging the second stack but not the first stack) over time, allowing the system to continuously provide an output fluid flow, and to do so while avoiding thermal runaway. This approach need not be limited to a first stack and a second stack, and may be used with more than two stacks (e.g., triples, quads, or the like) as will be described further below.
At the left side of chart 2060B, the beginning of the timing shown is associated with an end of the solar day. At this point the first stack and the second stack are both at the peak temperature, in this case 1000° C. At 2071b, the first stack is discharging hot air at 1000° C., while the second stack is not discharging hot air as indicated at 2070b, with an air flow of 0%. As explained above, the discharge temperature may vary between 800° C. to 1600° C., depending on various factors. The temperature of the bricks approaches the temperature of the conduit, usually within 25° C. to 50° C. For example, the conduits may be heated within a range of 800° C. to 1600° C., and more specifically, 900° C. to 1300° C., and even more specifically, 800° C. to 1100° C. Other factors that may impact the temperature include temperature impact on heater life, storage capacity, heating patterns, weather conditions, temperature, and heater materials. For example, a ceramic heater may have an upper conduit temperature range as high as 1500° C. to 1600° C., whereas other heaters may have a conduit temperature range of 600° C. to 700° C. The range of conduit temperatures may be varied vertically within the stack by varying the brick materials. Both of the stacks contain very hot air at the end of the solar day; the bypass unit is flowing in air at the inlet air temperature as the deep-discharge temperature 2063b.
As the flow of the first stack increases from about 60% to 100%, e.g., 60% to 100%, of the total airflow as indicated by 2072b, the discharge temperature of the first stack starts to decrease at 2073b. As the discharge temperature of the first stack starts to decrease, the bypass flow is also decreased downward from about 40%, e.g., 40%, of the total air flow.
When the discharge temperature at the first stack falls below delivery temperature 2065b, as depicted at 2075b, the flow of the first stack is now 100% of the total airflow as indicated by 2077b, and the flow of the bypass and the second stack are both 0%, as indicated by 2076b. At this point, in order to maintain the delivery temperature of the blended air at 2065b, air flow is turned on to the second stack at 2076b.
As the air flow at the second stack increases and the air flow at the first stack decreases, the first stack continues to cool, but the rate of cooling slows as the flow through the second stack is reduced, as shown at 2078b. Conversely, as the air flow at the second stack increases, the second stack begins to cool, and as the air flow of the second stack approaches 100% of the total air flow at 2074b, the discharge temperature at the second stack starts to rapidly decrease until it reaches the constant delivery temperature as shown in 2079b. At this point, the air flow of the first stack is 0% as shown at 2080b.
Once the discharge temperature of the second stack reaches the minimum temperature at which the constant delivery temperature 2065B can be maintained (as indicated by 2079b), the airflow through the second stack is decreased, and the discharge temperature of the second stack correspondingly rises at 2082b. At the same time, because this is occurring during the late solar day, the bypass flow is used to prevent overheating at 2076b′. Further, because there is no flow through the first stack, the discharge temperature of the first stack increases rapidly as the first stack charges, as indicated by 2081b. At 2083b, the first stack and the second stack have discharge temperatures equal to or approaching peak temperature 2061b.
At 2083b, the 24-hour cycle is now complete. The first and second stacks now switch roles, such that the second stack will “lead” and undergo deep cooling, and the first stack will “lag” and act as the second stack did in the first 24-hour cycle. The bypass will continue to operate in a similar manner. A second 24-hour period 2067ba and a solar day 2069ba are indicated along the horizontal axis.
At the end of the first 24-hour period cycle 2067b and the start of the second 24-hour period cycle 2067ba (i.e., at 2087ba), the timing is associated with an end of the solar day. At this point the second stack and the first stack are at the peak temperature, in this case 1000° C. As shown at 2071ba, the second stack is discharging hot air at 1000° C., while the first stack is not discharging hot air as indicated at 2070ba, with an air flow of 0%. As before, the bypass unit is flowing in air at the inlet air temperature (deep-discharge temperature 2063b).
As the flow of the second stack increases from about 60% to 100%, or 60% to 100%, of the total airflow as indicated by 2072ba, the discharge temperature of the second stack starts to decrease at 2073ba. As the discharge temperature of the second stack starts to decrease, the bypass flow is also decreased downward from about 40%, or 40%, of the total air flow.
When the discharge temperature at the second stack falls below the constant delivery temperature 2065b, as depicted at 2075ba, the flow of the second stack is 100% of the total airflow as depicted at 2077ba, and the flow of the bypass and the first stack are both 0%, as depicted by 2076ba. At this point, in order to maintain the constant delivery temperature of the blended air at 2065b, air flow is turned on to the first stack at 2076ba.
As the air flow at the first stack increases and the air flow at the second stack decreases, the second stack continues to cool, but the rate of cooling slows as the flow through the first stack is reduced, as shown at 2078ba. Conversely, as the air flow at the first stack increases, the first stack begins to cool, and as the airflow of the first stack approaches 100% of the total airflow at 2074ba, the discharge temperature at the first stack starts to rapidly decrease until it reaches the constant delivery temperature as shown in 2079ba. At this point, the air flow of the second stack is 0% as shown at 2080ba.
Once the discharge temperature of the first stack reaches the minimum temperature at which delivery temperature 2065b can be maintained (i.e., at 2079ba), the air flow through the first stack is decreased, and the discharge temperature of the first stack correspondingly rises at 2082ba. At the same time, because this is occurring during the late solar day, the bypass flow is used to prevent overheating at 2076ba. Further, because there is no flow through the second stack, the discharge temperature of the second stack increases rapidly as the second stack charges, as indicated by 2081ba. At 2083ba, the second stack and the first stack have discharge temperatures equal to or approaching peak temperature 2061b.
Structures such as valves, blowers, louvers and other mechanisms needed to accomplish the above-described operations are operated in response to commands received from the control system. The control system is configured to generate the instructions based on a variety of information, including a combination of sensed information, forecast information, and historical information, as well as models developed based on, for example, artificial intelligence. For example, sensors may be provided to ensure that the system is safe, in combination with a physical model of how the system performs with different inputs in energy—this model may thus serve as a substitute for some sensors in various embodiments. In some cases, sensors may be expensive and may wear out or need replacement, and could cause additional problems. For example, a defective sensor may lead to system overheating. The model may take temperature inputs, and may allow for predictions based on parameters such as sunrise and weather. The model may be adjusted based on the industrial application for a variety of reasons, such as to optimize output temperature, energy output, or a combination thereof.
As has been described with reference to 2060B, the control system is configured to direct fluid flows (e.g., a first flow associated with the first stack, a second flow associated with the second stack, and a bypass flow that bypasses the first and second stacks) in order to deeply discharge the first stack but not the second stack during first discharge period 2069bd1 and to deeply discharge the second stack but not first stack during second discharge period 2069bd2. The operations of the first and second discharge periods may be performed repeatedly in successive discharge periods, alternating between the operations of 2069bd1 and 2069bd2. In the first discharge period, the second stack is discharged to a lesser degree than the first stack—to the current value of the specified temperature profile. Similarly, in the second discharge period, the first stack is also discharged to a lesser degree than the second stack—to the current value of the specified temperature profile. The specified temperature profile 2065b shown in
It is understood that these temperature and flow illustrations are just examples, and the actual values and shapes of curves may vary. As one simple example, the peak temperature may be reduced during summer. Some examples of variations are provided as follows.
Instead of having the temperature of the second stack fall precisely to output temperature 2065c, the temperature may fall to a buffered amount 2085c that is slightly higher than the constant output temperature 2065c. In other words, the second stack does not completely discharge, but only partially discharges. On the other hand, the first stack continues to have the same temperature and air flow pattern as in
The partial discharge may be accomplished by adjusting the flow 2084c of the second stack, so that it is less than 100% of the total flow, for example approximately 90%, e.g., 90%, of the total flow. To compensate for the 10% of the total flow, the bypass is opened when the desired second stack discharge (buffer) temperature 2085c is reached, as shown at 2086c. At 2087c, the bypass and the second stack air flow essentially follow the air flow as shown above in
Similarly, during a second 24-hour cycle, the temperature of the first stack fall may fall to an amount 2085c that is slightly higher than constant output temperature 2065c. Thus, the first stack only partially discharges. The second stack has the same temperature and air flow pattern as described in
As with the first 24-hour period, the partial discharge may be accomplished by adjusting the flow 2084ca of the first stack, so that it is less than 100% of the total flow, for example approximately 90%, e.g., 90%, of the total flow. To compensate for the 10% of the total flow, the bypass is opened when the desired first stack discharge temperature 2085ca is reached, as shown at 2086ca. As explained above, the value of 10% is just an example, and may be varied depending on the discharge temperature, return air temperature, target heat content or target temperature of the output, the flow percentage through each stack, as well as the temperature of the stacks.
Accordingly, 2060C illustrates that the control system is configured maintain an output fluid flow at a specified constant temperature profile (2065c), while, in successive discharge periods 2069cd1 and 2069cd2, alternating between 1) deeply discharging the first stack while discharging the second stack to a first buffer temperature (2085c) above the specified temperature profile, and 2) deeply discharging the second stack while discharging the first stack to a second buffer temperature (2085ca) above the specified temperature profile.
As with the operation described in
Similarly, in the second 24-hour period, at the point at which the air flow of the first stack reaches a maximum, here about 90%, e.g., 90%, as shown at 2088da, the airflow of the second stack is not completely shut off, but is instead kept at a very low rate or a trickle, such as about 5% or less (for example, 5%), as shown at 2089da. To compensate for the flow at the second stack, the flow at the first stack is decreased, as can be seen in the drawings. Again, this mode may prevent or reduce the possibility of thermal runaway.
Accordingly, 2060D illustrates that the control system is configured to maintain a temperature 2065d of the output fluid flow according to a specified temperature profile (here, constant). This is accomplished by alternating, in successive discharge periods (2069dd1, 2069dd2), between 1) deeply discharging the first stack while discharging the second stack to a first buffer temperature (2085d) that is above the specified temperature, and 2) deeply discharging the second stack while discharging the first stack to a first buffer temperature (2085da) that is above the specified temperature. Furthermore, during discharge period 2069dd1, fluid flow is maintained to the first stack in a trickle mode, while during discharge period 2069dd2, fluid flow is maintained to the second stack in the trickle mode.
As can be seen in the drawings, the output temperature may vary within an acceptable range or the industrial application. (In some cases, a “specified temperature profile” may be a constant temperature, but as shown in
As shown, in the first 24-hour cycle (2067e), instead of having the flow through the first stack be 100% of the total flow as in
As noted above, the flow through the first stack is maintained at about 10%, e.g., 10%, during the charging phase of the first stack, as indicated by 2097e. When the output temperature is varied to about 700° C., e.g., 700° C., at 2091e, the discharge temperature of the second stack also approaches about 700° C., e.g., 700° C., at 2092e. Because the air flow of the first stack and the second stack are maintained at a relatively constant proportion during the charging phase (as indicated by 2096e and 2097e, respectively), the discharge temperatures of the first and second stack behave in a similar manner as in the above examples. During the latter part of the solar day, the bypass flow is increased at 2095e in order to cool the unit; the flow of the first and second stacks both decrease correspondingly.
In the second 24-hour cycle (2067ea), the constant temperature of 800° C. is also varied to 700° C. by adjusting the flow, as indicated by 2090ea and 2091ea. Again, instead of having the flow through the second stack be 100% of the total flow as in the above-described examples, the flow is instead only increased to about 90% of the total flow as indicated by 2094ea. Further, because the operating temperature is set at 800° C., the necessity of bypass air begins at a lower amount than in previous examples. Similarly, instead of having the flow in the second stack start from 60% and increase upward to 100%, the flow extends from about 75% to about 90%. To accommodate for the additional 10% of flow, additional air begins flowing through the first stack earlier than in previous examples. The first stack's discharge temperature thus cools slightly earlier than previously described.
As noted above, the flow through the second stack is maintained at about 10%, e.g., 10%, during the charging phase of the second stack, as indicated by 2097ea. When the output temperature is varied to about 700° C., e.g., 700° C., at 2091ea, the discharge temperature of the first stack also approaches about 700° C., e.g., 700° C., at 2092ea. Because the air flow of the second stack and the first stack are maintained at a relatively constant proportions (as indicated by 2096ea and 2097ea, respectively) the discharge temperatures of the first and second stack behave in a similar manner as in the above examples. During the latter part of the solar day, the bypass flow is increased at 2095ea in order to cool the unit; the flow of the first and second stacks both decrease correspondingly.
Accordingly, 2060E illustrates that different sets of flow parameters may be used during a discharge period to change a temperature of an output fluid flow having a non-constant temperature profile. Furthermore, the output fluid flow temperature may be maintained during a charging phase by keeping the fluid flows of the first and second stack at a relatively constant proportion.
To recap, deep discharging is the discharging of a thermal storage stack to a sufficient degree to reduce local temperature nonuniformities within the stack, and thus reduce, mitigate, or eliminate thermal runaway within the stack (and thus extends its life). In some cases, a period of deep discharging may result in a stack being discharged all the way to some temperature floor—namely, the temperature of the bypass fluid flow (the “bypass temperature”). As has been noted, the bypass flow is a flow of cooler fluid within the thermal storage structure—it may be based, for example, on a fluid flow that enters the thermal storage structure via an inlet valve. Accordingly, deep discharging may in some cases cause a stack to be discharged all the way to the bypass temperature or to a temperature approximately equal to the bypass temperature (say, within 10% of the bypass temperature).
But as noted above relative to
As shown, the range of temperature has an upper bound of delivery temperature 2065u (here 600° C.), a lower bound of bypass temperature 20631o (200° C.), and a midpoint temperature 2098m (400° C.), which is the midpoint between the delivery temperature and the bypass temperature. Another temperature reference is shown, 2098 mm (300°), which represents a midpoint between the midpoint temperature and the bypass temperature, and thus may be referred to as a quartile temperature. Nine possible temperatures are shown: 500° C. (2098t1), 450° C. (2098t2), 360° C. (2098t3), 325° C. (2098t4), 275° C. (2098t5), 245° C. (2098t6), 215° C. (2098t7), 204° C. (2098t8), and 2000 (2098t9).
Typically, the deep-discharge temperature region's upper bound will be below the delivery temperature. In the case in which the upper bound were at, say 550° C., all 9 temperatures 2098t1-9 would be within the deep-discharge temperature region. Alternately, if the deep-discharge temperature region's upper bound were defined to be substantially below the delivery temperature, this might exclude just temperature 2098t1 from the deep-discharge temperature region. Substantially below means at least 20% below, and in other cases could be defined to be 25%, below 30% below, 35%, 40%, 45%, and so on. Temperature 2098t2 is thus 25% below delivery temperature and could be included in the deep-discharge temperature region depending on how the range is defined relative to the delivery temperature. Note that the lower bound of the deep-discharge region can be set to the bypass temperature or some higher temperature as desired.
Another way of defining the deep-discharge temperature region is that the upper end of the deep-discharge temperature region is closer to the bypass temperature than to the delivery temperature, and the lower end of the deep-discharge temperature region is the bypass temperature. Referring to chart 2098c1, this would mean that the upper bound would be at midpoint temperature 2098m (400° C.) (and for purposes of this example, the upper bound could include midpoint temperature 2098m). This definition of the deep-discharge temperature region would include temperatures 2098t3-2098t9, and exclude temperatures 2098t1-2098t2.
Still another way of defining the deep-discharge temperature region is that the upper end of the deep-discharge temperature region is closer to the bypass temperature than to the midpoint temperature, and the lower end of the deep-discharge temperature region is the bypass temperature. Referring to chart 2098c1, this would mean that the upper bound would be at quartile temperature 2098 mm (300° C.) (and for purposes of this example, the upper bound could include quartile temperature 2098 mm). This definition would include temperatures 2098t5-2098t9, and exclude temperatures 2098t1-2098t4.
Still further, an upper bound of the deep-discharge temperature region could be defined as those temperatures that are approximately equal to the bypass temperature. Thus, with “approximately equal” meaning within 10% of the bypass temperature, this would include temperatures between 200 and 220° C., encompassing 2098t7-2098t9.
Yet another way of defining the deep-discharge temperature region is to define an absolute temperature range measured up from the bypass temperature. Several ranges of this sort are shown in
In a similar manner, although not shown, the upper bound of the deep-discharge temperature may also be defined by establishing a temperature distance measured down from the delivery temperature. For example, a first range might have an upper bound of the delivery temperature minus 100° C. and a lower bound of the bypass temperature. A second such range might have an upper bound of the delivery temperature minus 125° C. and a lower bound of the bypass temperature. A third such range might have an upper bound of the delivery temperature minus 150° C. and a lower bound of the bypass temperature. A fourth such range might have an upper bound of the delivery temperature minus 175° C. and a lower bound of the bypass temperature. A fifth such range might have an upper bound of the delivery temperature minus 200° C. and a lower bound of the bypass temperature. Other ranges are possible, such as a sixth range in which the upper bound of the deep-discharge temperature region is the 300° C. below the delivery temperature.
The preceding Figures have described implementations in which each of two thermal storage arrays are deeply discharged every other discharge period. But this disclosure is not limited to the two-thermal-storage-array implementation. First of all, deep discharging may be performed when only a single thermal storage array is used. In such a configuration, the outlet temperature of the single thermal storage array is allowed to drop to a deep-discharge temperature region periodically-either at regular intervals or on an as-needed basis. In configurations with three or more groups, deep discharging may be performed less frequently.
Consider a configuration with N storage arrays.
Thus, in one generalization of a thermal energy storage system with some number N thermal storage assemblages, one possible implementation is that each of the N assemblages (2099a) is deeply discharged once (2099e) every N discharge periods (2099dp).
Consider another embodiment illustrated by table 2099t2, in which N=3 and again involves arrays 1, 2, and 3 (2099a). At the end of a period of VRE availability (e.g. The end of daytime for solar-charged systems), arrays 1 and 2 may complete the day fully charged; full heat is applied, properly by zone, without significant gas flowing through their conduits. Array 3, however, is operated in a discharging mode with high gas flow in its conduits during charging.
Suppose that after charging stops, discharge period 1 begins, and array 3 begins to discharge to provide output fluid flow. During the discharge period, lower-temperature discharge fluid from array 3 is mixed with higher-temperature fluid of array 1 to deliver the output fluid flow. Array 3 deeply discharges by cooling to a temperature that is close to the return gas temperature. Then, when the discharge fluid temperature of array 1 begins to decrease, significant flow through array 3 is terminated, and flow through array 2 is initiated.
Mixing of lower-temperature fluid from array 1 with higher-temperature fluid from array 2 also allows array 1 to deeply discharge. In this example, near the end of the discharge period, flow from array 1 is terminated, leaving only array 2 in operation. Thus, array 3 and array 1 both deeply discharge during discharge period 1, with array 2 partially discharging.
During the next cycle of discharging and charging, the operation of the arrays is rotated-thus, during discharge period 2, array 2 discharges first, followed by array 3, and then array 1. Arrays 2 and 3, but not array 1, are deeply discharged as a result. Similarly, during discharge period 3, array 1 discharges first, its high-temperature energy being mixed with other array discharges. As array 1 reaches its minimum usable outlet temperature, array 2 begins to add higher-temperature gas, until by the end of the discharge period, arrays 1 and 2 are deeply discharged and array 3 has a temperature profile similar to conduit 2010 at point in time 2051 in
The above-described processes have various advantages. For example, in the two-array implementation for a solar use case, each stack is deeply discharged every other day by flow control of the two stacks and a bypass; accordingly, variations in temperature that would otherwise arise from nonuniform heating or cooling in the stack and cause thermal runaway problems are avoided. Deeply discharging a stack causes it to thermally reset such that any nonuniformities that would otherwise cause thermal runaway are avoided or reduced. Further, parasitic drag may be avoided by use of a blended output temperature.
While the foregoing aspects are disclosed in the context of a thermal storage array having an internal resistive heating element to provide radiant heat transfer, the present disclosure is not limited to this configuration. For example, the lead-lag approach of having stacks operating in tandem with one stack in the lead mode and the other stack in the lag mode is also applicable in scenarios in which heat is externally delivered by gas.
In various implementations, the control system is configured to provide one or more control signals to control various aspects of the thermal energy storage system, including the louvers, the bypass valve and the fan or blower associated with the circulation of fluid through the thermal storage arrays. Additionally, instead of using a single blower for all thermal storage arrays, separate blowers may be provided for each of the airflows, such as the flow of air to the first stack, the flow of air to the second stack, etc. In such an alternative, the control system would control the blowers instead of controlling louvers. In other implementations, however, a combination of blowers and louvers may be used together to control the flow of air through the first stack, the second stack, and bypass to implement the lead-lag paradigm.
The safe and effective start-up of an OTSG and steam network involves several challenges. All equipment must be brought to operating temperature safely, without discharging sub-temperature fluid, including water, into the system outlet, as such discharges can cause substantial “steam hammer” damage and safety risks. The present innovation addresses these matters to provide a safe, efficient start-up for an OTSG whose heat source is a thermal energy storage unit.
At 2201, the outlet valve is in a closed position, or is set to a closed position. As explained above, sensors and communication devices associated with the control system may sense the position of the outlet valve, and if the outlet valve is not in the closed position, the control system may send a signal to the outlet valve, such that the outlet valve is transited to the closed position.
At 2203, the blowdown valve is opened. In a manner similar to that explained above with respect to 2201, the blowdown valve may be moved to the open position, if not already in the open position. A blowdown valve allows release of water and/or steam whose temperature or quality is below the temperature and/or quality required, without introducing the requirement of recirculation of fluid within the OTSG system.
At 2205, operation of a water pump is started, and low water flow is established. The conduits of the steam generator are now receiving water in liquid form.
At 2207, the operation of the fan associated with the thermal storage structure is started. For example, the fan may be the blower as explained above. Accordingly, a low hot air flow is established. Heat is thus introduced to the tubes. The previous establishment of water flow within the tubes prevents thermal damage.
At 2209, as the low hot air flows, and the low water flow is established through the steam generator, the water is heated, and steam starts to form from the heated water, as the water changes phase from liquid to gaseous form.
At 2211, as the hot air continues to flow and the heating of the steam generator continues, the pressure of the steam increases, and the vapor fraction or quality of the output steam rises.
At 2213, once the quality of the steam is above a threshold, such as 40%, the outlet of the steam generator opens and the blowdown valve closes. At this point, the steam may be output to the industrial application without the risk of introducing water or sub-quality steam into the application network.
At 2215, as the outlet opens and the steam generator continues to provide steam, the quality and flow of the steam rise to the required level for the industrial application associated with the output. This increase in flow rate may be at a rate chosen so as to allow the rate of change of other steam generators serving the same industrial load to reduce their flow rates proportionally; or at a rate chosen to match the declining steam production rate associated with shutting down a fuel-fired heater; or at another rate.
In some implementations, as steam or heat output from a thermal storage unit begins, a controller reduces the steam or heat output of one or more fuel-fired heaters (boilers, OTSGs, HRSGs, furnaces) which serve the same industrial process load, in such a manner as to maintain an approximately constant total steam supply to the industrial load.
Additionally, with respect to the shutdown sequence, at 2202, the fan transits from the on state to the off state. For example, the air blower may stop its operation.
At 2204, the water pump slows or reduces the flow of liquid water to the conduits of the steam generator.
At 2206, as the flow of heat slows, and the flow of water slows, the quality of steam drops. For example, the quality of steam may drop to a lower quality level, such as 50% or 60%.
At 2208, once the quality of steam has dropped below a prescribed level, the outlet valve returns to the closed position. Thus, the industrial application is no longer receiving steam, as the quality of steam has dropped below the necessary level for the industrial application.
At 2210, the water pump pumps water into the tubing so that the tubing or conduit of the outlet is completely filled with water.
At 2212, the natural circulation of air within the thermal storage structure continues to maintain the dynamic cooling associated with the outer wall invalidation, as explained above.
The example implementations may have various advantages. For example, as explained above, there is a dynamic insulation approach, which provides passive cooling of the thermal storage structure. The incoming cool air absorbs the heat on the outside of the insulation layer, and is eventually passed into the lower portions of the stacks of bricks. As a result, the heat is not transferred to the outer surface of the thermal storage structure. The thermal storage structure can thus house equipment having a wider temperature tolerance.
Further, there is lower risk of equipment damage, wear and tear, system failure, injury to the personnel, or other safety issue associated with the presence of heat at the surface of the outer container.
Further, the present disclosure contemplated the use of recirculated air to provide cooling for the thermal storage structure, thus eliminating or reducing the need for a secondary cooling system. During shutdown periods, passive buoyancy-induced flow continues so as to provide foundation cooling without backup power or special equipment. This provides an advantage over thermal energy storage systems using molten salt which require active cooling of the foundations of the molten salt tanks, provided by blowers that add to cost and to parasitic electric power consumption and require redundant diesel generator backups. By cooling the foundation as described in this disclosure, energy that was otherwise lost in prior systems is captured as useful energy, and thermal safety in all conditions is provided.
Additionally, there is an environmental benefit over previous approaches. Because the control system allows the thermal energy storage system to use the source electricity based on the daily supply and demand of energy, the source electricity that is produced when the supply exceeds the demand can be used for storage during the charging mode. When the demand exceeds the supply, the thermal energy storage system can discharge and provide electricity or outputs for other industrial applications to support the additional demand. This paradigm desirably reduces the need to use nonrenewable energy. Further, various industrial applications such as calcining, carbon capture and others may be performed using heat derived from renewable energy sources rather than nonrenewable sources. As a result, the generation of carbon dioxide or other greenhouse gases may be reduced.
In terms of efficiency and cost, the various implementations described in the present disclosure provide a more efficient approach to managing energy input and output.
Charts 2111 and 2121 compare daily power profiles for different seasons. Chart 2111 illustrates a power profile during a winter day, while chart 2121 illustrates a power profile during a summer day. At points 2115 and 2117, it can be seen that on a winter day, the power available very roughly corresponds to the charging power. At 2125 and 2127, it can be seen that for a portion of the day the power available corresponds to the charging power, but during the afternoon of the summer day, the charging power is substantially lower than the available power. As explained above, the “day” is defined as a diurnal solar cycle that begins with the time of sunrise and ends with the time of sunset; it is understood that the time of sunrise and sunset can vary depending on physical location in terms of latitude and longitude, geography in terms of terrain, date, and season. At 2119 and 2129, the actual electricity generated to the customer by the solar energy is shown. At 2113 and 2123, steam delivery is shown, which reflects the energy that is output or produced.
At 2131 and 2141, a comparison is provided, for a summer day, of non-deferred charging at 2131, and deferred charging at 2141, such as associated with the example implementations. The elements of 2131 roughly correspond to the elements of 2121 and 2101. By comparison, at 2141, with deferred charging, it can be seen that the charging power 2147 can very roughly match the power available on a summer day during the afternoon periods. Thus, the example implementations can use deferred charging to use the available power more efficiently.
The lifetime of the system components and the efficiency of energy storage may benefit from maintaining the storage core at a lower temperature; however, doing so reduces the amount of energy storage capacity. A thermal energy storage system in which the electrical heaters are embedded within the storage media core causes the heaters to remain at the media temperature over extended periods; and the long-term temperature exposure of the heaters is a key factor in their operating life. An innovation presented here contributes to extended heater and equipment life, by mitigating the annual average temperature that heaters experience. In the case where the storage unit is operated to provide a continuous supply of heat from a variable source, a controller may choose a state of charge below “full charge” on a daily basis, based on forecast energy availability and planned energy demand. For example, in a system powered by solar energy, summer days are longer, so a smaller number of hours of stored energy are required; hence in midsummer the storage unit may be operated by a controller to remain at a lower temperature (or “partial charge”) so as to extend system life and reduce thermal losses, without any reduction in energy delivered to system output. And, for example, in a system powered by solar energy, winter days have lower total energy available, so that the entire energy produced by an associated solar facility can be stored using only a portion of the storage capacity. A controller may operate the storage system in these conditions to maintain only partial charge, again so as to extend system life, without any loss of energy delivery at the system output. Various advantages are provided by other features of the overall system, including those relating to the arrangement of thermal storage arrays, as well as the constituent thermal storage blocks. Those features are the subject of the next Section.
Additionally, the present example implementations mitigate thermal stress effects in several ways. The present disclosure mitigates thermal stress arising from thermal expansion due to rapid heating and cooling by partitioning the storage media into bricks of a size and shape which enables rapid radiative heat transfer while maintaining thermal stress levels and patterns within the bricks below levels which induce prompt or gradual failures. Heat transfer flow conduits and flow rates are arranged such that turbulent flow of heat transfer gas provides relatively uniform cooling across the entire exposed heat transfer surface. The storage media bricks are arranged in an array that allows relative movement to accommodate expansion and contraction by individual elements. Also, the array is arranged such that cycles of thermal expansion align the elements of the array to preserve the integrity of the array structure, the integrity of the heating element conduits, and the integrity of the heat transfer gas conduits.
In some example implementations, individual bricks are designed such that their center of mass is close to a heating element, and an expanded surface area allows high contact with flowing air.
Traditional approaches to the formation of energy storage cells may have various problems and disadvantages. For example, traditional approaches may not provide for uniform heating of the thermal energy storage cells. Instead, they may use structures that create uneven heating, such as hot spots and cold spots. Non-uniform heating may reduce the efficiency of an energy storage system, lead to earlier equipment failure, cause safety problems, etc. Further, traditional approaches may suffer from wear and tear on thermal energy storage cells. For example, stresses such as mechanical and thermal stress may cause deterioration of performance, as well as destabilization of the material, such as cracking of the bricks.
In some implementations, thermal storage blocks (e.g., bricks) have various features that facilitate more even distribution. As one example, blocks may be formed and positioned to define fluid flow pathways with chambers that are open to heating elements to receive radiative energy. Therefore, a given fluid flow pathway (e.g., oriented vertically from the top to bottom of a stack) may include two types of openings: radiation chambers that are open to a channel for a heating element and fluid flow openings (e.g., fluid flow slots) that are not open to the channel. The radiation chambers may receive infrared radiation from heater elements, which, in conjunction with conductive heating by the heater elements may provide more uniform heating of an assemblage of thermal storage blocks, relative to traditional implementations. The fluid flow openings may receive a small amount of radiative energy indirectly via the chambers, but are not directly open to the heating element. The stack of bricks may be used alone or in combination with other stacks of bricks to form the thermal storage unit, and one or more thermal storage units may be used together in the thermal energy storage system. As the fluid blower circulates the fluid through the structure during charge and discharge as explained above, a thermocline may be formed in a substantially vertical direction. Further, the fluid movement system may direct relatively cooler fluid for insulative purposes, e.g., along the insulated walls and roof of the structure. Finally, a venting system may allow for controlled cooling for maintenance or in the event of power loss, water loss, blower failure, etc., which may advantageously improve safety relative to traditional techniques.
The present teaching is an advance in exploiting the physics of heat transfer to enable the cost-effective construction of thermal energy storage systems. Compared to prior art using solid media, designs according to the present disclosure reduce reliance on and improve the reliability of conductive heat transfer; deliver uniform high-temperature heat via convective heat transfer; and principally exploit direct radiative heat transfer, with heat radiating from a heating element and reradiating from heated storage materials (“radiation echoes”) to heat other storage materials rapidly and uniformly.
All objects in the universe emit thermal radiation at a rate proportional to their absolute temperature to the fourth power. Specifically, per the Stefan-Boltzmann law, the total energy radiated per unit surface area of a black body per unit time is proportional to the fourth power of the black body's thermodynamic temperature (in kelvin). Accordingly, small differences in temperature cause large differences in the rate of thermal radiation.
All objects in the universe also absorb thermal radiation. For any two surfaces exposed only to each other, and absent any incoming or outgoing heat, the differences in temperature between such objects exposed to each other rapidly reduce until the objects are at the same temperature, and thus in radiation equilibrium.
It is desirable for a system based upon electrical heating elements that heat solid media to operate heaters at a relatively high power loading—that is, to operate with high wattage per square cm of surface area. Doing so reduces the amount of heating material and cost per unit of charging energy (cost per kW). However, heating element life varies inversely with temperature, so in order to maximize power loading while keeping heating element temperatures as low as practicable, it is accordingly desirable for heaters to radiatively expose materials of the lowest and most uniform surface temperatures possible.
In some existing designs, e.g. residential “storage heaters” and Stack disclose designs, heaters are exposed to only a relatively small surface area, for instance by being embedded in channels. Prior art based on Stack's teachings and related designs can be expected to suffer greatly from any nonuniformity in brick size, internal structure, or material composition, since the only means by which surface temperature is controlled is by internal conduction of heat away from the outer surface into the inner material.
Variations in aggregate content within the brick itself can contribute to varying thermal conductivity. Such variations in heat conduction will necessarily result in variations in surface temperature if incoming radiation is heating the surface, and such variations will be significant if thermal radiation is unable to carry away higher-temperature energy to lower-temperature regions. More significantly, any cracks formed within a brick can cause great reduction the thermal conductivity across the crack, and consequently if the brick is being radiatively heated this will reduce heat conduction away from the surface, and thus cause regions of higher surface temperature unless thermal radiation can carry away such energy. A design based on, e.g., the Stack design would experience large increases in surface temperature in both these cases, as only relatively small, local surface areas are in radiation communication due to the “channel” design concept. Mitigating these problems incurs costs. Because brick with higher thermal conductivity is more expensive than brick with lower thermal conductivity, and because electrical heating elements are expensive, previous teachings have had serious limitations in practically achievable temperatures and challenges in material usage (heater material usage per kW) and per kWh (storage material usage per kWh), due to requiring average temperatures be low enough to accommodate such local variations. Such previous designs are vulnerable to in-field failures arising from brick cracking contributing to heater failures. Any such crack formation would require reducing or ceasing the powering of heaters in the zone with cracking—as replacement heaters installed at that location would continue to experience such abnormal temperatures—and/or disassembly of the TSU and replacement of cracked bricks, both of which are quite impractical from a cost point of view. In consequence, units of such design would be vulnerable to degradation in their usable storage capacity and charging rate.
It is also desirable for systems that heat solid media to avoid high temperature gradients within the solid media, as differential expansion based on temperature results in stresses that may cause cracking or degradation of the media as it successively heats and cools during charging and discharging operations, with resulting large time-varying stress patterns. In designs in which heaters are exposed to only a relatively small surface area, only a relatively small fraction of the bulk material is heated by radiation, and a large proportion of the heating is accomplished via heat conduction within the material. As conductive heating is proportional to ΔT within the material, per Newton's law of cooling, the rapid heating required in VRE-charged storage media creates significant potential for such systems to experience degradation and cracking from thermally induced stresses. In this sense, a desired property for heater designs—high wattage per unit of surface area—is intrinsically in conflict with a desired property for brick designs—low wattage per surface area—when heaters are installed in channels or narrow passages such as taught by Stack and “storage heaters”.
It is further desirable for systems that deliver high-temperature heat from solid media to achieve “thermocline” conditions during discharge, in which portions of the media are cooled to much lower temperatures—releasing more energy per kg of material—than other portions, which remain at high temperatures—thus allowing the delivery of relatively high continuous outlet temperatures throughout an extended period of discharging while the bulk of the storage media swings across a large change in temperature (ΔT). In service of this goal, convective heat transfer by flowing air which is heated effectively and comes into balance with local media temperature as it flows through successive regions of material is advantageous. An example of such effective thermocline design is the Cowper stove, which incorporates a plurality of long narrow vertical air passages within a brick array, inducing turbulent airflow within the passages and thus effective heat transfer between air and adjacent brick in each zone as air proceeds through the material. Provisions that prevent the transfer of heat via radiation from relatively hotter zones to cooler zones are desirable, as such downward vertical radiative heat flow would decrease the temperature differential between the bottom and the top of the thermocline, reducing its effectiveness and thus lowering the available stored energy per unit of material. The Cowper stove's narrow air passages limit the mutual radiative exposure of surfaces in the vertical axis (due to cos Θ), and thus the Cowper stove design satisfies both these criteria for effective thermocline design.
However, the Cowper stove design contains a liability. The air passages in Cowper stoves are comprised of many bricks stacked vertically within the unit, each of which has a plurality of passages which must be properly aligned with their corresponding passages in bricks above and below during assembly. Any misalignment during assembly, or due to cyclic thermal expansion and contraction during operation, causes blocking of flow through the passages. Any cracking or spalling of brick, or any introduction of foreign material that introduces material within a passage at any point causes the blockage of flow in the entire passage. In a Cowper stove design, in which the system is heated and cooled convectively, this causes a partial loss of heat storage capacity, as such region is neither effectively cooled nor effectively heated. However, in an electrically radiant heated energy storage unit, such blockages of airflow have greater consequence, as they cause large reductions in cooling during discharge, but no reductions in incoming thermal radiation from heaters. Accordingly, passage blocking can cause larger consequences in electrically heated energy storage units, because as discussed above, variations in unit temperature can contribute to premature heater or brick failures, and in consequence an entire unit may have to be operated at a lower temperature so that the peak temperatures associated with the nonuniformity do not exceed safe material operating temperatures.
Some designs, e.g. Siemens ETES, incorporate unstructured media with randomly distributed air passages, causing zones of higher and lower temperature air to mix, and allowing low-temperature air to bypass regions of high temperature solids without being heated, thus reducing thermocline effectiveness and increasing the amount of solid media required to deliver a given amount of thermal energy while maintaining a target outlet temperature, increasing storage media usage per kWh.
Designs according to the present disclosure combine several key innovations, which together address these challenges and enable a cost-effective, safe, reliable high-temperature thermal energy storage system to be built and operated. A carefully structured solid media system according to the present teaching incorporates structured airflow passages which accomplish effective thermocline discharge; repeated mixing chambers along the direction of air flow which mitigate the thermal effects of any localized air channel blockages or nonuniformities; effective shielding of thermal radiation from propagating in the vertical direction; and a radiation chamber structure which uniformly and rapidly heats brick material with high heater power loading, low and uniform exposed surface temperature, and long-distance heat transfer within the storage media array via multi-step thermal radiation.
Innovative structures according to the present disclosure may comprise an array of bricks that form chambers. The bricks have structured air passages, such that in the vertical direction air flows upwards in a succession of open chambers and small air passages. In some embodiments, the array of bricks with internal air passages is organized in a structure such that the outer surface of each brick within the TSU core forms a wall of a chamber in which it is exposed to radiation from other brick surfaces, as well as radiation originating from an electrical heater.
The chamber structure is created by alternating brick materials into a checkerboard-type pattern, in which each brick is surrounded on all sides by open chambers, and each open chamber has adjacent bricks as its walls. In addition, horizontal parallel passages are provided that pass through multiple chambers. Electrical heating elements that extend horizontally through the array are installed in these passages. An individual heating element it may be exposed along its length to the interior spaces of multiple chambers. Each brick within such a checkerboard structure is exposed to open chambers on all sides. Accordingly, during charging, radiant energy from multiple heating elements heats all outer surfaces of each brick, contributing to the rapid and even heating of the brick, and reducing reliance on conductive heat transfer within the brick by limiting the internal dimensions of the brick.
Such a chamber structure further provides that a first portion of the heat that emanates from an electric heating element is absorbed by a given first brick surface and further transferred by conductive heat transfer within the brick, thus heating that brick; and another portion of the heat is absorbed by a second brick surface relatively closer to the heater than the first brick surface, raising the temperature of that second brick surface. Because the second brick surface grows hotter than brick surfaces farther away from the heater the second brick surface radiates heat to those farther brick surfaces due to the temperature differential. This process of radiation absorption of bricks, leading to temperature rise, and thence leading to increased thermal radiation, is referred herein as “reradiation.” The reradiation of thermal energy throughout the brick stacks is an important factor in the rapid, even heating of bricks. The structure is arranged such that heating elements are radiatively exposed to passages that extend in a horizontal direction, achieving relatively uniform heating across a given horizontal layer tier of bricks, while inhibiting radiative heating from the heating elements in a vertical direction, thus achieving and allowing persistent of an advantageous vertical thermocline.
The radiation chamber structure provides a key advance in the design and production of effective thermal energy storage systems that are charged by electrical energy. The large surface area, which is radiatively exposed to heaters, causes the average temperature of the large surface to determine the radiation balance and thus the surface temperature of the heater. This intrinsic uniformity enables a high wattage per unit area of heater without the potential of localized overheating. And exposed brick surfaces are larger per unit of mass than in prior systems, meaning that incoming wattage per unit area is correspondingly smaller, and consequently thermal stresses due to brick internal temperature differences are lower. And critically, re-radiation of energy—radiation by hotter brick surfaces that is absorbed by cooler brick surfaces—reduces by orders of magnitude the variations in surface temperature, and consequently reduces thermal stresses in brick materials exposed to radiant heat. Thus, the radiation chamber design effectively enables heat to be delivered relatively uniformly to a large horizontally oriented surface area and enables high wattage per unit area of heater with relatively low wattage per unit area of brick.
Note that while this configuration is described in terms of “horizontal” and “vertical”, these are not absolute degree or angle restrictions. Advantageous factors include maintaining a thermocline and providing for fluid flow through the stack in a direction that results in convective heat transfer, exiting the stack at a relatively hotter portion of the thermocline. An additional advantageous factor that may be incorporated is to position the stack in a manner that encourages buoyant, hot air to rise through the stack and exit at the hot end of the thermocline; in this case, a stack in which the hot end of the thermocline is at a higher elevation than the cold end of the thermocline is effective, and a vertical thermocline maximizes that effectiveness.
By arranging the chambers with a relatively high aspect ratio and predominantly horizontal axis, thermal energy is transferred by multiple steps of reradiation to regions of brick that extend far from the heating element; and as the bulk storage temperature rises, the effect of the ° K{circumflex over ( )}4 (the fourth power of the thermodynamic temperature) thermal radiation drives a very strong “temperature leveling” effect. That is, the hotter the cell becomes, the smaller the differences between the hottest and coolest portions of the cell. As a result, the charging heat transfer within the brick array becomes more effective as temperature rises, and the entire media structure is heated to a uniform temperature with a much smaller total amount of heating element than would be required in a design without a radiative heat transfer structure. This is in sharp contrast to previous teachings, including Siemens and Stack, which can be expected to experience lower heat transfer effectiveness relying on conductive ΔT, which diminishes as bulk storage media temperature rises.
An important advantage of this design is that uniformity of heating element temperature is strongly improved in designs according to the present disclosure. Any variations in brick heat conductivity, or any cracks forming in a brick that result in changed heat conductivity, are strongly mitigated by radiation heat transfer away from the location with reduced conductivity. That is, a region reaching a higher temperature than nearby regions due to reduced effectiveness of internal conduction will be out of radiation balance with nearby surfaces, and will as a result be rapidly cooled by radiation to a temperature relatively close to that of surrounding surfaces. As a result, both thermal stresses within solid media, and localized peak heater temperatures, are reduced by a large factor compared to previous teachings.
Equally important, the effect of any brick spalling, cracking, or the introduction of foreign materials within air passages is greatly minimized. An individual brick that experiences the blocking of a passage will experience reduced cooling during discharge cycles, and its surface and internal material will remain hotter than adjacent areas, and thus such an area will effectively store less energy, as energy storage is proportional to ΔT. Because the surface of the brick is in radiative communication with other bricks via the open radiation chamber, radiation will transfer heat from such blocked-passage area to other bricks. Thus, the final ΔT experienced in a heating-cooling cycle for a design with open radiation cavities will be larger than the ΔT for any design, such as Cowper stoves or Stack, that does not incorporate this concept. The effect of any brick spalling, cracking, or introduction of foreign materials into an air passage is further minimized due to the flow of air in the vertical axis during discharge. The presence of the radiation chambers eliminates any effect of passage blocking in one brick from affecting flow within the brick above it or below it, since air freely mixes in the chambers between bricks. Similarly, misalignments between bricks in the vertical direction cannot cause air passage blockage, as the narrow air passages in bricks are not in contact, but separated by open chambers.
Overview
As explained in the foregoing discussion, a system for thermal energy storage is provided that includes an input of electrical energy from a supply, one or more thermal storage units, and a fluid output (which may be or include a gas), such as steam and/or heat, to an application. As explained above, the supply may be an energy source, such as one or more photovoltaic cells. Other energy sources may be employed in combination with or substitution for the photovoltaic cells.
The electrical power sources may be any one or a combination of VRE power sources including wind and solar power, less variable renewable sources including hydroelectric and geothermal power, or other power sources including thermal power plants powered by coal, oil, gas nuclear, or any other method of electrical power generation that might be apparent to a person of ordinary skill in the art.
The thermal storage units may each include one or more heating elements (e.g., resistive heating elements) controlled by switches that manage and enable the heating elements to receive the electrical energy from the input, and an energy storage structure such as a brick. A fluid movement system, (e.g., one or more blowers that may be oriented to push fluid unto the system or pull fluid from the system) directs fluid through fluid flow paths in the thermal storage units.
The energy storage structure includes tiers of thermal storage blocks. For example, a first tier of thermal storage bricks may be arranged in an alternating pattern, such that a gap is formed between adjacent or neighboring bricks. A second tier of bricks is positioned adjacent to the first tier, also in an alternating pattern with a gap formed between adjacent or neighboring bricks. The first tier of bricks and the second tier of bricks are positioned with respect to one another such that the gaps of the first tier bricks are adjacent to the second tier bricks, and the gaps of the second tier bricks are adjacent to the first tier bricks.
One or more of the first-tier bricks in the second-tier bricks may have airflow channels formed therein. More specifically, the airflow channels may be formed as apertures, holes, conduits or slots. For example, the airflow channels may be formed as an elongate slot, with a longer dimension being nonparallel to a surface of each brick that is adjacent to a gap. In some implementations it may be advantageous for the air channels to have their longer dimension substantially orthogonal to a surface of each brick that is adjacent to a gap. In other implementations it may be beneficial for the air channels to have their longer dimension substantially parallel to a surface of each brick that is adjacent to a gap.
Because the air channels have one axis of short dimension oriented as explained above, turbulent flow may be induced, contributing to effective heat transfer between air and the brick as it passes through the brick. Accordingly, a benefit of the slot arrangement may be a more effective cooling of each brick as air passes through the brick, and consequently a more effective thermocline during discharging.
The airflow channels and the gaps between adjacent or neighboring bricks are formed in such a manner as to create airflow paths. More specifically, a first air flow path extends through the airflow channels of a first-tier brick and a second-tier gap adjacent to the first tier brick, and a second air flow path extends through the airflow channels of the second-tier brick and a first tier gap adjacent to the second tier brick.
The heater or heating element, which may be a resistive heating element coupled to the input of electrical energy from the supply in a means which includes at least one control switch which may adjust input power to any fraction of the currently available power, is positioned adjacent to the first tier of bricks and the second tier of bricks. For example, the heating element may extend parallel to a longitudinal direction of the tiers of thermal storage bricks. According to one example implementation, the heating element extends laterally in a curvilinear pattern, between rows of the plurality of blocks.
According to one example implementation, the second tier may be positioned above the first tier, such that the airflow paths are substantially vertical. However, the example implementations are not limited thereto, and other spatial arrangements between the first tier and the second tier as may be understood by those skilled in the art may be used in substitution or combination with the substantially vertical air flow paths.
Further, while the foregoing example implementation discloses a first tier and a second tier, the present example implementation is not limited thereto. For example, one or more additional tiers may be incorporated with the first tier and the second tier, to form additional alternating patterns having gaps and airflow channels. Further, the bricks in each of the additional tiers may be positioned to form additional portions of the first and second airflow paths, such that the additional airflow paths extend through airflow channels of a brick, and through a gap of a tier adjacent, such as above or below, the brick.
In the foregoing multiple tiers of bricks, the dimensions of the bricks may be varied, such that the tiers at or closer to an upper portion of the stack may be larger in at least one dimension, such as height, as compared with bricks at or closer to a lower portion of the stack. By having such variation in the dimensions of the bricks, brick size may be optimized to account for greater weight loads near the lower portion of the stack, and/or higher air temperatures closer to the upper portion of the stack. Example, bricks in the upper layers may be taller than the bricks in the lower layers. The reason for this is because as gas is constantly flowing in at the bottom of the stack and cooling the lower levels, more heat power is needed per unit mass to heat the bricks near the bottom of the stack.
More specifically, the heat from the heating element is not only heating up the brick itself, but also heating the gas within the volume of the brick up to a desired temperature. Moving vertically toward the upper portion of the staff, the same heater may heat larger bricks, because the bricks do not have the same incoming air that needs to the heated as the bricks near the bottom of the stack. Moreover, the heaters have a certain amount of power that they are capable of outputting, such that the heaters at the upper and lower portions of the stack may have a heater with similar or same power output. Thus, the cavities may be taller towards the upper portion of the stack, because the entering air has already been heated by the bricks at the lower portion of the stack, and the energy from the heating elements is heating up the mass of the brick itself, as opposed to the air within the volume of the mass of the brick.
In some implementations, a control system for the heater elements is configured to power heater elements at one or more different levels independently, e.g., to output more or less energy depending on the height (e.g., tier) of the heater elements in the assemblage.
Multiple stacks of bricks may be arranged adjacent to one another to form a thermal storage unit. Similarly, multiple thermal storage units may be arranged adjacent to one another to form the thermal energy storage system.
Example implementations may also provide an efficient and reliable thermal storage system that involves use of multiple thermally conductive and absorbing bricks being stacked together to form thermal energy storage cells having sizes and material compositions chosen to mitigate thermal stresses. The thermal storage system may also maintain a constant temperature profile across the length of the cells (stacked bricks) thereby slowing temperature ramp, and reducing the generation of hot and cold hot spots, mechanical stress, thermal stress, and cracking in the bricks.
In some example implementations, the system may include multiple cells to form a thermal unit. The system may include multiple cells, each cell being made of multiple stacks. During charging, a controller may provide power flowing at different rates at different times selectively to individual heating elements or groups of elements so as to control the rate of heating of specific subsections of stacks, or specific stacks within the unit, or specific sections (e.g., specific bricks or sections of bricks within a stack.
For example, if only 60% of maximum energy capacity is anticipated during a specific charging cycle, only elements in 60% of stacks or in 60% of bricks in the system may be heated. The selective heating of specific heating elements may ensure that 60% of bricks achieve maximum temperature during the charging period, instead of heating all of the elements causing 100% of bricks being heated to 60% of maximum temperature.
Such a charging configuration may have various benefits and advantages. For example, the efficiency discharge of energy during a discharging operation may be substantially increased.
The system may include one or more air blowing units including any combination of fans and, blowers, and configured at predefined positions in the housing to facilitate the controlled flow of air between a combination of the first section, the second section, and the outside environment. The first section may be isolated from the second section by a thermal barrier. The air blowing units may facilitate the flow of air through at least one of the channels of the bricks from the bottom end of the cells to the upper end of the cells in the first section at the predefined flow rate, and then into the second section, such that the air passing through the bricks and/or heating elements of the cells at the predefined flow rate may be heated to a second predefined temperature, and may absorb and transfer the thermal energy emitted by the heating elements and/or stored by the bricks within the second section. The air may flow from the second section across a steam generator or other heat exchanger containing one or more conduits, which carry a fluid, and which, upon receiving the thermal energy from the air having the second predefined temperature, may heat the fluid flowing through the conduit to a higher temperature or may convert the fluid into steam. Further, the system may facilitate outflow of the generated steam from the second end of the conduit, to a predefined location for one or more industrial applications. The second predefined temperature of the air may be based on the material being used in conduit, and the required temperature and pressure of the steam. In another implementation, the air leaving the second section may be delivered externally to an industrial process.
Additionally, the example implementations described herein disclose a resistive heating element. The resistive heating element may include a resistive wire. The resistive wire may have a cross-section that is substantially round, elongated, flat, or otherwise shaped to admit as heat the energy received from the input of electrical energy.
With regard to the composition of the resistive heating element, if the resistive heating element is a resistive wire, it may be metallic. Further, the resistive heating element need not be limited to metallic wire, and may instead be formed from another material, such as a ceramic, including but not limited to silicon carbide, magnesium silicide, or may be formed from a combination of these and/or other materials.
Bricks and Stacks
Example implementations of the energy storage system include a housing comprising at least two sections (also referred to as cells) which may be fluidically coupled to each other. A first section may include one or more thermally conductive bricks of being stacked together with each other to form a thermal storage cell within the housing. Note that some blocks may be relatively large and include multiple portions (e.g., rectangularly-shaped brick portions). Thus, a given block may include portions on multiple tiers and may cover multiple chambers. A heating element may be suspended from a support within a passage within the array, or may mechanically form part of the array itself (as, for example, a conductive ceramic material formed as one or more bricks within the array), or may be positioned adjacent to the array (as, for example, a heating element such as a tungsten or xenon element encapsulated in a material which is at least partially transparent to electromagnetic radiation in the infrared and visible spectrum).
One or more of the bricks may include at least one channel extending longitudinally between two opposite ends of the bricks. Accordingly, at least one of the channels of each of the stacked bricks corresponding to one of the cells are in line with each other. Alternatively, such channels by be arranged such that adjacent bricks channels are arranged together to create a channel. A number of bricks may be stacked over one another to form an assemblage of the required height. The height of the cells may be selected considering the height of the housing. Further, the dimension of the bricks that are stacked over one another may be the same, or it may be different. For example, the bricks and an upper portion of the cell may have a greater height than the bricks at a lower portion of the cell.
The system includes at least one heater or heating element disposed within at least one of the channels corresponding to each of the bricks. Each of the heating elements may be electrically connected to one or more electrical power generation sources (also referred to as electrical energy sources), either individually or collectively, and may be configured to receive electrical energy from the electrical power generation sources and generate thermal energy, such that temperature of each of the heating elements reaches to a temperature.
The application of electrical power to the heating element may be controlled based on optimal heating conditions configured to reduce thermal stresses in the bricks. Such electrical control may be implemented by switches of various types, including electromechanical contactors and semiconductor devices including thyristor and transistor type devices including insulated-gate bipolar transistors (IGBTs). The control of electrical power to the heating element may be determined by a controller that takes into account values of currently available total energy from a VRE source or other parameters in determining a desired rate of charging. The controller may operate a switch multiple times per second in a control circuit whereby such operation of the switch enables a heater to receive one of many average power levels. The controller may operate a plurality of such switches in a pattern such that an incoming amount of total power is distributed uniformly or nonuniformly across a varying number of heaters whose total power demand (if all operated at full power concurrently) may exceed the incoming available power. For example, electrical energy may be controlled to keep the heating element a fixed temperature above the surrounding bricks to reduce thermal stresses. As the brick temperature increases, more electrical energy may be applied to the heating element to increase the temperature of the heating element to the maximum temperature achievable by the heating element. Therefore, heater elements at different vertical elevations within an assemblage of thermal storage blocks may be operated at different temperatures, as higher blocks will typically have a greater temperature.
Further, in some example implementations, the electrical power applied to the heating element may be gradually ramped in during generation to prolong the life of the heating element. The means of this ramping may include a controller commanding external power conversion devices, including solar inverters, to adjust their power delivery, and may include a controller commanding semiconductor switching devices including thyristors and IGBTs to rapidly switch in a time-varying pattern. Additional optimizations of the charging of the system may be achieved by controlling the application of electrical power to the heating element.
In an example implementation, bricks may be made of thermally conductive and absorbing materials having a composition and dimensions, such that thermal energy emitted by the corresponding heating elements, upon receiving the electrical energy, may heat each of the bricks and the corresponding cells up to the first predefined temperatures. Further, the cells may be configured within the housing such that there is a predefined gap between adjacent cells, to facilitate the flow of fluid through the cells.
Brick Structure and Shape
The structure and shape of the bricks is configured to repeatedly heat and cool for the purpose of storing energy. Energy input is provided in the form of electrical energy, which heats wires, filaments, rods, or other solid conductive materials to emit radiant thermal energy. The energy output is in the form of heat delivered in a circulating gas introduced at one portion of the structure, and which leaves another portion of the structure at a higher temperature. The structure includes refractory materials (e.g., bricks), which may be in the form of one or more cast or extruded shapes, and so arranged as to have an alternating sequence, along both vertical and horizontal axes. The structure includes a plurality of open chambers and bricks, with the bricks including air passages having at least one dimension which is much smaller than the other two dimensions. The passages are open to the chambers at its top and bottom surfaces, and are internally exposed to a radiating surface heated by electrical resistance. In the chambers, heat is transferred by thermal radiation from relatively hotter surfaces to relatively cooler surfaces.
In more detail, as shown in
The system as above, in which the brick materials whose respective surfaces form the walls of the chamber each have internal flow passages 37005, which allow air to flow, having at least one dimension that is substantially smaller than other dimensions, which causes the flowing air to have at least partly a turbulence pattern. Additionally, the system incorporates one or more regions below the first heated chamber, with air passages which enable flow upwards into the heated chamber, but so arranged as so block thermal radiation emitted by the heated chamber.
Electrical switches (not shown) control the operation of the electrical heaters under the command of a control system (not shown). Further, louvers and/or variable speed fans may control the rate of flow of air upwards within the air passages and chambers.
The structure of bricks and stacks may promote the flow of energy in the horizontal plane by giving radiation a free line of sight, or capability to radiatively move energy rapidly in the horizontal plane. This approach may reduce or avoid hot spots. Simultaneously, energy is discharged the vertical axis to the top of the stack. By allowing radiation to move freely in the horizontal plane but not substantially in the vertical axis, the thermocline may be maintained (and vertical reradiation from the point of discharge back down the stack is obstructed, such that the energy flows to the output in an intended manner).
The overall shape of the brick 3301 includes a first section that extends longitudinally in a first direction, a second section that is oriented orthogonally to the first section and extends longitudinally in a second direction, and a third section that extends longitudinally in the first direction. Thus, the brick 3301 has a zigzag appearance. Each of the sections has the openings 3303 in a repeated pattern extending along the upper center surface, framed by the seating portion 3305 along the periphery. The seating portions of the second section and third section are shown as 3309 and 3311, respectively. Additional recesses 3315 and 3317 are provided at opposite ends of the first and third sections of the brick 3301.
In the illustrated implementation, fluid flow slots are elongated in one horizontal direction. As shown, fluid flow slots may be oriented with their longer direction parallel to heater channels and perpendicular to radiation cavities at a given level.
Thus, the bricks 3501 may be arranged in a stacked structure to form an assemblage, and multiple assemblage may be arranged to form a unit or cells, with a given TSU having one or more units or cells.
The chamber formed by the sections 3103, 3105 and 3107 is directly behind section 3103, directly below section 3105, and directly to the left of section 3107 as illustrated. Other bricks 3101 may be positioned in a stacking or interlocking manner with respect to the brick 3101, to form additional sides of the chamber.
In some implementations, the blocks are stacked adjacent in vertical tiers such that fluid cannot flow between tiers of blocks in a horizontal direction, but flows only through vertical fluid pathways defined by fluid slots and radiation chambers. This may facilitate controlled, even heating in various implementations.
By forming an interlocking pattern between bricks, the stack may be laterally supported on the sides. For example, separate bricks at 3909 and 3911 are spanned by a single brick at 3901 and 3903, to form the interlocking pattern with the underlying bricks. As explained above, an upper surface of the brick has slots in a central portion and a lip at the edge portion. The lip at the edge portion supports the load of another brick that is above the brick. Generally, lips or shelf portions on thermal storage blocks may interlock with other lips/shelves or with other block portions to prevent blocks from shifting laterally relative to one another. For example, in an earthquake, the bricks may not move because they are surrounded with other bricks that are interlocked using the lip structure. The lateral support may result in a more stable structure for the stack.
Additionally, the individual bricks may be formed at greater scale, with additional walls, rows, chambers, vertical levels, slots and the like used into a single block structure, such that multiple chambers are formed within the single block structure. The blocks may all be of the same size, or they may be of different sizes. For example, and as explained above, the height of bricks in the lower region of the stack may be less than the height of bricks in the upper region of the stack. By having larger structures, fewer structures are required to form a stack. Similarly, multiple bricks may be fused together prior to stacking, to have the same effect as a brick manufactured as a very large size and scale as a single block. In either case, a potential benefit of having fewer structures to form a stack is the ease of assembly, e.g., in requiring the fitting of less pieces to one another. Further, the approach with larger blocks may also avoid a potential disadvantage of assembling more and smaller bricks, in that the interlocked bricks that are stacked on top of each other may rub against one another during the thermal expansion, thus causing additional wear and tear. The larger bricks have a smaller surface area in contact with other bricks, which may result in less wear and tear.
In some implementations, the slots that are adjacent to the heating elements are parallel to the heating elements, while the slots that are above the heating elements are orthogonal to the heating elements. In these implementations, the slots may be perpendicular to a wall from which the energy will be radiatively received. As can be seen in the drawing, a long row of slots is formed above and parallel to the direction of the heating elements. The bricks have slots that are orthogonal to the long rows of slots, and those slots are spaced apart by the radiative chambers.
In some implementations, thermal storage blocks may be sized based on thermal conductivity. For example, in some implementations the thermal energy should be radiated into the brick with a certain thermal conductivity, within a certain amount of time, given the thermal mass. If the brick size is too large, the amount of time required for the energy to be radiated into the center portion of the brick may exceed the available time, and the central portion of the brick will not heat up in time for the charge and discharge cycles. On the other hand, if the chamber is dimensioned below a certain width, while the temperature may become more homogeneous, the chamber may become too narrow, which may cause problems with flow or structural integrity.
The overall shape of the blocks may also be varied. While the examples shown herein illustrate rectangular volumes with relatively flat walls and interlocking structures with orthogonally position structures formed above or below, the shape is not limited. For example, the bricks may be formed such that the overall shape is trapezoidal or oval instead of rectangular. Further, the wall need not be flat, and may be curved, serpentine or some other profile. Also, as an alternative to having slots in the bricks, the bricks may be configured to be stacked with substantially thinner elements to form gaps between the bricks, and alternating the bricks, to form the gaps as the equivalent of slots, such that the fluid passes between the bricks.
In the illustrated example, the blocks also include slots 4605 positioned above the channels for the heater elements. Fluid flow may also occur via these slots, e.g., due to movement caused by a blower or due to buoyancy of heated fluid. As shown, the heater channels 4607 are located adjacent to radiation cavities and orthogonal to the vertical direction of fluid flow, which may promote horizontal radiation and energy transfer. The heater elements may also heat the bricks via convection.
As shown, in some implementations the size of the radiation cavities is fairly large relative to the size of the block portions that bound the cavities. In some implementations, the area covered in a horizontal plane by a given radiation cavity is at least 40%, 60%, 70%, or 80% of the area of a surface of a portion of a thermal storage block that bounds the radiation cavity (where the area of the surface of the portion of the thermal storage block includes the area of any slots in the portion). The substantial size of the radiation cavities may facilitate even heating via radiated energy.
Note that the block(s) of
The system may include multiple units 4107, 4109 that are individually controlled for discharge and charge, as explained above. Each of the units 4107, 4109 include stacks of bricks formed in columns 4119. The bricks 4121 may include a passage or opening 4123, through which the resistive heating element may pass.
At the lower portion of the units 4107, 4109, the flow of incoming fluid may be controlled by louvers 4111 and 4113, respectively. The louvers may be operated in conjunction with the hot fluid bypass, which is explained above with respect to the overall system. As also explained above, each unit 4107, 4109 is controlled independently, such that the louver 4111 is open while the louver 4113 is closed. Similarly, fluid dams or louvers may be provided at the upper portions, as depicted at 4115 and 4117, respectively
Each of the units 4207, 4209 may be separated by one or more brick support structures or walls having insulated properties. Thus, the controller may independently control the charge and discharge of each of the units 4207, 4209. Further, as explained above louvers 4211 and 4213 are provided to control the flow of input pair to the units 4207, 4209. As shown at 4215, the heated fluid is channeled to the steam generator 4205. For reference, each of the units 4207 includes multiple columns 4221 of stacked bricks 4217, including heating elements in a space at 4219.
In some implementations, the system uses dynamic insulation to advantageously improve insulation of a TSU, allow use of less expensive insulation materials, increase equipment life, or some combination thereof. In some implementations, the system uses a stream of fluid that will eventually pass through one or more assemblages of thermal storage blocks to first facilitate passive insulation. In some implementations, the fluid is recycled, e.g., from a steam generator.
Further, the system may advantageously use failsafe venting to avoid overheating in certain failure scenarios. The venting may also be used for temperature reduction to allow TSU maintenance. Disclosed dynamic insulation and failsafe venting techniques may be implemented independently (e.g., a system may use dynamic insulation but not failsafe venting or vice versa). In some implementations, however, the two techniques operate in a synergistic manner. For example, the failsafe venting may use the chimney effect to passively draw fluid through passageways through which fluid is normally directed by a blower for dynamic insulation.
In some implementations, at least a portion of the steam generator is included within the outer enclosure 5801 (as shown in
The inner enclosure 5823 includes two vents 5815 and 5817 which include corresponding vent closures in some implementations (portions of vent door 5813, in this example). In some implementations, vents 5815 and 5817 define respective passages between an interior of the inner enclosure 5823 and an exterior of the inner enclosure. When the external vent closure 5803 is open, these two vents are exposed to the exterior of the outer enclosure as well.
As shown, the vent 5815 may vent heated fluid from the thermal storage blocks conducted by duct 5819. The vent 5817 may allow entry of exterior fluid into the fluid passageway and eventually into the bottoms of the thermal storage block assemblies via louvers 5811 (the vent closure 5809 may remain closed in this situation). In some implementations, the buoyancy of fluid heated by the blocks causes it to exit vent 5815 and a chimney effect pulls external fluid into the outer enclosure via vent 5817. This external fluid may then be directed through louvers 5811 due to the chimney effect and facilitate cooling of the unit. Speaking generally, a first vent closure may open to output heated fluid and a second vent closure may open to input external fluid for passive venting operation.
During passive cooling, the louvers 5811 may also receive external fluid directly, e.g., when vent closure 5809 is open. In this situation, both vents 5815 and 5817 may output fluid from the inner and outer enclosures.
Vent door 5813 in the illustrated implementation, also closes an input to the steam generator when the vents 5815 and 5817 are open. This may prevent damage to steam generator components (such as water tubes) when water is cut off, the blower is not operating, or other failure conditions. The vent 5817 may communicate with one or more blowers which may allow fluid to passively move through the blowers even when they are not operating. Speaking generally, one or more failsafe vent closure may close one or more passageways to cut off fluid heated by the thermal storage blocks and reduce or avoid equipment damage.
When the vent door 5813 is closed (e.g., as shown in
In the closed position, vent door 5813 may also define an input pathway for heated fluid to pass from the thermal storage blocks to the duct 5819 and beneath the vent door 5813 into the steam generator to generate steam.
In some implementations, one or more of vent door 5813, vent closure 5803, and vent closure 5809 are configured to open in response to a nonoperating condition of one or more system elements (e.g., nonoperation of the fluid movement system, power failure, water failure, etc.). In some implementations, one or more vent closures or doors are held in a closed position using electric power during normal operation and open automatically when electric power is lost or in response to a signal indicating to open.
As one example, the thermal storage unit may include a worm gear (not shown) configured to close a vent closure under electric power and an electric clutch configured to hold the vent closure in position. In some implementations, when the electric clutch is unpowered, the force of gravity pulls the vent closure open. In some implementations, the unit includes a counterweight configured to facilitate opening of one or more vent closures. In some implementations, the unit includes one or more resilient members, for example springs, configured to push or pull a vent closure open. In some implementations, one or more electrical switches are configured to control opening or closing of one or more vent closures. Further, one or more vent closures may be opened manually or based on manual control input, e.g., for maintenance mode.
In some implementations, one or more vent closures are opened while a fluid blower is operating, e.g., to rapidly cool the unit for maintenance.
As discussed above, dynamic insulation may be implemented in the TSU. The example system may also include passive failsafe safety features. When the system is switched off, thermal conduction might slowly heat up the foundation without passive venting features. One or more vents may create a chimney effect by allowing external fluid into the system, and allowing the hot fluid within the system to be vented upward out of the unit. This may allow the system fluid out at a slow rate without requiring a blower, due to the natural convective movement of fluid caused by the buoyancy of hot fluid rising through the columns. This buoyancy effect may pull cool fluid in and through the system as a passive safety measure, which opens the passage if power has been interrupted, and ensures that the system does not slowly overheat. This aspect of the example implementations may advantageously make the system intrinsically safe and allow the system to be placed in locations that may not be otherwise permitted if the exterior surfaces were unsafe (e.g., too hot) to the touch.
This passive cooling may prevent the bricks from reaching temperatures high enough to melt steel reinforcing structures that provide seismic reinforcement and structural support for the bricks. This reinforcing structure may be located within the unit but outside the dynamic insulation passageway.
The buoyancy of fluid may enable an automated flow of the fluid through at least one of the fluid pathways through thermal storage blocks from the bottom end of the cells to the upper end of the such that the fluid passing through the bricks and/or heating elements of the cells absorbs thermal energy from the brick and/or heating elements, even when the fluid blowing units fail to operate in case of power or mechanical failure, thereby maintaining the temperature of the unit outer walls and supports at or below their predefined temperatures. Such buoyancy-driven flow may be obtained by one or more movable panels or other ports which passively open at an upper location and a lower location within the system upon such component failure or power failure.
The design of such ports and fluid flow conduits may improve the intrinsic passive safety of the unit, ensuring that critical elements such as structural supports and safety-related elements such as external surfaces do not exceed their design limits, without active equipment or the requirement for supplied power. This configuration may allow the system to achieve a controlled, stable shutdown even in the event of unexpected mechanical failure, sensor failure, or power loss to the blowers or any other control system failure. This configuration may also facilitate controlled cooling for maintenance, passively or in conjunction with one or more active blowers.
Brick Materials
In some implementations, thermal storage blocks are made of a refractory material (e.g., castable) having high thermal conductivity and absorption capability. The brick may be made of a predefined composition of any or a combination of alumina, aggregates like magnetite or olivine, and binders. The material selection, sizing, and fraction of aggregate in binder may be chosen to optimize strength, thermal conductivity, temperature range, specific heat, and/or cost. For example, materials of higher thermal conductivity reduce temperature differences for given heat flux, and enable the use of fewer, larger bricks. Binder materials may be chosen which set during casting, or may be chosen as materials which are thermally fired prior to use or which change composition once heated in use.
The bricks may be manufactured using a mold. More specifically, the material may be provided in a powder form that is mixed with water, to achieve a consistency based on the amount of added water relative to the volume of power. The mixture is poured into a mold, and sets in the mold for a period of time. The mold is removed, and the set bricks are formed. Alternatively, the bricks may be manufactured using a brick press system or a brick extrusion system. Regardless of the method of fabrication, the bricks may be formed in a manner that reduces or eliminates unintended voids within solid block areas.
Brick elements may also include elements which improve the mechanical strength of the material, particularly in tension, such as needles or fibers or wires, and may include materials designed to change in physical ways that absorb and release heat, such as reversible thermochemical reactions or phase changes such as melting and freezing. These materials may be used selectively in some of the bricks, with different bricks having different compositions.
The predefined composition of the thermally conductive materials and the predefined dimension of the bricks being used, and the thermo-electrical attributes of the heating elements corresponding to each of the bricks, may be chosen such that each of the bricks corresponding to a cell may be heated uniformly so that a substantially constant temperature profile is maintained along the length (or height) of each of the cells for a predetermined time. The foregoing example implementation may have benefits and advantages, including slowing temperature ramp, as well as reducing the generation of hot and cold hot spots, mechanical stress, thermal stress, and cracking in the bricks. Further, the use of multiple bricks to form a single cell may facilitate larger channel surface area and lower heat flux per unit area.
Bricks—Pretreatment
Thermal storage blocks and other components may also benefit from pre-treatment and conditioning. For example, a brick may be exposed to one or more thermal cycle with controlled heating and cooling rates, either prior to installation or within the storage system prior to being put into service given that the initial cycles may have a larger impact on its mechanical properties than subsequent cycles.
Storage Unit Components/Integration
For the storage unit, shipping containers may be used, but are not limited thereto. For example, the storage unit may be on the order of 6 meters tall, housing the stacks of bricks. The containers include electronics and wires coupling the containers to the brick housing structure that is protected to avoid damage due to external elements such as rain. The electronics may remain at ambient temperature, allowing for the use of standard, off-the shelf components, and reliability. A steam generator is coupled to the storage system, and cool fluid flows over, under and around the stacks.
The heater elements may be integrated inside and with the brick to heat the storage media electrically during the charging period, such as during the day (or at a time that may be determined by other factors such as availability of electricity at a relatively lower cost). The structure houses a stack of bricks with fluid passages that run substantially vertically through them; the hot fluid exits through a duct at the top of the stack and adjacent to pipes, so as to convert water to steam. Cooler fluid may be recycled or may exit the back side of the structure, for example.
The unit may have, at an end, a wall with holes and the end of wires protruding and the jumpers to connect the wires from one side to the other. At the other end of the unit, the containers may be configured with a distribution of bus bars provided for electrical distribution to provide the power to the strings of wire heating elements. The bus bars are connected back to the controllers inside the containers.
The heating elements may be serviceable and replaceable, if needed, by sliding into and out of the openings passing through the building. Old elements, or elements that otherwise require servicing or replacement, may be pushed or pulled out and replaced with a new one without the need to move other elements such as the bus bars. Thus, the unit may be deenergized, the connections to the bus bar may be detached (e.g., unscrewed) from the container side, and the heating elements may be removed from the opposite side. New elements may be inserted from the opposite side and screwed into the bus bars from the container side, and the unit re-energized. During such a maintenance period, insulation may remain in place with the wire protruding through an insulating plug at the end.
The space between the inner and outer roof may contain the relatively cooler return fluid, and the inner enclosure may contain the very hot fluid coming off (e.g., exiting) the top of the stacks. An internal duct is provided that facilitates transport of the fluid through a duct through the steam generator, where the fluid exits. A fan located at the output of the steam generator may be placed in cold fluid, in the cavity between the inner and outer rooms. This configuration allows the fan to avoid needing to have the metallurgy required for higher temperature operations, and increases its reliability.
The hot fluid duct feeding into the steam generator may become expensive due to the high temperature of the fluid. It may also have a large pressure drop, since the fluid has expanded to multiple times the volume it was when it was cool. Thus, the hot fluid duct must be significantly larger than needed to handle the cool fluid. However, taking the fluid off at one side of the inner roof may reduce the cost of the high temperature duct for several reasons. For example, the quality of insulation that would otherwise be needed is not required, because any heat which is leaking out of that high temperature duct will warm the inlet fluid. Further, the hot fluid duct is very short and direct. A duct that needs to withstand such high temperatures is expensive, therefore limiting the length is beneficial. Further, the space between the inner roof and the outer roof may also include a divider, and a fan may be provided to control return fluid. On either side of this dividing wall, the return fluid is drawn back into the heating stack. Around the edges of the inner roof, a vertical duct is formed to allow the cooler fluid to descend to the bottom of the unit and return to the bottom of the brick stacks.
According to an example implementation, there is no other place (other than the duct connecting to the steam generator) where the outside of the unit experiences the full temperature of the system or the full temperature of the unit. This configuration may dramatically simplify the insulation in other locations and may dramatically reduce the losses and costs, at least because while there will be energy exiting this stack of bricks and through this wall, the incoming fluid is slightly preheated before it gets back to the stack of bricks.
The example implementation may be modified by optionally making it self-supporting and using a system of spacers to keep and maintain the spacing between the bricks. Conventionally, brick aspect ratio is chosen so that individual bricks do not topple in an earthquake, for example, by having a base width about 40%, e.g., 40%, of the height or greater. Spacers may be used to impart this stability on bricks that do not have the desired aspect ratio, but interlocking smaller bricks together to make a larger brick that has the desired stability. In this example, the spacers transfer forces from bricks above it and to the ones below and to the side through compression. This essentially makes the structure into a pyramid, an inherently self-supporting and stable structure, without the need for excessive wall bracing. The spacers may be made of a high temperature refractory or ceramic material and may also include features to interface with wire hangers.
Thermocline and Radiation Chamber
The first temperature of the bricks and the heating elements may be kept higher than the second temperature of the fluid for controlled discharge of thermal energy from the first section into the second section. For instance, the heating elements may be heated at a first predefined temperature of 1200° C. so that the bricks or cells also gets heated up to 1200° C., and fluid at 250° C. may be supplied through from the bottom end of the cells and heating elements, so that the fluid, upon absorbing thermal energy from the bricks and/or heating elements may attain the second temperature of 800° C. Further, the heated fluid of 800° C. may pass through the conduit such that the fluid inside the conduit may be converted into steam. Various structural aspects of the thermocline are provided below.
The bricks may be arranged to create a fluid passage between the bricks, in a repeating pattern. This results in the brick providing additional surface area for the heat in the brick to transfer to the fluid. The brick becomes a heat sink system. The fluid flow path is substantially vertically. Fluid comes into the bottom, goes up through these channels, gets heated as it goes up and escapes the top hot and goes into the roof area.
The bricks may optionally have a consistent amount of thermal mass along their length, to help maintain temperature uniformity and avoid significant narrowing that may cause hot spots. Optionally, the bricks may include a chamfer at the top and bottom, so that if the bricks are slightly misaligned, the fluid pathways are not closed. The fluid pathways may be relatively narrow and it may be important that the bricks are not offset from each other, which would close the fluid pathways and reduce the fluid flow. Accordingly, chamfers and other features at the top in the bottom of the bricks may have the advantage of preventing misalignment.
The bricks of the example may be stacked, such as in a stack six or more bricks high. Some of the bricks have a corresponding heating element that winds through and is hung from a feature in the structure. The bricks are spaced and designed such that they are self-supporting system.
From one slot for one set of heater wires to the next, a relatively small space, such as about 30 centimeters (for example, 30 centimeters), is required for the required performance because for the heating time available during the day, the dimension is limited by the conduction rate. Larger dimensions may result in sections of the brick not being efficiently used for thermal storage.
Optionally, the size of the fluid flow pathways may be adjusted to tune the fluid flow velocity in different areas, to counteract the temperature profile that already exists in the brick when it is heated. In other words, when the brick is heated, the side of the brick closest to the heater gets hottest and gets progressively cooler moving across the brick. If the energy is extracted equally from the whole system, the output fluid temperature would be a gradient reflecting the brick temperature gradient; hottest fluid near the wires and cooler fluid further from the heaters. Having larger pathways closer to the heater element may create less resistance to fluid flow, resulting in higher fluid velocity, and smaller channels further away from the heater element, which reduces fluid velocity in those regions, to obtain a more homogeneous fluid temperature. As the fluid traveling at higher velocity is in the pathway for less time and is in contact with the brick for less time, that fluid exits the pathway cooler than fluid traveling slower through the same section. The side of the brick with the bigger channels is hotter in the present example implementations; thus, size of these pathways may be tuned such that the fluid that comes out of the wide slots in the hottest part of the brick is nearly the same temperature as the fluid that comes out of the narrower slots in the lower temperature part of the brick.
Thus, by tuning the geometry of the brick and fluid pathways, the performance of the thermocline system may be improved and optimized to match the expected and desired charging and discharging characteristics. In addition to using differential fluid flow to even output temperature, by generally increasing or decreasing the overall fluid flow through the system, the temperature of the output fluid may be controlled.
According to some example implementations, the bricks are blocks that are separate and effectively have voids. These voids, which might be large voids, between the bricks in the stack create radiation chambers. In these example implementations, the energy may be transferred from the wire to the brick primarily by radiation energy transfer. When the wires get hot, the radiation contacts the brick and comes into radiative balance with a brick, where the brick is cooler than the wire trying to come up to temperature, and radiation from the brick cools the wire. Energy from the wire is thus exposed to more surface area of brick as compared with convective heating. The energy from this wire when it radiates down into this cavity energy penetrates into the cavity and becomes exposed to more surface and mass of brick, instead of just the surface right next to it, which gets a very high flux density and very high energy density. According to this example implementation, some bricks may radiatively heat each other after being heated by the wire. Thus, the system may achieve both direct and indirect radiant heating of brick surface as part of the heat transfer. This design allows the heater element wire to be further spread out.
Without radiative cavities designed to heat large surface of brick in this way, e.g., if conduction as the primary mechanism by which heat is being transferred, the design may be limited to a relatively small distance such as between 0.3 and 0.5 meters of space between wire curtains in some implementations, when matched to heating profiles for solar heating, as there is not enough time to heat the center of the mass of the bricks. By using radiation cavities, the wire curtain spacing may be spread out to more than 0.5 m and still efficiently utilize the entire mass of the brick. This allows for a reduction in the wire count. One benefit of this example implementation is that the total wire count may be reduced, for example, from 3,400 wires to potentially approximately 96 wires (for example, 96 wires) while transferring the same amount of energy as was being transferred from the 3,400 wires. Further, this example implementation, may use wire having a diameter in the range of 2.5 mm to 8 mm.
Design of Stack—Materials
During the course of normal operation of the thermal storage system, care may be taken to ensure that certain temperature ranges which may cause early failure are moved through quickly. For example, FeCrAl type alloys are known to embrittle if a significant amount of time is spent between 400-500° C. Different heating elements or bricks may have other sensitive temperature ranges where mechanical, thermal or physical properties are negatively affected. The control system may take this into consideration to avoid damaging the materials prematurely.
The thermal storage system may be designed in a way that some sections are made to handle higher temperatures. For example, a top section may comprise higher temperature rated heating elements, such as ones consisting of primarily SiC or MoSi2, and higher temperature rated brick, such as tabular alumina. Such a section could be heated, as required, to temperatures reaching 1500 C, 1600 C or higher. The geometry of bricks and wires may be different than those in another section of the thermal storage unit, to optimize performance, cost or mechanical stability. A second section of the storage, for example, in the lower part of the stack, could have lower temperature rated heating elements, such as metal heating elements in the FeCrAl class, and bricks that are a different material type, selected for cost, performance and mechanical properties as more load is placed on the bricks at the bottom.
Flow Mixing Structures
Additionally, the flow channel through the brick stack may be modified to facilitate or promote the mixing of gas. These modifications may reduce or eliminate hot spots and cool spots in the main stream. For example, the bricks may be structured (e.g., by fins or an arrangement of the slots) or assembled in a manner that directs the fluid to promote swirling or mixing of the fluid in the chambers, to improve heat transfer of the convection. Such mixing may even out temperature gradients, and have more even thermocline, and better performance, in addition to the benefits of radiative and reradiative heating, as explained above. This effect may be particularly advantageous at lower temperatures, or the beginning of the charge or late in the charge. Further, the greatest thermal gradient stress, which typically occurs most acutely at the beginning and end of the charge, is reduced.
Additionally, cool bypass gas in the upper region of the stack may be blended by inducing swirl or turbulent flow, by a stationary auger or other feature at the top of the stack, with the gas discharged from the stacks, to obtain a more homogeneous temperature. For example,
Heating Element
Traditional approaches may have problems and disadvantages associated with the heater for the thermal energy storage cells. For example, a traditional heater or heating element may experience problems and disadvantages such as mechanically induced chemical failure, which is also known as spalling. More specifically, scale growth may occur on the heater to a point where thermal stresses cause failure at an interface between the scale and the substrate. A result of the scale growth is flaking and loss of aluminum, until the aluminum reservoir reaches a critical point. Additionally, intrinsic chemical failure may occur when aluminum oxide breaks down, such that the aluminum migrates outward and the oxygen migrates inward, until the aluminum reservoir reaches a critical point.
As a result of the foregoing related art problems and disadvantages, a phenomenon known as “breakaway oxidation” may occur, where non-protective Cr2O3 (chromium oxide) and FexOy (iron oxide) scale quickly, and eventually lead to bulk oxidation and failure of the heating element. Thus, the reliability and lifetime of the heating element is substantially shortened.
As explained above, resistive heating elements are provided in channels that are formed between stacks of bricks at repeated horizontal and vertical positions in the units. The resistive heating elements receive electrical energy from the source, which may be a renewable or another source of variable electricity. The resistive heating elements release the electrical energy as heat, which is radiated to the stacks of bricks as explained above.
The resistive heating elements may be in the form of wire, which may be in the form of coils or wires, ribbons, or rods which pass through the stack in channels oriented in a direction parallel to heat transfer fluid flow or extend through the stack in channels transverse to heat transfer fluid flow.
According to an example implementation, coiled heating elements may be positioned in grooves running across the top and bottom of one or more bricks that may be stacked together. The heating elements may pass from one side of the unit to the other. With a jumper on one side and the coming back through the other side, an electrical circuit may be completed. The coils may be wired into series and parallel, to match the voltages that are being worked with.
This diameter of wire may reduce the resistance of the long wire string. As wire may be purchased on a mass basis, and thinner wire has additional processing costs, which may result in a cost savings of hundreds of thousands of dollars for one system, which is an added benefit. By using a thicker diameter wire, the overall life of the wire may be significantly increased because there is no longer cross-sectional wear from the heating or cooling of the wire, and the corrosion of the wire is much less rapid due to the larger cross section, even if the same corrosion rate. Further, increases of the wire diameter may further be feasible, potentially as high as 8 mm. One example implementation has features that restrict the heating elements from contacting the brick or each other, in case they undergo deformation. Such a feature could be a hook on multiple positions, for example, at the top and bottom extremes.
As shown at 4700a, heaters 4701, 4702 extend through the refractory material. Heaters are installed into conduits 4711 after assembly of the refractory material, or during assembly of the material. Protective tubing 4707 may be used during installation and may be removed mechanically or melted or combusted by application of heat by the heater. Electric power connections 4704 are joined to heaters at points 4703 with connections 4705a that prevent excessive heat build-up at connection points. Two or more heaters may be connected by successive connections 4705, 4706 before connection to power distribution 4704. As shown in the drawing at 4700, two coil-type heaters 4701 are connected by a connection 4706, followed by another two heaters in series along power connector 4704. Wire, rod, and ribbon-type heaters 4702 may be similarly connected.
As shown in 4700b, a refractory storage medium 4710, which may be the stacks of bricks, is provided with gaps or passages 4711 for the inclusion of the resistive heating elements. Further, the heaters may be of a ribbon type 4702, or a coil type 4701. Optionally, the heaters may be enclosed in a conduit 4707 as explained above.
As shown at 4700c, heaters 4701 with power connections 4704 are arranged with parallel links 4709 such that multiple heaters or series-sets of heaters are connected in parallel to a single power distribution connection. Operation of the power connections may be at voltages in the hundreds of volts to tens of thousands of volts. Voltages at or below 5 KV may be selected based on considerations such as safety, costs, and reliability.
In some exemplary implementations, the heater(s) or heating elements may be a resistance wire extending along the length of the channels of each brick, where each of the heating elements may have predefined electro-thermal attributes such as resistance, electrical conductivity, thermal conductivity, cross-section area, and the likes, such that each of the heating elements may be heated up to the predefined temperatures upon receiving electrical power from the electrical power sources.
Electrically, a loop may be formed by a heating wire that starts at an end of a first channel, passes through a jumper at the other end of the channel, and returns via another channel. Adjacent stacks of bricks may be phased apart (e.g., 3-phase, for adjacent stacks of bricks, such that the stacks forms a group, or cell). The group of stacks, or cell, may be resistance-matched so that the performance of the stacks is consistent with respect to one another. The entire two of groups may form a zone that is on a controller. Vertically, different zones (e.g., rows of stacks) may be on different controllers, and may thus be resistance-matched at a different resistance from different vertical levels.
Further, the resistive heaters may be controlled such that the stacks are heated in an uneven manner. More specifically, the upper portions of the stacks may be preferentially heated. The controllers may control the vertical layers of the stacks separately, such that the heaters on different layers of the stack may be turned on or turned off at different times. For example, the controllers for the upper layers of the stacks may turn on the heating elements of the upper layers of the stack in advance of the controllers for the middle or lower layers of the stack turning on those heating elements. Further, this approach takes into account the different in brick height and mass between the bricks at the lower layers, which have a lower height and mass, as compared with the bricks at the upper layers, which have a greater height and mass. Thus, the upper brick layers will have a hotter temperature than the lower brick layers, and the thermocline is maintained. The controller may set the temperature and the timing of the heating for the layers of the stack based on sensor feedback, or based on system models, to determine the temperature of the layers, or a combination thereof.
The above example implementation of the brick design may be modified by stretching the above design and the heater element vertically. Thus, instead of being a round spiral, the heater may be a flat coil which goes into the brick and this allows every wire to have more surface area and more exposure with the brick. This also allows the number of wires in the system to be reduced, which may have a benefit of lowering the cost of the heater elements.
A wire irradiating to a larger surface may allow for more watts per centimeter of energy to be pushed in. The larger the surface area, the more brick is heated, which may have substantial implications on the temperature of the wire, because the surface temperature of the brick that the wire is exposed to sets a limit. A top wire temperature has direct implications on its lifetime, and the brick wall temperature that the wire is exposed to determines how much energy flux can be safely pushed through the wire. Thus, the example implementation involves a brick volume, exposed surface area, and wire temperature.
According to an example implementation, service is provided for the heater wire by forming a tall system wound up and down vertically and heating the sides of two separate bricks. The bricks are formed with fluid flow channels, and are substantially taller than the bricks disclosed in the foregoing example implementations. Larger bricks with the substantially same efficiency may allow fewer parts to be manufactured, and for wires to be spaced out further. This example implementation may have the added benefit of reducing cost of materials and assembly. The bricks may be extruded, pressed or cast and are formed with channels for the fluid to flow through. These channels, or slots, may provide a superior surface to volume ratio over holes or other shapes. The slots may or may not extend all the way at the edge closest to the heating element to concentrate the thermal mass close to the elements so that the energy transfers quickly.
As shown in
For example, a twisted ribbon 6721 as shown in
Coating Heating Elements
Other methods which may be employed to increase service life includes material pre-treatment and conditioning. For example, FeCrAl type heating elements are known to grow a protective, α-alumina scale on the surface which greatly reduces the rate of oxidation of the bulk material. However, at temperatures below 800-1000° C., a less protective form of alumina initially forms. To impart the protective effect of the dense α-alumina, the heater elements may be heated to a controlled temperature and duration above 1000° C. prior to being placed into service. This may be performed pre-installation or inside the thermal storage system post installation. The wires may also be pre-treated to change the surface chemistry for longer life.
For example, it is known that the aluminum reserve in the bulk FeCrAl material is an important limiting factor for oxidative failure. Because FeCrAl materials with aluminum fraction significantly higher than about 5%, e.g., 5%, are not suitable for hot processing, a process which adds additional aluminum may be beneficial. Such processes may include hot aluminizing, aluminum electro-plating, sol-gel processing and aluminum plating followed by anodizing. The surface treatment may also be made to increase the emissivity of the surface such that the average temperature of the heating element may be lower than without the treatment.
Replaceable Heating Elements
Individual heating elements may be configured to be removed and replaced without disassembly of the cell. For example, a broken or failed heating element may be pushed or pulled through the cell using a mechanical puller or pipe to remove and a replacement element placed in the cell using a pipe or other specific tool. As may be understood by a person of ordinary skill in the art, the resistivity of heating elements may change over time due to gradual physical effects from normal operation including wear, oxidation, and changing in metal crystal structure and alloying. In some example implementations, the replacement element may be sized or constructed to produce a resistivity that mirrors a projected resistivity of surrounding elements that may have degraded over during operation of the system.
For example, it may be anticipated that a portion of heating elements will fail within a prescribed time, such as 3 years, of operation, and replacement elements installed after three years may be designed with a resistivity that mirrors projected resistivity of the remaining original elements that are still operation but have changed resistivity over the period of operation. Similarly, different resistivities may be chosen for heating elements installed during later periods.
Control System
In various implementations the system includes a control unit or control system operatively coupled to disclosed elements such as the electrical energy sources, the heating elements, the air blowing units, the pumps, etc. In one implementation, the control unit is configured to enable the electrical coupling of the heating elements with the electrical energy sources. The control unit may switch the electrical connection of the heating elements between different electrical energy sources based on availability and cost per kWh of the electrical energy sources. During low load hours, the cost per kWh of non-renewable energy sources is generally relatively lower and sometimes negative. However, it may not be feasible for the non-renewable energy sources to switch off electrical power generation during these low load hours. Thus, during these low load hours, the control unit may electrically couple the system with an electrical energy source that is providing a lower cost per kWh of energy. The control unit may further control the air blowing units to enable controlled flow of fluid between any combination of one or more insulated cells that include thermal storage block assemblies and the outside environment, and also control one or more pumps to facilitate the controlled flow of fluid and steam through the conduit.
In an example implementation, system pumps and blowers are operable at variable flow rates, such that energy production and steam generation may be adjusted from a nominal full rate in steps or continuously down to a lower rate. Such minimum rate may be 10%, 20%, 30% of peak output, or another rate. The system controller may be configured to issue commands to adjust the flow rate of the input liquid pump and the blower so as to allow energy delivery at multiple rates automatically, based on manual commands, or both.
In another example implementation, the control unit may be in communication with a system associated with an electrical load or other industrial loads. The control unit may be configured to monitor the demand for hot fluid, steam or electrical power at the load, as well the available energy being stored in the system, and may accordingly charge the system by electrically connecting the heating elements to the electrical energy sources. For instance, when the control unit finds that the demand of the load is higher than the available energy currently stored in the system, then the control unit may electrically couple the heating elements of the system to the renewable or non-renewable energy sources to meet the demand of the load.
If the available electrical energy being received by the electrical energy sources is reduced, then during charging mode, the control unit may electrically connect heating elements associated with a predetermined number of cells among all the cells of the housing, such that only the heating elements of a proper subset of cells may receive the limited electrical energy and become heated, and the other heating elements or cells remain electrically disconnected from the electrical energy sources. Later, during discharging, the control unit may allow fluid to be passed through the heated cells to transfer the stored thermal energy to the conduit so the temperature of the fluid at the conduit remains at the delivery temperature, thereby reducing or preventing any damages or failure in the steam production system, and potentially maintaining continuous and controlled steam production.
The control system may generate a signal such as a command to activate one or more switching elements which in turn control source electrical energy input to resistive heating elements. The control system may directly or indirectly command the operation of active switches which selectively interrupt current flow so as to deliver a chosen average power. Such switching patterns may be carried out by thyristor-type switches which are continuously on or selectively commanded to switch so as to deliver a lower power by selectively conducting during chosen patterns of half-cycles.
A plurality of such switches may be chosen to operate in a pattern such that during each half-cycle of an AC current flow, the average load is constant. One such pattern would have the same or similar number of switches turned on during each half-cycle, even though any given switch might be turned on only once during a sequence of multiple cycles. Other switching patterns may be carried out by insulated-gate bipolar transistor (IGBT)-type switches which operate at frequencies higher than 120 Hz and which selectively conduct or block current in a pattern to provide continuous conduction or partial power whether incoming power is in the form of AC or DC.
The control system may determine switching decisions based in part on various parameters, such as the design of the heating element, including its resistance per unit length, its material surface area, its material of construction including its performance with temperature (temperature-related effects may include metal recrystallization and/or dealloying, oxidation, spalling, creep, thermal expansion, and wear) the temperature and size of the surface area surrounding the heating element, local temperatures along the entire heating element length (including support points or points of contact with solid media and points of electrical connection with other conductors), etc., or some combination thereof. Overtemperature at points of connection may be reduced or prevented by arranging regions of lower electrical resistance proximate to such connections, e.g., by winding multiple strands of wire together, changing conductor cross-section, making such connections outside high-temperature regions of the storage unit, or providing local heat-sink/cooling elements at such points.
In one implementation, the surface temperature of the heating element depends on the wattage per unit surface area of heating element, the ambient air temperature around the element, whether or not air is flowing in the conduit, and the surface temperature of the enclosing material. The surface temperature depends on the bulk temperature distribution of the brick, its thermal conductivity, and the radiative heat flux. Radiative heat transfer may dominate in disclosed implementations. Because radiation transfer is proportional to the difference of the temperatures in degrees Kelvin to the fourth power, as the refractory material approaches the maximum operating temperature of the heater, the power flowing through the heater should approach zero.
In some implementations the control system algorithms include models of the thermal storage unit. These models approximately simulate the temperature at various points within the storage unit, as well as instantaneous and forecast temperatures based on heater power input. Accordingly, heater life is advantageously preserved, by incorporating weather and seasonal inputs into the controller, including the use of forecasting.
The models may adapt to changes in the configuration of the storage unit, including the presence of missing or failed heaters or heater controllers, the presence of blocked heat transfer channels, the presence of scale formation in the steam generation section, or other operating/maintenance matters.
In one implementation, the control system confirms and compares simulation models to select measurements of temperatures, flows, and power levels at various points within the system. The control system may consider the models in control calculations governing power to the heating elements. For example, wall temperatures may be a limiting factor in the current input power allowable for a given heater, with limits calculated based on peak refractory temperature and peak wire temperature. A constant-wattage (constant-Q heat flux) charging may not be feasible without the heater temperature significantly exceeding the refractory temperature.
The control system responding to such constraints may command charging wattage (e.g., Q heat flux) patterns in time during charging, where initial low-rate heating establishes heat conduction patterns, charging is raised to high rates for part of the charging time, and charging rate drops as material temperature rises, such that the final top temperature is approached asymptotically at slow rates, without exceeding top heater temperatures.
Heat transfer fluid may be flowing in the adjacent fluid conduits during charging, allowing charge plus discharge operation concurrently. In some example implementations, heat transfer fluid may be flowing in the conduit that carries the heater element. The resistance per unit length of the heating element may vary, and/or the heat production per unit length may vary, so that (for example) a conduit which has heat transfer fluid flowing axially along the heater may require less heat near the fluid outlet than near the fluid inlet.
In addition to those advantages described above in Section I, the example implementations relating to thermal blocks and assemblages may also afford various advantages relative to traditional approaches. For example, traditional approaches commonly suffer from uneven heat distribution, wear and tear due to the heating and cooling cycles of the bricks, and safety and maintenance issues. The implementations within this disclosure, however, attempt to mitigate various such problems by applying radiative heating (including horizontal radial radiation within the radiation chambers) in combination with fluid flow pathways, to produce a distribution of heat that is more uniform than that achieved by traditional heating techniques. As a result, problems and disadvantages associated the art may be overcome, such as inefficient power storage, degradation, damage and breakdown of various elements (e.g., the heating element, the bricks, the enclosures, etc.), unsafe hotspots, etc.
Disclosed dynamic insulation techniques may advantageously improve insulation efficiency, reduce insulation costs, or both relative to traditional techniques. Further, disclosed passive cooling techniques may improve the safety of the thermal storage system. Various disclosed techniques may reduce maintenance complexity relative to traditional techniques.
The storage media blocks may be arranged in an assemblage that allows relative movement to accommodate expansion and contraction by individual elements. Also, the array is arranged such that cycles of thermal expansion align the elements of the array to preserve the integrity of the array structure, the integrity of the heating element conduits, and the integrity of the heat transfer gas conduits.
Further, because the heat is more evenly stored, waste of heat is also reduced or avoided. Additionally, the example implementations may have another benefit, in that it may be easier to maintain and replace the heater modules, heating elements, and bricks. Further, the example implementations have increased efficiency. For example, the brick and stack configurations disclosed herein may produce an increase in the ΔT of the bulk material over the course of charging and discharging to allow the bricks to store more megawatt hours per kilogram of material, as compared with current designs.
In many power transfer systems, alternating current (AC) is employed to transfer power from a generating source to a load. In such systems, passive equipment and transformers need to be energized for the system to work, resulting in the circulation of reactive energy. Additionally, the transfer of AC over distances can result in losses due to impedance of transmission lines coupled between the generating source and the load. In some cases, the power generated may be intermittent. For example, when the generating source is photovoltaic cells, the power being transferred is based on the illumination of the photovoltaic cells, which can vary over the course of the day. As the power drops, the efficiency of the AC transfer system can be further degraded.
To improve the efficiency of such power transfers, direct current (DC) transfer can be employed which use multiple input DC voltages to generate a higher voltage for transmission. In some cases, the transmit voltage can be decomposed into multiple smaller voltages at the load end of the transfer system. As described below, the losses associated with converting DC sources to AC for transfer can be eliminated due to lower inductive and eddy current losses. Additionally, ohmic resistive loads can be lower further improving efficiency.
A block diagram of such a thermal storage system the employs DC power transfer is depicted in
Generator circuits 3103A-C are configured to generate DC voltages 3107A-C, respectively. In various implementations, generator circuits 3103A-C may employ renewable energy sources such as solar or wind. DC voltages 3107A-C may, in some implementations, be time-varying voltages. For example, in some cases, the respectively levels of DC voltages 3107A-C may be based on variation in illumination of photovoltaic panels. Although only three generator circuits are depicted in the implementation of
As described below, converter circuit 3101 includes multiple sub-converter circuits, each including a first input circuit and a first output circuit. The first input circuit is configured to receive one of DC voltages 3107A-C. The first output circuit is galvanically isolated from the first input circuit and is configured to generate a corresponding one of DC voltages 3109A. Converter circuit 3101 is configured to combine DC voltages 3109A to generate transmit voltage 3108.
As described below, converter circuit 3102 also includes multiple sub-converter circuits, each including a second input circuit and a second output circuit. The second input circuit is configured to receive, via transmission line 3106, a portion of transmit voltage 3108. The second output circuit is galvanically isolated from the second input circuit and configured to generate a corresponding one of DC voltages 3110 derived from the portion of transmit voltage 3108 received by the second input circuit. Converter circuit 3102 is configured to combine DC voltages 3110 on output bus 3105. It is noted that, in some implementations, DC voltages 3110 may be coupled, in parallel, onto output bus 3105.
Thermal storage unit 3104 includes heating element 3111 coupled to output bus 3105. In various implementations, heating element 3111 is positioned to heat thermal storage medium 3112 using power received via output bus 3105. As described elsewhere in the specification, thermal storage unit 3104 may be implemented using a variety of different thermal storage mediums.
In some cases, voltages from multiple energy sources can be combined into a transmit voltage that may be used directly by a load. A block diagram of an implementation of power transmission system for a renewable energy source system is depicted in
Renewable energy sources 3202A-C are configured to generate DC voltages 3205A-C, respectively. In various implementations, renewable energy sources 3202A-C may be implemented using photovoltaic cells, wind turbines, or any other suitable renewable energy source. DC voltages 3205A-C may, in some implementations, vary in time due to the intermittent nature of illumination of the photovoltaic cells, the absence of wind, and the like. Although only three renewable energy sources are depicted in the implementation of
Sub-converter circuits 3203A-C are configured to receive DC voltages 3205A-C, respectively. In various implementations, sub-converter circuits 3203A-C are configured to generate output voltages 3206A-C using corresponding ones of DC voltages 3205A-C. As described below, sub-converter circuits 3201A-C include respective input circuits and output circuits that are galvanically isolated by corresponding transformers.
Sub-converter circuits 3203A-C are coupled in series to combine output voltages 3206A-C to generate transmit voltage 3108. In various implementations, transmit voltage 3108 is a sum of output voltages 3206A-C. By coupling sub-converter circuits 3203A-C in series, a voltage larger than any of one of DC voltages 3205A-C can be generated to aid in the transmission of power to thermal storage unit 3104. Moreover, coupling sub-converter circuits 3203A-C in series eliminate the need to detect failures in any of renewable energy sources 3202A-C. If any one of renewable energy sources 3202A-C stops generating its corresponding one of DC voltages 3205A-C, the corresponding one of sub-converter circuits 3203A-C generates a zero output voltage which still allows the generation of transmit voltage 3207 by adding the output voltages of the remaining ones of sub-converter circuits 3203A-C.
Although converter circuit 3201 is depicted as including only three sub-converter circuits, in other embodiments, any suitable number of sub-converter circuits may be employed. In some cases, the number of sub-converter circuits included in converter circuit 3101 may correspond to a number of renewable energy sources. Alternatively, multiple renewable energy sources may be wired together and a number of sub-converter circuits may be based on a desired magnitude of transmit voltage 3108.
Thermal storage unit 3104 includes heating element 3108 configured to heat thermal storage medium 3109 using transmit voltage 3107. In various embodiments, thermal storage unit 3104 may be coupled to the output of up-converter circuit 3101 using a high-voltage DC cable capable of handling the current drawn by thermal storage unit 3104 at the value of transmit voltage 3107. As described elsewhere in the specification, thermal storage unit 3104 may be implemented using a heating element which can be used to heat a variety of different thermal storage mediums.
Turning to
Converter circuit 3102 includes sub-converter circuits 3302A-C that are coupled in series across transmit voltage 3108. It is noted that while sub-converter circuits 3302A-C are depicted as being across transmit voltage 3108, in other embodiments, sub-converter circuits 3302A-C may be coupled across any suitable DC voltage. By coupling sub-converter circuits 3302A-C in series, transmit voltage 3108 is divided into voltage portions 3303A-C, with corresponding inputs of each of sub-converter circuits 3302A-C being exposed to only a portion of transmit voltage 3108. In the illustrated embodiment, since there are three sub-converter circuits, each of voltage portions 3303A-C is a third of the value of transmit voltage 3108. Using series-coupled sub-converter circuits may, in various embodiments, allow for the use of lower voltage components in sub-converter circuits 3302A-C, thereby saving cost and circuit complexity.
Sub-converter circuits 3302A-C are configured to receive corresponding ones of voltage portions 3303A-C. For example, sub-converter circuit 3302A is configured to receive voltage portion 3303A, while sub-converter circuit 3302B is configured to receive voltage portion 3303B. Sub-converter circuits 3302A-C are further configured to generate, using corresponding ones of voltage portions 3303A-C, corresponding ones of load voltages 3304A-C. As with sub-converter circuits 3203A-C, sub-converter circuits 3302A-C include input and output circuits that are galvanically isolated from each other. Use of such isolation may prevent possible damaging currents flowing directly from cables carrying transmit voltage 3108 to load circuit 3306.
Although converter circuit 3102 is depicted as including only three sub-converter circuits, in other embodiments, any suitable number of converter circuits may be employed. In some cases, the number of sub-converter circuits included in converter circuit 3102 may be based on a value of transmit voltage 3108 and desired values of load voltages 3304A-C. For example, if smaller values are desired for load voltages 3304A-C, additional sub-converter circuits may be employed to split transmit voltage 3108 into a larger number of smaller portions.
Load circuit 3306 is coupled to output bus 3105 and is configured to perform a function or operation using a voltage level of output bus 3105. It is noted that load circuit 3306 may be any suitable circuit or unit that employs a DC voltage to perform a function or operation. In various embodiments, load circuit 3306 may be part of a thermal storage unit (e.g., thermal storage unit 3104) while, in other cases, load circuit 3306 may be part of an electric vehicle charging system, or other battery charging system. For example, load circuit 3306 may include charging circuit 3207 configured to charge battery 3208 using power received via output bus 3105.
Turning to
DC converter circuit 3401 is configured to receive DC input voltage 3409. In various embodiments, DC input voltage 3409 may correspond to any of DC voltages 3205A-C, or voltage portions 3303A-C. DC converter circuit 3401 is further configured to generate current 3410 in primary coil 3407 included in transformer 3402 using DC input voltage 3409 and based on control signals 3414. In some embodiments, current 3410 is an alternating current, and to generate current 3410, DC converter circuit 3401 may be further configured to switch the polarity of DC input voltage 3409 relative to the terminals of primary coil 3407 in order to change the direction of current 3410 through primary coil 3407. In various embodiments, a frequency of such switching may be based on at least one of control signals 3414.
In various embodiments, DC converter circuit 3401 is magnetically coupled to output circuit 3419 by transformer 3402. Since the DC converter circuit 3401 is coupled magnetically to output circuit 3419, no current can flow between DC converter circuit 3401 and output circuit 3419 thereby galvanically isolating the two circuits.
As current 3410 flows in primary coil 3407, a time-varying magnetic field is generated by primary coil 3407. The time-varying magnetic field induces current 3411 in secondary coil 3408 of transformer 3402. It is noted that due to the time-varying nature of the magnetic field, current 3411 may also be an alternating current. To enhance the inductive coupling between primary coil 3407 and secondary coil 3408, the respective windings of primary coil 3407 and secondary coil 3408 may be wound around a common core of ferrous material.
To provide additional granularity for the level of transmit voltage 3108, transformer 3402 may be used to change the value of DC output voltage 3413 relative to DC input voltage 3409. By adjusting the number of turns (or “windings”) of primary coil 3407 relative to the number of turns of secondary coil 3408, the magnitude of current 3411 can be adjusted, either up or down, relative to the magnitude of current 3410. For example, if the number of turns of secondary coil 3408 is greater than the number of turns of primary coil 3407, then the magnitude of current 3411 will be greater than the magnitude of current 3410. Different values of current 3411 can result in different values of DC output voltage 3413.
Since current 3411 is an alternating current, it must be converted to a DC voltage (or “rectified”) before it can be used by output voltage generator circuit 3404. Rectifier circuit 3403 is configured to generate internal supply voltage 3412 using current 3411 flowing in secondary coil 3408. In various embodiments, rectifier circuit 3403 may be implemented with multiple diodes to maintain a charge on a load capacitor in order to generate internal supply voltage 3412.
Output voltage generator circuit 3404 is configured to generate DC output voltage 3413 using internal supply voltage 3412 and based on control signals 3415. In various embodiments, DC output voltage 3413 may correspond to any of output voltages 3206A-C or load voltages 3304A-C. Output voltage generator circuit 3404 may, in some embodiments, include inductive choke 3418, which may be used to couple one instance of converter circuit 3400 to another instance of converter circuit 3400 as depicted in the embodiment of
Control circuit 3405 is configured to generate control signals 3414. Such signals may include timing and enable signals for DC converter circuit 3401. In various embodiments, control circuit 3405 may be configured to generate control signals 3414 using external communication signals 3417 and communication signals 3416. In various embodiments, external communication signals 3417 may be sent to and received from another sub-converter circuit or a master control circuit included in a power transfer system. It is noted that the transmission of external communication signals 3417 and communication signals 3416 may be performed using optical circuits to provide electrical isolation between control circuit 3405, control circuit 3406, and any external control circuits. In various embodiments, control circuit 3405 may be implemented using a processor configured to execute software or program instructions, a microcontroller, other suitable state machine.
Control circuit 3406 is configured to generate control signals 3415, which may include timing and enable signals for output voltage generator circuit 3404. In various embodiments, control circuit 3406 may be configured to generate control signals 3415 using communication signals 3416 received from control circuit 3405. Control circuit 3406 may also be configured to send information regarding the operation and status of output voltage generator circuit 3404 to control circuit 3405 via communication signals 3416. In various embodiments, control circuit 3406 may be implemented using a processor configured to execute software or program instructions, a microcontroller, other suitable state machine.
Turning to
The method includes receiving, by an input circuit of a given converter circuit of a first plurality of converter circuits, a DC input voltage from a renewable energy source (block 3502). In some embodiments, the method further includes generating, by a plurality of photovoltaic panels, the DC input voltage.
The method also includes generating, by an output circuit of the given converter circuit that is galvanically isolated from the input circuit, a second plurality of DC output voltage based on the DC input voltage (block 3503). In various embodiments, generating the DC output voltage includes inducing, by the given converter circuit using the DC input voltage, a first current in a primary coil of a transformer included in the given converter circuit. In such cases, the method also includes generating, by the given converter circuit using a second current in a secondary coil of the transformer, the DC output voltage. In various embodiments, the second current in the secondary coil is based on the first current in the primary coil of the transformer.
In some embodiments, the method may further include inducing the second current in the secondary coil based on the first current, a first number of turns on the primary coil, and a second number of turns on the secondary coil. The method may, in various embodiments, also include rectifying, by the given converter circuit, the second current to generate an internal supply voltage. In such cases, the method may further include generating, by the given converter circuit, the DC output voltage using the internal supply voltage.
The method further includes respective DC output voltages from the first plurality of converter circuits to produce a transmit voltage (block 3504). In some embodiments, the method includes adding the respective DC voltages to produce the transmit voltage. In various embodiments, coupling the first plurality of converter circuits includes coupling a first output of a first converter circuit to a particular node using a first inductive choke, and coupling a second output of a second converter circuit to the particular node using a second inductive choke.
The method also includes heating a thermal storage medium by a heating element using the transmit voltage (block 3505). In some embodiments, the method also includes receiving, by a second plurality of converter circuits coupled in series, the transmit voltage. The method may further includes generating, by the second plurality of converter circuits using corresponding portions of the transmit voltage, a plurality of DC output voltages, and combining the plurality of DC output voltages on a common power bus. The method concludes in block 3506.
Vehicle Charging Applications
The above described DC/DC converter can be used for a DC vehicle fast charging application. This example circuit illustrates how it is possible for a standard 500 MAC cable to transport 2MW. Existing charging stations are connected to AC grid and either have their own substation or are connected to a bigger substation at 5060 Hz and low voltage. To pull 2MW, a very high current is required (4,000 amps) exceeding the limits of the grid capacity.
By being able to transfer power using DC allows 1-2 MW power transfer at a much lower current allowing battery charging in 10-15 minutes to 80%, similar to a gas station stop. The DC/DC converter shown above may allow this high-speed DC charging. This structure uses multiple PV array microgrids as input, for example, and the DC/DC converters shown can provide high power and economical charging stations. Additionally, the charging station may also include on-site storage of the PV generated power using standard cabling.
Thus, relatively small conductors at substantial voltage can be used to power a set of charging ports that can operate independently or in parallel.
Power Transportation Applications
If a PV panel connected with an inverter that is converting to AC and using a transformer to step up to a higher voltage to transfer it over a distance, then at the destination such as a charging station, battery or storage system, there is a transformer or some sort of rectifier. When such a system is running at peak solar capacity, the losses of the inverters and the transformers and the energizing losses of that AC system the eddy current and the inductive losses add to just under 90 percent efficiency. However, when the system is running at low power, the losses remain similar and the net efficiency drops substantially.
Conversely, when doing a DC based system using the DC/DC converters described herein, losses are significantly lower since inductive or eddy current losses are not present in DC and ohmic resistive loads are lower. Thus, the efficiency increases slightly at low loads.
Thus, these chained DC/DC converter systems can have applications in fields such as power transportation, vehicle charging, customer applications, solar fields connected to lithium battery systems among others, including a thermal storage system. This may significantly reduce ohmic losses in solar fields because wiring would be running at higher voltage and may reduce ohmic and AC losses between solar fields and batteries or solar field batteries and charging stations. Many microgrids will have these same issues because reliability of that microgrid and its efficiency change if its frequency is decoupled from the main grid.
The DC/DC converter designs and implementations create the opportunity to run a fully DC microgrid, particularly at high voltage. For example, a 25 kV DC microgrid around a site and solar facilities can mean batteries can run at ultra-high efficiency. Some loads may be directly DC connected and some loads may be connected via inverters designed for power point loads. There may also be gateway inverters or rectifiers that gateway to an AC grid but the microgrid is not phase locked to the grid would mean that grid instabilities can't take it down. The value of 25 kV is just provided as an example, and other values may be used instead.
With AC systems, there is a need to energize all the passive equipment and transformers thus circulating a lot of reactive energy, and transferring AC over distances can additionally incur losses with line impedances and power bouncing.
DC power sharing over medium distances can be done very effectively using this DC/DC converter design, may enable more effective energy storage, more efficient energy transportation, using medium voltage DC for example up to 50 miles.
Further, the DC/DC converter design eliminates the transformers and allows building that voltage by scaling them in series, which can be essentially lossless. This is made possible by each cluster being fully galvanically isolated, with two separate controllers (master/slave control). Further, there may also be top level-level power management to prevent excessive voltage rise in the main conductor if power demand on the load drops.
In addition to the controller in each device (DC/DC converter) there may also be one overall controller that will be in charge of those conversions and conversion stages to set limits to those devices and how they can behave (limit power; limit current; limit voltage) to set boundary conditions.
Thus, voltage sharing can be based on the idea of power sharing because if sharing power is started, then logically the voltage will be shared across those devices and the system will experience the same voltage drop on the input, same voltage drops on the output.
The high voltage DC/DC conversion allows for very high efficiency connection of solar fields with suitable distance to loads such as a heated brick energy storage unit that can be coupled to electrolyzers and used for electric vehicle charging. Further, the system could have integrated hydrogen production and electric power generation from hydrogen and further have integration of lithium-ion batteries. The system can also be coupled to drive desalination to produce a completely off-grid facility or military base that is self-powering for its domestic loads, its heat loads and its vehicles.
The above-described thermal energy storage system provides a stable output of heat from electrical energy that may be supplied from a renewable source. The stable output of heat may be provided to various industrial applications, to address art problems, as explained below.
The ultrahigh temperatures capable of a radiatively heated thermal energy system 100 allow for application in a wide range of industrial processes. In particular, for processes that require ultrahigh temperatures, for example in glass production and metallurgical applications, such a high temperature thermal energy storage system powered by renewable energy provides the possibility of operating entirely or in large part from renewable energy around the clock, providing a path toward zero carbon processes.
A. Material Activation
1. Problems to be Solved
Cement production is one of the largest sources of global carbon emissions, responsible for as much as 8% of global CO2 emissions. The carbon emission from cement production, however, has been growing more quickly than fossil fuel production. The unmet need to decarbonize the manufacture of cement is thus becoming even more of a critical requirement to achieve reductions in global CO2 emissions in order to stabilize Earth's climate.
Cement is typically made from limestone and clay (or shale). These raw materials are mined, then crushed to a fine powder. The blended raw material (“raw feed” or “kiln feed” or “meal”) is heated in a rotary kiln where the blended raw material reaches a temperature of about 1400° C. to 1500° C., e.g., 1400° C. to 1500° C. In its simplest form, the rotary kiln is a tube that may be, for example, 200 meters long and 6 meters in diameter, with a long flame at one end. The raw feed enters the kiln at the cool end and gradually passes down to the hot end, then falls out of the kiln and cools down. In the initial stages at lower temperature (e.g., 70-600° C., and more specifically, 70-350° C.), free water evaporates from the raw feed, clay-like minerals and dolomite decompose into their constituent oxides, producing calcium carbonate, magnesium oxide and carbon dioxide.
Over intermediate temperatures (650-1050° C.), some calcium carbonate reacts with silica to form belite (Ca2SiO4) and carbon dioxide. Remaining calcium carbonate decomposes to calcium oxide and CO2. At the hottest regions (1300-1450° C.) of the kiln, partial melting takes place and belite reacts with calcium oxide to form alite (Ca3O·SiO4). The rotary kiln is used in more than 95% of modern world cement production.
The material exiting the kiln, referred to as “clinker”, is typically composed of rounded nodules. The hot clinker falls into a cooler, which may be designed to recover some of its heat, and cools to a temperature suitable for storage (or is directly passed to the cement mill where it is ground to a fine powder). Gypsum or other materials may be ground together with the clinker to form the final cement product.
The hottest end of the rotary kiln heated by a combination of recovered heat from the hot clinker and burning of fuels is at the exit of the clinker. The heated gas travels in a direction counter to the clinker process. The exhaust gas exits where raw feed enters the rotary kiln.
A majority of cement production uses a separate precalciner to increase production and efficiency for a given cement kiln. The precalciner is a suspension preheater which allows some of the energy required for the process to be burned at its base. The precalciner allows more thermal processing to be accomplished efficiently in the preheater, greatly increasing throughput for a given sized rotary kiln tube.
Depending on the system design, a precalciner can output feed that is 40-95% calcined, at high end, leaving the primary role of the rotary kiln for sintering. The input gas to the precalciner may be preheated by the hot air recovered from cooling clinkers, in addition to the fuel burned. The hot gases exiting the top of the precalciner are often used for drying raw materials. This process, however, tends to be intermittent, thereby wasting heat when the rawmill is stopped.
In some cement production systems, a bypass between the kiln inlet and the precalciner may be installed to extract the dust containing materials potentially damaging to equipment and to final product quality. The collected material, referred to as the cement kiln bypass dust (CBPD), can be approximately 2%, e.g., 2%, of the total clinker production by weight and consists primarily of calcium oxide, a key component of clinker, as well as salts such as KCl and other contaminants. CBPD is usually landfilled at a cost.
CBPD mainly includes already decarbonized calcium oxide. A recent study has shown that temperatures of approximately 900-1200° C., e.g., 900-1200° C., can transform CBPD into valuable clinker components such as belite, mayenite, alite and ferrite at lower temperatures than in the rotary kiln (assisted by other components in CBPD while vaporizing and removing contaminants such as KCl) leaving behind a cementitious product free from a majority of the undesired contaminants which are initially present.
In a traditional cement plant, fuel and oxygen are fired to provide heat into the clinker kiln. This fuel may be in the form of solid media such as refuse or coal (or may be natural gas) introduced along with combustion air into the kiln. At the outlet of the kiln, a stream of hot combustion gases provides a portion of the heat used to preheat the meal and then calcine the meal; the balance of that heat may be supplied by combustion of a fuel and/or heat recovered from hot clinker cooling. The process of calcination consumes about 20-75%, e.g., 20-75%, of thermal energy from fuel depending on precalciner design and operation.
The term “calcination” broadly refers to a process in which a solid chemical compound is heated to a controlled, high temperature in a controlled environment in the presence of little to no oxygen to remove impurities and/or to incur thermal decomposition to a desired product. The term calcination has traditionally referred to a process for decomposing limestone (or calcium carbonate) into quicklime (calcium oxide) and carbon dioxide. This reaction is widely used in industry given that limestone is an abundant mineral and that quicklime is used in the production of cement, mortar, plaster, paint, steel, paper and pulp as well as in the treatment of water and flue gases.
Other calcination processes include the dehydroxylation (i.e., removal of crystalline water) of gypsum used in producing building materials and other products and the dehydroxylation of alumina used in producing aluminum metal and other products. Another calcination process is the dehydroxylation of clay minerals, which may be used for the activation of clay for use as a supplementary cementitious material (SCM) in a cement mixture, such as alongside Portland cement. Clay mineral activation differs from its limestone counterpart in that the reaction releases water (—OH groups) instead of CO2.
Different calcination reactions require different operating conditions (e.g., temperature, environment compositions, etc.) to expose minerals to heat and drive calcination. Over time, different designs have been developed, including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors. Many associated processes have also been developed including internal radiant heating via fuel combustion within a kiln or reactor, internal convective heating via hot gas flow within a kiln or reactor, or external heating of a kiln or reactor. These traditional modes are referred to as soak-calcination processes, given that the material takes several minutes to hours in the reaction chamber to become fully activated.
Flash calcination is another approach, which is more rapid than the soak process, and takes place in a reactor that uses gases at velocities and temperatures creating gas-particle interactions including entrainment and suspension, so as to drive effective heat transfer and encourage chemical reactions. Systems using this principle commonly introduce a gas that has been heated via combustion of a fuel (including direct exhausted combustion products) and/or a gas that may be heated from cooling the products of calcination (or recovered from other heat sources, at the bottom of a reaction chamber in an up-flow configuration). The gas temperature may commonly range from 600° C. to 1100° C. In one implementation, raw clay material to be processed is finely divided and is fed into a chamber above the hot gas injection point. Upward flowing hot gases interact with raw material and may suspend the raw material through the chamber where the particles are quickly heated by the flowing gases.
Additional sources of heat may be incorporated within (or without) the chamber, including fuel combustion devices or additional hot gas introduction ports, to maintain a desired temperature profile or ambient gas composition. As the material exits the chamber, it has been heated to the desired state of calcination (or activation). The gas composition within the chamber may be selected to perform a function of controlling the quality of the product. For example, oxygen may be excluded or there may be a reducing atmosphere zone for quality control of the product. The material to be processed may contain iron that will become oxidized in non-reducing environments and cause the product to change color which may not be desired. This atmosphere reduction zone may be enforced via injection of reducing gases or supplied via supplemental burners in which any oxygen in the air is reduced via injected fuel. After heating and calcination, the material is then rapidly cooled, often by air in cooling cyclones or another form of air quench. Water can also be used as a cooling fluid in certain processes. The product is cooled to 100° C. to 200° C.
Some attempts have been made to analyze clay calcination in gas suspension heaters in order to determine the effect of operating conditions. In one example, a kaolinite particle feed was added above a burner and passed through the chamber with and without supplemental burners along the channel. Convection was the dominant form of heat transfer in the process where an ideal gas supply temperature was about 900° C., e.g., 900° C., without supplemental burners.
In these approaches, internal resistive heaters cannot be used to replace a burner in the calciner. The technical reason is that it is extremely hard to heat the large gas volume needed for gas suspension purely via resistive heaters, as the space and cost required would be too large. Additionally, the resistive heaters may experience degradation due to the particulate matter present in a calcination process.
2. Calciner Heated by Electric Power from Thermal Energy Storage
The present disclosure describes example implementations that involve the replacement of fired fuel and/or hot gas generators with a novel high-temperature thermal energy storage (TES) system. Example implementations cover multiple embodiments of a material activation system with different degrees of integration into material activation processes, which may be used to produce quicklime in some implementations or other activated materials such as activated clay or alumina. Example implementations relate to a novel TES system's integration with a material heating system using any of a variety of calciner/kiln configurations. In some implementations, the integration could be with an existing plant where the TES system and all process modifications are retrofitted to an existing material activation system. In other implementations, a new material activation system is built in which the material heating system is designed around the thermal energy storage system.
In one implementation, a thermal storage system may be used as a replacement for existing hot gas generators in material activation processes. Accordingly, one or more thermal energy storage arrays may provide hot gas as the primary heat transfer fluid for convective heat transfer demands of the material heating system. These demands may include the drying, preheating, cooling, or calciner heating and may be filled via direct tie-in to a thermal storage unit. Gas of any composition may be either recirculated through the TES system after use or fanned in from ambient air, to be used at higher temperatures in the process.
In various implementations, the material activation system includes the above-disclosed thermal energy storage system transferring heat into air, into CO2, into CO2 with a small air fraction, into gases which vary in composition with time (e.g., a dominant gas with a second gas such as air or O2 being present at a different concentration during some fraction of operating hours), and/or into gases arising from an interconnected industrial process, such as mineral calcination. In a further implementation, a small amount of hydrogen or other reducing gas may be included with the carbon dioxide. Example implementations may also include provisions for tolerating, separating, and/or removing entrained particulate matter in a structure such that periodic cleaning maintains long-term performance of the TES system.
In some implementations, carbon dioxide is used as the heat transfer fluid to deliver heat into the material activation process and is then combined with additional carbon dioxide released by calcination. Accordingly, no carbon dioxide separation processes are required (other than condensing any water which results from the combustion of fuel). In another example implementation, thermal energy storage systems employed in the process can heat multiple different gases or gas mixtures for use in the material activation system.
Example implementations as disclosed herein can be considered with regard to two subclasses. In the first subclass, a TES system directly supplies heat in the form of a heated fluid (such as air, CO2, gaseous combustion products, or a combination of multiple gases), replacing a combustion-based hot gas generator for some or all of its typical applications in a material activation process. These applications include, but are not limited to, drying raw material (such as limestone, clay, bauxite, or raw meal), aiding in reactor start up and cool down (getting a reactor to auto ignition temperature (600° C. to 1500° C.)), and preheating raw material (such as limestone, clay, bauxite, raw meal, or a mixture) to desired reactor operating conditions (400 to °1000° C.). Implementations in this first subclass may apply to combustion-based material heating systems such as fuel-fired calciner/kilns, where all auxiliary heat needs other than the burners in the calciner/kiln are provided by thermal energy stored in the TES system.
The second subclass is a more highly integrated process in which the TES system is used to supply thermal energy/heat in the material activation process and combustion may be used in moderation (if at all) to provide suitable atmosphere control for the desired reaction. Example implementations include different process configurations of the TES system integration. In various implementations, one or more high temperature TES units supply heat directly or indirectly to the calciner or kiln reactors as well as dryers and pre-heaters.
In implementations that employ direct heat transfer, the fluid used as the heat transfer medium in the TES system is being supplied directly to the raw material in the calciner and then recirculated back to the TES system after coming into direct contact with the raw material. In implementations that employ indirect heat transfer, the fluid used in the TES system does not come into direct, physical contact with the material in the material heating system. Rather, in some implementations, the fluid in the TES system is used to transfer thermal energy via a heat exchanger into a secondary fluid that comes into contact the material. In other implementations, the fluid used in the TES system may indirectly heat the raw material without the presence of a secondary fluid by heating the walls of the calciner or kiln reactor system, with the heated walls transferring heat to the raw material on the other side of the wall via conduction and radiation. This “indirect” heating mode of thermal storage operation can also be used in applications other than calcination or kiln reactors, including but not limited to biomass drying or food processing. The secondary fluid may be in the liquid state in some implementations.
There is also a combination of direct and indirect heating modes for the TES system fluid where the higher temperature TES system fluid exchanges heat indirectly with a secondary fluid (with a gas-to-gas heat exchanger, for example) and additionally raises the temperature of the secondary fluid stream via direct injection by a bypass configured to inject a portion of the higher temperature fluid from the TES system into the secondary fluid provided to the material heating system. This can be useful for atmosphere control within the material heating system (and within the TES system as well in some implementations). The secondary fluid mixed with some of the TES fluid is then exposed directly to the raw material of the material activation process to supply heat. After supplying heat, this secondary fluid may be treated to remove undesired components that were added to the stream via contact with the raw material such as water, undesired emissions (SOx, NOx, CO, etc. . . . ), and particulate matter. Some or all of this treated secondary fluid may be used to fill other auxiliary heat demands such as drying or preheating or treating or cooling demands (oftentimes, raw material must be cooled after reactions in the calciner/kiln reactor zones). Some or all of the secondary fluid may be returned to the heat exchanger where the stream can be reheated.
In some implementations, a small portion of the heat may also be supplied via supplementary combustion in the material activation process. This may raise the temperature of the gaseous heat transfer stream depending on the specific operating conditions associated with the combustion. Generally, the fuel would be combusted ‘fuel rich’ meaning that there is more fuel than stoichiometric oxygen in the reaction. The primary reason for this fuel rich combustion is atmosphere control as clay, for example, requires slightly reducing systems to not oxidize the iron in the clay and hence prohibit ‘color change’. For example, the amount of oxygen may be reduced, and the iron in the clay may be reduced. The TES system may, however, require slightly oxidizing conditions for nominal operation. The supplementary combustion would remove the small amount of oxygen and create color reducing conditions for the clay. The final product to be output is activated clay, which is used instead of clinker to make cement.
There are several relevant calcination processes that are covered by the material activation system described herein. Different processes often demand different operating conditions (temperature, pressure, residence time, gaseous composition in the calciner, etc. . . . ) although various components of the material activation system may be shared amongst different processes.
As discussed in greater detail in other sections, TES system 76020 is configured to store thermal energy derived from an energy source. In some implementations, this energy source is a renewable energy source (e.g., wind, solar, hydroelectric, etc.) or some other form of variable energy source. Thermal energy storages 76022 within TES system 76020 may include heating elements configured to heat a storage medium using electricity from the energy source. These heating elements may include any of the various examples described herein including, for example, thermal resistors, ceramic resistors, etc. The storage medium may include any of various examples described herein such as brick, stone, etc.
To facilitate extraction of thermal energy from the heated storage medium, blowers may be used that are configured to heat a non-combustive fluid (e.g., carbon dioxide, nitrogen, air, or others discussed previously) by circulating the non-combustive fluid through the heated storage medium. As noted above, the use of non-combustive fuel stands in contrast to prior combustion-based systems that rely on a combustive fluid (e.g., natural gas, propane, methane, etc.) to provide energy. In various implementations, TES system 76020 is configured to provide this circulated non-combustive fluid to the material heating system to facilitate activating a raw material. In some implementations, TES system 76020 is configured to provide the circulated non-combustive fluid to the material heating system at a temperature within a range of from 600° C. to 1100° C.; however, the fluid may have a different temperature in other implementations.
Material heating system 76030, in general, is configured to apply thermal energy to a raw material to produce an activated material. Techniques described with respect to the material heating system may be employed with respect to any of various material activation processes. As discussed above, in some implementations, material heating system 76030 is a calcination system configured to perform a calcination process that removes carbon dioxide from a supply of calcium carbonate to produce calcium oxide. In other implementations, material heating system 76030 is configured to perform a dehydroxylation process (i.e., use of heat energy to remove molecularly bound water) that removes hydroxide from clay minerals to produce activated clay. In other implementations discussed below with
In various implementations, material heating system 76030 is configured to receive thermal energy derived from the non-combustive fluid provided by TES system 76020. As previously discussed, the provided fluid may be used in a direct heating implementation in which material heating system 76030 brings the provided fluid into contact with the material. The provided fluid may alternatively be used in an indirect heating implementation in which a heat exchanger is configured to receive the circulated non-combustive fluid from TES system 76020, transfer heat from the circulated non-combustive fluid into a second fluid, and provide the heated second fluid to material heating system 76030 for applying the thermal energy to the raw material. In a mixed fluid implementation, material activation system 76010 may further include a bypass configured to inject a portion of the circulated non-combustive fluid received from TES system 76020 into the second fluid provided to material heating system 76030. In some implementations in which TES system 76020 is unable to supply enough thermal energy for material heating system 76030, material activation system 76010 may further include a burner (or some other combustion based energy source) configured to supply combustion energy to the material heating system in addition to the thermal energy supplied by the TES system.
Pre-heater 76032 is configured to apply thermal energy derived from the circulated non-combustive fluid to heat the raw material to a first temperature before providing the heated raw material to the kiln for heating to a second temperature. In some implementations in which the Bayer process is performed, pre-heater 76032 is configured to implement a first stage of the Bayer process that includes heating the bauxite to a temperature within a range from 300° C. to 480° C. and at a first pressure within a range of 6 bar to 8 bar. In the illustrated implementation, the thermal energy applied by pre-heater 76032 is received from TES system 76020; however, in other implementations, some or all of this thermal energy may be obtained from an exhaust fluid output by kiln 76034.
Kiln 76034, in various implementations, is the primary component responsible for applying thermal energy to a raw material to produce an activated material. Kiln 76034 may be implemented using any suitable techniques such as flash calcination, rotary kiln, or others discussed above. For example, in some implementations, kiln 76034 is configured to apply the received thermal energy by injecting the raw material via a first inlet of the kiln and injecting, via a second inlet underneath the first inlet, the heated non-combustive fluid in an up-flow configuration that suspends the raw material within the kiln in order to more efficiently heat the material. In one implementation in which the Bayer process is performed, kiln 76034 is configured to implement a second stage of the Bayer process that includes elevating a temperature of the bauxite within a temperature range from 750° C. to 950° C. and a second pressure lower than the first pressure.
Atmosphere reduction system 76036 is configured to reduce an amount of oxygen in contact with the activated material produced in kiln 76034 before the material is cooled. In implementations that produce activated clay, the removal of oxygen may prevent the activated clay from becoming discolored due to oxidation of any iron present in the clay. In one implementation, atmosphere reduction system 76036 includes a burner that combusts a rich fuel mixture to produce carbon monoxide to absorb any excess oxygen. In some implementations, atmosphere reduction system 76036 may not be used as either the activated material may not react with oxygen or the fluid in contact with the material may already include a low oxygen content, such as in a direct heating implementation in which carbon dioxide is used as the non-combustive fluid.
Cooling system 76038 is configured to receive the activated material of the material heating system and reduce a temperature of the activated material. Cooling system 76038 may employ any suitable techniques such as using cooling cyclones or other techniques noted above. In some implementations, the exhaust fluids are collected from cooling system 76038 for recirculation by recirculation system 76040.
Recirculation system 76040, in general, is configured to recover thermal energy that has not been consumed by the material activation process. In the illustrated implementation, this recovery includes recirculating exhaust fluid output from material heating system 76030 to TES system 76020. In implementations that produce carbon dioxide as a biproduct of the material activation process, recirculation system 76040 may recirculate produced carbon dioxide to TES system 76020 for use as the non-combustive fluid. In various implementations, recirculation system 76040 includes a filter configured to remove particulate from the exhaust fluid prior to the exhaust fluid being provided to the TES system.
As noted above and discussed in more detail below, in some implementations excess thermal energy may be used for various other purposes. For example, material activation system 76010 may include a steam cycle system that includes a heat exchanger configured to produce steam from thermal energy recovered from material heating system 76030 and a steam turbine configured to generate electricity from the produced steam.
By choosing appropriate materials for heating elements and heat storage media, the heat transfer gas may be selected among a wide range of compositions, including but not limited to any of, or any mixture of, air, N2, O2, CO2, H2O, and other gases or gas mixtures. Optionally, a minimum level of oxygen may be included, depending on the composition of the resistive heating element. In addition to carbon dioxide as explained above, in combination with a fraction of hydrogen gas or other reducing gas, nitrogen may also be used. A benefit of using nitrogen is that it is inert and the primary gas present in atmospheric air. Certain gases interact with metallic heaters in such a manner as to limit their operating temperatures. Heating materials which form protective oxide scales are compatible with the continuous or intermittent presence of oxygen. Other heaters, including conductive ceramics and encapsulated heaters, enable higher operating temperatures and selection of atmospheres which are oxidizing or reducing.
The CO2 stream is passed directly through the thermal energy storage as the principal heat transfer fluid. The solid media is heated by intermittently available renewable or grid electricity, and relatively continuously delivers a high temperature stream of CO2 which may be at 1000° C. or higher temperature and may deliver a significant fraction or all of the process energy required by kiln 76052 and preheater/calciner units. Each “unit” referred to may include one or multiple units to meet charging, discharging or other requirements. The thermal energy storage may not deliver high enough temperature or energy to the kiln 76052. The combustion of some fuel may supplement the energy flow and boost the temperature to what the process requires. Therefore, the heating process may optionally be a hybrid of heat derived from renewable electricity and heat derived from fuel combustion.
In one example implementation, this fuel combustion directly releases its combustion gases into the kiln, avoiding the expense of heat exchangers. Those combustion gases include principally or only carbon dioxide and water because an air separation unit has delivered a relatively pure stream of oxygen. In some example implementations, a stoichiometric or near stoichiometric amount of oxygen may be used in burning of the fuel to create a stream of syngas (i.e., synthetic gas) containing a desired amount of carbon monoxide.
The produced syngas may be used in a separate water gas shift reactor system to produce hydrogen and carbon dioxide, which can be used directly as fuel or separated and productized. Accordingly, nitrogen is not introduced into the gas stream flowing through the kiln, which may yield an additional benefit of avoiding nitrogen oxide formation at high temperature and making obsolete the non-catalytic reduction requirement (i.e., injection of ammonia solution into the kiln), avoiding unnecessary heating of a bystander gas such that a CO2 separation technology is not needed in the process to separate CO2 from nitrogen.
The combustion oxygen stream is optionally preheated to high temperatures, such as 800° C. or higher, by a thermal storage unit R4 in which oxygen is directly flowing through the thermal storage media core. Optionally, the oxygen stream may be mixed with recycled flue gas (predominantly CO2) to control the flame temperature and heat output of the combustion process. In another example implementation, the oxygen stream is mixed with both or either of flue gas (predominantly CO2) and/or gaseous fuel before entry into the kiln combustion system.
By tuning the quantity of CO2 mixed into the fuel stream, the heating profile can be controlled in a way to adjust, for example, fuel consumption, product production, quality and system configuration to allow retrofitting of existing kilns. The fuel, whether methane, propane, hydrogen, or other fuel, optionally combined with recycled CO2 stream, may be preheated by a separate thermal energy storage R3 in which the fuel gas flows directly through the thermal energy storage core.
This preheating allows the heat released by combustion to deliver only the high temperature heat, with lower temperature heat needed to heat the oxygen and fuel provided by captured thermal energy. The construction materials used in thermal energy storages R3 and R4 may be the same as those in storages R1 and R2 or may be different so as to tolerate the gas composition(s), temperature requirement or to improve performance, cost, durability, chemical interactions or other parameters.
In one implementation, the result of the foregoing example operations is that between storage R1 and combustion of fuel and oxygen optionally heated by storages R3 and R4, high temperature CO2 streams deliver the kiln heat required by the kiln reaction steps. The kiln exhaust gas stream is comprised principally of CO2 (potentially with H2O from combustion, if any). This gas stream is optionally combined with another superheated CO2 stream carrying high temperature heat at point C and introduced into the calcination and preheating process 76054, heated by thermal energy storage R2. In the calcination process, additional CO2 is released, and thus a higher volume of CO2 flows at D. The gas stream at D may be cleaned of particulate matter by, for example, a cyclone separator and/or ceramic filter. The gas stream is divided, with one portion returned to thermal energy storages R1 and R2 where it is reheated to continue to deliver heat into the process, and another portion partially cooled and extracted as captured CO2.
In one implementation, a control system matches the rate of CO2 extraction and compression to the rate of CO2 production in the calciner. That control system may use measurements of the relative gas pressure in the various process units or other ordinary means to control the rate of gas extraction. Two heat exchangers H1 and H2 are shown which may cool the CO2 by releasing heat to the environment or may cool the CO2 and use the heat for another purpose, for example drying of raw material or heating input CO2 stream for R2. This example operation allows for energy recovery even when the rawmill is not operational, as they tend to run intermittently to ensure a surplus of raw material to keep the kiln running continuously.
Alternatively, a separate TES system (not illustrated) may be coupled to the rawmill operation such that the drying process is powered from the thermal energy storage. The thermal energy storage may be charged convectively by exhaust at D or electrically. The cooled CO2 may be compressed, captured and stored or used for another purpose. Because the stream almost entirely consists of CO2 and potentially water, water removal through a condenser would produce a pure stream of CO2 ready for compression. Optionally, a relatively inexpensive CO2 purification unit may be used. In comparison, MEA absorption requires a considerable amount of energy for regeneration and fans and pumps.
In another optional example implementation, thermal storage system R2 or another heat system provides heat for the treatment of cement kiln bypass dust (CBPD) to increase product yield, reduce carbon emission and reduce costs associated with landfilling or otherwise disposing of the material. The separated or addition of salts may be beneficial as additives to the main material stream to lower the processing temperatures, reducing the energy and temperature requirement to form the desired product, potentially further reducing the need for fuel fired heat topping and allowing renewable energy to power a larger fraction of the cement production process.
Heat exchangers H1 and H2, which capture heat from the carbon dioxide streams, may release heat into the feedwater or inlet gas stream for the power generation cycle, thus capturing that otherwise waste heat as a heat recovery economizer in the power cycle. In various implementations, that power cycle may be a simple steam turbine cycle, an organic Rankine cycle, a supercritical carbon dioxide (sCO2) cycle, or it may be a combined cycle power generation system, including a combustion turbine whose exhaust is captured to drive a second thermal cycle.
In one example implementation, the combustion turbine is oxyfuel blown and its exhaust gas CO2 is introduced back to the overall CO2 cycle, eliminating any separate CO2 emissions from the power generation. The thermal energy storage R5 may be integrated into that combined cycle as shown. In one example implementation, supercritical carbon dioxide is used as the working fluid inside the heat storage unit and can directly run a sCO2 power cycle or be used for another application.
The CO2 stream extracted from the cement manufacturing process may be used for multiple purposes, including geologic sequestration, carbonation of supplementary cementitious materials, or as an element in the production of synthetic fuels.
Another example implementation includes a steam cycle for continuous power generation and additional heat recovery. In such an implementation, hot air from the cooling cyclones or a screw heat exchanger in contact with the hot calcined product exchanges heat with pressurized, recycled water from the steam cycle and some makeup water. This cooled gas/air is either released to the environment, used in the drying part of the process, or introduced as cool gas in a TES system. The preheated water is turned into steam via heat exchange with a TES system. This may be the same TES system involved in the calcination process or a supplementary unit. The air side of this heat exchange is circulated back into the TES system to reduce waste heat. The steam is then expanded in a steam turbine, generating electricity for the plant. The steam downstream of the steam turbine may exchange heat one last time with air or gas for use in the drying process before being mixed with any feed water makeup, pressurized and recirculated in the cycle.
Such a solid oxide electrolyzer may electrolyze water to produce hydrogen or may co-electrolyze a flow of steam and carbon dioxide, such that its outlet products are carbon monoxide and hydrogen, or syngas. The relative flow of CO2 and H2O may be so adjusted as to produce the desired proportions in the syngas of carbon monoxide to hydrogen. The desired syngas composition may also be attained by controlling the combustion and stoichiometry of the fuel fired inlet. The syngas may be used for a variety of purposes, including the drive of Sabatier or Fischer-Tropsch reactions to make various hydrocarbon molecules, or a water gas shift reaction producing H2 which may be used as fuels or feedstocks in other industrial processes.
The solid oxide electrolyzer (SOEC) may be integrated with thermal energy storage R6 in gas contact with the fluid flowing through the thermal storage core, where that circulating fluid is air. In one implementation, the SOEC may be swept by air at a higher temperature, such as 830° C., and the air exiting from the SOEC may be at a lower temperature such as 800° C. The heat in that air is then captured by a heat recovery unit to generate steam or heat another working fluid for another purpose. That heated fluid may for example be integrated into the electric power cycle previously described. The operation for the SOEC releases oxygen into the air sweep.
To manage overall oxygen concentration, relatively cooler air coming from the heat recovery unit is partially released, and ambient make up air is partially drawn into the thermal energy storage. This released gas is oxygen enhanced air. This stream may be supplied to an air separation unit, an alternative feedstock to the air separation unit, storage unit or fuel firing units shown on
As shown in
The foregoing approach is modified by the integration 76150 of a thermal energy storage system as shown in
As noted above, the TES system may be used to provide heat into the calcination step of the Bayer alumina process. Additionally, the heat inputs into other parts of the process may also replace fuel, including the fuel that is provided at the mine, at the lime kiln, and at the steam generator that provides energy to operate these modules.
With respect to the calciner stage, art approaches perform calcination in two stages: a first stage at a lower temperature associated with a decomposer and steam separation to perform partial, and a second stage at a higher temperature than the first stage, but at a lower temperature than would be required if calcination was performed in a single stage. The first stage may be at a temperature such as 350° C., and the second stage may be in the range of 750° C. to 950° C. The two-stage calcination process provides energy efficiency advantages over a single stage calcination process. Similar to clay calcination, a fuel is provided as an input to the first calcination stage and the second calcination stage. The heat that is output from calcination may be provided for reading and waste heat recovery, with the remaining heat being expelled after water cooling via stack gas output.
Conventional calcination involves heating the cooled, wet gibbsite to 950° C.-1100° C. to remove free and crystalline moisture in the gibbsite, which is derived from bauxite. Art approaches have used a rotary kiln or calciner using heat from combustion. According to some art approaches, the material first enters a high-pressure calcination step (e.g., the decomposer), for example at 6-8 bar and 300° C.-480° C., and removes all the free moisture (e.g., drying) and activates a significant portion of the gibbsite to alumina. These mechanisms produce water vapor as effluent. The partially calcined material passes through a pressure reducer to the lower pressure calcination stage. This occurs at ambient pressure and relatively lower temperatures of 850° C.-950° C. Fuel and air that is preheated in the cooling of the product material is combusted in a gas suspension calciner. The heat from the flue gas is further recovered by being passed into a steam generator/superheater where is exchanges heat with recycled steam from the first stage, recycled steam from other steps in the Bayer process, or makeup water to supply the first calcination step (or decomposer) with superheated steam.
These approaches may have problems and disadvantages. For example, when steam is used as a heat transfer medium in calcination stage, it is necessary to account for the plant balance, as the extremely high mass flow of superheated high-pressure steam must be filtered and cleaned before recirculating to other areas of the plant. The theoretically more favorable heat balance from collecting high temperature moisture from the decomposer also translates to a more complex, integrated process. The large mass flow leads to art problems in supplying the correct quantity of superheated steam. The steam generator/superheater is a major area for concern, both from the thermodynamic and operating standpoint. Additional fuel must be fired in this step. Additionally, buildup in process equipment is one of the largest issues in the concept, as the recirculated steam often must be cleaned and filtered of particulate matter before interacting with the steam generator and superheater.
To address these problems and disadvantages, the thermal energy storage system described above supplies heat to recirculating process steam, and may be integrated with heat recovery apparatuses to address art plant balance problems. For example, heat from the hot flue gases of the second gas suspension calciner may be utilized to supply a portion of the heat to either the thermal storage working fluid medium (e.g., gas-to-gas heat exchangers) or the process steam (e.g., gas to liquid heat exchanger). This will allow the plant greater flexibility in energy management as well as maintenance to fix solid buildup in heat transfer equipment. The thermal battery may be external to the plant and may either supply steam externally with an attached steam generator or supply steam indirectly, passing hot gases through existing or new heat exchangers replacing the duty of combustion gas products.
In another example implementation, the thermal storage relates to a fully integrated process where the thermal batteries replace all combustion on site. This implementation includes the above-described approach, with supplying all or the majority of the heat to the second calcination stage. The temperature of the partially calcined material is brought to near ambient pressure (from the high-pressure stage 1) and put in direct contact with hot flue gases bringing the temperature to 850-950 C. This reduced temperature range allows the heat from fired fuels to be replaced by high temperature stored heat.
In some example implementations, the primary working fluid of the thermal energy storage system would contact the material to be calcined. In other example implementations, this heating may occur indirectly, where the primary working fluid of the thermal battery does not directly contact the material. The hot gas would be blown through the calciner at sufficiently high velocities to achieve desired level of suspension and activation. The gas effluent would leave the chamber at a high temperature to be used in the steam generation and superheating of the process steam used in the first stage of calcination as well as any other steam needs in the system.
As shown in
The output byproduct of the second calcination stage 8303 is slightly cooled gas that can be used for the heat recovery steam generator 8307, instead of the additional fuel and air that may be present in the prior approaches. The steam output from the steam generator 8307 is provided to the first calcination unit 8309 at the temperature of the first calcination unit 8309, which may provide the recycled steam flow and solids as in the prior art. Additionally, instead of expelling excess heat or waste heat from the steam generator as a set gas, the heat byproduct of the steam generator is the gas that has passed through a heat recovery zone, and is injected into the alumina cooling cyclones 8311, along with ambient air. The byproduct heat from the alumina cooling cyclones is provided, through a baghouse and filter 8317, as the recirculated gas for the input of the thermal storage unit.
According to an alternative implementation, the TES system may only be used for providing the heat for the steam generator, so that the existing infrastructure of the alumina processing facility can be used without substantial modification.
The example material activation system may have various benefits and advantages. For example, because the output of the waste heat recovery is recirculated as an input to the thermal energy storage, emission of heat through the stack is avoided. Thus, unnecessary heat emissions to the atmosphere can be avoided. Additionally, by using the incoming heat from the TES system, it is not necessary to use fossil fuel to provide the input heat. Further, because the combustion aspect of generating heat is removed, the free moisture in the input combustion stream is eliminated, which avoids the problems introduced by the presence of that moisture, particularly with respect to the calcination of clay, as explained above. The example implementation also has a benefit of more favorable thermodynamics and lower maximum temperatures.
3. Advantages over Prior Systems
The material activation system described herein may have various advantages and benefits over prior calcination implementations. For example, the material activation system may reduce or eliminate carbon dioxide emissions associated with cement manufacturing, by running partially or exclusively on renewable electricity using thermal energy storage arrays heated by electric power.
Further, the modularity of the thermal energy storages and applicability in various parts of the cement production process allows for stepwise electrification, retrofitting and hybridization with fuel firing. Integration of thermal energy storage allows low cost, low carbon intensity, low capacity factor electricity to operate various processes in cement production or other industrial applications at high annual capacity factors that may be nearly equivalent to operation with fossil fuels.
The material activation system described herein also addresses problems associated with moisture in clay. Clay is generally a very moist substance as it is often acquired in wet areas with relatively large amounts of both free moisture and crystal water in the structure of the mineral. The fuel consumption in the activation rises dramatically with the amount of free moisture present in the clay, due mostly to energy being wasted on a water phase change. This problem is further compounded by additional water vapor produced in combustion. The TES system, however, overcomes this problem as combustion is not the primary form of heat transfer. Not relying on combustion also allows the thermal storage system to have a higher degree of freedom in operating conditions since the air flow rate will not dramatically change the gas composition inside the reactor chamber.
Another benefit to switching from combustion to electrically heated and stored energy is that, in clay activation, there exists an upper bound temperature at about 950° C., e.g., 950° C. where the clay mineral structure is destroyed to mullite and loses all of its desired qualities for use as an SCM. In combustion-driven processes, temperature profiles inside of reactors are much harder to control than with a fixed temperature gas heat source that is much easier to control and monitor.
By decoupling the hot exhaust air from the rotary kiln from the preheater/precalciner inlet, one or more multiple potential benefits may be achieved. By decoupling the gas flow between the kiln and precalciner, gas flow and heating rates can be independently controlled to optimize each process. For example, in an air-through system, the amount of fuel that can be burned at the calciner can be limited due to excessive gas flow rates that can cool the flame temperature. Also, the heated exhaust gas from the kiln can be captured and used for alternative purposes, such as providing thermal energy to a power cycle to generate electricity.
Further, the hot exhaust from the kiln may contain significant amounts of undesirable components such as alkali salts, which evaporate in the hotter sections of the kiln. These undesirable components may cause damage to equipment, cause clogging in the precalciner as it cools and reduce quality of the product as it recirculates. By decoupling the kiln and precalciner, the undesirable byproducts can be kept out of the precalciner and potentially captured. Additionally, heat required for the precalciner can be provided from a TES system powered by renewable energy or other sources, and optionally supplemented by a fuel fired source.
As another benefit, the kiln and precalciner can be run on different gas makeups in some implementations. For example, the kiln may be heated by an oxyfuel energy source with added methane, resulting in a gas makeup consisting of predominantly CO2 and H2O. This makeup avoids side reactions such as that of air nitrogen with oxygen, producing nitrogen oxides. Carbon dioxide and water can be utilized in processes described elsewhere in this disclosure. The precalciner can be run on air flowing through the thermal energy storage as it may be less expensive and may not have the problem of nitrogen gas reactions. The type of gas and combination of storage versus fuel energy source can be independently adjusted and potentially optimized in some embodiments.
The use of carbon dioxide has various benefits and advantages. For example, carbon dioxide does not require an air separator and has thermal properties that are more conducive to heat transfer. Carbon dioxide also has a higher emissivity at high temperatures. Further, carbon dioxide is inert and does not combust, which as stated at the benefit involved. Because the carbon dioxide does not react with the resistive heaters, there is less oxidation or wear and tear on the resistive heaters of the thermal energy storages. The byproduct gas is recirculated as input fluid for the TES system, and carbon dioxide is not released into the atmosphere, which has an environmental benefit of reducing greenhouse gases.
Prior approaches do not include an integrated process that uses hot gases generated from electric resistive heaters to supply all of the heat for a calcination process. Further, these approaches do not include an integrated process that uses a TES system that charges from electricity and discharges heated fluid directly into a flash-calcination process as the main mode of heat supply. Additionally, the material activation system may recirculate waste gases from the material heating system back to the TES system. This recirculated fluid may also have a desired composition to meet reaction and quality needs.
B. Electrolysis
The gas that is output from the TSU may be provided as the input for various industrial applications. One type of industrial application that uses and benefits from a continuous stream of heat at a constant temperature is electrolysis. The thermal energy storage system receiving electric power that can flow into a heat storage system (e.g., taking air in at 200° C. and delivering air in a range between 600° C. and 900° C. (such as 860° C.) when discharged for electrolysis). As explained below, art electrolysis systems can be improved by combination with the above described thermal energy storage system.
1. Problems to be Solved
Solid oxide electrolyzers according to conventional designs receive an input of heated gas and water in the form of superheated steam. The gas is heated prior to input to the solid oxide electrolyzer by an electric resistive heater, a fuel heater, or the like. The use of an electric resistive heater or fuel heater for this purpose may have various problems and disadvantages. For example, fuel heaters may consume fossil fuels such as natural gas, which is expensive and causes pollution. Electric heaters powered directly by VRE sources cause problems with changing temperatures and limited operating periods.
There are several types of fuel cells that take hydrogen or a mix of gases and make electric power, such as molten carbonate electrolyzer fuel cells, and solid oxide fuel cells. Such fuel cells use essentially the same as electrolyzers in reverse. However, solid oxide fuel cells have problems and disadvantages because the oxidation causes localized heating and issues with cell life. Solid oxide fuel cells require their inlet reactants and the fuel cell assembly to be maintained at particular temperatures. The operation of fuel cells delivers energy partly in the form of electrical energy and partly as heat. Further, solid oxide fuel cells require a recuperator (e.g., high temperature heat generator) to make use of a portion of the heat generated by the fuel cell. However, a substantial portion of the heat so generated is not used, which results in inefficiencies.
2. Reversible Solid Oxide Unit
Solid oxide electrolyzers may include an electrolyzer producing hydrogen by using electrical energy to break apart the molecular bonds and drive apart the elemental ions that into separate outlet streams. Solid oxide electrolyzers have a porous cathode with a porous electrolyte that is catalytic when operated at temperatures at or above 830° C., and thermal energy is contributing to cracking those bonds. A solid oxide fuel cell is typically 40-50% efficient at taking fuel energy and making electric energy, with the rest of the energy being released as heat at around 850° C., e.g., 850° C. to 860° C., e.g., 860° C., in some cases, which are slightly higher temperatures than the optimal operational point for the solid oxide electrolyzer. A system may incorporate one or more solid oxide electrolyzers and one or more solid oxide fuel cells; a single solid oxide unit may operate reversibly as an electrolyzer or fuel cell.
The product gas 4908 (e.g., hydrogen) is cooled via a heat exchanger. The heat exchanger may reject heat to the environment or, more efficiently, may deliver heat to a thermal load, such as a once-through steam generator (OTSG) 4911, as its input. The product gas flows through the heat exchangers of the OTSG 4911, which is supplied by cold water from a source 4913. As the product gas 4908 is cooled by the heat exchanger/OTSG 4911, much of its carried water is condensed, becoming condensed product gas 4912. The condensed product gas 4912 is primarily provided to a hydrogen processing unit 4915, which in turn provides the hydrogen gas in a storage ready form to storage 4917. A portion of the condensed product gas is recirculated at 4919 to be mixed with the input steam 4904. In one implementation, steam 4904, or a portion of the steam, may be the output of the OTSG 4911, as shown at 4921.
In a manner similar to that explained above for OTSG 4911, another OTSG 4931 may be provided, having water supplied from a source 4933. As previously discussed, the OTSG 4931 may be any heat exchanger heating a fluid, including a recirculating boiler with or without superheat, or a unit that heats circulating air, CO2, oil, water, or salt. The OTSG 4931 receives the oxygen enriched hot fluid, and outputs the cooled fluid at 4937. In some implementations, the OTSG 4931 may receive another stream of hot fluid from the thermal energy system 4901 so as to adjust the temperature or heat flow of the combined stream to a more useful condition. The cooled, oxygen-enriched fluid 4937 may be mixed with ambient or preheated air at 4935, to adjust the composition of oxygen to a desired level. The adjusted fluid 4939 may be provided as an input gas to the thermal energy storage system 4901.
In the fuel-cell mode of operation, the air 5030 may provide a cooling effect in solid oxide fuel cell 5007. The air 5002 from the thermal energy storage system 5001 and the heated hydrogen from the hydrogen storage 5003 are input as shown by 5004 and 5030 respectively to the solid oxide fuel cell 5007. As its output, the solid oxide fuel cell 5007 generates direct current electricity at 5006. In one implementation, the direct current electricity is provided to an inverter to convert to an alternating current power output, which can be provided to any use 5009 (which may, e.g., be a power grid). Additional outputs of the solid oxide fuel cell 5007 include water and hydrogen as a product fluid at 5011, and heated, oxygen-depleted air at 5021. The product fluid at 5011 is provided to heat exchanger 5013, which cools the product fluid by heating another fluid which may be water, air, or another fluid received as shown at fluid source 5015.
The output includes export steam, which may be provided as an input to an industrial application that requires steam, such as a steam turbine as explained above. Additionally, residual hydrogen may be recirculated, by way of a heat exchanger 5005, to the solid oxide fuel cell 5007, as shown at 5027. The oxygen-depleted fluid 5021, optionally supplemented with other hot fluid from the storage 5031, is provided as the heating gas for the heat exchanger 5013, and subsequently provided as the input fluid for the thermal energy storage system 5001, as shown at 5025. It is noted that the solid oxide fuel cell 5007 generates electricity and heat. Thus, the input fluid from the thermal energy storage system 5001, which is at about 650° C., e.g., 650° C. in this example, is provided as cooling air for the solid oxide fuel cell 5007.
In some implementations, the electrolyzer 4102 may co-electrolyze water and CO2 (separate electrolyzers may also be used to electrolyze water and CO2) with all or a portion of the resulting syngas directed to a methanation or Fischer-Tropsch type conversion unit 4109. Unit 4109 may make a synthetic gaseous or liquid hydrocarbon fuel, shown at 4106. Additionally, a once-through steam generator (OTSG) 4107 may be provided as a condenser that cools the output fluid of the solid oxide electrolysis unit 4102 and provides the steam as an input to the solid oxide electrolysis unit 4102. The byproduct hot fluid is recirculated back to the thermal energy storage system 4105 as an input fluid.
As explained above, the electrolyzer is reversible as a fuel cell. Thus, when the renewable input power such as the photovoltaic array is unavailable or when electricity is needed by the grid, hydrogen can be fed to the fuel cell and water, electricity, and heat can be output from the system. The heat is at a high enough temperature that the heat can be used to produce steam or utilized in another industrial process. Accordingly, less heat is extracted out of the heat storage unit as it is replaced with what would otherwise be waste heat coming from the fuel cell.
Alternatively, the gas flow can be reversed, and heat can be put convectively back into heat storage. Thus, when the system is performing co-generation and running heat, the waste heat from the fuel cell can be used to either displace energy that would otherwise have been discharged from heat storage or be returned to heat storage.
The efficiency in the electrolyzer dramatically improves when using hot fluid from the thermal energy storage system. Further, if none of the outlet steam is being used, the captured heat can be repurposed. For example, hydrogen is produced in one implementation, with a fraction being sold and another fraction being used for power generation. The waste heat from power generation may be recaptured and used to reduce the electricity used for electrolysis during the next period, such as the next day. Further, in some example implementations, one or both of the convective waste heat from the fuel cell and input electric heat may be used to charge the thermal storage unit.
In one implementation, the system may incorporate 1) a solar array or other intermittent electricity source; 2) a combination electrolyzer/fuel cell-heat storage unit; and 3) a lithium-ion battery and an electric vehicle charging station and a hydrogen filling station. This system can be used to store energy as hydrogen that may participate in providing the off-hours electricity for EV charging but is also available for dispensing to vehicles as hydrogen charging.
The hot fluid 4809 is provided to a solid oxide unit 4803. In this case, the solid oxide unit is a two-way reversible unit. For example, solid oxide unit 4803 can operate in electrolysis mode, which produces an endothermic reaction, or in fuel cell mode, which produces an exothermic reaction. The solid oxide unit 4803 is currently described in electrolysis mode.
The solid oxide cell 4803 in electrolysis mode receives the hot fluid 4809 from the thermal energy storage system 4801. Because the solid oxide unit 4803 in electrolysis mode operates such that the internal resistance does not generate enough heat to overcome the endothermic reaction, the solid oxide unit 4803 is operating in thermal neutral voltage mode. Although it is not shown, each of the cells receives an electrical input at 1.28 V. Other voltages may also be possible such as a voltage in a range between 1 volt and 3 volts. In various embodiments, hot fluid 4809 is passed through the solid oxide cells as a sweep fluid (e.g., sweep gas).
In addition to the hot fluid 4809 (e.g., sweep fluid) provided by the thermal energy storage unit, a reaction fluid (e.g., steam mixed with hydrogen) 4811 is also provided as an input to solid oxide unit 4803. In this example, the reaction fluid 4811 is provided having 96% water and 4% hydrogen gas, at a superheated temperature of 807° C. and at a flow rate of 814 kg per hour. The percentage of water, temperature, or flow rate of reaction fluid 4811 may be varied. In various implementations, the temperature of reaction fluid 4811 is at a temperature below hot fluid 4809 but at a temperature above 800° C. In some implementations, the flow rate of reaction fluid 4811 is balanced with the flow rate of hot fluid 4809 to provide desired reaction results in solid oxide unit 4803.
The reaction fluid 4811 is provided to the solid oxide unit 4803. As a result of the reaction in the solid oxide cell, the water molecule is split and the resulting ions form oxygen gas and hydrogen gas. At the same time, the sweep gas (e.g., hot fluid 4809) pulls the oxygen off of the air electrode as the water comes in on the cathode and strips the oxides off of the water.
As outputs, the solid oxide cell in electrolysis mode produces product fluid 4813 as well as oxygen enriched fluid 4815 (e.g., oxygen enriched air). In certain implementations, the temperature of the product gas is near a temperature of the oxygen enriched fluid. Both fluids may be at a temperature between a temperature of the reaction fluid and a temperature of the hot fluid 4809. In the illustrated embodiment, the product fluid 4813 is 76% hydrogen and 24% water by volume, which corresponds to 26% hydrogen and 74% water by weight. The temperature of the product fluid 4813 is 830° C. and it is provided at a flow rate of 274 kg per hour. The enriched fluid 4815 is a composition of 60% oxygen and 40% nitrogen by volume, at a temperature of 830° C., and at a flow rate of 2159 kg per hour. The composition, temperature, and flow rate of the product fluid 4813 and enriched fluid 4815 may vary based on the operating conditions of the system.
For product fluid 4813, a thermal load such as an OTSG 4805 including heat condensers is provided. OTSG 4805 uses water to cool and condense the hydrogen gas. More specifically, the product fluid 4813 enters the OTSG 4805, where it is exposed to water that is run through pipes. The source of the water for the OTSG 4805 is a water reservoir 4817, where the water is provided at a relatively cool temperature such as 25° C. As the water passes through the various condensers, the water becomes more and more heated from the exit to the entrance of the condenser. More specifically, the water reservoir 4817 provides the clean water and condensate to a first stage of the heat exchanger, where the product fluid is at its coolest point of the three heat exchangers.
The water then flows to a second heat exchanger that is upstream of the first heat exchanger, and the product fluid is warmer than at the first heat exchanger. At the third heat exchanger, the product fluid 4813 is incoming, and is at its hottest point. While the heat exchangers of the condenser are shown as having three stages, the heat exchanger may be varied to have more or fewer stages as a matter of design choice.
As a result of the heat exchange, the condenser operates as the OTSG 4805, because as the water absorbs the heat from the hot hydrogen product fluid 4813, the water is converted to steam, and the steam is provided to the input of the solid oxide unit at a temperature of around 830° C., e.g., 830° C. The steam is then provided as 4837 and input to the solid oxide unit at 4811. Because the solid oxide unit 4803 is sensitive to contamination, the source 4817 of the water for the condenser is purified water. Optionally, the purified water may be combined with the condensate output 1819 of the condenser.
As the hydrogen passes through the condenser, water is removed from the hydrogen gas as condensate due to the hot hydrogen gas passing over the cool pipes of the condenser. The output 4821 of the condenser is dry product fluid, namely dry hydrogen gas. The hydrogen gas is provided to an industrial application at 4823, as explained above.
At 4825, some of the hydrogen gas (e.g., knock-off hydrogen gas having some water mixed in) is fed back into the input of the solid oxide unit 4803 in combination with the steam that is formed at the output of the condenser as explained above. The hydrogen gas is combined with steam at the input of the solid oxide because 100% steam cannot be input to the solid oxide unit due to degradation issues. Optionally, the gas that is output from the thermal energy storage system may be provided at a temperature based on a parameter of the solid oxide electrolyzer, such as the operating temperature.
Because the thermal energy storage system provides the constant flow of heated fluid 4809 at the temperature required for the solid oxide cell in electrolysis mode, there is no need for electric resistive heaters as in prior systems. Thus, the solid oxide cell 4803 may be provided and used without a heater. However, electric resistive heaters (or other heaters) may be optionally added, to provide temperature adjustments or calibration at the entrance of the solid oxide unit.
As the oxygen enriched fluid 4815 is input to the OTSG 4807, the water from the water reservoir 4827 interacts with the enriched fluid, in a manner similar to that described above for the product fluid. Thus, heat is transferred to the water that passes through the heat exchangers. Such water is output as steam at 4839 and provided to the input of the solid oxide unit as part of reaction fluid 4811 along with the steam from the product fluid condenser and the recirculated hydrogen gas. The enriched fluid may also be vented at 4831.
The enriched fluid is output at 4829. The enriched fluid is output to the atmosphere as air at standard atmospheric composition at 4833. Additionally, oxygen enriched fluid may be recycled at 4835 after blending with atmospheric air, such that the composition of the fluid is 53% nitrogen and 47% oxygen, for example. This fluid is provided as an input to the thermal energy storage system 4801, where it is heated in the thermal storage arrays and provided as an output to the solid oxide unit as hot fluid at 4809, as explained above. Further, the blending of the oxygen enriched fluid with atmospheric air also has a benefit for the thermal energy storage system 4801, in that problems and disadvantages associated with having oxygen enriched fluid in the thermal energy storage system, such as potential oxidation of components, are avoided.
Additionally, the temperature of the heat that is generated by the thermal energy storage system may be provided to the solid oxide unit at a temperature that is thermally neutral. In other words, because the hot fluid 4809 is provided at an elevated temperature, such as 855° C., the system is in an isothermic condition, and the system does not have any net heat demands. In other words, the chemical reactions in the solid oxide unit 4803 will cool the system, whereas the only resistance within the thermal energy storage system is from the heating elements that generate heat from electrical energy. The result is that there is no net temperature change and a substantially lower energy cost. Accordingly, there is cost savings in that it is not necessary to add additional resistive heaters or fuel meters to the solid oxide unit to heat the incoming air. However, it should be noted that the electrolyzer need not be operated at the isothermal temperature and may instead use heat that is generated at a higher or lower temperature.
As noted above, the solid oxide unit is reversible, such that it can be used as an electrolyzer, as explained above, or as a fuel cell. The fuel cell operation may include, using the structures as explained above, with the thermal energy storage unit providing oxygenated enriched fluid that is combined with compressed hydrogen to produce direct current electricity and water, as described herein.
Additionally, in some implementations, when the solid oxide unit is not operating the hot fluid 4809 generated by the thermal energy storage system may continue to be provided through the solid oxide unit. The benefit of flowing such hot fluid through the solid oxide unit when the system is not in use is that the ramping down during the cooling process and the ramping up during the heating process before and after active operation (e.g., thermal cycling), respectively, is avoided. Additionally, the wear and tear on the unit during those processes is also avoided and, in addition, the time and cost of cooling and heating of the various components is reduced (such as the ceramic inside the solid oxide unit). Further, it is possible to switch loads, between the different modes of operation (such as electrolyzer and fuel cell), without shutting down and warming up the unit. In some implementations, the solid oxide unit may continue to be heated by hot fluid 4809 at temperatures around those utilized during fuel cell operations.
The composition of the fluid flowing within the thermal energy storage unit may be adjusted by the extraction of oxygen enriched fluid 4829 and/or the introduction of ambient fresh air. The oxygen enriched fluid extracted may be used for another purpose, including the purification and supply of oxygen for a commercial purpose.
In addition, hydrogen and oxygen production may be coupled with other processes such as hydrogenation of CO2 or CO to make liquid fuels or remediation of contaminated groundwater contamination using oxygen. Excess heat, such as from a Fischer-Tropsch process, could be used to convectively charge or pre-heat fluid for the thermal storage unit. Other electrolysis processes benefitting from renewable electricity or thermal energy can also be coupled to the storage system. As an example, a direct co-electrolysis of CO2 in combination with the water-gas shift reaction and steam to produce syngas, which can further be processed in a Fischer-Tropsch reactor for conversion to hydrocarbons, is optimal at a temperature serviceable from a renewable energy storage unit, as described above, and powered using the DC architecture described previously.
Nickel-based electrodes may also be utilized to obtain methanation of carbon monoxide (e.g., Sabatier reaction), with the ratios of various component products being controlled by temperature, pressure, and concentration of components in equilibrium. It may be particularly valuable to locate a facility that combines energy storage, Fischer-Tropsch, Sabatier, and co-electrolysis processes at a bio-refinery (such as an ethanol refinery (that has a large supply of biogenic CO2 available from the fermenter) or another processing facility such as a renewable diesel refinery (which has CO2 streams arising from process units and has fuel production equipment that can purify the products arising from the Fischer-Tropsch reaction).
The system may also be used in industrial loads such as renewable diesel refineries, petroleum refineries, or oil fields where there is very high value for hydrogen that is participating in the chemical process. There is also very high value for 24-hour, zero carbon electric power. For instance, instead of producing hydrogen and power at low efficiency, this set of systems allows conversion of essentially every kilowatt hour that comes into the system either leaving as a kilowatt hour of enthalpy and hydrogen or a kilowatt hour of heat or a kilowatt hour of electricity with very high efficiency (for example, 96 percent total system efficiency).
In various implementations, fluids that are flowing in and out of the heat storage unit can be directly coupled with the fluids that are flowing across one side of the electrolyzer (e.g., the oxygen side). As such integration of a directly heated contact and a directly cooled contact may assist with integration of the fuel cell.
In addition to being connected to the solid oxide electrolysis cell, the thermal energy storage system having electric power that can flow into a heat storage system taking fluid in at 200° C. and delivering fluid at a temperature of 800° C.-1600° C. when discharged as explained above, such as the system disclosed above, can perform district heating, driving of turbines, cogeneration, or other industrial uses. For example, in the case of the solid oxide fuel cell mode, the heat generated in the process of making electricity from a hydrogen input may be used as an industrial output for a steam generator in one implementation. Further, the excess electricity generated by the steam generator may be combined with the electricity provided from the source, such as the renewable source, as the electrical input for the thermal heaters of the thermal energy storage system according to the example implementations.
3. Advantages Over Prior Systems
The solid oxide unit of the example implementations may have various benefits and advantages over prior designs. For example, the solid oxide unit described herein receives stored heat from the thermal energy storage system as its input, instead of requiring an external heater, such as an electrical resistive heater or a fuel fired heater. Thus, the cost of operation may be reduced and the amount of pollution may also be reduced.
Further, while art approaches may burn the oxygen byproduct at the output of the solid oxide unit to generate heat for the heater that the input of the solid oxide unit, the example implementations do not require heat to be generated at the input of the solid oxide unit. Thus, the byproduct air is provided to the heat exchanger, without burning off the oxygen.
The enhanced concentration of oxygen in the flow may contribute to reductions in the cost of secondary oxygen separation. Such solid oxide electrolyzer integration with thermal energy storage has benefits including significantly enhanced efficiency in the conversion of electrical energy to energy and hydrogen and enabling such high efficiency electrolyzers to be combined and used effectively with variable supplies of renewable electricity. Accordingly, charging may be intermittent while temperature is held constant without continuous use of electrical power.
Also, a portion of the energy in the electrolytic process in this manner is supplied by stored heat. It is beneficial to do this because the time at which electricity may be captured and stored may be separated from the time at which electricity is captured and used for electrolysis. When electric power is available, the electric power can be used to heat charge the storage system and also drive electrolysis to convert water to hydrogen. Existing electrolyzers cost around $500-600/kW, whereas heat storage systems may be significantly less expensive. Heat storage may be less expensive on a per kilowatt basis than electrolyzer stacks and it may therefore be less costly to pull power in at a very high rate during periods of lower-cost power availability and apportion the power between the heat storage and the electrolyzer. The electrolyzer can be made to run longer and the peak load or the peak power can be dropped quickly into heat storage. Thus, there is a matching of electrolyzer capacity factor and cost against the availability of variable renewable electricity
C. Thermoelectric Power Generation
1. Problems to be Solved
Gasification is the thermal conversion of organic matter by partial oxidation into gaseous product, consisting primarily of H2, carbon monoxide (CO), and may also include methane, water, CO2 and other products. Biomass (e.g. wood pellets), carbon rich waste (e.g. paper, cardboard) and even plastic waste can be gasified to produce hydrogen rich syngas at high yields with high temperature steam, with optimum yields attained at >1000° C. The rate of formation of combustible gases are increased by increasing the temperature of the reaction, leading to a more complete conversion of the fuel. The yield of hydrogen, for example, increases with the rise of reaction temperature.
Turning waste carbon sources into a useable alternative energy or feedstock stream to fossil fuels is a potentially highly impactful method for reducing carbon emissions and valorizing otherwise unused carbon sources.
2. Thermoelectric Power Generation
Indirect gasification uses a Dual Fluidized Bed (DFB) system consisting of two intercoupled fluidized bed reactors—one combustor and one gasifier—between which a considerable amount of bed material is circulated. This circulating bed material acts as a heat carrier from the combustor to the gasifier, thus satisfying the net energy demand in the gasifier originated by the fact that it is fluidized solely with steam, i.e. with no air/oxygen present, in contrast to the classical approach in gasification technology also called direct gasification. The absence of nitrogen and combustion in the gasifying chamber implies the generation of a raw gas with much higher heating value than that in direct gasification. The char which is not converted in the gasifying chamber follows the circulating bed material into the combustor, which is fluidized with air, where it is combusted and releases heat which is captured by the circulating bed material and thereby transported into the gasifier in order to close the heat balance of the system.
Referring to
A control unit can control the flow of the heated air (and more generally, a fluid) into the HRSG 509, based on load demand, cost per KWH of available energy source, and thermal energy stored in the system. The steam turbine 515 can be operatively coupled to a steam generator 509, which can be configured to generate a continuous supply of electrical energy. Further, the steam turbine 515 can also release a continuous flow of relatively lower-pressure 521 steam as output to supply an industrial process. Accordingly, implementations are possible and contemplated in which steam is received by the turbine at a first pressure and is output therefrom at a second, lower pressure, with lower pressure steam being provided to the industrial process. Examples of such industrial process that may utilize the lower pressure output steam include (but are not limited to) production of liquid transportation fuels, including petroleum fuels, biofuel production, production of diesel fuels, production of ethanol, grain drying, and so on.
The production of ethanol as a fuel from starch and cellulose involves aqueous processes including hydrolysis, fermentation and distillation. Ethanol plants have substantial electrical energy demand for process pumps and other equipment, and significant demands for heat to drive hydrolysis, cooking, distillation, dehydrating, and drying the biomass and alcohol streams. It is well known to use conventional electric power and fuel-fired boilers, or fuel-fired cogeneration of steam and power, to operate the fuel production process. Such energy inputs are a significant source of CO2 emissions, in some cases 25% or more of total CO2 associated with total agriculture, fuel production, and transportation of finished fuel. Accordingly, the use of renewable energy to drive such production processes is of value. Some ethanol plants are located in locations where excellent solar resources are available. Others are located in locations where excellent wind resources are available.
The use of electrothermal energy storage may provide local benefits in such locations to grid operators, including switchable electricity loads to stabilize the grid; and intermittently available grid electricity (e.g. during low-price periods) may provide a low-cost continuous source of energy delivered from the electrothermal storage unit.
The use of renewable energy (wind or solar power) as the source of energy charging the electrothermal storage may deliver important reductions in the total. CO2 emissions involved in producing the fuel, as up to 100% of the driving electricity and driving steam required for plant operations may come from cogeneration of heat and power by a steam turbine powered by steam generated by an electrothermal storage unit. Such emissions reductions are both valuable to the climate and commercially valuable under programs which create financial value for renewable and low-carbon fuels.
The electrothermal energy storage unit having air as a heat transfer fluid may provide other important benefits to an ethanol production facility, notably in the supply of heated dry air to process elements including spent grain drying. One useful combination of heated air output and steam output from a single unit is achieved by directing the outlet stream from the HRSG to the grain dryer. In this manner, a given amount of energy storage material (e.g. brick) may be cycled through a wider change in temperature, enabling the storage of extra energy in a given mass of storage material. There may be periods where the energy storage material temperature is below the temperature required for making steam, but the discharge of heated air for drying or other operations continues.
In some implementations thermal storage structure 503 may be directly integrated to industrial processing systems in order to directly deliver heat to a process without generation of steam or electricity. For example, thermal storage structure 503 may be integrated into industrial systems for manufacturing lime, concrete, petrochemical processing, or any other process that requires the delivery of high temperature air or heat to drive a chemical process. Through integration of thermal storage structure 503 charged by VRE, the fossil fuel requirements of such industrial process may be significantly reduced or possibly eliminated.
The control unit can determine how much steam is to flow through a condenser 519 versus steam output 521, varying both total electrical generation and steam production as needed. As a result, the integrated cogeneration system 500 can cogenerate steam and electrical power for one or more industrial applications.
If implemented with an OTSG as shown in
The HRSG 509 can include a positive displacement (PD) pump 511 under variable frequency drive (VFD) control to deliver water to the HRSG 509. Automatic control of steam flow rate and steam quality (including feed-forward and feed-back quality control) can be provided by the TSOTG 500. In an exemplary example implementation, a built-in Local Operator Interface (LOI) panel operatively coupled to system 500 and the control unit can provide unit supervision and control. Further, thermal storage structure 503 can be connected to a supervisory control and data acquisition system (SCADA)) associated with the steam power plant (or other load system). In one implementation, a second electrical power source is electrically connected to the steam generator pumps, blowers, instruments, and control unit.
In some implementations, system 500 may be designed to operate using feedwater with substantially dissolved solids; accordingly, a recirculating boiler configuration is impractical. Instead, a once-through steam generation process can be used to deliver wet steam without the buildup of mineral contaminants within the boiler. A serpentine arrangement of conduits 507 in an alternative once-through configuration of the HRSG 509 can be exposed to high-temperature air generated by the thermal storage structure 503, in which preheating and evaporation of the feedwater can take place consecutively. Water can be forced through the conduits of HRSG 509 by a boiler feedwater pump, entering the HRSG 509 at the “cold” end. The water can change phase along the circuit and may exit as wet steam at the “hot” end. In one implementation, steam quality is calculated based on the temperature of air provided by the thermal storage structure 503, and feedwater temperatures and flow rates, and is measured based on velocity acceleration at the HRSG outlet. Embodiments implementing a separator to separate steam from water vapor and determine the steam quality based on their relative proportions are also possible and contemplated.
In the case of an OTSG implementation, airflow (or other fluid flow) can be arranged such that the hottest air is nearest to the steam outlet at the second end of the conduit. An OTSG conduit can be mounted transversely to the airflow path and arranged in a sequence to provide highly efficient heat transfer and steam generation while achieving a low cost of materials. As a result, other than thermal losses from energy storage, steam generation efficiency can reach above 98%. The prevention of scale formation within the tubing is an important design consideration in the selection of steam quality and tubing design. As water flows through the serpentine conduit, the water first rises in temperature according to the saturation temperature corresponding to the pressure, then begins evaporating (boiling) as flow continues through heated conduits.
As boiling occurs, volume expansion causes acceleration of the rate of flow, and the concentration of dissolved solids increases proportionally with the fraction of liquid phase remaining. Maintaining concentrations below precipitation concentration limits is an important consideration to prevent scale formation. Within a bulk flow whose average mineral precipitation, localized nucleate and film boiling can cause increased local mineral concentrations at the conduit walls. To mitigate the potential for scale formation arising from such localized increases in mineral concentration, conduits which carry water being heated may be rearranged such that the highest temperature heating air flows across conduits which carry water at a lower steam quality, and that heating air at a lower temperature flows across the conduits which carry the highest steam quality flow.
Returning to
An exemplary configuration specification of one implementation of a cogeneration system using an OTSG for steam generation is provided below.
Referring to
Further, the steam gas turbine 515 releases low-pressure steam that is condensed to a liquid by a condenser 519, and then de-aerated using a deaerator 513, and again delivered to the HRSG 509. For example, as shown in the expanded view, the steam turbine generator 515 receives high pressure steam from the HRSG 509. At a first turbine 515A that is powered by the high pressure steam, intermediate pressure steam is output to the deaerator 513, which may remove the oxygen from the steam, and provide as its output liquid fluid to the input of the HRSG 509 via PD pump 511. An output of the first turbine 515A may be low pressure steam, which is provided to an industrial process. A second turbine 515B that is powered by the remaining pressurized steam also generates electricity, and provides low pressure steam as its output to a condenser. An output of the condenser may be warm air, which may be used for an industrial process, such as grain drying or the like.
The thermal storage integrated combined cycle plant 550 can include the thermal energy storage structure 503 being fluidically coupled to the HRSG 509 of the combined cycle power plant. In one implementation, the heated air (at a predefined temperature) for the HRSG is provided by the thermal storage structure 503 alone or in combination with the exhaust emitted by the gas turbine 516. A control unit can control the flow of any combination of the heated air (from thermal storage structure 503) and exhaust gas by the gas turbine 516 into the HRSG 509, based on, for example, factors including load demand, availability and cost per KWH of available energy sources, cost per KWH for the operation of the combined cycle power plant, and thermal energy stored in the thermal storage structure 503.
In other example implementations, thermal storage structure 503 and a coal power plant may be integrated with a steam power plant through the HRSG 509 to provide another example implementation of a thermal storage integrated combined cycle plant for efficient and reliable operation of a steam power plant. The heated air being provided by thermal storage structure 503, alone or in combination with the exhaust emitted by the coal power plant can be supplied to the HRSG 509 for converting the water into steam for the steam turbine. A control unit may control the flow of any combination of the heated air (from the thermal storage structure) and exhaust gas by the coal power plant into the HRSG, based on, for example, factors including load demand, availability and cost per KWH of an available energy source, cost per KWH for the operation of the coal power plant, and thermal energy stored in the thermal storage structure.
Referring to
Referring to
In one implementation, stored VRE and an HRSG are coupled to an industrial process facility in such a manner as to eliminate gas combustion in auxiliary, emergency, or backup boilers. Referring to
Some industrial process units 91602, principally those with exothermic reactions, may generate all or a portion of the steam 91603 in the network during normal operation. In some implementations, however, for the safe and effective operation of the plant other sources of steam must be instantly available in the event of the shutdown of one such unit 91602. In some prior implementations gas-fired or oil-fired boilers 91611 have been used. In some implementations such equipment must be maintained at operating temperature continuously in order to be able to immediately increase its firing rate to provide the steam necessary in such a shutdown event. Such units may employ a conventional recirculating design with a steam drum 91613 which is open to the main steam network, and the heat necessary to keep the drum warm may be provided by excess steam produced by the process units 91602. However, the firebox or burner portion of the boiler must also be kept warm in some implementations, and this is commonly done by operating the burner 91612 continuously at a low firing rate. This is a source of continuous CO2 and other pollutants.
In the depicted implementation of a thermal energy storage system, the thermal storage unit 91608 has an HRSG with recirculating drum boiler process 91609, where the drum is again open to the steam header 91601 and the HRSG section is kept warm by excess steam.
The thermal storage unit may maintain its temperature via its insulation, with low energy losses. The storage unit may be charged by a directly-connected VRE source, or may be rapidly or slowly charged from an electricity grid or a local power generation source, in such a manner as to minimize energy cost. The storage unit is configured to instantly (within seconds) begin high-rate steam production from storage, and operate until storage capacity is exhausted. In this implementation the fuel-fired boiler 91611 may be left in a “cold storage” configuration, burning no fuel, until a shutdown requires its operation. The operating time of the thermal storage unit provides an extended time period to properly start and warm up the fuel-fired boiler before placing it into service for outages that extend beyond the discharge period of the storage unit.
Other Energy Usage Applications
More specifically, the time of operation or charging may be controlled in such a manner as to optimize other economic value, such as the supply of electricity to a grid at periods of high price or high value. Curve 10001 represents available energy during a solar day between the beginning of the solar day and the end of the solar day. While the times of 5 AM and 8 PM are shown by way of example, it is understood that the time will vary, depending on the location and time of year.
Curve 10001 shows the solar energy increasing from the beginning of the solar day to a maximum level and then decreasing towards the end of the solar day. Within the available solar energy, the chart illustrates that there may be multiple uses of the solar energy.
As shown in the additional charts, a first use 1 and a second use 2, as explained above, are shown. Additionally, outside factors 3, such as grid storage, capacity, energy supply, pricing variations due to energy markets or the like may influence the availability and demand of the solar energy for charging the thermal energy storage system. A control system, as described above, may incorporate these factors into determinations and recommendations to the operator regarding the operation of the thermal energy storage system, such as the charging and discharging of the stacks. Accordingly, the thermal energy storage system may dispatch energy for multiple purposes or uses from the output of the thermal energy storage system, while taking into account these factors.
As shown in the first additional chart at scenario 10007, less solar energy may be available for the thermal energy storage system later in the solar day. Alternatively, as shown in the second additional chart at 10009, less solar energy may be available for charging the thermal energy storage system during the early portion and the middle to later portion of the day. Other variations may exist, as would be understood by those skilled in the art.
For example, use 1 (represented by region 10005) may be a local electric load in one implementation. This may represent the electricity provided to a local area by a photovoltaic array. Additionally, other uses such as use 2 (represented by region 10003) may also use the available solar energy. As indicated by the shaded region, the remaining solar energy is available to charge a thermal energy storage system connect to the solar energy source exhibiting the energy profile of curve 10001.
In one implementation, use 2 is a second-high value use, which may be and industrial process such as electrolysis. Use 2 is then fully powered for as long as possible while excess energy beyond that needed for use 1 is available. As electricity production rises further later in the day, electricity is available for other purposes, including charging a thermal energy storage device, and/or participating in the supply of electricity, for example, to an electricity grid, where electricity may be valued at very different prices at different times. This system may be operated in such a way that, for example, electric power to a thermal storage unit may be turned off and electric power instead released to the grid as desired based upon demand, pricing or other factors, and/or power may be brought from the grid to power a storage unit or for one of other possible uses depending upon local grid conditions.
Self-Sufficient Off Grid Infrastructure
In some implementations, use of high voltage DC/DC conversion allows for very high efficiency connection of solar fields with suitable distance to loads such as a thermal energy storage unit that can be coupled to electrolyzers and used for electric vehicle charging. Further, a thermal energy storage system may have integrated hydrogen production in some implementations, with electric power generation from hydrogen and also have integration of lithium-ion batteries. A thermal energy storage system can also be coupled to drive desalination to produce a completely off-grid facility or military base that is self-powering for its domestic loads, its heat loads and its vehicles.
Refiring of Steam Plants
Since outlet temperatures from a thermal energy storage unit are higher than gas turbine outlet temperatures in some implementations, outlet from a thermal storage structure can fire the same HRSGs as a gas turbine, potentially cutting the storage unit cost by about, e.g., 40%. In some implementations, nearly all the off-specification operation of thermal plants can be reduced or eliminated by coupling to a thermal storage unit as disclosed herein. Combined cycle gas turbine (CCGT) plants were designed to run at nominal output at high capacity factor, but may not be operated in this way if connected to a power grid with variable load. In California, for example, such plants may spend significant time as “spinning reserve” running at idle so as to be able to respond to load changes. CCGT plants may also do daily start-stop operation requiring warmup of all components to bring the plant to ready-to-operate condition and spend significant time in a “load-following” mode of throttling generation in response to load. Such reserve and warmup operations are approximately 0% fuel efficient, and there is tension between fuel cost (dictating warming the plant as fast as possible) and operations and maintenance (O&M) cost (dictating warming the plant slowly to cause less stress damage). This load-following operation in CCGT plants results in efficiency losses of at least 5% and sometimes 15%.
Integrating thermal energy storage systems such as those in the example implementations disclosed herein with thermal plants may address the efficiency problems describe above. About, e.g., 90% of a plant's warmup process can be powered by intermittent renewable generation stored in a thermal storage unit. HRSG and steam turbine (ST) preheat energy is a significant factor in many plants. A “part spinning reserve” configuration can be achieved where a thermal energy storage unit fully powers the operating steam turbine, from idle to full power, so the plant can respond instantly with up to about, e.g., 40% of nominal output running completely zero-carbon, and can add then add the gas turbine (GT) in around 10 minutes.
Thermoelectrochemical converters are solid-state devices that utilize the electrochemical potential of a gas pressure applied throughout a membrane electrode assembly to convert heat into electricity via gas compression and expansion. A thermoelectrochemical converter that utilizes the electrochemical potential of a hydrogen pressure differential applied across a proton conductive membrane is known. The system consists of two membrane electrode assemblies (MEA) to convert heat into electricity via hydrogen compression and expansion. One stack is operated at a relatively low temperature and coupled to a heat sink, and the other stack is operated at a relatively high temperature and coupled to a heat source. Hydrogen gas circulates in a closed system. The net electrical power or voltage that can be achieved increases as the temperature differential between the two MEA stacks increases.
Thermophotovoltaic (TPV) Cogeneration
Thermophotovoltaic (TPV) energy conversion is a process of converting thermal radiation to electricity directly and includes a thermal emitter and a photovoltaic diode cell. The temperature of the thermal emitter needed varies based on system but typically ranges from about 900° C. to about 1300° C., e.g., 900° C. to 1300° C. At these TPV temperatures, radiation is radiated mostly in the form of near infrared and infrared frequencies. The photovoltaic diodes absorb some of the radiation and converts them into electricity. In art, a thermophotovoltaic cell with >29% power conversion efficiency was achieved, at an emitter temperature of 1207 C with potential for further efficiency improvement. Such a TPV system may allow for efficient cogeneration for heat and electricity.
The thermal emitter may be, for example, a graphite heated by resistive heating and operated with an inert atmosphere to prevent the oxidation of graphite. Indium gallium arsenide (InGaAs) or silicon (Si) type PV cells can be used for example to generate electricity.
The high temperature thermal storage system disclosed herein can be effectively coupled with a thermophotovoltaic cogeneration, offering benefits including but not limited to the following:
The high temperatures combined with the storage technology matches well with high efficiency TPV systems which utilize thermal radiation to generate electricity
Unlike other thermal storage systems relying largely on convective heat transfer, the “radiative echo chamber” concept described herein can work in concert with convective heat transfer to get radiation out of the thermal storage assembly or array. In one implementation, the arrays include relatively inexpensive materials with mediocre thermal transfer medium to keep costs low. The radiation chambers in effect increase the surface area from which energy can be extracted, allowing for faster discharge rates without rapidly degrading top temperatures.
Extremely high storage temperatures above 2000° C. are practically achievable with a thermal storage system of the kind described herein. Such temperatures allow for the use of lower cost, more available but higher bandgap cells using silicon semiconductors for TPV.
Inert gas compatible with the emitter (e.g. graphite) and TPV system can be used directly as the heat exchange fluid in the thermal storage system decreasing complexity and cost.
An optional feature may include movable shields or other means to shield or block the incoming radiation at the TPV cells during the time that the thermal storage system is being charged. This allows the cells to remain cool, reduce the design cooling load and extend cell lifetime. During periods when the thermal storage system is being heated electrically coincides with periods of low cost or abundant electrical supply, making TPV operation unnecessary.
In one example implementation, the lower temperature heat arising from cooling during charging and then during power generation is used for another purpose, such as steam generation, water preheating, supercritical CO2 heating for power generation or for industrial process heat. This heat can be blended with hotter air coming from the storage core or segregated (e.g., introduced into another heat exchanger which e.g., supplies preheat for a process that also employs high-temperature heat, or used for another process). This would further increase the total efficiency of energy use for a combined heat and power application, examples of which are disclosed in other parts of this application, such as cement and glass production.
The combination of high temperature thermal storage and TPV described herein could unlock significant value even in a pure electric power storage application. TPV can be used as a “topping” cycle and steam turbine as a “bottoming” cycle, resulting in high electricity-to-electricity efficiencies approaching 50%. The TPV component could provide “instant” services including load following, frequency and voltage regulation with rapid (e.g. millisecond) response times. The combined thermal storage-TPV system would function similarly to a lithium ion battery for part of the electric power output, providing grid stability value, with an added benefit of a long-term storage unit at a significantly lower cost and size.
As described above, the net efficiency of a thermoelectrochemical system can be increased by increasing the temperature differential between the two membrane electrode assemblies (MEA). Implementations of a thermal energy storage system disclosed herein can be coupled to the hot end of a thermoelectrochemical converter to provide near constant or constant high temperature heat. In the present example implementation, a heat exchanger in the high temperature outlet of the thermal storage system is coupled to the high temperature MEA in the thermoelectrochemical conversion system, at temperatures between 500° C. and 1200° C. The remaining heat may be used to generate steam in a Heat Recovery Steam Generator, for example, or used for another industrial application. In another example implementation, the high temperature portion of the thermoelectrochemical converter may be coupled to the heated gas from the secondary heat outlet (i.e. from cooling the high temperature energy sources) to generate electricity while the primary heat outlet (i.e., the highest temperatures, for example, at 1600° C.) is used for industrial applications such as power generation or cement production. Such cogeneration of heat and power could have combined efficiency of nearly 90% because waste heat from the thermoelectrochemical electric generation can be used for industrial purposes.
In some example implementations, the environment is used as the heat sink. In other example implementations, the cool side of the thermoelectrochemical converter could use the feedwater to the HRSG as the heat sink, raising the temperature of the feedwater, recovering that energy for steam generation useful for a steam power cycle or industrial processes. Preheating of thermal exchange fluid in this way can be applied to other processes, including, for example, the cement production process. A cooled stream of CO2 may first be used as the heat sink for the thermoelectrochemical converter, raising the temperature of CO2, when is then heated to operational temperatures of the cement kiln, preheater or precalciner. The heat/power balance allows retention of very high efficiency of heat and power cogeneration with high temperature heat loads for industrial processes.
While the energy source 9301 is shown as an off-grid renewable source of energy, and more specifically, solar photovoltaic cells, other renewable sources could be used in substitution or combination, such as wind. Further, grid electricity 9302 could be used in substitution or combination with the off-grid source of electricity. The electricity from the energy source 9301 is used to provide the electrical energy as inputs to the first and second heat batteries 9303 and 9305, as well as for the electric booster 9307. The first and TSUs 9303 and 9305 can include single stacks, double stacks or more, or some combination; the TSU's 9303 and 9305 do not have to contain the same number of stacks. In one embodiment, either or both of the TSUs 9303 and 9305 can include six stacks.
The first heat battery 9303 can be configured to store electricity as heat, to provide heated fluid as an input to an HRSG, or to provide steam to a steam turbine 9309. Alternatively, an OTSG may be used instead of the HRSG.
The second heat battery 9305 provides hot fluid as an output for use in an industrial application, such as in a cement kiln or steel production, referred to here as a process load 9311, also referred to as a drying load. It may be the heat battery 9305 provides the fluid at a temperature of 1000° C., which is below the drying load requirement, which for a given application may be much higher, such as 1300° C.
Different fluids may be used in the first and second heat batteries 9303, 9305. For example, air may be used as the fluid for the first heat battery 9303 to power the steam turbine 9309, while CO2 is used as the fluid for the second heat battery 9305, as needed for a particular industrial process. For example, in the case of the industrial process being a calciner, a closed loop is provided in which the fluid is recaptured for input to the heat battery 9305. The temperature of the return air is such that the air does not require preheating. In other industrial applications, an open loop may be provided, such that atmospheric air 9315 is preheated by the condenser 9313.
To raise the temperature of the heated fluid to the drying load requirement, the electric booster 9307 is provided at the discharge of the hot fluid. Accordingly, hot fluid output from the second heat battery 9305 passes through the booster heater 9307, and then to the process load 9311, at the required temperature for the industrial process.
In the second heat battery 9305, the fluid may be air, CO2, or other fluid, depending on the industrial application at an output temperature, such as 1000° C.-1100° C. Further, the byproduct fluid of the industrial process may be recirculated as the input fluid to the heat battery 9305, depending on the industrial process.
The electric booster 9307 may be an electric resistance heater that boosts the fluid temperature from the maximum output of the heat battery 9305 to the temperature required by the process load 9311. Example of the types of industrial applications that would require high temperature fluid input for the process load 9311 include calcining, steel production, ethylene production, and steam methane reforming of hydrogen. The electric booster 9307 may be an industrial electric furnace, and may optionally include fins or other structures to transfer electrical resistance heat to the air. The heaters of the electric booster may be metallic (e.g., resistive coil), ceramic or other known materials. The stream of fluid output from the first heat battery 9305 is heated by direct contact with the heaters of the electric booster 9307.
When the energy source 9301 is available, it may provide the electricity for the electric booster 9307, as shown in
The byproduct fluid from the steam turbine may be cooled by passing through a condenser 9313, such as a cooling tower, before being condensed to a liquid state, and provided as an input to the steam generator of the heat battery 9303. Optionally, the condenser 9313 may serve as a preheater to heat incoming air 9315, for use as the input to the second heat battery 9305. In other words, the condenser 9313 is a heat exchanger that transfers heat from the byproduct fluid (e.g., low-pressure steam) from the steam turbine 9309 to the input fluid 9315. As a result, the input fluid to the heat battery 9305 is preheated.
While
3. Advantages over Prior Systems
Stored high-temperature energy introduced as heated air into biomass combustion and gasification processes can make substantial contributions to the effective and safe operation of such facilities. This may cause various improvements in air emissions associated both with oxides of nitrogen and unburned fuel, ability to handle biomass fuels that are wetter during certain times, as well as improvements in plant reliability and capacity factor, particularly during periods of uncertain or limited biomass supply, reductions in corrosion due to shifts in operating point, ability to operate the plant during periods of limited or no fuel ability, ability to operate the plant as an energy storage facility.
Thus, in accordance with the above, a number of cogeneration system implementations are possible and contemplated, a number of examples of which are now provided.
In one implementation, a cogeneration apparatus includes a thermal storage assemblage 4100) including a plurality of thermal storage blocks, wherein at least some of the thermal storage blocks include multiple radiation cavities and multiple fluid flow slots, wherein some of the radiation cavities and some of the fluid flow slots are configured to define fluid pathways through the thermal storage blocks. The cogeneration apparatus further includes a plurality of heater elements positioned within the thermal storage assemblage and adjacent to at least some of the radiation cavities, wherein each of the plurality of heater elements is configured to heat at least one of the thermal storage blocks via energy radiated into multiple ones of the radiation cavities and onto surfaces that bound the respective radiation cavities. A fluid movement system is configured to direct a stream of fluid through the fluid pathways to heat the fluid to a specified temperature range, wherein the fluid movement device is configured to provide the heated fluid in the specified temperature range to a solid oxide electrolysis system configured to extract hydrogen from water and output the heated fluid at a lower temperature. A steam generator configured to receive the lower temperature fluid from the electrolysis system convert input feed water into steam. In various implementations, the steam generator is a once-through steam generator, and may also be a heat recovery steam generator. The steam generator includes a plurality of conduits coupled to receive the input feed water, wherein selected ones of the conduits are arranged to mitigate scale formation and overheating. In certain implementations, ones of the plurality of conduits are arranged in the steam generator transversely to a path of flow of the lower temperature fluid. The thermal storage assembly comprises an enclosure containing the plurality of thermal storage blocks and a thermal barrier separating a first subset of the plurality of thermal storage blocks from a second subset of the plurality of thermal storage blocks. The fluid movement system is configured to direct the stream of fluid through the fluid pathways of one of the first and second subsets of thermal concurrent with an electricity source adding heat to another one of the first and second subset. In some implementations, the fluid comprises oxygen and nitrogen. Various sources of electricity may be used to charge the thermal storage assemblage. In one implementation, the thermal storage assemblage is configured to store thermal energy generated by a conversion of input electricity from an first input energy supply, the first input energy supply having intermittent availability. Implementations are further contemplated in which the thermal storage assemblage is further configured to store thermal energy generated by a conversion of input electricity from an second input energy supply configured to provide electricity on demand.
In yet another implementation, a cogeneration apparatus includes a thermal storage assemblage having a plurality of thermal storage blocks, wherein at least some of the thermal storage blocks include multiple radiation cavities and multiple fluid flow slots, wherein some of the radiation cavities and some of the fluid flow slots are configured to define fluid pathways through the thermal storage blocks. The implementation further includes a plurality of heater elements positioned within the thermal storage assemblage and adjacent to at least some of the radiation cavities, wherein each of the plurality of heater elements is configured to heat at least one of the thermal storage blocks via energy radiated into multiple ones of the radiation cavities and onto surfaces that bound the respective radiation cavities. A fluid movement system is configured to direct a stream of fluid through the fluid pathways to heat the fluid to a specified temperature range. A steam generator is configured to receive the fluid to convert input feed water into input steam having a first pressure. A steam turbine configured to receive the input steam and provide output steam at a second pressure that is less than the first pressure. Such implementations may further include a second fluid movement device configured to move the output steam to an industrial plant for use in an industrial process.
The steam generator, in various implementations, is a once-through steam generator. The steam generator includes a plurality of conduits coupled to receive the input feed water, wherein selected ones of the conduits are arranged to mitigate scale formation and overheating. Ones of the plurality of conduits are arranged in the steam generator transversely to a path of flow of the lower temperature fluid.
With regard to the industrial process, a number of different processes are possible and contemplated. In one implementation, the industrial process comprises producing petroleum-based fuels. In another implementation, wherein the industrial process comprises producing biofuels. In yet another implementation, the industrial process comprises producing diesel fuels. In still a further implementation, the industrial process comprises drying grains. These industrial processes are provided here as examples, and do not constitute an exhaustive list of possible industrial processes that may be used with the various implementations. The present disclosure contemplates a wide variety of industrial processes beyond the examples given here. It is further noted that implementations are possible and contemplated wherein the steam turbine is configured to cause an electrical generator to provide electricity to the industrial process.
In yet another possible implementation, a cogeneration apparatus includes a thermal storage assemblage having a plurality of thermal storage blocks, wherein at least some of the thermal storage blocks include multiple radiation cavities and multiple fluid flow slots, wherein some of the radiation cavities and some of the fluid flow slots are configured to define fluid pathways through the thermal storage blocks. A plurality of heater elements is positioned within the thermal storage assemblage and adjacent to at least some of the radiation cavities, wherein each of the plurality of heater elements is configured to heat at least one of the thermal storage blocks via energy radiated into multiple ones of the radiation cavities and onto surfaces that bound the respective radiation cavities. A fluid movement system is configured to direct a stream of a first fluid through the fluid pathways to heat the first fluid to a specified temperature range. A first steam generator is configured to, using the first fluid, convert input feed water into steam. A steam turbine configured to cause generation of electricity using the steam. The implementation also includes a preheater configured to, using waste heat from the steam turbine, preheat feed water provided to a second steam generator.
In an implementation, the first steam generator is a heat recovery steam generator, and may also be (or alternatively be) a once-through steam generator. Various implementations also include a condenser coupled to the steam turbine, wherein the condenser is configured to condense steam received from the steam turbine into water a recirculation pump configured to provide, as feed water to the first steam generator, water produced by the condenser. The second steam generator in various implementations is configured to generate steam using a second fluid from a second storage medium configured to store thermal energy. The preheater in various implementations is configured to output a third fluid to the thermal storage assemblage.
A further implementation of a cogeneration apparatus includes a thermal storage assemblage) including a plurality of thermal storage blocks, wherein at least some of the thermal storage blocks include multiple radiation cavities and multiple fluid flow slots, wherein some of the radiation cavities and some of the fluid flow slots are configured to define fluid pathways through the thermal storage blocks. A plurality of heater elements is positioned within the thermal storage assemblage and adjacent to at least some of the radiation cavities, wherein each of the plurality of heater elements is configured to heat at least one of the thermal storage blocks via energy radiated into multiple ones of the radiation cavities and onto surfaces that bound the respective radiation cavities. A fluid movement system is configured to direct a stream of fluid through the fluid pathways to heat the fluid to a specified temperature range. A steam generator is configured to receive the fluid to convert input feed water into input steam. Various implementations also include a measurement unit configured to determine a measured steam quality value of steam output from the steam generator. A controller is configured to cause the cause the fluid movement system to direct the stream of fluid, and further configured to use the measured steam quality as feedback to adjust a flow rate of the fluid to maintain the measured steam quality within a specified steam quality range.
In some implementations, the measurement unit includes a separator configured to separate steam output from the steam generator from water vapor output from the steam generator, wherein the measurement unit is configured to determine the measured steam quality based on fraction of the water vapor output from the steam generator relative to the steam output from the steam generator. Implementations are further possible and contemplated in which the measurement unit is configured to determine the steam quality based on a flow velocity of steam output from the steam generator and a mass flow rate of the input feed water. With regard to the steam generator, implementations are possible and contemplated in which the steam generator is a once-through steam generator. The controller of such implementations may be configured to cause delivery of steam in accordance within a specified range of steam delivery rates. Accordingly, the controller is configured to specify the range of steam delivery rates based on forecast information. Various types of forecast information are possible and contemplated as a basis for the controller to specify the range of steam delivery rates. In various implementations, the forecast information includes weather forecast information. Implementations in which the forecast information includes expected electricity rates are also possible and contemplated. Similarly, implementations in which the forecast information includes expected steam demand are contemplated. It is noted that the controller may use one or more types of the forecast information mentioned here, while other types of forecast information not explicitly discussed herein may also be used in various implementations.
In still another implementation, a cogeneration system includes a storage medium configured to store thermal energy generated by a conversion of input electricity from an input energy supply, the input energy supply having intermittent availability. A fluid movement device is configured to move fluid through the storage medium to heat the fluid to a specified temperature, the fluid comprising oxygen and nitrogen, wherein the fluid movement device is configured to provide the fluid at the specified temperature to a solid oxide cell electrolysis system that converts water to hydrogen and enriches the fluid with oxygen. Such implementations may also include a once-through steam generator configured to, using the fluid received from the electrolysis system convert input feed water into steam.
These implementations may further include a steam turbine configured to cause an electrical generator to generate of electricity using steam received from the steam generator. With regard to thermal storage, the thermal storage unit may comprise a plurality of bricks. A controller in an implementation is configured to cause the fluid movement device to move fluid at a particular rate. Further contemplated in various implementations is a measurement unit configured to measure a parameter of steam output from the steam generator. The controller is configured to adjust the particular rate based on the measurement of the parameter of steam output. Meanwhile, the measurement unit in various implementations comprises a separator configured to measure a quality of the steam output from the steam generator by separating the steam into a liquid phase and a vapor phase. Alternatively, implementations in which the measurement unit is configured to measure a velocity of steam output from the steam generator are also possible and contemplated. The controller is configured to control an amount of fluid moved through the storage medium based on a weather forecast. The controller may also be configured to control and amount of fluid moved through the storage medium based on an expected difference in electricity costs on a first day and a second day.
Various types of electrical sources may comprise the intermittent energy supply in various implementations. In one implementation, the intermittent energy supply comprises a thermophotovoltaic generation system configured to convert thermal radiation into electrical energy. The intermittent energy supply may also, or alternatively, comprise a wind turbine configured to generate electricity. The intermittent energy supply may also a solar energy source configured to convert solar energy into electricity, which may be used singularly or with various ones of the other types mentioned herein.
The fluid movement device in one implementation comprises a closed fluid recirculation loop. Implementations may a pump, and wherein the pump is configured to force the input feed water through one or more conduits of the steam generator. With regard to the steam generator, one or more conduits may be provided in which feed water flows. In such implementations, the one or more conduits may be mounted in the steam generator transversely to a path fluid flow.
In yet another implementation, a cogeneration system include a storage medium configured to store thermal energy generated by a conversion of input electricity from an input energy supply, the first input energy supply having intermittent availability. A first fluid movement device is configured to move fluid through the storage medium to heat the fluid to a specified temperature. A once-through steam generator is configured to, using the fluid, convert input feed water into an input steam having a first pressure. The system may include a steam turbine configured to provide an output steam at a second pressure that is less than the first pressure. A second fluid movement device may in various implementations is configured to move the output steam to an industrial plant for use in an industrial process.
The steam turbine in various implementations is configured to cause generation of electricity by an electrical generator. The electrical generator is configured in some implementations to provide electricity to a power grid.
Various types of industrial processes are possible and contemplated in accordance with the above. In one implementation, the industrial process comprises production of biofuels. In another implementation, the industrial process comprises production of petroleum-based fuels. In yet another implementation, the industrial process comprises production of diesel fuels. Implementations in which the industrial process comprises drying of grains are also possible and contemplated. The disclosure contemplates industrial processes other than those measured here that may also benefit from use of an implementation of the cogeneration system/apparatus per this disclosure.
The cogeneration system in various implementations includes a controller configured to cause the steam generator to generate steam at a specified steam quality based on steam quality. The steam quality may be calculated by a comprising a measurement unit configured to determine the steam quality based on separation of steam and water vapor output from the steam generator. In another implementation, the steam quality may be calculated by a measurement unit configured to determine the steam quality based on measurements of steam outlet flow and feed water input flow. The steam quality may, in various implementations, be affected by the rate at which fluid is moved through the storage device. Accordingly, implementations are possible an contemplated in which the controller is configured to control a rate at which fluid is moved through the storage medium by the first fluid movement device. In some implementations, the storage medium comprises a plurality of bricks.
Yet another implementation of a cogeneration system includes a first storage medium configured to store thermal energy generated by a conversion of input electricity from an input energy supply, the input energy supply having intermittent availability. The system further includes a fluid movement device configured to move fluid through the storage medium to heat the fluid to a specified temperature. A first steam generator is configured to, using the fluid, convert first input feed water into steam. A steam turbine is configured to, using the steam, cause an electrical generator to generate electricity. Implementations may further include a preheater configured to, using waste heat from the steam turbine, preheat second feed water provided to a second steam generator.
The steam generator in one implementation is a once-through steam generator. However, implementations in which the steam generator performs at least some recirculation of feed water are also possible and contemplated. Accordingly, some implementations include a condenser configured to receive at least a portion of the steam from the steam turbine and configured to condense the portion of steam into third feed water, while a recirculation pump is configured to provide the third feed water to the first steam generator.
In various implementations, the steam generator is a heat recovery steam generator. The measurement of steam quality output by the steam generator may be performed in various implementations, which may thus include a measurement unit configured to determine a measured output steam quality and a controller configured to adjust a current output steam quality to within a specified range using the measured output steam quality as feedback. In such implementations, the controller is configured to cause fluid movement device to adjust a rate of fluid flow through the storage medium in accordance with the feedback and the specified range of steam quality.
D. Carbon Removal
1. Problems to be Solved
Carbon dioxide is the largest contributor to global greenhouse gas emissions, with fossil fuel use being the primary source of carbon. About 20% of emissions come from industrial processes, which primarily involve fossil fuel combustion for energy. In the U. S. alone, greenhouse gas emissions totaled 6,577 million metric carbon tons of carbon dioxide equivalents. At least 16 states and Puerto Rico have enacted legislation establishing reduction requirements for greenhouse gas (GHG) emissions. California, for example, has implemented GHG emissions reduction targets through SB32, which requires that the state Air Resource Board (CARB) ensure GHG emissions reductions to 40% below 1990 levels by 2030.
These forces, combined with falling renewable energy prices, have driven a boom in renewables adoption, thus increasing the challenge of balancing energy supply and demand with added intermittent energy supply. Renewable energy curtailment has steadily increased, and oversupply conditions are expected to occur more often going forward. At the same time, in order to respond quickly to sudden losses of generation and/or unexpected changes in load, there may be greater need for expensive spinning and other operating reserves.
In addition, the energy produced through renewable means, for example, solar and wind, typically does not match the demand. Accordingly, the value of efficient solutions for energy storage has become increasingly clear in order to continue increasing renewable fraction in our energy supply. Energy storage is able to provide backup power or heat when traditional sources of energy (e.g., grid electricity) are lost or interrupted. Energy stored as high temperature heat has multiple advantages, including higher energy density, lower cost, increased flexibility for use in industrial high temperature applications as well as for producing power. Decarbonization may be particularly difficult for industrial processes requiring very high temperatures, such as above 1000° C.
Existing industrial heat processes are generally fired by fossil fuels, sometimes with enriched oxygen atmosphere for applications requiring very high temperatures, for example greater than 1500° C. Such processes cannot be switched to an intermittent renewal source because of the need for continuous, high temperature heat. Meanwhile, some governments around the world limit greenhouse gas emissions. For example, in Europe, the EU emissions trading system (EU ETS) uses a cap-and-trade method to limit carbon emissions. Carbon dioxide prices are expected to significantly increase in the future.
At the end of 2019, the average price of carbon dioxide in Europe was €25/ton. Germany has announced prices in the range of €55-65 per ton after 2026 and by 2050, carbon dioxide prices in the range of €100-€150 per ton is expected. In the European cement industry alone, which emitted 117 megatons of CO2 in 2018, the current cost of the emission is approximately €3 billion. Globally, energy-related CO2 emissions were around 33 gigatons in 2019.
Therefore, there is significant unmet need for technologies that can significantly reduce carbon emissions in industry, such as using renewable electricity. However, for very high temperature operations such as cement, glass, power and steel production, there are no reliable ways to achieve the high temperatures needed by using only intermittent energy sources.
Processes for separating carbon dioxide gas from exhaust gases that are generated by combustion of fuels may require a continuous flow of heat and electricity. Exhaust gases may increase during time periods of high demand, when generated electricity costs are highest, and therefore, not desirable for use in a carbon capture process. Alternatively, use of renewable sources of electricity are intermittent, and therefore not reliable for generating the required continuous flow of heat and electricity. It is noted that use of “continuous source of heat and electricity” is not intended to imply zero variation in temperature and/or electrical power. Rather the term “continuous,” as used herein, indicates that the source of heat and/or electricity are capable of providing a sufficient amount of electricity and heat to maintain proper operation of a carbon dioxide separation process.
Calcium Looping is one example of a CO2 capture technology that is based on cyclic calcination/carbonation reaction of, for example, CaO. CaO reacts with CO2 to generate CaCO3. The forward reaction is called carbonation, and is exothermic, where CO2 is captured onto the sorbent. The reverse reaction, calcination, is endothermic and releases a pure stream of CO2 which can be captured, compressed and stored. Such a cycle may include an intermediate step of hydration to increase the cycle life of the sorbent. The calcination reaction (releasing of CO2) requires high temperatures above 900° C. whereas the carbonation reaction (adsorption of CO2) requires temperatures around 600-700° C. Intermediate hydration reactions may occur at temperatures 100-200° C.
While calcium looping with CO2 and sometimes other gases such as SO2 is an important technology to decrease the carbon footprint, the large energy requirement, often met by burning fossil fuels in a pure stream of oxygen, poses additional challenges toward reducing the carbon intensity of the process.
There is an unmet need for a high temperature thermal energy storage system powered by renewable electricity that can provide the energy required to run such a process, making the calcium looping process carbon negative.
2. Carbon Capture
While calcium looping offers promising methods for capturing and storing CO2, the requirement in existing technologies for high temperature heat provided by a fuel stream combined with pure oxygen reduces the overall carbon capture efficiency. Such technologies may further require an air separator which adds cost and complexity to the system.
The problem of generating constant power and heat from an intermittent power source for use in a calcium-looping carbon dioxide separation process may be resolved by charging thermal storage units when the intermittent power source is available and generating the heat and power from the thermal storage units. Use of such thermal storage units may allow for continuous generation of heat and electricity from an inconsistent power source. Referring to
One application of the heated brick storage system is to drive a cryogenic carbon removal process. In one case, the unit is used to power a continuous electric power generation source which in turn drives a carbon dioxide separation process, which uses cryogenic effects, compressing and cooling CO2 to reduce its temperature until it becomes a solid, or in some embodiments a liquid. A supply of the electrical energy needed to drive that process is derived from energy supplied by a turbine generator whose input heat can be provided by a thermal energy storage unit.
Many carbon capture processes, such as calcium looping, rather than purely using electric power (like the cryogenic process described above) also use thermal energy. The thermal energy may be used to regenerate a solid or liquid medium which captures carbon dioxide, then releases it (by being regenerated), and then is used again for one or more cycles to capture further carbon dioxide. Thermal energy from a heat storage unit described above can provide renewable based energy for this process.
High temperature heat may drive one implementation of a calcination process, in a multi-step chemical reaction which involves the repeated conversion of a calcium oxide to calcium carbonate using captured carbon dioxide, and then calcination to release the carbon dioxide. Such reactions take place at high temperatures, and high temperature heat from a heat storage unit described above can power this process, followed by the use of the remaining lower temperature heat to drive an electrical generator, via a turbine heat-to-work process, including steam, CO2 or Rankine cycle processes.
Such heat may be supplied as lower grade heat from the outlet of a turbine generator, into which high grade heat is supplied by a thermal storage unit, such that some portion of energy is used in the form of electricity to drive pumps, and another portion of energy, in the form of heat, is used to drive regeneration. Both forms of energy may be supplied in an efficient manner using high temperature thermal energy storage.
Referring to
Stored thermal energy derived from VRE may provide a continuous supply of the necessary heat to drive this process. High-temperature air, or other type of fluid, may be directed to calcine or otherwise regenerate a high-temperature capture media. In one, steam may be directly supplied by an HRSG to drive a capture process element such as an amine solvent reboiler or adsorbent regenerator. In addition, or in place of steam from an HRSG, lower-pressure extracted steam from a steam turbine power cycle may be directed to provide heat to a solvent reboiler.
Electrical power generated by a steam turbine, organic Rankine cycle turbine, or supercritical CO2 turbine may provide electric power to drive the CO2 capture and compression equipment. Thus stored VRE may provide all energy necessary to drive a zero-emission carbon capture system 702 to enable separation of CO2 from exhaust gases or ambient air.
One example of using thermal storage units in a carbon capture process includes a carbon dioxide capture system that is configured to separate carbon dioxide from exhaust gases using, for example, a calcium looping process as described above.
The carbon dioxide capture system may include thermal energy storage 11005, which is configured to use a portion of stored thermal energy as heat to separate the carbon dioxide from the exhaust gases. For example, the heat may be used as part of a calcination cycle at calciner 11009 used to release carbon dioxide from an adsorbent material that has been used to capture the carbon dioxide. The thermal energy storage system, in some implementations, is configured to generate the output electricity in a substantially continuous manner, thus allowing the carbon dioxide capture system to be operational as needed.
An example method for operating a thermal energy storage system is presented in
An example method for operating a carbon dioxide capture system is shown in
3. Advantages of Disclosed Implementations
The example implementations related to carbon capture may have various advantages and benefits relative to traditional techniques. For example, the approaches described herein may address oversupply issues, as well as promote additional carbon capture for very high temperature industrial applications.
For example, use of thermal storage units may allow use of electricity generated by the combustion of fuels. During time periods of low electricity demand, power generated from combustible fuels is used to charge thermal storage units. During time periods of high electricity demand, charging of the thermal units is ceased and the carbon capture process is powered by the charged thermal storage units. Accordingly, the thermal units may be charged when electricity costs are low and the produced electricity, therefore, has less value. During the time periods of high electricity demand, the produced has greater value and can be sold to an electrical grid rather than being routed to the carbon capture process.
E. Additional Industrial Applications
1. Renewable desalination
Desalination processes traditionally run continuously and a significant amount of the world's desalination currently comes from membrane systems. The vast majority of the desalination in some regions (e.g., the Middle East), however, uses older thermal desalination technology that is coupled to a combined cycle power station. The combined cycle power station may have a combustion turbine and a steam turbine which outputs, for example, 70° C. condensation, which powers either a multi-stage flash or a multi-effect distillation production system. This may reduce the steam turbine electricity output by a few percent but may significantly reduce the electricity used to make water by desalination. In one example one ton of input steam makes four tons to seven tons of output water.
In some use cases, the power station remains running to keep desalination operational even when there is no other demand for the electricity generated by the power station, which results in power being wasted. With more renewable energy coming online, this may be an increasingly pressing problem.
By incorporating a heat storage system in accordance with example implementations, these problems may be addressed. The heat storage system may have an outlet temperature hotter than the outlet temperature of the combustion turbine. Thus, the heat storage system may be connected to a heat recovery steam generator with a separate air inlet port, or a steam generator of the heat storage system may be run to make water, firing no natural gas. The heat storage system may be charged by PV or run from grid power to absorb what would otherwise be over generation in the daytime and transition to true zero carbon water.
Thus, this system may be used to buffer peak electricity and provide level load power. If the combustion turbine is not been de-installed, during periods of high electricity demand, such as during a hot summer day, the combustion turbine remains available and thermal storage can be additionally deployed to run the steam turbine above nominal if desired.
One challenge in certain geographical regions (e.g., in the Middle East) is that a combustion turbine may produce around 18% less electricity on a hot day than it would on a cold day due to the lower combustion air density on the hot day. The disclosed heat storage system may be used to bring this steam mass flow and/or temperature back up when power from the turbine is drooping. All that can be electric so base load water can be made, but also includes its built-in topping power for peak electricity demand.
The heated brick energy storage systems described herein may be capable of producing higher output temperatures which may allow direct integration into existing desalination systems or may serve as the basis for a dedicated desalination system.
One beneficial element of these heated brick heat storage systems is that they may be retrofitted into existing plants to capture what would otherwise be overgeneration in the system. It should be noted that the disclosed heat storage system, coupled with a combined cycle power station can also drive a reverse osmosis system or other industrial processes, which may require round the clock power, with renewable energy.
2. Glass Production
Glass production typically requires temperatures ranging from 1500-1700° C. in a melting furnace where raw materials transform through a sequence of chemical reactions to form molten glass. The melting process represents over half of energy use in glass production.
The metal bath may require temperatures from 1100° C. to around 600° C. at the outlet before the molten glass is annealed at 600° C. In some traditional implementations, the thermal energy required for glass production is provided by fossil fuel combustion and in some cases, electrical heating. Glass production is thus a highly energy-intensive process and global demand continues to increase for glass. According to the International Energy Agency, the container and flat glass industries (which combined account for 80% of glass production) emit over 60 megatons of CO2 per year (IEA 2007) and energy use accounts for about 15% of total glass production costs.
Glass melting furnaces are complemented by a set of heat recovery regenerators which recover heat from the end of a melt furnace and use it to pre-heat the combustion air, e.g., to 900-1200° C. prior to the temperature being raised further through the burner to about 1700° C., e.g., 1700° C.
The high temperature energy storage system disclosed herein may have the capability to provide all thermal needs of the glass production system, including the high temperature melt furnace. In one example implementation, glass regenerators can be replaced by high temperature thermal energy storage systems disclosed herein to provide high temperature air or another gas and eliminate the need for a burner.
Because glass production is a round-the-clock process, an energy storage system may be used in one implementation to replace a significant amount of the input energy with intermittent renewable energy. The reduction or elimination of combustion gases may also reduce the amount of undesirable combustion products in the glass furnace. Nitrogen or another gas can be used in a closed loop through the high temperature thermal energy storage system, and into the float tank, reducing cost of air separation and reducing the production of undesirable side product of nitrogen oxides (NOx) produced by thermal reaction of nitrogen and oxygen in air.
In an alternative example implementation, the heated air from existing regenerators can be fed into the high temperature thermal energy storage system disclosed herein which then produces output fluid at a temperature utilized by the melt furnace. This may also reduce or eliminate need for a burner and additional combustion of fossil fuels.
3. Iron and Steel Production
Traditionally, crude steel is made using blast furnaces. Steelmaking may require high temperatures, such as approximately 1600° C., e.g., 1600° C. Every ton of steel produced in 2018 emitted on average 1.85 tons of carbon dioxide including agglomeration, iron- and steelmaking, casting and hot rolling, and accounts for approximately 30% of the global industrial CO2 emissions. Therefore, there is a substantial unmet need for reduction of the carbon intensity of steelmaking. The European steel industry aims to reduce CO2 emission by 80-95% by 2050 to meet the requirements of the Paris Agreement. Such drastic reduction may be difficult or impossible to achieve using traditional equipment.
Direct reduction processes used with an electric arc furnace may provide a pathway for substantial CO2 emission reduction in the steel industry. Use of natural gas as the reducing agent reduces CO2 emissions by approximately ⅓ compared to the traditional blast furnace route. Using renewable H2 as a reducing agent further reduces emissions. However, the process may be thermally unfavorable due to the endothermic nature of the reaction between hydrogen and iron oxide.
For example, 800 m{circumflex over ( )}3 (STP)/t DRI (cubic meters at standard temperature and pressure per metric ton of direct reduced iron) of hydrogen may be necessary for operation with hydrogen alone. The reduction process itself needs 550 m{circumflex over ( )}3 (STP)/t DRI, whereas 250 m{circumflex over ( )}3 STP/t DRI of hydrogen is required as fuel for the gas heater. An additional ˜50 m{circumflex over ( )}3(STP)/t DRI of natural gas may be needed in order to maintain the temperature and carbon content of the DRI. The temperature reduction from the hydrogen reaction can be compensated by the addition of natural gas. The exothermic reaction is between iron oxide and CO. In comparison, natural gas process requires approximately 259 m{circumflex over ( )}3 STP/t DRI.
The ultrahigh temperatures produced by the thermal energy storage system of the example implementations may reduce carbon emissions from the steelmaking process. The ability to obtain some of the highest temperatures of the steelmaking operation near 1600-2000° C. means that thermal process heat needs in the blast furnace can be met using a renewable-energy-charged thermal storage system around the clock as described above. In addition, the gas composition heated inside the thermal storage unit may be tuned/selected to further increase production efficiency, to retrofit fossil fuel systems to a direct reduction process without the need for significant equipment modification, or both. In other words, a traditional system may be relatively simply retrofitted to be electrified using intermittent electricity sources such as a PV system. For example, hydrogen or natural gas can directly be used as the heat exchange fluid which is heated by the thermal storage system and also to directly reduce the ore into steel.
To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing. For example, the following terminology may be used interchangeably, as would be understood to those skilled in the art:
Additionally, the term “heater” is used to refer to a conductive element that generates heat. For example, the term “heater” as used in the present example implementations may include, but is not limited to, a wire, a ribbon, a tape, or other structure that can conduct electricity in a manner that generates heat. The composition of the heater may be metallic (coated or uncoated), ceramic or other composition that can generate heat.
While foregoing example implementations may refer to “air”, including CO2, the inventive concept is not limited to this composition, and other fluid streams may be substituted therefor for additional industrial applications. For example but by way of limitation, enhanced oil recovery, sterilization related to healthcare or food and beverages, drying, chemical production, desalination and hydrothermal processing (e.g. Bayer process.) The Bayer process includes a calcination step. The composition of fluid streams may be selected to improve product yields or efficiency, or to control the exhaust stream.
In any of the thermal storage units, the working fluid composition may be changed at times for a number of purposes, including maintenance or re-conditioning of materials. Multiple units may be used in synergy to improve charging or discharging characteristics, sizing or ease of installation, integration or maintenance. As would be understood by those skilled in the art, the thermal storage units disclosed herein may be substituted with other thermal storage units having the necessary properties and functions; results may vary, depending on the manner and scale of combination of the thermal storage units.
As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain example implementations herein is intended merely to better illuminate the example implementation and does not pose a limitation on the scope of the example implementation otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the example implementation.
Groupings of alternative elements or example implementations of the example implementation disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, devices, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” “first”, “second” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.
In interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
While the foregoing describes various example implementations of the example implementation, other and further example implementations of the example implementation may be devised without departing from the basic scope thereof. The scope of the example implementation is determined by the claims that follow. The example implementation is not limited to the described example implementations, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the example implementation when combined with information and knowledge available to the person having ordinary skill in the art.
The present application is a continuation of U.S. application Ser. No. 18/171,602, filed Feb. 20, 2023, which is a divisional of U.S. application Ser. No. 17/650,522, filed Feb. 9, 2022 (now U.S. Pat. No. 11,585,243), which is a continuation of U.S. patent application Ser. No. 17/537,407, filed Nov. 29, 2021, which in turn claims the benefit of each of the following applications under 35 USC § 119(e): U.S. Provisional Application No. 63/119,443, filed on Nov. 30, 2020, U.S. Provisional Application No. 63/155,261, filed on Mar. 1, 2021, U.S. Provisional Application No. 63/165,632, filed on Mar. 24, 2021, U.S. Provisional Application No. 63/170,370, filed on Apr. 2, 2021, and U.S. Provisional Application No. 63/231,155, filed on Aug. 9, 2021. U.S. patent application Ser. No. 17/650,522 also claims the benefit under 35 USC § 119(a)-(d) of PCT/US21/61041, filed Nov. 29, 2021, which in turn claims the benefit of the each of the following as priority applications: U.S. Provisional Application No. 63/119,443, filed on Nov. 30, 2020, U.S. Provisional Application No. 63/155,261, filed on Mar. 1, 2021, U.S. Provisional Application No. 63/165,632, filed on Mar. 24, 2021, U.S. Provisional Application No. 63/170,370, filed on Apr. 2, 2021, and U.S. Provisional Application No. 63/231,155, filed on Aug. 9, 2021. The contents of each of the aforementioned applications are all incorporated by reference in their entireties and for all purposes.
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| Number | Date | Country | |
|---|---|---|---|
| 20240229682 A1 | Jul 2024 | US |
| Number | Date | Country | |
|---|---|---|---|
| 63231155 | Aug 2021 | US | |
| 63170370 | Apr 2021 | US | |
| 63165632 | Mar 2021 | US | |
| 63155261 | Mar 2021 | US | |
| 63119443 | Nov 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17650522 | Feb 2022 | US |
| Child | 18171602 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18171602 | Feb 2023 | US |
| Child | 18404000 | US | |
| Parent | 17537407 | Nov 2021 | US |
| Child | 17650522 | US | |
| Parent | PCT/US2021/061041 | Nov 2021 | WO |
| Child | 17650522 | US |
