Patent Application
20140013735
In various embodiments, the present invention relates to gas storage, gas distribution, pneumatics, power generation, and energy storage, and more particularly, to fluid systems for energy storage and recovery.
It is often desirable to store energy in the form of a fluid, such as compressed air or a fluid fuel (e.g., methane), that may be at non-ambient temperature and under high pressure (e.g., 3,000 psi). The energy may be stored at times of low demand or over supply, and the stored energy may be utilized at times of high demand or low supply in various ways: for example, methane may be used to generate industrial process heat, compressed air may be used to power mechanical devices directly, and methane or compressed air may be used by power generators that produce electricity. Retrievable or reversible modes of energy storage include chemical potential energy (i.e., fuel), elastic potential energy (i.e., the energy inherent in a compressed gas or liquid or in a compressed or stretched elastic solid), gravitational potential energy (i.e., the energy inherent in any mass by virtue of its altitude), latent energy (i.e., the energy inherent in a body by virtue of its phase state), electric energy (e.g., the energy inherent in separated electrical charges, as in a charged battery or capacitor), and exergy (i.e., the extractable work latent in a body that is at a temperature higher or lower than the temperature of a heat reservoir such as the body's environment). In systems that employ an energy-storing fluid, the cost of insulated and/or pressure-resistant vessels to contain the fluid is often a large part of the net cost, over the lifetime of the system, of storing and retrieving an average unit of energy.
Storing energy in the form of compressed gas has a long history and components tend to be well tested and reliable, and have long lifetimes. The general principle of compressed-gas or compressed-air energy storage (CAES) is that generated energy (e.g., electric energy) is used to compress gas (e.g., air), thus converting the original energy to pressure potential energy; this potential energy is later recovered in a useful form (e.g., converted back to electricity) via gas expansion coupled to an appropriate mechanism. Advantages of compressed-gas energy storage include low specific-energy costs, long lifetime, low maintenance, reasonable energy density, and good reliability.
If a body of gas is at the same temperature as its environment, and expansion occurs slowly relative to the rate of heat exchange between the gas and its environment, then the gas will remain at approximately constant temperature as it expands. This process is termed “isothermal” expansion. Isothermal expansion of a quantity of high-pressure gas stored at a given temperature recovers approximately three times more work than would “adiabatic expansion,” that is, expansion where no heat is exchanged between the gas and its environment—e.g., because the expansion happens rapidly or in an insulated chamber. Gas may also be compressed isothermally or adiabatically.
An ideally isothermal energy-storage cycle of compression, storage, and expansion would have 100% thermodynamic efficiency. An ideally adiabatic energy-storage cycle would also have 100% thermodynamic efficiency, but there are many practical disadvantages to the adiabatic approach. These include the production of higher temperature and pressure extremes within the system, heat loss during the storage period, and inability to exploit environmental (e.g., cogenerative) heat sources and sinks during expansion and compression, respectively. In an isothermal system, the cost of adding a heat-exchange system is traded against resolving the difficulties of the adiabatic approach. In either case, mechanical energy from expanding gas is typically converted to electrical energy before use.
An efficient and novel design for storing energy in the form of compressed gas utilizing near isothermal gas compression and expansion has been shown and described in U.S. Pat. No. 7,832,207, filed Apr. 9, 2009 (the '207 patent) and U.S. Pat. No. 7,874,155, filed Feb. 25, 2010 (the '155 patent), the disclosures of which are hereby incorporated herein by reference in their entireties. The '207 and '155 patents disclose systems and techniques for expanding gas isothermally in staged cylinders and intensifiers over a large pressure range in order to generate electrical energy when required. Mechanical energy from the expanding gas may be used to drive a hydraulic pump/motor subsystem that produces electricity. Systems and techniques for hydraulic-pneumatic pressure intensification that may be employed in systems and methods such as those disclosed in the '207 and '155 patents are shown and described in U.S. Pat. No. 8,037,678, filed Sep. 10, 2010 (the '678 patent), the disclosure of which is hereby incorporated herein by reference in its entirety.
In the systems disclosed in the '207 and '155 patents, reciprocal mechanical motion is produced during recovery of energy from storage by expansion of gas in the cylinders. This reciprocal motion may be converted to electricity by a variety of techniques, for example as disclosed in the '678 patent as well as in U.S. Pat. No. 8,117,842, filed Feb. 14, 2011 (the '842 patent), the disclosure of which is hereby incorporated herein by reference in its entirety. The ability of such systems to either store energy (i.e., use energy to compress gas into a storage reservoir) or produce energy (i.e., expand gas from a storage reservoir to release energy) will be apparent to any person reasonably familiar with the principles of electrical and pneumatic machines.
The net monetary cost at which energy-storage systems deliver from storage a unit of energy (e.g., a kilowatt hour [kWh] of electrical energy, a BTU of natural gas) depends in part on the cost at which the system stores each unit of compressed gas. The net cost of energy storage by a system employing compressed gas is also influenced by the cost of conditioning the stored, compressed gas by heating, cooling, and/or the addition and removal of other gases or fluids. There is therefore a need for facilities that can store and in some cases thermally condition large quantities of compressed gas at relatively low cost, including the costs of construction and maintenance.
In various embodiments, the invention includes the employment of one or more pressure vessels and/or one or more insulated pipeline vessels (IPVs) and/or one or more lined underground reservoirs (LURs) as pressurized-fluid storage containers for a system that stores energy in the form of a compressed fluid (e.g., high pressure gas). The terms “IPV” and “LUR” will be clarified shortly, below. In general, the quantity of energy to be stored may be characterized as “low,” “medium,” or “large.” The cost-effectiveness of a storage container type is, in general, affected by the quantity of energy (i.e., fluid) to be stored. For storage of low energy quantities, pressure vessels (e.g., commercially-produced cylindrical tanks) and/or IPVs will in general be most cost-effective for fluid storage; for storage of medium energy quantities, IPVs and/or LURs will in general be most cost-effective for fluid storage; and for storage of large energy quantities, LURs and/or large scale geological storage (e.g., salt cavern, aquifer) will be in general be most cost-effective for fluid storage.
Herein, the terms “thermal energy” and “exergy” are employed interchangeably, usually to signify extractable work latent in a body that is at a temperature higher than that of the body's environment. Hybrid systems that store energy in one or more fluids that contain energy in one or more retrievable or reversible forms can also be envisaged and are contemplated herein even when not explicitly mentioned or described.
The term “insulated pipeline vessel” or “IPV” refers herein to a segment of pressure-resistant pipeline (e.g., pipeline designed to transport natural gas), of whatever length, that has been sealed at its ends (other than to the extent that perforations are provided for the delivery of fluids into and removal of fluids from the IPV) and covered by one or more layers of insulation and possibly by other protective materials as well. Herein, “IPV” may also refer to a series of pipe segments joined together and sealed, or an array of such segments or series of joined segments. An array of pipe segments employed as an IPV is herein referred to as an “IPV array.” An IPV also may be equipped with perforations, valves, and other devices to control the admission and release of gas and/or liquid; may be equipped with sensors for detecting and reporting flow, volume, temperature, pressure, strain, or other qualities of the vessel's contents or of the vessel's own fabric; may contain devices for the exchange of heat between the vessel's fluid contents and external sources or sinks of thermal energy; and may be encased in or buried under a layer or layers of earth, gravel, or other materials. The term “insulated pipeline vessel” or “IPV” may also refer herein to two or more IPVs, as just described, interconnected so as to form a single system for the storage of fluid. IPVs may have lengths well in excess (e.g., >100×) of their diameters, and may not fall within ASME regulations for pressure vessels. IPVs may include or consist essentially of (i) a thermally insulating material (e.g., one or more plastics or polymers) or (ii) a base material that is more conductive (e.g., one or more metals or metal alloys such as steel) that is (a) at least partially buried within an insulating material (e.g., earth, soil, gravel, etc.), (b) has a thermally insulating material impregnated therewithin, and/or (c) has a thermally insulating material disposed on its inner and/or outer surface. In various embodiments, the thermal heat conduction through the walls of the IPV is no greater than 5 Watts per degree Celsius per cubic meter of storage volume (e.g., no more than 250 Watts lost due to heat conduction for fluid contained in an IPV, where the fluid is 50° C. warmer than the surroundings, for every 1.3 meter length of a 1 meter inner diameter pipe), and in preferred embodiments the thermal conductance is no greater than 2 Watts per degree Celsius per cubic meter of storage volume, or even no greater than 1 Watt per degree Celsius per cubic meter of storage volume. For reference, an uninsulated pipe may lose more than 1000 watts (W) per degree Celsius per cubic meter of storage volume (e.g., more than 50,000 W lost due to heat conduction for fluid contained in the pipe, where the fluid is 50° C. warmer than the surroundings, for every 1.3 meter length of a 1 meter inner diameter pipe).
An LUR is a cavity in rock (primarily crystalline bedrock) that is lined with steel, concrete, and/or other materials that enable the cavity to serve as a vessel containing fluids (e.g., natural gas, air, an air-water mixture) at high pressure (e.g., 150 atmospheres, 250 atmospheres, or higher) without significant fluid leakage either into or out of the cavity. Various embodiments of the invention employ techniques for the excavation of open, vertical shafts in the construction of LURs and for the thermal conditioning of fluids stored in LURs that have been constructed by open-shaft and other techniques.
Typically, construction of an LUR entails excavation of a large, vertically cylindrical cavity (e.g., 20-50 meters in diameter and 50-115 meters tall) with a domed roof and rounded invert (floor). Excavation may be via sloping access tunnels or the sinking of a vertical shaft. The domed roof may be constructed after excavation of the cavity. A vertically oriented shape enhances the stability of the excavation by minimizing roof area, while rounding of the roof and the invert increases roof strength and enables fluid-pressure stresses on the inner liner (e.g., steel skin) to be distributed more evenly.
An LUR cavity may be located at various depths below the ground (e.g., 100 meters to 200 meters), depending on rock type and other constraints, and may be lined with a multi-layer lining that may be constructed, wholly or partly, either during excavation or after excavation. The lining typically includes a layer of reinforced concrete (e.g., approximately 1 meter thick) and a thin (e.g., 12-15 mm) inner liner of carbon steel. The lining may also include other layers, such as a layer of thermal insulation (e.g., perlite concrete) and/or a network of pipes to drain groundwater away from the cavity liner. One purpose of the inner liner is to act as an impermeable barrier, both to retain the fluid contents of the cavity and to keep fluids (e.g., groundwater) from entering the cavity. A purpose of the concrete layer is to act as a distributor of forces exerted by the contents of the LUR on the surrounding lining layers and rock mass, and by the surrounding rock mass on the LUR lining layers: that is, the concrete layer assures the most even possible transfer of forces from fluid within the LUR to the surrounding rock mass and distributes any local strains in the rock mass (e.g., from the opening of natural rock fractures) at the concrete/rock interface) as evenly as possible across the concrete and thus across the inner liner. Smooth distribution of forces across the inner liner is desirable because the inner liner is typically thin (to conserve materials and so reduce cost): its composition and thickness, and hence its cost, will depend on the maximum local circumferential strain that any part of it must be able to resist during operation. Therefore, preventing the occurrence of excessive local strain on any part of the inner liner is advantageous.
To further minimize local circumferential strains on the inner liner, a viscous layer (e.g., approximately 5 mm thick and made of a bituminous (tarry) material) may be placed between the steel and the concrete layers of the liner. This viscous layer will allow some slippage between the inner liner and the concrete, contributing to the reduction of local strains.
These and other features and advantages of LUR linings in various embodiments of the invention will be further disclosed and clarified in the drawings and accompanying explanations. The foregoing description of liner construction techniques and materials is exemplary: other techniques for construction, and other materials for the inner liner and various other portions of the cavity liner, may be employed.
Conventional storage facilities for compressed gas rely primarily on (a) compressed-gas bottles, or (b) depleted oil fields, salt caverns, or aquifer formations, into which compressed gas may be injected. The use of oil fields, salt caverns, and aquifers tightly constrains site selection, which is disadvantageous. The various surface-vessel options tend to occupy relatively large areas of land, which can be site-constraining, and are materials-intensive, which raises cost. For a commercially realistic energy-storage capacity, the areal footprint of a compressed gas energy storage and generation facility located at or near the surface of the earth will typically consist mostly of storage.
A number of advantages are realized by using LURs with energy storage systems relying on compressed gas. An LUR facility, both during and after construction, tends to disturb its surface environs relatively little compared to surface-sited storage facilities of comparable capacity, which, as noted above, can occupy significant area. The ability to site an LUR wherever suitable earth material (e.g., bedrock) allows for the construction of energy storage and generation facilities nearer to demand in some cases, reducing transmission costs. Herein, any earth material suitable for the construction of an LUR is referred to as “bedrock.” Being embedded deeply in bedrock, LURs are relatively secure from accidental or malicious damage, making compressed-gas LURs a particularly safe way to store large amounts of energy; indeed, compressed-air LUR storage is probably one of the safest ways to store large amounts of energy yet devised, since LUR air storage is not accompanied by the possibility of detonation, deflagration, explosive decompression, dam bursting, release of toxins, release of suffocating gases, and other hazards associated with various other energy-storage technologies. The environmental impact of a compressed-air LUR is low both because its surface footprint is low and its water usage is low compared to pumped-reservoir storage, the latter being especially of advantage in arid or semiarid regions.
Another advantage of compressed-gas LUR storage is that an LUR may enable the storage of compressed gas fluids at lower per-unit cost than most other methods of storage. Lower cost is achieved because in an LUR, outward-acting pressure forces are borne by surrounding bedrock rather than by the constructed fabric of the vessel itself. This greatly reduces the quantities of relatively expensive materials (e.g., steel, carbon fiber, reinforced concrete) needed to contain each unit of pressurized fluid as compared to free-standing high-pressure vessels that must bear all loads internally. Further, because an LUR may be relatively large (e.g., approximately 30,000 m3), its surface-to-volume ratio is low compared to that of a multiplicity of smaller vessels, further reducing material and construction costs per unit of fluid stored.
Another potential advantage is that an LUR may, when the temperature of its contents is lower than that of the surrounding rock, harvest energy from the earth's innate heat. Heat that flows from surrounding rock to fluids in an LUR may be partially converted to electricity by the energy-conversion portion of an energy storage and generation system.
Provisions may be made for the exchange of heat between a heat-transfer fluid (e.g., water with additives) and the air (or other gas) within an LUR: for example, water may be sprayed or foamed into the LUR to either warm or cool the air within, and may then be pumped out to partake in further heat exchanges and/or to be recycled within the system. Such provisions may be advantageous for the operation of an energy storage and generation system. For example, lowering the temperature of fluids within an LUR may be employed to reduce energy loss to, or increase energy gain from, surrounding rock, or may be employed to reduce pressure changes and associated mechanical stresses on the LUR's lining layers and surrounding rock. Such provisions may enable the conveyance of heat obtained from external surface sources (e.g., waste heat from a thermal power plant) to the fluid contents of the LUR, in which case the LUR will store energy both as the elastic potential energy of compressed air and as the thermal energy of warm fluids.
The construction of LURs as storage reservoirs for energy-storage systems employing compressed air and near-isothermal compression and expansion is therefore advantageous as regards surface footprint, siting flexibility, safety, cost per unit of energy stored, and other aspects of cost and operation.
Embodiments of the present invention may be utilized in energy storage and generation systems utilizing compressed gas. In a compressed-gas energy storage system, gas is stored at high pressure (e.g., approximately 3,000 psi). This gas may be expanded into a cylinder having a first compartment (or “chamber”) and a second compartment separated by a piston slidably disposed within the cylinder (or by another boundary mechanism). A shaft may be coupled to the piston and extend through the first compartment and/or the second compartment of the cylinder and beyond an end cap of the cylinder, and a transmission mechanism may be coupled to the shaft for converting a reciprocal motion of the shaft into a rotary motion, as described in the '678 and '842 patents. Moreover, a motor/generator may be coupled to the transmission mechanism. Alternatively or additionally, the shaft of the cylinders may be coupled to one or more linear generators, as described in the '842 patent.
As also described in the '842 patent, the range of forces produced by expanding a given quantity of gas in a given time may be reduced through the addition of multiple, series-connected cylinder stages. That is, as gas from a high-pressure reservoir is expanded in one chamber of a first, high-pressure cylinder, gas from the other chamber of the first cylinder is directed to the expansion chamber of a second, lower-pressure cylinder. Gas from the lower-pressure chamber of this second cylinder may either be vented to the environment or directed to the expansion chamber of a third cylinder operating at still lower pressure; the third cylinder may be similarly connected to a fourth cylinder; and so on.
The principle may be extended to more than two cylinders to suit particular applications. For example, a narrower output force range for a given range of reservoir pressures is achieved by having a first, high-pressure cylinder operating between, for example, approximately 3,000 psig and approximately 300 psig and a second, larger-volume, lower-pressure cylinder operating between, for example, approximately 300 psig and approximately 30 psig. When two expansion cylinders are used, the range of pressure within either cylinder (and thus the range of force produced by either cylinder) is reduced as the square root relative to the range of pressure (or force) experienced with a single expansion cylinder, e.g., from approximately 100:1 to approximately 10:1 (as set forth in the '853 application). Furthermore, as set forth in the '678 patent, N appropriately sized cylinders can reduce an original operating pressure range R to R1/N. Any group of N cylinders staged in this manner, where N≧2, is herein termed a cylinder group.
Every compression or expansion of a quantity of gas, where such a compression or expansion is herein termed “a gas process,” is generally one of three types: (1) adiabatic, during which the gas exchanges no heat with its environment and, consequently, rises or falls in temperature, (2) isothermal, during which the gas exchanges heat with its environment in such a way as to remain at constant temperature, and (3) polytropic, during which the gas exchanges heat with its environment but its temperature does not remain constant. Perfectly adiabatic gas processes are not practical because some heat is always exchanged between any body of gas and its environment (ideal insulators and reflectors do not exist); perfectly isothermal gas processes are not practical because for heat to flow between a quantity of gas and a portion of its environment (e.g., a body of liquid), a nonzero temperature difference must exist between the gas and its environment—e.g., the gas must be allowed to heat during compression in order that heat may be conducted to the liquid. Hence real-world gas processes are typically polytropic, though they may approximate adiabatic or isothermal processes.
The Ideal Gas Law states that for a given quantity of gas having mass m, pressure p, volume V, and temperature T, pV=mRT, where R is the gas constant (R=287 J/K·kg for air). For an isothermal process, T is a constant throughout the process, so pV=C, where C is some constant.
For a polytropic process, as will be clear to persons familiar with the science of thermodynamics, pVn=C throughout the process, where n, termed the polytropic index, is some constant generally between 1.0 and 1.6. For n=1, pVn=pVl=pV=C, i.e., the process is isothermal. In general, a process for which n is close to 1 (e.g., 1.05) may be deemed approximately isothermal.
For an adiabatic process, pVγ=C, where γ, termed the adiabatic coefficient, is equal to the ratio of the gas's heat capacity at constant pressure CP to its heat capacity at constant volume, CV, i.e., γ=CP/CV. In practice, γ is dependent on pressure. For air, the adiabatic coefficient γ is typically between 1.4 and 1.6.
Herein, we define a “substantially isothermal” gas process as one having n≦1.1. The gas processes conducted within cylinders described herein are preferably substantially isothermal with n≦1.05. Herein, wherever a gas process taking place within a cylinder assembly or storage reservoir is described as “isothermal,” this word is synonymous with the term “substantially isothermal.”
The amount of work done in compression or expansion of a given quantity of gas varies substantially with polytropic index n. For compressions, the lowest amount of work done is for an isothermal process and the highest for an adiabatic process, and vice versa for expansions. Hence, for gas processes such as typically occur in the compressed-gas energy storage systems described herein, the end temperatures attained by adiabatic, isothermal, and substantially isothermal gas processes are sufficiently different to have practical impact on the operability and efficiency of such systems. Similarly, the thermal efficiencies of adiabatic, isothermal, and substantially isothermal gas processes are sufficiently different to have practical impact on the overall efficiency of such energy storage systems. For example, for compression of a quantity of gas from initial temperature of 20° C. and initial pressure of 0 psig (atmospheric) to a final pressure of 180 psig, the final temperature T of the gas will be exactly 20° C. for an isothermal process, approximately 295° C. for an adiabatic process, approximately 95° C. for a polytropic compression having polytropic index n=1.1 (10% increase in n over isothermal case of n=1), and approximately 60° C. for a polytropic compression having polytropic index n=1.05 (5% increase in n over isothermal case of n=1). In another example, for compression of 1.6 kg of air from an initial temperature of 20° C. and initial pressure of 0 psig (atmospheric) to a final pressure of approximately 180 psig, including compressing the gas into a storage reservoir at 180 psig, isothermal compression requires approximately 355 kilojoules of work, adiabatic compression requires approximately 520 kilojoules of work, and a polytropic compression having polytropic index n=1.045 requires approximately 375 kilojoules of work; that is, the polytropic compression requires approximately 5% more work than the isothermal process, and the adiabatic process requires approximately 46% more work than the isothermal process.
It is possible to estimate the polytropic index n of gas processes occurring in cylinder assemblies such as are described herein by empirically fitting n to the equation pVn=C, where pressure p and volume V of gas during a compression or expansion, e.g., within a cylinder, may both be measured as functions of time from piston position, known device dimensions, and pressure-transducer measurements. Moreover, by the Ideal Gas Law, temperature within the cylinder may be estimated from p and V, as an alternative to direct measurement by a transducer (e.g., thermocouple, resistance thermal detector, thermistor) located within the cylinder and in contact with its fluid contents. In many cases, an indirect measurement of temperature via volume and pressure may be more rapid and more representative of the entire volume than a slower point measurement from a temperature transducer. Thus, temperature measurements and monitoring described herein may be performed directly via one or more transducers, or indirectly as described above, and a “temperature sensor” may be one of such one or more transducers and/or one or more sensors for the indirect measurement of temperature, e.g., volume, pressure, and/or piston-position sensors.
The systems described herein, and/or other embodiments employing foam-based heat exchange, liquid-spray heat exchange, and/or external gas heat exchange, may draw or deliver thermal energy via their heat-exchange mechanisms to external systems (not shown) for purposes of cogeneration, as described in U.S. Pat. No. 7,958,731, filed Jan. 20, 2010 (the '731 patent), the entire disclosure of which is incorporated by reference herein.
The compressed-air energy storage and recovery systems described herein are preferably “open-air” systems, i.e., systems that take in air from the ambient atmosphere for compression and vent air back to the ambient atmosphere after expansion, rather than systems that compress and expand a captured volume of gas in a sealed container (i.e., “closed-air” systems). The systems described herein generally feature one or more cylinder assemblies for the storage and recovery of energy via compression and expansion of gas. The systems also include (i) a reservoir for storage of compressed gas after compression and supply of compressed gas for expansion thereof, and (ii) a vent for exhausting expanded gas to atmosphere after expansion and supply of gas for compression. The storage reservoir may include or consist essentially of, e.g., one or more IPVs, LURs, pressure vessels, (i.e., containers for compressed gas that may have rigid exteriors or may be inflatable, that may be formed of various suitable materials such as metal or plastic, and that may or may not fall within ASME regulations for pressure vessels), or caverns (i.e., naturally occurring or artificially created cavities that are typically located underground). Open-air systems typically provide superior energy density relative to closed-air systems.
Furthermore, the systems described herein may be advantageously utilized to harness and recover sources of renewable energy, e.g., wind and solar energy. For example, energy stored during compression of the gas may originate from an intermittent renewable energy source of, e.g., wind or solar energy, and energy may be recovered via expansion of the gas when the intermittent renewable energy source is nonfunctional (i.e., either not producing harnessable energy or producing energy at lower-than-nominal levels). As such, the systems described herein may be connected to, e.g., solar panels or wind turbines, in order to store the renewable energy generated by such systems.
In an aspect, embodiments of the invention feature a method of fabricating a lined underground reservoir. Rock is excavated at a site location to form an open shaft extending below ground level. A fluid-impermeable (i.e., impermeable to liquid such as water and/or gas such as air or natural gas) liner substantially enclosing an interior volume for containing at least one of compressed gas or heat-transfer liquid is assembled within or above the shaft. The interior volume is smaller than the total volume of the open shaft. The liner includes or consists essentially of an invert section enclosing a bottom of the interior volume, a dome section enclosing a top of the interior volume opposite the bottom, and a sidewall section substantially gaplessly spanning the invert and dome sections. After assembly, the liner is disposed within the shaft below ground level. A surround material is disposed to at least partially fill a gap between an outer surface of the liner and an inner surface of the shaft around at least a portion of the outer surface of the liner. After assembly of the liner and disposal of the surround material so as to form a surrounded liner, an overfill material is disposed over the surrounded liner to fill at least a portion of a space between the ground level and the surrounded liner. The interior volume enclosed by the liner is fluidly connected to a fluid source or fluid sink external to the surrounded liner, thereby forming the lined underground reservoir.
Embodiments of the invention may feature one or more of the following in any of a variety of different combinations. The surround material may include or consist essentially of concrete or metal-reinforced concrete (e.g., concrete internally reinforced with a network of metal such as rebar). The liner may include or consist essentially of steel and/or plastic. The overfill material may include or consist essentially of rock, concrete, and/or metal-reinforced concrete. The overfill material may include or consist essentially of a volume of heat-transfer liquid (e.g., water). The overfill material may be the fluid source and/or fluid sink. Prior to disposing the overfill material, a plug, shaped to laterally distribute upward-acting forces resulting when the liner contains pressurized fluid, may be formed within the shaft. A width of the shaft around the plug may be larger than a width of the shaft around the surrounded liner. A cross-section of the plug, e.g., a cross-section in a plane approximately perpendicular to ground level, may be substantially trapezoidal or hexagonal. Prior to disposing the surround material, spacer may be disposed on the liner that defines at least a portion of the gap between the outer surface of the liner and the inner surface of the shaft around at least a portion of the outer surface of the liner. The shaft may be substantially fully formed prior to any portion of the liner being disposed therein. At least a portion of the surround material may be disposed within the shaft prior to the liner being disposed within the shaft. A mechanism for generating a foam or droplet spray may be disposed within the interior volume. The mechanism may be fluidly connected to a source of heat-transfer fluid external to the surrounded liner. An area within the interior volume of the liner proximate the invert section may be fluidly connected to a sink of heat-transfer fluid external to the surrounded liner.
Assembling the liner may include or consist essentially of supporting a first portion of the liner above a bottom surface of the shaft such that a top surface of the first portion of the liner is proximate ground level, disposing a second portion of the liner on the top surface of the first portion of the liner to form an at least partially assembled liner, and lowering the at least partially assembled liner such that a top surface of the second portion of the liner is proximate ground level. Supporting the first portion of the liner may include or consist essentially of floating the first portion of the liner on a liquid within the shaft. Lowering the at least partially assembled liner may include or consist essentially of removing liquid from the shaft. Assembling the liner may include or consist essentially of filling at least a portion of the shaft with a liquid, floating a first portion of the liner on the liquid, proximate ground level, disposing a second portion of the liner on the first portion of the liner, and removing liquid from the shaft until a top surface of the second portion of the liner is proximate ground level. At least a portion of the surround material may be disposed on the inner surface of the shaft prior to filling the at least a portion of the shaft with the liquid. A spacer may be disposed on the first portion of the liner. The spacer may define at least a portion of the gap between the outer surface of the liner and the inner surface of the shaft around at least a portion of the outer surface of the liner. After the surround material is disposed within the gap, the surround material may have a substantially uniform thickness, defined by the spacer, around the liner. A portion of the surround material may be attached to each of the first and second sections of the liner proximate ground level. Each portion of the surround material may include or consist essentially of a network of metal.
During disposal of the surround material, the interior volume of the liner may be at least partially filled with a liquid such that a top surface of the liquid is approximately coplanar with a top surface of the surround material. The sidewall section of the liner may include or consist essentially of a plurality of substantially cylindrical segments, and each cylindrical segment may include or consist essentially of a plurality of discrete curved portions connected at interfaces therebetween. The plurality of discrete curved portions may be welded together at the interfaces to form each of the substantially cylindrical segments. The fluid source or fluid sink external to the surrounded liner may be a compressed-gas energy storage and recovery system configured to store gas in the interior volume after compression thereof and extract gas from the interior volume before expansion thereof. The energy storage and recovery system may store, e.g., compressed air or natural gas, within the interior volume and/or extract it therefrom. A network of drainage pipes for channeling liquid away from the liner may be disposed between the outer surface of the liner and the inner surface of the shaft. Concrete may be sprayed on the network of drainage pipes. At least a portion of the surround material may be disposed within the shaft before the liner is assembled. The surround material may include or consist essentially of (i) a network of drainage pipes and (ii) concrete reinforced with metal. The shaft may be deepened after a first portion of the surround material is disposed within the shaft, and, thereafter, a second portion of the surround material may be disposed on the first portion of the surround material. The assembled liner may not be self-supporting in the absence of the surround material. The shaft may be deepened after a first portion of the liner is assembled within the shaft, and, thereafter, a second portion of the liner may be attached to the first portion of the liner.
A portion of the surround material may be disposed over the dome section of the liner. The surround material may include or consist essentially of a concrete layer and, disposed between the concrete layer and the liner, a viscous layer for mitigating force on the liner. The concrete layer may include therewithin a network of metal (e.g., the concrete may be metal-reinforced concrete). The shaft may be substantially vertical. A region of the shaft disposed above the assembled liner may have a width or diameter approximately equal to or greater than a width or diameter of the assembled liner. The entire shaft may have a width or diameter approximately equal to or greater than a width or diameter of the assembled liner. During assembly of the liner and disposal of the surround material, the site location may be free of sub-surface access tunnels having a sufficiently large size and/or sufficiently shallow slope to accommodate vehicular traffic. Excavating rock may include or consist essentially of (a) excavating one or more holes at the site location where the shaft is to be formed, (b) placing an explosive in the one or more holes, (c) detonating the explosive to pulverize the rock, (d) removing the pulverized rock, and (e) optionally, repeating steps (a)-(d). Excavating rock may include or consist essentially of (a) pulverizing rock with a cutting mechanism mounted on a translatable telescoping boom to form at least a portion of the shaft, (b) removing the pulverized rock, and (c) optionally, lowering the cutting mechanism and boom into the at least a portion of the shaft and repeating steps (a) and (b). The surrounded liner may be configured to contain a fluid pressure of at least 200 bar, and the rock at the site location may have a rock mass rating of at least 50. The rock at the site location may have a rock mass rating RMR, and the surrounded liner may be configured to contain a maximum fluid pressure P in MPa defined by P≦(RMR×0.83)−25. A thickness of the liner may be insufficient to withstand a maximum internal fluid pressure of the lined underground reservoir, and the lined underground reservoir may be configured to withstand the maximum internal fluid pressure, notwithstanding the insufficient thickness of the liner, via at least one of the overfill or rock surrounding the surrounded liner withstanding a portion of the internal fluid pressure.
In another aspect, embodiments of the invention feature a method of energy storage utilizing a compressed-gas energy storage system selectively fluidly connected to a lined underground reservoir at least partially surrounded by rock. Gas is substantially isothermally compressed with the energy storage system at a compression temperature. The compressed gas is transferred to the lined underground reservoir for storage. Thereafter, heat is exchanged between the stored compressed gas and the rock at least partially surrounding the lined underground reservoir to change a temperature of the stored gas to a storage temperature different from the compression temperature. The compressed gas may be thermally conditioned during transfer to the lined underground reservoir by (i) spraying droplets of a heat-transfer liquid into the gas and/or (ii) forming a foam comprising the gas and a heat-transfer liquid. The storage temperature may be lower than the compression temperature. The storage temperature may be higher than the compression temperature.
In yet another aspect, embodiments of the invention feature a compressed-gas energy storage and recovery system that includes or consists essentially of a cylinder assembly for compressing gas to store energy and/or expanding gas to recover energy, a heat-exchange subsystem for thermally conditioning the gas during the compression and/or expansion via heat exchange between the gas and a heat-transfer liquid, a lined underground reservoir for storing compressed gas and/or heat-transfer fluid in an interior volume thereof, the lined underground reservoir being substantially impermeable to fluid and comprising an inner steel layer surrounded by an outer concrete layer, a source of heat-transfer fluid fluidly connected to the interior volume of the lined underground reservoir, and a sink for heat-transfer fluid fluidly connected to the interior volume of the lined underground reservoir.
Embodiments of the invention may feature one or more of the following in any of a variety of different combinations. A nozzle for introducing heat-transfer fluid into the interior volume as a spray of droplets or as a foam may be disposed within the interior volume of the lined underground reservoir. A first pipe may fluidly connect the cylinder assembly to the interior volume of the lined underground reservoir. A second pipe may fluidly connect the source of heat-transfer fluid to the nozzle. A third pipe may fluidly connect an area proximate a bottom portion of the interior volume of the lined underground reservoir and the sink for heat-transfer fluid. A pump may be configured to transfer heat-transfer fluid through the third pipe to the sink for heat-transfer fluid. The source of heat-transfer fluid and the sink for heat-transfer fluid may be the same body of liquid. The source of heat-transfer fluid and the sink for heat-transfer fluid may be two discrete and separate bodies of liquid.
In a further aspect, embodiments of the invention feature a compressed-gas energy storage and recovery system that includes or consists essentially of a cylinder assembly for at least one of compressing gas to store energy or expanding gas to recover energy, a heat-exchange subsystem for thermally conditioning the gas via heat exchange between the gas and a heat-transfer liquid, and selectively fluidly connected to the cylinder assembly, one or more insulated pipeline vessels (IPVs) for at least one of (i) storage of gas after compression, (ii) supply of compressed gas for expansion, (iii) storage of heat-transfer liquid, or (iv) supply of heat-transfer liquid.
Embodiments of the invention may feature one or more of the following in any of a variety of different combinations. Each IPV may include or consist essentially of a base material at least partially surrounded by insulation for retarding heat exchange between contents of the IPV and surroundings of the IPV. Each IPV may include, disposed on at least a portion of its interior surface, a corrosion-resistant coating. At least one IPV may contain gas at a pressure higher than an ambient pressure and/or at a temperature higher than an ambient temperature. The one or more IPVs may be at least partially buried underground. At least one IPV may include an unburied access point for the inflow and outflow of gas and/or heat-transfer liquid. Each IPV may be at least partially disposed within a separate fill capsule (i) containing insulating fill and (ii) including an outer envelope substantially impermeable to liquid and/or air. Each fill capsule may be at least partially buried underground. The one or more IPVs may include or consist essentially of a plurality of IPVs, and two or more IPVs may be at least partially disposed within a fill capsule (i) containing insulating fill and (ii) including an outer envelope substantially impermeable to at least one of liquid or air. The fill capsule may be at least partially buried underground. All of the plurality of IPVs may be at least partially disposed within the fill capsule. The one or more IPVs may be each substantially linear and disposed lengthwise at a first non-zero angle to the horizontal such that a downhill end of each IPV is lower than an uphill end. At least one IPV may include, proximate the downhill end thereof, a first access point for the inflow and outflow of heat-transfer liquid. The at least one IPV may include, proximate the first access point, a second access point for the inflow and outflow of gas. The second access point may be disposed at a distance from the downhill end sufficient to prevent blockage of the second access point by heat-transfer liquid accumulating proximate the downhill end. A manifold pipe may be fluidly connectable to the first access points of one or more IPVs. The manifold pipe may be inclined lengthwise at a second non-zero angle to the horizontal. The manifold pipe may be disposed approximately perpendicular to lengths of the one or more IPVs. The second non-zero angle may be different from the first non-zero angle. At least two of the one or more IPVs may be fluidly connected by a connector. The connector may include or consist essentially of a manifold and/or a U-bend connector. At least one IPV may include therewithin a mechanism for the introduction of heat-transfer liquid. The mechanism for the introduction of heat-transfer liquid may include or consist essentially of a nozzle, a spray head, and/or a spray rod. A pump may supply heat-transfer liquid to the mechanism. Each IPV may have a length exceeding its diameter by a factor of at least 100. Each IPV may not fall within ASME regulations for pressure vessels. The heat-exchange subsystem may include a mechanism for (i) the introduction of heat-transfer liquid into gas in the form of droplets and/or (ii) the mingling of heat-transfer liquid with gas to form foam.
In yet a further aspect, embodiments of the invention feature a compressed-gas energy storage and recovery system that includes or consists essentially of a cylinder assembly for compressing gas to store energy and/or expanding gas to recover energy, and a storage system for the storage of compressed gas and/or heat-transfer liquid. The storage system includes or consists essentially of a first approximately planar array of insulated pipeline vessels (IPVs). The first array is inclined at a first non-zero angle to the horizontal in a first direction and disposed at a second angle to the horizontal in a second direction perpendicular to the first direction.
Embodiments of the invention may feature one or more of the following in any of a variety of different combinations. The second angle may be approximately zero or may be non-zero. The second angle may be different from the first angle. At least two of the IPVs of the first array may be fluidly connected to each other via at least one connector. The at least one connector may include or consist essentially of a manifold and/or at least one U-bend connector. The storage system may include, disposed over the first array, a second approximately planar array of IPVs. The second array may be approximately parallel to the first array. The second array may be inclined at a third non-zero angle to the horizontal in the first direction and disposed at a fourth angle to the horizontal in the second direction. The fourth angle may be approximately zero or may be non-zero. The second angle may be approximately equal to the fourth angle. The first angle may be approximately equal to the third angle. The first angle may be different from the third angle. Relative to the horizontal, an absolute value of the first angle may be approximately equal to an absolute value of the third angle. At least one of the IPVs of the first array may be fluidly connected to at least one of the IPVs of the second array by at least one connector. The at least one connector may include or consist essentially of a manifold or at least one U-bend connector. Each IPV may include or consist essentially of a base material at least partially surrounded by insulation for retarding heat exchange between contents of the IPV and surroundings of the IPV.
In another aspect, embodiments of the invention feature a compressed-gas energy storage and recovery system that includes or consists essentially of a cylinder assembly for at least one of compressing gas to store energy or expanding gas to recover energy, a heat-exchange subsystem for thermally conditioning the gas via heat exchange between the gas and a heat-transfer liquid, and selectively fluidly connected to the cylinder assembly, a lined underground reservoir for at least one of (i) storage of gas after compression, (ii) supply of compressed gas for expansion, (iii) storage of heat-transfer liquid, or (iv) supply of heat-transfer liquid.
Embodiments of the invention may feature one or more of the following in any of a variety of different combinations. The lined underground reservoir may include a liner at least partially surrounded by at least one of earth, dirt, or gravel. The liner may include or consist essentially of steel and/or concrete. A coating for sealing the liner to prevent fluid flow therethrough, preventing corrosion or degradation of the liner, and/or for thermally insulating the liner may be disposed on an inner surface of the liner and/or an outer surface of the liner. At least a portion of the lined underground reservoir may be disposed below ground level. The lined underground reservoir may include therein a liquid containment region disposed above a bottom surface of the lined underground reservoir. A spray head and/or nozzle for introducing heat-transfer liquid and/or foam may be disposed within the lined underground reservoir. The lined underground reservoir may include a container buried beneath and surrounded by at least one of earth, dirt, or gravel. The container may include or consist essentially of steel. Concrete, an insulating material, fiberglass, and/or carbon fiber may be disposed between the container and the earth, dirt, and/or gravel. The concrete, insulating material, fiberglass, and/or carbon fiber may be disposed directly on the container with substantially no gap or air therebetween. A circulation apparatus for pumping liquid disposed proximate a bottom surface of the lined underground reservoir to a point outside of the lined underground reservoir may be disposed within the lined underground reservoir. The lined underground reservoir may include therein a liquid containment region disposed above a bottom surface of the lined underground reservoir. A second circulation apparatus for pumping liquid disposed in the liquid containment region to a point outside of the lined underground reservoir may be disposed within the lined underground reservoir. A pipe for transferring gas between the cylinder assembly and the lined underground reservoir may extend from the cylinder assembly to a point within an interior volume of the lined underground reservoir. The lined underground reservoir may include or consist essentially of a plurality of discrete containers disposed within a shaft extending below ground level.
These and other objects, along with advantages and features of the invention, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. Note that as used herein, the terms “pipe,” “piping” and the like shall refer to one or more conduits that are rated to carry gas or liquid between two points. Thus, the singular term should be taken to include a plurality of parallel conduits where appropriate. Herein, the terms “liquid” and “water” interchangeably connote any mostly or substantially incompressible liquid, the terms “gas” and “air” are used interchangeably, and the term “fluid” may refer to a liquid, a gas, or a mixture of liquid and gas (e.g., a foam) unless otherwise indicated. As used herein unless otherwise indicated, the terms “approximately” and “substantially” mean±10%, and, in some embodiments, ±5%. Herein, any fluid at a pressure higher than ambient atmospheric pressure is said to be “pressurized.” A “valve” is any mechanism or component for controlling fluid communication between fluid paths or reservoirs, or for selectively permitting control or venting. The term “cylinder” refers to a chamber, of uniform but not necessarily circular cross-section, which may contain a slidably disposed piston or other mechanism that separates the fluid on one side of the chamber from that on the other, preventing fluid movement from one side of the chamber to the other while allowing the transfer of force/pressure from one side of the chamber to the next or to a mechanism outside the chamber. At least one of the two ends of a chamber may be closed by end caps, also herein termed “heads.” As utilized herein, an “end cap” is not necessarily a component distinct or separable from the remaining portion of the cylinder, but may refer to an end portion of the cylinder itself. Rods, valves, and other devices may pass through the end caps. A “cylinder assembly” may be a simple cylinder or include multiple cylinders, and may or may not have additional associated components (such as mechanical linkages among the cylinders). The shaft of a cylinder may be coupled hydraulically or mechanically to a mechanical load (e.g., a hydraulic motor/pump or a crankshaft) that is in turn coupled to an electrical load (e.g., rotary or linear electric motor/generator attached to power electronics and/or directly to the grid or other loads), as described in the '678 and '842 patents. As used herein, “thermal conditioning” of a heat-exchange fluid does not include any modification of the temperature of the heat-exchange fluid resulting from interaction with gas with which the heat-exchange fluid is exchanging thermal energy; rather, such thermal conditioning generally refers to the modification of the temperature of the heat-exchange fluid by other means (e.g., an external heat exchanger). The terms “heat-exchange” and “heat-transfer” are generally utilized interchangeably herein. Unless otherwise indicated, motor/pumps described herein are not required to be configured to function both as a motor and a pump if they are utilized during system operation only as a motor or a pump but not both. Gas expansions described herein may be performed in the absence of combustion (as opposed to the operation of an internal-combustion cylinder, for example). The term “thermal well” refers herein to any mass (e.g., a quantity of fluid in an insulated container, or a solid thermal mass in an insulated container, or a portion of the earth) with which heat may be exchanged, whose temperature may be raised or lowered compared to some other mass (e.g., the environment), and which tends to retain rather than to dissipate any thermal energy stored within itself. Alternatively or additionally, a thermal well may employ material phase changes (e.g., melting and solidifying of a material) to store and release energy. As used herein, a “recessed” or “underground” storage reservoir is at least partially surrounded by and/or buried in material such as earth, dirt, gravel, and/or water or other liquid. Recessed storage reservoirs may be formed in (and may occupy substantially all of the space of) artificial and/or natural caverns.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Cylinders, rods, and other components are depicted in cross section in a manner that will be intelligible to all persons familiar with the art of pneumatic and hydraulic cylinders. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
To generate electricity from compressed air released from storage, compressed air from the LUR 102 is expanded to a near-ambient pressure in the compressor/expander 132 in a manner that performs mechanical work. Heat from a thermal energy source (e.g., combusted methane, waste heat from a fuel-burning generator) may be added to the air being expanded in the compressor/expander 132 and is partially converted to mechanical work. The mechanical work derived from the compressed air and the thermal energy added thereto is directed to the motor/generator 130. Electricity produced by the motor/generator 130 is directed through the transformer 128 and thence to the source/sink 126.
In various other embodiments, system 100C does not include a discrete thermal energy sink 134 or thermal energy source 136. Motor/generator 130 may be a single electric machine, or may consist of a separate motor and separate generator. Compressor/expander 132 may be a single system or may be separate compressor unit and separate expander unit.
An electric motor/generator 202 (e.g., a rotary or linear electric machine) is in physical communication (e.g., via hydraulic pump, piston shaft, or mechanical crankshaft) with the expansion/compression assembly 201. The motor/generator 202 may be electrically connected to a source and/or sink of electric energy not explicitly depicted in
The expansion/compression assembly 201 may be in fluid communication with a heat-transfer subsystem 204 that alters the temperature and/or pressure of a fluid (i.e., gas, liquid, or gas-liquid mixture such as a foam) extracted from expansion/compression assembly 201 and, after alteration of the fluid's temperature and/or pressure, returns at least a portion of it to expansion/compression assembly 201. Heat-transfer subsystem 204 may include pumps, valves, and other devices (not depicted explicitly in
Connected to the expansion/compression assembly 201 is a pipe 206 with a control valve 208 that controls a flow of fluid (e.g., gas) between assembly 201 and a storage reservoir 212 (e.g., one or more pressure vessels, IPVs, and/or LURs). The storage reservoir 212 may be in fluid communication with a heat-transfer subsystem 214 that alters the temperature and/or pressure of fluid removed from storage reservoir 212 and, after alteration of the fluid's temperature and/or pressure, returns it to storage reservoir 212. A second pipe 216 with a control valve 218 may be in fluid communication with the expansion/compression assembly 201 and with a vent 220 that communicates with a body of gas at relatively low pressure (e.g., the ambient atmosphere).
A control system 222 receives information inputs from any of expansion/compression assembly 201, storage reservoir 212, and other components of system 200 and sources external to system 200. These information inputs may include or consist essentially of pressure, temperature, and/or other telemetered measurements of properties of components of system 201. Such information inputs, here generically denoted by the letter “T,” are transmitted to control system 222 either wirelessly or through wires. Such transmission is denoted in
The control system 222 may selectively control valves 208 and 218 to enable substantially isothermal compression and/or expansion of a gas in assembly 201. Control signals, here generically denoted by the letter “C,” are transmitted to valves 208 and 218 either wirelessly or through wires. Such transmission is denoted in
The control system 222 may be any acceptable control device with a human-machine interface. For example, the control system 222 may include a computer (for example a PC-type) that executes a stored control application in the form of a computer-readable software medium. More generally, control system 222 may be realized as software, hardware, or some combination thereof. For example, control system 222 may be implemented on one or more computers, such as a PC having a CPU board containing one or more processors such as the Pentium, Core, Atom, or Celeron family of processors manufactured by Intel Corporation of Santa Clara, Calif., the 680×0 and POWER PC family of processors manufactured by Motorola Corporation of Schaumburg, Ill., and/or the ATHLON line of processors manufactured by Advanced Micro Devices, Inc., of Sunnyvale, Calif. The processor may also include a main memory unit for storing programs and/or data relating to the methods described above. The memory may include random access memory (RAM), read only memory (ROM), and/or FLASH memory residing on commonly available hardware such as one or more application specific integrated circuits (ASIC), field programmable gate arrays (FPGA), electrically erasable programmable read-only memories (EEPROM), programmable read-only memories (PROM), programmable logic devices (PLD), or read-only memory devices (ROM). In some embodiments, the programs may be provided using external RAM and/or ROM such as optical disks, magnetic disks, or other storage devices.
For embodiments in which the functions of controller 222 are provided by software, the program may be written in any one of a number of high-level languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, LISP, PERL, BASIC or any suitable programming language. Additionally, the software can be implemented in an assembly language and/or machine language directed to the microprocessor resident on a target device.
As described above, the control system 222 may receive telemetry from sensors monitoring various aspects of the operation of system 200, and may provide signals to control valve actuators, valves, motors, and other electromechanical/electronic devices. Control system 222 may communicate with such sensors and/or other components of system 200 (and other embodiments described herein) via wired or wireless communication. An appropriate interface may be used to convert data from sensors into a form readable by the control system 222 (such as RS-232 or network-based interconnects). Likewise, the interface converts the computer's control signals into a form usable by valves and other actuators to perform an operation. The provision of such interfaces, as well as suitable control programming, is clear to those of ordinary skill in the art and may be provided without undue experimentation.
System 200 may be operated so as to compress gas admitted through the vent 220 and store the gas thus compressed in reservoir 212. For example, in an initial state of operation, valve 208 is closed and valve 218 is open, admitting a quantity of gas into expansion/compression assembly 201. When a desired quantity of gas has been admitted into assembly 201, valve 218 may be closed. The motor/generator 202, employing energy supplied by a source not explicitly depicted in
During compression of the gas within assembly 201, fluid (i.e., gas, liquid, or a gas-liquid mixture) may be circulated between assembly 201 and heat-exchange assembly 204. Heat-exchange assembly 204 may be operated in such a manner as to enable substantially isothermal compression of the gas within assembly 201. During or after compression of the gas within assembly 201, valve 208 may be opened to enable high-pressure fluid (e.g., compressed gas or a mixture of liquid and compressed gas) to flow to reservoir 212. Heat-exchange assembly 214 may be operated at any time in such a manner as alter the temperature and/or pressure of the fluid within reservoir 212.
That system 200 may also be operated so as to expand compressed gas from reservoir 212 in expansion/compression assembly 201 in such a manner as to deliver energy to the motor/generator 202 will be apparent to all persons familiar with the operation of pneumatic, hydraulic, and electric machines.
System 300 further includes a first control valve 320 (208 in
In an initial state, the cylinder assembly 301 may contain a gas 306 (e.g., air introduced to the cylinder assembly 301 via valve 321 and vent 323) and a heat-transfer fluid 308 (which may include or consist essentially of, e.g., water or another suitable liquid). When the gas 306 enters the cylinder assembly 301, piston 302 is operated to compress the gas 306 to an elevated pressure (e.g., approximately 3,000 psi). Heat-transfer fluid (not necessarily the identical body of heat-transfer fluid 308) flows from pipe 313 to the pump 314. The pump 314 may raise the pressure of the heat-exchange fluid to a pressure (e.g., up to approximately 3,015 psig) somewhat higher than the pressure within the cylinder assembly 301, as described in U.S. Pat. No. 8,359,856, filed Jan. 19, 2011 (the '856 patent), the entire disclosure of which is incorporated by reference herein. Alternatively or in conjunction, embodiments of the invention add heat (i.e., thermal energy) to, or remove heat from, the high-pressure gas in the cylinder assembly 301 by passing only relatively low-pressure fluids through a heat exchanger or fluid reservoir, as detailed in U.S. patent application Ser. No. 13/211,440, filed Aug. 17, 2011 (the '440 application), the entire disclosure of which is incorporated by reference herein.
Heat-transfer fluid is then sent through a pipe 316, where it may be passed through a heat exchanger 303 (where its temperature is altered) and then through a pipe 318 to the spray mechanism 310. The heat-transfer fluid thus circulated may include or consist essentially of liquid or foam. Spray mechanism 310 may be disposed within the cylinder assembly 301, as shown; located in the storage reservoir 322 or vent 323; or located in piping or manifolding around the cylinder assembly, such as pipe 318 or the pipes connecting the cylinder assembly to storage reservoir 322 or vent 323. The spray mechanism 310 may be operated in the vent 323 or connecting pipes during compression, and a separate spray mechanism may be operated in the storage reservoir 322 or connecting pipes during expansion. Heat-transfer spray 311 from spray mechanism 310 (and/or any additional spray mechanisms), and/or foam from mechanisms internal or external to the cylinder assembly 101, enable substantially isothermal compression of gas 306 within cylinder assembly 301.
In some embodiments, the heat exchanger 303 is configured to condition heat-transfer fluid at low pressure (e.g., a pressure lower than the maximum pressure of a compression or expansion stroke in cylinder assembly 301), and heat-transfer fluid is thermally conditioned between strokes or only during portions of strokes, as detailed in the '440 application. Embodiments of the invention are configured for circulation of heat-transfer fluid without the use of hoses that flex during operation through the use of, e.g., tubes or straws configured for non-flexure and/or pumps (e.g., submersible bore pumps, axial flow pumps, or other in-line style pumps) internal to the cylinder assembly (e.g., at least partially disposed within the piston rod thereof), as described in U.S. patent application Ser. No. 13/234,239, filed Sep. 16, 3011 (the '239 application), the entire disclosure of which is incorporated by reference herein.
At or near the end of the compression stroke, control system 326 opens valve 320 to admit the compressed gas 306 to the storage reservoir 322. Operation of valves 320 and 321 may be controlled by various inputs to control system 326, such as piston position in cylinder assembly 301, pressure in storage reservoir 322, pressure in cylinder assembly 301, and/or temperature in cylinder assembly 301.
As mentioned above, the control system 326 may enforce substantially isothermal operation, i.e., expansion and/or compression of gas in cylinder assembly 301, via control over, e.g., the introduction of gas into and the exhausting of gas out of cylinder assembly 301, the rates of compression and/or expansion, and/or the operation of the heat-exchange subsystem in response to sensed conditions. For example, control system 326 may be responsive to one or more sensors disposed in or on cylinder assembly 301 for measuring the temperature of the gas and/or the heat-exchange fluid within cylinder assembly 301, responding to deviations in temperature by issuing control signals that operate one or more of the system components noted above to compensate, in real time, for the sensed temperature deviations. For example, in response to a temperature increase within cylinder assembly 301, control system 326 may issue commands to increase the flow rate of spray 311 of heat-exchange fluid 308.
Furthermore, embodiments of the invention may be applied to systems in which cylinder assembly 301 (or a chamber thereof) is in fluid communication with a pneumatic chamber of a second cylinder (e.g., as shown in
The fluid circuit of heat exchanger 303 may be filled with water, a coolant mixture, an aqueous foam, or any other acceptable heat-exchange medium. In alternative embodiments, a gas, such as air or refrigerant, is used as the heat-exchange medium. In general, the fluid is routed by conduits to a large reservoir of such fluid in a closed or open loop. One example of an open loop is a well or body of water from which ambient water is drawn and the exhaust water is delivered to a different location, for example, downstream in a river. In a closed-loop embodiment, a cooling tower may cycle the water through the air for return to the heat exchanger. Likewise, water may pass through a submerged or buried coil of continuous piping where a counter heat-exchange occurs to return the fluid flow to ambient temperature before it returns to the heat exchanger for another cycle.
In various embodiments, the heat-exchange fluid is conditioned (i.e., pre-heated and/or pre-chilled) or used for heating or cooling needs by connecting the fluid inlet 338 and fluid outlet 340 of the external heat-exchange side of the heat exchanger 303 to an installation such as a heat-engine power plant, an industrial process with waste heat, a heat pump, and/or a building needing space heating or cooling, as described in the '731 patent. Alternatively, the external heat-exchange side of the heat exchanger 303 may be connected to a thermal well 342 as depicted in
In the energy recovery or expansion mode of operation, storage reservoir 420 is filled with high-pressure air (or other gas) 432 and a quantity of heat-transfer fluid 434. The heat-transfer fluid 434 may be an aqueous foam or a liquid that tends to foam when sprayed or otherwise acted upon. The liquid component of the aqueous foam, or the liquid that tends to foam, may include or consist essentially of water with 2% to 5% of certain additives; these additives may also provide functions of anti-corrosion, anti-wear (lubricity), anti-biogrowth (biocide), freezing-point modification (anti-freeze), and/or surface-tension modification. Additives may include a micro-emulsion of a lubricating fluid such as mineral oil, a solution of agents such as glycols (e.g. propylene glycol), or soluble synthetics (e.g. ethanolamines). Such additives tend to reduce liquid surface tension and lead to substantial foaming when sprayed. Commercially available fluids may be used at an approximately 5% solution in water, such as Mecagreen 127 (available from the Condat Corporation of Michigan), which consists in part of a micro-emulsion of mineral oil, and Quintolubric 807-WP (available from the Quaker Chemical Corporation of Pennsylvania), which consists in part of a soluble ethanolamine. Other additives may be used at higher concentrations (such as at a 50% solution in water), including Cryo-tek 100/Al (available from the Hercules Chemical Company of New Jersey), which consists in part of a propylene glycol. These fluids may be further modified to enhance foaming while being sprayed and to speed defoaming when in a reservoir.
The heat-transfer fluid 434 may be circulated within the storage reservoir 420 via high-inlet-pressure, low-power-consumption pump 436 (such as described in the '731 patent). In various embodiments, the fluid 434 may be removed from the bottom of the storage reservoir 420 via piping 438, circulated via pump 436 through a heat exchanger 440, and introduced (e.g., sprayed) back into the top of storage reservoir 420 via piping 442 and spray head 444 (or other suitable mechanism). Any changes in pressure within reservoir 420 due to removal or addition of gas (e.g., via pipe 412) generally tend to result in changes in temperature of the gas 432 within reservoir 420. By spraying and/or foaming the fluid 434 throughout the storage reservoir gas 432, heat may be added to or removed from the gas 432 via heat exchange with the heat-transfer fluid 434. By circulating the heat-transfer fluid 434 through heat exchanger 440, the temperature of the fluid 434 and gas 432 may be kept substantially constant (i.e., isothermal). Counterflow heat-exchange fluid 446 at near-ambient pressure may be circulated from a near-ambient-temperature thermal well (not shown) or source (e.g., waste heat source) or sink (e.g., cold water source) of thermal energy, as described in more detail below.
In various embodiments of the invention, reservoir 420 contains an aqueous foam, either unseparated or partially separated into its gaseous and liquid components. In such embodiments, pump 436 may circulate either the foam itself, or the separated liquid component of the foam, or both, and recirculation of fluid into reservoir 420 may include regeneration of foam by apparatus not shown in
In the energy recovery or expansion mode of operation, a quantity of gas may be introduced via valve 416 and pipe 412 into the upper chamber 406 of cylinder 402 when piston 404 is near or at the top of its stroke (i.e., “top dead center” of cylinder 402). The piston 404 and its rod 430 will then be moving downward (the cylinder 402 may be oriented arbitrarily but is shown vertically oriented in this illustrative embodiment). Heat-exchange fluid 434 may be introduced into chamber 406 concurrently via optional pump 450 (alternatively, a pressure drop may be introduced in line 412 such that pump 450 is not needed) through pipe 452 and directional valve 454. This heat-exchange fluid 434 may be sprayed into chamber 406 via one or more spray nozzles 456 in such a manner as to generate foam 460. (In some embodiments, foam 460 is introduced directly into chamber 406 in foam form.) The foam 460 may entirely fill the entire chamber 406, but is shown in
System 400 is instrumented with pressure, piston position, and/or temperature sensors (not shown) and controlled via control system 462. At a predetermined position of piston 404, an amount of gas 432 and heat-transfer fluid 434 have been admitted into chamber 406 and valve 416 and valve 454 are closed. (Valves 416 and 454 may close at the same time or at different times, as each has a control value based on quantity of fluid desired.) The gas in chamber 406 then undergoes free expansion, continuing to drive piston 404 downward. During this expansion, in the absence of foam 460, the gas would tend to decrease substantially in temperature. With foam 460 largely or entirely filling the chamber, the temperature of the gas in chamber 406 and the temperature of the heat-transfer fluid 460 tend to approximate to each other via heat exchange. The heat capacity of the liquid component of the foam 460 (e.g., water with one or more additives) may be much higher than that of the gas (e.g., air) such that the temperature of the gas and liquid do not change substantially (i.e., are substantially isothermal) even over a many-times gas expansion (e.g., from 250 psig to near atmospheric pressure, or in other embodiments from 3,000 psig to 250 psig).
When the piston 404 reaches the end of its stroke (bottom dead center), the gas within chamber 406 will have expanded to a predetermined lower pressure (e.g., near atmospheric). Valve 424 will then be opened, allowing gas from chamber 406 to be vented, whether to atmosphere through pipe 422 and vent 426 (as illustrated here) or, in other embodiments, to a next stage in the expansion process (e.g., chamber in a separate cylinder), via pipe 422. Valve 424 remains open as the piston undergoes an upward (i.e., return) stroke, emptying chamber 406. Part or substantially all of foam 460 is also forced out of chamber 406 via pipe 422. A separator (not shown) or other means such as gravity separation is used to recover heat-transfer fluid, preferably de-foamed (i.e., as a simple liquid with or without additives), and to direct it into a storage reservoir 464 via pipe 466.
When piston 404 reaches top of stroke again, the process repeats with gas 432 and heat-transfer fluid 434 admitted from vessel 420 via valves 416 and 454. If additional heat-transfer fluid is needed in reservoir 420, it may be pumped back into reservoir 420 from reservoir 464 via piping 467 and optional pump/motor 468. In one mode of operation, pump 468 may be used to continuously refill reservoir 420 such that the pressure in reservoir 420 is held substantially constant. That is, as gas is removed from reservoir 420, heat-transfer fluid 434 is added to maintain constant pressure in reservoir 420. In other embodiments, pump 468 is not used or is used intermittently, the pressure in reservoir 420 continues to decrease during an energy-recovery process (i.e., involving removal of gas from reservoir 420), and the control system 462 changes the timing of valves 416 and 454 accordingly so as to reach approximately the same ending pressure when the piston 404 reaches the end of its stroke. An energy-recovery process may continue until the storage reservoir 420 is nearly empty of pressurized gas 432, at which time an energy-storage process may be used to recharge the storage reservoir 420 with pressurized gas 432. In other embodiments, the energy-recovery and energy-storage processes are alternated based on operator requirements.
In either the energy-storage or energy-compression mode of operation, storage reservoir 420 is typically at least partially depleted of high-pressure gas 432, as storage reservoir 420 also typically contains a quantity of heat-transfer fluid 434. Reservoir 464 is at low pressure (e.g., atmospheric or some other low pressure that serves as the intake pressure for the compression phase of cylinder 402) and contains a quantity of heat-transfer fluid 470.
The heat-transfer fluid 470 may be circulated within the reservoir 464 via low-power-consumption pump 472. In various embodiments, the fluid 470 may be removed from the bottom of the reservoir 464 via piping 467, circulated via pump 472 through a heat exchanger 474, and introduced (e.g., sprayed) back into the top of reservoir 464 via piping 476 and spray head 478 (or other suitable mechanism). By spraying the fluid 470 throughout the reservoir gas 480, heat may be added or removed from the gas via the heat-transfer fluid 470. By circulating the heat-transfer fluid 470 through heat exchanger 474, the temperature of the fluid 470 and gas 480 may be kept near constant (i.e., isothermal). Counterflow heat-exchange fluid 482 at near-ambient pressure may be circulated from a near-ambient-temperature thermal well (not shown) or source (e.g., waste heat source) or sink (e.g., cold water source) of thermal energy. In one embodiment, counterflow heat-exchange fluid 482 is at high temperature to increase energy recovery during expansion and/or counterflow heat-exchange fluid 482 is at low temperature to decrease energy usage during compression.
In the energy-storage or compression mode of operation, a quantity of low-pressure gas is introduced via valve 424 and pipe 422 into the upper chamber 406 of cylinder 402 starting when piston 404 is near top dead center of cylinder 402. The low-pressure gas may be from the ambient atmosphere (e.g., may be admitted through vent 426 as illustrated herein) or may be from a source of pressurized gas such as a previous compression stage. During the intake stroke, the piston 404 and its rod 430 will move downward, drawing in gas. Heat-exchange fluid 470 may be introduced into chamber 406 concurrently via optional pump 484 (alternatively, a pressure drop may be introduced in line 486 such that pump 484 is not needed) through pipe 486 and directional valve 488. This heat exchange fluid 470 may be introduced (e.g., sprayed) into chamber 406 via one or more spray nozzles 490 in such a manner as to generate foam 460. This foam 460 may fill the chamber 406 partially or entirely by the end of the intake stroke; for illustrative purposes only, foam 460 is shown in
At the end of the stroke, with piston 404 at the end-of-stroke position, valve 424 is closed. Valve 488 is also closed, not necessarily at the same time as valve 424, but after a predetermined amount of heat-transfer fluid 470 has been admitted, creating foam 460. The amount of heat-transfer fluid 470 may be based upon the volume of air to be compressed, the ratio of compression, and/or the heat capacity of the heat-transfer fluid. Next, piston 404 and rod 430 are driven upwards via mechanical means (e.g., hydraulic fluid, hydraulic cylinder, mechanical crankshaft) to compress the gas within chamber 406.
During this compression, in the absence of foam 460, the gas in chamber 406 would tend to increase substantially in temperature. With foam 460 at least partially filling the chamber, the temperature of the gas in chamber 406 and the temperature of the liquid component of foam 460 will tend to equilibrate via heat exchange. The heat capacity of the fluid component of foam 460 (e.g., water with one or more additives) may be much higher than that of the gas (e.g., air) such that the temperature of the gas and fluid do not change substantially and are near-isothermal even over a many-times gas compression (e.g., from near atmospheric pressure to 250 psig, or in other embodiments from 250 psig to 3,000 psig).
The gas in chamber 406 (which includes, or consists essentially of, the gaseous component of foam 460) is compressed to a suitable pressure, e.g., a pressure approximately equal to the pressure within storage reservoir 420, at which time valve 416 is opened. The foam 460, including both its gaseous and liquid components, is then transferred into storage reservoir 420 through valve 416 and pipe 412 by continued upward movement of piston 404 and rod 430.
When piston 404 reaches top of stroke again, the process repeats, with low-pressure gas and heat-transfer fluid 470 admitted from vent 426 and reservoir 464 via valves 424 and 488. If additional heat-transfer fluid is needed in reservoir 464, it may be returned to reservoir 464 from reservoir 420 via piping 467 and optional pump/motor 468. Power recovered from motor 468 may be used to help drive the mechanical mechanism for driving piston 404 and rod 430 or may be converted to electrical power via an electric motor/generator (not shown). In one mode of operation, motor 468 may be run continuously, while reservoir 420 is being filled with gas, in such a manner that the pressure in reservoir 420 is held substantially constant. That is, as gas is added to reservoir 420, heat-transfer fluid 434 is removed from reservoir 420 to maintain substantially constant pressure within reservoir 420. In other embodiments, motor 468 is not used or is used intermittently; the pressure in reservoir 420 continues to increase during an energy-storage process and the control system 462 changes the timing of valves 416 and 488 accordingly so that the desired ending pressure (e.g., atmospheric) is attained within chamber 406 when the piston 404 reaches bottom of stroke. An energy-storage process may continue until the storage reservoir 420 is full of pressurized gas 432 at the maximum storage pressure (e.g., 3,000 psig), after which time the system is ready to perform an energy-recovery process. In various embodiments, the system may commence an energy-recovery process when the storage reservoir 420 is only partly full of pressurized gas 432, whether at the maximum storage pressure or at some storage pressure intermediate between atmospheric pressure and the maximum storage pressure. In other embodiments, the energy-recovery and energy-storage processes are alternated based on operator requirements.
Assembly 502 is in selective fluid communication with a storage reservoir 512 (e.g., 212 in
System 500 may compress air at atmospheric pressure (admitted to system 500 through the vent 520) stagewise through assemblies 506 and 502 to high pressure for storage in reservoir 512. System 500 may also expand air from high pressure in reservoir 512 stagewise through assemblies 502 and 506 to a low pressure (e.g., approximately 5 psig) for venting to the atmosphere through vent 520.
As described in U.S. Pat. No. 8,191,362, filed Apr. 6, 2011 (the '362 patent), the entire disclosure of which is incorporated by reference herein, in a group of N cylinder assemblies used for expansion or compression of gas between a high pressure (e.g., approximately 3,000 psig) and a low pressure (e.g., approximately 5 psig), the system will contain gas at N−1 pressures intermediate between the high-pressure extreme and the low pressure. Herein each such intermediate pressure is termed a “mid-pressure.” In illustrative system 500, N=2 and N−1=1, so there is one mid-pressure (e.g., approximately 250 psig during expansion) in the system 500. In various states of operation of the system, mid-pressures may occur in any of the chambers of a series-connected cylinder group (e.g., the cylinders of assemblies 502 and 506) and within any valves, piping, and other devices in fluid communication with those chambers. In illustrative system 500, the mid-pressure, herein denoted “mid-pressure P1,” occurs primarily in valves, piping, and other devices intermediate between assemblies 502 and 506.
Assembly 502 is a high-pressure assembly: i.e., assembly 502 may admit gas at high pressure from reservoir 512 to expand the gas to mid-pressure P1 for transfer to assembly 502, and/or may admit gas at mid-pressure P1 from assembly 506 to compress the gas to high pressure for transfer to reservoir 512. Assembly 506 is a low-pressure assembly: i.e., assembly 506 may admit gas at mid-pressure P1 from assembly 502 to expand the gas to low pressure for transfer to the vent 520, and/or may admit gas at low pressure from vent 520 to compress the gas to mid-pressure P1 for transfer to assembly 502.
In system 500, extended cylinder assembly 502 communicates with extended cylinder assembly 506 via a mid-pressure assembly 514. Herein, a “mid-pressure assembly” includes or consists essentially of a reservoir of gas that is placed in fluid communication with the valves, piping, chambers, and other components through or into which gas passes. The gas in the reservoir is at approximately at the mid-pressure which the particular mid-pressure assembly is intended to provide. The reservoir is large enough so that a volume of mid-pressure gas approximately equal to that within the valves, piping, chambers, and other components with which the reservoir is in fluid communication may enter or leave the reservoir without substantially changing its pressure. Additionally, the mid-pressure assembly may provide pulsation damping, additional heat-transfer capability, fluid separation, and/or house one or more heat-transfer sub-systems such as part or all of sub-systems 504 and/or 508. As described in the '362 patent, a mid-pressure assembly may substantially reduce the amount of dead space in various components of a system employing pneumatic cylinder assemblies, e.g., system 500 in
Alternatively or in conjunction, pipes and valves (not shown in
A control system 528 (e.g., 222 in
It will be clear to persons reasonably familiar with the art of pneumatic machines that a system similar to system 500 but differing by the incorporation of one, two or more mid-pressure extended cylinder assemblies may be devised without additional undue experimentation. It will also be clear that all remarks herein pertaining to system 500 may be applied to such an N-cylinder system without substantial revision, as indicated by elliptical marks 522. Such N-cylinder systems, though not discussed further herein, are contemplated and within the scope of the invention. As shown and described in the '678 patent, N appropriately sized cylinders, where N≧2, may reduce an original (single-cylinder) operating fluid pressure range R to R1/N and correspondingly reduce the range of force acting on each cylinder in the N-cylinder system as compared to the range of force acting in a single-cylinder system. This and other advantages, as set forth in the '678 patent, may be realized in N-cylinder systems. Additionally, multiple identical cylinders may be added in parallel and attached to a common or separate drive mechanism (not shown) with the cylinder assemblies 502, 506 as indicated by ellipsis marks 532, 536, enabling higher power and air-flow rates.
Pressurized fluids may also be stored in accordance with various embodiments of the present invention, alternatively or additionally to the use of LURs, in insulated pipeline vessels (IPVs).
The single length of pipeline 602 may include or consist essentially of two or more shorter lengths of pipe (e.g., in this illustrative pipeline 602, the sub-lengths 604, 606), welded together or otherwise joined in fluid-proof manner at one or more joints 608. End caps 610, 612 seal the ends of the pipeline 602 to form an enclosed volume: in this illustrative case, end-caps 610, 612 are bolted to flanges on the ends of pipeline 602. Pipeline 602 is generally tilted at some angle θ1 from the horizontal. A layer of insulation 614 covers the outer surface of the pipeline 602. Additional insulation or protective coatings (not shown) may be applied as layers to the interior of the pipeline 602. Pipeline 602 may be substantially or wholly buried within a berm or fill capsule 616 including or consisting essentially of fill 618 and a substantially impermeable envelope 620. The fill 618 may include or consist essentially of various forms of earth (e.g., sand, crushed rock), an artificial thermal insulation material, or a mixture of earth and insulating material. The fill 618 is preferably dry (i.e., contains no substantial fraction of liquid water), in order that the thermal insulating power of the fill capsule 616 may be maximal. The impermeable envelope 620 prevents circulation of liquid and possibly air into and through the fill capsule 616, increasing the thermal insulating power of the fill capsule 616. The thickness of the fill capsule 616 as measured from various points on the outer surface of the pipeline 612 to the impermeable envelope 620 may vary from point to point, but will preferably be chosen to meet structural requirements and produce an insulating effect on the pipeline 602 that justifies the cost of constructing the fill capsule 616 (e.g., justifies the cost of constructing the fill capsule 616 in terms of levelized cost of energy of the storage subsystem comprising IPV system 600).
The lower end 622 of the pipeline 602 in the illustrative IPV system 600 is allowed to protrude from the fill capsule 616. The system 600 may be partly or entirely buried in earth (e.g., the earth naturally present at a given installation site; not shown), in which case a trench, pit, or vault (not shown) may be constructed to allow maintenance access to the lower end 622 of the pipeline 602.
The first insulation layer 614 and the insulating fill capsule 616 serve jointly to slow to an acceptable rate the exchange of thermal energy between the fluid contents of pipeline 616 and the ambient environment of system 600.
The preferable value of the angle θ1, and of other angles of IPV tilt in other illustrative systems described herein, depends on the amounts of liquid found in each IPV in various states of system operation, the rates at which liquid is introduced into and removed from each IPV, and the inner dimensions of each IPV (e.g., diameter, length, locations of points of piping insertion). In accordance with various embodiments of the invention, the angle of IPV tilt may even be altered during operation via mechanical means, e.g., a tiltable stage.
The pipeline sections 702 of the illustrative array 700 are parallel to each other and lie in a common plane; in various embodiments, the pipeline sections 702 may not be co-planar. The plane in which the pipeline sections 702 lie is tilted at some angle θ1 from the horizontal, with the lower end of the plane at the left-hand side of
At the downhill end of each IPV section in
Uniformly spaced, straight, parallel (at least in one plane) IPV pipeline sections of uniform diameter and identical length and diameter are depicted in
In illustrative IPV array 700, the manifold pipe 710 is tilted at some angle θ with sufficient to guarantee downhill flow of liquid from all N IPV pipeline sections to the low point 722 of manifold 710. A sump or reservoir (not shown) located approximately at point 722 may allow an accumulation of liquid. A pump (not shown) may be employed to raise liquid from point 722 or from a sump located approximately at point 722 to the liquid access point 712. Gas pressure in the N IPV pipeline sections may contribute to or entirely cause the movement of liquid from the IPV s to the access point 712. In various other embodiments, angle θ is zero and pumping and/or gas pressure are entirely responsible for the movement of liquid from the N IPV pipeline sections to the access point 712.
In various embodiments, system 800 includes a storage reservoir recessed into a shaft 802 in the earth and containing fluid that may be pressurized and/or thermally conditioned (e.g., heated, cooled, or maintained at an approximately constant temperature). Pressurization of the fluid stored by system 800 enables the storage of elastic potential energy; heating or cooling of the fluid enables the storage of exergy (work available from a system in disequilibrium). Typically, although not necessarily, the fluid is thermally conditioned by heating or by maintenance at an approximately constant temperature rather than by cooling. A fluid may be both pressurized and thermally conditioned. Such pressurization and thermal conditioning may be controlled functions of time. Shaft 802 may be lined with a material that prevents leakage of fluids into or out of the shaft 802; the material may also act as a thermal insulator to assist in thermal conditioning or in mitigating the exchange of heat between the fluid and the surrounding earth. Alternatively or additionally, shaft 802 may be lined with a material that acts primarily as a thermal insulator.
In the illustrative embodiment depicted in
As the shaft 802 is sunk, a shaft liner 804 (which includes or consists essentially of reinforced concrete and/or some other material) forming an interior wall of the shaft 802 may be installed in a series of rings, each ring being added below previous rings as the excavating machine increases the depth of the bore by a suitable amount. The inner and/or outer surface of the shaft liner 804 may be coated with one or more coatings or additional layers of material (not shown in
In general, a lined underground reservoir constructed within a shaft 802 of larger depth and/or radius will be capable of storing more fluid and more thermal and elastic potential energy than a shaft 802 of relatively small depth and/or radius.
In various embodiments including the illustrative embodiment depicted in
The cavity liner 808 (including its dome 814), the load-bearing cap 816, the infill 818, the shaft liner 804, and the surrounding rock 820 constitute a sealed recessed storage reservoir. The reservoir may include other components and materials in various other embodiments (e.g., an insulating layer within or around the cavity liner 808).
In various other embodiments, the invert (floor) and sides of the cavity liner 808 may be in direct contact with the surrounding rock 820; the dome 814 may not be a distinct structure from the concrete cap 816; and/or a system of piping may surround the cavity liner 808 in a manner that tends to drain water away from the cavity liner 808. Water so diverted from the cavity liner 808 may be conducted away through piping not depicted in
In the illustrative embodiment depicted in
Piping 826 passes from the surface, through the infill 818 (as shown in
Fluid expelled from shaft 802 by pump 828 may be directed via piping 826 to reservoirs, cylinders, or other components of an energy storage and recovery system (not shown). Fluid may be directed via piping 830 to a spray head or nozzle (not explicitly shown), or array of spray heads and/or nozzles, for the generation of a foam or droplet spray 832 within the gas-filled portion of liner 808. The foam or droplet spray 832 may exchange heat with the fluids inside liner 808. In various embodiments, fluid exiting the interior of the liner 808 through piping 826 is passed through pumps, valves, heat exchangers, and other devices (not shown) before being returned to the interior of liner 808 through piping 830. Additional piping 834 allows the addition to or removal from the interior of liner 808 of fluid (e.g., gas).
In another embodiment, not shown, multiple fluid liners 808 may be situated in a single shaft 802. The fluid liners 808 may be stacked one atop another, or arranged in a vertically-oriented bundle of tube-like liners, or otherwise arranged in order to enable convenient construction, spatially even distribution of forces, and/or other advantages. In some cases, multiple narrower-diameter fluid liners (e.g., capped pipes, such as one or more IPVs) may be less expensive than a single liner 808 of comparable capacity endowed with a single large, welded inner liner 812.
Although the storage capacity and functions of system 900 may be similar to those of system 800 in
Once cavity 902 has been excavated, it is lined with a cavity liner 912. In this illustrative embodiment, the cavity liner 912 may include or consist essentially of multiple layers, not all of which are depicted in
System 800 and similar embodiments may have advantages over system 900 and similar embodiments. In particular, the access tunnels 904, 906, 908 and cavity 902 are, in general, excavated by workers working in situ, underground, and the lining 912 of the cavity 902 is typically excavated by workers working with in the cavity 902. Such work may be slow, expensive, and relatively dangerous. In contrast, the wide vertical shaft 802 of system 800 may be excavated, in some instances, mostly or entirely by a machine operated from the surface, and the cavity liner 808, with its inside liner 812, may be partly or entirely constructed at the surface and lowered into the shaft 802. Greater speed, lower cost, and higher safety for comparable capacity may thus, in some instances, be achieved in the construction of system 800. Additionally, system 800 does not need additional access areas and underground tunnel for access as may be required for system 900.
In various embodiments it may be advantageous to locate the access tunnel entrance 926 at a point closer a point on the surface directly above the cavity 902.
The cavity 902 in
The method of shaft-sinking depicted in
The joint 1212 is capable of raising, lowering, and rotating the boom 1214; the boom 1214 may extend and retract. By appropriately combining (e.g., under the direction of a human operator, automatic control system, or both) the motions of the stage 1206, joint 1212, and boom 1214, the working surface of the cutting head 1216 may be brought into contact with any point on the walls or invert of the shaft 1204.
Rock fragments broken from the walls and/or invert of the shaft 1204 by the cutting head 1216 typically accumulate as debris 1218 upon the invert of the shaft 1204. Such debris may be removed by a variety of techniques. The illustrative system 1200 introduces water through piping (not shown) that mixes with the debris 1218 to form a slurry. Alternatively, the shaft 1204 may be wholly or partly filled with water during operation of the system 1200. The slurrified debris 1218, whether its water portion is introduced through piping or through filling of the shaft 1204 with water, is pumped through a pipe 1220 to the surface. (Two portions of pipe 1220 are depicted in
In
It is clear that by lowering the roadheader rig, breaking up rock with the cutting head, and removing debris from the shaft 1204, the shaft 1204 may be sunk to any depth to which the support rig 1202 is capable of lowering the roadheader rig and at which the walls of the shaft 1204 remain stable. The walls of the shaft 1200 may be segmentally covered and strengthened by a liner (not shown) as the shaft 1200 is incrementally deepened. Within shaft 1200, a recessed storage reservoir such as that depicted in
The network of drainage pipes within the lining 1400 may be used to pump water out of the shaft during construction. Various illustrative methods of construction of the lining 1400 are considered further in
The storage of relatively hot (e.g., 60° C. or higher) pressurized fluid within a lined underground reservoir (e.g., cavern 1402 in
The strain undergone by the steel liner over the first cycle 1602 varies over a range R1. In a second hypothetical temperature-pressure cycle 1608, the contents of the reservoir, and thus the lining in contact with the contents, vary moderately in temperature as the pressure of the contents changes from a low pressure 1604 to a high pressure 1606 and then back to the low pressure 1604 again: i.e., the temperature increases with increasing pressure and decreases with decreasing pressure. The strain undergone by the steel liner over the second cycle 1608 varies over a range R2 that is significantly smaller than the stress range R1 of the first cycle 1602, and the peak strain undergone by the steel liner for cycle 1608 is less than that undergone for cycle 1602.
In a third hypothetical temperature-pressure cycle 1610, the contents of the reservoir, and thus the lining, vary more widely than in cycle 1608 as the pressure within the reservoir is raised from a low pressure 1604 to a high pressure 1606 and then lowered to the low pressure 1604 again: i.e., the temperature increases with increasing pressure and decreases with decreasing pressure. The strain undergone by the steel liner over the second cycle 1608 varies over a range R3 which is smaller than the range R1 and larger than the range R2; moreover, the sense or sign of the relationship between strain and pressure/temperature has been reversed from that of cycle 1602 and cycle 1608, that is, the liner experiences less strain at peak pressure 1606 and temperature than at lowest pressure 1604 and temperature. Different relationships between temperature, pressure, and strain than those shown in
Illustrative methods of constructing portions of a lined underground reservoir in various embodiments of the present invention are now considered.
After the concrete 1714 hardens, firmly undergirding the invert liner 1700, the water 1716 is removed from the invert liner 1710. A steel liner dome 1718 is then constructed atop the invert liner 1710 (Stage B). The dome 1718 may be jacked up or otherwise raised incrementally as sections of wall-lining material 1720 are assembled (e.g., by welding) into rings 1722 beneath the dome 1718. In this manner, the steel liner dome 1718 is raised until it is close to the domed ceiling of the cavity 1702, at which point an approximately cylindrical set of rings 1722 has been fabricated thereunder.
At Stage C, a complete inner steel liner 1724 has been constructed within the cavity 1702. Trucks (e.g., truck 1726) bring concrete to the worksite through the middle access tunnel 1706 and pour and/or inject additional concrete 1728 into the space between the liner 1724 and the surrounding rock face. Some of the concrete 1728 forms a plug 1730 in the lower access tunnel. Water within the liner 1724 prevents the liner 1724 from being deformed by the weight of the concrete 1728.
After Stage C, in phases of construction not depicted in
When the lined underground reservoir 1700 has been completed, the water within the liner 1724 may be used to pressure-test the liner 1724. After completed testing, the water is removed by injection of the stored product, e.g., compressed air. This procedure ensures the stability of the storage, as there is always an internal overpressure from the water and/or the stored product.
In Stage B, the wall-lining portions of the liner 1806 have all been emplaced, and a dome liner 1816 is being lowered into the shaft 1802. Following emplacement of the dome liner 1816, a concrete liner or surround 1808 may be poured and/or injected into the space between the liner 1806 and the surrounding rock, as depicted in
In Stage C, the concrete liner 1808 has been emplaced, overfill 1818 (e.g., crushed rock; concrete; reinforced concrete) has been emplaced, and at least three conduits or pipes 1820, 1822, and 1824 have been emplaced to enable fluid communication (and, in various embodiments, electrical, informatic, and mechanical communication) between the interior of the lined underground reservoir 1800 and facilities (not shown) on the surface. Gas may be injected into or removed from the reservoir 1800 through pipe 1820, heat-exchange fluid (e.g., liquid, foam; not shown in
The method of construction depicted in
In Stage B, further segmental portions 1914 have been joined to the liner 1904. The depth of the body of water 1906 has been lowered in order to keep the level at which further segmental portions 1914 are added to the liner 1904 at or near the surface.
In Stage C, the liner 1904 has been completed and rests in the prefabricated undergirding concrete liner 1908.
In Stage D, additional concrete 1916 has been added to cover, protect, and strengthen a dome liner 1918, and at least three conduits or pipes 1920, 1922, and 1924 have been emplaced to enable fluid communication (and, in various embodiments, electrical, informatic, and mechanical communication) between the lined underground reservoir 1900 and facilities (not shown) on the surface. Gas may be injected into or removed from the reservoir 1900 through pipe 1920, heat-exchange fluid (e.g., liquid, foam; not shown in
In Stage E, overfill 1926 (e.g., crushed rock; concrete; reinforced concrete) has been added above the concrete 1916. The weight and/or mechanical strength of the overfill 1916 serve to restrain expansion of the lined underground reservoir 1900 when the reservoir 1900 is filled with fluid at high pressure.
The method of construction partly depicted in
In Stage B, a body of water 2006 mostly fills the shaft 2002. An invert liner (e.g., dome shaped liner) 2020 and a segmental portion 2018 of the liner 2004 have been assembled at or near the surface and are floating upon the body of water 2006. One or more spacers 2014 (e.g., beams, ribs, struts) that can hold the liner 2004 a desired distance away from the surrounding rock face at all points are attached to the outside of the liner 2004. Also, a network or basket of rebar 2016 has been constructed around and attached to the portion of the liner 2004 constructed as of Stage B. As further segmental portions of steel liner 2018 and rebar network 2016 of the liner 2004 are added to the liner 2004, water may be removed from the shaft 2002 through the pipe network 2010, lowering the level of the body of water 2006 and thus permitting the joining of further segmental portions 2018 and portions of network 2016 to the liner 2004 to proceed at or near the surface of the earth. When the liner 2004 is completed, it may be lowered to the bottom of the shaft 2002 by the removal of all water from the shaft 2002. Concrete is then poured and/or injected into the space between the liner 2004 and the surrounding rock face, approximately as described for the emplacement of the concrete liner 1728 in
The construction of cavity liners for lined underground reservoirs—e.g., the multi-layered liner depicted in
In other embodiments, not shown, a cavity liner (e.g., a reinforced concrete base lining) may be constructed by using slip-form casting, in which concrete is poured into a continuously moving form. This may be very efficient for a long vertical shaft and produces a very smooth surface on which may be installed the impermeable lining.
Plastic liners may include or consist essentially of pre-manufactured sheets or plates of polymer material (e.g., approximately 10 mm thick) that are welded or melted together in situ to form a liner, or of liners constructed in situ by spraying or painting, or by other means (e.g., in situ inflation and emplacement of a liner manufactured elsewhere). Pre-manufactured sheet-type polymer liners may include or consist essentially of thermoplastics such as polypropylene and high-density polyethylene. Spray-on liners may include or consist essentially of thermosetting plastics such as epoxy and polyurethane. Liners may also consist of sandwich or composite materials, e.g., a combination of polyurethane for flexibility and glass-fiber reinforced epoxy for high strength and chemical resistance.
In Stage F, additional material 2314 such as a reinforced concrete plug (not shown), additional concrete, and overfill has been emplaced over the liner 2312. The additional material 2314 may additionally include a plug (not shown) that may extend into the surrounding rock and may serve as or separately consist of a plug to distribute upward pressure forces from the dome of the liner 2312, in part or entirely. In other stages of the illustrative construction process depicted in
A range of materials may be used for the infill barrier 2418: e.g., the infill barrier 2418 may include or consist essentially of rock tailings produced during the excavation of the shaft holding system 2400, or of such rock tailings mixed or grouted with a binding agent (e.g., cement), or of concrete, or of reinforced concrete. Although infill barrier 2418 is represented in
The depth at which cavity 2402 is located beneath the earth's surface, the temperatures of the fluids stored within the cavity 2402 at various times, and the nature of the layering materials with which the cavity 2402 is surrounded (e.g., insulating, non-insulating), are among the factors that may influence the exchange of thermal energy between the contents of cavity 2402 and the surrounding rock 2422. Since the mass of the Earth is effectively infinite compared to the mass of the contents of cavity 2402, the temperature-depth gradient of rock mass 2422 will tend to retain its undisturbed, natural value away from the immediate vicinity of the lined underground reservoir 2400. Therefore, if the cavity 2402 is not lined with an effective insulator, exchange of heat between the contents of cavity 2402 and the rock 2422 may constitute either (a) a path of net energy loss for system 2400, i.e., if the contents of the cavity 2402 are warmer on average than surrounding rock 2422, or (b) a path of net energy gain for system 2400, if the contents of the cavity 2402 are cooler on average than the rock 2422. For example, an adiabatic compressed-air energy storage system with stored air cycled (stored and released) daily with a maximum storage pressure of 5 MPa (725 psi) and a constant air injection temperature of 21.5° C. may experience approximately 3.3% thermal energy loss. For a relatively deep cavity 2402, and/or relatively cool fluid contents of cavity 2402, and/or a locally steep temperature/depth gradient, this relationship may be reversed: i.e., the system 2400 may function not only as a system for storing energy, but also as a harvester of geothermal energy. The ability of any particular embodiment to function partly as a harvester of geothermal energy may depend on depth, construction materials, fluid operating temperatures, operational cycling, and/or local geothermal conditions, among other factors. The concrete used in the lined underground reservoir walls may be of an insulating type having a the thermal conductivity less than a standard concrete mixture, decreasing the rate of exchange between the surrounding rock 2422 and the fluid within the cavity 2402. The insulating concrete may be located throughout or only at certain layers such as closest to the surrounding rock 2422. Examples of insulating concrete include cellular concretes (e.g., where air voids are incorporated into concrete) and aggregate concretes (e.g., concrete made with insulating aggregates such as expanded perlite, vermiculate, and/or polystyrene pellets). Physical properties of insulating concrete vary according to mix designs, with lower density typically corresponding to higher insulating value. Insulating concretes may have thermal conductivities on the order of 2 to 10 times lower than a non-insulating concrete (where heavyweight non-insulating concrete may have a thermal conductivity exceeding 1 W/m-K). Thus, the thermal conductivity of insulating concrete utilized in various embodiments of the invention may be between approximately 0.1 W/m-K and approximately 0.5 W/m-K. Insulating layers (not shown) of other materials (e.g., polyurethane foam) may also be applied interior or exterior to the cavity 2402, decreasing the rate of exchange between the surrounding rock 2422 and the fluid with the cavity 2402.
Given the finite flexibility of real (i.e., not idealized) earth material, some degree of uplift or doming of the area 2428—though preferably no shearing along surface 2430—may occur in any real-world setting. Such doming is deemed acceptable if it does not damage components of the system 2400, either immediately or over repeated fill-and-empty cycles; such doming is deemed unacceptable if it destroys components of the system 2400 or shortens their working lifespan significantly. The system 2400 is preferably designed, therefore, to contain the upward-acting forces 2432 generated by the pressurized contents of cavity 2402 not only to the extent that catastrophic failure of the cavity 2402 (i.e., breakthrough of gas to the surface, or explosion of part or all of the overlying area 2428) is practically impossible, but, further, to the extent that the longevity of system 2400 is not compromised.
In the absence of an advantageously shaped top-plug, as depicted in
Plugs (pressure barriers) of orientations or cross-sectional forms different from those illustratively depicted in
Storage of a volume of heat-exchange liquid may also be achieved in various other embodiments without use of surface vessels for liquid storage.
If the lining surrounding the inner cavity of a lined underground reservoir storage system is of sufficient strength, infilling may be dispensed with, and the lined portion of the storage system may protrude above the surface of the ground.
In various embodiments, system 2700 is a recessed LUR containing fluid that may be pressurized and/or heated. Pressurization of the fluid enables the storage of elastic potential energy; heating of the fluid enables the storage of thermal energy; and a stored fluid may be both pressurized and heated. Shaft 2702 may be lined with an impermeable material that prevents leakage of fluids into or out of the shaft 2702; the material may also act as a thermal insulator. Alternatively or additionally, shaft 2702 may be lined with a distinct layer that acts primarily as a thermal insulator.
In the illustrative embodiment depicted in
Additionally, a cap or dome 2708 is connected to the top of the shaft 2702 and liner 2704 in order to produce a sealed recessed storage reservoir. Cap 2708 may include or consist essentially of reinforced concrete and/or one or more other durable materials and, like the liner 2704 of shaft 2702, may be coated with one or more coatings or additional layers of material (not shown in
In the illustrative embodiment depicted in
Piping 2714 passes through cap 2708 (or, in various other embodiments, some portion of the liner 2704 of reservoir 2700) and extends to near the bottom of the shaft 2702. A pump 2716 is capable of drawing fluid 2710 into piping 2714 and expelling the fluid from the shaft 2702. Power, control, and data cables (not shown) may also enter reservoir 2700, enabling the control and operation of pump 2716 and communication with sensors (not shown) inside shaft 2702 that provide information to operators of reservoir 2700 on various physical variables, e.g., pressure and temperature of the fluid contents of reservoir 2700 and depth of fluid 2710.
Fluid expelled from reservoir 2700 by pump 2716 may be directed via piping 2718 to reservoirs, cylinders, or other components of an energy storage and recovery system (not shown), or may be directed via piping 2720 to a spray head or nozzle (not explicitly shown) for the generation of a foam or droplet spray 2722 within the gas-filled portion of reservoir 2700. The foam or droplet spray 2722 may exchange heat with the fluids inside reservoir 2700. In various embodiments, fluid passing through piping 2720 is additionally passed through pumps, valves, heat exchangers, and other devices (not shown) before being returned to the interior of reservoir 2700. Additional piping 2724 allows the addition to or removal from reservoir 2700 of gas 2712.
A liner 2804 (which may include or consist essentially of, e.g., reinforced concrete and steel and/or other durable materials) within the interior wall of the shaft 2802 may be installed to construct a recessed reservoir capable of holding fluids at high pressure and/or at elevated temperature, as described with respect to
The separated high pressure and/or elevated temperature gas may be delivered to shaft 2802 via a pipe 2824. Liquid 2810 and 2830 may be removed from shaft 2802 via pumps 2816 and 2836. Pump 2836 will generally consume less power to pump the liquid 2830 (at least as a function of volume of liquid pumped) than will pump 2816 to pump liquid 2810, as the vertical distance from liquid 2830 to the ground surface is much less. Thus, in preferred embodiments of the invention, most or substantially all of the liquid in shaft 2802 is directed to secondary containment 2814, with only a fraction of the liquid being at the bottom of shaft 2802.
Fluid expelled from shaft 2802 by pump 2816 and from secondary containment 2814 by pump 2836 may be directed via piping 2818 to reservoirs, cylinders, or other components of an energy storage and recovery system (not shown), or may be directed via to a spray head or nozzle for the generation of a foam or droplet spray 2822 within the gas-filled portion of shaft 2802 and/or secondary containment 2814 (spray or foam in containment 2814 is not shown). The foam or droplet spray 2822 may exchange heat with the fluids inside shaft 2802 and/or secondary containment 2814. In various embodiments, fluid passing through piping 2818 is additionally passed through pumps, valves, heat exchangers, and other devices (not shown) before being returned to the interior of shaft 2802. Additional piping 2824 allows the addition to or removal from shaft 2802 of gas 2812.
Generally, the systems described herein featuring IPVs, LURs and/or recessed reservoirs may be operated in both an expansion mode and in compression mode as part of a full-cycle energy storage system with high efficiency. For example, the systems described herein may be operated so as to efficiently (e.g., substantially isothermally) store pressure and thermal potential energy delivered from an energy storage system and possibly from other sources as well, or so as to efficiently deliver to the energy storage system pressure and thermal potential energy stored within the systems described herein.
Heat-exchange liquid may be caused to exchange heat with pressurized gas in a lined underground reservoir or IPV by several methods, e.g., bringing the heat-exchanged fluid and pressurized gas into direct contact with each other or by employing a non-mixing heat exchanger that permits the liquid and gas to exchange heat through impermeable, heat-conductive barriers. If heat-exchange liquid is brought into contact with pressurized gas for the purpose of exchanging heat, it is in general preferable that the heat-exchange liquid be divided into droplets or mixed with the gas in the form of a foam in order to increase surface area over which the gas and liquid may exchange heat; or, if the volume of liquid is large relative to the volume of gas, the gas may be bubbled through the liquid to increase the surface area of contact. Lower cost for a given rate of heat exchange between bodies of liquid and gas is generally achieved by bringing the liquid and gas into direct contact with each other.
Gas stored in lined underground reservoirs or IPVs may be thermally conditioned either in situ, that is, within the reservoir or IPV, or in external devices (e.g., sprayers, bubblers, or heat exchangers located in a facility on the surface of the earth). It is generally preferable, for in situ thermal conditioning, that the heat-exchange liquid and stored gas be brought into direct contact with each other by spraying or foaming the heat-exchange liquid into the stored gas. Alternatively or additionally, heat-exchange fluid may be mixed with stored gas in order to maintain the gas at an approximately constant temperature as it is expanded in, e.g., cylinder. That is, approximately isothermal expansion of the gas may be achieved by mixing of heat-exchange liquid at an appropriate rate and temperature, as droplets or the liquid component of a foam, with the gas. Thermal conditioning of a gas may occur during compression of the gas, storage of the gas, or expansion of the gas.
A pump 2914 and piping 2916 may convey the heat-exchange liquid to a device herein termed a “mixing chamber” 2918. Gas from the reservoir 2910 may also be conveyed (via piping 2920) to the mixing chamber 2918. Within the mixing chamber 2918, a foam-generating mechanism 2922 combines the gas from the reservoir 2910 and the liquid conveyed by piping 2916 to create foam 2924 of a certain grade (i.e., bubble size variance, average bubble size, void fraction), herein termed Foam A, inside the mixing chamber 2918.
The mixing chamber 2918 may contain a screen 2926 or other mechanism (e.g., source of ultrasound) to vary or homogenize foam structure. Screen 2926 may be located, e.g., at or near the exit of mixing chamber 2918. Foam that has passed through the screen 2926 may have a different bubble size and other characteristics from Foam A and is herein termed Foam B (2928). In other embodiments, the screen 2926 is omitted, so that Foam A is transferred without deliberate alteration to chamber 2906.
The exit of the mixing chamber 2918 is connected by piping 2930 to a port in the cylinder 2902 that is gated by a valve 2932 (e.g., a poppet-style valve) that permits fluid from piping 2930 to enter the upper chamber (air chamber) 2906 of the cylinder 2902. Valves (not shown) may control the flow of gas from the reservoir 2910 through piping 2920 to the mixing chamber 2918, and from the mixing chamber 2918 through piping 2928 to the upper chamber 2906 of the cylinder 2902. Another valve 2934 (e.g., a poppet-style valve) permits the upper chamber 2906 to communicate with other components of the system 2900, e.g., an additional separator device (not shown), the upper chamber of another cylinder (not shown), or a vent to the ambient atmosphere (not shown).
The volume of reservoir 2910 may be large (e.g., at least approximately four times larger) relative to the volume of the mixing chamber 2918 and cylinder 2902. Foam A and Foam B are preferably statically stable foams over a portion or all of the time-scale of typical cyclic operation of system 2900: e.g., for a 120 RPM system (i.e., 0.5 seconds per revolution), the foam may remain substantially unchanged (e.g., less than 10% drainage) after 5.5 seconds or a time approximately five times greater than the revolution time.
In an initial state of operation of a procedure whereby gas stored in the reservoir 2910 is expanded to release energy, the valve 2932 is open, the valve 2934 is closed, and the piston 2904 is near top dead center of cylinder 2902 (i.e., toward the top of the cylinder 2902). Gas from the reservoir 2910 is allowed to flow through piping 2920 to the mixing chamber 2918 while liquid from the reservoir 2910 is pumped by pump 2914 to the mixing chamber 2918. The gas and liquid thus conveyed to the mixing chamber 2918 are combined by the foam-generating mechanism 2922 to form Foam A (2924), which partly or substantially fills the main chamber of the mixing chamber 2918. Exiting the mixing chamber 2918, Foam A passes through the screen 2926, being altered thereby to Foam B. Foam B, which is at approximately the same pressure as the gas stored in reservoir 2910, passes through valve 2932 into chamber 2906. In chamber 2906, Foam B exerts a force on the piston 2904 that may be communicated to a mechanism (e.g., an electric generator, not shown) external to the cylinder 2902 by a rod 2936 that is connected to piston 2904 and that passes slideably through the lower end cap of the cylinder 2902.
The gas component of the foam in chamber 2906 expands as the piston 2904 and rod 2936 move downward. At some point in the downward motion of piston 2904, the flow of gas from reservoir 2910 into the mixing chamber 2918 and thence (as the gas component of Foam B) into chamber 2906 may be ended by appropriate operation of valves (not shown). As the gas component of the foam in chamber 2906 expands, it will tend, unless heat is transferred to it, to decrease in temperature according to the Ideal Gas Law; however, if the liquid component of the foam in chamber 2906 is at a higher temperature than the gas component of the foam in chamber 2906, heat will tend to be transferred from the liquid component to the gas component. Therefore, the temperature of the gas component of the foam within chamber 2906 will tend to remain constant (approximately isothermal) as the gas component expands.
When the piston 2904 approaches bottom dead center of cylinder 2902 (i.e., has moved down to approximately its limit of motion), valve 2932 may be closed and valve 2934 may be opened, allowing the expanded gas in chamber 2906 to pass from cylinder 2902 to some other component of the system 2900, e.g., a vent or a chamber of another cylinder for further expansion.
In some embodiments, pump 2914 is a variable-speed pump, i.e., may be operated so as to transfer liquid 2912 at a slower or faster rate from the reservoir 2910 to the foam-generating mechanism 2922 and may be responsive to signals from the control system (not shown). If the rate at which liquid 2912 is transferred by the pump 2914 to the foam-mechanism 2922 is increased relative to the rate at which gas is conveyed from reservoir 2910 through piping 2920 to the mechanism 2922, the void fraction of the foam produced by the mechanism 2922 may be decreased. If the foam generated by the mechanism 2922 (Foam A) has a relatively low void fraction, the foam conveyed to chamber 2906 (Foam B) will generally also tend to have a relatively low void fraction. When the void fraction of a foam is lower, more of the foam consists of liquid, so more thermal energy may be exchanged between the gas component of the foam and the liquid component of the foam before the gas and liquid components come into thermal equilibrium with each other (i.e., cease to change in relative temperature). When gas at relatively high density (e.g., ambient temperature, high pressure) is being transferred from the reservoir 2910 to chamber 2906, it may be advantageous to generate foam having a lower void fraction, enabling the liquid fraction of the foam to exchange a correspondingly larger quantity of thermal energy with the gas fraction of the foam.
All pumps shown in subsequent figures herein may also be variable-speed pumps and may be controlled based on signals from the control system. Signals from the control system may be based on system-performance (e.g., gas temperature and/or pressure, cycle time, etc.) measurements from one or more previous cycles of compression and/or expansion.
Embodiments of the invention increase the efficiency of a system 2900 for the storage and retrieval of energy using compressed gas by enabling the surface area of a given quantity of heat-exchange liquid 2912 to be greatly increased (with correspondingly accelerated heat transfer between liquid 2912 and gas undergoing expansion or compression within cylinder 2902) with less investment of energy than would be required by alternative methods of increasing the surface of area of the liquid, e.g., the conversion of the liquid 2912 to a spray.
In other embodiments, the reservoir 2910 is a separator rather than a high-pressure storage reservoir as depicted in
In various other embodiments, the reservoir 3010 is a separator rather than a high-pressure storage reservoir as depicted in
In other embodiments, the reservoir 3110 is a separator rather than a high-pressure storage reservoir as depicted in
The geophysical properties of a given site may affect the feasibility of constructing a lined underground reservoir at the site. To rate the geological suitability of proposed lined underground reservoir sites, a rock mass rating may be assigned to the rock mass in which construction of a lined underground reservoir is being considered. The rock mass rating system is a geological classification system developed by Z. T. Bieniawski in 1973 and revised in 1989, and is tabulated in
In
Construction time for open-shaft-style construction of a lined underground reservoir (e.g., as depicted in
In various embodiments of the invention, the heat-exchange fluid utilized to thermally condition gas within one or more cylinders and/or storage vessels (e.g., IPVs and/or recessed storage reservoirs) incorporates one or more additives and/or solutes, as described in U.S. Pat. No. 8,171,128, filed Apr. 8, 2011 (the '128 patent), the entire disclosure of which is incorporated herein by reference. As described in the '128 patent, the additives and/or solutes may reduce the surface tension of the heat-exchange fluid, reduce the solubility of gas into the heat-exchange fluid, and/or slow dissolution of gas into the heat-exchange fluid. They may also (i) retard or prevent corrosion, (ii) enhance lubricity, (iii) prevent formation of or kill microorganisms (such as bacteria), and/or (iv) include an agent to modify surface tension, as desired for a particular system design or application.
Embodiments of the invention may, during operation, convert energy stored in the form of compressed gas and/or recovered from the expansion of compressed gas into gravitational potential energy, e.g., of a raised mass, as described in U.S. patent application Ser. No. 13/221,563, filed Aug. 30, 2011, the entire disclosure of which is incorporated herein by reference.
Generally, the systems described herein may be operated in both an expansion mode and in the reverse compression mode as part of a full-cycle energy storage system with high efficiency. For example, the systems may be operated as both compressor and expander, storing electricity in the form of the potential energy of compressed gas and producing electricity from the potential energy of compressed gas. Alternatively, the systems may be operated independently as compressors or expanders.
The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.
This application is a continuation of U.S. patent application Ser. No. 13/827,465, filed Mar. 14, 2013, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/659,164, filed Jun. 13, 2012, and U.S. Provisional Patent Application No. 61/695,393, filed Aug. 31, 2012. The entire disclosure of each of these applications is hereby incorporated herein by reference.
This invention was made with government support under DE-OE0000231 awarded by the DOE. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61659164 | Jun 2012 | US | |
| 61695393 | Aug 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13827465 | Mar 2013 | US |
| Child | 14024960 | US |
