Patent Grant
12241691
The present invention generally relates to the field of energy storage and retrieval. More specifically, embodiments of the present invention pertain to methods and systems for thermal energy storage and retrieval using an improved trilateral cycle and/or heat recovery during discharge/energy retrieval.
The demand for inexpensive energy storage and retrieval is great now. The cost of fossil fuels and hydrocarbon gasses is high, and their availability is low, particularly in Europe. This is having extraordinary effects on the price and availability of electricity, particularly in times of high demand.
Carbon dioxide is a readily-available, inexpensive material. There is a great demand to find new uses for carbon dioxide, at least in part to remove it from the Earth's atmosphere.
When the high-temperature storage tank in a thermal energy storage systems empties, the pressure in the tank drops, and some of the thermal energy storage medium (which is generally in the liquid phase) evaporates. The heat of vaporization taken from the thermal energy storage medium when it evaporates can be significant, and the lost heat of vaporization lowers the system's capacity.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.
Embodiments of the present invention relate to methods and systems for thermal energy storage and retrieval. In one aspect, the invention relates to an energy storage and retrieval system, comprising a thermal energy storage subsystem and a new, improved thermodynamic cycle. The thermal energy storage subsystem comprises a high-temperature energy storage tank storing an energy storage medium at a first temperature, one or more first pressure changing devices configured to transport the energy storage medium between the high-temperature energy storage tank and a source of the energy storage medium, and a first heat exchanger through which the energy storage medium passes. The first heat exchanger is configured to exchange heat between the first energy storage medium and a working fluid (in the thermodynamic cycle) over a first temperature range. The thermodynamic cycle contains the working fluid, has a high-pressure side and a low-pressure side, and comprises a compressor/expander configured to change a pressure of the working fluid between the high-pressure and low-pressure sides of the thermodynamic cycle, a second heat exchanger, a substantially isothermal heat exchanger through which the working fluid passes, and one or more second pressure changing devices configured to transport the working fluid from the substantially isothermal heat exchanger to the second heat exchanger when the energy storage and retrieval system is discharging and from the second heat exchanger to the substantially isothermal heat exchanger when the energy storage and retrieval system is charging. The substantially isothermal heat exchanger is configured to exchange heat at a substantially constant temperature between the working fluid and the energy storage medium or an external environment, and is in fluid communication with the second heat exchanger. The first heat exchanger may comprise a high-temperature gradient heat exchanger. The second heat exchanger is configured to (i) transfer excess heat from the high-pressure side of the thermodynamic cycle to the low-pressure side of the thermodynamic cycle and thus preheat the working fluid to be compressed by the compressor/expander when charging, and (ii) transfer heat from the working fluid expanded by the compressor/expander in the low-pressure side of the thermodynamic cycle to the high-pressure side of the thermodynamic cycle when discharging. The thermodynamic cycle may comprise a trilateral cycle (e.g., a modified trilateral cycle with an internal superheat transfer).
In some embodiments, the source of the energy storage medium comprises a low-temperature energy storage tank storing the energy storage medium at a second temperature less than the first temperature and greater than the substantially constant temperature. In other embodiments, the source of the energy storage medium is an external environment, such as an external atmosphere or a large body of water (e.g., a large, man-made storage tank or pool, a natural body of water such as a lake, river, bay, basin, sea, etc.).
In other or further embodiments, the high-temperature energy storage tank and the low-temperature energy storage tank have a pressurized gas therein, and the energy storage and retrieval system further comprises a first conduit (e.g., one or more pipes or tubes) fluidly connecting the pressurized gas in the low-temperature energy storage tank and the pressurized gas in the high-temperature energy storage tank. Typically, the first conduit is configured to balance (e.g., partially or fully equalize) a first pressure in the high-temperature energy storage tank with a second pressure in the first low-temperature energy storage tank. In one example, the first conduit may pass through at least the first heat exchanger, and the pressurized gas in the first conduit exchanges heat with the energy storage medium and/or the working fluid in the first heat exchanger.
In various embodiments, the second heat exchanger may comprise one or more low-temperature gradient heat exchangers configured to exchange heat over a second temperature range lower than the first temperature range. In one example, the second heat exchanger comprises a low-temperature gradient heat exchanger configured to exchange heat between the first energy storage medium and the working fluid in both the high-pressure and low-pressure sides of the thermodynamic cycle over the second temperature range. In another example, the second heat exchanger comprises a first low-temperature gradient heat exchanger configured to exchange heat between the first energy storage medium and the working fluid in the high-pressure side of the thermodynamic cycle, and a second low-temperature gradient heat exchanger configured to exchange heat between the high-pressure and low-pressure sides of the thermodynamic cycle.
In some embodiments, the energy storage medium comprises water. In other or further embodiments, the working fluid comprises carbon dioxide, although the invention is not limited to either water as the energy storage medium or carbon dioxide as the working fluid.
In some embodiments, the first pressure changing device(s) may comprise a reversible propeller pump. In other embodiments, the first pressure changing devices may comprise a conventional one-way pump (e.g., a circulation pump) configured to move the energy storage medium from the source of the energy storage medium to the high-temperature energy storage tank when the energy storage and retrieval system is charging, and a turbine in parallel with the one-way pump, configured to convert a flow of the energy storage medium to another form of energy (e.g., electricity, rotary mechanical energy, etc.) when the energy storage and retrieval system is discharging. In such other embodiments, the first pressure changing devices may further comprise first and second three-way valves upstream and downstream from the one-way pump and the turbine, configured to control a direction of the flow of the energy storage medium when the system is charging and/or discharging, and optionally, a second one-way pump configured to move the energy storage medium from the high-temperature energy storage tank to the turbine, or from the turbine to the source of the energy storage medium, when the energy storage and retrieval system is discharging. The second one-way pump may be advantageous when the system includes the conduit connecting the low- and high-temperature energy storage tanks. Alternatively, the first pressure changing devices may comprise first and second one-way pumps, configured to move the energy storage medium in a first direction (e.g., from the high-temperature energy storage tank to the source of the energy storage medium) when the energy storage and retrieval system is charging, and in a second direction opposite from the first direction when the energy storage and retrieval system is discharging.
In other or further embodiments, the second pressure changing device(s) may comprise a first pump configured to transport the working fluid from the substantially isothermal heat exchanger to the gradient heat exchanger when the energy storage and retrieval system is discharging, and a second one-way pump, configured to transport the working fluid from the gradient heat exchanger to the substantially isothermal heat exchanger when the energy storage and retrieval system is charging. Alternatively, in place of the second one-way pump, the second pressure changing devices may comprise a turbine between the gradient heat exchanger and the substantially isothermal heat exchanger, driven by the working fluid when the energy storage and retrieval system is charging.
In one particular application, the present invention concerns a submarine, comprising the present thermal energy storage and retrieval system, and a hull enclosing at least the high-temperature energy storage tank, the first and second heat exchangers, the first and second pressure changing device(s), and the compressor/expander. The hull may further enclose a low-temperature energy storage tank, and in some embodiments, the substantially isothermal heat exchanger may be in the hull or in thermal contact with the hull. The submarine may use the thermal energy stored in the high-temperature energy storage tank for air-independent propulsion (AIP) or air-independent power, and may be nuclear or non-nuclear.
In another aspect, the invention relates to a thermal energy storage and retrieval system, comprising a low-temperature energy storage tank storing a thermal energy storage medium at a first temperature and having a pressurized gas therein, a high-temperature thermal energy storage tank storing the thermal energy storage medium at a second temperature higher than the first temperature and having the pressurized gas therein, one or more first pressure changing devices configured to transport the thermal energy storage medium between the low-temperature thermal energy storage tank and the high-temperature thermal energy storage tank, a first heat exchanger through which the thermal energy storage medium passes, a first conduit (i) fluidly connecting the pressurized gas in the low-temperature thermal energy storage tank and the pressurized gas in the high-temperature thermal energy storage tank and (ii) passing through the first heat exchanger, and a thermodynamic cycle. The first heat exchanger is configured to exchange heat between the thermal energy storage medium and a working fluid in the thermodynamic cycle. The pressurized gas in the first conduit exchanges heat with the thermal energy storage medium and/or the working fluid in the first heat exchanger. The thermodynamic cycle comprises a second heat exchanger configured to exchange heat between the working fluid and an external environment or a heat source/sink, a compressor/expander in fluid communication with the heat exchanger and (directly or indirectly) the second heat exchanger, and one or more second pressure changing devices between and in fluid communication with the first heat exchanger and the second heat exchanger. The compressor/expander is configured to change a pressure of the working fluid between the first heat exchanger and the second heat exchanger. The second pressure changing device(s) are configured to transport the working fluid from the second heat exchanger to the first heat exchanger when the thermal energy storage and retrieval system is discharging, and from the first heat exchanger to the second heat exchanger when the thermal energy storage and retrieval system is charging. In various embodiments, the thermodynamic cycle comprises a Brayton cycle or a trilateral cycle, either of which may be further combined with a Rankine cycle, a Stirling cycle, or the other of the Brayton cycle or the trilateral cycle.
In some advantageous embodiments, the thermal energy storage medium may comprise water, and/or the second heat exchanger may comprise a substantially isothermal heat exchanger, as described above/herein. In further embodiments, the thermal energy storage and retrieval system further comprises one or more first valves configured to open and close the first conduit, one or more vents or second valves on each of the low-temperature thermal energy storage tank and the high-temperature thermal energy storage tank, the vent(s) or second valve(s) may be configured to reduce a pressure of the pressurized gas in the respective low-temperature thermal energy storage tank or high-temperature thermal energy storage tank.
In the thermal energy storage and retrieval system including the first conduit, when the thermal energy storage and retrieval system is discharging, the pressurized gas in the first conduit may recover a first amount of heat from the thermal energy storage medium and/or the working fluid, the thermal energy storage medium may lose a second amount of heat due to evaporation in the high-temperature thermal energy storage tank (e.g., in the absence of the first conduit), and the first amount of heat offsets at least some of the second amount of heat. Additionally or alternatively, the high-temperature thermal energy storage tank may at times be in a partially-charged, partially-discharged state for a length of time sufficient for vaporization of the thermal energy storage medium therein to be appreciable in an otherwise identical system in which the high-temperature thermal energy storage tank is closed or sealed. For example, the length of time may be a minimum of four (4) hours, eight (8) hours, or another value during which the pressurized gas in the first conduit recovers a sufficient amount of heat from the thermal energy storage medium and/or the working fluid to offset at least half of the heat that would have been lost to evaporation of the thermal energy storage medium in the high-temperature thermal energy storage tank.
Yet another aspect of the invention relates to a method of recovering heat when discharging a thermal energy storage medium stored in a high-temperature thermal energy storage tank, comprising pressurizing a gas in each of the high-temperature thermal energy storage tank and a low-temperature thermal energy storage tank in fluid communication with the high-temperature thermal energy storage tank, discharging the thermal energy storage medium from the high-temperature thermal energy storage tank to the low-temperature thermal energy storage tank, passing the thermal energy storage medium through one or more heat exchangers between and in fluid communication with the high-temperature thermal energy storage tank and the low-temperature thermal energy storage tank when discharging the thermal energy storage medium, and passing the pressurized gas through a first conduit fluidly connecting the low-temperature thermal energy storage tank and the high-temperature thermal energy storage tank, and in or passing through at least one of the heat exchanger(s). The high-temperature thermal energy storage tank stores the thermal energy storage medium at a first temperature, and the low-temperature thermal energy storage tank storing the thermal energy storage medium at a second temperature lower than the first temperature. The pressurized gas in the first conduit exchanges heat with the thermal energy storage medium, thereby recovering at least some of the heat when the thermal energy storage medium is discharged.
In some embodiments, discharging the thermal energy storage medium comprises pumping the thermal energy storage medium from the high-temperature thermal energy storage tank to the low-temperature thermal energy storage tank. Alternatively, discharging the thermal energy storage medium may comprise driving a turbine with a flow of the thermal energy storage medium. Further embodiments of the method may comprise rejecting heat from the thermal energy storage medium to a working fluid in the thermodynamic cycle (e.g., the trilateral cycle or the Brayton cycle) in the heat exchanger(s) when discharging the thermal energy storage medium.
The present system and method can use carbon dioxide as a working fluid and water as a storage medium. Both water and carbon dioxide are inexpensive and plentiful, and water is environmentally friendly. Water is an advantageous heat storage medium due to its relatively large heat capacity (e.g., in comparison with other materials that are in a liquid phase at ambient temperatures).
The tanks for the storage medium may be relatively simple and inexpensive, because the heat storage medium may be stored and used at a relatively low temperature and at moderate pressure. The system may include as few as two storage tanks, yet remain independent of the environment, or as few as one storage tank, while also using the external environment as a heat source/sink.
Other advantages of the present invention will become readily apparent from the detailed description of various embodiments below.
Reference will now be made in detail to one or more embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the following embodiments, it will be understood that the descriptions are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be readily apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the present invention. Furthermore, it should be understood that the possible permutations and combinations described herein are not meant to limit the invention. Specifically, variations that are not inconsistent may be mixed and matched as desired.
The technical proposal(s) of embodiments of the present invention will be fully and clearly described in conjunction with the drawings in the following embodiments. It will be understood that the descriptions are not intended to limit the invention to these embodiments. Based on the described embodiments of the present invention, other embodiments can be obtained by one skilled in the art without creative contribution and are in the scope of legal protection given to the present invention.
Furthermore, all characteristics, measures or processes disclosed in this document, except characteristics and/or processes that are mutually exclusive, can be combined in any manner and in any combination possible. Any characteristic disclosed in the present specification, claims, Abstract and Figures can be replaced by other equivalent characteristics or characteristics with similar objectives, purposes and/or functions, unless specified otherwise.
For the sake of convenience and simplicity, “part,” “portion,” and “region” may be used interchangeably herein, but are generally given their art-recognized meanings. Wherever one such term is used, it also encompasses the other terms. Also, unless indicated otherwise from the context of its use herein, the terms “known,” “fixed,” “given,” “certain” and “predetermined” generally refer to a value, quantity, parameter, constraint, condition, state, process, procedure, method, practice, or combination thereof that is, in theory, variable, but is typically set in advance and not varied thereafter when in use.
The term “ambient temperature,” which may also be known as room temperature, refers to a temperature typically in the range of 15-30° C. (e.g., 18-25° C., or any temperature or range of temperatures therein).
An Exemplary Energy Storage and Retrieval System
The trilateral cycle 100 is reversible. Consequently, the diagram of
The trilateral cycle 100 takes advantage of the specific heat of carbon dioxide being different in different temperature ranges. For example, at a relatively high given pressure (e.g., 124.5 bar, as shown in
In addition, the expansion ratio in the cycle 100 when the working fluid is carbon dioxide is 1:2.6, whereas with other working fluids such as dimethyl ether (DME) or pentane, the expansion ratio is much higher (e.g., >1:10, and in the case of DME, as high as 1:36). The expansion ratio is the ratio of the pressure in the low-pressure heat transfer process 5-6 to the pressure in the high-pressure heat transfer processes 2-3-4. Thus, the expansion process 4-5 and the compression process 5-4 can be done in a single step (e.g., with a single-stage reversible expander/compressor).
In part, the present invention concerns a method and system for thermal energy storage and retrieval.
In general, the conduit 13 equalizes the pressure of the gas(es) in the low-temperature energy storage tank 11 and the high-temperature energy storage tank 12. For example, the pressure gas pressure in energy storage tanks 11 and 12 may be 2-40 bar, or any pressure or range of pressures therein (such as 15-20 bar), but the invention is not limited to this range. Furthermore, in various embodiments, there may be a valve (not shown) in each of the energy storage tanks 11 and 12 configured to vent or relieve excess gas pressure in the tank and/or open the tank to atmospheric pressure, as well as a valve in the conduit 13 configured to open and close the conduit 13. For example, when the pressure in the energy storage tanks 11 and 12 is >1 atm, one may close the valve in the conduit 13 and open the valve in one of the energy storage tanks 11 and 12 to use the excess pressure in the other energy storage tank to help drive the flow of the thermal energy storage medium 22 from the energy storage tank retaining the excess pressure to the energy storage tank from which the excess pressure was relieved, thereby reducing stress and wear on the pump 14.
The trilateral heat engine/heat pump 130 implements the trilateral cycle 100 shown in
Referring to
Referring back to
In some embodiments, a turbine or throttle valve (not shown) can be configured in parallel with the pump 19, in which first and second three-way valves (also not shown) direct the flow of the working fluid through either the pump 19 or the turbine/throttle valve in the trilateral cycle 130. The turbine may drive the generation of electricity or other form of usable energy (e.g., mechanical energy), and the throttle valve may regulate and/or maintain the pressure of the working fluid in the low-pressure side of the cycle 130 so that the inlet conditions for the expansion are constant. It does this by introducing a flow restriction, inducing a significant localized pressure drop in the fluid.
When the system is discharging, the two-way pump 14 moves the thermal energy storage medium 22 from the high-temperature energy storage tank 12, through the heat exchangers 15 and 17, to the low-temperature energy storage tank 11, and the working fluid is pumped by the pump 19 through the heat exchangers 17 and 15, where the thermal energy storage medium 22 rejects stored heat to the working fluid (which in the case of carbon dioxide, is in a supercritical phase at 2-3-4 in the cycle 130). The working fluid then drives a mechanical energy recovery process (e.g., by expansion) in the expander/compressor 16, where it transitions from supercritical to gas phase, then rejects remaining heat in the heat exchanger 17 (at 5-6) to the working fluid in the high-pressure segment of the cycle 130 (i.e., at 2-3). The working fluid then passes through the isothermal heat exchanger 23, where it undergoes a phase change (e.g., from gas to liquid), thereby rejecting additional heat. In some embodiments, the medium to which the working fluid rejects heat in the isothermal heat exchanger 23 is an external environment (e.g., the external atmosphere; a large body of water, such as a lake, sea, bay, basin, river, etc.). When the medium in the isothermal heat exchanger 23 is the external atmosphere (e.g., the air outside or above a building), the energy storage medium 22 may pass through a pipe or tube (which may, for example, be thermally connected to a plurality of cooling fins) in the outside/outdoor air. The circulating device 18 may help circulate the isothermal medium to help maintain its constant temperature.
When the working fluid is carbon dioxide, its high density at 0° C. means that the isothermal heat exchanger 23 can be relatively compact, with a relatively small surface area. Furthermore, when maintained at a temperature of 0° C., the medium to which the working fluid rejects heat in the isothermal heat exchanger 23 may be a relatively large tank of water containing both liquid water and ice. The ice may be maintained by periodic additions of ice to the isothermal exchange medium (and, optionally, withdrawals of liquid water from the isothermal exchange medium), or by external cooling of the tank (e.g., using a conventional refrigeration system or Peltier cooler).
However, the working fluid is not limited to carbon dioxide, nor is the temperature of the medium in the isothermal heat exchanger 23 limited to 0° C. One of the advantages of the present modified trilateral cycle is that the superheat at 5-6/6-5 (
Furthermore, when the high-temperature storage tank 12 in
To increase the useful heat capacity in the system 110, the low-temperature thermal energy storage tank 11 and the high-temperature thermal energy storage tank 12 may be pressurized with a gas 24 therein. The upper parts of the low- and high-temperature thermal energy storage tanks 11 and 12 are connected with a pipe 13. When the pressure decreases in the high-temperature thermal energy storage tank 12 (e.g., when the thermal energy storage medium 22 is pumped or transferred from the high-temperature thermal energy storage tank 12), the pressurized gas 24 flows from the low-temperature thermal energy storage tank 11 to the high-temperature thermal energy storage tank 12. Thus, in its simplest form, the pressure in the low-temperature thermal energy storage tank 11 and the high-temperature thermal energy storage tank 12 is substantially the same. As a result, the power consumed by the pump 14 that pumps the thermal energy storage medium 22 between the low-temperature thermal energy storage tank 11 and the high-temperature thermal energy storage tank 12 is much less than without the pressurized gas 24. For example, the pump 14 may comprise a single reversible propeller pump or a reversible flow pump that needs only to overcome frictional losses in the conduits between the low-temperature thermal energy storage tank 11 and the high-temperature thermal energy storage tank 12. In a more specific embodiment, the reversible propeller pump includes a relatively precise variable speed control, to optimize its operation. Alternatively, the reversible pump 14 may comprise first and second parallel low-pressure, unidirectional circulation pumps, configured so that the direction of flow can be selected using first and second three-way valves, one upstream and one downstream of the parallel pumps. Such a dual-pump arrangement is disclosed in U.S. patent application Ser. No. 18/337,561, filed Jun. 20, 2023, the relevant portion(s) of which are incorporated herein by reference.
In various modifications, there may also be a pressure sensor (not shown) in the pipe 13 to monitor and/or measure the pressure of the gas 24, a valve through which additional pressurized gas can be added to (or excess pressurized gas can be removed from) the pipe 13 or the low-temperature thermal energy storage tank 11 (e.g., for safety reasons), and/or one or more pressure-activated valves (e.g., between one of the tanks 11 or 12 and the pipe 13) to control when the pressurized gas 24 is transferred from one of the tanks to the other (e.g., when the pressure differential on opposite sides of the valve exceeds a predetermined value, such as in the range of 1-10 atm). On the other hand, when the water flows from the low-temperature thermal energy storage tank 11 to the high-temperature thermal energy storage tank 12, the pressure decreases in the low-temperature thermal energy storage tank 11, and the pressurized gas 24 flows from the high-temperature thermal energy storage tank 12 to the low-temperature thermal energy storage tank 11 to balance the pressures in the tanks.
The pressurized gas 24 can be air when the high-temperature thermal energy storage tank 12 is galvanized or coated with a protective layer. When the high-temperature thermal energy storage tank 12 is made of steel, the pressurized gas 24 may be an inert gas, such as nitrogen or argon, to prevent corrosion of the steel.
An Exemplary Energy Storage and Retrieval System with Heat Recovery
An advantageous embodiment is shown in
The exemplary system 200 in
The low-temperature energy storage tank 11 and the high-temperature thermal energy storage tank 12 have a pressurized gas 24 therein. The first conduit 13′ fluidly connects the pressurized gas 24 in the low-temperature thermal energy storage tank 11 and the pressurized gas 24 in the high-temperature thermal energy storage tank 12, and also passes through the first heat exchanger 15′ and the optional third heat exchanger 17′. In each of the first heat exchanger 15′ and the third heat exchanger 17′, the pressurized gas 24 in the first conduit 13′ exchanges heat with the thermal energy storage medium 20 and the working fluid in the thermodynamic cycle 130. In some embodiments, the conduit 13′ passes through only the first heat exchanger 15′. In such embodiments, when the thermodynamic cycle 130 includes the third heat exchanger 17′ and the system 200 is charging, the pressurized gas 24 flows from the high-temperature thermal energy storage tank 12 to the low-temperature thermal energy storage tank 11, and enters the low-temperature thermal energy storage tank 11 at a temperature higher than the first temperature (i.e., the temperature of the thermal energy storage medium 20 in the low-temperature thermal energy storage tank 11). This may raise the first temperature very slightly, but when the low-temperature thermal energy storage tank 11 is sufficiently large, it may have substantially no effect on the first temperature.
In various embodiments, the thermodynamic cycle or heat engine in the system 200 may comprise a Brayton cycle, instead of the trilateral cycle 130. Either the Brayton cycle or the trilateral cycle may be further combined with a Rankine cycle, a Stirling cycle, or the other of the Brayton cycle and the trilateral cycle. As is known in the art, each of these thermodynamic cycles has at least one heat exchanger configured to exchange heat between the working fluid and an external environment or a heat source/sink, at least one heat exchanger that can be configured to exchange heat between the working fluid and a storage medium, a compressor/expander in fluid communication with the heat exchangers, and one or more pressure changing devices that change the pressure of the working fluid in a direction opposite from that of the compressor/expander. However, the Rankine and Stirling cycles have at least one substantially isothermal heat exchanger therein.
When the thermal energy storage and retrieval system 200 is discharging, the pressurized gas 24 in the conduit 13′ may recover a first amount of heat from the thermal energy storage medium 22 and/or the working fluid. In some configurations of the first and third heat exchangers 15′ and 17′, the conduit 13′ may be in thermal the thermal contact with one of the thermal energy storage medium 22 and the working fluid, but not (or not very much) with the other. The thermal energy storage medium 22 may lose a second amount of heat in the high-temperature thermal energy storage tank 12 due to evaporation, as the medium 22 is removed from the tank 12. In the absence of the first conduit, this second amount of heat may be appreciable. For example, the heat of vaporization of water at 208° C. and 1900 kPa (about 18.75 atm) is 1907.9 kJ/kg. In the system 200, the first amount of heat recovered by the pressurized gas 24 in the conduit 13′ offsets at least some of the second amount of heat lost to vaporization of the thermal energy storage medium 22.
When the high-temperature thermal energy storage tank 12 is not full for a sufficiently long time, the pressurized gas 24 in the tank 12 becomes saturated with vapor of the thermal energy storage medium 22 (e.g., water). However, that heat (e.g., of vaporization) is not lost because it is returned by the pressurized gas 24 in the conduit 13′ to the hot storage medium in the tank 12 via the heat exchanger 15′ (and optionally the heat exchanger 17′) during charging. On the other hand, if evaporation of the thermal energy storage medium 22 in the tank 12 is negligible, and discharge of the medium is sufficiently fast (e.g., there is a relatively short cycle time between discharging and charging processes), then including a heat exchanger in the gas connection (i.e., passing the conduit 13′ through the heat exchangers 15′ and 17′) is not necessary, and the system 110 in
Vaporization of liquid-phase materials is not necessarily an instantaneous process, however. Heat losses due to vaporization of a liquid-phase thermal energy storage medium 22 is more appreciable when the high-temperature thermal energy storage tank 12 in a partially-charged, partially-discharged state for a length of time sufficient for vaporization of the thermal energy storage medium 22 therein to be appreciable in an otherwise identical system in which the high-temperature thermal energy storage tank is closed or sealed (e.g., in which the conduit 13′ is absent). Thus, in some embodiments, the pressurized gas 24 in the conduit 13′ recovers a sufficient amount of heat from the thermal energy storage medium 22 and/or the working fluid to offset at least half of the heat that would have been lost to evaporation of the thermal energy storage medium 22 in the high-temperature thermal energy storage tank 22 in the absence of the conduit 13′. For example, the length of time may be a minimum of four (4) hours, eight (8) hours, or another value during which heat losses due to vaporization of the thermal energy storage medium 22 is sufficiently large to justify the recovery of the heat lost.
In various embodiments, the heat exchanger 23 exchanges heat between the working fluid and an external environment or a heat source/sink. In some embodiments, the working fluid exchanges heat in the heat exchanger 23 with an external environment, such as an external and/or ambient atmosphere, a large body of water, such as a lake, pond, river, sea, etc., or a thermally-stable underground heat reservoir. In some embodiments, the working fluid exchanges heat in the heat exchanger 23 with a heat source/sink, such as a man-made pool (e.g., containing water), a large block of concrete, a composite structure containing both thermally-conductive materials such as steel or aluminum and an insulator such as concrete, glass, brick and/or stone (e.g., a high-rise building or skyscraper), etc. As for the system 110 in
In some advantageous embodiments, the thermal energy storage medium 22 may comprise water, and the heat exchanger 23 may comprise a substantially isothermal heat exchanger, as described herein. In further embodiments, the thermal energy storage and retrieval system 200 further comprises one or more valves (not shown) configured to open and close the conduit 13′, and/or one or more vents or valves (not shown) on each of the low-temperature thermal energy storage tank 11 and the high-temperature thermal energy storage tank 12. The valves may be configured to add a gas (e.g., air, nitrogen, argon, etc.) to the respective storage tank 11 or 12, and the tank vents or valves may be configured to reduce a pressure of the pressurized gas 24 in the respective storage tank 11 or 12 (e.g., for safety purposes).
In embodiments in which the pressure difference between the high- and low-pressure sides of the thermodynamic cycle/heat engine 130 is sufficiently low (e.g., where the expansion ratio is <10:1), the second pressure changing device(s) may comprise the reversible pump 19. However, in embodiments in which the pressure difference between the high- and low-pressure sides of the thermodynamic cycle/heat engine 130 is sufficiently high (e.g., where the expansion ratio is >10:1), the second pressure changing device(s) may comprise a conventional one-way pump (e.g., a circulation pump) configured to move the working fluid from the heat exchanger 23 to the first or third heat exchanger 15′ or 17′ when the energy storage and retrieval system 200 is charging, and a turbine in parallel with the one-way pump, configured to convert a flow of the working fluid to another form of energy (e.g., electricity, rotary mechanical energy, etc.) when the energy storage and retrieval system 200 is discharging. In such embodiments, the thermodynamic cycle/heat engine 130 may further comprise first and second three-way valves upstream and downstream from the one-way pump and the turbine, configured to control a direction of the flow of the working fluid when the system is charging and/or discharging.
Alternatively, to prevent the energy storage medium 22 from evaporating and the resulting vapor from mixing with the pressurized gas 24 in the high-temperature thermal energy storage tank 12, the surface of the energy storage medium 22 can be covered with a floating body or a layer of a liquid that does not mix with the medium 22 and that has a lower density than the medium 22. For example, when the medium 22 comprises water, the floating body or layer of liquid may comprise silicone oil or, at the operating temperatures in the high-temperature thermal energy storage tank 12, paraffin wax.
An Exemplary Single-Tank Energy Storage and Retrieval System
In the system 300 of
The thermal energy storage subsystem 320 in
The trilateral cycle 330 in
Determination and control of the proportion of the working fluid in the trilateral cycle 330 diverted to the internal gradient heat exchanger 325 from the first gradient heat exchanger 315 is within the level of skill in the art. For example, referring to the example of
In the high-temperature heat exchanger 317, the heat capacity of the working fluid is significantly lower (e.g., on average) than it is in the first (low-temperature) heat exchanger 315. For example, when the working fluid is carbon dioxide at a pressure of 124.5 bar, the heat capacity in the low-temperature heat exchanger 315 ranges from 2.19 to 1.80 kJ/kg-K (over a corresponding temperature range of 7-100° C.), but in the high-temperature heat exchanger 317, it ranges from 1.80 to 1.22 kJ/kg-K (over a corresponding temperature range of 100-208° C.). As a result, the amount of heat transferred to/by carbon dioxide in the low-temperature heat exchanger 315 (i.e., Q8-9) is 274 kJ/kg, whereas in the high-temperature heat exchanger 317 (i.e., Q9-10), it is 150 kJ/kg.
An Exemplar Application of the Present System(s)
One application of the present systems 110, 200 and 300 (
Thus, the submarine may comprise the present thermal energy storage and retrieval system and a hull enclosing at least the high-temperature energy storage tank, the first and second heat exchangers, the first and second pressure changing device(s), and the compressor/expander. In some embodiments, the hull may further enclose a low-temperature energy storage tank. In other or further embodiments, the substantially isothermal heat exchanger may be in the hull or in thermal contact with the hull. The submarine may include other parts or components conventionally found in submarines, such as one or more propellers, one of more sources of stored air or oxygen, one or more fuel storage tanks, one or more propulsion mechanisms, one or more control systems, one or more communication systems, one or more living and/or sleeping quarters, etc.
An Exemplary Method of Recovering Heat Loss During Thermal Energy Retrieval
The invention concerns a method of recovering heat when discharging a thermal energy storage medium stored in a high-temperature thermal energy storage tank, such as the thermal energy storage medium 22 in the high-temperature thermal energy storage tank 12 (
The method is conducted in accordance with the operation of (e.g., heat recovery in) the thermal energy storage and retrieval system 220, as described herein. Thus, in some embodiments, discharging the thermal energy storage medium may comprise pumping the thermal energy storage medium 22 from the high-temperature thermal energy storage tank 12 to the low-temperature thermal energy storage tank 11 using a pump 14. Alternatively, discharging the thermal energy storage medium may comprise driving a turbine (not shown) with a flow of the thermal energy storage medium 22. The flow of the thermal energy storage medium 22 may be driven through the turbine using a one-way pump (not shown), either upstream (e.g., at node 8) or downstream from the turbine. Further embodiments of the method may comprise rejecting heat from the thermal energy storage medium 22 to the working fluid in the thermodynamic cycle/heat engine 130 in the heat exchanger 15′ (and optionally in the heat exchanger 17′) when discharging the thermal energy storage medium 22.
When the system 200 includes a valve in the conduit 13′, the method may further comprise opening the valve in the conduit 13′, or confirming that the valve in the conduit 13′ is open, before discharging the thermal energy storage medium 22 from the high-temperature thermal energy storage tank 12. In addition, when the system 200 includes a vent or a valve in the high-temperature thermal energy storage tank 12, the method may further comprise confirming that the vent or valve in the high-temperature thermal energy storage tank 12 is closed, or closing the vent or valve in the high-temperature thermal energy storage tank 12, before discharging the thermal energy storage medium 22 from the high-temperature thermal energy storage tank 12.
Exemplary Methods of Storing and Retrieving Thermal Energy
The invention further concerns to a method of storing thermal energy, using the system 110 in
Some embodiments of this method may further comprise adding a pressurized gas 24 to each of the low-temperature thermal energy storage tank 11 and the high-temperature thermal energy storage tank 12, then balancing the pressure of the gas 24 in the low-temperature and high-temperature thermal energy storage tanks 11 and 12. Such balancing may comprise opening the conduit 13/13′ that is in fluid communication with both of the storage tanks 11 and 12.
In other or further embodiments of this method, rejecting heat from the compressed working fluid to the thermal energy storage medium 22 may comprise pumping the thermal energy storage medium 22 through the first and second gradient heat exchangers 15/15′ and 17/17′ using a pump (e.g., reversible pump 14), and/or driving a turbine (e.g., in the thermodynamic cycle or heat engine 130) with the cooled, compressed working fluid. Other aspects of the method of storing thermal energy may comprise or concern operations or functions of the systems 110, 200 and/or 300 described above.
The invention also concerns a method of retrieving energy, comprising storing the thermal energy storage medium 22 at the second, higher temperature in the high-temperature thermal energy storage tank 12, passing the thermal energy storage medium 22 through the first and second gradient heat exchangers 15/15′ and 17/17′, passing the working fluid through the first and second gradient heat exchangers 15/15′ and 17/17′, rejecting heat from the thermal energy storage medium 22 to the working fluid in the first and second gradient heat exchangers 15/15′ and 17/17′, thereby heating the working fluid and cooling the thermal energy storage medium 22, storing the cooled thermal energy storage medium 22 in the low-temperature thermal energy storage tank 11, expanding the heated working fluid (e.g., in the thermodynamic cycle/heat engine 130), rejecting heat from the expanded working fluid to compressed working fluid in the second gradient heat exchanger 17/17′, and exchanging heat between the expanded working fluid and the heat source/heat sink at a substantially constant temperature, thereby changing the phase of the expanded working fluid (e.g., from gas to liquid).
Some embodiments of this method may further comprise balancing the pressure of the pressurized gas 24 in the high-temperature thermal energy storage tank is balanced with the pressurized gas 24 in the low-temperature thermal energy storage tank 11 using the conduit 13/13′ (similar to the method of storing thermal energy), and recovering heat from the working fluid and/or the thermal energy storage medium 22 when discharging the system 110, 200 or 300. Other or further aspects of the method may further comprise driving a turbine with the cooled thermal energy storage medium 22 prior to storing the cooled thermal energy storage medium 22 in the low-temperature thermal energy storage tank 11. When driving the turbine, the method of retrieving energy may further comprise closing a valve in the conduit 13/13′ before discharging the system 110, 200 or 300 (e.g., passing the thermal energy storage medium 22 through the first and second gradient heat exchangers 15/15′ and 17/17′).
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
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