Energy storage systems and methods

Abstract

The energy storage system includes a pressure vessel exposed to ambient temperature and containing a condensable working fluid (CWF) at ambient temperature, a liquid reservoir in communication with one of the vessels and containing a non-vaporizable liquid in the reservoir and in the vessel, and a device for pumping liquid from the reservoir to the vessel. The CWF is compressible by direct contact with the liquid in the vessel and can be stored in a liquid state after being compressed to a saturation pressure. In one method, at least a portion of the liquid in the vessel is propelled by the CWF towards a turbine to generate power. In one embodiment, the module includes a first vessel having at least four ports, a second vessel at ambient temperature, and a flow control component operably connected to a corresponding conduit for selectively controlling the flow of the fluid.

Description

Technical Field

[0001] The present invention relates to the field of mechanical energy storage. More particularly, the present invention relates to an energy storage system capable of releasing compressed gas for later use and a method therefor.

Background Art

[0002] Energy collected from various sustainable energy sources, such as wind power, solar power, and wave power, is known to be stored in the form of compressed gas. During periods of high electricity demand, the compressed gas is discharged from the storage container, enabling power generation. Alternatively, the stored compressed gas can be utilized for various industrial applications.

[0003] Many compressed air energy storage (CAES) systems are known in the prior art. Compressed air has conventionally been stored in large-scale and expensive underground caverns or underwater elastic balloons. CAES plants have a large rated power and storage capacity, but have several major drawbacks. First, air has a large amount of compression heat, and there is approximately 85% heat loss when compressed. As the temperature rises, the amount of compressed air that can be stored decreases. Second, the pressure inside the cavern where the compressed air is stored gradually decreases as additional air is released, which adversely affects the amount of electricity that can be generated by a turbine driven by the released compressed air.

[0004] Attempts have been made to reduce compression heat by charging and discharging air isothermally, but since it is necessary to use a heat exchanger to facilitate isothermal compression, it incurs unnecessary costs for the storage facility.

[0005] In other CAES systems, non-adiabatic (D-CAES), adiabatic (A-CAES), and liquid (LAES) air energy storage means have been used. Since the air temperatures of these prior art systems deviate significantly from normal temperature, even these prior art systems require the use of expensive heat exchangers and rotating machinery, namely compressors and gas turbines.

[0006] The objective of the present invention is to provide a compressed gas energy storage system with improved energy density compared to prior art systems.

[0007] A further object of the present invention is to provide a compressed gas energy storage system with improved system reciprocating efficiency compared to prior art systems.

[0008] A further objective of the present invention is to provide a compressed gas energy storage system and method that reduces capital costs and operating costs compared to the prior art.

[0009] Other objectives and advantages of the present invention will become apparent as the description progresses. [Overview of the Initiative]

[0010] A multiphase energy storage system comprising: a first pressure vessel having at least four ports through which corresponding conduits are in fluid communication; and a second pressure vessel set to a temperature below room temperature and comprising one or more ports that are in fluid communication with the first pressure vessel, wherein a condensable working fluid (CWF) that can be condensed at room temperature can be introduced into the first pressure vessel through the first port of the at least four ports, and a liquid that is not vaporizable in the first and second pressure vessels and can be introduced into the first pressure vessel through the second port of the at least four ports can be compressed in the first pressure vessel, and a sufficient volume of CWF or non-vaporizable liquid can be stored in the first pressure vessel. An energy storage system in which, after being introduced into a force vessel, at least a portion of the compressed CWF can be transferred from the first pressure vessel to the second pressure vessel via one or more ports through a third port of at least four ports by direct contact with a non-vaporizing liquid, all or most of the CWF in the second pressure vessel can be stored in the second pressure vessel in a liquid state after being compressed and condensed to saturation pressure, and at least a portion of the non-vaporizing liquid in the first pressure vessel can be propelled through a fourth port of at least four ports by the compressed CWF discharged from the second pressure vessel to discharge the stored energy.

[0011] In one embodiment, the system further comprises a gas source that is in fluid communication with a first pressure vessel and contains CWF, the CWF being supplied from the gas source to the first pressure vessel.

[0012] In one embodiment, the energy storage system further comprises at least one hydraulic turbine that can be driven by a non-vaporous liquid, and at least a portion of the non-vaporous liquid in a first pressure vessel is propelled toward the at least one hydraulic turbine by compressed CWF released from a second pressure vessel.

[0013] In one embodiment, the system further comprises a liquid reservoir that is in fluid communication with a first pressure vessel and contains a non-vaporizing liquid, and means for distributing the non-vaporizing liquid from the liquid reservoir to the first pressure vessel, wherein the non-vaporizing liquid can be introduced into the first pressure vessel by the distributing means via a second port of at least four ports.

[0014] It is understood that "non-vaporizing liquids" may vaporize under other conditions. Under conditions of multiphase energy storage systems, particularly the first and second pressure vessels, and optionally the liquid reservoir, the liquid, also called the "transfer liquid," is non-vaporizing.

[0015] In one embodiment, a non-vaporizing liquid discharged from at least one hydraulic turbine can be received in a liquid reservoir.

[0016] In one embodiment, the CWF is substantially isothermally compressible and expandable during direct contact with a non-vaporizing liquid in a first pressure vessel.

[0017] In one embodiment, the dispensing means is at least one hydraulic pump for dispensing a non-vaporizing liquid from a liquid reservoir to a first pressure vessel.

[0018] In one embodiment, the energy storage system further comprises at least one additional hydraulic pump for delivering a non-vaporizing liquid from a first pressure vessel to a liquid reservoir.

[0019] In one embodiment, the CWF in the first pressure vessel is continuously and additionally compressed while additional non-vaporizing liquid is introduced into the first pressure vessel.

[0020] In one embodiment, the energy storage system may further include a gas-liquid separator positioned between the first and second pressure vessels to prevent the flow of a non-vaporous liquid into the second pressure vessel, and a liquid-liquid separator positioned between the first and second pressure vessels to prevent the flow of a non-vaporous liquid into the second pressure vessel.

[0021] In one aspect, the energy storage system further includes a liquid-liquid separator disposed between the first pressure vessel and the second pressure vessel to prevent the flow of non-vaporizable liquid into the second pressure vessel.

[0022] In one aspect, the energy storage system further includes a third pressure vessel that can be in fluid communication with the first pressure vessel. Before performing either a charging cycle or a discharging cycle, the third pressure vessel is completely filled with a first fluid selected from CWF gas or non-vaporizable liquid, and the first pressure vessel is completely filled with a second fluid selected from CWF gas or non-vaporizable liquid and different from the first fluid. When finished, the third pressure vessel is completely filled with the second fluid, and the first pressure vessel is completely filled with the first fluid.

[0023] In one aspect, the first pressure vessel is also exposed to room temperature.

[0024] In one aspect, the energy storage system includes a plurality of first pressure vessels.

[0025] In one aspect, all of the first pressure vessels are in fluid communication with each other, or selected first pressure vessels are in fluid communication with each other.

[0026] In one aspect, the energy storage system includes a plurality of second pressure vessels.

[0027] In one aspect, all of the second pressure vessels are in fluid communication with each other, or selected second pressure vessels are in fluid communication with each other.

[0028] In one aspect, the gas holder further contains a non-CWF gas that can be mixed with CWF, and the non-CWF gas can be further compressed after the liquefaction of CWF.

[0029] In one aspect, the energy storage system further includes flow control components operably connected to each of the corresponding conduits to selectively control the flow of fluid through the corresponding conduits.

[0030] In one aspect, the second pressure vessel is exposed to a temperature at or below room temperature.

[0031] A method of generating electric power with stored energy, comprising providing a first pressure vessel and a second pressure vessel, the second pressure vessel being in fluid communication with the first pressure vessel and being set to a temperature below room temperature, in the first pressure vessel, substantially isothermally compressing a condensable working fluid (CWF) that can condense at room temperature during direct contact with a non-vaporizable liquid, transferring at least a portion of the compressed CWF from the first pressure vessel to the second pressure vessel in response to an interaction with the non-vaporizable liquid, transferring an additional amount of the compressed CWF to the second pressure vessel, compressing all or most of the CWF in the second pressure vessel to a saturation pressure and condensing it to produce a liquid CWF, propelling at least a portion of the non-vaporizable liquid in the first pressure vessel toward at least one hydraulic turbine by the compressed CWF discharged from the second pressure vessel, and rotationally driving at least one hydraulic turbine with the propelled non-vaporizable liquid to generate electric power, wherein the flow of the non-vaporizable liquid to the second pressure vessel is blocked while at least a portion of the compressed CWF is being transferred from the first pressure vessel to the second pressure vessel.

[0032] As used herein, the phrase "the flow of the non-vaporizable liquid to the second pressure vessel is blocked" includes the possibility that only a negligible volume of the non-vaporizable liquid relative to the volume of the liquid CWF in the second pressure vessel is introduced into the second pressure vessel. The blocking of the flow of the non-vaporizable liquid to the second pressure vessel is effected by a suitable device such as a demister.

[0033] [[ID=一三]]

[0034] In one aspect, a unit of a mixing device in fluid communication with the first pressure vessel or the second pressure vessel is operated to eliminate a temperature gradient in the CWF, whereby the CWF is substantially isothermally compressed.

[0035] In one embodiment, at least a portion of the non-vaporizing liquid in a first pressure vessel is propelled toward at least one hydraulic turbine by compressed CWF discharged from a second pressure vessel, when the discharged compressed CWF is in a liquid state, a gaseous state, or a multiphase state.

[0036] In one embodiment, the step of transferring at least a portion of the compressed CWF from a first pressure vessel to a second pressure vessel is performed between multiple charging cycles.

[0037] In one embodiment, the step of propelling at least a portion of the non-vaporizing liquid in the first pressure vessel with compressed CWF discharged from the second pressure vessel is performed between multiple discharge cycles.

[0038] In one embodiment, the method further includes the steps of providing a third pressure vessel capable of fluid communication with a first pressure vessel, and before performing either a charge cycle or a discharge cycle, the third pressure vessel is completely filled with a first fluid selected from CWF gas or a non-vaporous liquid, the first pressure vessel is completely filled with a second fluid different from the first fluid, selected from CWF gas or a non-vaporous liquid, and when completed, the third pressure vessel is completely filled with the second fluid and the first pressure vessel is completely filled with the first fluid.

[0039] In one embodiment, the method further includes performing the other of a charge cycle or a discharge cycle when the third pressure vessel is completely filled with the second fluid and the first pressure vessel is completely filled with the first fluid.

[0040] In one embodiment, the compressed CWF discharged from the second pressure vessel undergoes substantially isothermal expansion while in direct contact with the non-vaporizing liquid in the first pressure vessel.

[0041] The system comprises a first pressure vessel having at least four ports through which corresponding conduits are in fluid communication, a second pressure vessel having one or more ports and set to a temperature below room temperature, and flow control components operably connected to each corresponding conduit for selectively controlling the flow of fluid through the conduits, wherein a condensable working fluid (CWF) that can be condensed at room temperature can be introduced into the first pressure vessel via the first of the at least four ports, and a non-vaporizing liquid can be introduced into the first pressure vessel via the second of the at least four ports, thereby causing substantial isothermal compression of the CWF upon direct contact with the non-vaporizing liquid, and the first pressure A direct contact fluid transfer (DCFT) module, wherein, after adding a sufficient amount of non-vaporizing liquid to the container, at least a portion of the compressed CWF can be transferred from the first pressure vessel to the second pressure vessel via one or more ports through a third port of at least four ports in direct contact with the non-vaporizing liquid, and after being compressed and condensed to saturation pressure, can be stored in liquid form in the second pressure vessel, and at least a portion of the non-vaporizing liquid in the first pressure vessel can be propelled through a fourth port of at least four ports by the compressed CWF discharged from the second pressure vessel, thereby releasing the stored energy. [Brief explanation of the drawing]

[0042] [Figure 1] Figure 1 is a schematic diagram showing one embodiment of a multiphase energy storage system. [Figure 2] Figure 2 is a schematic diagram showing another embodiment of the multiphase energy storage system. [Figure 3] Figure 3 is a flowchart illustrating various steps related to the execution of a charging mode cycle according to one embodiment. [Figure 4] Figure 4 shows a gas delivery method using suction flow. [Figure 5] Figure 5 is a flowchart illustrating various steps related to the execution of a discharge mode according to one embodiment. [Figure 6]Figure 6 is a schematic diagram showing another embodiment of the multiphase energy storage system. [Figure 7] Figure 7 is an exemplary pressure-volt diagram of the energy storage system shown in Figure 1. [Figure 8] Figure 8 is an illustrative temperature entropy diagram of the energy storage system shown in Figure 1. [Figure 9] Figure 9 is a schematic diagram showing another embodiment of the multiphase energy storage system, illustrating the charge state. [Figure 10] Figure 10 is a schematic diagram showing another embodiment of a multiphase energy storage system, illustrating the operations performed during a charging cycle. [Figure 11] Figure 11 is a schematic diagram of the multiphase energy storage system shown in Figure 10, illustrating the operations performed during a discharge cycle. [Modes for carrying out the invention]

[0043] The multiphase compressed gas energy storage system of the present invention employs a condensable working fluid (CWF), which is normally a gas but condenses at room temperature when sufficiently compressed. This advantageously avoids the large heat losses experienced by working fluids in conventional systems. In conjunction with the CWF, a liquid-based direct contact fluid transfer (DCFT) module is employed to ensure that the CWF undergoes a substantially isothermal phase change in both charging and discharging modes. Since the DCFT module can operate in conjunction with a transfer fluid that reliably maintains a liquid state, it is advantageous to employ relatively inexpensive hydraulic equipment that works in conjunction with the flowing transfer fluid, thereby achieving both reduced system costs and improved system round-trip efficiency (RTE).

[0044] In this specification, “direct contact” means a heat transfer process involving heat exchange between two fluids that are in physical contact with each other at different temperatures. “Substantially isothermal” means a state in which heat transfer occurs at a nearly constant temperature, defined as an adiabatic heat transfer process having the same initial thermodynamic state as a given heat transfer process, where the absolute temperature difference between the final temperature and the initial temperature is 5% or less. A deviation from a purely isothermal heat transfer process is due to a heat transfer coefficient lower than required, a heat transfer area smaller than required, or a shorter time than required for heat transfer to occur.

[0045] Figure 1 schematically illustrates one embodiment of a multiphase energy storage system, denoted as 1 throughout, which can operate in both charging and discharging modes. In system 1, two fluids interact: the first is a multiphase CWF fluid, and the second is a transfer fluid.

[0046] The multiphase energy storage system 1 includes a gas holder 2 exposed to ambient temperature for holding CWF gas at a low pressure close to atmospheric pressure. The gas holder 2 is an inexpensive, high-capacity container, such as one separated by a low-strength membrane. Furthermore, the system 1 includes one or more compression tanks 4, which constitute at least part of a DCFT module and are in fluid communication with the gas holder 2, and one or more storage tanks 3, which are exposed to ambient temperature and are in fluid communication with each compression tank 4, for storing high-energy-density liquid CWF at the end of the charging mode. One or more compression tanks 4 may also be exposed to ambient temperature, not limited to. Preferably, one or more storage tanks 3 and compression tanks 4 are pressure vessels capable of withstanding the relatively high pressure of the compressed CWF gas. Transfer fluids, such as hydraulic oil or water, may be exposed to air at atmospheric pressure and ambient temperature so that the transfer fluid is maintained in the liquid phase when held in the liquid reservoir 5. The liquid reservoir 5 is in fluid communication with each compression tank 4, and also with the hydraulic supply pump 7 and hydraulic turbine 6 used to utilize the gas energy stored in the discharge mode. The transfer fluid is optionally immiscible with the CWF fluid.

[0047] As shown in Figure 2, the operating cost of the multiphase energy storage system 1 can be reduced by supplying power not only to the supply pump 7 but also to the return pump, if in use, during the charging mode of electrical energy generated from a renewable energy source 11 such as a solar power generation system or a wind power plant, or from another energy source such as a power plant. The power generated by the renewable energy source 11 is usually supplied to the power grid 14. If the power demand is lower than the power generated by the renewable energy source, the surplus power can be supplied to the pumps to charge the system. Any surplus power generated by the renewable energy source 11 can be used to supply power to the supply pump and the return pump. Similarly, power generated by a generator connected to the hydraulic turbine 6 can be supplied to the power grid 14. The system can also be powered by other means well known to those skilled in the art under certain conditions.

[0048] Figure 6 shows another embodiment of the multiphase energy storage system, denoted 21 throughout. System 21 is similar to System 1, and is configured with additional devices such as a gas discharge conduit 23, a mixer 24, a gas-liquid separator 26, and a heat exchanger 28, each of which differs in its components, to constitute a further embodiment that provides advantageous features. With respect to the energy storage system 21, the liquid reservoir 25 is not exposed to ambient air, but rather is in fluid communication with the gas holder 2 by the gas discharge conduit 23, allowing any gas absorbed into the transfer fluid during a charging or discharging mode and then withdrawn from the transfer fluid to flow back into the gas holder by a closed conduit circuit arrangement. The transfer fluid remains non-vaporable under predetermined thermodynamic conditions of the charging and discharging modes, where the pressure of the transfer fluid is significantly higher than its saturation pressure within a controlled temperature range.

[0049] Figure 9 shows another embodiment of the multiphase energy storage system, denoted 71 throughout. The cost-effective system 71 does not require a storage tank and comprises a single compression tank 74 exposed to ambient temperature that can hold CWF and condense the CWF in direct contact with a non-vaporizing transfer fluid. A liquid reservoir 5 configured to receive the transfer fluid is exposed to the atmosphere and atmospheric pressure and is in liquid communication with a liquid supply conduit to which a hydraulic pump 7 is operably connected, and a turbine inlet conduit to which a hydraulic turbine 6 is operably connected. System 71 can also be coupled with a renewable energy source 11 and a power grid 14, as described with reference to Figure 2.

[0050] If the mass of gas currently held in System 1 in Figure 1 or System 71 in Figure 9 is less than the minimum required for efficient operation to generate electricity from the stored gas energy, an auxiliary gas tank (not shown) can be used to inject an auxiliary amount of gas into the compression tank or gas holder.

[0051] Charging mode First, referring to the multiphase energy storage system 71 in Figure 9, the transfer fluid is held in the liquid reservoir 5, and the low-pressure CWF is held in the compression tank 74, with all valves closed. When the liquid supply valve is opened and the supply pump 7 is activated, the transfer fluid is delivered to the compression tank 74. The introduced transfer fluid reduces the available volume that the CWF can occupy in the compression tank 74, thereby compressing the CWF. As additional transfer fluid is introduced, the CWF is further compressed until its pressure exceeds the saturation pressure and it condenses. The CWF is substantially isothermally compressed through direct contact with the transfer fluid. When the charging mode ends, the liquid supply valve is closed and the supply pump is stopped.

[0052] Referring to System 1 in Figure 1 and System 21 in Figure 6, in the pre-charge state, the CWF is held in the gas holder 2 in a gas phase state at atmospheric pressure or slightly above atmospheric pressure, the transfer fluid is held in the liquid reservoir 5, one or more storage tanks 3 are pre-compressed with gas, and one or more compression tanks 4 are filled with atmospheric gas or the transfer fluid.

[0053] If one or more compression tanks 4 are filled with transfer fluid, the procedure described with reference to Figure 4 is performed to facilitate the delivery of the transfer fluid to the liquid reservoir 5 while the gas flows from the gas holder 2 to one or more compression tanks 4.

[0054] When there is a sufficient volume of gas in one or more compression tanks 4, an isolation valve 3B at at least one port to each storage tank 3 is opened, providing a combined internal volume shared by each compression tank 3 and storage tank 4 via a terminal conduit 3A extending between them. The gaseous CWF flowing in from each compression tank 4 through the terminal conduit 3A flows through the isolation valve 3B without being discharged and is then received by the storage tank 3. If there are multiple storage tanks 3, the gaseous CWF flows in parallel through the corresponding isolation valves 3B and ports to the storage tanks, but not all isolation valves 3B are open at the same time.

[0055] After the initial portion of the CWF gas is introduced into one or more tanks 3 and 4, a liquid supply valve 1B is opened, which is operably connected to a region of liquid supply conduit 1A extending from the liquid reservoir 5 to one or more compression tanks 4, and is located downstream of a supply pump 7, which is also operably connected to the liquid supply conduit 1A. The hydraulic supply pump 7 is activated, causing the transfer liquid to be delivered from the reservoir 5 to one or more compression tanks 4.

[0056] The transfer fluid introduced into one or more compression tanks 4 reduces the combined volume of tanks 3 and 4 occupied by the CFW gas. As a result, the CFW gas is compressed inside the compression tank 4. As more transfer fluid is introduced into one or more compression tanks 4, the combined volume of tanks 3 and 4 occupied by the CFW gas decreases, and the CFW in both gas tanks 3 and 4 is further compressed. During compression, the CWF gas is cooled by direct contact with the transfer fluid, reducing the heat of compression, so that the CWF gas can be compressed at a substantially constant temperature. Finally, one or more compression tanks 4 are completely occupied by the transfer fluid, while the CWF gas that was in one or more compression tanks 4 moves to one or more storage tanks 3, where the CFW gas is further compressed. The CFW received in one or more storage tanks 3 liquefies once it is compressed to at least the saturation pressure. All valves are then closed, completing the charge mode cycle.

[0057] If the pressure of the CWF received in one or more storage tanks 3 is below the saturation pressure, an additional cycle of the charging mode may be performed. During each additional cycle, an additional gas portion is supplied to the compression tank 4 to increase the pressure of the stored CWF fluid.

[0058] Figure 3 shows various steps related to the execution of a charging mode cycle in conjunction with System 1 in Figure 1 and System 21 in Figure 6, according to one embodiment.

[0059] In order to initiate an additional cycle of the charging mode, or to start the first cycle of the charging mode, when one or more compression tanks 4 are filled with transfer fluid in step 29, a return valve 5B, which is operably connected in step 31 to another conduit 5A, i.e., a return conduit, extending from the liquid reservoir 5 to one or more compression tanks 4, is opened, and the transfer fluid is discharged from one or more compression tanks 4 back to the reservoir 5. Simultaneously, a gas supply valve 4B is momentarily opened to cause a flow of gas from the gas holder 2 to one or more compression tanks 4.

[0060] As the transfer fluid returns to reservoir 5, all valves are closed. Then, in step 36, each isolation valve 3B is opened. Next, in step 37, the supply pump 7 is activated to supply the transfer fluid to one or more compression tanks 4. As a result, the CWF gas supplied from the gas holder to one or more compression tanks 4 in the current cycle is compressed in step 39 and then moved by the transfer fluid to one or more storage tanks 3 in step 41. In step 43, the pressure of the stored CWF gas increases due to the additional introduction of CWF gas into one or more storage tanks 3. Finally, after one or more cycles, the pressure of the ambient temperature CWF received in one or more storage tanks 3 rises to the saturation pressure and liquefies in step 45.

[0061] If one or more compression tanks 4 are filled with gas in step 35, the charging mode cycle proceeds to step 36.

[0062] In another embodiment, gas is supplied to one or more compression tanks via a gas supply valve in step 33, and steps 37 and 39 are performed to compress the supplied gas in one or more compression tanks while closing isolation valves at the inlet ports of each storage tank to increase the pressure applied in the compression tanks. After the isolation valves are opened, the compressed fluid is transferred to the storage tanks by a transfer fluid. The transferred fluid may be in a gaseous state or a gas-liquid two-phase state, and undergoes a first stage of compression in the compression tanks and a second stage of compression in the storage tanks until it is completely liquefied.

[0063] In another embodiment shown in Figure 4, for example, if the pressure difference between the gas holder and the compression tank is relatively low, some of the gas is drawn out of the gas holder by suction. Such suction flow is possible when one or more compression tanks are filled with transfer fluid in step 31. While the gas supply valve is open, in step 44, a return pump operably connected to a return conduit extending between one or more compression tanks and a reservoir is activated. The flow of transfer fluid through the return conduit toward the reservoir generates a suction that draws gas from the gas holder to one or more compression tanks in step 48.

[0064] The volume of CWF fluid that can be stored in liquid form at a given pressure is significantly smaller than that provided in gaseous form. Therefore, the ability of systems 1, 21, and 71 to store CWF in liquid form significantly increases the energy density of the working fluid, i.e., the potential stored energy per unit volume, compared to prior art that stores working fluid in gaseous form. The energy density achievable with CWF can also be favorably increased by the reduction of heat loss due to substantial isothermal compression and expansion. The capital cost of the small-capacity storage tank 3 is significantly lower than that of the large-capacity storage tank required to store compressed gas in gaseous form.

[0065] As shown in System 21 of Figure 6, if the gas holder 2 contains additional low-pressure gases that are non-CWF but can be mixed with CWF, such as air or non-condensable gas (NCG), the energy density of the fluid stored in one or more storage tanks 3 can be further increased. This mixed gas is compressed in step 39 and transferred to one or more storage tanks in step 41. After the CWF is liquefied in step 45, the non-CWF gas can be further compressed to further increase the energy density of the stored fluid, such as when an additional volume of the transferred fluid is introduced into the compression tank 4. In Systems 1 and 71, it will be understood that non-CWF can also be mixed with CWF to increase the energy density of the stored compressed fluid.

[0066] A high energy density of CWF received in one or more storage tanks 3 is advantageous because it allows for the release of more energy from the stored CWF in discharge mode.

[0067] Referring to a multiphase energy storage system 21 schematically shown in Figure 6, which relates to another embodiment, the energy density of the CWF transferred to the storage tank 3 can be further increased by preventing the inflow of the transfer liquid into each storage tank, allowing more CWF to occupy and condense inside the storage tank. The inflow of the transfer liquid into the storage tank can be prevented by providing a gas-liquid separator 26 at the inlet of the storage tank's port, or a liquid-liquid separator if the CWF also condenses in the compression tank. The gas-liquid separator 26 may, for example, allow the transfer liquid to fall under the influence of gravity within the gas-liquid separator and return it to the compression tank 4. The gas-liquid separator 26 may also be embodied by a buffer tank positioned above the height of each compression tank 4. The gas-liquid separator 26 or liquid-liquid separator may be operably connected to a conduit 27 extending from a dedicated outlet provided in the corresponding compression tank 4 to a terminal conduit 3A with which it is in fluid communication.

[0068] If systems 1 and 21 employ a gas-liquid separator 26, the CFW can be isothermally compressed as a result of the cooling effect of ambient temperature air or ground surrounding one or more storage tanks 3, even if the transferred liquid and the CFW fluid are not in direct contact within one or more storage tanks 3. Furthermore, by compressing the CFW slowly, for example over several hours, the heat of compression can be reduced or completely removed.

[0069] Alternatively or additionally, isothermal compression may be ensured by a mixer, as schematically shown in the multiphase energy storage system 21 of Figure 6 and the multiphase energy storage system 71 of Figure 9. A mixer unit 24B, installed to be in fluid communication with the corresponding storage tank 3, can be activated when the CWF begins to liquefy, for example, when it becomes a gas-liquid two-phase state. The liquid and gaseous portions of the CWF can be mixed to provide a fluid with a substantially uniform temperature and heat transfer coefficient, and eliminate temperature gradients within the stored CWF by absorbing the released heat of compression. Unit 24B can be activated in response to the detection of a predetermined pressure in the corresponding storage tank 3 or the detection of the presence of liquid by a relevant sensor. Similarly, a mixer unit 24A, which may be identical or different from unit 24B, may be in fluid communication with the corresponding compression tank 4.

[0070] Mixing devices can take various forms. Mixing devices, such as agitators, may be rotatably mounted to the corresponding tank. The agitator provides homogeneity of the stored fluid in terms of temperature, heat transfer coefficient, and composition in order to mix any particles that may have settled from the compressed liquefied solution.

[0071] The mixing device may also be located outside the corresponding tank. In one embodiment, the mixing device comprises a set of conduits and nozzles, thereby allowing a portion of the fluid in one area of ​​the tank to flow through one of the conduits, for example, in conjunction with a pump, and be injected into another area of ​​the tank through one or more nozzles. This arrangement can also facilitate the circulation of the transfer fluid between two or more compression tanks 4, which may be interconnected, or from one or more compression tanks 4 to one or more storage tanks 3, which may also be interconnected.

[0072] Furthermore, to assist in achieving isothermal compression, heat exchangers 28A in heat exchange relationship with one or more compression tanks 4, or heat exchangers 28B in heat exchange relationship with one or more storage tanks 3, may be provided. Each heat exchanger may be of shell-and-tube type, finned-tube type, plate heat exchanger type, air-cooled type, or other heat exchanger types well known to those skilled in the art. The tubing through which the cooling medium flows may be shared with conduits associated with the mixing device, such as when one or more valves are selectively opened and closed to allow flow to the heat exchanger or to the mixing device unit. Two or more heat exchangers may be used, and each heat exchanger may be of the same type or of a different type.

[0073] Discharge mode Condensed CWF can be stored in a charged state for extended periods until the discharge mode is initiated. The discharge mode is generally initiated during periods of peak demand or when energy availability is insufficient. This is because the energy stored in the multiphase energy storage system can be discharged whenever needed to generate power for the grid.

[0074] During the discharge mode, the transfer fluid is propelled toward the hydraulic turbine by the high-pressure liquid CWF to generate power. By using the transfer fluid to induce compression of the CWF during the charging mode and to be propelled by the CWF during the discharge mode, a hydraulic turbine can be favorably employed to generate power, in contrast to the gas turbines used in prior art compressed gas storage systems. Advantages of using a hydraulic turbine compared to a gas turbine include high efficiency, low rotational speed, easy maintenance, and low running costs.

[0075] These advantages are also related to the fact that, in contrast to prior art compressed gas storage systems which use compressors to introduce compressed gas, multiphase energy storage systems use hydraulic pumps.

[0076] Referring to the multiphase energy storage system 71 in Figure 9, the CWF liquid and the high-pressure transfer fluid are held in the compression tank 74 in anticipation of the subsequent start of the discharge mode. The CWF fluid is compressed to its saturation pressure, which is considerably higher than the pressure under pre-charge conditions, and since the transfer fluid is held in the same closed compression tank 74 as the CWF liquid, the CWF liquid exerts a force on the transfer fluid that pressurizes it to the same saturation pressure as the CWF liquid. The pressurized transfer fluid in the compression tank 74 is at a pressure considerably higher than the atmospheric pressure to which the transfer fluid held in the liquid reservoir 5 is exposed.

[0077] When the turbine injection valve opens and the discharge mode begins, the high pressure difference between the high-pressure transfer fluid in the compression tank 74 and the low-pressure transfer fluid in the liquid reservoir 5 prompts the high-pressure transfer fluid to be discharged from the compression tank 74 with sufficient kinetic energy to rotate the hydraulic turbine and generate electricity. As the high-pressure transfer fluid is discharged from the compression tank 74, the additional volume of the compression tank 74 that is not occupied by the transfer fluid becomes available to the CWF, and as a result the CWF can expand into a gas-liquid two-phase state. Note that since the multiphase CWF expands isobarically, the pressure of the CWF and the transfer fluid pressurized by the CWF does not change, thereby allowing the power output to be sustained for a certain period of time. When the CWF becomes gaseous, the pressure of the high-pressure transfer fluid decreases. Nevertheless, the pressure of the propelled transfer fluid is high enough to rotate the hydraulic turbine 6 and generate electricity until it falls below the turbine's inherent threshold. When the discharge mode ends, the turbine injection valve closes and the liquid supply valve opens.

[0078] The simplicity of system 71 allows the transferred fluid to circulate back and forth in a piston-like manner between the liquid reservoir 5 and the compression tank 74 while the charging and discharging modes are performed alternately, thereby generating additional power.

[0079] In the pre-charge state, referring to System 1 in Figure 1 and System 21 in Figure 6, all valves are closed, and the CWF fluid held in one or more storage tanks 3 is exposed to ambient temperature in the storage tanks, compressed to a relatively high pressure, and then in the liquid phase. Non-CWF gases, which, when mixed with the CWF fluid, are compressed to a higher pressure than the CWF liquid, are also held in one or more storage tanks 3.

[0080] Figure 5 shows various steps related to the execution of a discharge mode according to one embodiment.

[0081] In the first step 51 of the discharge mode, if there is no transfer fluid in any of the compression tanks 4 after the final cycle of the charge mode, the return valve 5B is momentarily opened, and the transfer fluid received in the reservoir 5 with a relatively high head value flows through the return conduit 5B, allowing one or more compression tanks to be filled. Alternatively, the liquid supply valve 1B may be momentarily opened to activate the supply pump 7 and supply the required amount of transfer fluid to one or more compression tanks 4. This step may be omitted if there is a sufficient volume of transfer fluid in one or more compression tanks 4. Each compression tank may be equipped with a sensor, such as a capacitive level sensor or a float switch, and possibly a pressure sensor, to determine that the transfer fluid is at a predetermined liquid level. Subsequently, the return valve 1B or valve 5B is closed to prevent the return flow of the transfer fluid.

[0082] In step 53, the turbine injection valve 2B and at least one storage tank isolation valve 3B are opened. As a result, the high-pressure compressed liquid, including at least the CWF liquid, is exposed to the lower pressure in the compression tank 4 and is released from the storage tank 3 in step 55 through the terminal conduit 3A, to which the corresponding opened isolation valve 3B is in fluid communication, and expands slightly. The released CWF liquid is forced into contact with the transfer liquid in each compression tank 4 in step 57 and, as a result of the pressure difference between the transfer liquid in the liquid reservoir and the CWF liquid, propels the transfer liquid through the turbine inlet conduit 2A to which the turbine injection valve 2B is operably connected. The transfer liquid can be propelled as long as the pressure difference between the transfer liquid, which is at the same pressure as the CWF and propelled by the CWF, and the transfer liquid in the liquid reservoir 5 downstream of the hydraulic turbine 6 is greater than a predetermined threshold. As the volume occupied inside the combined tanks 3 and 4 increases with the movement of the transfer liquid, the CWF liquid can evaporate while expanding isobarically in step 59, resulting in a gas-liquid two-phase state. The pressure of the multiphase CWF fluid, and the pressure of the CWF when it is entirely in the gas phase, are high enough to keep the transfer fluid propelled through the turbine inlet conduit 2A. Direct contact between the CWF gas and the transfer fluid reduces the temperature change of the CWF gas, allowing the CWF gas to expand substantially isothermally. This expansion process continues as the transfer fluid is increasingly propelled and the CWF fluid, now entirely in a gaseous state, occupies the increased volume. The transfer fluid propelled through the turbine inlet conduit 2A consequently drives the hydraulic turbine 6 to rotate in step 61, generating electricity. The transfer fluid exiting the hydraulic turbine 6 flows into the reservoir 5 in step 63, raising the liquid level in the liquid reservoir. When the volume of transfer fluid remaining in one or more compression tanks falls below the propellable volume, all valves are closed in step 65 to complete the discharge mode cycle. Subsequently, in step 67, the gas supply valve 4B is opened, and the pressure difference between one or more compression tanks 4 and the gas holder 2 causes the gas remaining in one or more compression tanks to flow back into the gas holder 2 through the gas supply conduit 4A.

[0083] Therefore, using a CWF fluid that undergoes phase change during the discharge mode does not reduce the amount of power that can be extracted; rather, the multiphase CWF fluid is involved in continuing to propel the transfer fluid toward the hydraulic turbine, generating an additional amount of power. This power extraction capability, in addition to the advantages provided by the condensing fluid, allows for a reduction in the volume of the compression tank and storage tank.

[0084] If the pressure of the fluid, including at least CWF, remaining in one or more storage tanks 3 is sufficiently greater than atmospheric pressure to facilitate the propulsion of the transfer fluid, one or more cycles including the above steps may be repeated in discharge mode. That is, step 51 is performed to refill the transfer fluid from the reservoir 5 when one or more compression tanks 4 are sufficiently empty, and the refilled transfer fluid is then propelled by the fluid released from one or more storage tanks in step 57. In step 69, additional cycles may be repeated until the pressure of the gas in one or more storage tanks 3 drops to a pressure below the propulsion pressure at which the transfer fluid can be propelled.

[0085] The sequence of steps in both the charging and discharging modes can be manually controlled when operating the various flow control devices, or it can be automatically controlled in response to the operation of the control devices. Each step may be executed according to a time-sensitive or sensed action commanded by the control device. With the intervention of the control device, the charging and discharging steps can be synchronized to provide a continuous discharge operation.

[0086] By employing a large-capacity gas holder 2 and performing multiple charge-discharge cycles, it is advantageous that the volume of one or more compression tanks 4 can be reduced, thereby lowering costs. Depending on the gas energy storage needs, systems 1 and 21 can be scaled up or down by changing the number or size of one or more tanks. If system 1 or system 21 comprises multiple storage tanks 3 and compression tanks 4, each storage tank and each compression tank may be connected to one another. For more efficient transfer operations, different steps may be performed simultaneously in relation to two different tanks. For example, liquid transfer can be flowed into the first compression tank 4 at the start of the next discharge cycle, while simultaneously, in another discharge step, the CWF can be expanded in the second compression tank to propel the liquid transfer and rotate a hydraulic turbine.

[0087] Figures 7 and 8 show various exemplary thermodynamic states of a CWF fluid. In state F, the CWF gas is introduced into a compression tank at a relatively low pressure, for example, from a gas holder, and the pressure of the CWF gas steadily increases to the saturation pressure of the CWF in state G, as the transfer fluid is introduced into the compression tank. The CWF undergoes a phase change in state G to become a two-phase fluid, and then condenses isobarically in state H until it is completely liquefied and occupies the minimum volume. Due to direct contact with the transfer fluid and ambient influences, the CWF is isothermally compressed through a charging mode from state F to state H, and these states are reversed when the CWF fluid isothermally expanded through a discharge mode from state H to state F.

[0088] Although Figures 1, 6, and 9 show only a single hydraulic turbine 6, it is understood that two or more hydraulic turbines may be employed. If the pressure of the CWF propelling the transfer fluid is sufficiently high, as detected by the sensor, two or more hydraulic turbines may be used to generate additional power. Different types of turbines may be used for each stage to maximize efficiency with respect to the designed operating conditions of a particular stage, such as a given range of pressure drop, specific speed, or head. Alternatively, multiple turbines may be used in parallel. Upon receiving the pressure measurement detected by the sensor, the control device can command flow control components, such as a valve at the outlet of the first-stage turbine, to send the transfer fluid leaving the first-stage turbine to the inlet of the second-stage turbine, thereby driving the second-stage turbine to rotate.

[0089] It will be understood that multiple supply pumps may be used in parallel or in series.

[0090] As described above in this specification, with respect to the energy storage system, it is possible to alternately perform multiple charging and discharging cycles, the charging cycle being repeatable when the pressure of the CWF is below the saturation pressure, and the discharging cycle being repeatable when the pressure of the propulsion fluid, which includes at least the CWF, is sufficiently greater than atmospheric pressure to promote the propulsion of the transfer fluid.

[0091] Figures 10 and 11 show another embodiment of a multiphase energy storage system, denoted 91 throughout. System 91 is a closed system, each comprising a gas holder, one or more storage tanks, a hydraulic turbine, and two or more DCFT modules that are in fluid communication with at least one other DCFT module. The presence of two or more DCFT modules is advantageous because it allows charge or discharge cycles to be repeatedly performed with minimal waiting time between subsequent cycles.

[0092] The multiphase energy storage system 91 includes a gas holder 92 exposed to ambient temperature, which is indicated to hold CWF gas at a low pressure close to atmospheric pressure and additional low-pressure non-CWF gas such as air or NCG, but may hold only CWF. Furthermore, the system 91 includes two or more DCFT modules, for example DCFT modules 93a and 93b, one or more storage tanks exposed to ambient temperature, for example three storage tanks 94a to 94c, for storing CWF, particularly liquid CWF, or a mixture of liquid CWF and NCG that will have a high energy density at the end of the charging mode, at least one hydraulic turbine 96, a low-pressure liquid reservoir 98 for receiving liquid discharged from the hydraulic turbine 96, and pumps 108 and 109. The DCFT modules 93a to 93b may be referred to as the “first module” and the “second module,” respectively, and are preferably pressure vessels capable of withstanding the relatively high pressure of the compressed CWF gas. The fluid held by the gas holder 92 and capable of flowing within the energy storage system may also be called the "CWF-based fluid." At least pumps 108 and 109 and a schematically illustrated control device 107, which communicates data with valves, synchronize the flow of the transfer fluid and the CWF-based fluid.

[0093] Figure 10 shows the operation of system 91 in charging mode. In the pre-charging state, all valves are closed. The first DCFT module 93a is filled with a non-vaporizing transfer fluid, and the second DCFT module 93b and storage tanks 94a-94c are filled with CWF or a mixture of CWF and non-CWF gas, which is maintained at a predetermined pre-compression pressure in the gas phase before being compressed by the transfer fluid. The first DCFT module 93a, the second DCFT module 93b, and storage tanks 94a-94c can be pre-filled by well-known means such as pumps and valves, or by any other suitable means.

[0094] A pressure control means 103B connected to the second DCFT module 93b can communicate data with a control device and ensure that the inside of the second module reaches a predetermined pre-compression pressure. The pressure control means 103B may be implemented by means well known to those skilled in the art, such as a pressure gauge or pressure regulator, and may optionally include an isothermal compressor for rapidly increasing the gas pressure inside the second module while minimizing compression heat. A similar pressure control means 103A may be connected to the first DCFT module 93a.

[0095] To initiate the first charging cycle, the liquid discharge valve 101A of the first module, the liquid inlet valve 102B and liquid supply valve 114 of the second module, the gas inlet valve 111A of the first module, the gas inlet valve 111B of the second module, and the gas transfer valve 117B of the second module are opened. Since the gas inlet valve 111B of the second module is opened and in fluid communication with the gas holder 92, the pressure of the gas in the gas holder is also maintained at a predetermined pre-compression pressure. Next, the first pump 108 is activated, and the transfer fluid is sent from the first module 93a to the second module 93b, flowing in the direction of arrow A through conduit 121 extending from the first port of the first module, flowing through conduit 123 to which the first pump 108 and liquid supply valve 114 are operably connected, and flowing in the direction of arrow B through conduit 124 extending from the end of conduit 123 to the second port of the second module 93b.

[0096] The transfer fluid introduced into the second module 93b reduces the volume occupied by the gas held within the second module 93b. As a result, the held gas can be compressed inside the second module 93b. During compression, the held gas is cooled by direct contact with the transfer fluid, reducing the heat of compression, so that the held gas can be compressed substantially isothermally. When the second module 93b is filled with the transfer fluid, the compressed CWF-based gas is encouraged to move and flow across the sixth port of the second module 93b, flow through conduit 127 in the direction of arrow C, and through conduit 128 and the corresponding conduit 129 in the direction of arrow D to the first port of one or more storage tanks 94a-94c. The compressed gas transferred from the second module 93b further compresses the CWF-based gas stored in each of the one or more storage tanks 94a-94c.

[0097] Substantial isothermal compression of the CWF-based fluid can be ensured by circulating the cooling transfer fluid located at the bottom of the second module 93b in a closed loop through the fourth and fifth ports of the second module and through conduits 136-138 by the second pump 109 when the isolation valve 116B, which is operatively connected to conduit 136, and the isolation valve 118B, which is operably connected to conduit 138, are opened. The degree of cooling provided by the circulating transfer fluid can be increased by the heat exchanger 104, which is in heat exchange relationship with conduit 137. Alternatively or additionally, a mixing device or spray nozzle used when isolation valves 116B and 118B are open can be used to assist in ensuring substantial isothermal compression.

[0098] In response to the pump-driven discharge of the transfer fluid from the first module 93a, a portion of the CWF-based gas held in the gas holder 92 flows to the first module 93a in the directions of arrows E and F via conduits 131-133 and the third port of the first module, maintaining the non-liquid volume within the first module at a pre-compression pressure in anticipation of subsequent charging cycles.

[0099] The first charging cycle ends when the second module 93b is completely filled with the transfer fluid, the first module 93a is filled with CWF-based gas at a pre-compression pressure, and one or more storage tanks 94a-94c are compressed by the CWF-based gas transferred from the second module 93b and then completely filled with CWF-based gas at a pressure higher than the initial pre-compression pressure, i.e., when no other fluid is received into one or more storage tanks. Thereafter, all valves are closed.

[0100] To initiate the second charging cycle, the liquid discharge valve 101B of the second module, the liquid inlet valve 102A and liquid supply valve 114 of the first module, the gas inlet valve 111A of the first module, the gas inlet valve 111B of the second module, and the gas transfer valve 117B of the first module are opened. Then, the first pump 108 is activated, and the transfer fluid is sent from the second module 93b to the first module 93a, flows through conduit 141 extending from the first port of the second module in the direction of arrow G, through conduit 123, and flows through conduit 144 extending from the end of conduit 123 to the second port of the first module 93a in the direction of arrow H. The same process that was performed in the first charging cycle is repeated in the second charging cycle. Thus, once the first module 93a is filled with the transfer fluid, the compressed gas is encouraged to move and flow across the sixth port of the first module 93a, flow through conduit 147 in the direction of arrow I, and through conduit 128 and the corresponding conduit 129 in the direction of arrow D to one or more storage tanks 94a to 94c. The compressed gas transferred from the first module 93a further compresses the CWF-based gas stored in each of the one or more storage tanks 94a to 94c.

[0101] The second charging cycle ends when the first module 93a is completely filled with the transfer fluid, the second module 93b is filled with CWF-based gas at a pre-compression pressure, and one or more storage tanks 94a-94c are compressed by the CWF-based gas transferred from the first module 93a and then completely filled with CWF-based fluid at a pressure higher than the pressure reached at the end of the first charging cycle. All valves are then closed.

[0102] The charging cycle can be repeated in the same manner, as long as the first and second modules are alternately filled with the transfer fluid and CWF-based gas at a pre-compression pressure in each subsequent charging cycle. During each subsequent charging cycle, the transfer fluid is circulated back and forth between the first and second modules, and the volume of the module from which the transfer fluid has been discharged is replenished with CWF-based gas from the gas holder, so that the two modules are ready for immediate use in the subsequent charging cycle when the previous charging cycle is completed. The charging process continues until the CWF-based fluid in one or more storage tanks 94a-94c condenses and undergoes a phase change from gas to liquid. The liquid CWF-based fluid is stored in one or more storage tanks 94a-94c until discharge is required.

[0103] During any charging cycle, the stored CWF-based fluid can, if necessary, be cooled, heated, or mixed in conjunction with the appropriate device 122 by opening an isolation valve 119 operably connected to the conduit 126, and the conduit 126 is in fluid communication in parallel with the second and third ports of each of the storage tanks 94a-94c to facilitate the circulation of the stored CWF-based fluid in a closed loop. Alternatively, the conduit 126 is configured to deliver a cooling medium such as water that can flow through a cooling coil located inside one or more storage tanks.

[0104] Figure 11 shows the operation of system 91 during discharge mode. In the pre-discharge state, all valves are closed. Also, one module is completely filled with the transfer fluid, and the other module is completely filled with CWF-based gas at pre-compression pressure. In the following exemplary first discharge cycle, the first module 93a is completely filled with the transfer fluid, and the second module 93b is completely filled with CWF-based gas at pre-compression pressure.

[0105] To initiate the first discharge cycle, the liquid discharge valve 101A, the gas transfer valve 117A, and the turbine injection valve 151 of the first module are opened. A predetermined amount of CWF-based fluid, which can be controlled by instantaneously opening the gas transfer valve 117A of the first module for a predetermined time or depending on a sensed value, flows through conduits 129, 128, and 147 in directions J and K until it is released from one or more storage tanks 94a-94c and introduced into the interior of the first module 93a. The released CWF-based fluid is forced into contact with the transfer fluid within the first module 93a, thereby pressurizing the transfer fluid to the same pressure as the released CWF-based fluid. As a result of the pressure difference between the turbine inlet, which is at a pressure substantially equal to that of the pressurized transfer fluid, and the turbine outlet, which is exposed to the low-pressure reservoir 98, the transfer fluid is propelled through conduits 121, 148, and 153 toward the hydraulic turbine 96 in directions L and M. A conduit 153, to which the turbine injection valve 151 is operably connected, extends from the junction between conduits 141 and 148 to the reservoir 98. The transferred fluid drives the hydraulic turbine 96, generating electricity that can be supplied to the power grid. The reservoir 98 is fluid-communicated with the gas holder 92 via the connecting conduit 143 and is not exposed to the environment, or is fluid-communicated with the ambient air, and receives the transferred fluid discharged from the hydraulic turbine 96.

[0106] As the high-pressure transfer fluid is discharged from the first module 93a, the additional volume of the first module 93a not occupied by the transfer fluid becomes available to the CWF-based fluid, and as a result the CWF-based fluid expands and can become a gas-liquid two-phase state or entirely gaseous. Direct contact between the CWF-based fluid and the transfer fluid reduces the temperature change of the CWF-based fluid, allowing the CWF-based fluid to undergo substantially isothermal expansion.

[0107] Substantial isothermal expansion of the CWF-based fluid in the first module 93a can be ensured by circulating the heated transfer fluid located at the bottom of the first module 93a in a closed loop through conduits 135, 137, and 139, across the fourth and fifth ports of the first module, using the second pump 109, when the isolation valve 116A operably connected to conduit 135 and the isolation valve 118A operably connected to conduit 139 are opened while the CWF-based fluid undergoes a cooling process. Alternatively or additionally, a mixer or spray nozzle used when the isolation valves 116A and 118A are open may assist in ensuring substantial isothermal expansion.

[0108] Simultaneously with the discharge of the high-pressure transfer fluid from the first module 93a, the liquid inlet valve 102b, the gas outlet valve 113b, and the return valve 156 of the second module are opened. As a result, while the transfer fluid flows into the reservoir 98, the received transfer fluid is sent to the second module 93b by the first pump 108 in anticipation of the next discharge cycle, and flows in the N and O directions through the return conduit 158, conduits 123 and 124. Accordingly, the CWF-based gas is moved by the delivered transfer fluid from the seventh port of the second module 93b through conduits 131 and 149 to the gas holder 92 in the P and Q directions. The first discharge cycle ends when the first module 93a is completely filled with CWF-based gas at a predetermined low pressure and the second module 93b is completely filled with transfer fluid at approximately atmospheric pressure. After that, all valves are closed.

[0109] To initiate the second discharge cycle, the liquid discharge valve 101B and turbine injection valve 151 of the second module are opened. When the gas transfer valve 117B of the second module is opened instantaneously, a predetermined amount of CWF-based fluid is released from one or more storage tanks 94a-94c and flows through conduits 127-129, 128 in the J and R directions until it is introduced into the second module 93b for a predetermined duration or until a sensing value is detected. Once the predetermined amount of CWF-based fluid has been introduced into the second module 93b, valve 117b is closed. As a result, the transfer fluid in the second module 93b is propelled by the released CWF-based fluid through conduits 141 and 153 toward the hydraulic turbine 96 in the S and M directions, generating electricity that can be supplied to the power grid.

[0110] The same process performed in the first discharge cycle is repeated in the second discharge cycle, but with respect to the other module. Thus, the transfer fluid that flows into reservoir 98 is returned to module 93a by pump 108 in anticipation of the next discharge cycle, while the liquid inlet valve 102A, gas outlet valve 113A, and return valve 156 of module 1 are open, and flows in the N and T directions through return conduit 158 ​​and conduits 123 and 159. Accordingly, the CWF-based gas is moved by the delivered transfer fluid from port 7 of module 93a through conduits 131, 149, and 161 to gas holder 92 in the U, P, and Q directions. The second discharge cycle ends when module 93b is completely filled with CWF-based gas at a predetermined low pressure and module 93a is completely filled with transfer fluid at approximately atmospheric pressure. All valves are then closed.

[0111] The discharge cycle can be repeated in the same manner for each subsequent discharge cycle, provided that the first and second modules are alternately filled with the transfer fluid and CWF-based gas at a predetermined low pressure. Between each subsequent discharge cycle, the transfer fluid is circulated back and forth between the first and second modules, and the CWF-based gas is received in the modules from which the transfer fluid has been discharged from one or more storage tanks, so that the two modules are ready for immediate use in the subsequent discharge cycle at the end of the previous discharge cycle. The discharge process continues until the pressure of the CWF-based liquid in one or more storage tanks 94a-94c drops to a predetermined pre-compression pressure.

[0112] As can be understood from the above description, by using conventional hydraulic equipment, namely a hydraulic pump in charging mode and a hydraulic turbine in discharge mode, cost reductions for mechanical energy storage and improvements in the overall reciprocating efficiency of the system can be achieved in the system of the present invention compared to the implementation of the prior art. Since the working fluid used in the system of the present invention can be advantageously subjected to substantial isothermal compression, cost reductions can also be achieved by avoiding the need for additional thermal energy storage that is typically required in the prior art to absorb the heat of compression.

[0113] While several embodiments of the present invention have been described for illustrative purposes, it will be apparent that the present invention can be implemented without departing from the claims by many modifications, variations and adaptations that are within the scope of the art, as well as by the use of numerous equivalents or alternative solutions.

Claims

1. a) A first pressure vessel having at least four ports through which the corresponding conduits are in fluid communication, b) A second pressure vessel set to a temperature below room temperature and comprising one or more ports that are in fluid communication with the first pressure vessel, c) A gas holder that is in fluid communication with the first pressure vessel and contains a condensable working fluid (CWF) that can be condensed at room temperature, and d) A liquid reservoir that is in fluid communication with the first pressure vessel and contains a non-vaporizing liquid, A multiphase energy storage system comprising, The CWF is introduced into the first pressure vessel from the gas holder via the first port of the at least four ports, and is substantially isothermally compressible in the first pressure vessel by direct contact with a non-vaporizing liquid that is not vaporizable in the first and second pressure vessels and is introduced into the first pressure vessel via the second port of the at least four ports. After introducing a sufficient volume of the CWF or the non-vaporizing liquid into the first pressure vessel, at least a portion of the compressed CWF in the first pressure vessel can be transferred from the first pressure vessel to the second pressure vessel via one of the one or more ports through a third port of the at least four ports by direct contact with the non-vaporizing liquid, and all or most of the compressed CWF in the second pressure vessel can be stored in liquid form after being compressed and condensed to saturation pressure. At least a portion of the non-vaporizing liquid in the first pressure vessel can be propelled through the fourth of the at least four ports by the compressed CWF discharged from the second pressure vessel. A multiphase energy storage system in which, under ambient temperature conditions, the CWF circulates between the gas holder, the first pressure vessel, and the second pressure vessel, and the non-vaporizing liquid circulates between the liquid reservoir and the first pressure vessel to isothermally compress the CWF, thereby releasing the stored energy.

2. The energy storage system according to claim 1, wherein the gas holder is a gas source that fluidly communicates with the first pressure vessel and contains the CWF, and the CWF can be supplied from the gas source to the first pressure vessel.

3. The energy storage system according to claim 1, further comprising at least one hydraulic turbine drivable by the non-vaporous liquid, wherein at least a portion of the non-vaporous liquid in the first pressure vessel is propelled toward the at least one hydraulic turbine by the compressed CWF released from the second pressure vessel.

4. The means for discharging the non-vaporizing liquid from the liquid reservoir to the first pressure vessel, The energy storage system according to claim 3, wherein the non-vaporizing liquid can be introduced into the first pressure vessel by the dispensing means through a second port of the at least four ports.

5. The energy storage system according to claim 4, wherein the non-vaporizing liquid discharged from at least one hydraulic turbine can be received in the liquid reservoir.

6. The energy storage system according to claim 1, wherein the CWF is substantially isothermally compressible and expandable during direct contact with the non-vaporizing liquid in the first pressure vessel.

7. The energy storage system according to claim 4, wherein the delivery means is at least one hydraulic pump for delivering the non-vaporizing liquid from the liquid reservoir to the first pressure vessel.

8. A minimum of the following means for discharging the non-vaporizing liquid from the first pressure vessel to the liquid reservoir The energy storage system according to claim 7, further comprising one additional hydraulic pump.

9. The energy storage system according to claim 1, wherein the CWF in the first pressure vessel is continuously and additionally compressed while an additional non-vaporizing liquid is introduced into the first pressure vessel.

10. The energy storage system according to claim 1, further comprising a gas-liquid separator disposed between the first pressure vessel and the second pressure vessel to prevent the flow of the non-vaporizing liquid into the second pressure vessel.

11. The energy storage system according to claim 10, further comprising a liquid-liquid separator positioned between the first pressure vessel and the second pressure vessel to prevent the flow of the non-vaporizing liquid into the second pressure vessel.

12. The energy storage system according to claim 1, further comprising a liquid-liquid separator disposed between the first pressure vessel and the second pressure vessel to prevent the flow of the non-vaporizing liquid into the second pressure vessel.

13. The system further comprises a third pressure vessel capable of fluid communication with the first pressure vessel, The energy storage system according to claim 1, wherein, before performing either a charging cycle, which is a series of operations relating to energy storage, or a discharging cycle, which is a series of operations relating to energy release, the third pressure vessel is completely filled with a first fluid selected from CWF gas or the non-vaporous liquid, the first pressure vessel is completely filled with a second fluid, selected from CWF gas or the non-vaporous liquid, and different from the first fluid, and when completed, the third pressure vessel is completely filled with the second fluid and the first pressure vessel is completely filled with the first fluid.

14. The energy storage system according to claim 1, wherein the second pressure vessel is exposed to a temperature of room temperature or below room temperature, and the first pressure vessel is also exposed to room temperature.

15. The energy storage system according to claim 1, comprising a plurality of the first pressure vessels.

16. The energy storage system according to claim 15, wherein all of the first pressure vessels are in fluid communication with each other, or selected first pressure vessels are in fluid communication with each other.

17. The energy storage system according to claim 1, comprising a plurality of the second pressure vessels.

18. The energy storage system according to claim 17, wherein all of the second pressure vessels are in fluid communication with each other, or selected second pressure vessels are in fluid communication with each other.

19. The energy storage system according to claim 2, wherein the gas holder further contains a non-CWF gas that can be mixed with the CWF, the non-CWF gas is further compressible after the liquefaction of the CWF, and further comprises a first heat exchanger in heat exchange relationship with the first pressure vessel and a second heat exchanger in heat exchange relationship with the second pressure vessel to assist in achieving isothermal compression.

20. The energy storage system according to claim 1, further comprising flow control components operably connected to each of the corresponding conduits for selectively controlling the flow of fluid through the corresponding conduits.

21. The energy storage system according to claim 1, wherein the second pressure vessel is exposed to a temperature of room temperature or below room temperature.

22. A method for generating electricity from stored energy, a) Provide a first pressure vessel and a second pressure vessel, and a gas holder that is in fluid communication with the first pressure vessel and contains a condensable working fluid (CWF) that can be condensed at room temperature, wherein the second pressure vessel is in fluid communication with the first pressure vessel and is set to a temperature below room temperature. b) In a room temperature environment, the CWF is introduced from the gas holder into the first pressure vessel, the CWF is substantially isothermally compressed in direct contact with a non-vaporizing liquid within the first pressure vessel, and at least a portion of the CWF compressed in the first pressure vessel is transferred from the first pressure vessel to the second pressure vessel in response to the interaction with the non-vaporizing liquid. c) Transfer the additional amount of compressed CWF to the second pressure vessel, compress all or most of the compressed CWF in the second pressure vessel to saturate pressure, and condense it to produce the compressed CWF in a liquid state. d) The compressed CWF discharged from the second pressure vessel propels at least a portion of the non-vaporizing liquid in the first pressure vessel toward at least one hydraulic turbine. e) A step comprising driving the propelled non-vaporous liquid to rotate the at least one hydraulic turbine to generate electricity, A method in which the flow of the non-vaporizing liquid into the second pressure vessel is blocked while at least a portion of the compressed CWF is being transferred from the first pressure vessel to the second pressure vessel.

23. The method according to claim 22, wherein the CWF is substantially isothermally compressed by operating a unit of a mixing device that is in fluid communication with the first pressure vessel or the second pressure vessel, thereby eliminating the temperature gradient within the CWF.

24. The method according to claim 23, wherein the mixing device unit is operated in accordance with a sensed state indicating liquefaction of the CWF.

25. At least a portion of the non-vaporizing liquid in the first pressure vessel is propelled toward the at least one hydraulic turbine by the compressed CWF discharged from the second pressure vessel. The method according to claim 22, wherein the compressed CWF is in a liquid state, a gaseous state, or a multiphase state when it is discharged from the second pressure vessel.

26. The method according to claim 22, wherein the step of transferring at least a portion of the compressed CWF from the first pressure vessel to the second pressure vessel is performed between a series of charging cycles that repeat a series of operations relating to energy storage.

27. The method according to claim 26, wherein the step of propelling at least a portion of the non-vaporizing liquid in the first pressure vessel with the compressed CWF discharged from the second pressure vessel is performed between a plurality of discharge cycles which repeat a series of operations relating to the release of energy.

28. i. To provide a third pressure vessel capable of fluid communication with the first pressure vessel, wherein, before performing either the charging cycle or the discharging cycle, the third pressure vessel is completely filled with a first fluid selected from CWF gas or the non-vaporizing liquid, and the first pressure vessel is completely filled with a second fluid different from the first fluid, selected from CWF gas or the non-vaporizing liquid, and ii. The method according to claim 27, further comprising the step of performing the charge cycle or the discharge cycle such that, upon completion, the third pressure vessel is completely filled with the second fluid and the first pressure vessel is completely filled with the first fluid.

29. The method according to claim 28, further comprising performing the other of the charging cycle or the discharging cycle when the third pressure vessel is completely filled with the second fluid and the first pressure vessel is completely filled with the first fluid.

30. The method according to claim 28, wherein the compressed CWF discharged from the second pressure vessel undergoes substantially isothermal expansion while in direct contact with the non-vaporizing liquid in the first pressure vessel.

31. a) A first pressure vessel having at least four ports through which the corresponding conduits are in fluid communication, b) A second pressure vessel having one or more ports and set to a temperature below room temperature, c) A flow control component that is operably connected to each of the corresponding conduits and selectively controls the flow of fluid through the conduits, d) A gas holder that is in fluid communication with the first pressure vessel and contains a condensable working fluid (CWF) that can be condensed at room temperature, and e) A liquid reservoir having fluid communication with the first pressure vessel and containing a non-vaporizing liquid, The CWF can be introduced from the gas holder into the first pressure vessel via the first port of the at least four ports. The non-vaporizing liquid can be introduced into the first pressure vessel through the second port of the at least four ports, thereby causing substantial isothermal compression of the CWF within the first pressure vessel upon direct contact with the non-vaporizing liquid. After a sufficient amount of the non-vaporizing liquid is added to the first pressure vessel, at least a portion of the compressed CWF in the first pressure vessel can be transferred from the first pressure vessel to the second pressure vessel via one of the one or more ports through the third port of the at least four ports, upon direct contact with the non-vaporizing liquid, and after being compressed and condensed to saturation pressure, can be stored in liquid form in the second pressure vessel. At least a portion of the non-vaporizing liquid in the first pressure vessel can be propelled through the fourth of the at least four ports by the compressed CWF discharged from the second pressure vessel. A direct contact fluid transfer (DCFT) module in which, under ambient temperature conditions, the CWF circulates between the gas holder, the first pressure vessel, and the second pressure vessel, and the non-vaporizing liquid circulates between the liquid reservoir and the first pressure vessel to isothermally compress the CWF, thereby releasing the stored energy.

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