Method and apparatus for preheating process gas

Abstract

The present invention provides an energy recovery subsystem (10) for a cryogenic energy storage system (1), the subsystem comprising: an evaporator; a first heat exchanger (21) for transferring thermal energy from a heat conduction fluid (6) to a working fluid (5); one or more expansion stages (30) for extracting work from the working fluid (5); a recuperator (40) for transferring thermal energy from one working fluid (5) to another; and the working fluid The conduit (100) of the first configuration for passing through (5) and the conduit (200) of the second configuration which is connectable to the thermal energy storage device (TESD) (3) and connected to the first heat exchanger (21) for passing the heat conduction fluid (6) through the first heat exchanger (21), the conduit (100) of the first configuration sequentially connects the evaporator (14), the recuperator (40), the first heat exchanger (21), the second recuperator (40), and one or more expansion stages (30).

Description

Technical Field

[0001] The present invention relates to a cryogenic energy storage system and an operation method thereof, and more particularly to an energy recovery method and its subsystems.

Background Art

[0002] The power transmission and distribution network (or grid) needs to balance power generation and consumer demand. This is usually achieved by turning power plants on and off to adjust the generation side (supply side), and reducing the load to operate a part. Most existing thermal power plants and nuclear power plants are most efficient when operating continuously at full load, so there is an efficiency penalty in balancing the supply side in this way. It is expected to introduce large-scale intermittent renewable power generation facilities such as wind turbines and solar power generation devices into the network, but this creates uncertainty in the availability of some of the power sources, making grid balance adjustment even more complicated. An efficient means of storing the energy generated during low-demand periods for later use during high-demand periods or when the output from intermittent generators is low is a great advantage in adjusting grid balance and providing supply stability.

[0003] There are many emerging and established energy storage methods in the market, including, among others, cryogenic energy storage, pumped hydroelectric power, compressed air, and chemical batteries. Such energy storage devices have three operating stages: charging, storage, and discharging. During low-demand periods, the energy storage device is charged using surplus energy from the grid. The energy is stored by the energy storage device in respective media such as cryogenic fluids, hydroelectric dam reservoirs, or the internal chemical potential of batteries. During high-demand periods, this energy is returned to the grid to meet demand.

[0004] Cryogenic energy storage using cryogenic gases such as liquid air CES (Cryogenic Energy Storage) technology offers several advantages over other available energy storage technologies. Cryogenic gas is a liquefied gas. CES systems generally have high energy density due to the physical properties of cryogenic gas, are highly installable (because they use relatively small storage tanks with no geographical constraints), are environmentally friendly (because their operating principle does not involve the use or production of hazardous substances or carbon emissions as seen in most batteries), and are relatively inexpensive (because CES systems use equipment that has been used for many years in the liquid natural gas industry).

[0005] CES technology can liquefy air from the external environment or another suitable gas, store it at low pressure, and later vaporize it to drive a turbine for power generation. During the charging or liquefaction phase of a CES system, low-cost electricity is used to compress, cool, purify, and liquefy ambient air or other gases in a liquefaction unit or subsystem during periods of low demand (off-peak periods) or intermittent oversupply from renewable generators. Two compressors are commonly used in the liquefaction process. The airflow is first compressed to approximately 15–20 barA in a main air compressor (MAC), then purified in an air purification unit (APU), and finally compressed to approximately 55–65 barA in a second recirculating air compressor (RAC). The flow can then enter a cooling and liquefaction system, commonly called a cold box. The cold box can typically be embodied as an insulating (usually metal) box filled with high-performance insulating material such as perlite. The cryogenic heat exchange process takes place in a cold box via components such as a multi-pass heat exchanger, phase separator, and at least one expansion turbine stage and / or valves. The gas is cooled in the cold box until it condenses substantially into a liquid. The liquid product is separated from the gas and sent from the cold box to a cryogenic storage tank, where it is stored for later use. The gas is returned via the multi-pass heat exchanger, which cools the original inflow airflow and may further liquefy it by capturing the airflow upstream of a recycle air compressor. The liquid product, such as liquefied air or cryogenic material, is stored in the storage tank during the storage phase. During the discharge or energy recovery phase, the liquid product is released into an energy recovery unit or subsystem, where it is pressurized, vaporized, and heated to drive one or more expansion stages as part of one or more expansion turbines, driving a generator to produce electricity. The discharge or energy recovery phase is often performed during peak periods when electricity costs are high. CES technology relies on the thermodynamic energy potential between cryogenic liquid air and gaseous air above ambient temperature. CES systems can perform various operations simultaneously from the charging and discharging phases.

[0006] The pressurized stream of the gas to be liquefied within the liquefaction subsystem and the pressurized cryogenic gas or liquefied gas within the energy recovery subsystem are typically referred to as the "process stream of the liquefaction subsystem" and the "working fluid of the energy recovery subsystem," respectively.

[0007] The round-trip efficiency of a CES system is simply defined as the ratio of the net electrical energy output of the system, measured over the period of complete discharge, to the net electrical energy input of the system, measured over the period of complete discharge. In a CES system, the heat generated as a result of the electrical energy input should be captured and reused to maintain high round-trip efficiency, while heat that is not captured and reused is eventually dissipated into the environment and can negatively impact round-trip efficiency.

[0008] For example, in a liquefaction process, the process stream is compressed, cooled, and then expanded again. This process is repeated until the process stream is completely liquefied, with each compression step increasing the temperature of the process stream and each cooling and expansion step significantly decreasing the temperature. The term “heat of compression” refers to the high-temperature thermal energy embedded in the compressed fluid. In other words, “heat of compression” means the increase in temperature that the fluid experiences as a result of compression. Wherever heat is described as being “transferred” from one place, fluid, or component to another place, fluid, or component, this is a process in which thermal energy is transferred between two places, fluids, or components. The method of transfer may include any of the typical methods, such as conduction, convection, or radiation, or any combination thereof, which will be apparent to those skilled in the art.

[0009] A CES system may utilize an energy capture subsystem designed to capture the heat of compression of the process stream generated in the liquefaction subsystem during the liquefaction phase and then store it in one or more thermal energy storage devices (TESDs). Such a CES system may release this captured heat into the working fluid in the energy recovery subsystem during the energy recovery phase. These subsystems are collectively known as a compression heat recycling system or energy recycling subsystem.

[0010] Cryogenic substances, such as liquid air, occupy a smaller volume when stored compared to their gaseous state. During the energy recovery phase, the cryogenic substance is pumped from a cryogenic storage tank for use as a working fluid and is then vaporized, heated, and expanded by passing it through a series of interleaved or alternating heat exchangers and expansion stages. Vaporizing the working fluid produces a very cold gas with a much larger volume than the cryogenic substance, which expands further as it warms up. Once the working fluid is heated and expanded through the expansion turbine, it acts against the turbine to drive its rotation and lower the temperature and pressure of the working fluid. The turbine may be coupled to a power energy user, such as a generator, which generates electrical energy that can then be exported to the grid. Increasing the temperature of the working fluid increases its pressure, and accordingly, the energy available to drive the expansion turbine increases. This allows the turbine to extract more energy from the hotter working fluid and rotate faster and / or with more torque, thus increasing the power output provided by the energy recovery subsystem during the energy recovery phase and leading to improved round-trip efficiency of the CES system. The heat of compression that is rejected during the liquefaction phase and captured by the energy capture subsystem can be used to raise the temperature of the working fluid in the energy recovery subsystem before expansion.

[0011] In the energy recovery subsystem, compression heat is transferred from the process stream of the liquefaction subsystem to at least one TESD within the energy recovery subsystem. A heat exchanger located downstream of the compressor in the liquefaction subsystem transfers heat from the process stream to a heat conduction fluid (HTF), which then passes it to the one or more TESDs. Compression heat is transferred from the at least one TESD to the working fluid of the energy recovery subsystem by the heat conduction fluid (HTF) or by a second separate HTF, using an expansion stage and interleaved heat exchanger. The heat conduction fluid used in the TESD varies depending on the temperature or quality of the thermal energy captured by the TESD. For example, water, water-glycol mixtures, and hot oil can be used in lower or ambient temperature applications. Molten salts, such as molten nitrates, can be used in higher temperature applications. Molten salts have the advantages of high heat capacity, high boiling point, good stability, low toxicity, and are non-flammable and low cost. High-quality thermal energy has higher temperatures.

[0012] Energy recycling subsystems designed to store high-quality thermal energy often use heat transfer fluids (HTFs) with melting points much higher than ambient temperature to store and / or transfer heat of compression. Some fluids can be used as both HTF and heat storage media within the same energy recycling subsystem. Molten salt is one such fluid. The temperature at which molten salt freezes depends on the blend and type of salt used. The salt blends and types associated with CES systems typically freeze at around 130°C and have a safe working temperature above around 150°C. The safe working temperature is the temperature above which no crystals form in the salt and includes an acceptable safety margin for the operator or engineer running the CES system. The high freezing point of HTF presents a challenge because recently evaporated cryogenic substances or working fluids may be substantially lower in temperature than the freezing point of the HTF, posing a risk of the HTF freezing or crystallizing within the heat exchanger.

[0013] In known energy recovery subsystems, a pump moves the working fluid from a cryogenic storage tank through an evaporator to an expansion turbine. To raise the temperature of the working fluid and improve its efficiency in the turbine, the working fluid can pass through a gas-to-molten salt heat exchanger located between the evaporator and the expansion turbine. The working fluid passing from the evaporator is at approximately ambient temperature, i.e., 20°C. Since the freezing point of the molten salt is higher than the process airflow discharged from the evaporator, there is a risk of the molten salt freezing in this heat exchanger over time. During system startup, the risk of the molten salt freezing in this heat exchanger is even higher because the system or the heat exchanger has not yet reached its temperature.

[0014] Freezing of molten salt can lead to production losses and catastrophic equipment failure. In the event of HTF events such as molten salt freezing, the entire CES system may need to be taken offline for maintenance and inspection. The conduits and heat exchangers through which the working fluid and HTF pass are often under high pressure, and even minimal damage can pose a safety hazard. Defrosting heat exchangers on the scale seen in commercial CES plants is difficult, and assessing damage, and therefore safety, is challenging, so the heat exchanger may need to be completely replaced. The time scale for this maintenance can be weeks or even months. [Overview of the project]

[0015] Aspects and / or embodiments of the present invention address the problem of freezing or crystallization of heat conduction fluid (HTF) and thus provide a more robust energy recovery subsystem that reduces the risk of freezing or crystallization of HTF in the conduits or heat exchangers of the HTF flow path.

[0016] According to a first embodiment, an energy recovery subsystem for a cryogenic energy storage system (CES) is provided, the energy recovery subsystem comprising: a pump for moving a working fluid; an evaporator; one or more heat exchangers including a first heat exchanger for transferring thermal energy from a heat conduction fluid to the working fluid; one or more expansion stages for extracting work from the working fluid; a recuperator for transferring thermal energy from the working fluid to the working fluid; a conduit of a first configuration for passing the working fluid; and a conduit of a second configuration that is connectable to a thermal energy storage device (TESD) and connected to the first heat exchanger for passing the heat conduction fluid. The conduit of the first configuration has an upstream end and a downstream end that can be connected to a working fluid source. The conduit of the first configuration connects the evaporator, the recuperator, the first heat exchanger, the second recuperator, and one or more expansion stages in order from the upstream end.

[0017] Advantageously, the recuperator increases the temperature of the working fluid entering the first heat exchanger by transferring heat from the working fluid that has already passed through the first heat exchanger to the working fluid upstream of the first heat exchanger, thereby reducing the possibility of the HTF freezing in the first heat exchanger.

[0018] Optionally, the recuperator has a first input, a first output, a second input, and a second output, wherein the first input of the recuperator is connected downstream of the evaporator by a conduit of the first configuration, the first output of the recuperator is connected to the first heat exchanger by a conduit of the first configuration, the second input of the recuperator is connected to the first heat exchanger by a conduit of the first configuration, and the second output of the recuperator is connected upstream of one or more expansion stages by a conduit of the first configuration.

[0019] Optionally, the one or more heat exchangers further include a second heat exchanger for transferring thermal energy from the heat conduction fluid to the working fluid, the second heat exchanger being connected to a conduit of the second configuration for the heat conduction fluid to pass through, and connected along a conduit of the first configuration between the recuperator and a first expansion stage of the one or more expansion stages for the working fluid to pass through.

[0020] By passing the working fluid through a recuperator after the first heat exchanger, its temperature decreases, and then the second heat exchanger raises the working fluid's temperature again before it enters one or more expansion stages, thereby improving the efficiency of the first expansion stage.

[0021] Optionally, in the energy recovery subsystem, the one or more expansion stages include one or more second expansion stages for extracting work from the working fluid, and the one or more heat exchangers include one or more third heat exchangers for transferring thermal energy from the heat conduction fluid to the working fluid. Optionally, each of the third heat exchangers receives working fluid from one of the one or more expansion stages located upstream along a conduit of the first configuration and is connected by the conduit of the first configuration to yet another stage of the one or more expansion stages downstream of each of the one or more third heat exchangers.

[0022] By passing the working fluid through a third heat exchanger before it enters each of the one or more second expansion stages, the temperature of the working fluid is increased, thereby increasing the amount of work that can be extracted from the working fluid in each second expansion stage.

[0023] Optionally, the energy recovery subsystem further includes a final expansion stage for extracting work from the working fluid, the final expansion stage being connected by conduits of the first configuration downstream of all other expansion stages along the conduits of the first configuration, and the final expansion stage being further connected by conduits of the first configuration to an exhaust system for discharging used working fluid from the energy recovery subsystem at the downstream end of the conduits of the first configuration. Preferably, the final or third expansion stage is connected downstream of the preceding expansion stages without passing through one or more heat exchangers.

[0024] This extracts any remaining energy from the working fluid before it is released from the energy recovery system. This is likely to be a lower-pressure expansion stage than the first and second expansion stages.

[0025] Optionally, one or more of the expansion stages rotate a common shaft that can be connected to a power sink, such as a generator.

[0026] Optionally, the energy recovery subsystem includes a second recuperator for transferring thermal energy from the working fluid to the working fluid, and a fourth heat exchanger for transferring thermal energy from the heat conduction fluid to the working fluid, wherein the second recuperator is connected downstream of the first recuperator by a conduit of the first configuration, and the conduit of the first configuration sequentially connects the second recuperator, the fourth heat exchanger and the second second recuperator upstream of one or more expansion stages.

[0027] Optionally, the second recuperator has a first input, a first output, a second input, and a second output. The first input of the second recuperator is connected to the first recuperator by a conduit of the first configuration. The first output of the second recuperator is connected to the fourth heat exchanger by a conduit of the first configuration. The fourth heat exchanger is connected to the second input of the second recuperator by a conduit of the first configuration. The second output of the second recuperator is connected by a conduit of the first configuration upstream of the one or more expansion stages.

[0028] Optionally, the first recuperator and, optionally, the second recuperator are gas / gas heat exchangers.

[0029] Optionally, the first heat exchanger is a liquid / gas heat exchanger. Further optionally, the second heat exchanger is a liquid / gas heat exchanger. Optionally, the third heat exchanger is a liquid / gas heat exchanger.

[0030] Optionally, the working fluid is one or more of air, nitrogen, oxygen, hydrogen, or carbon dioxide.

[0031] Optionally, the source of the working fluid is a cryogenic storage tank.

[0032] Optionally, the one or more heat exchangers are connected in parallel to the TESD by conduits of the second configuration. Thereby, each heat exchanger is guaranteed to benefit from the yet unused high-temperature HTF.

[0033] Optionally, the conduits of the second configuration include a first subset of conduits and a second subset of conduits separate from the first subset of conduits, each of which is for passing heat exchange fluid and is connectable to the TESD, the first subset of conduits being connected to the first heat exchanger and optionally to a fourth heat exchanger for passing HTF, and the second subset of conduits being connected to the second heat exchanger and / or the third heat exchanger for passing HTF.

[0034] The separate circuits for the first heat exchanger and, optionally, the fourth heat exchanger, mean that the flow rate of HTF through the heat exchanger associated with the recuperator can be varied independently of the remaining heat exchangers. This can be particularly useful during the warm-up phase, when the risk of freezing events is highest.

[0035] Optionally, the energy recovery subsystem described in any of the preceding claims further includes a preheater that heats the working fluid and is located upstream of the first recuperator along the conduit of the first configuration.

[0036] Optionally, a preheater for heating the working fluid may be located downstream of the first recuperator along the conduit of the first configuration.

[0037] This configuration of the preheater downstream of the recuperator is particularly advantageous because the heat from the first heat exchanger is subsequently captured by the recuperator and recovered into the air upstream of the first heat exchanger, thereby reducing the risk of freezing of the molten salt in the second heat exchanger 22.

[0038] Optionally, a TESD is included, and the conduit of the second configuration is connected to the TESD to supply HTF from the TESD.

[0039] Optionally, the conduit of the second configuration includes a circuit for supplying a heat conduction fluid to one or more heat exchangers and returning the heat conduction fluid to the TESD after use.

[0040] According to a second aspect of the present invention, a cryogenic energy storage system including the above-described energy recovery subsystem is provided.

[0041] Optionally, the CES system includes a liquefaction subsystem for storing energy in the form of a cryogenic agent, the liquefaction subsystem being connected to a cryogenic agent storage tank for storing and supplying the cryogenic agent; and an energy capture subsystem for capturing the heat of compression generated by the liquefaction subsystem, the energy capture subsystem being connected to a TESD for storing the captured thermal energy, the energy recovery subsystem being connected to the cryogenic agent storage tank and the TESD for releasing energy from the cryogenic agent.

[0042] According to another aspect of the present invention, a method for operating an energy recovery subsystem is provided. The method includes receiving a working fluid at the upstream end of a conduit of a first configuration. The method further includes, in order to recover energy from the working fluid, using a pump to cause the working fluid to pass along the conduit of the first configuration, through an evaporator, then a recuperator, then a first heat exchanger, then through the recuperator a second time, and then through one or more expansion stages. The method further includes receiving a heat conduction fluid (HTF) in a conduit of a second configuration. The method further includes causing the heat conduction fluid to pass along the conduit of the second configuration via the first heat exchanger in order to exchange thermal energy between the working fluid and the heat conduction fluid.

[0043] Optionally, the method may further include ensuring that the working fluid passes along the conduit of the first configuration through the second heat exchanger between the recuperator and the first expansion stage of the one or more expansion stages, and that the heat conducting fluid passes along the conduit of the second configuration through the second heat exchanger.

[0044] Optionally, the one or more expansion stages may include one or more second expansion stages, and the one or more heat exchangers may include one or more third heat exchangers. Optionally, the method may further include ensuring that the working fluid travels along the conduit of the first configuration from one of the one or more expansion stages, through one of the one or more third heat exchangers, and then through yet another of the one or more expansion stages.

[0045] Optionally, the method may further include ensuring that the working fluid passes along the conduit of the first configuration through a final expansion stage downstream of all other expansion stages, and then through an exhaust device to discharge the used working fluid from the energy recovery subsystem at the downstream end of the conduit of the first configuration.

[0046] Optionally, the method further includes ensuring that the working fluid passes along the conduit of the first configuration through the second recuperator downstream of the first recuperator, then through a fourth heat exchanger, and then through a second second recuperator upstream of the conduit of the first configuration of one or more expansion stages.

[0047] Optionally, the working fluid is received from a cryogenic storage tank.

[0048] Optionally, the heat conduction fluid is passed in parallel from the TESD to each of the one or more heat exchangers along the conduit of the second configuration.

[0049] Optionally, the conduits of the second configuration include a first subset of conduits and a second subset of conduits separate from the first subset of conduits. Optionally, the method includes allowing the heat exchange fluid to pass through the first heat exchanger along the first subset of conduits and optionally through the fourth heat exchanger, and allowing the heat exchange fluid to pass through the second heat exchanger and / or the third heat exchanger along the second subset of conduits. Preferably, the heat exchange fluid that has passed through the first subset of conduits does not pass through the second and / or third heat exchangers. Preferably, the heat exchange fluid that has passed through the second subset of conduits does not pass through the first and / or fourth heat exchangers.

[0050] Optionally, the working fluid passes through a preheater upstream of the recuperator.

[0051] Optionally, the working fluid passes through a preheater downstream of the recuperator.

[0052] Optionally, the conduit of the second configuration includes a circuit, and the method may further include causing the heat-conducting fluid to pass through the circuit through one or more heat exchangers, and causing the heat-conducting fluid to return to the TESD after use.

[0053] Optionally, the heat conduction fluid is received from a thermal energy storage device (TESD). [Brief explanation of the drawing]

[0054] Hereinafter, an embodiment will be described as an example with reference to the attached drawings having the same reference numerals. [Figure 1] Figure 1 shows a cryogenic energy storage system including the recovery subsystem according to the present invention. [Figure 2] Figure 2 shows a modified version of the system in Figure 1, in which the energy recovery subsystem further includes a second recuperator and associated heat exchangers. [Figure 3]Figure 3 shows a modified version of the system in Figure 1, in which the energy recovery subsystem includes a separate subset of conduits supplying heat exchange fluid from the thermal energy storage device to the remaining heat exchanger, and supplying heat exchange fluid to the heat exchanger associated with the recuperator 2. [Figure 4A] Figure 4A shows a modified version of the system in Figure 1, in which a preheater located upstream of the working fluid flow to the recuperator is added. [Figure 4B] Figure 4B shows a modified version of the system in Figure 1, in which a preheater is added, located downstream of the working fluid flow to the recuperator. [Figure 5] Figure 5 shows a modified version of the system in Figure 1, without a heat exchanger between the recuperator and the first expansion stage in the process flow of the working fluid. [Modes for carrying out the invention]

[0055] A first embodiment will be described with reference to Figure 1. Figure 1 shows a cryogenic energy storage (CES) system 1 having an energy capture subsystem 2, a liquefaction subsystem 4, and an energy recovery subsystem 10.

[0056] The liquefaction subsystem 4 is for storing energy as potential energy in the form of cryogenic gas. The liquefaction subsystem 4 receives air or another suitable gas, compresses and cools the gas to transform it into a cryogenic liquid known as a cryogenic liquid, and then supplies it to a cryogenic gas storage means 8a, such as a cryogenic storage tank 8b. The CES system 1 and / or any subsystems 2, 4, 10 described herein are operable to use any suitable gas that can be liquefied for use as a cryogenic gas for energy storage purposes. For example, the working fluid 5 may be one or more of air, nitrogen, oxygen, hydrogen, or carbon dioxide. Since the CES system 1 and / or any subsystems 2, 4, 10 are operable to use such combinations of gases, they may include the necessary gas separator 80 and / or liquid separator 82 and separate storage devices necessary for using and processing different gases or liquids.

[0057] The energy capture subsystem 2 is for capturing the heat of compression released during the liquefaction process in the liquefaction subsystem 4. The energy capture subsystem 2 transfers the heat recovered from the liquefaction subsystem 4 to the thermal energy storage device 3 (TESD) via the thermal energy transfer fluid 6. The thermal energy transfer fluid 6 may also be called the heat conduction fluid 6 (HTF).

[0058] The CES system 1 also includes an energy recovery subsystem 10 for recovering energy from stored cryogenic fluid used as a working fluid 5 within the energy recovery subsystem 10. The energy recovery subsystem 10 includes a conduit 100 of a first configuration for passing the working fluid 5 and a conduit 200 of a second configuration, which is connectable to a thermal energy storage device (TESD) 3 and for passing a heat conduction fluid (HTF) 6. The conduit 100 of the first configuration has an upstream end 120 that is fluidly connected to a downstream end 121 for passing the working fluid 5 between them. The downstream end 121 of the conduit 100 of the first configuration is connected to an outlet 70 for releasing the used working fluid 5 from the energy recovery subsystem 10. The outlet 70 may be connected to the atmosphere or another system for capturing the working fluid 5 and / or making the working fluid 5 available for further use. The working fluid 5 used by the energy recovery subsystem 10 is received from a working fluid 8 supply source. The working fluid supply source may be a cryogenic gas storage means 8a supplied by the liquefaction subsystem 4 described above.

[0059] The energy recovery subsystem 10 further includes a pump 12 for moving the working fluid 5 along the conduit 100 of the first configuration, an evaporator 14 for evaporating the liquid working fluid 5, a recuperator 40 for transferring thermal energy to and from the working fluid 5 at another point along the conduit 100 of the first configuration, one or more heat exchangers 20 for transferring thermal energy between the heat conduction fluid 6 and the working fluid 5, and one or more expansion stages 30 for extracting energy from the working fluid 5.

[0060] One or more expansion stages 30 are connected to an output shaft 36 which is connected to a power sink 60, such as a generator 61. If there are multiple expansion stages 30, they may share a common output shaft 36. The power sink 60 may be another machine that requires a power source of a generator 61 or a power 62.

[0061] The evaporator 14, the recuperator 40, the first heat exchanger 21 of one or more heat exchangers 20, the second recuperator 40, and one or more expansion turbines 30 are fluid-connected in this order from the upstream end 120 of the conduit 100 of the first configuration to allow the working fluid 5 to pass through. The recuperator 40 includes a first input 42, a first output 44, a second input 46, and a second output 48. The first input is connected by the conduit 100 of the first configuration to receive the working fluid from the evaporator 14, the first output 44 is connected by the conduit 100 of the first configuration to allow the working fluid to pass to the first heat exchanger 21, the second input 46 is connected by the conduit 100 of the first configuration to receive the working fluid 5 from the first heat exchanger 21, and the second output 48 may be connected to the conduit of the first configuration upstream of one or more heat exchangers 20. In the embodiment shown in Figure 1, the second output unit 48 is connected to deliver the working fluid to the second heat exchanger 22.

[0062] Pump 12 is also connected to the conduit 100 of the first configuration to allow the working fluid 5 to move through pump 12. In Figure 1, pump 12 is shown connected between the upstream end 120 of the conduit 100 of the first configuration and the evaporator 14. Pump 12 can be located at any suitable location along the conduit 100 of the first configuration for moving the working fluid 5.

[0063] Figure 1 shows a second heat exchanger 22 located along the conduit 100 of the first configuration between the recuperator 40 and one or more expansion stages 30. The second heat exchanger 22 raises the temperature of the working fluid 5, which has decreased as it passes through the recuperator 40, in order to improve the efficiency of the first expansion stage 31 of the one or more expansion stages 30.

[0064] A single expansion stage 30 is possible, but it is preferable to include multiple expansion stages 30. Figure 1 shows multiple expansion stages 30, including a first expansion stage 31 connected downstream of a recuperator 40 to receive working fluid 5 from the recuperator 40, which is sequentially connected downstream of the first expansion stage 31 by a conduit 100 of the first configuration, two second expansion stages 32, and a third expansion stage 33.

[0065] Each of the one or more second expansion stages 32 receives working fluid from a third heat exchanger 23 connected along the conduit 100 of the first configuration, located upstream along the conduit 100 between the second expansion stage 32 and the next expansion stage 30. Figure 1 shows two second expansion stages 32 supplied by two third heat exchangers 23. However, one or more second expansion stages 32 and / or third heat exchangers 23 may be included in the energy recovery subsystem 10, and the second expansion stages 32 are interleaved with the third heat exchangers 23 along the conduit 100 of the first configuration.

[0066] The third expansion stage 33 is connected to a conduit 100 of the first configuration downstream of another expansion stage among the one or more expansion stages 30, without the working fluid passing through the heat exchanger 20 in between. One or more third expansion stages 33 may be included. Figure 1 shows a third expansion stage as a final expansion stage 33 connected by a conduit 100 of the first configuration downstream of all the other expansion stages 30 among the one or more expansion stages 30. The final expansion stage 33 is further connected to the output 70 by a conduit 100 of the first configuration to discharge the used working fluid 5 from the energy recovery subsystem 10 at the downstream end 121 of the conduit 100 of the first configuration. The third expansion stage 33 is connected by a conduit 100 of the first configuration downstream of all the other expansion stages 30 among the one or more expansion stages 30, and preferably receives the working fluid 5 from the beginning to the end of the second expansion stage 32 without passing through the heat exchanger 20. Alternatively, the last of the one or more expansion stages 30 may be connected to the output 70 by the conduit 100 of the first configuration in order to discharge the spent working fluid 5 from the energy recovery subsystem 10 at the downstream end 121 of the conduit 100 of the first configuration.

[0067] The conduit 200 of the second configuration is connectable to the thermal energy storage device 3 and is intended to pass heat exchange fluid 6 from the thermal energy storage device 3 through one or more heat exchangers 20 in order to warm the working fluid 5. Figure 1 shows the conduit 200 of the second configuration, which is connectable to the TESD 3 and includes a supply conduit 202 connected to each of the one or more heat exchangers 20 to pass HTF 6 through each of the one or more heat exchangers 20, and a return conduit 204 for receiving the HTF 6 after it has passed through the one or more heat exchangers 20. The one or more heat exchangers 20 are connected in parallel by the conduit 200 of the second configuration between the supply conduit 202 and the return conduit 204. Figure 1 shows the conduit 200 of the second configuration as a circuit that passes HTF 6 from the TESD 3 through each of the one or more heat exchangers 20 and returns HTF 6 to the TESD 3.

[0068] In the diagram, TESD3 is shown as a single block, but it will be understood that TESD3 may include one or more hot tanks 3a for high-energy HTF6 connected to the supply conduit 202 and one or more cool tanks 3b for used HTF6 supplied by the return conduit 204.

[0069] As shown in Figure 1, the conduit 100 of the first configuration is connectable to a source of working fluid 8, and includes a first conduit 101 extending between the upstream end 120 of the conduit 100 of the first configuration and the pump 12, a second conduit 102 extending between the pump 12 and the evaporator 14, a third conduit 103 extending between the evaporator 14 and the first input section 42 of the recuperator 40, and the first output section 44 of the recuperator 40 and A fourth conduit 104 extending between the first heat exchanger 21 and the second input section 46 of the recuperator 40, a fifth conduit 105 extending between the first heat exchanger 21 and the second input section 46 of the recuperator 40, a sixth conduit 106 extending between the second output section 48 of the recuperator 40 and the second heat exchanger 22, a seventh conduit 107 extending between the second heat exchanger 22 and the first expansion stage 31, and the first expansion stage 31 and the third heat exchanger The configuration includes an eighth conduit 108 extending between the first heat exchanger of the 23, a ninth conduit 109 extending between the first heat exchanger of the 33 and the first expansion stage of the 2nd expansion stage 32, a tenth conduit 110 extending between the 2nd expansion stage 32 and the second heat exchanger of the 33, an eleventh conduit 111 extending between the second heat exchanger of the 33 and the second expansion stage of the 2nd expansion stage 32, a twelfth conduit 112 extending between the second and last heat exchangers of the 2nd expansion stage 32 and the 33, and a thirteenth conduit 113 extending between the 3rd expansion stage and the downstream end 121 of the conduit 100 of the first configuration, which incorporates an outlet 70 for allowing the working fluid 5 to pass through.

[0070] Figure 2 shows a modified CES system of Figure 1, which has the same features as Figure 1, indicated by the same reference numerals, but with the addition of a fourth heat exchanger 24 located downstream from the first heat exchanger 40 along the conduit 100 of the first configuration and upstream of one or more expansion stages 30, and a second recuperator 50. The first recuperator 40, the second recuperator 50, the fourth heat exchanger 24, and again the second recuperator 50 are connected along the conduit 100 of the first configuration in the aforementioned order to allow the working fluid 5 to pass between them.

[0071] The second recuperator 50 includes a first input 52, a first output 54, a second input 56, and a second output 58. The first input 52 is connected downstream of the first recuperator 40 by a conduit 100 of the first configuration, the first output 54 is connected by a conduit 100 of the first configuration to deliver working fluid to the fourth heat exchanger 24, the second input 56 is connected by a conduit 100 of the first configuration to receive working fluid 5 from the fourth heat exchanger 24, and the second output 58 is connected upstream of one or more heat exchangers 30 by a conduit 100 of the first configuration. In the embodiment of Figure 2, the second output 58 is connected to deliver working fluid to the second heat exchanger 22.

[0072] In the embodiment of Figure 2, the sixth conduit 106 of the conduit 100 in the first configuration of the embodiment of Figure 1 is replaced by a tenth conduit 114 extending between the second outlet 48 of the first recuperator 40 and the first input 52 of the second recuperator 50, and includes a fifteenth conduit 115 extending between the first output 54 of the second recuperator 50 and the fourth heat exchanger 24, a sixteenth conduit 116 extending between the fourth heat exchanger 24 and the second input 56 of the second recuperator 50, and a seventeenth conduit 117 extending between the second output 58 of the second recuperator 50 and the second heat exchanger 22 to pass the working fluid 5. The conduit 200 of the second configuration is connected to the fourth heat exchanger 24 to pass HTF 6 to the fourth heat exchanger 24.

[0073] Figure 3 shows a modified version of the CES system of Figure 1, which has the same reference numerals and features as Figure 1. The configuration of Figure 3 differs from the configuration shown in Figure 1 in that the conduit 200 of the second configuration includes conduit 210 of the first subset and conduit 220 of the second subset. Conduit 210 of the first subset and conduit 220 of the second subset each have feeds 202, 212, 222 and returns 204, 214, 224. Conduit 210 of the first subset is connectable to TESD3 and is connected to supply HTF6 to the first heat exchanger 21. This allows for independent control of the flow rate of HTF6 through the first heat exchanger 21 supplied by the recuperator 40. This may be particularly useful during the startup phase of the energy reuse system 10. Conduit 220 of the second subset is connectable to TESD3 and is connected to the second heat exchanger 22 and / or one or more third heat exchangers 23. Preferably, the second heat exchanger 22 and / or one or more third heat exchangers 23 are connected in parallel.

[0074] On the other hand, Figure 3 shows only one recuperator 40 associated with the first heat exchanger. It will be understood that the conduits 210 of the first subset can also supply a second recuperator 50 associated with the fourth heat exchanger 24, as shown in Figure 2. Preferably, in such a configuration, the first heat exchanger 21 and the fourth heat exchanger 24 are connected in parallel by the conduits 210 of the first subset and supplied with HTF 6.

[0075] Figure 4A shows a modified version of the CES system 1 of Figure 1, which has the same reference numerals as Figure 1 and includes the same features. The configuration of Figure 4A differs from the configuration shown in Figure 1 in that the conduit 100 of the first configuration of the energy recovery subsystem 10 includes a preheater 16 located along the conduit 100 of the first configuration between the evaporator 14 and the recuperator 40. Specifically, the preheater 16 is located between the evaporator 14, which is located upstream along the conduit 100 of the first configuration, and the first input 42 of the recuperator 40, which is located downstream along the conduit 100 of the first configuration. The third conduit 103 of the embodiment of Figure 1 is replaced by the 18th conduit 118 and the 19th conduit 119 to allow the working fluid 5 to pass between the 18th conduit 118 extending between the evaporator 14 and the preheater 16 and the 19th conduit 119 extending between the preheater 16 and the recuperator 40.

[0076] Figure 4B also shows a modified version of the CES system 1 of Figure 1, which has the same reference numerals and features as Figure 1. Similar to Figure 4A, the configuration of Figure 4B shows the conduit 100 of the first configuration of the energy recovery subsystem 10, which includes a preheater 16 located along the conduit 100 of the first configuration. The preheater 16 differs from Figure 4A in that it is located along the conduit 100 of the first configuration between a second outlet 48 of a recuperator 40 located upstream along the conduit 100 of the first configuration and a second heat exchanger 22 located downstream along the conduit 100 of the first configuration. In the embodiment of Figure 1, the sixth conduit 106 is replaced by a 20th conduit 106a and a 21st conduit 106b to allow the working fluid 5 to flow between the 20th conduit 106a, which extends between the second outlet 48 of the recuperator 40 and the preheater 16, and the 21st conduit 106b, which extends between the preheater 16 and the second heat exchanger 22.

[0077] This configuration of the preheater 16 downstream of the recuperator 40 is advantageous because it reduces the risk of the molten salt freezing in the second heat exchanger 22. As air passes through the first heat exchanger 21, it is heated by the molten salt, but this heat is then captured by the recuperator 40 and returned to the air upstream of the first heat exchanger 21. This lowers the temperature of the air leaving the recuperator and entering the second heat exchanger 22, thus increasing the risk of the molten salt freezing in the second heat exchanger 22. As described elsewhere in this disclosure, the freezing of the molten salt results in production losses and can lead to catastrophic equipment failure, which is particularly critical during system startup.

[0078] The preheater 16 is connected to a conduit 200 of a second configuration and provides heat from a heat source 18 which may be different from the TESD 3 used to raise the temperature of the working fluid 5 before it enters the first heat exchanger 21. The heat source 18 may be located within the preheater 16 or separate from the preheater 16. If the heat source 18 is separate from the preheater 14, a second HTF may be used to transfer thermal energy from the heat source 18 to the preheater 16. The second HTF may have a different and / or lower freezing or crystallization temperature than the first HTF 6 used in the conduit 200 of the second configuration. The preheater 16 may be an electric heater 16a or a combustion heater 16b or may receive waste heat energy from an external source of the energy recovery subsystem 10, such as waste heat from an industrial system located in the same location. The preheater 16 may preferably be used during the startup phase of the energy recovery subsystem 10, when the temperature of the HTF 6 reaching the first heat exchanger 21 may be low.

[0079] Figure 5 shows a modified version of the CES system 1 of Figure 1. In this modification, one or more heat exchangers 20 of the energy recovery subsystem 10 do not include a second heat exchanger 22. The conduit 100 of the first configuration includes a 20th conduit 122 extending between the recuperator 40 and one or more expansion stages 30 to flow the working fluid 5 between the recuperator 40 and one or more expansion stages 30, instead of the 6th conduit 106 and 6th conduit 107 of the Figure 1 configuration. This configuration is advantageous in that it reduces the number of parts and eliminates the pressure drop across the second heat exchanger 22, as fewer heat exchangers 20 are required, which may outweigh the disadvantage of providing a lower temperature working fluid 5 by the first expansion stages 31, which may reduce efficiency.

[0080] The drawings show the energy recovery subsystem 10 as part of the CES system 1, but it will be understood that such an energy recovery subsystem 10 may be supplied by any source of working fluid 8, thereby realizing the advantages of the energy recovery subsystem 10 of the present invention. It will be further understood that the modifications of Figure 1 provided by the embodiments and configurations of Figures 2 to 5 can be combined in any combination.

[0081] Recuperators 40, 50 may be gas / gas heat exchangers for passing thermal energy between the working fluid 5 and the working fluid 6 at different points along the conduit 100 of the first configuration. Each of the one or more heat exchangers 20 may be a liquid / gas heat exchanger for passing thermal energy between the HTF 6 and the working fluid 5.

[0082] One or more expansion stages 30 can be arranged in the form of one turbine having multiple expansion stages or multiple turbines having any combination of one or more expansion stages 30 in each turbine. The drawings show one or more expansion stages 30 including a first expansion stage 31, one or more second expansion stages 32, and a third expansion stage 33. Those skilled in the art will understand that one or more expansion stages 30 may include one or more of each of the first expansion stage 31, the second expansion stage 32, and / or the third expansion stage 33.

[0083] During operation, the working fluid 5 is received by the energy recovery system 10 from the source of the working fluid 8 at the upstream end 120 of the conduit 100 of the first configuration. In the CES system 1 shown in Figures 1 to 5, this working fluid 5 is a cryogenic fluid provided by the energy recovery subsystem 2, which includes a liquefaction subsystem 4 for generating the cryogenic fluid. Pump 12 moves the working fluid 5 along the conduit 100 of the first configuration, passing it through the evaporator 14 where the liquid cryogenic working fluid 5 evaporates into a gas. The working fluid 5 then travels along the conduit 100 of the first configuration, passing through the preheater 16 as needed, through the recuperator 40, through the first heat exchanger 21, and back to the recuperator 40. The recuperator 40 transfers heat from the working fluid 5, which has been heated by the first heat exchanger 21, to the first heat exchanger 21 upstream along the conduit 5 of the first configuration. This raises the temperature of the working fluid 5 before it enters the first heat exchanger 21, reducing the possibility of the HTF freezing in the first heat exchanger 21 or crystallization occurring in the HTF 6. An optional preheater 16 can further raise the temperature of the working fluid 5 before it enters the first heat exchanger 21. Downstream along the conduit 100 of the first configuration, the working fluid 5 is passed to one or more expansion stages 30 to extract the workpiece from there. After the working fluid 5 leaves the recuperator 40, its temperature is lower than when it left the first heat exchanger 21 or recuperator heat exchanger 21. Optionally, the conduit 100 of the first configuration passes the working fluid 5 through a second heat exchanger 22 or booster heat exchanger 22 to raise the temperature of the working fluid 5 before it enters one or more expansion stages 30, thereby increasing the efficiency and / or output of the first expansion stage 31 of the one or more expansion stages 30. If one or more expansion stages 30 include two or more expansion stages 30, the conduit of the first configuration may pass the working fluid 5 through one or more third heat exchangers 23 or interstage heat exchangers 23 before passing the working fluid 5 through further expansion stages downstream of the third heat exchanger 23.Each of the third heat exchangers 23 increases the temperature of the working fluid 5 before it enters the next expansion stage along the conduit 100 of the first configuration, thereby increasing the pressure of the working fluid 5 and the work that can be extracted from the working fluid, thereby increasing the efficiency of the second expansion stage 32. The conduit 100 of the first configuration can pass the working fluid 5 to a further third expansion stage 33 or final expansion stage 33 without passing through the third heat exchangers 23. This third expansion stage may also be called the final expansion stage 33 and is for extracting the remaining work from the working fluid 5 before it is released from the energy recovery system 10 at the downstream end 121 of the conduit 100 of the first configuration. One or more heat exchangers 30 are supplied with HTF 6 by the conduit 200 of the second configuration to heat the working fluid 5. Preferably, one or more heat exchangers 20 are connected in parallel so that each is supplied with hot HTF 6 from TESD 3.

[0084] The HTF6 used in the conduit 200 of the second configuration has a freezing point higher than the ambient temperature. In particular, the use of molten salt as HTF6 has been found to be very efficient for both the transfer and storage of high-temperature thermal energy. As mentioned above, this presents a problem if the energy recovery system 10 allows the HTF6 to cool below the temperature at which it begins to freeze, known as the crystallization temperature or the temperature at which salt crystals begin to appear in the molten fluid. Crystallization or complete freezing of HTF6 poses a risk when the energy recovery subsystem 10 is operating, in particular when the system is started, as the HTF6 enters the upstream end of the first arrangement of the conduit 100 as a cryogenic liquid that can easily freeze at the first or furthest upstream of one or more heat exchangers 20 in the energy recovery subsystem 10 at very low temperatures.

[0085] The conduits 100 of the first configuration and 200 of the second configuration fluid-connect the components connected to them. Unless otherwise stated herein, "connected in sequence" means the order in which a given feature passes through the working fluid or is connected to the conduits 100, 200 of the first configuration in relation to one another. This does not mean that the components are directly connected to each other upstream or downstream. Further components, such as valves, sensors, connectors, or other components, may be connected between the components along the conduits 100, 200 of the configuration in a given order.

[0086] Each of the conduits 200 of the second configuration and the conduits 210, 220 of a subset of the conduits 200 of the second configuration includes supply conduits 202, 212, 222 and return conduits 204, 214, 224. One or more heat exchangers 20 are connected across the supply conduits 202 and return conduits 204 to supply high-temperature heat conduction fluid 6 and to remove used heat conduction fluid 6. If the TESD3 includes a single reservoir for HTF 6, the conduits 200 of the first configuration may form one or more circuits. However, it is preferable that the TESD3 includes a high-temperature tank 3a for storing high-temperature HTF 6 and a low-temperature tank 3b for storing used HTF 3. Even in the low-temperature tank, the temperature 6 is maintained at a safe working temperature substantially above the freezing point of the HTF.

[0087] Any system feature described herein may be provided as a method feature or vice versa. As used herein, means-plus-function features may be expressed alternatively with respect to their corresponding structures.

[0088] Any feature in one aspect, variation, or embodiment may be applied to other aspects, variations, or embodiments in any suitable combination. In particular, an aspect of a method may be applied to an aspect of a system, and an aspect of a system may be applied to an aspect of a method. Furthermore, any, some, and / or all features in one aspect may be applied to any, some, and / or all features in other aspects in any suitable combination.

[0089] Furthermore, it should be understood that certain combinations of the various features described and defined in any of these embodiments may be independently implemented and / or supplied and / or used.

Claims

1. An energy recovery subsystem for a cryogenic energy storage system (CES), A pump for moving the working fluid, Evaporator and, One or more heat exchangers, including a first heat exchanger for transferring thermal energy from a heat conduction fluid to the working fluid, One or more expansion stages for extracting work from the working fluid, A recuperator for transferring thermal energy from one working fluid to another, A conduit of the first configuration for passing the working fluid, A conduit of a second configuration which can be connected to a thermal energy storage device (TESD) and is connected to the first heat exchanger to allow a heat conducting fluid to pass through, Includes, The conduit of the first configuration has an upstream end and a downstream end connectable to a working fluid source, and connects the evaporator, the recuperator, the first heat exchanger, the second recuperator, and one or more expansion stages in order from the upstream end, in an energy recovery subsystem.

2. The recuperator has a first input unit, a first output unit, a second input unit, and a second output unit. The first input section of the recuperator is connected downstream of the evaporator by a conduit of the first configuration, The first output section of the recuperator is connected to the first heat exchanger by a conduit of the first configuration, and the second input section of the recuperator is connected to the first heat exchanger by a conduit of the first configuration. The energy recovery subsystem according to claim 1, wherein the second output section of the recuperator is connected upstream of one or more expansion stages by a conduit of the first configuration.

3. The energy recovery subsystem according to claim 1 or 2, wherein the one or more heat exchangers further include a second heat exchanger for transferring thermal energy from the heat conduction fluid to the working fluid, the second heat exchanger being connected to a conduit of the second configuration for the heat conduction fluid to pass through, and connected along a conduit of the first configuration between the recuperator and a first expansion stage of the one or more expansion stages for the working fluid to pass through.

4. The one or more expansion stages include one or more second expansion stages for extracting work from the working fluid, and the one or more heat exchangers include one or more third heat exchangers for transferring thermal energy from the heat conduction fluid to the working fluid. The energy recovery subsystem according to any one of claims 1 to 3, wherein each of the third heat exchangers receives a working fluid from one of the one or more expansion stages located upstream along a conduit of the first configuration, and is connected by the conduit of the first configuration to yet another stage of the one or more expansion stages downstream of each of the one or more third heat exchangers.

5. The energy recovery subsystem according to any one of claims 1 to 4, further comprising a final expansion stage for extracting work from a working fluid, the final expansion stage being connected by a conduit of the first configuration downstream of all other expansion stages along a conduit of the first configuration, and the final expansion stage being further connected by a conduit of the first configuration to an exhaust system for discharging used working fluid from the energy recovery subsystem at the downstream end of the conduit of the first configuration.

6. The energy recovery subsystem according to any one of claims 1 to 5, wherein one or more expansion stages rotate a common shaft that can be connected to a power sink such as a generator.

7. A second recuperator for transferring thermal energy from the working fluid to the working fluid, A fourth heat exchanger for transferring thermal energy from the heat conduction fluid to the working fluid, It has, The energy recovery subsystem according to any one of claims 1 to 6, wherein the second recuperator is connected downstream of the first recuperator by a conduit of the first configuration, and the conduit of the first configuration sequentially connects the second recuperator, the fourth heat exchanger and the second second recuperator upstream along the conduit of the first configuration of one or more expansion stages.

8. The second recuperator has a first input section, a first output section, a second input section, and a second output section. The first input section of the second recuperator is connected to the first recuperator by a conduit of the first configuration. The first output section of the second recuperator is connected to the fourth heat exchanger by a conduit of the first configuration, and the fourth heat exchanger is connected to the second input section of the second recuperator by a conduit of the first configuration. The energy recovery subsystem according to claim 7, wherein the second output section of the second recuperator is connected upstream of one or more expansion stages by a conduit of the first configuration.

9. The energy recovery subsystem according to any one of claims 1 to 8, wherein the first recuperator and, optionally, the second recuperator, if dependent on claim 7 or 8, are gas / gas heat exchangers.

10. The energy recovery subsystem according to any one of claims 1 to 9, wherein one or more of the heat exchangers are liquid / gas heat exchangers.

11. The energy recovery subsystem according to any one of claims 1 to 10, wherein the working fluid is one or more of air, nitrogen, oxygen, hydrogen, or carbon dioxide.

12. The energy recovery subsystem according to any one of claims 1 to 11, wherein the source of the working fluid is a cryogenic storage tank.

13. The energy recovery subsystem according to any one of claims 1 to 12, wherein one or more heat exchangers are connected in parallel to the TESD by conduits of the second configuration.

14. The conduit of the second configuration includes a first subset of conduits and a second subset of conduits separate from the first subset of conduits, each of which is for passing heat exchange fluid and is connectable to the TESD. The conduits of the first subset are connected to the first heat exchanger, optionally via a fourth heat exchanger, to allow a heat-conducting fluid to pass through, and the conduits of the second subset are connected to the second heat exchanger and / or the third heat exchanger. The energy recovery subsystem according to any one of claims 3 to 13.

15. The energy recovery subsystem according to any one of claims 1 to 14, further comprising a preheater for heating the working fluid and located upstream of the first recuperator along the conduit of the first configuration.

16. The energy recovery subsystem according to any one of claims 1 to 14, further comprising a preheater for heating the working fluid and located downstream of the first recuperator along the conduit of the first configuration.

17. The energy recovery subsystem according to any one of claims 1 to 16, comprising a TESD, wherein the conduit of the second configuration is connected to the TESD for supplying HTF from the TESD.

18. The energy recovery subsystem according to claim 17, wherein the conduit of the second configuration includes a circuit for supplying a heat conduction fluid to one or more heat exchangers and for returning the heat conduction fluid to the TESD after use.

19. A cryogenic energy storage system comprising the energy recovery subsystem according to any one of claims 1 to 18.

20. A liquefaction subsystem for storing energy in the form of a cryogenic agent, wherein the liquefaction subsystem is connected to a cryogenic agent storage tank for storing and supplying the cryogenic agent. An energy capture subsystem for capturing the heat of compression generated by the liquefaction subsystem, the energy capture subsystem being connected to a TESD for storing the captured thermal energy, Includes, The cryogenic energy storage system according to claim 19, wherein the energy recovery subsystem is connected to the cryogenic storage tank and the TESD in order to release energy from the cryogenic material.

21. A method for operating an energy recovery subsystem, The first configuration involves receiving the working fluid at the upstream end of the conduit, To recover energy from the working fluid, a pump is used to cause the working fluid to pass along the conduit of the first configuration, through the evaporator, then through the recuperator, then through the first heat exchanger, then through the recuperator a second time, and then through one or more expansion stages. The second configuration involves receiving the heat conduction fluid in the conduit, In order to exchange thermal energy between the working fluid and the heat conducting fluid, the heat conducting fluid is to pass through the first heat exchanger along the conduit of the second configuration, Methods that include...

22. The working fluid is to pass along the conduit of the first configuration, through the second heat exchanger, between the recuperator and the first expansion stage of the one or more expansion stages, The heat-conducting fluid is to pass through the second heat exchanger along the conduit of the second configuration, The method according to claim 21, further comprising:

23. The one or more expansion stages include one or more second expansion stages, the one or more heat exchangers include one or more third heat exchangers, and the method is The working fluid is to flow along the conduit of the first configuration, from one of the one or more expansion stages, through one of the one or more third heat exchangers, and then through yet another of the one or more expansion stages. The method according to claim 21 or 22, further comprising:

24. The aforementioned method, The working fluid is to pass along the conduit of the first configuration, through the final expansion stage downstream of all other expansion stages, and then through an exhaust device to discharge the used working fluid from the energy recovery subsystem at the downstream end of the conduit of the first configuration. The method according to any one of claims 21 to 23, further comprising:

25. The aforementioned method, The working fluid is to pass along the conduit of the first configuration, through the second recuperator downstream of the first recuperator, then through the fourth heat exchanger, and then through the second recuperator a second time upstream along the conduit of the first configuration of one or more expansion stages. The method according to any one of claims 21 to 24, further comprising:

26. The method according to any one of claims 21 to 25, wherein the working fluid is received from a cryogenic storage tank.

27. The method according to any one of claims 21 to 26, wherein the heat conducting fluid is passed in parallel from the TESD to each of the one or more heat exchangers along the conduit of the second configuration.

28. The conduit of the second configuration includes a first subset of conduits and a second subset of conduits separate from the first subset of conduits, and the method is The heat exchange fluid is to pass through the first heat exchanger along the conduit of the first subset, and optionally through the fourth heat exchanger, The heat exchange fluid is to pass through the second heat exchanger and / or the third heat exchanger along the conduit of the second subset, The method according to any one of claims 21 to 27, including the method described in that claim.

29. The method according to any one of claims 21 to 28, wherein the working fluid passes through a preheater upstream of the recuperator.

30. The method according to any one of claims 21 to 28, wherein the working fluid passes through a preheater downstream of the recuperator.

31. The conduit of the second configuration includes a circuit, and the method is The method according to any one of claims 21 to 30, further comprising causing the heat conduction fluid to pass through one or more heat exchangers along the circuit and causing the heat conduction fluid to return to the TESD after use.

32. The method according to any one of claims 21 to 31, wherein the heat conduction fluid is received from a thermal energy storage device (TESD).

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