阅读说明：本技术 压缩热再循环系统及其子系统 (Compression heat recycling system and subsystem thereof ) 是由 尼克拉·卡斯泰卢奇 科姆约翰·科克伦 于 2019-02-13 设计创作，主要内容包括：公开了电力回收子系统、低温能量存储系统以及用于采集、存储和再利用热能的方法。(An electrical power recovery subsystem, a cryogenic energy storage system and methods for harvesting, storing and reusing thermal energy are disclosed.)

1. A power recovery subsystem for a cryogenic energy storage system, the power recovery subsystem comprising:

a first heat source;

a first heat exchanger;

a second heat exchanger;

a first expansion stage;

a second expansion stage;

a first conduit arrangement having an upstream end and a downstream end and configured to convey a working fluid through the first heat exchanger, the first expansion stage, the second heat exchanger, and the second expansion stage; and

a second pipe arrangement configured to convey a first heat transfer fluid from the first heat source through the first heat exchanger and the second heat exchanger,

wherein the second piping arrangement is further configured to convey a first portion of the first heat transfer fluid through the first heat exchanger and to convey a second portion of the first heat transfer fluid through the second heat exchanger.

2. The subsystem of claim 1, further comprising:

a third heat exchanger; and

a third expansion stage;

wherein the first piping arrangement is further configured to convey the working fluid through the third heat exchanger and the third expansion stage; and is

Wherein the second piping arrangement is further configured to convey a third portion of the first heat transfer fluid through the third heat exchanger.

3. The subsystem according to claim 1 or 2, further comprising;

a second heat source;

a fourth heat exchanger;

a fourth expansion stage; and

a third conduit arrangement configured to convey a second heat transfer fluid from the second heat source through the fourth heat exchanger,

wherein the first piping arrangement is further configured to route the working fluid through the fourth heat exchanger and the fourth expansion stage.

4. The subsystem of claim 3, further comprising:

a fifth heat exchanger; and

a fifth expansion stage;

wherein the first piping arrangement is further configured to convey the working fluid through the fifth heat exchanger and the fifth expansion stage; and is

Wherein the third tubing arrangement is further configured to pass a first portion of the second heat transfer fluid through the fourth heat exchanger and to pass a second portion of the second heat transfer fluid through the fifth heat exchanger.

5. A subsystem according to claim 3 or claim 4, wherein the or each heat exchanger through which the third conduit arrangement passes is located along the first conduit arrangement upstream of the heat exchanger through which the second conduit arrangement passes.

6. A subsystem according to claim 3 or claim 4, wherein the or each heat exchanger through which the third conduit arrangement passes is located along the first conduit arrangement downstream of the heat exchanger through which the second conduit arrangement passes.

7. The subsystem according to any preceding claim, further comprising:

a sixth heat exchanger for the heat-exchange of the air-conditioning system,

wherein the first conduit arrangement is further configured to convey the working fluid through the sixth heat exchanger upstream of both (i) the most upstream heat exchanger through which the second conduit arrangement passes and (ii) the most upstream heat exchanger through which the third conduit arrangement passes, and

wherein the first piping arrangement is further configured to convey the working fluid output from the most downstream expansion stage through the sixth heat exchanger to an exhaust.

8. The subsystem according to any preceding claim, further comprising:

a fourth piping arrangement configured to divert a portion of the working fluid from a downstream location in the first piping arrangement through an evaporator and a first compressor, and to return the working fluid to an upstream location in the first piping arrangement.

9. The subsystem according to claim 8, wherein the evaporator is positioned upstream of an upstream-most heat exchanger along the first piping arrangement, wherein the downstream location is downstream of a downstream-most expansion stage; and wherein the upstream location is immediately upstream of the most downstream expansion stage.

10. The subsystem according to claims 3 to 9, configured such that the second tubing arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchangers, and such that the third tubing arrangement passes through the fourth heat exchanger, and preferably no other heat exchangers, and wherein the heat exchanger through which the third tubing arrangement passes is upstream of the heat exchanger through which the second tubing arrangement passes.

11. The subsystem according to claims 4 to 9, configured such that the second tubing arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchangers, and such that the third tubing arrangement passes through the fourth and fifth heat exchangers, and preferably no other heat exchangers, wherein the heat exchanger through which the second tubing arrangement passes is upstream of the heat exchanger through which the third tubing arrangement passes.

12. The subsystem according to claims 3 to 9, configured such that the second tubing arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchangers, and such that the third tubing arrangement passes through the fourth heat exchanger, and preferably no other heat exchangers, wherein the heat exchanger through which the second tubing arrangement passes is upstream of the heat exchanger through which the third tubing arrangement passes.

13. The subsystem according to any preceding claim, wherein the first heat source is a first thermal energy storage device and the second piping arrangement is further configured to return the first heat transfer fluid to the first thermal energy storage device after passing the first heat transfer fluid through each heat exchanger through which the second piping arrangement is configured to pass, such that the second piping arrangement forms a first closed loop.

14. The subsystem according to any one of claims 3 to 13, wherein the second heat source is a second thermal energy storage device, and the third piping arrangement is further configured to return the second heat transfer fluid to the second thermal energy storage device after passing the second heat transfer fluid through each heat exchanger through which the third piping arrangement is configured to pass, such that the third piping arrangement forms a second closed loop.

15. The subsystem according to claim 14, wherein the first thermal energy storage device is configured to store at least a portion of the compressed heat generated by the recycle air compressor and the second thermal energy storage device is configured to store at least a portion of the compressed heat generated by the main air compressor, optionally wherein the second thermal energy storage device may comprise a pipe system adapted to transport molten salt.

16. The subsystem according to any one of claims 3 to 13, further comprising:

a tenth heat exchanger; and

an eleventh heat exchanger, wherein:

the second heat source is a second thermal energy storage device,

the first piping arrangement is further configured to convey the working fluid through the tenth heat exchanger immediately upstream of the fourth heat exchanger, and wherein;

the third conduit arrangement being configured to form two closed loops, a first closed loop passing through the second thermal energy storage device and the eleventh heat exchanger, and a second closed loop passing through the eleventh heat exchanger and the fourth heat exchanger,

optionally wherein the heat transfer fluid in the first closed loop comprises molten salt, further optionally wherein the heat transfer fluid in the second closed loop comprises a diathermic oil or a mixture of diathermic oils.

17. The subsystem according to claim 16, wherein the first thermal energy storage device is configured to store at least a portion of the heat of compression generated by a main air compressor and at least a portion of the heat of compression generated by a recycle air compressor, and the second thermal energy storage device is configured to store at least a portion of the heat of compression generated by the main air compressor, optionally wherein the second thermal energy storage device may comprise a piping system adapted to transport molten salt.

18. The sub-system of any one of claims 14 to 17, wherein the second thermal energy storage device is configured to store thermal energy at a temperature higher than the temperature of the thermal energy stored in the first thermal energy storage device, optionally wherein the second thermal energy storage device is configured to store thermal energy between 150 ℃ and 550 ℃, preferably between 200 ℃ and 400 ℃, and the first thermal energy storage device is configured to store thermal energy between 150 ℃ and 350 ℃.

19. A cryogenic energy storage system comprising:

an electricity recovery subsystem comprising a plurality of expansion stages configured to receive hot thermal energy from first and second thermal energy storage devices via a respective plurality of heat exchangers and to transfer the hot thermal energy to a working fluid conveyed through the plurality of expansion stages and the plurality of heat exchangers, preferably wherein the electricity recovery subsystem is an electricity recovery subsystem according to any one of claims 3 to 14; and

a liquefaction subsystem configured to supply thermal energy to the first thermal energy storage device and the second thermal energy storage device, and further comprising;

a main air compressor;

a circulating air compressor;

an eighth heat exchanger;

a ninth heat exchanger;

a fifth piping arrangement configured to route a process stream through the main air compressor, eighth heat exchanger, recycle air compressor, and ninth heat exchanger;

a sixth piping arrangement forming a third closed loop and configured to convey a third heat transfer fluid between the second thermal energy storage device and the eighth heat exchanger; and

a seventh piping arrangement forming a fourth closed loop and configured to convey a fourth heat transfer fluid between the first thermal energy storage device and the ninth heat exchanger,

wherein the eighth heat exchanger is positioned immediately downstream of the primary air compressor along the fifth piping arrangement and is configured to transfer at least a portion of the heat of compression of the process stream from the primary air compressor to the second thermal energy storage device via the third heat transfer fluid, and

wherein the ninth heat exchanger is positioned immediately downstream of the recycle air compressor along the fifth piping arrangement and is configured to transfer at least a portion of the heat of compression of the process stream from the recycle air compressor to the first thermal energy storage device via the fourth heat transfer fluid.

20. A thermal energy recovery system comprising:

a main air compressor;

a circulating air compressor;

a second thermal energy storage device;

a first thermal energy storage device;

a working fluid; and

a plurality of expansion stages comprising a first subset and a second subset;

wherein the system is configured to collect and store in the second thermal energy storage device at least a portion of the compression heat generated by the main air compressor during a liquefaction phase and to apply the compression heat stored in the second thermal energy storage device to the working fluid upstream of each of the expansion stages of the first subset during an electricity recovery phase, and

wherein the system is further configured to collect and store at least a portion of the heat of compression generated by the recycle air compressor in the first thermal energy storage device during a liquefaction phase, and to apply the heat of compression stored in the first thermal energy storage device to the working fluid upstream of each of the second subset of expansion stages during an electricity recovery phase.

21. A method for recycling thermal energy in a cryogenic energy storage system, comprising:

providing a liquefaction subsystem, comprising:

a main air compressor;

a circulating air compressor;

a second thermal energy storage device; and

a first thermal energy storage device;

providing a power recovery subsystem comprising:

a working fluid; and

a plurality of expansion stages comprising a first subset and a second subset;

collecting and storing at least a portion of the heat of compression from the main air compressor in the second thermal energy storage device;

collecting and storing at least a portion of the heat of compression from the recycle air compressor in the first thermal energy storage device;

applying heat of compression stored in the second thermal energy storage device to the working fluid upstream of each of the expansion stages of the first subset; and

applying the heat of compression stored in the first thermal energy storage device to the working fluid upstream of each of the expansion stages of the second subset.

Technical Field

The present invention relates to power recovery subsystems and cryogenic energy storage systems having liquefaction and power recovery subsystems, and in particular to systems and methods for harvesting, storing and reusing thermal heat energy.

Background

Power transmission and distribution networks (or grids) must balance the generation of power with the demand from consumers. This is typically achieved by: the power generation side (supply side) is modulated by switching the power plants on and off and operating some of the power plants at reduced load. Since most existing thermal and nuclear power plants operate most efficiently continuously at full load, there is a loss of efficiency in balancing the supply side in this way. Significant intermittent renewable power generation capabilities (such as wind turbines and solar collectors) are expected to be introduced into the network, but balancing of the grid is further complicated by the uncertainty in the availability of the components of the power generation cluster. The means of storing energy during periods of low demand for later use during periods of high demand, or storing energy during periods of low output from intermittent generators, would have major benefits in balancing the grid and providing supply safety.

The power storage device has three phases of operation: charging, storing and discharging. The power storage device generates electric power (discharge) in a highly intermittent manner when the power generation capacity of the transmission and distribution network is insufficient. This may be signaled to the storage operator by a high price of electricity in the local electricity market or by a request for additional capacity from the organization responsible for network operation. In some countries, such as the uk, network operators contract with operators of power plants with fast start-up capability to provide backup reserves to the network. Such contracts may cover months or even years, but typically the time during which the electricity supplier will operate (generate electricity) is very short. This is illustrated in fig. 1, which shows a typical operating curve of a storage device. Additionally, the storage device may provide supplemental services in providing additional load when power is over-supplied to the grid from intermittent renewable generators. Wind speed is usually high at night, but the demand is low at this time. The network operator must arrange for additional demands on the network to take advantage of the surplus supply, either by low energy price signals or specific contracts with consumers, or by restricting the supply of electricity from other power stations or wind farms. In some cases, especially in markets where wind generators are subsidized, the network operator will have to pay the wind farm operator to "turn off" the wind farm. The storage device provides a useful additional load for the network operator, which can be used to balance the grid in the event of over-provisioning.

In order for a power storage device to be commercially viable, the following factors must be considered: capital cost per MW (power capacity) and MWh (energy capacity), round trip (trip) cycle efficiency and lifetime relative to the number of charging and discharging cycles, which can be expected from the initial investment and its environmental impact (relevant regulations in different countries regarding their carbon footprint and their potential use or production of hazardous chemicals). For wide utility scale applications, the power storage device should be deployable in the grid where it is needed. In other words, it should have a small footprint and its operating principle should not require specific geographical restrictions, such as those required by a hydro-power generation system or a compressed air energy storage device.

Cryogenic energy storage technologies using refrigerants such as liquid air offer many advantages over other available electrical storage technologies. Cryogenic energy storage systems are typically energy intensive, highly locatable (because they use relatively small storage tanks that are not geographically constrained), environmentally friendly (because their operating principle does not involve the use or production of hazardous materials or the production of carbon emissions), and relatively inexpensive due to the physical properties of liquid air. During the charging or liquefaction phase, low cost electricity during periods of low demand (off-peak periods) or periods of excess supply from intermittent renewable generators is used to liquefy the air. It is then stored as refrigerant in a storage tank and subsequently released, pumped and heated to drive a turbine and generate electricity during the discharge or power recovery stage (during peak periods of high electricity costs). Cryogenic energy storage technology relies on the thermodynamic potential between liquid air at cryogenic temperatures and gaseous air at ambient and higher temperatures. The abbreviation CES stands for cryogenic energy storage and is thus used throughout the specification. The round-trip efficiency of a CES system is defined as the ratio of the net electrical energy output of the power recovery unit to the net electrical energy input of the liquefaction unit.

In the simplified view depicted in fig. 2, the CES system is composed of a liquefaction unit (1), a refrigerant tank (2) and a power recovery unit (3). They can be divided into two categories:

standalone CES systems, which are self-sufficient in terms of thermal energy, i.e. they do not need to be integrated with an external hot and an external cold thermal energy source;

and a thermally integrated CES system, i.e. a CES system that receives hot and/or cold waste heat energy from a system external to and co-located with the CES system, such as a nuclear power plant for hot waste heat energy, a thermal power plant (e.g. an open cycle gas turbine power plant; a combined cycle gas turbine power plant and a conventional steam cycle), a data center, a steel plant, a furnace used in the ceramic, terracotta, glass manufacturing and cement manufacturing industries; and LNG regasification terminals for cold waste heat energy, for example.

The thermal energy may be cold or hot.

The term "cold waste thermal energy" covers any cold thermal energy that is a by-product of the first system and that is used in a system different from the first system. Likewise, the term "hot waste thermal energy" encompasses any hot thermal energy that is a byproduct of the first system and that is used in a system different from the first system.

The term "heat of compression" refers to the thermal energy of heat embedded in the fluid that has been compressed. In other words, "heat of compression" refers to the increase in sensible heat (sensible energy) experienced by the process stream of the liquefaction unit as a result of compression. Thus, the term may also encompass any thermal energy generated during compression of a fluid, which is then stored in a thermal energy storage device and subsequently supplied to another fluid. The heat of compression referred to in this patent application cannot be used as waste heat energy as it is produced and used by the same system that generated it, i.e. the CES system.

The present invention addresses embodiments in the practice of a compressed heat recycling system in both a standalone CES system and a thermally integrated CES system, such that different levels and amounts of compressed heat released and collected during the liquefaction phase are subsequently used to increase the power output provided by the power recovery unit during the power recovery phase. Furthermore, increasing the temperature of the working fluid before it is expanded through pre-stage heating or inter-stage reheating using stored compression leads to an increase in the power output of the power recovery unit, which leads to an increase in the round-trip efficiency of the CES system.

Above ambient temperature, the level of thermal energy of the heat increases with increasing temperature. Conversely, below ambient temperature, the level of cold thermal energy increases as the temperature decreases.

The present invention is directed to the configuration of the expansion stages of the turboexpander to apply the stored heat of compression to increase the efficiency of the power recovery subsystem. It is also an object of the present invention to provide a compression heat recycling system capable of improving a round trip efficiency of a CES system into which the compression heat recycling system is integrated, and a method for recycling compression heat, which is utilized during a liquefaction stage and recovered during an electric power recovery stage, so as to improve the round trip efficiency of the CES system.

The compression heat generated in the compression process is characterized not only by its level but also by its amount. The level and amount of thermal energy embedded in a given fluid processed by a compressor can be said to be a function of the mass flow rate processed by the compressor, the inlet temperature of the compressor, the inlet pressure of the compressor, the total compressor pressure ratio, and the efficiency of the compressor.

CES systems may use a subsystem designed to collect the heat of compression generated in the liquefaction unit, i.e. the thermal energy of the heat embedded in the pressurized flow of gas to be liquefied, during the liquefaction phase, and then store it in a Thermal Energy Storage Device (TESD), and to release this thermal energy to the working fluid of the power recovery unit during the power recovery phase. The collection and release of thermal energy of the heat may be dependent on the use of at least one heat exchanger. Such subsystems are referred to throughout this specification as compression heat recycling systems.

The pressurized stream of gas to be liquefied present in the liquefaction unit and the pressurized refrigerant present in the power recovery unit are generally referred to as "process stream of the liquefaction unit" and "working fluid of the power recovery unit", respectively.

Known compression heat recycling systems typically include at least one compressor, at least one turboexpander, and at least one thermal energy storage device.

Compressors suitable for use in compression heat recycling systems, including those of the present invention, are characterized by the inlet and outlet pressures of the fluid being processed by the compressor. The compressor may be axial, centrifugal, reciprocating or rotary, or any combination of the above, and the like. The compressor may have at least one compression stage, each compression stage being defined by its pressure ratio. The number of compression stages and their respective pressure ratios are typically determined by a thermal process engineer through optimization of turbine performance through computer simulation, assuming given operating conditions (e.g., desired temperature at the output of each compression stage, minimization of pressure drop between the compression stages, taking into account equipment parts disposed between the stages, manufacturer equipment specifications, etc.). Typically, a cooler (i.e., a heat exchanger that uses air or water to cool the process stream) is placed either upstream of the compression stages of a compressor to cool the process stream before it is compressed by them, or downstream of the compressor output to cool the process stream and facilitate its subsequent liquefaction. In a first configuration, the power input to drive the downstream compression stage is reduced by reducing its compression stage input temperature. The second configuration allows more hot thermal energy to be removed from the gas stream output by the compressor, thus facilitating its subsequent liquefaction. Thus, the cooler may remove some or all of the heat of compression embedded in the liquefied process stream. The compression heat recycling system of the present invention allows collecting compression heat via at least one compression heat collecting heat exchanger downstream of any compression stage and downstream of any combination of compression stages.

Turboexpanders suitable for use in compression heat recycling systems including those of the present invention are characterized by the inlet and outlet pressures of the fluid processed by the turboexpander. The turboexpander may be axial or radial or any combination of the above. The turboexpander may have at least one expansion stage; each expansion stage is defined by its pressure ratio. The number of expansion stages and their respective pressure ratios are typically determined by a thermodynamic process engineer through optimization of turbine performance through computer simulations, assuming given operating conditions (e.g., amount and temperature of hot thermal energy to be achieved at the output of each expansion stage, taking into account equipment parts disposed between stages, manufacturer plant specifications, minimization of pressure drop between expansion stages, etc.).

Typically, an electrical recovery heater (i.e. heat exchanger) is placed either immediately upstream of the input to the turboexpander or between its expansion stages to heat the gas stream prior to expansion, as the expansion process involves a reduction in the temperature of the fluid. Both configurations allow for an increase in the electrical output of the turboexpander.

The purpose of a Thermal Energy Storage Device (TESD) is to capture, store and release thermal energy (i.e., hot or cold thermal energy) in a controlled manner. There are different types of TESDs that typically differ in their internal structure. Some TESDs, commonly referred to as "packed beds," are filled with an immobilized solid phase through which a thermal energy transfer fluid is circulated to charge or discharge the TESD with thermal energy in order to supply it where needed. The immobilized solid phase can be made of a packed bed or porous solid media composed of solid particles capable of retaining thermal energy. The purpose of the finer packed bed TESD disclosed in WO2012020233a2 is to provide a flexible system that can accommodate asymmetric charging and discharging while maintaining the pressure drop at an acceptable level and minimizing end effects by increasing the flow rate of the thermal energy transfer fluid towards the end of TESD charging and discharging. The other TESDs are filled with a fixed liquid phase through which at least one heat exchange coil passes to allow the passage of a thermal energy transfer fluid. Other TESDs, commonly referred to as thermoclines, are made of containers containing two density-dependent regions of a single thermal energy transfer fluid at different temperatures, stacked on top of each other (due to density differences). One form of thermocline includes two separate containers, each containing the same thermal energy transfer fluid at two different temperatures (i.e., there is a warm tank and a cold tank).

Known compression heat recycling systems can collect and store (in TESD) the compression heat in the process fluid embedded in the liquefaction unit after compression by the compressor and transfer it to the working fluid of the electric power recovery unit before it is expanded by the turboexpander.

The type of TESD conventionally used in compression heat recycling systems determines the type of heat exchange that takes place between the process stream of the liquefaction unit and the thermal storage medium of the TESD, and between the thermal storage medium of the TESD and the working fluid of the power recovery unit. Table 1 summarizes the mechanism of thermal energy transfer for the different types of TESDs. (the symbols "+" and "-" mentioned in Table 1 indicate that a given heat exchange type is possible or impossible, respectively). The heat exchange between the process fluid of the liquefaction unit or the working fluid of the power recovery unit and the thermal storage medium of the TESD is in fact of a direct or indirect nature. Direct heat exchange between a fluid (e.g., a process fluid of a liquefaction unit or a working fluid of a power recovery unit) and the thermal storage medium of the TESD relies on direct physical contact therebetween. Indirect heat exchange between a fluid (e.g. a process fluid of a liquefaction unit or a working fluid of an electricity recovery unit) and the thermal storage medium of the TESD means that an intermediate heat exchanger is used which enables heat transfer between the fluid and an intermediate heat transfer fluid circulating through the TESD.

	Direct heat exchange	Indirect heat exchange
			Packed bed	+	+
TESD based on a fixed liquid phase	-	+
			Thermocline	-	+
Two-tank TESD	-	+

TABLE 1

Fig. 3A-3D show schematic diagrams of the manner in which heat transfer from the compressor to the turboexpander may occur. Each schematic includes a compressor, a packed bed TESD, and a turboexpander. The compression heat generated by the compressor during the liquefaction phase is collected via a compression heat collection heat exchanger and stored in the TESD. The stored heat of compression is then applied to the working fluid of the power recovery unit during the power recovery stage. The liquefaction stage and the electricity recovery stage may occur at different times. Therefore, the arrows indicating the direction of the flow flowing in the compression heat recycling system are only for information, and do not represent the fact that the liquefaction stage and the power recovery stage occur simultaneously. However, in some cases, the liquefaction stage and the power recovery stage may occur simultaneously.

Table 2 summarizes information related to the nature of the heat exchange that occurs in fig. 3A-3D.

TABLE 2

In fig. 3A, the heat of compression is collected and released by TESD (4) via direct heat exchange, such that the TESD (4) is fluidly connected with and downstream of a compressor (5) and fluidly connected with and upstream of a turboexpander (6). After compression by the compressor (5), the process stream of the liquefaction unit is sent through the packed bed of TESD (4) to transfer its hot thermal energy to it. The working fluid of the power recovery unit is then circulated through the packed bed of TESD (4) to collect the heat of compression stored in the TESD (4) before it is expanded by the turbo-expander (6). The output pressure of the compressor (5) applies a TESD pressure which in turn applies the input pressure of the turbo-expander (6). However, if the pressure used to collect and store the heat of compression is different from the pressure of the working fluid supplying the stored heat of compression to the power recovery unit, it is also possible to recycle the TESD pressure, which is detrimental to the capital expenditure of the overall system.

In fig. 3B, the compression heat is collected and released by TESD (4) via indirect heat exchange, so that the pair of TESD (4) and compression heat collection heat exchanger (7) and the pair of TESD (4) and heat exchanger (8) are enclosed in a first closed loop and a second closed loop, respectively, sharing part of the TESD (4) and the pipe arrangement through which the heat transfer fluid circulates. The circulation pump allows the heat transfer fluid to circulate through the two closed loops. The compression heat collection heat exchanger (7) tries to extract as much compression heat as possible from the compressed fluid, i.e. the process fluid of the liquefaction unit, and therefore cannot act as a cooler (as defined above) whose function is to discard at least some of the compression heat embedded in the process fluid of the liquefaction unit. The heat exchanger (8) is suitable as an electric power recovery heater (as defined above). The heat of compression, after compression via compressor (5), is transferred from the process stream of the liquefaction unit to the working fluid of the power recovery unit before expansion via turboexpander (6) via the sequential action of the heat transfer fluid circulating through the first and the packed beds of TESD (4) and the heat transfer fluid circulating through the packed beds of TESD (4) and the second closed loop. This configuration has the advantage that the pressure within the first and second closed loops is completely independent of the pressure of the process fluid of the liquefaction unit and the pressure of the working fluid of the power recovery unit.

Fig. 3C-3D show the case of compression heat collection and release by TESD (4), each via heat exchange of different nature from each other.

In fig. 3C, TESD (4) is fluidly connected to and downstream of compressor (5). The TESD (4) and the power recovery heater (8) are enclosed in a third separate closed loop through which the heat transfer fluid is circulated. The heat of compression in the process stream embedded in the liquefaction unit after compression by compressor (5) is transferred directly to the packed bed of TESD (4). The third closed loop heat transfer fluid then transfers the heat of compression stored in the TESD (4) to the working fluid of the power recovery unit via the power recovery heater (8) before being expanded by the turbo-expander (6). If the pressure at the output of the compressor (5) is different from the pressure of the heat transfer fluid circulating in the third separate closed loop, a pressure to circulate the TESD (4) may be necessary.

In fig. 3D, the TESD (4) and the compression heat collection heat exchanger (7) are enclosed in a fourth separate closed loop through which the heat transfer fluid circulates. The TESD (4) is fluidly connected to and upstream of the turbo-expander (6). The heat of compression in the process stream embedded in the liquefaction unit after compression by the compressor (5) is transferred first via the compression heat recovery heat exchanger (7) to the heat transfer fluid of the fourth closed loop and then to the packed bed of TESD (4). The working fluid of the power recovery unit strips the stored heat of compression from the TESD (4) by circulating through the TESD before it is expanded by the turbo-expander (6). If the pressure at the input of the turboexpander (6) is different from the pressure of the heat transfer fluid circulating through the fourth separate closed loop, a pressure to circulate the TESD (4) may be necessary.

When selecting the most energy efficient compression heat recycle system configuration from the four mentioned in table 2, there are several technical factors to consider, namely: heat transfer efficiency, pumping energy requirements, and pressure drop. Direct heat exchange does not involve the use of an intermediate heat transfer fluid, thus promoting higher heat transfer efficiency than indirect heat exchange. The density of the heat transfer fluid is most important in terms of pumping energy requirements: the higher the density of the fluid, the lower the work input that the fluid needs to be compressed for a given pressure differential. Selecting the most energy efficient compression heat recycle system configuration may be accomplished by running a computer based simulation.

For direct heat exchange to occur during the liquefaction stage, a single TESD cannot simultaneously capture the heat of compression generated by each compression stage of the compressor because the output pressures of the various compression stages of the compressor are different from one another. A single TESD may be placed downstream of any compression stage of the compressor and should therefore be able to withstand the output pressure of the compression stage upstream of the TESD. This technical requirement has a large impact on capital expenditure, since the higher the pressure, the greater the amount of steel required for the TESD pressure vessel to support it and the greater the TESD cost.

For direct heat exchange to occur during the power recovery stage, a single TESD cannot supply the stored compression heat to each expansion stage of the turboexpander simultaneously, since the input pressures of the various expansion stages of the turboexpander are different from each other.

For indirect heat exchange to occur during the liquefaction stage, a single TESD may simultaneously collect the compression heat generated by each compression stage of the compressor by placing a compression heat collection heat exchanger downstream of each compression stage. It is important to remember that the heat of compression generated by multiple compression stages typically exhibits different temperatures.

For indirect heat exchange to occur during the power recovery stage, by placing the power recovery heater upstream of the turboexpander and between each expansion stage of the turboexpander, a single TESD can supply the stored heat of compression simultaneously before each expansion stage.

The capture of compression heat by TESD via direct heat exchange means that the compression heat is stored at the compressor output pressure, which impacts the cost of the TESD pressure vessel. Also, the compression heat released by the TESD via direct heat exchange, or the pressure involved in the TESD, is the same as the pressure input to the turboexpander, which, due to the high pressure, affects the cost of the turboexpander (which must be made of a material capable of withstanding high pressures, which increases its cost); or involve cycling the TESD pressure, which results in higher capital expenditure.

The present inventors have noted that having the TESD interact with the compressor and turboexpander via indirect heat exchange has a number of advantages over what is done by direct heat exchange: it not only allows the TESD pressure to be adjusted to balance the thermal energy transfer efficiency and capital expenditure of heat, but also allows the heat of compression to be collected and stored (via a compression heat collection heat exchanger placed downstream of any compressor or any compression stage) and subsequently supplied via an electrical power recovery heater before any expansion stage of the turboexpander or any turboexpander.

Recycling of the heat of compression generated by the liquefaction unit to increase the power output of the power recovery unit has been mentioned in some patent applications (e.g. WO2007096656a 1). Other patent applications show some embodiments of concepts for implementing compression heat recycling.

US20150218968a1 proposes a simple arrangement in which the liquefaction unit and the electric power recovery unit respectively comprise four compressors (reference numbers 101, 105, 109 and 113 and four turboexpanders (602, 603, 604, 605). each given compressor/turboexpander pair is associated with a given TESD integrated with a cooler, as shown in figures 6-8 of that application, a first TESD is associated with a first compressor/fourth turboexpander, a second TESD is associated with a second compressor/third turboexpander, a third TESD is associated with a third compressor/second turboexpander and a fourth TESD is associated with a fourth compressor/first turboexpander The temperature and amount of compression heat obtained and the way in which the compression heat is distributed to the expansion stages to optimize the power output of the power recovery unit.

WO2015154862a1 shows an arrangement in which the liquefaction unit comprises two compressors: a first compressor capable of operating adiabatically in a pressure range between 10 bar and 60 bar; and a second quasi-isothermally operable compressor for pressures exceeding 60 bar. The heat of compression is extracted only from the first compressor, since the second compressor requires a cooler to work efficiently. Downstream of the first compressor, two TESDs are placed in parallel: both TESDs are either packed bed TESDs operating by direct heat exchange (fig. 4) or indirect heat exchange (fig. 5), or dual reservoir TESDs (fig. 6). Each TESD is assigned to a given turbo-expander. Having the two TESDs in parallel allows the mass flow rate of the pressurized flow for each branch to be controlled according to the available space in each TESD for storing thermal energy of the heat. However, the thermal energy of the heat supplied by the two TESDs is of the same grade, since it originates from a single compressor.

Fig. 14 of WO2013034908a2 shows a CES system in which the compressed heat recycling system consists of two separate closed loops sharing a single TESD. The first closed loop indirectly receives the heat of compression generated by the two compressors (i.e., the main air compressor and the recycle air compressor) and stores the thermal energy of that heat in a single TESD. A recycle air compressor is located downstream of the main air compressor and the air purification unit. The input pressure of the recycle air compressor is equal to or greater than the output pressure of the main air compressor, and the mass flow rate of the liquefaction unit process stream processed by the recycle air compressor is equal to or greater than the mass flow rate of the process stream processed by the main air compressor, because the gaseous output stream of the phase separator is combined with the output of the main air compressor before being processed by the recycle air compressor. Thus, the main air compressor and the recycle air compressor generate two different amounts of different levels of compression heat and store it in a single TESD. Although not disclosed in WO2013034908a2, there are three ways to handle two heat of compression stored in different amounts and different levels in a single TESD:

they can be mixed in the conduit of the first closed loop;

by using at least one cooler, the temperature of one heat of compression can be adjusted to the temperature of another heat of compression;

by using at least one cooler for each compressor, the temperature of both compression heats can be adjusted to reach the same target temperature.

All three of these ways result in an undesirable loss of thermal energy levels.

The second closed loop in WO2013034908a2 indirectly transfers the stored heat of compression to the two expansion stages of the turboexpander via an electric power recovery heater. There is no flexibility in providing the stored heat of compression because the first expansion stage receives a higher level of heat of compression than the second expansion stage because the electrical recovery heaters providing the thermal energy of the heat to the first and second expansion stages are in series. Furthermore, this configuration does not provide the possibility of adjusting the amount of heat experienced by each expansion stage and having both expansion stages feel the same temperature.

The compression heat recycling system of WO2015138817a1 is designed to extract and store compression heat of different grades (350 ℃ -580 ℃ with respect to the first compressor, 240 ℃ -260 ℃ with respect to the second compressor) from the two liquefaction compressors by using two TESDs, each TESD being in direct or indirect heat exchange with a given compressor. Each TESD comprises a given cooler and a given water-cooled balancing heat exchanger (balancing HEX) in order to further reduce the temperature after a portion of the thermal energy of the heat is collected by each TESD. The first set of coolers/balances HEX located downstream of the first compressor reduces the mechanical work input required by the second compressor. A second set of coolers/balances HEX located downstream of the second compressor facilitates the liquefaction that occurs subsequently. The first cooler and the first equilibrium HEX are maintained at temperatures between 40 c and 60 c and around 30 c, respectively. The second cooler and the second equilibrium HEX are maintained at temperatures between 40 c and 120 c and around 30 c, respectively. WO2015138817a1 does not allow the amount of compression heat that can be generated from the two compressors to be optimized. According to fig. 1B of WO2015138817a1, a first TESD is associated with a first compressor/first turbo-expander and a second TESD is associated with a second compressor/second turbo-expander. WO2015138817a1 does not disclose any further relationship between TESD and compressor/turboexpander pairs and does not suggest any way of optimizing the round-trip efficiency of a CES system by somehow improving the compressed heat recycle system. Furthermore, no information is disclosed about the nature of the heat exchange between the TESD and the expansion stage.

Accordingly, the present inventors have developed known compression heat recycling systems and subsystems thereof that solve some or all of the above-described problems, while taking advantage of the following advantages: there are two compressors (i.e., a main air compressor and a recycle air compressor) within the CES system to store different levels and different amounts of compression heat in a given TESD during the liquefaction phase, and to release this compression heat during the power recovery phase via a power recovery heater upstream of the expansion stage of the turbo-expander of the power recovery unit to increase its power output and thus increase the round trip efficiency of the overall system.

Disclosure of Invention

In a first aspect, the present invention provides a power recovery subsystem for a cryogenic energy storage system, the power recovery subsystem comprising:

a first heat source;

a first heat exchanger;

a second heat exchanger;

a first expansion stage;

a second expansion stage;

a first conduit arrangement having an upstream end and a downstream end and configured to convey a working fluid through the first heat exchanger, the first expansion stage, the second heat exchanger, and the second expansion stage; and

a second piping arrangement configured to convey a first heat transfer fluid from the first heat source through the first heat exchanger and the second heat exchanger,

wherein the second piping arrangement is further configured to convey a first portion of the first heat transfer fluid through the first heat exchanger and to convey a second portion of the first heat transfer fluid through the second heat exchanger.

The power recovery subsystem may, for example, employ a single heat source, such as a thermal energy storage device, to provide pre-stage heating at the same temperature or level to multiple expansion stages. Such an electrical power recovery subsystem may include piping and valves configured to divide the heat transfer fluid flowing from the heat source (e.g., flowing through the thermal energy storage device) into a plurality of portions, each of which may be routed through a single heat exchanger associated with an expansion stage. The mass flow rate of these portions of the fluid is less than the mass flow rate of the combined stream, but at the same temperature. In other words, they have the same thermal energy level. The portions may be passed through separate heat exchangers associated with respective expansion stages to apply pre-stage heating to multiple expansion stages at the same temperature.

The amount of thermal energy of the heat provided during pre-stage heating is determined primarily by the temperature of the portion of the first heat transfer fluid and the mass flow rate of the first heat transfer fluid.

Advantageously, the amount of thermal energy of heat provided during pre-stage heating can be adjusted to maximize the work output of the expansion stage for a given level of thermal energy of heat delivered by the thermal energy storage device. This may be achieved by further heating or cooling the first heat transfer fluid, however, this requires more energy input or wastes stored compression heat by removing it via cooling. A first aspect of the invention provides an efficient way of achieving thermal energy conditioning between expansion stages by means of a pipe arrangement.

One way to implement the pipe arrangement according to the first aspect of the invention is to use a valve to regulate the mass flow rate of fluid from the thermal energy storage device. The valve causes very little fluid pressure drop loss and very little fluid temperature loss while allowing the flow rate through the section to control the amount of thermal energy of heat provided to each expansion stage by pre-stage heating. (the temperature of each portion of the heat transfer fluid circulating through the power recovery subsystem is the same as the temperature of the heat transfer fluid.)

By controlling the amount of thermal energy provided to each expansion stage by pre-stage heating, the efficiency of the power recovery subsystem is maximized. In other words, the combined work output from each expansion stage is maximised by providing each expansion stage with an amount of pre-stage heating, so controlling the amount of pre-stage heating is advantageous as it increases the efficiency of the power recovery subsystem.

Increasing the efficiency of the power recovery subsystem, of which the power recovery subsystem forms a part, increases the efficiency of the cryogenic energy storage system. In other words, it is advantageous to control the amount of heating provided to each expansion stage by pre-stage heating because it increases the efficiency of the cryogenic energy storage system.

The subsystem may further comprise

A third heat exchanger; and

a third expansion stage;

wherein the first piping arrangement is further configured to convey the working fluid through the third heat exchanger and the third expansion stage; and is

Wherein the second piping arrangement is further configured to convey a third portion of the first heat transfer fluid through the third heat exchanger.

By further configuring the second conduit arrangement in three sections, the first heat transfer fluid may be split, wherein each section provides pre-stage heating to the associated expansion stage. This provides further control over the amount of thermal energy provided to each expansion stage by pre-stage heating.

Again, one way to achieve the above further configuration of the second pipe arrangement is to use a valve to regulate the mass flow rate of fluid from the thermal energy storage device. Using the valve in this manner provides the advantages described above.

The subsystem may further comprise

A second heat source;

a fourth heat exchanger;

a fourth expansion stage; and

a third tube arrangement configured to convey a second heat transfer fluid from the second heat source through the fourth heat exchanger,

wherein the first piping arrangement is further configured to route the working fluid through the fourth heat exchanger and the fourth expansion stage.

The second heat source (e.g., a second thermal energy storage device) may provide pre-stage heating to at least one expansion stage that does not receive thermal energy from the first heat source (e.g., a first thermal energy storage device). This provides further control over the amount of thermal energy provided to each expansion stage by pre-stage heating, as it allows different fluid temperatures to be used for different subsets of expansion stages. In other words, utilizing two heat sources provides further control over the amount of thermal energy provided to each expansion stage by pre-stage heating.

The subsystem may further comprise

A fifth heat exchanger; and

a fifth expansion stage;

wherein the first piping arrangement is further configured to convey the working fluid through the fifth heat exchanger and the fifth expansion stage; and is

Wherein the third tubing arrangement is further configured to pass a first portion of the second heat transfer fluid through the fourth heat exchanger and to pass a second portion of the second heat transfer fluid through the fifth heat exchanger.

First and second heat sources (e.g., thermal energy storage devices) may provide pre-stage heating of five expansion stages. When there are five expansion stages, preferably pre-stage heating will be provided by the first thermal energy storage device for three of the five expansion stages and pre-stage heating will be provided by the second thermal energy storage device for the remaining two of the five expansion stages. This provides further control over the amount of thermal energy provided to each expansion stage by pre-stage heating.

The subsystem may be configured such that the or each heat exchanger through which the third conduit arrangement passes is positioned along the first conduit arrangement upstream of the heat exchanger through which the second conduit arrangement passes.

Alternatively, the or each heat exchanger through which the third conduit arrangement passes is positioned along the first conduit arrangement downstream of the heat exchanger through which the second conduit arrangement passes.

In other words, where there are a first subset and a second subset of heat exchangers to be treated by heat from a first heat source and a second heat source (e.g. a thermal energy storage device), respectively, they may be arranged along the first pipe arrangement such that the first subset is upstream of the second subset, or the second subset is upstream of the first subset.

As described elsewhere herein, the heat exchanger may be used to transfer heat from the first heat transfer fluid to the working fluid of the power recovery unit. The working fluid of the power recovery unit may be referred to as a working fluid. Such heat exchangers may be placed immediately upstream of the expansion stages they heat. A first heat transfer fluid and a working fluid flow through the heat exchanger. Preferably, the heat exchanger is a counter-flow heat exchanger, wherein the first heat transfer fluid and the working fluid flow in opposite directions through the heat exchanger.

The heat exchanger transferring thermal energy from the second thermal energy storage device may be upstream of the heat exchanger transferring thermal energy from the first thermal energy storage device, wherein upstream is referred to herein as the flow direction of the working fluid of the power recovery unit.

Alternatively, the heat exchanger transferring thermal energy from the first thermal energy storage device may be upstream of the heat exchanger transferring thermal energy from the second thermal energy storage device, where upstream is referred to herein as the flow direction of the working fluid of the power recovery unit.

These arrangements of heat exchangers allow greater control over the thermal energy of the heat transferred to the expansion stage by pre-stage heating. By using the control, an optimized heat transfer to each expansion stage may be achieved, which in turn increases the power output of the power recovery unit, which in turn provides an improved efficiency of the cryogenic energy storage system.

The subsystem may further comprise

A sixth heat exchanger for the heat-exchange of the air-conditioning system,

wherein the first conduit arrangement is further configured to convey the working fluid through the sixth heat exchanger upstream of both (i) the most upstream heat exchanger through which the second conduit arrangement passes and (ii) the most upstream heat exchanger through which the third conduit arrangement passes, and

wherein the first piping arrangement is further configured to convey working fluid output from a most downstream expansion stage through the sixth heat exchanger to an exhaust.

The additional power recovery heater may be used to heat the working fluid of the power recovery unit before it passes through any heat exchanger that provides thermal energy from the first or second thermal energy storage device. This provides an advantage in that the temperature of the output stream of the most downstream expansion stage may be higher than the temperature of the input stream to the most upstream heat exchanger which provides thermal energy from the first or second thermal energy storage device. The thermal energy of the otherwise wasted heat in the output stream of the downstream expansion stage may be transferred to the power recovery unit by the additional power recovery heater to increase the efficiency of the cryogenic energy storage system.

The subsystem may further include a fourth piping arrangement configured to divert a portion of the working fluid from a downstream location in the first piping arrangement through the evaporator and the first compressor, and to return it to an upstream location in the first piping arrangement.

The subsystem may be configured such that the evaporator is positioned upstream of the most upstream heat exchanger along the first conduit arrangement, wherein the downstream location is downstream of the most downstream expansion stage; and wherein the upstream location is immediately upstream of the most downstream expansion stage.

A portion of the power-recovered working fluid may be taken at a location downstream of the most downstream expansion stage. This portion may be passed through an evaporator and a compressor before returning to the working fluid of the power recovery unit immediately upstream of the most downstream expansion stage. This portion not only heats the working fluid of the power recovery unit in the evaporator before it reaches the compressor (i.e. it is cooled before compression), but the compressed portion rejoins the working fluid of the power recovery unit increasing the mass flow rate of the working fluid of the power recovery unit through the most downstream expansion stage. Both of these effects increase the expansion work output of the power recovery unit, thereby increasing the power output of the power recovery unit, its efficiency and the efficiency of the cryogenic energy storage system.

The subsystem may be configured such that the second conduit arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchanger, and the third conduit arrangement passes through the fourth heat exchanger, and preferably no other heat exchanger, and wherein the heat exchanger through which the third conduit arrangement passes is upstream of the heat exchanger through which the second conduit arrangement passes.

The subsystem may be configured such that the second conduit arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchanger, and the third conduit arrangement passes through the fourth and fifth heat exchangers, and preferably no other heat exchanger, wherein the heat exchanger through which the second conduit arrangement passes is upstream of the heat exchanger through which the third conduit arrangement passes.

The subsystem may be configured such that the second conduit arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchanger, and the third conduit arrangement passes through the fourth heat exchanger, and preferably no other heat exchanger, wherein the heat exchanger through which the second conduit arrangement passes is upstream of the heat exchanger through which the third conduit arrangement passes.

These arrangements of heat exchangers allow greater control over the thermal energy of the heat transferred to the expansion stage by pre-stage heating. By using the control, an optimized heat transfer to each expansion stage may be achieved, which in turn provides an improved efficiency of the power recovery unit, which in turn provides an improved efficiency of the cryogenic energy storage system. The particular arrangement specified above has been found to be particularly effective.

The first heat source in the subsystem may be a first thermal energy storage device, and the second pipe arrangement may be further configured to return the first heat transfer fluid to the first thermal energy storage device after passing through each heat exchanger, wherein the second pipe arrangement is configured to pass through said each heat exchanger such that the second pipe arrangement forms a first closed loop.

Furthermore, the second heat source may be a second thermal energy storage device, and the third pipe arrangement may be further configured to return the second heat transfer fluid to the second thermal energy storage device after passing through each heat exchanger through which the second pipe arrangement is configured to pass such that the third pipe arrangement forms a second closed loop.

The first thermal energy storage device may be configured to store at least a portion of the compression heat generated by the recycle air compressor, and the second thermal energy storage device may be configured to store at least a portion of the compression heat generated by the main air compressor, and the second thermal energy storage device may comprise a conduit system adapted to transport molten salt.

These configurations of thermal energy storage devices are advantageous because they allow different levels of heat generated by the recycle air compressor and the main air compressor to be separately and efficiently stored. By storing different levels of heat separately, they can be applied separately to different portions of the process stream. It has been found that applying different levels of heat at different locations in the power recovery system provides for particularly efficient power recovery.

The subsystem may further comprise

A tenth heat exchanger; and

an eleventh heat exchanger, wherein:

the second heat source may be a second thermal energy storage device,

the first conduit arrangement may be further configured to convey the working fluid through the tenth heat exchanger immediately upstream of the fourth heat exchanger, and wherein;

the third conduit arrangement may be configured to form two closed loops, the first closed loop passing through the second thermal energy storage device and the eleventh heat exchanger, and the second closed loop passing through the eleventh heat exchanger and the fourth heat exchanger,

optionally, wherein the heat transfer fluid in the first closed loop may comprise molten salt, further optionally wherein the heat transfer fluid in the second closed loop may comprise a diathermic oil or a mixture of diathermic oils.

The first thermal energy storage device may be configured to store at least a portion of the heat of compression generated by the main air compressor and at least a portion of the heat of compression generated by the recycle air compressor, and the second thermal energy storage device may be configured to store at least a portion of the heat of compression generated by the main air compressor, and the second thermal energy storage device may comprise a pipe system adapted to transport molten salt.

It can be advantageous to store a portion of the heat of compression from the main air compressor in both the first thermal energy storage device and the second thermal energy storage device. In particular, the inventors have found that it is advantageous to store a higher grade of heat from the main air compressor in the second thermal energy storage means and a lower grade of heat from the main air compressor in the first thermal energy storage means. Storing different levels of heat separately from each other has many advantages, including efficient storage and efficient power recovery when the stored heat is applied to the process stream.

The second thermal energy storage device may be configured to store thermal energy at a temperature higher than the temperature of the thermal energy stored in the first thermal energy storage device, and the second thermal energy storage device may be configured to store thermal energy between 150 ℃ and 550 ℃, preferably between 200 ℃ and 400 ℃, and the first thermal energy storage device may be configured to store thermal energy between 150 ℃ and 350 ℃.

It has been found that configuring the thermal energy storage device to store the above specified temperatures is particularly effective and results in more efficient electrical power recovery.

In a second aspect, the present invention provides a cryogenic energy storage system comprising:

an electric power recovery subsystem comprising a plurality of expansion stages configured to receive hot thermal energy from first and second thermal energy storage devices via a corresponding plurality of heat exchangers and to transfer the hot thermal energy to a working fluid passing through the plurality of expansion stages and the plurality of heat exchangers; and

a liquefaction subsystem configured to supply hot thermal energy to the first thermal energy storage device and the second thermal energy storage device, and further comprising;

a main air compressor;

a circulating air compressor;

an eighth heat exchanger;

a ninth heat exchanger;

a fifth piping arrangement configured to convey a process stream through the main air compressor, eighth heat exchanger, recycle air compressor, and ninth heat exchanger;

a sixth piping arrangement forming a third closed loop and configured to convey a third heat transfer fluid between the second thermal energy storage device and the eighth heat exchanger; and

a seventh piping arrangement forming a fourth closed loop and configured to route a fourth heat transfer fluid between the first thermal energy storage device and the ninth heat exchanger,

wherein the eighth heat exchanger is positioned immediately downstream of the primary air compressor along the fifth piping arrangement and is configured to transfer at least a portion of the heat of compression of the process stream from the primary air compressor to the second thermal energy storage device via the third heat transfer fluid, and

wherein the ninth heat exchanger is positioned immediately downstream of the recycle air compressor along the fifth piping arrangement and is configured to transfer at least a portion of the heat of compression of the process stream from the recycle air compressor to the first thermal energy storage device via the fourth heat transfer fluid.

Preferably, the power recovery subsystem is as described above.

This aspect of the invention may be applied to CES systems comprising at least a power recovery unit and a liquefaction unit, and may be applied not only to standalone CES systems, but also to thermally integrated CES systems, preferably (i) those receiving cold waste heat energy only, (ii) those receiving cold waste heat energy and whose hot waste heat energy requirement is partially met by a system external to and co-located with the CES system, and (iii) those not receiving cold waste heat energy and whose hot waste heat energy requirement is partially met by a system external to and co-located with the CES system. The invention can also be used in any technical field where a gas is to be liquefied, then stored and subsequently regasified at the same site.

The CES system according to the invention takes advantage of the following advantages: the presence of two compressors (i.e., a main air compressor and a recycle air compressor) within the CES system to store different levels and different amounts of compression heat during the liquefaction stage in a given TESD, and to release the compression heat via an electric power recovery heater upstream of the expansion stage of the turbo-expander of the electric power recovery unit to increase its mechanical work output during the electric power recovery stage, thus increasing the round trip efficiency of the overall system.

The liquefaction unit may provide heat of compression, which may be stored in a thermal energy storage device and applied to the power recovery unit. Recycling the compression heat increases the efficiency of the cryogenic energy storage system. In particular, the main air compressor and the recycle air compressor of the liquefaction subsystem each output heat of compression.

The cryogenic energy storage system may further comprise:

a cold box;

a liquefaction turboexpander;

an eighth piping arrangement configured to pass at least a portion of the process stream through a portion of the cold box and then through the liquefaction turboexpander before returning through the cold box and merging with the fifth piping arrangement upstream of the recycle air compressor such that a mass flow rate of fluid through the main air compressor is less than a mass flow rate of fluid through the recycle air compressor;

a ninth pipe arrangement configured to pass at least a portion of the process stream through the cold box, an expansion device, preferably a joule-thomson valve or a wet turbine expander, to a phase separator such that the portion of the process stream in the eighth pipe arrangement transfers cold thermal energy via the cold box to the portion of the process stream in the ninth pipe arrangement; and

a first cold circulation loop, wherein the first cold circulation loop passes through the cold box and is configured to transfer cold waste heat energy from a system external to but thermally integrated with the cryogenic energy storage system to the portion of the process stream in the ninth piping arrangement.

The system may include a cold box via which cold waste heat energy may be transferred from an external system to the liquefaction unit. Applying cold waste heat energy from an external source to the portion of the gaseous circulating air compressor output stream that is subsequently passed through an expansion device to reach a phase separator by the cold box improves the liquefaction process. The lower the amount of compression heat collected from the recycle air compressor via the ninth heat exchanger, the higher the temperature of the gaseous recycle air compressor output stream, which then requires more cold thermal energy. The cold thermal energy is provided by expanding a portion of the process stream of the liquefaction unit and using it as a cooling stream for the remainder of the process stream of the liquefaction unit, and/or by delivering cold waste thermal energy from a source external to the CES system. The higher the availability of the cold waste heat energy, the lower the required mass flow of the diverted portion of the process stream of the liquefaction unit. Thus, maximizing the capture of the compression heat generated by the recycle air compressor reduces the power input to the liquefaction unit and increases the power output of the power recovery unit by supplying said compression heat to the power recovery unit during the power recovery stage. This results in an increase in the round trip efficiency of the cryogenic energy storage system.

The same advantages apply to a method of recycling thermal energy comprising using cold waste thermal energy to cool a second portion of the gaseous recycle air compressor output stream.

The cryogenic energy storage system may be configured such that the power recovery subsystem further comprises an evaporator and a compressor; the system further comprises:

a second cold cycle loop passing through the evaporator and configured to transfer cold waste heat energy from a system external to but thermally integrated with the low temperature energy storage system to at least a portion of the working fluid, at least a portion of the working fluid passing from the output of the power recovery unit through the evaporator and the compressor, and re-entering the power recovery unit.

The system may include using an evaporator in the power recovery subsystem to cool a working fluid passing through the evaporator. An external cold waste source may be used to cool a portion of the working fluid that is withdrawn from the output of the power recovery unit before being compressed and combined with the working fluid upstream of the final expansion stage. Using cold waste heat energy to cool the portion before it enters the compressor reduces the compression work input required to compress the portion. Combining this portion with the working fluid immediately upstream of the most downstream expansion stage increases the mass flow rate processed by the expansion stage. Depending on the amount of compression heat provided by the thermal energy storage device (which is thermally connected to the most downstream expansion stage), the combined effect of cooling the portion of the output of the power recovery unit before it is compressed and increasing the mass flow rate of the working fluid expanded by the most downstream expansion stage may result in an increase in the power output of the power recovery unit and hence an increase in the round trip efficiency of the cryogenic energy storage system. Both the heat of compression extracted from the main and recycle air compressors and the increase in mass flow rate handled by the final expansion stage contribute to an increase in expansion work output and thus to increase the round trip efficiency of the cryogenic energy storage system. The same advantages apply to a method of recycling cold thermal energy, which comprises cooling a portion of the working fluid using cold waste thermal energy before it is compressed to reduce the work input to the compressor, and which is combined with the working fluid upstream of the most downstream expansion stage.

The cryogenic energy storage system may be configured such that the main air compressor has a different input pressure and output pressure than the recycle air compressor, and the main air compressor and/or the recycle air compressor are adiabatic.

The inventors have discovered that by optimizing the output pressures of the main and recycle air compressors and allowing the main and recycle air compressors to be thermally isolated, the round-trip efficiency of the CES system can be increased by having two different temperatures, i.e., two different thermal heat energy levels.

Adiabatic compression means that there is no heating/cooling during compression and between the compression stages of the compressor. On the one hand, adiabatic compression results in an increase in the power input of the liquefaction unit, since the compression work increases with the temperature of the gaseous stream to be compressed. However, on the other hand, the absence of a cooler means that there is no pressure drop introduced by the cooler, thus reducing the power input to the liquefaction unit. In addition, adiabatic compression allows the highest temperature at the output of the compressor: the heat of compression extracted from the adiabatic main air compressor and the adiabatic recycle air compressor is of a higher grade than the heat of compression extracted from the non-adiabatic main air compressor and the recycle air compressor. Thus, adiabatic compression allows increasing the power output of the power recovery unit. The net effect of having an adiabatic main air compressor and an adiabatic recycle air compressor is to increase the round-trip efficiency of the CES system. This conclusion is also valid if only one of the main air compressor or the recycle air compressor is adiabatic.

In a third aspect, the present invention provides a thermal energy recycling system comprising:

a main air compressor;

a circulating air compressor;

a second thermal energy storage device;

a first thermal energy storage device;

a working fluid; and

a plurality of expansion stages comprising a first subset and a second subset;

wherein the system is configured to collect and store in the second thermal energy storage device the heat of compression generated by the main air compressor during a liquefaction phase, and to apply the heat of compression stored in the second thermal energy storage device to the working fluid upstream of each of the expansion stages of the first subset during an electricity recovery phase, and

wherein the system is further configured to collect and store in the first thermal energy storage device the heat of compression generated by the recycle air compressor during a liquefaction phase, and to apply the heat of compression stored in the first thermal energy storage device to the working fluid upstream of each of the second subset of expansion stages during an electricity recovery phase.

Storing the heat of compression from the main air compressor in a thermal energy storage device separate from the thermal energy storage device used to store the heat of compression from the recycle air compressor is advantageous in that the temperature of the heat of compression is different, i.e. the main air compressor and the recycle air compressor are readily available sources of thermal energy at different temperatures, i.e. they are readily available sources of different levels of thermal energy.

The heat of compression from the main air compressor is collected and stored at a higher temperature than the heat of compression from the recycle air compressor. In other words, the compression heat collected and stored from the main air compressor has a higher level than the compression heat collected and stored from the recycle air compressor. It is therefore further advantageous to store the compression heat from the main air compressor and the recycle air compressor in different thermal energy storage devices, so that each thermal energy storage device can be optimized for the temperature of the thermal energy it is designed to store.

The first thermal energy storage device is thermally connected to the circulating air compressor, and the second thermal energy storage device is thermally connected to the main air compressor.

The first thermal energy storage device may be configured to store thermal energy of lower grade heat from the recycled air compressor. The first thermal energy storage means may preferably comprise water or a mixture of water and glycol, which is optimised for storing the thermal energy of the lower grade heat. The first thermal energy storage means may comprise a thermal oil or a molten salt, or may be a packed bed.

The second thermal energy storage device may be configured to store thermal energy of a higher level of heat from the main air compressor. The second thermal energy storage means may preferably comprise a thermal oil or molten salt, or may be a packed bed, which is optimised for storing the thermal energy of higher levels of heat. The second thermal energy storage device may comprise water or a mixture of water and glycol.

The multiple inflation stages may be organized into subsets of inflation stages, the subsets defined as: some subset of the expansion stages are pre-stage heated by the same thermal energy storage device.

A subset of the expansion stages may comprise one expansion stage. Alternatively, a subset of the expansion stages may comprise a plurality of expansion stages, but preferably no more than three.

Each expansion stage may be preheated by a heat exchanger. Preferably, the heat exchangers transfer thermal energy from the first thermal energy storage device or the second thermal energy storage device to the working fluid of the power recovery unit.

In a fourth aspect, the present invention relates to a method for recycling thermal energy in a cryogenic energy storage system, the method comprising:

providing a liquefaction subsystem, comprising:

a main air compressor;

a circulating air compressor;

a second thermal energy storage device; and

a first thermal energy storage device;

providing a power recovery subsystem comprising:

a working fluid; and

a plurality of expansion stages comprising a first subset and a second subset;

collecting and storing compression heat from the main air compressor in the second thermal energy storage device;

collecting and storing compression heat from the circulating air compressor in the first thermal energy storage device;

applying the heat of compression stored in the second thermal energy storage device to the working fluid upstream of each of the first subset of expansion stages; and

applying the heat of compression stored in the first thermal energy storage device to the working fluid upstream of each of the expansion stages of the second subset.

The method and cryogenic energy storage system may be configured such that the co-located process is a Liquefied Natural Gas (LNG) regasification terminal.

The method and cryogenic energy storage system may be configured such that: the second thermal energy storage device is configured to acquire, store and apply the compression heat at a temperature different from a temperature of the compression heat acquired, stored and applied by the first thermal energy storage device.

Storing the heat of compression from the main air compressor and the recycle air compressor in this manner avoids losing the thermal energy level of heat due to mixing. Mixing will also result in a storage temperature being produced that is somewhere between the higher main air compressor temperature and the lower cycle air compressor temperature. This may be inefficient for storage in any of the thermal energy storage devices described above.

The working fluid may be a working fluid of a power recovery unit.

The first and fourth heat transfer fluids may be fluids flowing through a first thermal energy storage device.

The second and third heat transfer fluids may be fluids flowing through a second thermal energy storage device.

The process stream may be a process stream of a liquefaction unit.

Drawings

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 illustrates a conventional power generation scheme for an energy storage device;

FIG. 2 shows a schematic diagram of a conventional Cryogenic Energy Storage (CES) system;

fig. 3A illustrates direct heat exchange between the process fluid of the liquefaction unit and the packed bed TESD and between the packed bed TESD and the working fluid of the power recovery unit.

Fig. 3B illustrates indirect heat exchange between the process fluid of the liquefaction unit and the packed bed TESD and between the packed bed TESD and the working fluid of the power recovery unit.

Fig. 3C illustrates direct heat exchange between the process fluid of the liquefaction unit and the packed bed TESD, and subsequent indirect heat exchange between the packed bed TESD and the working fluid of the power recovery unit.

Fig. 3D illustrates indirect heat exchange between the process fluid of the liquefaction unit and the packed bed TESD, and then direct heat exchange between the packed bed TESD and the working fluid of the power recovery unit.

Fig. 4A illustrates a standalone CES system according to the present invention, showing a TESD associated with a main air compressor and associated with a recycle air compressor storing at least some heat of compression, another TESD storing at least some cold thermal energy embedded in a refrigerant, and a power island according to the present invention as may be shown in any of fig. 5A through 5F.

Fig. 4B illustrates a thermally integrated CES system according to the present invention receiving some cold waste thermal energy from an LNG regasification terminal showing a TESD associated with the main air compressor storing at least some heat of compression and a recycle air compressor storing at least some cold thermal energy embedded in the refrigerant, two LNG based cooling circuits and a power island according to the present invention as may be shown in any of fig. 6A to 6F.

Fig. 4C illustrates a thermally integrated CES system according to the present invention receiving a sufficient amount of cold thermal energy from an LNG regasification terminal showing TESD associated with the main air compressor and associated with the recycle air compressor storing at least some of the heat of compression, three LNG-based cooling loops, and an electrical island according to the present invention as may be shown in any of fig. 6A through 6F.

Fig. 5A-5F depict six alternative embodiments of a power island for a standalone CES system in accordance with the present invention.

Fig. 6A-6F depict six alternative embodiments of a power island for a thermal integrated system according to the present invention.

Fig. 7A, 7B, and 7C illustrate embodiments of cryogenic energy storage systems similar to the systems illustrated in fig. 4A, 4B, and 4C, respectively.

Fig. 8A and 8B represent two further alternative embodiments of a power island (33) for a standalone CES system as shown in fig. 7A.

Fig. 9A and 9B illustrate two additional alternative arrangements of power islands (330) for a thermally integrated CES system as shown in fig. 7B and 7C, which are embodiments of the present invention.

Fig. 10 depicts an embodiment of a CES system according to the present invention and shows a first (501) and a second (502) intermediate closed loop.

Detailed Description

A first embodiment of the invention is shown in fig. 4A and relates to a standalone CES system showing a liquefaction unit (1), a cryogenic tank (2) and a power recovery unit (3) presenting a power island (33) that may adopt any of the configurations shown in fig. 5A-5F, wherein each of said configurations is also an embodiment of the invention. The standalone CES system has a compression heat recycle (11, 12, 15, 16, 12A, 16A) and a first separate closed dual loop (130) that transfers cold thermal energy embedded in a refrigerant to a process stream of a liquefaction unit. The thermal energy of the heat provided to the working fluid of the power recovery unit via the at least one power recovery heater may be derived from a compression heat recycling device of a closed double loop separated by a second (11, 12A) and a third (15, 16A). Although it is a stand-alone system, embodiments are possible that not only use the hot thermal energy provided by the compression heat recycling device to heat the working fluid of the power recovery unit via at least one power recovery heater, but also use some of the hot waste thermal energy from at least one system co-located with and external to the CES system that generates the hot waste thermal energy, such as nuclear power plants, thermal power plants (e.g., open cycle gas turbine power plants, combined cycle gas turbine power plants, and conventional steam cycles), data centers, steel plants, furnaces used by the ceramic, terra cotta, glass manufacturing, and cement manufacturing industries.

The liquefaction unit (1) converts the ambient air flow (0) into liquid air, which is then stored in a refrigerant tank (2). The liquefaction unit (1) may include at least a main air compressor (10), a first compression heat collection heat exchanger (11), a main air compressor-associated TESD (12) to store compression heat from the main air compressor, an Air Purification Unit (APU) (13), a recycle air compressor (14), a second compression heat collection heat exchanger (15), a recycle air compressor-associated TESD (16) to store compression heat from the recycle air compressor, a cold box (17), a set of two liquefaction turbo expanders (100, 101) placed in series, an expansion device (18) (e.g., a Joule-Thomson valve, a wet turbo expander, etc.), a phase separator (19), a process stream to convey process stream from the main air compressor through the first compression heat collection heat exchanger, an APU, a recycle air compressor, A second compression heat collection heat exchanger, a cold box, a first conduit of an expansion device to the phase separator, a second conduit to divert a portion of the process stream of the first liquefaction unit (carried by the first conduit) when intersected by the cold box, a third conduit (merging downstream of the APU and upstream of the recycle air compressor) to carry the gaseous output stream (121) of the phase separator through the cold box to the input of the recycle air compressor, a fourth conduit to carry the liquid output stream (122) of the phase separator to the cryogenic tank 2, and a fifth conduit to carry the heat transfer fluid circulated through the first split closed double loop (130) through the cold box.

The main air compressor compresses ambient air (i.e., air present in the atmosphere surrounding the CES system) from ambient air pressure to a first pressure, which may be between two and tens of bars, before it is purified in an APU disposed downstream of the main air compressor. The APU consists of an adsorption vessel capable of adsorbing hydrocarbons, water and carbon dioxide to obtain cleaned air at its output. Downstream of said APU, a circulating air compressor compresses the cleaned air from a pressure slightly lower than the first pressure (to take into account the pressure drop introduced by the APU) to a second pressure, equal to tens of bars, with an upper limit of 200 bars.

The cleaned air treated by the recycled air compressor comprises not only the cleaned air output by the APU, but also the cleaned air from the gaseous output stream (121) of the phase separator, whose cold thermal energy has been stripped off as it passes through the cold box (before reaching the recycled air compressor) to be transferred to the process stream of the liquefaction unit conveyed by the first duct. Thus, the mass flow rate of air output by the recycle air compressor is greater than the mass flow rate of air of the main air compressor and affects the amount of heat generated by compression.

The cleaned air output by the recycle air compressor is sent through the cold box to be cooled and then through the expansion device to reduce its pressure to a first pressure, or to a pressure greater than the first pressure and less than a second pressure, allowing it to be fully or partially liquefied, depending on the conditions to which the stream output by the recycle air compressor is subjected (i.e., the pressure of the stream output by the recycle air compressor relative to the critical pressure of air, the amount of cold thermal energy supplied through the cold box, the pressure change produced via expansion through the expansion device, etc.). The gas and liquid mixture output by the expansion device (18) is then fed to a phase separator where it is separated into a liquid phase and a gaseous phase.

A portion (120) of the liquefaction unit process stream (delivered by the first conduit) is diverted upon intersection with the cold box via the second conduit, it exits the cold box to pass through the first liquefaction turboexpander (100) and re-enters the cold box (via a re-entry point controlled by the amount of cooling embedded in the liquefaction turboexpander (100) output) to cool the liquefaction unit process stream (delivered by the first conduit) over a given length of the cold box, after which it exits the cold box and is processed by the second liquefaction turboexpander (101). The gas/liquid mixture output by the second liquid turboexpander (101) is then sent to the phase separator.

The gaseous output flow of the phase separator delivered by the third conduit comprises a gaseous phase resulting from the expansion of the flow delivered by the first conduit through an expansion device (18) and a gaseous phase resulting from the flow delivered by the second conduit, which is subjected to two successive expansions through two liquefaction turboexpanders (100, 101) placed in series and then injected into the phase separator.

The gaseous output stream (121) of the phase separator passes through the cold box to transfer its cold thermal energy to the process stream of the liquefaction unit conveyed by the first conduit and is then conveyed to the input of the recycled air compressor (merging taking place downstream of the APU and upstream of the recycled air compressor).

The liquid output stream (122) of the phase separator is conveyed by a fourth conduit to the cryogenic tank 2.

The term "split closed double loop" is closely related to the presence of TESD: one single loop through which the heat transfer fluid is circulated collects thermal energy from one fluid, while another single loop through which another heat transfer fluid is circulated supplies the thermal energy to the other fluid. The single loops may be of simple design, i.e. each loop has a circulation pump, a piping arrangement through the TESD and a heat transfer fluid. Alternatively, the single loops may have the same heat transfer fluid and may share a circulation pump and a portion of their piping arrangement that passes through a TESD involving the presence of a valve (e.g., a three-way valve), as shown in the first split closed double loop (130) of fig. 4A.

The single loops of the first split closed double loop (130) share a TESD (131), a portion of their piping arrangement, a heat transfer fluid, and a circulation pump (132) to circulate the heat transfer fluid through the two single loops. During the power recovery phase, one single loop allows to pick up at least part of the cold thermal energy embedded in the refrigerant via the evaporator (32) after pumping via the refrigerant pump (31) and store it in the TESD (131). During the liquefaction phase, another single loop allows providing cold thermal energy stored in TESD (131) to the process stream of the liquefaction unit via a fifth conduit.

The process stream of the liquefaction unit conveyed by the first conduit is cooled by the streams conveyed by the second, third and fifth conduits so as to be partially liquefied after passing through said expansion device (18).

Refrigerant produced by the liquefaction unit during a liquefaction phase, i.e. the liquid output stream (122) of the phase separator, is sent to a cryogenic tank (2). During the power recovery phase, some of the refrigerant contained in the cryogenic tank is conveyed to the power recovery unit (3): it is pumped to high pressure by a cryogenic pump (31), heated in an evaporator (32) and conveyed to a power island 33 where it is superheated via at least one power recovery heater and expanded via at least one expansion stage of at least one turboexpander. Whatever the number of turboexpanders present in the power island, they are mechanically coupled to a generator to produce electrical power.

The power island (33) may take any of the configurations shown in fig. 5A-5F, each of which is also an embodiment of the present invention.

The turboexpander of the power recovery unit may preferably exhibit four expansion stages.

The TESD (16) associated with the recycle air compressor may supply hot thermal energy to the working fluid of the power recovery unit via power recovery heaters (81, 82, 83) prior to each of the first three expansion stages (61, 62, 63), while the TESD (12) associated with the main air compressor may supply hot thermal energy to the working fluid of the power recovery unit via power recovery heaters (84) prior to the last fourth stage (64) (see fig. 5A). An additional power recovery heater 80 may be placed upstream of the power recovery heater (81) located upstream of the first expansion stage (61), wherein the working fluid of the power recovery unit may be heated by the output of the fourth expansion stage (64) before being further heated by the power recovery heater (81) placed upstream of the first expansion stage (see fig. 5B). The output of the fourth expansion stage can be vented to atmosphere or used to regenerate the adsorption vessel of the APU after having transferred its hot thermal energy to the working fluid of the power recovery unit via the additional power recovery heater (80).

Alternatively, the TESD (12) associated with the main air compressor may supply hot thermal energy to the working fluid of the power recovery unit via the power recovery heater (8100) before the first expansion stage (6100), while the TESD (16) associated with the recycle air compressor may supply hot thermal energy to the working fluid of the power recovery unit via the power recovery heater (8200, 8300, 8400) before each of the last three expansion stages (6200, 6300, 6400) (see fig. 5E). An additional power recovery heater (8000) may be placed upstream of the power recovery heater (8100) located upstream of the first expansion stage (6100), wherein the working fluid of the power recovery unit may be heated by the output of the fourth expansion stage (6400) before being further heated by the power recovery heater (8100) placed upstream of the first expansion stage (6100) (see fig. 5F). The output of the fourth expansion stage may be vented to the atmosphere, or used to regenerate the adsorption vessel of the APU, after its hot thermal energy has been transferred to the working fluid of the power recovery unit via the additional power recovery heater.

The turboexpander may exhibit five expansion stages.

The TESD (16) associated with the recycle air compressor may supply hot thermal energy to the working fluid of the power recovery unit via the power recovery heater (810, 820, 830) prior to each of the first three expansion stages (610, 620, 630), while the TESD (12) associated with the main air compressor may supply hot thermal energy to the working fluid of the power recovery unit prior to the final fourth and fifth expansion stages (640, 650) (see fig. 5C). An additional power recovery heater (800) may be placed upstream of the power recovery heater (810) located upstream of the first expansion stage (610), wherein the working fluid of the power recovery unit may be heated by the output of the fifth expansion stage before being further heated by the power recovery heater (810) placed upstream of the first expansion stage (610) (see fig. 5D). The output of the fifth expansion stage may be vented to the atmosphere, or used to regenerate the adsorption vessel of the APU, after its hot thermal energy has been transferred to the working fluid of the power recovery unit via the additional power recovery heater.

The additional power recovery heater (80, 800, 8000) may be placed downstream of the evaporator (32).

A second embodiment of the invention is shown in fig. 4B and relates to a thermal integrated system showing a liquefaction unit (1), a cryogenic tank (2) and a power recovery unit (3) exhibiting a power island 330 that may take any of the configurations shown in fig. 6A-6F, each of which is also an embodiment of the invention. The thermally integrated CES system has a compression heat recycling device (11, 12, 15, 16, 12A, 16A) and a first separate closed dual loop (130) that transfers cold thermal energy embedded in a refrigerant to a process stream of the liquefaction unit. The CES system receives some cold waste heat energy from an LNG regasification terminal external to and co-located with the CES system via first (401) and second (403) separate closed single loops. The cold waste heat energy provided by the LNG regasification terminal does not fully satisfy the needs of the liquefaction unit, which still requires the presence of a first separate closed double loop (130). Reference numeral 400, appended to several streams, refers to the LNG stream.

The thermal energy of the heat provided to the working fluid of the power recovery unit via at least one power recovery heater may be derived from a compression heat recycling device of a closed double loop separated by a second (11, 12A) and a third (15, 16A). The hot thermal energy provided to the working fluid of the power recovery unit via at least one power recovery heater may be from the compression heat recycling device and at least one system co-located with and external to the CES system generating hot waste thermal energy, such as a nuclear power plant, a thermal power plant (e.g., open cycle gas turbine power plant; combined cycle gas turbine power plant and conventional steam cycle), a data center, a steel plant, a furnace used by the ceramic, terracotta, glass manufacturing and cement manufacturing industries.

The liquefaction unit (1) converts the ambient air flow (0) into liquid air, which is then stored in a refrigerant tank (2). The liquefaction unit (1) may include at least a main air compressor (10), a first compression heat recovery heat exchanger (11), a TESD (12) associated with the main air compressor to store compression heat from the main air compressor (10), an Air Purification Unit (APU) (13), a recycle air compressor (14), a second compression heat recovery heat exchanger (15), a TESD (16) associated with the recycle air compressor to store compression heat from the recycle air compressor, a cold box (17), a liquefaction turbo expander (102), an expansion device (18) (e.g., a Joule-Thomson valve, a wet turbo expander, etc.), a phase separator (19), a second compression heat recovery heat exchanger to transport a process stream of the liquefaction unit from the main air compressor through the first compression heat recovery heat exchanger, the APU, the recycle air compressor, the second compression heat recovery heat exchanger, and a heat recovery heat exchanger, A first conduit to the phase separator, a second conduit to divert a portion of a process stream of the liquefaction unit (carried by the first conduit) and intersect the cold box, a third conduit to carry the gaseous output stream (124) of the phase separator to atmosphere, a fourth conduit to carry the liquid output stream (122) of the phase separator to the cryogenic tank (2), a fifth conduit to carry the heat transfer fluid of the first split closed double loop (130) through the cold box, a sixth conduit to carry the heat transfer fluid of the first split closed single loop (401) through the cold box.

The main air compressor compresses ambient air (i.e., air present in the atmosphere surrounding the CES system) from ambient air pressure to a first pressure, which may be between two and tens of bars, before it is purified in an APU arranged downstream of the main air compressor. The APU consists of an adsorption vessel capable of adsorbing hydrocarbons, water and carbon dioxide to obtain cleaned air at its output. Downstream of the APU, said circulating air compressor compresses the cleaned air from a pressure slightly lower than the first pressure (to take into account the pressure drop introduced by the APU) to a second pressure, equal to tens of bars, with an upper limit of 200 bars.

The cleaned air processed by the recycle air compressor comprises not only the cleaned air output by the APU, but also the cleaned air from the gaseous stream (123) output by the liquefaction turbo-expander (102), the cold thermal energy of which has been stripped off when passing through the cold box (before reaching the recycle air compressor) to be transferred to the process stream of said liquefaction unit conveyed by the first duct. Thus, the mass flow rate of air output by the recycle air compressor is greater than the mass flow rate of air output by the main air compressor and affects the amount of compression heat generated.

The cleaned air (delivered by the first conduit) output by the recycle air compressor is delivered through the cold box (17) to be cooled and then through an expansion device (18) to reduce its pressure to a first pressure, or to a pressure greater than the first pressure and lower than the second pressure, allowing it to be fully liquefied. The liquid stream output by the expansion device (18) is then sent to a phase separator.

A portion (123) of the liquefaction unit process stream (carried by the first conduit) is diverted upon intersection with the cold box via a second conduit, exits the cold box, passes through a liquefaction turboexpander (102) to re-enter the cold box via the cold side of the cold box (i.e., the underside of the cold box) to cool the remainder of the liquefaction unit process stream carried by the first conduit, and exits the cold box via the warm side of the cold box to eventually merge with the first conduit downstream of the APU and upstream of the recycle air compressor.

A third conduit carrying the gaseous output stream (124) of the phase separator allows any gases present after expansion of the process stream of the liquefaction unit by the expansion device (18) to escape from the phase separator to the atmosphere. This situation typically occurs at start-up of the CES system, since complete liquefaction is only achieved when steady state is established.

The liquid output stream (122) of the phase separator is conveyed by a fourth conduit to the cryogenic tank (2).

The single loops of the first split closed double loop (130) share a TESD (131), a portion of their piping arrangement, a heat transfer fluid, and a circulation pump (132) to circulate the heat transfer fluid through both single loops. During the electricity recovery phase, one single loop allows to pick up at least part of the cold thermal energy embedded in the refrigerant via the evaporator (32) after pumping via the refrigerant pump (31) and store it in the TESD (131). During the liquefaction phase, another single loop allows providing cold thermal energy stored in the TESD (131) to the process stream of the liquefaction unit via a fifth conduit.

The first separate closed single loop (401) is a refrigeration loop that increases the level of cold waste heat energy supplied by the LNG stream (400): the heat transfer fluid (circulating through the first separate closed single loop (401)) is compressed, then cooled by the LNG stream (400) via heat exchanger (402), then compressed again, and cooled again by the LNG stream (400) via heat exchanger (402), then expanded by the turboexpander, and heated by the process stream of the liquefaction unit, which is then cooled, while intersecting the entire cold box (from its cold side to its warm side).

The process stream of the liquefaction unit conveyed by the first conduit is cooled by the streams conveyed by the second, fifth and sixth conduits so as to be completely liquefied after passing through the expansion device (18).

The refrigerant produced by the liquefaction unit during the liquefaction stage, i.e. the liquid output stream (122) of the phase separator, is sent to a cryogenic tank (2). During the power recovery phase, some of the refrigerant contained in the cryogenic tank is conveyed to the power recovery unit (3): it is pumped to high pressure by a cryogenic pump (31), heated in an evaporator (32), and transferred to a power island (330) where it is superheated via at least one power recovery heater and expanded via at least one expansion stage of at least one turboexpander. Whatever the number of turboexpanders present in the power island, they are mechanically coupled to a generator to produce electrical power. However, the power recovery unit of the second embodiment is different from the power recovery unit of the first embodiment in its configuration.

The power recovery unit (3) thermally interacts with a second separate closed single loop (403). The second, separate, closed, single loop (403) contains a recirculation pump to circulate a heat transfer fluid that is cooled by the LNG stream (400) via a heat exchanger (404) and heated by the stream (35) (diverted from the output of the power island (330)) via a vaporizer (320). The diverted stream (35) is thus cooled by a second separate closed single loop heat transfer fluid to be subsequently compressed by the power recovery compressor (34) and re-injected into the power island (330), which may take any of the configurations shown in fig. 6A-6F, each of which is also an embodiment of the present invention.

The turboexpander of the power recovery unit may preferably show four expansion stages, as shown in fig. 6A, 6B, 6E and 6F.

The turboexpander of the power recovery unit may exhibit five expansion stages as shown in fig. 6C and 6D.

For each of configurations 6A-6F, all embodiments of the invention, the diverted stream (35) from the output of the power island (330) is cooled via an evaporator (32), then recompressed by a power recovery compressor (34), and injected back into the power island (330) downstream of the penultimate expansion stage and upstream of the last power recovery heater and the last expansion stage. The work input to the compressor (34) is reduced by having its input cooled by a second separate closed single loop (403) of heat transfer fluid via an evaporator (32), and the work output of the last expansion stage is increased by increasing the mass flow rate processed by the last expansion stage. The remainder of the output stream of the power island can be vented to the atmosphere or can be used to regenerate the adsorption vessel of the APU (13).

The power island may take any of the configurations described in fig. 6A-6F, each of which is also an embodiment of the present invention. One difference between fig. 5A and 6A, fig. 5B and 6B, fig. 5C and 6C, fig. 5D and 6D, fig. 5E and 6E, and fig. 5F and 6F is the presence of a diverted stream (35) from the output of the power island of fig. 6A-6F, which is then cooled via an evaporator (32) and recompressed by a compressor (34), and injected back into the power island 330 downstream of the penultimate expansion stage and upstream of the last power recovery heater (84, 850, 8400) and the last expansion stage (64, 650, 6400). Fig. 6B, 6D and 6F show additional power recovery heaters (80, 800, 8000). The additional power recovery heater (80, 800, 8000) may be placed upstream of the power recovery heater (81, 810, 8100) and upstream of the first expansion stage (61, 610, 6100), wherein the working fluid of the power recovery unit may be heated by the output of the last expansion stage (64, 650, 6400) before being further heated by the power recovery heater (81, 810, 8100) placed upstream of the first expansion stage.

The additional power recovery heater (80, 800, 8000) may be placed downstream of the evaporator (32).

A third embodiment of the invention is shown in fig. 4C and relates to a thermal integrated system showing a liquefaction unit (1), a cryogenic tank (2) and a power recovery unit (3) exhibiting a power island 330 that may take any of the configurations shown in fig. 6A-6F, each of which is also an embodiment of the invention. The thermally integrated CES system has a compressed heat recycling device (11, 12, 15, 16, 12A, 16A). The CES system receives a large amount of cold waste heat energy from an LNG regasification terminal that is co-located with and external to the CES system. In other words, the amount of cold waste heat energy provided by the LNG regasification terminal may meet the cold thermal energy needs of the liquefaction unit in such a way that: a first separate closed double loop (130) as shown in the first and second embodiments is not required. Cold waste heat energy is transferred from the LNG stream (400) to the liquefaction unit via a third (405) and a fourth (407) separate closed single loop, in order to completely liquefy the process stream of the liquefaction unit.

The cold thermal energy embedded in the refrigerant is used directly in the power recovery unit to cool the portion of the output flow of the power island (330) that is diverted to be recompressed by the compressor (34) and injected back into the power island (330) downstream of the penultimate expansion stage and upstream of the last power recovery heater (see fig. 6A-6F: 84, 850, 8400) and the last expansion stage (see fig. 6A-6F: 64, 650, 6400). The cold thermal energy provided by the second separate closed single loop (403) is used to further cool the output stream (35) in the evaporator (32).

The thermal energy of the heat provided to the working fluid of the power recovery unit via at least one power recovery heater may be derived from a compression heat recycling device of a closed double loop separated by a second (11, 12A) and a third (15, 16A). The hot thermal energy provided to the working fluid of the power recovery unit via the at least one power recovery heater may be from a compressed heat recycling device and at least one system co-located with and external to a CES system generating hot waste thermal energy, such as a nuclear power plant, a thermal power plant (e.g., an open cycle gas turbine plant; a combined cycle gas turbine plant and a conventional steam cycle), a data center, a steel plant, a furnace used by the ceramic, terracotta, glass manufacturing and cement manufacturing industries.

The liquefaction unit (1) converts the ambient air flow (0) into liquid air, which is then stored in a refrigerant tank (2). The liquefaction unit (1) may include at least a main air compressor (10), a first compression heat collection heat exchanger (12), a TESD associated with the main air compressor (12) to store compression heat from the main air compressor, an Air Purification Unit (APU) (13), a recycle air compressor (14), a second compression heat collection heat exchanger (15), a TESD associated with the recycle air compressor (16) to store compression heat from the recycle air compressor, a cold box (17), an expansion device (18) (e.g., a Joule-Thomson valve, a wet turbo expander, etc.), a phase separator (19), a first conduit to convey a process stream of the liquefaction unit from the main air compressor through the first compression heat collection heat exchanger, the APU, the recycle air compressor, the second compression heat collection heat exchanger, the cold box, the expansion device to the phase separator, A second conduit to convey the gaseous output stream (124) of the phase separator to atmosphere, a third conduit to convey the liquid output stream (122) of the phase separator to the cryogenic tank (2), a fourth conduit to convey the heat transfer fluid of the third separate closed single loop (405) through the cold box, a fifth conduit to convey the heat transfer fluid of the fourth separate closed single loop (407) through the cold box.

The main air compressor compresses ambient air (i.e., air present in the atmosphere surrounding the CES system) from ambient air pressure to a first pressure, which may be between two and tens of bars, which is then purified in an APU disposed downstream of the main air compressor. The APU consists of an adsorption vessel capable of adsorbing hydrocarbons, water and carbon dioxide to obtain cleaned air at its output. Downstream of the APU, a circulating air compressor compresses the cleaned air from a pressure slightly lower than the first pressure (to take into account the pressure drop introduced by the APU) to a second pressure, equal to tens of bars, with an upper limit of 200 bars.

The cleaned air (delivered by the first conduit) output by the recycle air compressor is delivered through the cold box (17) to be cooled and then through an expansion device (18) to reduce its pressure to a first pressure, or to a pressure greater than the first pressure and lower than the second pressure, allowing it to be fully liquefied. The liquid stream output by the expansion device (18) is then sent to a phase separator.

A second conduit carrying the gaseous output stream (124) of the phase separator allows any gases present after expansion of the process stream of the liquefaction unit through the expansion device (18) to escape from the phase separator to the atmosphere. This situation typically occurs at start-up of the CES system, since complete liquefaction is only achieved when steady state is established.

The liquid output stream (122) of the phase separator is conveyed to the cryogenic tank (2) through a third conduit.

The heat transfer fluid is circulated through a third separate closed single loop (405) by means of a circulation pump, extracts some cold thermal energy from the LNG stream (400) via a heat exchanger (406) and enters the cold box (see cold box of fig. 4C) at a distance "a" from the warm side of the cold box to give up its cold thermal energy to the process stream of the liquefaction unit (conveyed by the first conduit) proceeding in the opposite direction. The length of the cold box is equal to the sum of the distances "a" and "b".

In a fourth separate closed single loop (407) as a refrigeration loop, its heat transfer fluid is compressed by a compressor, then cooled by the LNG stream (400) via a heat exchanger (408), expanded by a turboexpander, heated in the cold box by the process stream of the liquefaction unit transported by the first conduit from the cold side of the cold box to a distance "b" (where it leaves the cold box).

The process stream of the liquefaction unit conveyed by the first conduit is cooled by a third (405) and a fourth (407) separate closed single loop heat transfer fluid conveyed by the second and third conduits, respectively, to be fully liquefied after passing through an expansion device (18).

The refrigerant produced by the liquefaction unit during the liquefaction stage, i.e. the liquid output stream (122) of the phase separator, is sent to a cryogenic tank (2). During the power recovery phase, some of the refrigerant contained in the cryogenic tank is sent to the power recovery unit (3): it is pumped to high pressure by a cryogenic pump (31), heated in an evaporator (32) and transferred to the power island (330) where it is superheated via at least one power recovery heater and expanded via at least one expansion stage of at least one turboexpander. Whatever the number of turboexpanders present in the power island, they are all mechanically coupled to a generator to produce electrical power. However, the power recovery unit of the third embodiment is different from that of the first embodiment in its configuration, but is similar to that of the second embodiment.

The power recovery unit (3) thermally interacts with a second separate closed single loop (403). The second, separate, closed, single loop (403) contains a circulation pump to circulate a heat transfer fluid that is cooled by the LNG stream (400) via a heat exchanger (404) and heated by a diverted stream (35) from the output of the power island (330) via a vaporizer (320). The diverted stream (35) is cooled by the heat transfer fluid of the second separate closed single loop (403) and also by the cold thermal energy embedded in the refrigerant, to be subsequently compressed and reinjected by the power recovery compressor (34) into the power island (330), which may take any of the configurations shown in fig. 6A-6F, each of which is also an embodiment of the present invention.

The turboexpander of the power recovery unit may preferably show four expansion stages, as shown in fig. 6A, 6B, 6E and 6F.

The turboexpander of the power recovery unit may exhibit five expansion stages, as shown in fig. 6C and 6D.

For each of configurations 6A-6F, all embodiments of the invention, the diverted stream (35) from the output of the power island (330) is cooled via an evaporator (32), then recompressed by a power recovery compressor (34), and injected back into the power island (330) downstream of the penultimate expansion stage and upstream of the last power recovery heater and the last expansion stage. The work input to the compressor (34) is reduced by having its input cooled via the evaporator (32) by the heat transfer fluid of the second separate closed single loop (403) and the pressurized refrigerant, and the work output of the last expansion stage is increased by increasing the mass flow rate handled by the last expansion stage. The remainder of the output stream of the power island can be vented to the atmosphere or can be used to regenerate the adsorption vessel of the APU (13).

The power island may take any of the configurations described in fig. 6A-6F, each of which is also an embodiment of the present invention. One difference between fig. 5A and 6A, fig. 5B and 6B, fig. 5C and 6C, fig. 5D and 6D, fig. 5E and 6E, and fig. 5F and 6F is the presence of a diverted stream (35) from the output of the power island in fig. 6A-6F, which is then cooled via an evaporator (32) and recompressed by a compressor (34), and injected back into the power island (600) downstream of the penultimate expansion stage and upstream of the last power recovery heater (84, 850, 8400) and the last expansion stage (64, 650, 6400). Fig. 6B, 6D and 6F show additional power recovery heaters (80, 800, 8000). The additional power recovery heater (80, 800, 8000) may be placed upstream of the power recovery heater (81, 810, 8100) and upstream of the first expansion stage (61, 610, 6100), wherein the working fluid of the power recovery unit may be heated by the output of the last expansion stage (64, 650, 6400) before further heating by the power recovery heater (81, 810, 8100) placed upstream of the first expansion stage.

The additional power recovery heater (80, 800, 8000) may be placed downstream of the evaporator (32).

The following is common to the first, second and third embodiments of the invention described in fig. 4A-4C, and also common to the other embodiments of the invention described in fig. 5A-5F and 6A-6F.

The cold box (17) is an assembly of heat exchangers, pipes and pressure vessels, contained within a metal structure filled with a high-quality insulating material, such as perlite. The cold box may comprise at least one single multi-pass heat exchanger. The cold box shows a warm side (upper side) and a cold side (lower side).

The main air compressor (10) may have at least one compression stage, preferably two compression stages, more preferably four compression stages. Downstream of at least one compression stage of the main air compressor, preferably downstream of the last compression stage thereof, there may be a compression heat collection heat exchanger. The task of the compression heat collection heat exchanger is to collect at least a part of the compression heat generated by the compressor or a group of compression stages or a compression stage. Downstream of at least one compression stage there may be a cooler. Downstream of the at least one compression heat collection heat exchanger there may be a cooler. Typically, a cooler (i.e., a heat exchanger using air or water) is placed upstream of the compression stages of the compressor to pre-cool the gas stream (reduction in compression work) before it is compressed by them, or downstream of the output of the compressor to cool the gas stream and make it subsequently susceptible to liquefaction. Preferably, there may be no cooling/heating during compression and between the compression stages of the main air compressor, i.e. the main air compressor may be adiabatic.

The recycle air compressor (14) may preferably have one compression stage, or at least one compression stage, or more preferably four compression stages. Downstream of at least one compression stage of the recycle air compressor, preferably downstream of the last compression stage thereof, there may be a compression heat collection heat exchanger. Downstream of at least one compression stage there may be a cooler. Downstream of the at least one compression heat collection heat exchanger there may be a cooler. Preferably, there may be no cooling/heating during compression and between the compression stages of the recycle air compressor, i.e. the recycle air compressor may be adiabatic.

With respect to the main and recycle air compressors, the amount of the compression heat collection heat exchangers and coolers and their respective positions relative to the compression stages of the main and recycle air compressors depend on the output temperature targets of the main and recycle air compressors and the parasitic losses (e.g., pressure drop, etc.) they introduce, which can increase power consumption while affecting the level of compression heat generated by the main and recycle air compressors.

The power recovery unit of the CES system may comprise at least one, preferably one, turboexpander. Each turboexpander may in turn comprise at least one expansion stage, preferably four or five expansion stages. There may be an electric power recovery heater upstream of each expansion stage.

The compression heat recycling device may include a second split closed double loop (11, 12A) and a third split closed double loop (15, 16A). The advantage of having separate closed double loops (due to the occurrence of indirect heat exchange from the compressor to the TESD and from the TESD to the turboexpander) is the ease of replenishing the heat transfer fluid in the event of a leak, as well as controlling the pressure of the heat transfer fluid circulating through the separate closed double loops.

The second split closed dual loop may include a TESD (12) associated with the main air compressor. Each single loop of the second split closed double loop has a heat transfer fluid, a circulation pump, and a piping arrangement that passes a TESD associated with the main air compressor. A portion of their respective piping arrangements through the TESD associated with the main air compressor may be common, assuming the presence of a three-way valve and a single heat transfer fluid.

One single loop of the second divided closed double loop collects at least some of the heat of compression generated by the main air compressor (10) by using at least one compression heat collection heat exchanger (11) placed downstream of the main air compressor and stores it in a TESD (12) associated with the main air compressor. The other single loop (12A) of the second split closed double loop provides hot thermal energy to the working fluid of the power recovery unit via at least one power recovery heater (84, 840, 850, 8100) before it is expanded via at least one of the expansion stages (64, 640, 650, 6100) of the power recovery turboexpander, as shown with respect to fig. 5A-5F and 6A-6F, which are also embodiments of the present invention. The single loop may include at least one valve (e.g., a three-way valve).

The TESD (12) associated with the main air compressor is thermally coupled to the main air compressor (10) via a compression heat collection heat exchanger (11).

The TESD (12) associated with the main air compressor may be a packed bed TESD, a fixed liquid phase based TESD or a dual reservoir TESD or preferably a thermocline TESD.

If the TESD (12) associated with the main air compressor is a packed bed TESD, the packed bed matrix may include randomly stacked particles made of a sensible substance (e.g., pebbles) or a latent heat phase change substance or a combination thereof. If the TESD associated with the main air compressor is a packed bed TESD, the packed bed matrix may include non-randomly stacked particles made of a sensible material (e.g., metal oxide beads), or a latent heat phase change material, or a combination thereof. If the TESD associated with the main air compressor is a packed bed TESD, the packed bed matrix may include fused particles (e.g., ceramic).

The TESD associated with the main air compressor may store heat of compression at a temperature between 200 ℃ and 400 ℃. The heat transfer fluid circulating through the second divided closed double loop may be a gas or a liquid. The heat transfer fluid may comprise water or a mixture of water and glycol, or a diathermic oil, or a mixture of diathermic oils (synthetic, natural, mineral), or molten salts.

The third separate closed dual loop may include TESD (16) associated with the recycle air compressor. Each single loop of the third split closed double loop has a heat transfer fluid, a circulation pump, and a piping arrangement that passes through the TESD associated with the circulating air compressor. A portion of their respective piping arrangements through the TESD associated with the recycle air compressor may be common, assuming that there is a three-way valve and a single heat transfer fluid.

One single loop of the third split closed double loop captures at least some of the heat of compression generated by the recycle air compressor (14) by using at least one compression heat capture heat exchanger (15) placed downstream of the recycle air compressor and stores it in a TESD (16) associated with the recycle air compressor. The other single loop (16A) of the third split closed double loop provides thermal energy to the working fluid of the power recovery unit via at least one power recovery heater (81, 82, 83, 810, 820, 830, 8200, 8300, 8400) before the working fluid of the power recovery unit is expanded via at least one of the expansion stages (61, 62, 63, 610, 620, 630, 6200, 6300, 6400) of the power recovery turboexpander, as shown with respect to fig. 5A-5F and fig. 6A-6F, which are also embodiments of the present invention. The single loop may include at least one valve (e.g., a three-way valve).

The TESD (16) associated with the circulating air compressor is thermally coupled to the circulating air compressor (14) via a compression heat collection heat exchanger (15).

The TESD associated with the circulating air compressor may be a packed bed TESD, a TESD based on a fixed liquid phase or a dual reservoir TESD or preferably a thermocline TESD.

If the TESD (16) associated with the circulating air compressor is a packed bed TESD, the packed bed matrix may comprise randomly stacked particles made of a sensible substance (e.g. pebbles) or a latent heat phase change substance or a combination thereof. If the TESD associated with the circulating air compressor is a packed bed TESD, the packed bed matrix may include non-randomly stacked particles made of a sensible substance (e.g., metal oxide beads), or a latent heat phase change substance, or a combination thereof. If the TESD associated with the circulating air compressor is a packed bed TESD, the packed bed matrix may include fused particles (e.g., ceramic).

The TESD (16) associated with the circulating air compressor may store heat of compression at a temperature between 150 ℃ and 350 ℃. The heat transfer fluid circulating through the third separate closed double loop may be a gas or a liquid. The heat transfer fluid may comprise water or a mixture of water and glycol, or a diathermic oil, or a mixture of diathermic oils (synthetic, natural, mineral) or molten salts.

The gas to be liquefied by the liquefaction unit of the CES system may be ambient air, nitrogen or any air having an oxygen and nitrogen concentration different from the oxygen and nitrogen concentration in ambient air. The refrigerant produced by the liquefaction unit, which then fills the refrigerant tank and is processed by the power recovery unit may be liquid air, liquid nitrogen or any liquid air with a concentration of oxygen and nitrogen different from that of ambient air.

The thermal energy of the heat provided to the working fluid of the power recovery unit via the at least one power recovery heater may be derived from a compression heat recycling device of a closed double loop separated by a second (11, 12A) and a third (15, 16A).

Fig. 7A, 7B and 7C illustrate cryogenic energy storage systems similar to the systems illustrated in fig. 4A, 4B and 4C, respectively. The differences between the systems of fig. 7 and fig. 4 are as follows:

the first compression heat collection heat exchanger (11) shown in fig. 4A-4C is divided into a third compression heat collection heat exchanger (110) and a fourth compression heat collection heat exchanger (150).

-the third compression thermal collection heat exchanger (110) and the fourth compression thermal collection heat exchanger (150) are heat-coupled to the main air compressor (10). In other words, the third compression heat collection heat exchanger (110) and the fourth compression heat collection heat exchanger (150) each collect compression heat from the main air compressor (10).

-the third compression heat collection exchanger (110) is thermally coupled to the second thermal energy storage means (12);

-the fourth compression heat collection exchanger (150) is thermally coupled to the first thermal energy storage means (16);

the second (11, 12A) and third (15, 16A) separate closed double loops shown in fig. 4A, 4B and 4C are now replaced by the fourth (110, 12A) and fifth (500; 16, 16A) separate closed double loops shown in fig. 7A, 7B and 7C.

The fourth split closed double loop (110, 12A) has two single loops (110, 12) and (12A): a heat transfer fluid circulates through the single loop (110, 12) and a portion of the compression heat may be collected from the main air compressor (10) via a compression heat collection heat exchanger (110). The temperature of the heat of compression stored in the second thermal energy storage device (12) may be between 150 ℃ and 550 ℃. The heat of compression is transferred from the heat exchanger (110) by the heat transfer fluid and stored in the second thermal energy storage device (12). The additional heat transfer fluid circulating through the single loop (12A) transfers at least some of the stored compression heat to the power recovery heater (85000) to heat the working fluid of the power recovery unit (3), as shown in fig. 8A-8B and 9A-9B.

The fifth split closed double loop (500; 16, 16A) has two single loops (500) and (16A): a heat transfer fluid circulates through the single loop (500) and a portion of the compression heat may be collected from the main air compressor (10) via a compression heat collection heat exchanger (150) and from the recycle air compressor (14) via a second compression heat collection heat exchanger (15). The temperature of the compression heat stored in the first thermal energy storage means (16) may be between 150 ℃ and 350 ℃, the portion of the compression heat collected by the compression heat collection heat exchanger (150) from the main air compressor and the portion of the compression heat collected by the compression heat collection heat exchanger (15) from the recycle air compressor may be at the same temperature, and they are each stored in the first thermal energy storage means (16). The additional heat transfer fluid circulating through the single loop (16A) transfers at least some of the stored compression heat to the power recovery heater (81000; 82000; 83000; 84000) to heat the working fluid of the power recovery unit (3), as shown in FIGS. 8A-8B and 9A-9B. The power recovery heater (85000) is located downstream of the power recovery heater (84000) and upstream of a fourth expansion stage (64000).

The temperature of the heat of compression stored in the second thermal energy storage device (12) is higher than the temperature of the heat of compression stored in the first thermal energy storage device (16).

The turboexpander of the power recovery unit (3) may preferably show four expansion stages.

Fig. 8A and 8B illustrate two further alternative schemes for power islands (33) for standalone CES systems, such as that shown in fig. 7A, which are embodiments of the present invention.

Fig. 9A and 9B illustrate two additional alternative arrangements of power islands (330) for a thermally integrated CES system as shown in fig. 7B and 7C, which are embodiments of the present invention.

Fig. 10 depicts an alternative view of a CES system according to the present invention. Fig. 10 shows an arrangement of a first intermediate closed loop (501) and a second intermediate closed loop (502). Fig. 10 provides an alternative view of the embodiment of the invention as shown in fig. 7A-7C, 8A-8B, 9A-9B when introducing a first (501) and second (502) intermediate closed loop.

Fig. 7-10 illustrate a power recovery subsystem and a cryogenic energy storage system as embodiments of the claimed invention, and are also implemented by the numbered clauses of the present invention.

The first thermal energy storage device (16) may supply hot thermal energy to the working fluid of the power recovery unit via a power recovery heater (81000, 82000, 83000, 84000) before each of the four expansion stages (61000, 62000, 63000, 64000), while the second thermal energy storage device (12) may supply hot thermal energy to the working fluid of the power recovery unit via a power recovery heater (85000) placed downstream of the power recovery heater (84000) and upstream of the last expansion stage (64000) before the last fourth expansion stage (64000) (see fig. 8A). An additional power recovery heater (80000) may be placed upstream of the power recovery heater (81000) upstream of the first expansion stage (61000), wherein the working fluid of the power recovery unit may be heated by the output of the fourth expansion stage (64000) before being further heated by the power recovery heater (81000) disposed upstream of the first expansion stage (see fig. 8B). The output of the fourth expansion stage can be vented to the atmosphere, or used to regenerate the adsorption vessel of the APU, after its hot thermal energy has been transferred to the working fluid of the power recovery unit by an additional power recovery heater (80000).

For each of configurations 9A-9B, which are embodiments of the present invention, the diverted stream (35) from the output of the power island (330) is cooled via an evaporator (32), then recompressed by a power recovery compressor (34), and injected back into the power island (330) downstream of the penultimate expansion stage and upstream of the power recovery heaters (84000, 85000) and the last expansion stage (64000). The work input to the compressor (34) is reduced by having its input cooled by the heat transfer fluid of the second separate closed single loop (403) via the evaporator (32), and the work output of the final expansion stage is increased by increasing the mass flow rate processed by the final expansion stage. The remainder of the output flow of the power island can be vented to the atmosphere or used to regenerate the adsorption vessel of the APU (13).

One difference between fig. 8A and 9A and between fig. 8B and 9B is that the flow (35) is present. In fig. 9A and 9B, at least a portion of the output from the power island (330) downstream of the last expansion stage (64000) is diverted, cooled via an evaporator (32) and recompressed by a compressor (34) before being injected back into the power island (330) downstream of the penultimate expansion stage (63000) and upstream of the power recovery heaters (84000, 85000) and the last expansion stage (64000). Fig. 9B shows an additional power recovery heater (80000). The additional power recovery heater (80000) may be placed upstream of the power recovery heater (81000) and upstream of the first expansion stage (61000), wherein the working fluid of the power recovery unit may be heated by the output of the last expansion stage (64000) before the power recovery heater (81000) placed upstream of the first expansion stage (61000) is further heated.

In fig. 7A-7C, 8A-8B, 9A-9B and 10, the first thermal energy storage device (16) is thermally coupled to the recycle air compressor (14) via a compression heat collection heat exchanger (15) and to the main air compressor (10) via a compression heat collection heat exchanger (150). The heat transfer fluid circulating through the two single loops of the fifth separate closed double loop (500; 16, 16A) may comprise water alone or may comprise a mixture of water and ethylene glycol. The first thermal energy storage device (16) may store heat of compression at a temperature between 150 ℃ and 350 ℃.

In fig. 7A-7C, 8A-8B, 9A-9B and 10, the second thermal energy storage device (12) is thermally coupled to the main air compressor (10) via a compression heat collection heat exchanger (110). The heat transfer fluid circulating through the two single loops of the fourth split closed double loop (110, 12A) may comprise molten salt. The second thermal energy storage means (12) may store compression heat at a temperature between 150 ℃ and 550 ℃, preferably between 200 ℃ and 400 ℃.

As shown in fig. 7A-7C and 10, an advantage of providing third (110) and fourth (150) compression heat collection exchangers is to ensure that the process stream remains hot enough while passing through the third (110) compression heat collection exchanger to avoid solidification of molten salt circulating in the single loop (110, 12).

An advantage of providing two power recovery heaters (84000; 85000) in fig. 8A-8B and 9A-9B is that the working fluid is heated sufficiently when passing through the power recovery heater (84000) to avoid solidification of molten salt circulating through the single loop 12A of the fourth split closed double loop (110, 12A) when passing through the power recovery heater (85000).

Molten salt may advantageously be used as the heat transfer fluid in the fourth separate closed double loop. The use of molten salts as heat transfer fluids may provide the following advantages:

they have an ultra-low vapour pressure (about 0kPa), i.e. they can be kept in liquid state by moderately pressurizing them, so that only low pressure vessels (e.g. pressurized to e.g. several hundred mbar, which is inexpensive) need to be used to store them;

they require less energy to pressurize via the pump than the gaseous heat transfer fluid via the compressor;

they have a high density, typically for example in the range 1600 and 2500kg/m³To (c) to (d);

they are stable at high temperatures;

they are non-flammable;

they have a low viscosity at high temperatures;

they have a high heat capacity per unit volume;

they are used in a wide range of applications, from energy storage to nuclear reactors and Concentrated Solar Power (CSP) plants.

However, the transportation of molten salts through piping requires the use of a custom made and expensive type of piping system which is capable of maintaining the temperature of the molten salts above the temperature at which they solidify or "freeze" through the use of heat tracing. Without this type of piping, molten salts in the piping between the main air compressor (10) and the power recovery heater (85000) can freeze, causing operational and maintenance problems for the entire system. Furthermore, molten salts are corrosive and may damage expensive mechanical equipment within the piping and CES systems.

An example of the type of piping required to transport molten salts is described in US8,895,901B2 to BASF (BASF). The molten salt conduit system differs from conventional conduit systems such that conventional conduit systems may not be suitable for transporting molten salt. For example, a molten salt piping system may maintain the salt above the freezing point to avoid a remelting process. In another example, the molten salt conduit system may comprise a circulation pump specifically designed for pumping molten salt.

The second thermal energy storage device may in particular be configured to store thermal energy or heat at a higher level than the thermal energy stored by the first thermal energy storage device. This may include custom piping systems required to be constructed to contain molten salts as described in detail above.

A first intermediate closed loop (501) and a second intermediate closed loop (502) may be incorporated in the present invention as shown in figure 10 to solve the above problem of molten salts. In other words, the first and second intermediate closed loops reduce the number of piping required to provide heat tracing, thereby reducing capital expenditure, and keeping separate the piping carrying molten salt from the piping carrying the process stream of the liquefaction unit and the working fluid of the power recovery unit.

A first intermediate closed loop (501) may be introduced between the main air compressor (10) and a single loop (110, 12) of the fourth separate closed double loop (110, 12A). In this case, the fourth split closed-double loop (110, 12A) becomes a sixth split closed-double loop (503, 12, 504). The first intermediate closed loop (501) passes through the compression heat collection heat exchanger (110) and an additional heat exchanger (110A), the additional heat exchanger (110A) allowing heat transfer between the compression heat collection heat exchanger (110) and the single loop (503) of the sixth separate closed double loop (503, 12, 504).

A second intermediate closed loop (502) may be introduced between the single loop (504) of the fourth split closed double loop (110, 12A) and the power recovery heater (85000). In this case, the fourth split closed-double loop (110, 12A) becomes a sixth split closed-double loop (503, 12, 504). A second intermediate closed loop (502) passes through the heat exchanger (110B) and a power recovery heater (85000). The additional heat exchanger (110B) allows heat transfer between the single loop (504) of the sixth split closed double loop (503, 12, 504) and the power recovery heater (85000).

Each of the first intermediate closed loop (501) and the second intermediate closed loop (502) may include:

-a heat transfer fluid;

-a pump (if the heat transfer fluid is a liquid) or a mechanical blower (if the heat transfer fluid is a gas) to circulate the heat transfer fluid through the intermediate closed loop;

-a pressurizing unit that accommodates variations in the volume occupied by the heat transfer fluid in the intermediate closed loop caused by thermal variations applied to the heat transfer fluid.

The heat transfer fluid in the intermediate closed loop may be a single type of thermal oil or a mixture of thermal oils. An example of a heat transfer oil that may be used is from Dow Therm^TMRange of heat transfer fluids and SylTherm^TMA range of fluids of silicone fluids, both manufactured by Dow Chemical Company (Dow Chemical Company). Other suitable fluids may also be used.

A mechanical blower or pump is used to counteract the pressure drop affecting the heat transfer fluid as it circulates through the first (501) and second (502) intermediate closed loops.

The first (501) and second (502) intermediate closed loops thus keep the molten salts above their "freezing" temperature to avoid their solidification which would otherwise lead to operational and maintenance problems in the piping system between the main air compressor (10) and the power recovery heater (85000) and in the entire system. Furthermore, the first intermediate closed loop (501) and the second intermediate closed loop (502) keep the molten salt away from the piping system transporting the process stream of the liquefaction unit and the working fluid of the power recovery unit.

The numbered clauses of the present invention:

1. a power recovery subsystem for a cryogenic energy storage system, the power recovery subsystem comprising:

a first heat source;

a first heat exchanger;

a second heat exchanger;

a first expansion stage;

a second expansion stage;

a first conduit arrangement having an upstream end and a downstream end and configured to convey a working fluid through the first heat exchanger, the first expansion stage, the second heat exchanger, and the second expansion stage; and

a second piping arrangement configured to convey a first heat transfer fluid from the first heat source through the first heat exchanger and the second heat exchanger,

wherein the second piping arrangement is further configured to convey a first portion of the first heat transfer fluid through the first heat exchanger and a second portion of the first heat transfer fluid through the second heat exchanger.

2. The subsystem of clause 1, further comprising:

a third heat exchanger; and

a third expansion stage;

wherein the first piping arrangement is further configured to route the working fluid through the third heat exchanger and the third expansion stage; and is

Wherein the second piping arrangement is further configured to convey a third portion of the first heat transfer fluid through the third heat exchanger.

3. The subsystem according to clause 1 or 2, further comprising;

a second heat source;

a fourth heat exchanger;

a fourth expansion stage; and

a third conduit arrangement configured to convey a second heat transfer fluid from a second heat source through a fourth heat exchanger,

wherein the first piping arrangement is further configured to route the working fluid through a fourth heat exchanger and a fourth expansion stage.

4. The subsystem of clause 3, further comprising:

a fifth heat exchanger; and

a fifth expansion stage;

wherein the first piping arrangement is further configured to route the working fluid through the fifth heat exchanger and the fifth expansion stage; and is

Wherein the third tubing arrangement is further configured to pass a first portion of the second heat transfer fluid through the fourth heat exchanger and a second portion of the second heat transfer fluid through the fifth heat exchanger.

5. The subsystem according to clause 3 or clause 4, wherein the or each heat exchanger through which the third conduit arrangement passes is positioned along the first conduit arrangement upstream of the heat exchanger through which the second conduit arrangement passes.

6. The subsystem according to clause 3 or clause 4, wherein the or each heat exchanger through which the third conduit arrangement passes is positioned along the first conduit arrangement downstream of the heat exchanger through which the second conduit arrangement passes.

7. The subsystem of any preceding clause, further comprising:

a sixth heat exchanger for the heat-exchange of the air-conditioning system,

wherein the first conduit arrangement is further configured to pass the working fluid through the sixth heat exchanger upstream of both (i) the most upstream heat exchanger through which the second conduit arrangement passes and (ii) the most upstream heat exchanger through which the third conduit arrangement passes, and

wherein the first piping arrangement is further configured to convey the working fluid output from the most downstream expansion stage through the sixth heat exchanger to an exhaust.

8. The subsystem of any preceding clause, further comprising:

a fourth piping arrangement configured to divert a portion of the working fluid from a downstream location in the first piping arrangement, through an evaporator and a first compressor, and back to an upstream location in the first piping arrangement.

9. The subsystem of clause 8, wherein the evaporator is positioned along a first conduit arrangement upstream of an upstream-most heat exchanger, wherein the downstream location is downstream of a downstream-most expansion stage; and wherein the upstream location is immediately upstream of the most downstream expansion stage.

10. The subsystem according to clauses 3 to 9, configured such that the second tubing arrangement passes through the first, second and third heat exchangers, and preferably does not pass through the other heat exchangers, and the third tubing arrangement passes through the fourth heat exchanger, and preferably does not pass through the other heat exchangers, and wherein the heat exchanger through which the third tubing arrangement passes is upstream of the heat exchanger through which the second tubing arrangement passes.

11. The subsystem according to clauses 4 to 9, configured such that the second pipe arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchanger, and the third pipe arrangement passes through the fourth and fifth heat exchangers, and preferably no other heat exchanger, wherein the heat exchanger through which the second pipe arrangement passes is upstream of the heat exchanger through which the third pipe arrangement passes.

12. The subsystem according to clauses 3 to 9, configured such that the second pipe arrangement passes through the first, second and third heat exchangers, and preferably no other heat exchanger, and the third pipe arrangement passes through the fourth heat exchanger, and preferably no other heat exchanger, wherein the heat exchanger through which the second pipe arrangement passes is upstream of the heat exchanger through which the third pipe arrangement passes.

13. The subsystem according to any preceding clause, wherein the first heat source is a first thermal energy storage device, and the second piping arrangement is further configured to return the first heat transfer fluid to the first thermal energy storage device after passing the first heat transfer fluid through each heat exchanger through which the second piping arrangement is configured to pass, such that the second piping arrangement forms a first closed loop.

14. The subsystem according to any one of clauses 3 to 13, wherein the second heat source is a second thermal energy storage device, and the third pipe arrangement is further configured to return the second heat transfer fluid to the second thermal energy storage device after passing the second heat transfer fluid through each heat exchanger through which the third pipe arrangement is configured to pass, such that the third pipe arrangement forms a second closed loop.

15. The subsystem according to clause 14, wherein the first thermal energy storage device is configured to store at least a portion of the heat of compression generated by the recycle air compressor and the second thermal energy storage device is configured to store at least a portion of the heat of compression generated by the main air compressor, optionally wherein the second thermal energy storage device may comprise a piping system suitable for transporting molten salt.

16. The subsystem according to any of clauses 3 to 13, further comprising:

a tenth heat exchanger; and

an eleventh heat exchanger, wherein:

the second heat source is a second thermal energy storage device,

the first conduit arrangement is further configured to convey the working fluid through the tenth heat exchanger immediately upstream of the fourth heat exchanger, and wherein;

the third conduit arrangement being configured to form two closed loops, a first closed loop passing through the second thermal energy storage device and the eleventh heat exchanger, and a second closed loop passing through the eleventh heat exchanger and the fourth heat exchanger,

optionally wherein the heat transfer fluid in the first closed loop comprises molten salt, further optionally wherein the heat transfer fluid in the second closed loop comprises a diathermic oil or a mixture of diathermic oils.

17. The subsystem according to clause 16, wherein the first thermal energy storage device is configured to store at least a portion of the heat of compression generated by the main air compressor and at least a portion of the heat of compression generated by the recycle air compressor, and the second thermal energy storage device is configured to store at least a portion of the heat of compression generated by the main air compressor, optionally wherein the second thermal energy storage device may comprise a piping system suitable for transporting molten salt.

18. The subsystem according to any one of clauses 14 to 17, wherein the second thermal energy storage device is configured to store thermal energy at a temperature higher than the temperature of the thermal energy stored in the first thermal energy storage device, optionally wherein the second thermal energy storage device is configured to store thermal energy between 150 ℃ and 550 ℃, preferably between 200 ℃ and 400 ℃, and the first thermal energy storage device is configured to store thermal energy between 150 ℃ and 350 ℃.

19. A cryogenic energy storage system comprising:

an electricity recovery subsystem comprising a plurality of expansion stages configured to receive hot thermal energy from first and second thermal energy storage devices via a corresponding plurality of heat exchangers and to transfer the hot thermal energy to a working fluid passing through the plurality of expansion stages and the plurality of heat exchangers, preferably wherein the electricity recovery subsystem is a subsystem according to any of clauses 3 to 18; and

a liquefaction subsystem configured to supply thermal energy to the first thermal energy storage device and the second thermal energy storage device, and further comprising;

a main air compressor;

a circulating air compressor;

an eighth heat exchanger;

a ninth heat exchanger;

a fifth piping arrangement configured to pass a process stream through the main air compressor, eighth heat exchanger, recycle air compressor, and ninth heat exchanger;

a sixth piping arrangement forming a third closed loop and configured to pass a third heat transfer fluid between the second thermal energy storage device and the eighth heat exchanger; and

a seventh piping arrangement forming a fourth closed loop and configured to pass a fourth heat transfer fluid between the first thermal energy storage device and the ninth heat exchanger,

wherein the eighth heat exchanger is positioned immediately downstream of the primary air compressor along the fifth piping arrangement and is configured to transfer at least a portion of the heat of compression of the process stream from the primary air compressor to the second thermal energy storage device via the third heat transfer fluid, and

wherein the ninth heat exchanger is positioned immediately downstream of the recycle air compressor along the fifth piping arrangement and is configured to transfer at least a portion of the heat of compression of the process stream from the recycle air compressor to the first thermal energy storage device via the fourth heat transfer fluid.

20. The system of clause 19, further comprising:

a cold box;

a liquefaction turboexpander;

an eighth piping arrangement configured to pass at least a portion of the process stream through the liquefaction turbo expander and a portion of the cold box before passing through the cold box and merging with the fifth piping arrangement upstream of the recycle air compressor such that a mass flow rate of fluid through the main air compressor is less than a mass flow rate of fluid through the recycle air compressor;

a ninth pipe arrangement configured to pass at least a portion of the process stream through the cold box, an expansion device, preferably a joule-thomson valve or a wet turbo expander, to a phase separator such that the portion of the process stream in the eighth pipe arrangement transfers cold thermal energy to the portion of the process stream in the ninth pipe arrangement via the cold box; and

a first cold circulation loop, wherein the first cold circulation loop passes through the cold box and is configured to transfer cold waste heat energy from a system external to but thermally integrated with the cryogenic energy storage system to at least the portion of the process stream in the ninth piping arrangement.

21. The system of clause 19 or 20, wherein the power recovery subsystem further comprises an evaporator; the system further comprises:

a second cold cycle loop passing through the evaporator and configured to transfer cold waste heat energy from a system external to but thermally integrated with the cryogenic energy storage system to at least a portion of the working fluid, preferably to a portion of the working fluid downstream of the plurality of expansion stages and the plurality of heat exchangers of the power recovery subsystem.

22. The cryogenic energy storage system of any of clauses 19 to 21 wherein the main air compressor has a different input and output pressure than the recycle air compressor and the main air compressor and/or recycle air compressor is adiabatic.

23. The cryogenic energy storage system of any of clauses 19 to 22 further comprising a twelfth heat exchanger, wherein:

the fifth piping arrangement is further configured to route the process stream through a twelfth heat exchanger downstream of the eighth heat exchanger and upstream of the recycle air compressor,

the seventh tubing arrangement is further configured to convey a fourth heat transfer fluid through a twelfth heat exchanger, and wherein

The twelfth heat exchanger is configured to transfer at least a portion of the heat of compression of the process stream from the main air compressor to the first thermal energy storage device via the fourth heat transfer fluid.

24. The cryogenic energy storage system of any of clauses 19 to 23 wherein the temperature of the thermal energy received from the second thermal energy storage device is greater than the temperature of the thermal energy received from the first thermal energy storage device, optionally wherein the second thermal energy storage device is configured to store thermal energy between 150 ℃ and 550 ℃, preferably between 200 ℃ and 400 ℃, and the first thermal energy storage device is configured to store thermal energy between 150 ℃ and 350 ℃.

25. The cryogenic energy storage system of any of clauses 19 to 24 further comprising a thirteenth heat exchanger, and wherein:

wherein the sixth piping arrangement is configured to form two closed acquisition loops, a first closed acquisition loop passing through the eighth heat exchanger and the thirteenth heat exchanger, and a second closed acquisition loop passing through the thirteenth heat exchanger and the second thermal energy storage device,

optionally wherein the heat transfer fluid in the second closed acquisition loop may comprise molten salt, further optionally wherein the heat transfer fluid in the first closed acquisition loop may comprise a diathermic oil or a mixture of diathermic oils

26. A thermal energy cycle system comprising:

a main air compressor;

a circulating air compressor;

a second thermal energy storage device;

a first thermal energy storage device;

a working fluid; and

a plurality of expansion stages comprising a first subset and a second subset;

wherein the system is configured to collect and store in the second thermal energy storage device at least a portion of the compression heat generated by the main air compressor during a liquefaction phase, and to apply the compression heat stored in the second thermal energy storage device to the working fluid upstream of each of the first subset of expansion stages during an electricity recovery phase, and

wherein the system is further configured to collect and store in the first thermal energy storage device at least a portion of the compression heat generated by the recycle air compressor during a liquefaction phase, and to apply the compression heat stored in the first thermal energy storage device to the working fluid upstream of each of the second subset of expansion stages during an electricity recovery phase.

27. A method for recycling thermal energy in a cryogenic energy storage system, comprising:

providing a liquefaction subsystem, the liquefaction subsystem comprising:

a main air compressor;

a circulating air compressor;

a second thermal energy storage device; and

a first thermal energy storage device;

providing a power recovery subsystem, the power recovery subsystem comprising:

a working fluid; and

a plurality of expansion stages comprising first and second subsets;

collecting at least a portion of the heat of compression from the main air compressor and storing it in the second thermal energy storage device;

collecting at least a portion of the heat of compression from the recycle air compressor and storing it in the first thermal energy storage device;

applying the heat of compression stored in the second thermal energy storage device to the working fluid upstream of each of the expansion stages of the first subset; and

applying the heat of compression stored in the first thermal energy storage device to the working fluid upstream of each of the expansion stages of the second subset.

28. The system of clause 26 or the method of clause 27, further comprising:

a cold box;

a first cold circulation loop configured to pass through the cold box and transfer cold waste heat energy from a system external to but thermally integrated with the low temperature energy storage system to a portion of a process stream passing through the cold box, an expansion device, preferably a Joule-Thomson valve or a wet turbo-expander, to a phase separator.

29. The system of clause 26 or 28, or the method of clause 27 or 28, further comprising:

the second cold circulation circuit is provided with a cold circulation loop,

and wherein the power recovery subsystem further comprises:

an evaporator; and

a compressor;

wherein the second cold circulation loop is configured to pass through the evaporator and transfer cold waste heat energy from a system external to but thermally integrated with the cryogenic energy storage system to a portion of the working fluid that passes from the output of the power recovery unit through the evaporator and the compressor and re-enters the power recovery unit.

30. The system of clause 26, 28 or 29, or the method of clauses 27 to 29, wherein the mass flow rate of the fluid through the primary air compressor is less than the mass flow rate of the fluid through the recycle air compressor.

31. The system of clauses 26, 28, 29, or 30, or the method of clauses 27-30, wherein the main air compressor has a different input and output pressure than the recycle air compressor, and the main air compressor and/or the recycle air compressor are adiabatic.

32. The system of clause 26, 28, 29, 30, or 31, or the method of clause 27-31, wherein the external system is a liquefied natural gas regasification terminal.

33. The system of clauses 26, 28, 29, 30, 31 or 32, or the method of clauses 27 to 32, wherein the second thermal energy storage device is configured to collect, store and apply the compression heat at a temperature different from, preferably higher than, the temperature of the compression heat collected, stored and applied by the first thermal energy storage device, optionally wherein the second thermal energy storage device is configured to store thermal energy between 150 ℃ and 550 ℃, preferably between 200 ℃ and 400 ℃, and the first thermal energy storage device is configured to store thermal energy between 150 ℃ and 350 ℃.

34. The system of clauses 26, 28-33, wherein the system is further configured to collect and store at least a portion of the compression heat generated by the main air compressor during the liquefaction stage and store it in the first thermal energy storage device.

35. The system of clause 34, wherein the system is configured to apply the heat of compression stored in the first thermal energy storage device to the working fluid via the heat transfer fluid during the electricity recovery phase.

36. The system of clause 34 or 35, wherein the system is further configured to collect and store at least a portion of the heat of compression from the main air compressor in the first thermal energy storage device via the heat transfer fluid during the liquefaction phase, and to collect and store at least a portion of the heat of compression from the cycle air compressor in the first thermal energy storage device.

37. The system of any of clauses 26, 28-36, wherein the system further comprises:

a first pair of conduit loops configured to thermally interact with each other via a first intermediate heat exchanger; and

a second pair of piping loops configured to thermally interact with each other via a second intermediate heat exchanger, wherein the system is configured to collect and store the at least a portion of the compression heat from the main air compressor in the second thermal energy storage device via the first pair of piping loops, and wherein the system is configured to apply the compression heat stored in the second thermal energy storage device to the working fluid via the second pair of piping loops.

38. The system of clause 37, wherein the first pair of conduit loops comprises a first conduit loop and a second conduit loop, and wherein the first pair of conduit loops is configured to transfer at least a portion of the heat of compression from the main air compressor to the first intermediate heat exchanger via the first conduit loop and from the first intermediate heat exchanger to the second thermal energy storage device via the second conduit loop, optionally wherein the heat transfer fluid in the second conduit loop may comprise molten salt.

39. The system of clause 37 or 38, wherein the second pair of conduit loops comprises a third conduit loop and a fourth conduit loop, and wherein the second pair of conduit loops is configured to transfer at least a portion of the heat of compression stored in the second thermal energy storage device to the second intermediate heat exchanger via the third conduit loop and from the second intermediate heat exchanger to the working fluid via the fourth conduit loop, optionally wherein the heat transfer fluid in the third conduit loop may comprise molten salt.

40. The method of any of clauses 27 to 33, further comprising capturing at least a portion of the heat of compression from the main air compressor and storing it in the first thermal energy storage device.

41. The method of clause 37, wherein the heat of compression stored in the first thermal energy storage device is transferred via a heat transfer fluid during the application of the heat of compression to the working fluid.

42. The method of clauses 37 or 38, wherein the heat of compression is transferred via a heat transfer fluid during the period when at least a portion of the heat of compression is collected from the main air compressor and stored in the first thermal energy storage device and during the period when at least a portion of the heat of compression is collected from the recycle air compressor and stored in the first thermal energy storage device.

43. The method of any of clauses 27 to 33 or 40, wherein capturing at least a portion of the compression heat from the main air compressor and storing it in the second thermal energy storage device comprises:

transferring at least a portion of the heat of compression from the main air compressor to a first intermediate heat exchanger via a first conduit loop and from the first intermediate heat exchanger to the second thermal energy storage device via a second conduit loop, optionally wherein the heat transfer fluid in the second conduit loop may comprise molten salts.

44. The method of any of clauses 27 to 33 or 40 or 43, wherein applying the heat of compression stored in the second thermal energy storage device to the working fluid comprises:

transferring at least a portion of the heat of compression stored in the second thermal energy storage device to a second intermediate heat exchanger via a third conduit loop and from the second intermediate heat exchanger to the working fluid via a fourth conduit loop, optionally wherein the heat transfer fluid in the third conduit loop may comprise molten salts.