Liquid medium-pressure air energy storage system based on LNG cold energy utilization

Abstract

The application relates to the technical field of energy storage, and provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, wherein a liquid air storage tank is used for storing medium-pressure liquid air; an LNG cold storage system is connected with a heat exchange port of a cold box, and is used for cooling high-pressure air through the cold box into liquid air in an energy storage stage; the LNG cold storage system is also used for warming high-pressure liquid air through the cold box to normal temperature in an energy releasing stage, so that part of cold storage medium in the LNG cold storage system absorbs liquid air cold and is stored; the LNG cold storage system is also used for gasifying and superheating LNG through an LNG gasifier and a natural gas superheater every 24 hours, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs LNG cold and is stored into a cold storage medium cold fluid storage tank. The application can fully recover medium and high-grade cold energy of LNG, the capacity of the system is larger, the structure is simple, and the complexity can be reduced under the conditions of supplying the same LNG cold and realizing the same efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a liquid medium-pressure air energy storage system based on LNG cold energy utilization. BACKGROUND

[0002] The LNG cold energy utilization mode mainly includes air separation, cold storage, dry ice production, low-temperature crushing, etc. Due to the limitation of downstream user demand, the above-mentioned cold energy utilization industry is difficult to realize large-scale production. Although the cold energy power generation technology is not limited by the production scale, the recovery rate of LNG cold energy is low, and sea water needs to be used as a heat source to heat the intermediate medium for power generation in the recovery process, which causes certain "cold pollution" to the environment. In addition, the cold energy power generation technology needs relatively stable LNG supply, which is difficult to achieve.

[0003] As a new type of large-scale long-time energy storage technology, liquid air energy storage has the characteristics of not being limited by geographical factors and a wide working temperature range, which enables it to be coupled with LNG cold energy utilization. LNG cold energy can provide a large amount of cold energy required for the air liquefaction process, thereby increasing the air liquefaction rate. At the same time, it can be used to reduce the compressor inlet temperature and reduce the compressor power consumption. The liquid air energy storage system realized has a high system efficiency, which is conducive to the large-scale promotion of liquid air energy storage technology.

[0004] Therefore, in order to realize the high system efficiency of the liquid air energy storage system, the LNG cold energy is usually used to cool the compressor inlet to reduce the compression power consumption. In this process, the heat generated by the original system compressed air is lost. In the energy release stage, sea water or the possible medium and low grade heat source near the station is used to heat the air, which still causes the "cold pollution" problem to the environment. In addition, the above-mentioned scheme requires the inlet temperature of each stage of compressor to be extremely low, and it is difficult to remove water and carbon from the air before the first stage of compressor. At this time, if the supply amount of LNG cold energy in the compression process of the energy storage system is reduced, the efficiency of the energy storage system will be significantly reduced.

[0005] In order to further increase the liquid air production rate, in the related technology, LNG cold energy is often supplemented in the cold box part of the liquid air energy storage system. However, due to the difference in working temperature range between the cold energy storage medium on the LNG cold energy side and the cold energy storage medium on the cold box side of the liquid air energy storage system, lower temperature cold energy is required in the air liquefaction process. The introduction of LNG cold energy does not significantly improve the liquid air production rate. In addition, due to the difference in temperature range, multiple storage tanks need to be arranged for cold storage, which increases the system complexity and affects the economic performance of the energy storage system, which is not conducive to the promotion of the liquid air energy storage technology coupled with LNG cold energy utilization. Therefore, the present application provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization. SUMMARY

[0006] The application provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, which can solve the technical defects in the prior art, can fully recover LNG medium and high grade cold energy, has a larger capacity under the condition of supplying the same LNG cold energy and realizing the same efficiency, has a simple system structure, can reduce the complexity, and can avoid "cold pollution".

[0007] The application provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, which comprises an air compression system, an expansion power generation system, a liquid air storage tank, a cold box and an LNG cold storage system.

[0008] The liquid air storage tank is used for storing medium-pressure liquid air.

[0009] The air compression system is connected with the high-pressure air inlet of the cold box, the medium-pressure liquid air outlet of the cold box is connected with the inlet of the liquid air storage tank, the outlet of the liquid air storage tank is connected with the high-pressure liquid air inlet of the cold box, and the expansion power generation system is connected with the normal-temperature air outlet of the cold box.

[0010] The LNG cold storage system is connected with the heat exchange port of the cold box, and is further connected with an LNG gasifier and a natural gas superheater in sequence; the LNG cold storage system is used for cooling high-pressure air passing through the cold box into liquid air in an energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and is stored into a cold storage medium heat fluid storage tank; the LNG cold storage system is also used for heating high-pressure liquid air passing through the cold box to normal temperature by using the heat absorbed in the energy storage stage in an energy release stage, so that part of the cold storage medium in the LNG cold storage system absorbs liquid air cold energy and is stored into a cold storage medium cold fluid storage tank; meanwhile, the LNG cold storage system is also used for gasifying and superheating LNG passing through the LNG gasifier and the natural gas superheater every day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs LNG cold energy and is stored into the cold storage medium cold fluid storage tank.

[0011] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization, the first-stage heat exchanger and the second-stage heat exchanger are arranged in the cold box in sequence.

[0012] The LNG cold storage system is provided with a first-stage cold storage medium loop corresponding to the first-stage heat exchanger, and the natural gas superheater is arranged in the first-stage cold storage medium loop, and the outlet of the natural gas superheater is connected to a pipe network.

[0013] The LNG cold storage system is provided with a secondary cold storage medium circuit corresponding to the second stage heat exchanger. The LNG vaporizer is located in the secondary cold storage medium circuit. The inlet of the LNG vaporizer is connected to the LNG storage tank, and the outlet of the LNG vaporizer is connected to the inlet of the natural gas superheater.

[0014] The temperature of the liquid air cooled by the cold box is the same as or similar to the temperature of the cold fluid in the secondary cold storage medium circuit.

[0015] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the primary cold storage medium circuit consists of a primary cold storage medium hot fluid storage tank, a primary cold storage medium hot fluid pump, a primary cold storage medium cold fluid pump, and a primary cold storage medium cold fluid storage tank connected end to end in sequence; a first-stage heat exchanger is disposed between the primary cold storage medium cold fluid pump and the primary cold storage medium hot fluid storage tank, and the heat exchange outlet of the first-stage heat exchanger is connected to one inlet of the primary cold storage medium cold fluid storage tank; a natural gas superheater is disposed between the primary cold storage medium hot fluid pump and the primary cold storage medium cold fluid storage tank, and the heat exchange outlet of the natural gas superheater is connected to the other inlet of the primary cold storage medium cold fluid storage tank;

[0016] The secondary cold storage medium circuit consists of a secondary cold storage medium hot fluid storage tank, a secondary cold storage medium hot fluid pump, a secondary cold storage medium cold fluid pump, and a secondary cold storage medium cold fluid storage tank connected sequentially end to end; the second-stage heat exchanger is located between the secondary cold storage medium cold fluid pump and the secondary cold storage medium hot fluid storage tank, and the heat exchange outlet of the second-stage heat exchanger is connected to one inlet of the secondary cold storage medium cold fluid storage tank; the LNG vaporizer is located between the secondary cold storage medium hot fluid pump and the secondary cold storage medium cold fluid storage tank, and the heat exchange outlet of the LNG vaporizer is connected to the other inlet of the secondary cold storage medium cold fluid storage tank.

[0017] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the reflux outlet of the gas-liquid separator in the cold box is connected to the medium-pressure reflux gas inlet of the heat exchanger in the cold box, and the medium-pressure reflux gas outlet of the heat exchanger in the cold box is connected to the inlet of the booster unit in the air compression system or the inlet of the reflux gas compressor in the cold box.

[0018] The pressure of the medium-pressure reflux gas flowing back from the heat exchanger in the cold box is the same as or similar to the pressure of the gas to be mixed at the inlet of the booster unit.

[0019] The LNG cold energy utilization based liquid medium pressure air energy storage system is characterized in that the air compression system is connected with the high pressure air inlet of the heat exchanger in the cold box, the backflow outlet of the gas-liquid separator is connected with the medium pressure backflow gas inlet of the heat exchanger in the cold box, and the medium pressure backflow gas outlet of the heat exchanger in the cold box is connected with the air inlet of the heat exchanger in the cold box through the backflow gas compression system.

[0020] The LNG cold energy utilization based liquid medium pressure air energy storage system is characterized in that the backflow gas compression system comprises a plurality of backflow gas compressors and a backflow gas supercooling device arranged between two adjacent backflow gas compressors.

[0021] The medium pressure backflow gas outlet of the second heat exchanger in the cold box is connected with the inlet of the first backflow gas compressor, the outlet of the last backflow gas compressor is connected with the air inlet of the first heat exchanger in the cold box, and the gas pressure of the outlet of the last backflow gas compressor is the same as or close to the air pressure at the outlet end of the booster set.

[0022] The LNG cold energy utilization based liquid medium pressure air energy storage system is characterized in that at least one of a heat exchanger and a Rankine cycle system is arranged in the cold box, the heat exchanger is connected with the LNG cold storage system and exchanges heat with the LNG cold storage system, and the heat source of the Rankine cycle system is the heat generated by the air compression system.

[0023] The LNG cold energy utilization based liquid medium pressure air energy storage system is characterized in that the Rankine cycle system comprises a first Rankine cycle subsystem, a second Rankine cycle subsystem and a third Rankine cycle subsystem, each Rankine cycle subsystem comprises, in sequence and in a first-to-last connection mode, a Rankine cycle condenser, a Rankine cycle working medium pump, a Rankine cycle turbine and a Rankine cycle evaporator.

[0024] The Rankine cycle condenser is used for warming the high pressure liquid air passing through the cold box to normal temperature in the energy releasing stage, and the heat source of the Rankine cycle evaporator is the heat generated by the air compression system.

[0025] The LNG cold energy utilization based liquid medium pressure air energy storage system is characterized in that the Rankine cycle evaporator in the first Rankine cycle subsystem serves as the Rankine cycle condenser in the second Rankine cycle subsystem.

[0026] The air compression system comprises an air filter, a molecular sieve purifier, a multi-stage air compressor and an inter-stage cooler, the inter-stage cooler is connected with the outlet of the corresponding air compressor group, the air filter is connected with the inlet of the first-stage air compressor, the inlet of the molecular sieve purifier is connected with the outlet of the corresponding inter-stage cooler, and the outlet of the molecular sieve purifier is connected with the inlet of the corresponding air compressor.

[0027] An air precooling system and a gas-liquid separator are arranged between the corresponding inter-stage cooler and the molecular sieve purifier, the air precooling system is used for precooling and washing raw material air, and the gas-liquid separator is used for separating water in the air entering the molecular sieve purifier.

[0028] The LNG cold energy utilization based liquid medium-pressure air energy storage system provided by the application increases the medium-pressure air liquefaction rate by increasing the storage pressure of the liquid air storage tank, stores medium-pressure liquid air in the liquid air storage tank, and uses the LNG cold storage system to cool high-pressure air through a cold box into liquid air in the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and is stored in a cold storage medium heat fluid storage tank; the LNG cold storage system is also used to warm high-pressure liquid air through the cold box to normal temperature by using the heat absorbed in the energy storage stage in the energy release stage, so that part of the cold storage medium in the LNG cold storage system absorbs the cold of the liquid air and is stored in a cold storage medium cold fluid storage tank; meanwhile, the LNG cold storage system is also used to gasify and superheat LNG through an LNG gasifier and a natural gas superheater every day for 24 hours, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and is stored in the cold storage medium cold fluid storage tank.

[0029] In this way, the LNG cold energy recovered by the LNG cold storage system and the cold energy of the liquid air in the energy releasing stage have the same quality, and are all used in the high-pressure air liquefaction process in the energy storage stage. Since the temperature of the liquid air is high at this time, the air liquefaction rate after the throttle valve is maintained high by increasing the liquid air storage pressure, and the power consumption of the backflow gas re-compression process is reduced. The medium and high-grade cold energy in the LNG can be fully recovered. Under the condition of supplying the same LNG cold energy and achieving the same efficiency, the capacity of the liquid medium-pressure air energy storage system provided by the application is larger. Moreover, the energy storage process and the energy releasing process of the liquid medium-pressure air energy storage system provided by the application can be deeply decoupled, the liquid air in the energy releasing stage can be pumped to a higher pressure, the working potential of unit liquid air is greatly improved, the heat stored in the energy storage stage is all used for air expansion work in the energy releasing stage, and there is no need to absorb environmental heat for heating air in the energy releasing stage, thereby avoiding the formation of "cold pollution" (i.e. requiring environmental heat) to the local environment. Without the intervention of external low-grade heat sources, a high-efficiency and large-capacity liquid air energy storage system can be realized, which is conducive to the large-scale promotion of the liquid air energy storage technology on the LNG cold energy utilization side.

[0030] In addition, since the cold storage working medium on the LNG cold energy side and the cold box side has the same working temperature range, the cold storage medium storage tanks can be integrated to reduce the number of storage tanks by half, thereby simplifying the system structure and reducing the complexity of the system. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0032] Figure 1 is a schematic diagram of the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by embodiment 1 of the present application.

[0033] Figure 2 is a schematic diagram of the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by embodiment 2 of the present application.

[0034] Figure 3 is a partial schematic diagram of the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by embodiment 3 of the present application.

[0035] Reference signs:

[0036] 1, air filter; 2, air compressor unit; 3, first stage intercooler; 4, molecular sieve purifier; 5, booster compressor unit; 6, second stage intercooler; 7, air subcooler; 8, cryogenic booster compressor unit; 9 / 17, first stage heat exchanger; 10 / 16, second stage heat exchanger; 11, liquid expander; 12, cryogenic throttle valve; 13, gas-liquid separator; 14, liquid air storage tank; 15, liquid air pump; 18, first stage heater; 19, first stage air expander; 20, second stage heater; 21, second stage air expander; 22, third stage heater; 23, third stage air expander; 24, air cooler; 25, cold water tank; 26, cold water pump; 27, hot water tank; 28, hot water pump; 29, second stage cold thermal fluid pump of cold storage medium; 30, second stage cold thermal fluid storage tank of cold storage medium; 31, first stage cold thermal fluid pump of cold storage medium; 32, first stage cold thermal fluid storage tank of cold storage medium; 33, first stage cold fluid pump of cold storage medium; 34, first stage cold fluid storage tank of cold storage medium; 35, natural gas superheater; 36, LNG gasifier; 37, second stage cold fluid pump of cold storage medium; 38, second stage cold fluid storage tank of cold storage medium; 39, first stage reverse flow gas compressor; 40, reverse flow gas subcooler; 41, second stage reverse flow gas compressor; 50, reverse flow gas compression system;

[0037] ORC1, first Rankine cycle subsystem; 61, first Rankine cycle condenser; 62, first Rankine cycle working fluid pump; 63, first Rankine cycle turbine; 64, first Rankine cycle evaporator;

[0038] ORC2, second Rankine cycle subsystem; 71, second Rankine cycle working fluid pump; 72, second Rankine cycle turbine; 73, second Rankine cycle evaporator;

[0039] ORC3, third Rankine cycle subsystem; 81, third Rankine cycle condenser; 82, third Rankine cycle working fluid pump; 83, third Rankine cycle turbine; 84, third Rankine cycle evaporator. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present application.

[0041] In the description of the embodiments of the present application, it should be noted that unless specifically defined and limited otherwise, the terms "connected", "connected to", "connection" should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0042] In the embodiments of the present application, unless otherwise specifically defined and limited, the first feature is "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0043] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, the skilled in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0044] In the existing liquid air energy storage system coupled with LNG cold energy utilization, in order to sufficiently reduce the power consumption of the compressor unit, the air inlet of each stage of compressor is usually cooled to an extremely low temperature, and the number of stages of the compressor unit is increased. With such a setting, although the efficiency of the liquid air energy storage system is improved, the difficulty and cost of removing water and carbon dioxide from the air in the low-temperature environment are increased. In addition, the heat generated in the air compression process is used for indirect heating of LNG, and there is no available heat in the system during the energy release stage to make the over-heated air work to generate electricity. The over-heated air can only be expanded by using the ambient heat, and the shaft work of unit air output is less, and the system has the characteristics of high efficiency and low power generation. At the same time, in the process of consuming ambient heat, the environment is formed with "cold pollution". Moreover, when the number of stages of the liquid air energy storage system is too large and the air temperature at the inlet and outlet of each stage of compressor is too low, the temperature difference of the air at the inlet and outlet of each stage of compressor is small, and the system absorbs more high-grade LNG cold energy, and the recovery of medium and low-grade LNG cold energy is not sufficient. Under the condition of the quantitative LNG cold energy resources, the amount of air available for compression is small, and finally the capacity of the energy storage system is greatly affected by the amount of LNG cold energy. In the LNG cold energy utilization scenario, the liquid air energy storage technology is difficult to realize large-scale application. Since the traditional scheme does not make full use of LNG cold energy, in the case of a large amount of low-grade LNG cold energy exported by the energy storage system, the local industry is in a situation of "more supply than demand" of cold energy, and the remaining cold energy can only be discharged to the environment, further causing "cold pollution" to the environment.

[0045] In addition, when the cold box part of the liquid air energy storage system is supplemented with LNG cold energy, the problem that the required cold energy temperature of the air liquefaction process during the energy storage stage is lower than the LNG available cold energy temperature is ignored. The cold energy provided by the LNG can only supplement the cold energy of part of the temperature zone of the energy storage system, which means that the higher-grade cold energy required by the air liquefaction process is still provided by the liquid air during the energy release stage. Therefore, the liquid air during the energy release stage cannot be pressurized to a higher pressure, and the cold energy of the liquid air needs to be transferred to the energy storage stage in the form of temperature. The energy storage and energy release processes of the system are difficult to decouple. Therefore, the existing LNG cold energy supplement scheme for the cold box part has little effect on the improvement of the performance of the system. Moreover, there are multiple cold storage units in the coupled system, and even if the cold storage medium is the same, due to the difference in the working temperature range, it is difficult to integrate. The increase in the number of cold storage medium storage tanks increases the investment cost, which is not conducive to the improvement of the economic performance of the system and the promotion of the energy storage system in the LNG cold energy utilization scenario. Therefore, the present embodiment provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization.

[0046] Figure 1 FIG. 1 is a schematic diagram of the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Embodiment 1 of the present application.

[0047] Referring to Figure 1The embodiment of the present application provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, which comprises an air compression system, an expansion power generation system, a liquid air storage tank 14, a cold box and an LNG cold storage system.

[0048] The liquid air storage tank 14 can be a sub-tank, a low-temperature spherical tank, a vacuum tank or the like, and the air storage pressure in the liquid air storage tank 14 can be 0.6-1.8 MPa.A. The liquid air storage tank 14 is used for storing medium-pressure liquid air.

[0049] The air compression system comprises an air filter 1, a molecular sieve purifier 4, a multi-stage air compressor and an inter-stage cooler. The air filter 1 is used for removing dust and other impurities in the ambient air. The molecular sieve purifier 4 is used for removing water, CO2 and other hydrocarbons in the air. In the air compression process, the water, CO2 and other hydrocarbons in the air passing through the cold box are removed by the molecular sieve purifier 4, so as to prevent the water, CO2 and other hydrocarbons from being frozen and blocking the heat exchange channels of the cold box in the low-temperature environment of the cold box.

[0050] The number of air compressors corresponds to the number of inter-stage coolers. The air compressors can be one-stage, two-stage or three-stage, etc. The air compressors are used for compressing air. The inter-stage coolers are connected to a heat storage system composed of an air cooler 24, a cold water tank 25, a cold water pump 26, a hot water tank 27 and a hot water pump 28, and are used for collecting the heat generated by the air compression system in the air compression process in the energy storage stage. With the increase of the number of air compressors, the heat storage temperature of the inter-stage coolers decreases.

[0051] For example, the three-stage air compressors are used in the embodiment of the present application, i.e. a one-stage air compressor, a two-stage air compressor and a three-stage air compressor. The one-stage air compressor is an air compressor set 2. The ambient air with dust and impurities removed enters the air compressor set 2 to be pressurized to medium pressure. The two-stage air compressor is a booster set 5. The air with water and carbon dioxide removed by the molecular sieve purifier 4 is mixed with the backflow air to enter the booster set 5 to be pressurized. The three-stage air compressor is a low-temperature booster set 8. The air cooled to low temperature by the cold water and the cold storage medium of the LNG cold storage system enters the low-temperature booster set 8 to be pressurized to high pressure.

[0052] Correspondingly, a one-stage inter-stage cooler 3 is connected between the one-stage air compressor and the two-stage air compressor. A two-stage inter-stage cooler 6 is connected between the two-stage air compressor and the three-stage air compressor. An air cooler for heat exchange with the LNG cold storage system is further connected between the two-stage inter-stage cooler 6 and the three-stage air compressor. Of course, a four-stage air compressor set or more can be arranged according to the use requirement.

[0053] The expansion power generation system uses stored liquid air to generate power by expansion, and the expansion power generation system comprises multiple sets of air expanders and heaters connected between the air expanders. The expansion power generation system can be set to two, three, four or more stages, and the number of stages is selected according to actual use.

[0054] For example, in the embodiment of the present application, three sets of air expanders are used, i.e., a first air expander 19, a second air expander 21 and a third air expander 23. A first heater 18 is connected between the heat exchanger of the cold box and the first air expander 19, a second heater 20 is connected between the first air expander 19 and the second air expander 21, and a third heater 22 is connected between the second air expander 21 and the third air expander 23. Of course, the present application can also set four sets of air expanders or more according to the needs of use.

[0055] The low-temperature booster set 8 of the air compression system is connected with the high-pressure air inlet of the cold box, the medium-pressure liquid air outlet of the cold box is connected with the inlet of the liquid air storage tank 14, the outlet of the liquid air storage tank 14 is connected with the liquid air inlet of the cold box through the liquid air pump 15, and the medium-pressure liquid air stored in the liquid air storage tank 14 needs to be pressurized by the liquid air pump 15 to form high pressure before entering the cold box. The expansion power generation system is connected with the normal-temperature air outlet of the cold box.

[0056] The LNG cold storage system is connected with the heat exchange port of the cold box, and is further connected with an LNG gasifier 36 and a natural gas superheater 35 in sequence. The LNG cold storage system is used to cool the high-pressure air passing through the cold box to liquid air in the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and is stored in the cold storage medium hot fluid storage tank. The LNG cold storage system is also used to warm the high-pressure liquid air passing through the cold box to normal temperature in the energy release stage by using the heat absorbed in the energy storage stage, so that part of the cold storage medium in the hot fluid storage tank of the LNG cold storage system absorbs cold and is stored in the cold storage medium cold fluid storage tank. At the same time, the LNG cold storage system is also used to gasify and superheat the LNG passing through the LNG gasifier 36 and the natural gas superheater 35 every day for 24 hours, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and is stored in the cold storage medium cold fluid storage tank, i.e., the remaining cold storage medium needs to store the cold generated in the LNG regasification process after 24 hours of continuous recovery of the cold, and then store it in the cold storage medium cold fluid storage tank.

[0057] It should be noted that the cold box is equipped with a first-stage heat exchanger 9 / 17 and a second-stage heat exchanger 10 / 16. These two heat exchangers are connected in series to form a continuous processing line. The LNG cold storage system has a primary cold storage medium loop corresponding to the first-stage heat exchanger 9 / 17. This loop is used for heat exchange in the first-stage heat exchanger 9 / 17. A natural gas superheater 35 is located within this loop, and its outlet is connected to the pipeline network. The primary cold storage medium can be one or more of methanol, ethylene glycol, and propylene glycol mixed with water in different proportions to obtain an alcohol-water solution.

[0058] The LNG cold storage system includes a secondary cold storage medium loop corresponding to the second-stage heat exchanger 10 / 16. This loop is used for heat exchange in the second-stage heat exchanger 10 / 16. An LNG vaporizer 36 is located within this secondary cold storage medium loop. The inlet of the LNG vaporizer 36 is connected to the LNG storage tank, and its outlet is connected to the inlet of the natural gas superheater 35. The temperature of the liquid air cooled by the cold box is the same as or close to the temperature of the cold fluid in the secondary cold storage medium loop.

[0059] Specifically, such as Figure 1 As shown, during off-peak electricity demand, the liquid medium-pressure air energy storage system based on LNG cold energy utilization operates in energy storage mode. At ambient temperature and pressure, air is filtered by air filter 1 to remove dust and impurities, then pressurized to medium pressure by air compressor unit 2. It is then cooled by cold water and passes through molecular sieve purifier 4 to remove water and carbon dioxide. The air mixes with backflow air and enters booster unit 5 for further pressurization. It is then cooled to low temperature by cold water and the cold storage medium of the LNG cold storage system, before entering low-temperature booster unit 8 for high pressure. The high-pressure air then enters the first stage of the cold box for heat exchange. Heaters 9 / 17 and the second-stage heat exchangers 10 / 16 are successively cooled and liquefied by the cold fluid of the first-stage and second-stage cold storage media of the LNG cold storage system. The high-pressure liquid air is expanded and throttled to medium pressure through the liquid expander 11 and the cryogenic throttle valve 12, forming a gas-liquid mixture. The mixture is then separated by the gas-liquid separator 13. The medium-pressure liquid air enters the liquid air storage tank 14 for storage, and the medium-pressure gaseous air is returned to the heat exchangers of each stage of the cold box as backflow gas to make up for the cooling. The backflow gas after making up for the cooling then flows back to the booster unit 5 to mix with the medium-pressure air.

[0060] The heat generated by the air compressor unit 2 and the booster unit 5 during the air compression process is carried away by the high-pressure cold water, and the resulting high-pressure high-temperature hot water is stored in the hot water tank 27.

[0061] Specifically, such as Figure 1As shown, in the energy release mode of the LNG cold energy utilization based liquid medium pressure air energy storage system in the power consumption peak period, the low-temperature medium pressure liquid air is pressurized to high pressure by the liquid air pump 15, sequentially enters the second stage heat exchanger 10 / 16 and the first stage heat exchanger 9 / 17 of the cold box, absorbs the heat of the heat fluid of the second stage and the first stage of the LNG cold storage system, is gasified and is warmed to normal temperature, a part of the cold storage medium in the LNG cold storage system absorbs the cold of the liquid air and is stored in the cold fluid storage tank of the cold storage medium, at the same time, the LNG cold storage system is also used for gasifying and superheating the LNG passing through the LNG gasifier 36 and the natural gas superheater 35 every 24 hours, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and is stored in the cold fluid storage tank of the cold storage medium. Then, the air enters the multi-stage air expander, is heated by the high-pressure hot water stored in the hot water tank 27, is expanded to output shaft power to the external, drives the generator to generate electricity and is transmitted to the power grid.

[0062] The air pressure range entering the first stage heat exchanger 9 / 17 of the cold box is 4-10 MPa.A. The pressure range of the high-pressure liquid air after the liquid air pump 15 is 4-25 MPa.A.

[0063] It can be understood that the LNG cold energy utilization based liquid medium pressure air energy storage system provided by the embodiment of the present application increases the medium pressure air liquefaction rate by increasing the storage pressure of the liquid air storage tank 14, the liquid air storage tank 14 is used for storing medium pressure liquid air, the LNG cold storage system is used for cooling the high-pressure air passing through the cold box to liquid air in the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and is stored in the hot fluid storage tank of the cold storage medium; the LNG cold storage system is also used for warming the high-pressure liquid air passing through the cold box to normal temperature in the energy release stage, so that a part of the cold storage medium in the LNG cold storage system absorbs the cold of the liquid air and is stored in the cold fluid storage tank of the cold storage medium; at the same time, the LNG cold storage system is also used for continuously gasifying and superheating the LNG passing through the LNG gasifier and the natural gas superheater every 24 hours, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and is stored in the cold fluid storage tank of the cold storage medium.

[0064] In this way, the LNG cold energy recovered by the LNG cold storage system and the cold energy of the liquid air in the energy releasing stage have the same quality, and are all used for liquefying the liquid high-pressure air. Since the temperature of the liquid air is relatively high at this time, the air liquefaction rate is maintained to be relatively high by increasing the storage pressure of the liquid air, and the power consumption of the backflow gas re-compression process is reduced. The medium and high-grade cold energy in the LNG can be fully recovered. Under the condition of supplying the same LNG cold energy and realizing the same efficiency, the capacity of the liquid medium-pressure air energy storage system provided by the application is larger. Moreover, the energy storage process and the energy releasing process of the liquid medium-pressure air energy storage system provided by the application can be deeply decoupled. The liquid air in the energy releasing stage can be pumped to a higher pressure by the liquid air pump, the working potential of unit liquid air is greatly improved, the heat stored in the energy storage stage is all used for air expansion work in the energy releasing stage, and the environment heat does not need to be absorbed for heating the air in the energy releasing stage, thereby avoiding the formation of "cold pollution" (i.e. the demand for environment heat) to the local environment. Without the intervention of external medium and low-grade heat sources, a high-efficiency and large-capacity liquid air energy storage system can be realized, and the liquid air energy storage technology is conducive to large-scale promotion on the LNG cold energy utilization side.

[0065] In addition, since the cold storage working medium on the LNG cold energy side and the cold tank side has the same working temperature range, the cold storage medium storage tanks can be integrated to reduce the number of storage tanks by half, thereby simplifying the system structure and reducing the complexity of the system.

[0066] In addition, since the liquid air storage tank 14 stores liquid air at a medium pressure, which is generally higher than 0.6 MPa.A, although the equipment cost of the liquid air storage tank 14 is increased, the system can realize a high air liquefaction rate under a poor medium cold energy quality. Moreover, the air compression pressure in the system of the application can be greatly reduced. The air compression pressure needs to be higher than the critical pressure of air, the pressure bearing of the first and second heat exchangers in the cold tank is reduced, and the manufacturing difficulty of the equipment is reduced.

[0067] In some embodiments of the application, the primary cold storage medium circuit is composed of a primary cold storage medium hot fluid storage tank 32, a primary cold storage medium hot fluid pump 31, a primary cold storage medium cold fluid pump 33 and a primary cold storage medium cold fluid storage tank 34 connected in sequence. The first-stage heat exchanger 9 / 17 is arranged between the primary cold storage medium cold fluid pump 33 and the primary cold storage medium hot fluid storage tank 32. The heat exchange outlet of the first-stage heat exchanger 9 / 17 is connected with one inlet of the primary cold storage medium cold fluid storage tank 34. The natural gas superheater 35 is arranged between the primary cold storage medium hot fluid pump 31 and the primary cold storage medium cold fluid storage tank 34. The heat exchange outlet of the natural gas superheater 35 is connected with the other inlet of the primary cold storage medium cold fluid storage tank 34.

[0068] The secondary cold storage medium loop is composed of a secondary cold storage medium hot fluid tank 30, a secondary cold storage medium hot fluid pump 29, a secondary cold storage medium cold fluid pump 37 and a secondary cold storage medium cold fluid tank 38 connected in sequence; the second stage heat exchanger 10 / 16 is arranged between the secondary cold storage medium cold fluid pump 37 and the secondary cold storage medium hot fluid tank 30, the heat exchange outlet of the second stage heat exchanger 10 / 16 is connected with one inlet of the secondary cold storage medium cold fluid tank 38, and the LNG gasifier 36 is arranged between the secondary cold storage medium hot fluid pump 29 and the secondary cold storage medium cold fluid tank 38, the heat exchange outlet of the LNG gasifier 36 is connected with the other inlet of the secondary cold storage medium cold fluid tank 38.

[0069] Accordingly, the embodiment of the present application can combine the cold energy side of the LNG cold storage system and the cold storage side of the cold box by keeping the working temperature range of the cold storage medium of the cold energy side of the LNG cold storage system and the cold storage side of the cold box consistent, thereby reducing the number of storage tanks in the energy storage system, reducing the operation cost of the energy storage system and simplifying the structure of the energy storage system.

[0070] Accordingly, in the energy storage stage, the LNG cold storage system cools the high-pressure air passing through the cold box into liquid air, and the liquefied air is cooled to the temperature of the cold fluid in the secondary cold storage medium loop of the LNG cold storage system, that is, the temperature of the liquefied air before the liquid expander 11 is higher. That is, in the energy storage stage, the LNG cold storage system cools the high-pressure air passing through the cold box into liquid air, and the temperature of the cooled liquid air is the same as or close to the temperature of the cold fluid in the secondary cold storage medium loop of the LNG cold storage system, so that the temperature ranges of the liquid air energy storage system and the LNG cold storage system are unified, the medium and high-grade LNG cold energy liquefied air can be fully recovered, and the energy storage capacity is greatly increased. By adjusting the storage pressure of the liquid air tank 14 to medium pressure, the liquefaction rate of air can be improved, the liquid air energy storage system can better adapt to LNG cold energy, and the recovery of LNG medium and high-grade cold energy is better than that of the conventional coupled LNG cold energy utilization liquid air energy storage system. Therefore, the liquid air energy storage system provided by the present application can liquefy more air under the premise of a certain amount of LNG cold energy, so as to effectively improve the capacity of the liquid air energy storage system.

[0071] Moreover, since the quality of the liquid air cold energy recovered by the liquid air energy storage system in the energy release process is the same as that of the cold energy recovered in the LNG regasification process, it can be considered that the energy storage process and the energy release process of the liquid air energy storage system are deeply decoupled. In this way, in the energy storage stage, the liquid air can be pressurized to a higher pressure to improve the work capacity of the air in the energy release stage, increase the power generation capacity, more fully recover the heat generated in the air compression process in the energy storage stage, and the air cooler 24 of the conventional cold storage system releases less cold to the environment, thereby avoiding the formation of "cold pollution" to the local environment.

[0072] Compared with the traditional liquid air energy storage system, the power generation of the liquid medium-pressure air energy storage system provided by the embodiment of the present application is greatly improved. Moreover, the larger the energy storage capacity of the system is, the lower the unit capacity cost of the system is, and therefore the economic performance of the liquid medium-pressure air energy storage system provided by the embodiment of the present application is more excellent.

[0073] In some embodiments of the present application, the backflow outlet of the gas-liquid separator 13 in the cold box is connected with the medium-pressure backflow gas inlet of the heat exchanger in the cold box, and the medium-pressure backflow gas outlet of the heat exchanger in the cold box is connected with the booster set inlet in the air compression system. While recovering the medium-pressure backflow gas, it can be considered that the refrigeration cycle composed of the backflow gas circuit can be used to supplement the cold quantity for the heat exchanger in the cold box, further improving the liquefaction rate of air.

[0074] In the embodiment, the pressure of the medium-pressure backflow gas entering the compressor set is the same as or close to the pressure of the to-be-mixed gas at the inlet end of the compressor set, that is, the pressure of the medium-pressure backflow gas from the heat exchanger in the cold box is the same as or close to the pressure of the to-be-mixed gas at the inlet end of the booster set, so as to avoid the change of the pressure of the mixed medium-pressure air.

[0075] Since the high-pressure liquid air is expanded and throttled to medium pressure by the liquid expander 11 and the low-temperature throttle valve 12, the generated medium-pressure backflow gas is directly mixed with the medium-pressure air at the rear end of the air compression set 2. In order to avoid the change of the pressure of the mixed medium-pressure air, it is necessary to limit the air pressure at the outlet of the air compression set 2 so that it is the same as or close to the pressure of the medium-pressure backflow gas before mixing. However, such a setting is not conducive to the optimization of system parameters, and the flexibility of the system is poor. Therefore, the embodiment 2 of the present application provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, which is improved based on the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in the embodiment 1 of the present application.

[0076] Figure 2 is a schematic diagram of the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in the embodiment 2 of the present application.

[0077] Referring to Figure 2 On the basis of the above-mentioned embodiment 1, and different from the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in the above-mentioned embodiment 1, the air compression system is connected with the high-pressure air inlet of the first-stage heat exchanger 9 / 17, the backflow outlet of the gas-liquid separator 13 is connected with the medium-pressure backflow gas inlet of the second-stage heat exchanger 10 / 16, and the medium-pressure backflow gas outlet of the second-stage heat exchanger 10 / 16 is connected with the air inlet of the first-stage heat exchanger 9 / 17 through the backflow gas compression system 50.

[0078] The embodiment of the present application realizes the recovery of the medium-pressure backflow gas by adding the backflow gas compression system 50 between the medium-pressure backflow gas outlet of the second-stage heat exchanger 10 / 16 and the backflow gas inlet of the first-stage heat exchanger 9 / 17, the outlet pressure of the air compressor set is no longer limited, the number of stages of the supercharging set can be reduced, and the pressure ratio, the heat storage temperature and the heat storage capacity of each stage of compressor can be flexibly adjusted.

[0079] With reference to the foregoing Figure 2 In some embodiments of the present application, the backflow gas compression system 50 comprises a plurality of stages of backflow gas compressors and a backflow gas subcooler 40 arranged between two adjacent stages of backflow gas compressors, wherein the embodiment of the present application is provided with a first-stage backflow gas compressor 39 and a second-stage backflow gas compressor 41, and the backflow gas subcooler 40 is connected between the first-stage backflow gas compressor 39 and the second-stage backflow gas compressor 41, the backflow gas subcooler 40 is connected with the first-stage heat storage medium of the LNG heat storage system for cooling the backflow gas to reduce the power consumption of the backflow gas compression system 50. The first-stage heat storage medium of the LNG heat storage system simultaneously exchanges heat with the first-stage heat exchanger 9 / 17 and the backflow gas subcooler 40.

[0080] The medium-pressure backflow gas outlet of the second-stage heat exchanger 10 / 16 is connected with the inlet of the first-stage backflow gas compressor 39, and the outlet of the second-stage backflow gas compressor 41 is connected with the air inlet of the first-stage heat exchanger 9 / 17, through the backflow gas compression system 50, the backflow gas is compressed to the same pressure as the forward-flow air, and then mixed and sent into the cold box first-stage heat exchanger 9 / 17.

[0081] As shown in the drawings, Figure 2 During the low electricity consumption period, the liquid medium-pressure air energy storage system based on the LNG cold energy utilization operates in the energy storage mode, the ambient air at normal temperature and pressure is filtered by the air filter 1 to remove dust and impurities, and the surplus power of the power grid drives the three-stage air compressor to work, the air is compressed and pressurized by the three-stage air compressor with an inter-stage cooler, that is, the air is pressurized to medium pressure by the air compressor set 2, and then cooled by the cold water in the first-stage inter-stage cooler 3, the medium-pressure air cooled is purified by the molecular sieve purifier 4 to remove water and carbon dioxide, and then pressurized by the supercharging set 5, and sequentially cooled to low temperature by the cold water in the second-stage inter-stage cooler 6 and the first-stage heat storage medium in the air subcooler 7, and then pressurized to high pressure by the low-temperature supercharging set 8.

[0082] The high-pressure air then sequentially enters the first-stage heat exchanger 9 / 17 and the second-stage heat exchanger 10 / 16 of the cold box. Simultaneously, the primary and secondary cold storage media of the LNG cold storage system sequentially pass through the first-stage heat exchanger 9 / 17 and the second-stage heat exchanger 10 / 16 to recover the heat of compression. This causes the compressed air to be cooled and liquefied by the cold fluids of the primary and secondary cold storage media. The high-pressure liquid air is expanded and throttled to medium pressure via the liquid expander 11 and the cryogenic throttle valve 12 to form a gas-liquid mixture. The gas-liquid mixture then passes through the gas-liquid separator 13 for gas-liquid separation. After separation, the medium-pressure liquid air enters the liquid air storage tank 14 for storage, and the separated medium-pressure gaseous air serves as reflux gas. The reflux gas returns to the second-stage heat exchanger 10 / 16 of the cold box for make-up cooling. The reflux gas discharged from the second-stage heat exchanger 10 / 16 passes through the reflux gas compression system 50, which consists of a first-stage reflux gas compressor 39, a reflux gas subcooler 40, and a second-stage reflux gas compressor 41, to adjust the pressure and mix with the high-pressure air pressurized by the low-temperature booster unit 8. The mixed high-pressure air then enters the first-stage heat exchanger 9 / 17 for further liquefaction.

[0083] like Figure 2 As shown, during peak electricity consumption periods, the liquid medium-pressure air energy storage system based on LNG cold energy utilization operates in energy release mode. The low-temperature medium-pressure liquid air stored in the liquid air storage tank 14 is pressurized to high pressure by the liquid air pump 15. The high-pressure liquid air then enters the second-stage heat exchanger 10 / 16 and the first-stage heat exchanger 9 / 17 of the cold box, successively absorbing the heat from the secondary and primary cold storage media of the LNG cold storage system, vaporizing and reheating to room temperature (i.e., heated to near ambient temperature). The room-temperature air absorbs the heat from the high-pressure, high-temperature hot water generated during the compression process and is superheated to a high temperature. It then enters the first-stage air expander 19, the second-stage air expander 21, and the third-stage air expander 23 in sequence. The multi-stage air expanders output shaft power, driving the generator to generate electricity and supplying it to the power grid, achieving the purpose of peak shaving and valley filling.

[0084] During energy storage operation, the heat generated by air compressor unit 2 and booster unit 5 during air compression is carried away by high-pressure cold water stored in cold water tank 25 by cold water pump 26, forming high-pressure, high-temperature hot water which is stored in hot water tank 27. During energy release, the high-pressure, high-temperature hot water stored in hot water tank 27 generated during compression is pumped by hot water pump 28 to the primary heater 18, secondary heater 20, and tertiary heater 22 located between the multi-stage air expanders for heating.

[0085] In addition, during the energy storage process, the warmed secondary cold storage medium discharged from the second heat exchanger 10 / 16 is pumped to the secondary cold storage medium hot fluid storage tank 30 by the secondary cold storage medium hot fluid pump 29 for storage, and the warmed primary cold storage medium discharged from the first heat exchanger 9 / 17 is pumped to the primary cold storage medium hot fluid storage tank 32 by the primary cold storage medium hot fluid pump 31 for storage. During the energy release process and the LNG regasification process, the primary and secondary cold storage mediums of the LNG cold storage system recover the cold energy of the liquid air and LNG, the cooled secondary cold storage medium discharged from the second heat exchanger 10 / 16 enters the secondary cold storage medium cold fluid storage tank 38 through the corresponding pump, and the cooled primary cold storage medium discharged from the first heat exchanger 9 / 17 enters the primary cold storage medium cold fluid storage tank 34 through the corresponding pump, so as to be used for cooling the compressed air during the energy storage process.

[0086] Figure 3 Figure 3 is a partial schematic view of an LNG cold energy based liquid medium-pressure air energy storage system provided by an embodiment of the present application.

[0087] Continuing to refer to Figure 1 , Figure 2 , and referring to Figure 3 , the cold box is provided with at least one of a heat exchanger and a Rankine cycle system, the heat exchanger is connected with the LNG cold storage system and exchanges heat with the LNG cold storage system, and the heat source of the Rankine cycle system is the heat generated by the air compression system.

[0088] That is, the cold box can be provided with multiple groups of heat exchangers, which exchange heat with the cold storage system, and the cold box can also be provided with multiple groups of Rankine cycle systems, which exchange heat with the air compression system.

[0089] In addition, the cold box can also be provided with a heat exchanger and a Rankine cycle system, the heat exchanger exchanges heat with the cold storage medium of the LNG cold storage system, the cold energy of the primary and secondary cold storage medium cold fluids of the LNG cold storage system in the energy storage stage comes from the LNG and the liquid medium-pressure air in the energy release stage, and the Rankine cycle system exchanges heat with the heat generated by the air compression system in the air compression process.

[0090] Continuing to refer to Figure 3 , in some embodiments of the present application, the Rankine cycle system includes a first Rankine cycle subsystem ORC1, a second Rankine cycle subsystem ORC2 and a third Rankine cycle subsystem ORC3, and each Rankine cycle subsystem includes a Rankine cycle condenser, a Rankine cycle working medium pump, a Rankine cycle turbine and a Rankine cycle evaporator connected in sequence.

[0091] The Rankine cycle condenser is used for warming the high-pressure liquid air passing through the cold box to normal temperature in the energy releasing stage, and the heat source of the Rankine cycle evaporator is the heat generated by the air compression system.

[0092] The embodiment of the present application utilizes the cold energy of liquid air to generate electricity, and no longer recovers the cold energy by the cold storage unit, and the cold energy required by the air liquefaction process is only provided by the cold energy of the LNG cold storage system, at this time, the cold energy of the LNG cold storage system is directly related to the energy storage capacity of the system, so that the system capacity is reduced, but the increase of the cold energy generation capacity helps to further improve the system efficiency.

[0093] Continuing to refer to Figure 3 In some embodiments of the present application, the Rankine cycle evaporator in the first Rankine cycle subsystem ORC1 serves as the Rankine cycle condenser in the second Rankine cycle subsystem ORC2.

[0094] Part of the devices in the first Rankine cycle subsystem ORC1 and the second Rankine cycle subsystem ORC2 are shared with each other.

[0095] On the basis of the above-mentioned embodiments 1 and 2, the energy releasing stage of the liquid medium-pressure air energy storage system is improved in the embodiment of the present application, the cold energy of the liquid air is not stored by the first and second cold storage media of the LNG cold storage system, or the cold energy of the liquid air is only stored by the first cold storage medium of the LNG cold storage system, and part of the cold energy is recovered by the Rankine cycle system, so that the system efficiency can be further improved.

[0096] On the basis of the above-mentioned embodiments 1 and 2, based on the cascade utilization of the cold energy of the liquid air, a multi-stage organic working medium Rankine cycle (ORC) is arranged to fully recover the cold energy in this interval, and in the energy releasing period, the Rankine cycle system and the energy releasing system of the liquid air jointly generate electricity, so that the comprehensive efficiency of the system can be improved.

[0097] The Rankine cycle system comprises a first Rankine cycle subsystem ORC1, a second Rankine cycle subsystem ORC2 and a third Rankine cycle subsystem ORC3.

[0098] The first Rankine cycle subsystem ORC1 comprises a first Rankine cycle condenser 61, a first Rankine cycle working medium pump 62, a first Rankine cycle turbine 63 and a first Rankine cycle evaporator 64 connected in sequence and end to end. The second Rankine cycle subsystem ORC2 comprises the first Rankine cycle evaporator 64, a second Rankine cycle working medium pump 71, a second Rankine cycle turbine 72 and a second Rankine cycle evaporator 73 connected in sequence and end to end. The third Rankine cycle subsystem ORC3 comprises a third Rankine cycle condenser 81, a third Rankine cycle working medium pump 82, a third Rankine cycle turbine 83 and a third Rankine cycle evaporator 84 connected in sequence and end to end.

[0099] The first Rankine cycle evaporator 64 simultaneously serves as an evaporator of the first Rankine cycle subsystem ORC1 and a condenser of the second Rankine cycle subsystem ORC2, and the heat sources of the ORC2 and the ORC3 are the heat generated by the compression process.

[0100] The first Rankine cycle subsystem ORC1 and the second Rankine cycle subsystem ORC2 are integrated, so that the number of devices in the system is reduced, and the system structure is simplified.

[0101] In some embodiments of the present application, an air pre-cooling system and another gas-liquid separator are arranged between the corresponding inter-stage cooler and the molecular sieve purifier 4, the air pre-cooling system is used to pre-cool and wash the raw air, and the gas-liquid separator is used to separate the water in the air entering the molecular sieve purifier 4.

[0102] Since the LNG receiving terminal is located on the coast, the coastal air carries too much water, and in view of the problem that the molecular sieve purifier 4 in the liquid air energy storage system processes too much water, resulting in high raw material cost and high regeneration cost of the adsorbent, an air pre-cooler and a gas-liquid separator are added between the molecular sieve purifier 4 and the first inter-stage cooler 3, the air temperature is reduced by using the abundant low-grade cold energy on site, and after gas-liquid separation, the water content of the air entering the molecular sieve purifier 4 is greatly reduced, so that the raw material of the adsorbent can be saved, the size of the adsorber can be reduced, and the regeneration cost of the purification unit can be reduced.

[0103] However, since the air inlet temperature of the booster set 5 is reduced in the embodiments of the present application, on the basis of the embodiment 1 and the embodiment 2, it is often necessary to recover the high-grade heat generated in the compression process of the booster set 5, the power consumption is increased due to the increase of the pressure ratio of the booster set 5, and the expansion work is reduced due to the decrease of the heat quality of the heat storage unit, so when the scheme is improved in practice, the influence of the improvement measures on the electric-electric efficiency of the system and the economic performance of the system needs to be comprehensively analyzed.

[0104] It should be noted that the air compressor set 2, the booster set 5 and the inter-stage cooler in the embodiments of the present application can be divided into 1-3 stages, and the number of stages is increased, so that the storage temperature is reduced; the low-temperature booster set 8 and the air supercooler 7 can be divided into 1-4 stages, and the increase of the number of stages of the low-temperature booster set 8 helps to improve the system efficiency in a small range.

[0105] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A liquid medium pressure air energy storage system based on LNG cold energy utilization, characterized in that, The air compression system, the expansion power generation system, the liquid air storage tank, the cold box and the LNG cold storage system are connected in series. The liquid air storage tank is used for storing medium-pressure liquid air. The air compression system is connected with the high-pressure air inlet of the cold box, the medium-pressure liquid air outlet of the cold box is connected with the inlet of the liquid air storage tank, the outlet of the liquid air storage tank is connected with the high-pressure liquid air inlet of the cold box, and the expansion power generation system is connected with the normal-temperature air outlet of the cold box. The LNG cold storage system is connected with the heat exchange port of the cold box, and is further connected with an LNG gasifier and a natural gas superheater in sequence; the LNG cold storage system is used for cooling high-pressure air passing through the cold box into liquid air in the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and is stored into a cold storage medium heat fluid storage tank; the LNG cold storage system is also used for warming the high-pressure liquid air passing through the cold box to normal temperature by using the heat absorbed in the energy storage stage in the energy release stage, so that part of the cold storage medium in the LNG cold storage system absorbs the cold of the liquid air and is stored into a cold storage medium cold fluid storage tank; meanwhile, the LNG cold storage system is also used for gasifying and superheating LNG passing through the LNG gasifier and the natural gas superheater every day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and is stored into the cold storage medium cold fluid storage tank. The cold box is provided with a first-stage heat exchanger and a second-stage heat exchanger, and the first-stage heat exchanger and the second-stage heat exchanger are connected in sequence; the LNG cold storage system is provided with a first-stage cold storage medium loop corresponding to the first-stage heat exchanger, and the natural gas superheater is arranged in the first-stage cold storage medium loop and connected to a pipe network through an outlet thereof; The LNG cold storage system is provided with a second-stage cold storage medium loop corresponding to the second-stage heat exchanger, and the LNG gasifier is arranged in the second-stage cold storage medium loop and connected with an LNG storage tank through an inlet thereof and connected with the natural gas superheater through an outlet thereof; The temperature of the liquid air cooled by the cold box is the same as or similar to the temperature of the cold fluid in the second-stage cold storage medium loop; The first-stage cold storage medium loop is composed of a first-stage cold storage medium heat fluid storage tank, a first-stage cold storage medium heat fluid pump, a first-stage cold storage medium cold fluid pump and a first-stage cold storage medium cold fluid storage tank connected in sequence; the first-stage heat exchanger is arranged between the first-stage cold storage medium cold fluid pump and the first-stage cold storage medium heat fluid storage tank, a heat exchange outlet of the first-stage heat exchanger is connected with one inlet of the first-stage cold storage medium cold fluid storage tank, and the natural gas superheater is arranged between the first-stage cold storage medium heat fluid pump and the first-stage cold storage medium cold fluid storage tank, and a heat exchange outlet of the natural gas superheater is connected with the other inlet of the first-stage cold storage medium cold fluid storage tank. The secondary cold storage medium circuit is composed of a secondary cold storage medium thermal fluid storage tank, a secondary cold storage medium thermal fluid pump, a secondary cold storage medium cold fluid pump and a secondary cold storage medium cold fluid storage tank connected in sequence; the second stage heat exchanger is arranged between the secondary cold storage medium cold fluid pump and the secondary cold storage medium thermal fluid storage tank, the heat exchange outlet of the second stage heat exchanger is connected with one inlet of the secondary cold storage medium cold fluid storage tank, and the LNG gasifier is arranged between the secondary cold storage medium thermal fluid pump and the secondary cold storage medium cold fluid storage tank, and the heat exchange outlet of the LNG gasifier is connected with the other inlet of the secondary cold storage medium cold fluid storage tank. 2.The LNG cold energy based liquid medium pressure air energy storage system according to claim 1, wherein, The backflow outlet of the gas-liquid separator in the cold box is connected with the medium-pressure backflow gas inlet of the heat exchanger in the cold box, and the medium-pressure backflow gas outlet of the heat exchanger in the cold box is connected with the inlet of the booster unit in the air compression system or the inlet of the backflow gas compressor in the cold box. The pressure of the medium-pressure backflow gas backflowing from the heat exchanger in the cold box is the same as or close to the pressure of the to-be-mixed gas at the inlet end of the booster unit. 3.The LNG cold energy based liquid medium pressure air energy storage system according to claim 1, wherein, The air compression system is connected with the high-pressure air inlet of the heat exchanger in the cold box, the backflow outlet of the gas-liquid separator in the cold box is connected with the medium-pressure backflow gas inlet of the heat exchanger in the cold box, and the medium-pressure backflow gas outlet of the heat exchanger in the cold box is connected with the air inlet of the heat exchanger in the cold box through the backflow gas compression system.

4. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 3, characterized in that, The backflow gas compression system comprises multiple backflow gas compressors and a backflow gas supercooler arranged between adjacent two backflow gas compressors. The medium-pressure backflow gas outlet of the second stage heat exchanger in the cold box is connected with the inlet of the primary backflow gas compressor, and the outlet of the last backflow gas compressor is connected with the air inlet of the first stage heat exchanger in the cold box, and the gas pressure at the outlet of the last backflow gas compressor is the same as or close to the air pressure at the outlet end of the booster unit.

5. The LNG cold energy utilization based liquid medium-pressure air energy storage system according to claim 1, characterized in that, The cold box is provided with at least one of a heat exchanger and a Rankine cycle system, the heat exchanger is connected with the LNG cold storage system and exchanges heat with the LNG cold storage system, and the heat source of the Rankine cycle system is the heat generated by the air compression system. 6.The liquid medium-pressure air energy storage system based on LNG cold energy utilization of claim 5, wherein, The Rankine cycle system comprises a first Rankine cycle subsystem, a second Rankine cycle subsystem and a third Rankine cycle subsystem, and each Rankine cycle subsystem comprises a Rankine cycle condenser, a Rankine cycle working medium pump, a Rankine cycle turbine and a Rankine cycle evaporator connected in sequence. The Rankine cycle condenser is used for warming the high-pressure liquid air passing through the cold box to normal temperature in the energy releasing stage, and the heat source of the Rankine cycle evaporator is the heat generated by the air compression system.

7. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 6, characterized in that, The Rankine cycle evaporator in the first Rankine cycle subsystem serves as the Rankine cycle condenser in the second Rankine cycle subsystem.

8. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to any one of claims 1 to 7, characterized in that, The air compression system comprises an air filter, a molecular sieve purifier, a multi-stage air compressor and an inter-stage cooler, the inter-stage cooler is connected with the outlet of the corresponding air compressor group, the air filter is connected with the inlet of the first-stage air compressor, the inlet of the molecular sieve purifier is connected with the outlet of the corresponding inter-stage cooler, and the outlet of the molecular sieve purifier is connected with the inlet of the corresponding air compressor; An air pre-cooling system and a gas-liquid separator are arranged between the corresponding inter-stage cooler and the molecular sieve purifier, the air pre-cooling system is used for pre-cooling and washing raw material air, and the gas-liquid separator is used for separating water in the air entering the molecular sieve purifier.

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