Liquid medium-pressure air energy storage system based on LNG (Liquefied Natural Gas) cold energy utilization

Abstract

The invention relates to the technical field of energy storage, and provides a liquid medium-pressure air energy storage system based on LNG (Liquefied Natural Gas) cold energy utilization. The LNG cold storage system is connected with a heat exchange opening of the cold box and used for cooling high-pressure air passing through the cold box into liquid air in the energy storage stage. The energy storage system is further used for rewarming the high-pressure liquid air passing through the cold box to normal temperature in the energy release stage, so that part of cold storage media in the LNG cold storage system absorb the cold energy of the liquid air and store the cold energy; and the LNG cold storage system is further used for gasifying and overheating the LNG passing through the LNG gasifier and the natural gas superheater for 24 hours every day, so that the remaining cold storage medium in the LNG cold storage system absorbs the cold quantity of the LNG and stores the cold quantity of the LNG in the cold storage medium cold fluid storage tank. According to the LNG cold energy recovery system, medium-grade and high-grade cold energy of LNG can be fully recovered, and under the conditions that the same LNG cold energy is supplied and the same efficiency is achieved, the capacity of the system is larger, the structure is simple, and the complexity can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a liquid medium-pressure air energy storage system based on LNG cold energy utilization. Background Art

[0002] The main ways to utilize LNG cold energy include air separation, cold storage, dry ice production, low-temperature crushing, etc. Due to the limitations of downstream user demand, the above-mentioned cold energy utilization industry is difficult to achieve large-scale production; although cold energy power generation technology is not limited by production scale, the recovery rate of LNG cold energy is low. During the recovery process, seawater is required as a heat source to heat the intermediate medium for power generation, which causes certain "cold pollution" to the environment. In addition, cold energy power generation technology requires a relatively stable LNG supply, which is difficult to achieve.

[0003] As a new type of large-scale long-term energy storage technology, liquid air energy storage is not restricted by geographical factors and has a wide operating 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; it can also be used to reduce the compressor inlet temperature and reduce the compressor power consumption; the realized liquid air energy storage system has a high system efficiency, which is conducive to the large-scale promotion of liquid air energy storage technology.

[0004] Therefore, in order to achieve a higher system efficiency of the liquid air energy storage system, LNG cold energy is usually used to cool the compressor intake air to fully reduce the compression power consumption. In this process, the heat generated by the original system compressed air is lost, and the air can only be heated by seawater or medium and low-grade heat sources that may exist near the station during the energy release stage, which will still cause "cold pollution" to the environment. The above scheme requires that the intake temperature of each stage of compressor is extremely low, and it is more difficult to dehydrate and decarbonize the air before the first-stage compressor. At this time, if the supply 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 used to supplement the cold box part of the liquid air energy storage system. However, due to the different operating temperature ranges of the cold storage medium on the LNG cold energy side and the cold 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, and the introduction of LNG cold energy has not significantly increased the liquid air production rate. In addition, due to the difference in temperature zones, multiple storage tanks need to be arranged for cold storage, which increases the complexity of the system, affects the economic performance of the energy storage system, and is not conducive to the promotion of liquid air energy storage technology coupled with LNG cold energy utilization. To this end, an embodiment of the present invention provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization. Summary of the invention

[0006] The present invention provides a liquid medium-pressure air energy storage system based on the utilization of LNG cold energy, which is used to solve the above-mentioned technical defects in the prior art and can fully recover the medium and high-grade cold energy of LNG. Under the conditions of supplying the same LNG cold amount and achieving the same efficiency, the liquid medium-pressure air energy storage system provided by the present invention has a larger capacity, a simple system structure, and can reduce the complexity, and can also avoid the generation of "cold pollution".

[0007] The present invention provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, including an air compression system, an expansion power generation system, a liquid air storage tank, a cold box and an LNG cold storage system; The liquid air storage tank is used to store medium-pressure liquid air; The air compression system is connected to the high-pressure air inlet of the cold box, the medium-pressure liquid air outlet of the cold box is connected to the inlet of the liquid air storage tank, the outlet of the liquid air storage tank is connected to the high-pressure liquid air inlet of the cold box, and the expansion power generation system is connected to the normal-temperature air outlet of the cold box; The LNG cold storage system is connected to the heat exchange port of the cold box, and the LNG cold storage system is also connected to the LNG vaporizer and the natural gas superheater in sequence; the LNG cold storage system is used to cool the high-pressure air passing through the cold box into liquid air during the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and stores it in the cold storage medium hot fluid storage tank; the LNG cold storage system is also used to use the heat absorbed during the energy storage stage to restore the high-pressure liquid air passing through the cold box to normal temperature during 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 stores it in the cold storage medium cold fluid storage tank; at the same time, the LNG cold storage system is also used to vaporize and superheat the LNG passing through the LNG vaporizer and the natural gas superheater 24 hours a day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and stores it in the cold storage medium cold fluid storage tank.

[0008] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, 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 primary cold storage medium loop corresponding to the first-stage heat exchanger, the natural gas superheater is provided in the primary cold storage medium loop, and the outlet of the natural gas superheater is connected to the pipeline network; The LNG cold storage system is provided with a secondary cold storage medium loop corresponding to the second-stage heat exchanger, the LNG vaporizer is provided in the secondary cold storage medium loop, 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; 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.

[0009] 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 is composed 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; the first-stage heat exchanger is arranged 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 an inlet of the primary cold storage medium cold fluid storage tank, and the natural gas superheater is arranged 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 another inlet of the primary cold storage medium cold fluid storage tank; 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 which are connected end to end in sequence; the second-stage heat exchanger is arranged 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 an inlet of the secondary cold storage medium cold fluid storage tank; the LNG gasifier is arranged 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 gasifier is connected to another inlet of the secondary cold storage medium cold fluid storage tank.

[0010] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the backflow outlet of the gas-liquid separator in the cold box is connected to 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 to 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 counterflow gas that flows back from the heat exchanger in the cold box is the same as or close to the pressure of the gas to be mixed at the inlet end of the booster unit.

[0011] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the air compression system is connected to the high-pressure air inlet of the heat exchanger in the cold box, the backflow outlet of the gas-liquid separator is connected to 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 to the air inlet of the heat exchanger in the cold box through the backflow gas compression system.

[0012] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the backflow gas compression system includes a multi-stage backflow gas compressor and a backflow gas subcooler arranged between two adjacent stages of the backflow gas compressors; The medium-pressure backflow gas outlet of the second-stage heat exchanger in the cold box is connected to the inlet of the first-stage backflow gas compressor, and the outlet of the last-stage backflow gas compressor is connected to the air inlet of the first-stage heat exchanger in the cold box. The gas pressure at the outlet of the last-stage backflow gas compressor is the same as or close to the air pressure at the outlet end of the booster unit.

[0013] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, at least one of a heat exchanger and a Rankine cycle system is provided in the cold box, the heat exchanger is connected to the LNG cold storage system, and the LNG cold storage system performs heat exchange for it; the heat source of the Rankine cycle system is the heat generated by the air compression system.

[0014] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the Rankine cycle system includes a first Rankine cycle subsystem, a second Rankine cycle subsystem and a third Rankine cycle subsystem; each Rankine cycle subsystem includes a Rankine cycle condenser, a Rankine cycle working fluid pump, a Rankine cycle turbine and a Rankine cycle evaporator connected end to end in sequence; The Rankine cycle condenser is used to restore the high-pressure liquid air that has passed through the cold box to room temperature during the energy release stage, and the heat source of the Rankine cycle evaporator is the heat generated by the air compression system.

[0015] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the Rankine cycle evaporator in the first Rankine cycle subsystem serves as the Rankine cycle condenser in the second Rankine cycle subsystem.

[0016] According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention, the air compression system includes an air filter, a molecular sieve purifier, a multi-stage air compressor and an interstage cooler, the interstage cooler is connected to the outlet of the corresponding air compressor group, the air filter is connected to the inlet of the first-stage air compressor, the inlet of the molecular sieve purifier is connected to the outlet of the corresponding interstage cooler, and the outlet of the molecular sieve purifier is connected to the inlet of the corresponding air compressor; An air precooling system and a gas-liquid separator are provided between the corresponding interstage cooler and the molecular sieve purifier. The air precooling system is used for precooling and washing the raw air, and the gas-liquid separator is used for separating the moisture in the air entering the molecular sieve purifier.

[0017] The liquid medium-pressure air energy storage system based on LNG cold energy utilization provided by the present invention increases the storage pressure of the liquid-to-air storage tank and increases the liquefaction rate of the medium-pressure air, so that the liquid-to-air storage tank is used to store medium-pressure liquid air. The LNG cold storage system is used to cool the high-pressure air that has passed through the cold box into liquid air during the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and stores it in the cold storage medium hot fluid storage tank; the LNG cold storage system is also used to restore the high-pressure liquid air that has passed through the cold box to room temperature during the energy release stage by utilizing the heat absorbed during the energy storage stage, so that a part of the cold storage medium in the LNG cold storage system absorbs the cold of the liquid air and stores it in the cold storage medium cold fluid storage tank; at the same time, the LNG cold storage system is also used to vaporize and overheat the LNG that has passed through the LNG vaporizer and the natural gas superheater 24 hours a day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and stores it in the cold storage medium cold fluid storage tank.

[0018] With this arrangement, the LNG cold energy recovered by the LNG cold storage system is of the same quality as the cold energy of the liquid air in the energy release stage, and all of them are used in the high-pressure air liquefaction process in the energy storage stage. Given that the liquid air temperature is relatively high at this time, the liquid air storage pressure is increased to maintain a relatively high air liquefaction rate after the throttle valve, thereby reducing the power consumption of the reflux gas recompression process. The medium and high-grade cold energy of LNG can be fully recovered. Under the conditions of supplying the same LNG cold capacity and achieving the same efficiency, the liquid medium-pressure air energy storage system provided by the present invention has a larger capacity. Furthermore, the energy storage process and the energy release process of the liquid medium-pressure air energy storage system provided by the present invention can be deeply decoupled. During the energy release stage, the liquid air can be raised to a higher pressure by the liquid air pump, which greatly improves the work potential of a unit of liquid air. The heat stored in the energy storage stage is all used for the air expansion work in the energy release stage. During the energy release stage, there is no need to absorb ambient heat for heating the air, thereby avoiding "cold pollution" to the local environment (i.e., requiring ambient heat). Under the premise of no external medium or low-grade heat source intervention, a high-efficiency, large-capacity liquid air energy storage system can be realized, which is conducive to the large-scale promotion of liquid air energy storage technology in the utilization of LNG cold energy.

[0019] In addition, since the cold storage media on the LNG cold energy side and the cold box side have the same operating 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 THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 1 of the present invention.

[0022] Figure 2 It is a schematic diagram of a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 2 of the present invention.

[0023] Figure 3 It is a partial schematic diagram of a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 3 of the present invention.

[0024] Reference numerals: 1. Air filter; 2. Air compressor unit; 3. First-stage intercooler; 4. Molecular sieve purifier; 5. Booster unit; 6. Second-stage intercooler; 7. Air subcooler; 8. Low-temperature booster unit; 9 / 17. First-stage heat exchanger; 10 / 16. Second-stage heat exchanger; 11. Liquid expander; 12. Low-temperature 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. ​​Secondary cold storage medium thermal fluid pump; 30. Secondary cold storage medium thermal fluid storage tank; 31. Primary cold storage medium thermal fluid pump; 32. Primary cold storage medium thermal fluid storage tank; 33. Primary cold storage medium cold fluid pump; 34. Primary cold storage medium cold fluid storage tank; 35. Natural gas superheater; 36. LNG gasifier; 37. Secondary cold storage medium cold fluid pump; 38. Secondary cold storage medium cold fluid storage tank; 39. Primary reverse flow gas compressor; 40. Reverse flow gas supercooler; 41. Secondary reverse flow gas compressor; 50. Reverse flow gas compression system; 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; ORC2, second Rankine cycle subsystem; 71, second Rankine cycle working fluid pump; 72, second Rankine cycle turbine; 73, second Rankine cycle evaporator; 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

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0027] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean 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, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0028] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. 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 embodiments of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0029] In the existing liquid air energy storage system coupled with LNG cold energy utilization, in order to fully reduce the power consumption of the compressor unit, the intake air of each compressor is usually cooled to an extremely low temperature, and the number of compressor units is increased. Although this setting is conducive to improving the efficiency of the liquid air energy storage system, the difficulty and cost of removing water and carbon dioxide from air in a low-temperature environment increase. In addition, the heat generated during the air compression process is used to indirectly heat LNG. During the energy release stage, there is no available heat inside the system to superheat the air to generate power. The air can only be expanded by superheating the ambient heat. The shaft work per unit of air is small, and the system has the characteristics of high efficiency and low power generation. At the same time, it forms "cold pollution" to the environment in the process of consuming ambient heat. In addition, when the liquid air energy storage system has too many compression stages and the compression temperature is too low, the temperature difference between the inlet and outlet air of each 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 quantitative LNG cold energy resources, the amount of air available for compression is small, which ultimately leads to the capacity of the energy storage system being greatly affected by the amount of LNG cold energy. In the scenario of LNG cold energy utilization, liquid air energy storage technology is difficult to achieve large-scale application. Since traditional solutions do not fully utilize LNG cold energy, when a large amount of low-grade LNG cold energy is exported from the back end of the energy storage system, a situation of "oversupply" of cold energy is formed for local industries. The remaining cold energy can only be discharged into the environment, further causing "cold pollution" to the environment.

[0030] In addition, when the cold box part of the liquid air energy storage system is supplemented with LNG cold energy, the problem that the temperature of the cold energy required for the air liquefaction process in the energy storage stage is lower than the temperature of the cold energy that LNG can provide is ignored. The cold energy provided by LNG can only supplement the cold energy of some temperature zones for the energy storage system, which means that the higher-quality cold energy required for the air liquefaction process is still provided by the liquid air in the energy release stage. Therefore, the liquid air in the energy release stage cannot be pressurized to a higher pressure, and the cold energy exergy of the liquid air needs to be transferred to the energy storage stage in the form of temperature exergy. It is difficult to deeply decouple the system energy storage and energy release processes. Therefore, the existing cold box part supplemented with LNG cold energy has little improvement on the system performance. Moreover, even if the cold storage working fluid is the same, it is difficult to integrate the multiple cold storage units in the coupling system due to the difference in the working temperature range. The increase in the number of cold storage medium storage tanks leads to an increase in investment costs, 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. To this end, an embodiment of the present invention provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization.

[0031] Figure 1 It is a schematic diagram of a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 1 of the present invention.

[0032] See also Figure 1An embodiment of the present invention provides a liquid medium-pressure air energy storage system based on the utilization of LNG cold energy. The liquid medium-pressure air energy storage system based on the utilization of LNG cold energy includes an air compression system, an expansion power generation system, a liquid air storage tank 14, a cold box and an LNG cold storage system.

[0033] The liquid air storage tank 14 can be a tank body in the form of a mother-and-child tank, a cryogenic spherical tank, a vacuum tank, etc. 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 to store medium-pressure liquid air.

[0034] The air compression system includes an air filter 1, a molecular sieve purifier 4, a multi-stage air compressor and an interstage cooler; the air filter 1 is used to remove dust and other impurities in the ambient air. The molecular sieve purifier 4 is used to remove moisture, CO2 and other hydrocarbons in the air. During the air compression process, the molecular sieve purifier 4 removes moisture, CO2 and other hydrocarbons from the air passing through the cold box, which can prevent them from solidifying in the low temperature environment of the cold box and blocking the heat exchange channel of the cold box.

[0035] The number of air compressors and interstage coolers are set in a one-to-one correspondence. The air compressor can be one-stage, two-stage, three-stage, etc. The air compressor is used to compress air. The interstage cooler is connected to the heat storage system composed of the air cooler 24, the cold water tank 25, the cold water pump 26, the hot water tank 27 and the hot water pump 28, and is used to collect the heat generated by the air compression process of the air compression system during the energy storage stage. Among them, as the number of stages of the air compressor increases, the heat storage temperature of the interstage cooler decreases accordingly.

[0036] For example, a three-stage air compressor is used in the embodiment of the present invention, namely, a primary air compressor, a secondary air compressor and a tertiary air compressor, wherein the primary air compressor is an air compressor unit 2, and the ambient air with dust and impurities removed enters the air compressor unit 2 and is pressurized to a medium pressure. The secondary air compressor is a booster unit 5, which is cooled by cold water, and the air from which water and carbon dioxide are removed by the molecular sieve purifier 4 is mixed with the backflow gas and enters the booster unit 5 for pressurization. The tertiary air compressor is a low-temperature booster unit 8, and the air that is cooled to a low temperature by cold water and the cold storage medium of the LNG cold storage system successively enters the low-temperature booster unit 8 and is pressurized to a high pressure.

[0037] Correspondingly, a first-stage inter-stage cooler 3 is connected between the first-stage air compressor and the second-stage air compressor, a second-stage inter-stage cooler 6 is connected between the second-stage air compressor and the third-stage air compressor, and an air cooler for heat exchange with the LNG cold storage system is also connected between the second-stage inter-stage cooler 6 and the third-stage air compressor. Of course, the embodiment of the present invention can also be provided with a four-stage air compressor group or more according to the use requirements.

[0038] The expansion power generation system uses the stored liquid air to expand and generate electricity. The expansion power generation system includes multiple groups 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 specific number of stages is selected according to actual use.

[0039] For example, a three-stage air expansion unit is used in the embodiment of the present invention, namely, a primary air expansion machine 19, a secondary air expansion machine 21 and a tertiary air expansion machine 23, a primary heater 18 is connected between the heat exchanger of the cold box and the primary air expansion machine 19, a secondary heater 20 is connected between the primary air expansion machine 19 and the secondary air expansion machine 21, and a tertiary heater 22 is connected between the secondary air expansion machine 21 and the tertiary air expansion machine 23. Of course, the embodiment of the present invention can also be provided with four or more stages of air expansion machines according to the use requirements.

[0040] Among them, the low-temperature booster unit 8 of the air compression system is connected to the high-pressure air inlet of the cold box, the medium-pressure liquid air outlet of the cold box is connected to the inlet of the liquid air storage tank 14, and the outlet of the liquid air storage tank 14 is connected to the liquid air inlet of the cold box through the liquid air pump 15. 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, and the expansion power generation system is connected to the normal temperature air outlet of the cold box.

[0041] The LNG cold storage system is connected to the heat exchange port of the cold box, and the LNG cold storage system is also connected to the LNG vaporizer 36 and the natural gas superheater 35 in sequence. The LNG cold storage system is used to cool the high-pressure air passing through the cold box into liquid air during the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and stores it in the cold storage medium hot fluid storage tank; the LNG cold storage system is also used to use the heat absorbed during the energy storage stage to reheat the high-pressure liquid air passing through the cold box to room temperature during the energy release stage, so that part of the cold storage medium in the hot fluid storage tank of the LNG cold storage system absorbs cold energy and stores it 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 vaporizer 36 and the natural gas superheater 35 24 hours a day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the LNG cold energy and stores it in the cold storage medium cold fluid storage tank, that is, the remaining cold storage medium needs to continuously recover the cold energy generated by the LNG regasification process for 24 hours and then store it in the cold storage medium cold fluid storage tank.

[0042] It should be noted that the cold box is provided with a first-stage heat exchanger 9 / 17 and a second-stage heat exchanger 10 / 16, which are connected in series to form a continuous processing line, and the LNG cold storage system is provided with a first-stage cold storage medium loop corresponding to the first-stage heat exchanger 9 / 17, which is used to exchange heat for the first-stage heat exchanger 9 / 17, and the natural gas superheater 35 is provided in the first-stage cold storage medium loop, and the outlet of the natural gas superheater 35 is connected to the pipeline network. Among them, the first-stage cold storage medium can be an alcohol-water solution obtained by mixing one or more of methanol, ethylene glycol, and propylene glycol with water in different proportions.

[0043] The LNG cold storage system is provided with a secondary cold storage medium loop corresponding to the second stage heat exchanger 10 / 16, and the secondary cold storage medium loop is used for heat exchange for the second stage heat exchanger 10 / 16, and the LNG vaporizer 36 is provided in the secondary cold storage medium loop, the inlet of the LNG vaporizer 36 is connected to the LNG storage tank, and the outlet of the LNG vaporizer 36 is connected to the inlet of the natural gas superheater 35. Among them, 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 loop.

[0044] Specific as Figure 1 As shown, during the low electricity consumption period, the liquid medium-pressure air energy storage system based on LNG cold energy utilization operates in energy storage mode. The normal temperature and pressure air in the environment is removed from dust and impurities by the air filter 1, pressurized to medium pressure by the air compressor unit 2, then cooled by cold water, and removed from water and carbon dioxide by the molecular sieve purifier 4. The air and the backflow gas are mixed and enter the booster unit 5 for pressurization, and then are cooled to low temperature by cold water and the cold storage medium of the LNG cold storage system in turn, and enter the low-temperature booster unit 8 for pressurization to high pressure. The high-pressure air then enters the first stage exchange unit of the cold box. The heat exchangers 9 / 17 and the second-stage heat exchangers 10 / 16 are successively cooled and liquefied by the cold fluid of the first-stage cold storage medium and the cold fluid of the second-stage cold storage medium 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 low-temperature throttle valve 12 to form a gas-liquid mixture, which is separated into gas and liquid through the gas-liquid separator 13. The medium-pressure liquid air enters the liquid air storage tank 14 for storage. The medium-pressure gaseous air is returned to the heat exchangers of each stage of the cold box as reflux gas to supplement cooling. The reflux gas after supplementing cooling then flows back to the front of the booster unit 5 to mix with the medium-pressure air.

[0045] The heat generated by the air compressor unit 2 and the booster unit 5 during the air compression process is taken away by the high-pressure cold water, and the formed high-pressure and high-temperature hot water is stored in the hot water tank 27 .

[0046] Specific as Figure 1As shown, during the peak period of electricity consumption, the liquid medium-pressure air energy storage system based on the utilization of LNG cold energy operates in the energy release mode, and the low-temperature medium-pressure liquid air is pressurized to high pressure by the liquid air pump 15, and enters the second-stage heat exchanger 10 / 16 and the first-stage heat exchanger 9 / 17 of the cold box in turn, absorbs the heat of the hot fluid of the secondary cold storage medium and the primary cold storage medium of the LNG cold storage system, vaporizes and reheats to room temperature, and a part of the cold storage medium in the LNG cold storage system absorbs the cold energy of the liquid air and stores it in the cold storage medium cold fluid storage tank. At the same time, the LNG cold storage system is also used to vaporize and superheat the LNG that passes through the LNG vaporizer 36 and the natural gas superheater 35 24 hours a day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold energy of the LNG and stores it in the cold storage medium cold fluid storage tank. Then it enters the multi-stage air expander, is heated by the high-pressure hot water stored in the hot water tank 27, and the air expands to output shaft work to the outside, driving the generator to generate electricity and transmit it to the power grid.

[0047] The air pressure entering the first stage heat exchanger 9 / 17 of the cold box is in the range of 4-10 MPa.A. The pressure of the high pressure liquid air after the liquid air pump 15 is in the range of 4-25 MPa.A.

[0048] It can be understood that the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in the embodiment of the present invention increases the storage pressure of the liquid air storage tank 14 to increase the medium-pressure air liquefaction rate, so that the liquid air storage tank 14 is used to store medium-pressure liquid air, and the LNG cold storage system is used to cool the high-pressure air passing through the cold box into liquid air during the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and stores it in the cold storage medium hot fluid storage tank; the LNG cold storage system is also used to use the heat absorbed during the energy storage stage to restore the high-pressure liquid air passing through the cold box to room temperature during 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 stores it in the cold storage medium cold fluid storage tank; at the same time, the LNG cold storage system is also used to continuously vaporize and superheat the LNG passing through the LNG vaporizer and the natural gas superheater 24 hours a day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and stores it in the cold storage medium cold fluid storage tank.

[0049] With this arrangement, the LNG cold energy recovered by the LNG cold storage system is of the same quality as the cold energy of the liquid air in the energy release stage, and all of them are used for the liquefaction of liquid high-pressure air. Given that the temperature of the liquid air is relatively high at this time, the liquid air storage pressure is increased to maintain a relatively high air liquefaction rate, thereby reducing the power consumption of the reflux gas recompression process. The medium and high-grade cold energy of LNG can be fully recovered. Under the conditions of supplying the same LNG cold capacity and achieving the same efficiency, the capacity of the liquid medium-pressure air energy storage system provided by the present invention is larger. Furthermore, the energy storage process and the energy release process of the liquid medium-pressure air energy storage system provided by the present invention can be deeply decoupled. During the energy release stage, the liquid air can be raised to a higher pressure by the liquid air pump, which greatly improves the work potential of a unit of liquid air. The heat stored in the energy storage stage is all used for the air expansion work in the energy release stage. During the energy release stage, there is no need to absorb ambient heat for heating the air, thereby avoiding "cold pollution" to the local environment (i.e., requiring ambient heat). Under the premise of no external medium or low-grade heat source intervention, a high-efficiency, large-capacity liquid air energy storage system can be realized, which is conducive to the large-scale promotion of liquid air energy storage technology in the utilization of LNG cold energy.

[0050] In addition, since the cold storage media on the LNG cold energy side and the cold box side have the same operating 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.

[0051] In addition, since the pressure of the liquid air stored in the liquid air storage tank 14 is medium pressure, generally higher than 0.6 MPa.A, although the equipment cost of the liquid air storage tank 14 is increased, the system can achieve a higher air liquefaction rate under poor medium cooling quality. In addition, the air compression pressure in the system of the present invention can be greatly reduced, and the air compression pressure needs to be higher than the critical pressure of the air. The pressure of the first and second stage heat exchangers in the cold box is reduced, and the difficulty of manufacturing the equipment is reduced.

[0052] In some embodiments of the present invention, 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 which are connected end to end in sequence; the first-stage heat exchanger 9 / 17 is arranged between the first-stage cold storage medium cold fluid pump 33 and the first-stage cold storage medium hot fluid storage tank 32, and the heat exchange outlet of the first-stage heat exchanger 9 / 17 is connected to an inlet of the first-stage cold storage medium cold fluid storage tank 34; the natural gas superheater 35 is arranged between the first-stage cold storage medium hot fluid pump 31 and the first-stage cold storage medium cold fluid storage tank 34, and the heat exchange outlet of the natural gas superheater 35 is connected to another inlet of the first-stage cold storage medium cold fluid storage tank 34.

[0053] The secondary cold storage medium circuit is composed of a secondary cold storage medium hot fluid storage 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 storage tank 38 which are connected end to end 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 storage tank 30, and the heat exchange outlet of the second-stage heat exchanger 10 / 16 is connected to an inlet of the secondary cold storage medium cold fluid storage tank 38, and the LNG vaporizer 36 is arranged between the secondary cold storage medium hot fluid pump 29 and the secondary cold storage medium cold fluid storage tank 38, and the heat exchange outlet of the LNG vaporizer 36 is connected to another inlet of the secondary cold storage medium cold fluid storage tank 38.

[0054] Equivalently, the embodiment of the present invention maintains the same operating temperature range of the cold storage medium on the cold energy side of the LNG cold storage system and the cold storage side of the cold box, thereby merging the cold energy side of the LNG cold storage system and the cold storage side of the cold box, thereby reducing the number of storage tanks in the energy storage system, reducing the operating cost of the energy storage system, and simplifying the structural setting of the energy storage system.

[0055] This is equivalent to the case where, during the energy storage stage, the LNG cold storage system cools the high-pressure air that has passed through the cold box into liquid air, and cools the liquefied air to a temperature close to the temperature of the cold fluid in the secondary cold storage medium loop in the LNG cold storage system, that is, the temperature of the liquefied air before entering the liquid expansion machine 11 is higher. That is, during the energy storage stage, when the LNG cold storage system cools the high-pressure air that has passed through the cold box into liquid air, the temperature of the cooled liquid air is the same as or similar to the temperature of the cold fluid in the secondary cold storage medium loop in the LNG cold storage system, so that the temperature zones of the liquid air energy storage system and the LNG cold storage system are unified, and the medium and high-grade LNG cold energy liquefied air can be fully recovered, greatly increasing the energy storage capacity. By adjusting the storage pressure of the liquid air storage tank 14 to medium pressure, the liquefaction rate of air can be increased, and the liquid air energy storage system can better adapt to LNG cold energy, and the recovery of medium and high-grade LNG cold energy is better than that of the traditional liquid air energy storage system coupled with LNG cold energy utilization. Therefore, the liquid air energy storage system provided by the present invention can liquefy more air under the premise of quantitative LNG cold energy, so as to effectively increase the capacity of the liquid air energy storage system.

[0056] In addition, since the quality of the cold energy of liquid air recovered by the liquid air energy storage system during the energy release process is the same as the quality of the cold energy recovered during 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 have achieved deep decoupling. In this way, during 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, and recover the heat generated by the air compression process in the energy storage stage more fully. The air cooler 24 of the conventional cold storage system releases less cold to the environment, avoiding the formation of "cold pollution" to the local environment.

[0057] Compared with the traditional liquid air energy storage system, the liquid medium-pressure air energy storage system provided by the embodiment of the present invention has a greatly improved power generation capacity. And because the larger the energy storage capacity of the system, the lower the unit capacity cost of the system, the liquid medium-pressure air energy storage system provided by the embodiment of the present invention has better economic performance.

[0058] In some embodiments of the present invention, the reflux outlet of the gas-liquid separator 13 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. While recovering the medium-pressure reflux gas, it can be considered that the refrigeration cycle composed of the reflux gas loop can be used to supplement the cold capacity of the heat exchanger in the cold box, further improving the liquefaction rate of the air.

[0059] Among them, the pressure of the medium-pressure reflux gas entering the compressor unit is the same as or close to the pressure of the gas to be mixed at the inlet end of the compressor unit, that is, the pressure of the medium-pressure reflux gas flowing back from the heat exchanger in the cold box is the same as or close to the pressure of the gas to be mixed at the inlet end of the booster unit, thereby avoiding changes in the pressure of the medium-pressure air after mixing.

[0060] When the high-pressure liquid air is expanded and throttled to medium pressure through the liquid expansion machine 11 and the low-temperature throttle valve 12, the medium-pressure backflow gas generated is directly mixed with the medium-pressure air at the rear end of the air compressor unit 2. In order to avoid changes in the pressure of the medium-pressure air after mixing, it is necessary to limit the air pressure at the outlet of the air compressor unit 2 so that it is the same or close to the pressure of the medium-pressure backflow gas before mixing. However, such a setting is not conducive to system parameter optimization, and the flexibility of the system is poor. To this end, Example 2 of the present invention provides a liquid medium-pressure air energy storage system based on LNG cold energy utilization, which is improved based on a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 1 of the present invention.

[0061] Figure 2 It is a schematic diagram of a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 2 of the present invention.

[0062] See also Figure 2 On the basis of the above-mentioned Example 1, the difference from the liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in the above-mentioned Example 1 is that the air compression system is connected to the high-pressure air inlet of the first-stage heat exchanger 9 / 17, the backflow outlet of the gas-liquid separator 13 is connected to 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 to the air inlet of the first-stage heat exchanger 9 / 17 through the backflow gas compression system 50.

[0063] In the embodiment of the present invention, a backflow gas compression system 50 is added 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 to realize the recovery of the medium-pressure backflow gas. The outlet pressure of the air compressor unit is no longer restricted, the number of booster unit stages can be reduced, and the pressure ratio, heat storage temperature and heat storage capacity of each stage of the compressor can be flexibly adjusted.

[0064] Continue reading Figure 2 In some embodiments of the present invention, the backflow gas compression system 50 includes a multi-stage backflow gas compressor and a backflow gas subcooler 40 disposed between two adjacent backflow gas compressors, wherein in the embodiment of the present invention, a first-stage backflow gas compressor 39 and a second-stage backflow gas compressor 41 are provided, and a backflow gas subcooler 40 is connected between the first-stage backflow gas compressor 39 and the second-stage backflow gas compressor 41, and the backflow gas subcooler 40 is connected to the first-stage cold storage medium of the LNG cold storage system to cool the backflow gas and reduce the power consumption of the backflow gas compression system 50. The first-stage cold storage medium of the LNG cold storage system simultaneously exchanges heat with the first-stage heat exchanger 9 / 17 and the backflow gas subcooler 40.

[0065] The medium-pressure backflow gas outlet of the second-stage heat exchanger 10 / 16 is connected to the inlet of the first-stage backflow gas compressor 39, and the outlet of the second-stage backflow gas compressor 41 is connected to the air inlet of the first-stage heat exchanger 9 / 17. The backflow gas is compressed to the same pressure as the forward flow air through the backflow gas compression system 50, and after mixing, it is sent to the first-stage heat exchanger 9 / 17 of the cold box.

[0066] like Figure 2 As shown, during the low electricity consumption period, the liquid medium-pressure air energy storage system based on the utilization of LNG cold energy operates in the energy storage mode. After the normal temperature and pressure air in the environment is removed from dust and impurities by the air filter 1, the surplus electric energy of the power grid drives the three-stage air compressor to work, and the air is compressed and boosted by the three-stage compression with an interstage cooler, that is, the air is pressurized to medium pressure by the air compressor unit 2, and then cooled by the cold water in the first-stage interstage cooler 3. The cooled medium-pressure air is removed from water and carbon dioxide by the molecular sieve purifier 4, enters the booster unit 5 for pressurization, and is successively cooled to low temperature by the cold water in the second-stage interstage cooler 6 and the first-stage cold storage medium in the air supercooler 7. The low-temperature air enters the low-temperature booster unit 8 for pressurization to high pressure.

[0067] The high-pressure air then enters the first-stage heat exchanger 9 / 17 and the second-stage heat exchanger 10 / 16 of the cold box in sequence. At the same time, the first-stage cold storage medium and the second-stage cold storage medium of the LNG cold storage system successively pass through the first-stage heat exchanger 9 / 17 and the second-stage heat exchanger 10 / 16 to recover the compression heat, so that the compressed air is cooled and liquefied by the cold fluid of the first-stage cold storage medium and the cold fluid of the second-stage cold storage medium. The high-pressure liquid air is expanded and throttled to medium pressure through the liquid expander 11 and the low-temperature throttle valve 12 to form a gas-liquid mixture, and the gas-liquid mixture is separated into gas and liquid through the gas-liquid separator 13. The separated medium-pressure liquid air enters the liquid air storage tank 14 for storage, and the separated medium-pressure gaseous air serves as the backflow gas, and the backflow gas returns to the second-stage heat exchanger 10 / 16 of the cold box for supplementary cooling. The backflow gas discharged from the second-stage heat exchanger 10 / 16 passes through the backflow gas compression system 50 composed of a first-stage backflow gas compressor 39, a backflow gas subcooler 40 and a second-stage backflow gas compressor 41 in sequence to adjust the pressure and mix with the high-pressure air pressurized by the low-temperature booster unit 8. The mixed high-pressure air enters the first-stage heat exchanger 9 / 17 to continue liquefaction.

[0068] like Figure 2 As shown, during the peak period of electricity consumption, the liquid medium-pressure air energy storage system based on the utilization of LNG cold energy operates in the 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 enters the second-stage heat exchanger 10 / 16 and the first-stage heat exchanger 9 / 17 of the cold box in turn, and absorbs the heat of the hot fluid of the secondary cold storage medium and the primary cold storage medium of the LNG cold storage system in turn to vaporize and reheat to room temperature (i.e., heated to near ambient temperature). The room-temperature air absorbs the heat in the high-pressure and high-temperature hot water generated during the compression process and is superheated to high temperature, and then enters the first-stage air expander 19, the second-stage air expander 21 and the third-stage air expander 23 in turn. The multi-stage air expander outputs shaft power to the outside, drives the generator to generate electricity and transmits it to the power grid, achieving the purpose of peak shaving and valley filling.

[0069] During the energy storage operation, the heat generated by the air compressor unit 2 and the booster unit 5 during the air compression process is pumped away by the high-pressure cold water stored in the cold water tank 25 by the cold water pump 26, forming high-pressure and high-temperature hot water stored in the hot water tank 27. During the energy release process, the high-pressure and high-temperature hot water generated during the compression process and stored in the hot water tank 27 is pumped by the hot water pump 28 to the first-stage heater 18, the second-stage heater 20 and the third-stage heater 22 located between the multi-stage air expanders for heating.

[0070] In addition, during the energy storage operation, the heated secondary cold storage medium discharged from the second-stage heat exchanger 10 / 16 is pumped to the secondary cold storage medium hot fluid storage tank 30 for storage via the secondary cold storage medium hot fluid pump 29, and the heated primary cold storage medium discharged from the first-stage heat exchanger 9 / 17 is pumped to the primary cold storage medium hot fluid storage tank 32 for storage via the primary cold storage medium hot fluid pump 31. During the energy release process and LNG regasification process, the primary cold storage medium and the secondary cold storage medium of the LNG cold storage system recover all the cold energy of the liquid air and LNG, the cooled secondary cold storage medium discharged from the second-stage heat exchanger 10 / 16 enters the secondary cold storage medium cold fluid storage tank 38 via the corresponding pump, and the cooled primary cold storage medium discharged from the first-stage heat exchanger 9 / 17 enters the primary cold storage medium cold fluid storage tank 34 via the corresponding pump, so as to be used for cooling the compressed air during the energy storage process.

[0071] Figure 3 It is a partial schematic diagram of a liquid medium-pressure air energy storage system based on LNG cold energy utilization provided in Example 3 of the present invention.

[0072] Continue reading Figure 1 , Figure 2 , and also see 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 to the LNG cold storage system, and the LNG cold storage system performs heat exchange for it. The heat source of the Rankine cycle system is the heat generated by the air compression system.

[0073] In other words, the cold box can be provided with multiple sets of heat exchangers, which are connected to the cold storage system for heat exchange. Multiple sets of Rankine cycle systems can also be provided in the cold box, and the heat generated by the air compression system during the air compression process is used for heat exchange.

[0074] In addition, a heat exchanger and a Rankine cycle system can be set in the cold box. The heat exchanger uses the cold storage medium of the LNG cold storage system for heat exchange. In the energy storage stage of the system, the cold capacity of the first and second cold storage medium cold fluids of the LNG cold storage system comes from LNG and liquid medium-pressure air in the energy release stage. The Rankine cycle system uses the heat generated by the air compression system during the air compression process for heat exchange.

[0075] Continue reading Figure 3 In some embodiments of the present invention, the Rankine cycle system includes a first Rankine cycle subsystem ORC1, a second Rankine cycle subsystem ORC2 and a third Rankine cycle subsystem ORC3; each Rankine cycle subsystem includes a Rankine cycle condenser, a Rankine cycle working fluid pump, a Rankine cycle turbine and a Rankine cycle evaporator connected end to end in sequence.

[0076] The Rankine cycle condenser is used to restore the high-pressure liquid air that has passed through the cold box to room temperature during the energy release stage. The heat source of the Rankine cycle evaporator is the heat generated by the air compression system.

[0077] The embodiment of the present invention utilizes the cold energy of liquid air to generate electricity, and no longer utilizes the cold storage unit to recover this part of cold energy. The cold energy required for 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 system energy storage capacity. Although this setting reduces the system capacity, the increase in cold energy power generation helps to further improve the system efficiency.

[0078] Continue reading Figure 3 In some embodiments of the present invention, the Rankine cycle evaporator in the first Rankine cycle subsystem ORC1 serves as the Rankine cycle condenser in the second Rankine cycle subsystem ORC2.

[0079] This is equivalent to that some components in the first Rankine cycle subsystem ORC1 and the second Rankine cycle subsystem ORC2 are shared with each other.

[0080] This is equivalent to improving the energy release stage of the liquid medium-pressure air energy storage system based on the above-mentioned embodiments 1 and 2, canceling the storage of liquid air cold energy by the first and second stage cold storage media of the LNG cold storage system, or only canceling the storage of liquid air cold energy by the first stage cold storage medium of the LNG cold storage system, increasing the Rankine cycle system to recover part of the cold energy, and further improving the system efficiency.

[0081] On the basis of the above-mentioned Embodiments 1 and 2, based on the cascade utilization of liquid air cold energy, a multi-stage organic working fluid Rankine cycle (ORC) is arranged to fully recover the cold energy in this interval. During the energy release period, the Rankine cycle system and the liquid air energy release system jointly generate electricity, which can improve the overall efficiency of the system.

[0082] The Rankine cycle system includes a first Rankine cycle subsystem ORC1 , a second Rankine cycle subsystem ORC2 , and a third Rankine cycle subsystem ORC3 .

[0083] The first Rankine cycle subsystem ORC1 includes a first Rankine cycle condenser 61, a first Rankine cycle working fluid pump 62, a first Rankine cycle turbine 63 and a first Rankine cycle evaporator 64 connected end to end in sequence. The second Rankine cycle subsystem ORC2 includes a first Rankine cycle evaporator 64, a second Rankine cycle working fluid pump 71, a second Rankine cycle turbine 72 and a second Rankine cycle evaporator 73 connected end to end in sequence. The third Rankine cycle subsystem ORC3 includes a third Rankine cycle condenser 81, a third Rankine cycle working fluid pump 82, a third Rankine cycle turbine 83 and a third Rankine cycle evaporator 84 connected end to end in sequence.

[0084] The first Rankine cycle evaporator 64 serves as both the evaporator of the first Rankine cycle subsystem ORC1 and the condenser of the second Rankine cycle subsystem ORC2 , and the heat source of ORC2 and ORC3 is the heat generated during the compression process.

[0085] The embodiment of the present invention can reduce the number of devices in the system and simplify the system structure by integrating the first Rankine cycle subsystem ORC1 and the second Rankine cycle subsystem ORC2. In addition, the circulating working fluid of each level of Rankine cycle subsystem can be improved to a mixed working fluid, and the temperature matching of the power cycle condensation process and the liquid air gasification process can be enhanced through the "temperature glide" of the two-phase region, which can increase the Rankine cycle power generation.

[0086] In some embodiments of the present invention, an air precooling system and another gas-liquid separator are provided between the corresponding interstage cooler and the molecular sieve purifier 4, the air precooling system is used to precool and wash the raw air, and the gas-liquid separator is used to separate the moisture in the air entering the molecular sieve purifier 4.

[0087] Since the LNG receiving terminal is located at the seaside, the coastal air carries too much water. In order to solve the problem that the molecular sieve purifier 4 in the liquid air energy storage system processes too much water, resulting in high raw material costs and adsorbent regeneration costs, an air precooler and a gas-liquid separator are added between the molecular sieve purifier 4 and the first-stage interstage cooler 3. The air temperature is lowered by using the abundant low-grade cold energy on site. After gas-liquid separation, the water content of the air entering the molecular sieve purifier 4 is greatly reduced, which can save adsorbent raw materials, reduce the adsorber size, and reduce the regeneration cost of the purification unit.

[0088] However, since the embodiment of the present invention reduces the intake temperature of the booster unit 5, on the basis of embodiments 1 and 2 of the present invention, it is often necessary to recover the high-grade heat generated during the air compression process of the booster unit 5. The increase in the pressure ratio of the booster unit 5 leads to greater power consumption, and the reduction in the expansion work caused by the decrease in the heat quality of the heat storage unit. When actually improving the solution, it is necessary to comprehensively analyze the impact of the improvement measures on the system's electrical-electrical efficiency and the system's economic performance.

[0089] It should be noted that the air compressor unit 2, booster unit 5 and interstage cooler in the embodiment of the present invention can be divided into 1-3 levels. As the number of levels increases, the heat storage temperature decreases accordingly; the low-temperature booster unit 8 and the air subcooler 7 can be divided into 1-4 levels. Increasing the number of levels of the low-temperature booster unit 8 helps to improve the system efficiency in a small range.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid medium-pressure air energy storage system based on LNG cold energy utilization, characterized in that: Including air compression system, expansion power generation system, liquid air storage tank, cold box and LNG cold storage system; The liquid air storage tank is used to store medium-pressure liquid air; The air compression system is connected to the high-pressure air inlet of the cold box, the medium-pressure liquid air outlet of the cold box is connected to the inlet of the liquid air storage tank, the outlet of the liquid air storage tank is connected to the high-pressure liquid air inlet of the cold box, and the expansion power generation system is connected to the normal-temperature air outlet of the cold box; The LNG cold storage system is connected to the heat exchange port of the cold box, and the LNG cold storage system is also connected to the LNG vaporizer and the natural gas superheater in sequence; the LNG cold storage system is used to cool the high-pressure air passing through the cold box into liquid air during the energy storage stage, so that the cold storage medium in the LNG cold storage system absorbs heat and stores it in the cold storage medium hot fluid storage tank; the LNG cold storage system is also used to use the heat absorbed during the energy storage stage to restore the high-pressure liquid air passing through the cold box to normal temperature during 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 stores it in the cold storage medium cold fluid storage tank; at the same time, the LNG cold storage system is also used to vaporize and superheat the LNG passing through the LNG vaporizer and the natural gas superheater 24 hours a day, so that the remaining part of the cold storage medium in the LNG cold storage system absorbs the cold of the LNG and stores it in the cold storage medium cold fluid storage tank.

2. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 1 is characterized in that: 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 primary cold storage medium loop corresponding to the first-stage heat exchanger, the natural gas superheater is provided in the primary cold storage medium loop, and the outlet of the natural gas superheater is connected to the pipeline network; The LNG cold storage system is provided with a secondary cold storage medium loop corresponding to the second-stage heat exchanger, the LNG vaporizer is provided in the secondary cold storage medium loop, 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; 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.

3. According to the liquid medium-pressure air energy storage system based on LNG cold energy utilization in claim 2, the primary cold storage medium circuit is composed 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; the first-stage heat exchanger is arranged 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 an inlet of the primary cold storage medium cold fluid storage tank, and the natural gas superheater is arranged 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 another inlet of the primary cold storage medium cold fluid storage tank; 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 which are connected end to end in sequence; the second-stage heat exchanger is arranged 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 an inlet of the secondary cold storage medium cold fluid storage tank; the LNG gasifier is arranged 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 gasifier is connected to another inlet of the secondary cold storage medium cold fluid storage tank.

4. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 1 is characterized in that: 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; The pressure of the medium-pressure counterflow gas that flows back from the heat exchanger in the cold box is the same as or close to the pressure of the gas to be mixed at the inlet end of the booster unit.

5. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 1 is characterized in that: The air compression system is connected to the high-pressure air inlet of the heat exchanger in the cold box, the reflux outlet of the gas-liquid separator 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 air inlet of the heat exchanger in the cold box through the reflux gas compression system.

6. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 5 is characterized in that: The counterflow air compression system comprises a multi-stage counterflow air compressor and a counterflow air subcooler arranged between two adjacent stages of the counterflow air compressor; The medium-pressure backflow gas outlet of the second-stage heat exchanger in the cold box is connected to the inlet of the first-stage backflow gas compressor, and the outlet of the last-stage backflow gas compressor is connected to the air inlet of the first-stage heat exchanger in the cold box. The gas pressure at the outlet of the last-stage backflow gas compressor is the same as or close to the air pressure at the outlet end of the booster unit.

7. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 1 is 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 to the LNG cold storage system, and the LNG cold storage system performs heat exchange for it. The heat source of the Rankine cycle system is the heat generated by the air compression system.

8. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 7 is characterized in that: The Rankine cycle system includes a first Rankine cycle subsystem, a second Rankine cycle subsystem and a third Rankine cycle subsystem; each Rankine cycle subsystem includes a Rankine cycle condenser, a Rankine cycle working fluid pump, a Rankine cycle turbine and a Rankine cycle evaporator which are connected end to end in sequence; The Rankine cycle condenser is used to restore the high-pressure liquid air that has passed through the cold box to room temperature during the energy release stage, and the heat source of the Rankine cycle evaporator is the heat generated by the air compression system.

9. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to claim 8 is characterized in that: The Rankine cycle evaporator in the first Rankine cycle subsystem serves as a Rankine cycle condenser in the second Rankine cycle subsystem.

10. The liquid medium-pressure air energy storage system based on LNG cold energy utilization according to any one of claims 1 to 9, characterized in that: The air compression system comprises an air filter, a molecular sieve purifier, a multi-stage air compressor and an interstage cooler, wherein the interstage cooler is connected to the outlet of the corresponding air compressor unit, the air filter is connected to the inlet of the first-stage air compressor, the inlet of the molecular sieve purifier is connected to the outlet of the corresponding interstage cooler, and the outlet of the molecular sieve purifier is connected to the inlet of the corresponding air compressor; An air precooling system and a gas-liquid separator are provided between the corresponding interstage cooler and the molecular sieve purifier. The air precooling system is used for precooling and washing the raw air, and the gas-liquid separator is used for separating the moisture in the air entering the molecular sieve purifier.

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