A liquid air energy storage system and method coupled with an lng and air separation plant

Abstract

The application provides a liquid air energy storage system and method coupled with LNG and air separation devices, and relates to the technical field of energy storage. The liquid air energy storage system coupled with LNG and air separation devices comprises an LNG tank, an air compression device, a main heat exchanger, a nitrogen circulation device, a liquid air storage tank, a rectification device and a power generation device. By adopting circulating nitrogen as a heat exchange intermediate medium, the temperature zone of the liquefied natural gas vaporization process and the compressed air cooling process is matched, the liquefied natural gas is isolated from the compressed air, and the safety of the system is ensured. By adjusting the system flow, the air separation subsystem can absorb the cold energy of the liquefied natural gas during the peak period without affecting the liquefied natural gas vaporization process, the cold storage unit of the LNG-LAES is cancelled, and the oxygen production energy consumption is effectively reduced. By adjusting the operation load of the air separation subsystem, the multi-cogeneration system can effectively cope with the seasonal fluctuation of the liquefied natural gas vaporization amount, and the system peak shaving capacity is enhanced.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, and in particular to a liquid air energy storage system and method that couples LNG with an air separation unit. Background Technology

[0002] Utilizing renewable energy is a crucial way to address environmental issues. It is projected that by 2030, renewable energy will account for 30% of China's electricity generation. However, the volatility and intermittency of renewable energy sources negatively impact grid stability. Energy storage technology can effectively reduce peak-valley differences in the power grid, ensuring stable operation. Among these technologies, liquid air energy storage (LAES) offers advantages such as high energy density, lack of geographical limitations, and storage at atmospheric pressure. The storage process involves compressing and liquefying air to store electricity in liquid air form. During energy release, the liquid air is pressurized and vaporized, entering an expander to drive a turbine and ultimately a generator. Independent liquid air energy storage has a relatively low round-trip efficiency, typically between 50% and 60%.

[0003] During the vaporization of liquefied natural gas (LNG), its temperature rises from -162°C to 15°C, releasing 830-860 kJ / kg of cold energy. By coupling liquid air energy storage with the LNG vaporization process, the power consumption of the liquid air energy storage system during charging can be effectively reduced, thereby improving the round-trip efficiency of the system. Air separation units (ASUs) are the cornerstone of heavy industry, but their high production costs limit the development of related industries. Combining liquid air energy storage with air separation units can not only significantly reduce energy consumption to improve energy efficiency and economic value, but also provide a flexible and efficient energy release method. Coupled with an LNG-LAES-ASU combined heat and power system, it can not only effectively utilize the cold energy of LNG, but also cope with the seasonal fluctuations in LNG vaporization volume by adjusting the load of the air separation unit.

[0004] In studies of LNG-LAES energy storage coupling, there are two main methods for utilizing the cold energy of LNG. The first is cooling the interstage air of the compressor, which reduces energy consumption but fails to fully utilize the high-grade cold energy of LNG. The second is cooling the air in the cold box heat exchanger to liquefy it; however, the LNG vaporization temperature range does not match the air liquefaction temperature range, resulting in a low air liquefaction rate and affecting the system's round-trip efficiency. In these studies, LNG and air exchange heat in the same heat exchanger, posing safety risks. Due to changes in natural gas demand, the vaporization rate of LNG also fluctuates seasonally. In LNG-LAES coupling systems, these fluctuations threaten the stable operation of liquid air energy storage. Summary of the Invention

[0005] This invention provides a liquid air energy storage system that couples LNG and an air separation unit to solve the problems of low liquefaction rate and low safety in existing LNG-LAES coupling systems.

[0006] This invention provides a liquid air energy storage system coupling LNG and an air separation unit, comprising:

[0007] LNG tank;

[0008] An air compression device, which is used to compress air and cool the air to obtain room temperature high-pressure air;

[0009] The main heat exchanger is connected to the air compression device;

[0010] A nitrogen circulation device is connected to the main heat exchanger, the LNG tank and the air compression device. The nitrogen circulation device is used to use nitrogen as a heat exchange medium to transfer the cold energy of LNG to the air compression device and the main heat exchanger. The main heat exchanger is used to liquefy room temperature high-pressure air.

[0011] A liquid air storage tank, which is connected to the main heat exchanger, is used to store liquid air;

[0012] A distillation apparatus, wherein the distillation apparatus is connected to the nitrogen circulation apparatus and the main heat exchanger;

[0013] A power generation device, which is connected to the main heat exchanger.

[0014] According to the present invention, a liquid air energy storage system coupling LNG and an air separation unit is provided, wherein the air compression device includes:

[0015] Multistage compressor;

[0016] Hot water tank;

[0017] An LNG heat exchanger, wherein the first inlet of the LNG heat exchanger is connected to the outlet of the hot water tank, and the second inlet of the LNG heat exchanger is connected to the first outlet of the main heat exchanger;

[0018] A cold water tank, the inlet of which is connected to the first outlet of the LNG heat exchanger;

[0019] The system includes a multi-stage intercooler, with adjacent compressor stages connected via corresponding intercoolers. The inlet of the lowest-stage intercooler is connected to the atmosphere, and the outlet of the highest-stage compressor is connected to the third and fifth inlets of the main heat exchanger. The third outlet of the main heat exchanger is connected to the distillation unit via a third throttle valve. The inlet of the hot water tank is connected to the outlet of each stage of the intercooler, and the outlet of the cold water tank is connected to the inlet of each stage of the intercooler.

[0020] According to the liquid air energy storage system coupled to an LNG and air separation unit provided by the present invention, the air compression device further includes:

[0021] A multi-stage cooler is provided, with a corresponding cooler installed at the outlet of each stage of the compressor.

[0022] According to the liquid air energy storage system coupled to an LNG and air separation unit provided by the present invention, the air compression device further includes:

[0023] The first connecting pipe connects to one end of the air inlet of one stage of the multi-stage interstage cooler, and the other end of the first connecting pipe connects to the fourth inlet of the main heat exchanger. The fourth outlet of the main heat exchanger is connected to the distillation unit via a cryogenic expander.

[0024] According to the present invention, a liquid air energy storage system coupling LNG and an air separation unit is provided, wherein the nitrogen circulation device includes:

[0025] A first nitrogen heat exchanger, the first inlet of which is connected to the second outlet of the main heat exchanger; the LNG tank is connected to the third inlet of the first nitrogen heat exchanger via a first liquid air pump, and the third outlet of the first nitrogen heat exchanger is connected to the third inlet of the LNG heat exchanger.

[0026] The second nitrogen heat exchanger has its first outlet connected to the first inlet of the main heat exchanger, and its second inlet connected to the first outlet of the first nitrogen heat exchanger.

[0027] The nitrogen compressor has its inlet connected to the second outlet of the second nitrogen heat exchanger, its outlet connected to the second inlet of the first nitrogen heat exchanger, its second outlet connected to the third inlet of the second nitrogen heat exchanger, and its third outlet connected to the second inlet of the main heat exchanger via a first throttle valve.

[0028] According to the present invention, a liquid air energy storage system coupling an LNG and an air separation unit is provided, wherein the liquid air energy storage system further includes:

[0029] A liquid expander, the inlet of which is connected to the fifth outlet of the main heat exchanger;

[0030] The second throttle valve has its inlet connected to the outlet of the liquid expander and its outlet connected to the inlet of the liquid air storage tank.

[0031] According to the present invention, a liquid air energy storage system coupling an LNG and an air separation unit is provided, wherein the liquid air energy storage system further includes:

[0032] The second liquid air pump connects the outlet of the liquid air storage tank to the seventh inlet of the main heat exchanger, and the seventh outlet of the main heat exchanger connects to the inlet of the power generation device.

[0033] According to the present invention, a liquid air energy storage system coupling LNG and an air separation unit is provided, wherein the power generation device includes:

[0034] A multi-stage expander, wherein the outlet of the previous stage expander is connected to the inlet of the next stage expander;

[0035] Multiple heaters are provided, with one heater installed at the air inlet of each stage of the expander, and the air inlet of the lowest stage expander is connected to the seventh outlet of the main heat exchanger through one of the heaters.

[0036] According to the present invention, a liquid air energy storage system coupling LNG and an air separation unit is provided, wherein the distillation unit comprises:

[0037] Subcooler; the fourth outlet of the subcooler is connected to the first inlet of the second nitrogen heat exchanger;

[0038] The high-pressure tower has a first inlet connected to the cryogenic expander, a second inlet connected to the third throttling valve, a first outlet connected to the first inlet of the subcooler, a second outlet connected to the second inlet of the subcooler, and a third outlet connected to the third inlet of the subcooler.

[0039] A low-pressure tower is located above the high-pressure tower. The first inlet of the low-pressure tower is connected to the first outlet of the subcooler through a fourth throttling valve. The second inlet of the low-pressure tower is connected to the second outlet of the subcooler through a fifth throttling valve. The third inlet of the low-pressure tower is connected to the third outlet of the subcooler through a sixth throttling valve. The first outlet of the low-pressure tower is connected to the fourth inlet of the subcooler.

[0040] The present invention also provides a liquid air energy storage method coupled with an LNG and an air separation unit, the energy storage method being based on the liquid air energy storage system coupled with an LNG and an air separation unit as described in any of the preceding claims, comprising:

[0041] An air compressor compresses and cools the air to obtain room-temperature, high-pressure air.

[0042] The nitrogen circulation device uses nitrogen as a heat exchange medium to transfer the cold energy of LNG to the air compression device and the main heat exchanger, so that the main heat exchanger liquefies the ambient temperature and high pressure air, and the liquefied liquid air is stored in the liquid air storage tank.

[0043] The liquid air output from the liquid air storage tank enters the main heat exchanger to provide cooling energy for the room temperature high-pressure air, and the liquid air is restored to room temperature high-pressure air;

[0044] The power generation device expands and heats the input room-temperature high-pressure air to drive the electric motor to generate electricity.

[0045] The liquid air energy storage system coupled with an LNG and air separation unit provided by this invention uses circulating nitrogen as the intermediate heat exchange medium, which matches the temperature range of the LNG vaporization process and the compressed air cooling process, and also isolates the LNG from the compressed air, ensuring system safety. By adjusting the system flow, without affecting the LNG vaporization process, the air separation subsystem can absorb the cold energy of LNG during peak periods, eliminating the need for the LNG-LAES cold storage unit and effectively reducing oxygen production energy consumption. By adjusting the operating load of the air separation subsystem, the combined cooling, power, and power system can effectively cope with the seasonal fluctuations in LNG vaporization, and the system's peak-shaving capacity is enhanced. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the liquid air energy storage system that couples LNG and an air separation unit, provided by the present invention.

[0048] Figure label:

[0049] 1. First-stage compressor; 2. Second-stage compressor; 3. Third-stage compressor; 4. Fourth-stage compressor; 5. First-stage interstage cooler; 6. Second-stage interstage cooler; 7. Third-stage interstage cooler; 8. Fourth-stage interstage cooler; 9. First-stage cooler; 10. Second-stage cooler; 11. Third-stage cooler; 12. Fourth-stage cooler; 13. Main heat exchanger; 14. Liquid expander; 15. Second throttle valve; 16. Liquid air storage tank; 17. Third throttle valve; 18. Cryogenic expander; 19. High-pressure tower; 20. Subcooler; 21. Low-pressure tower; 22. First nitrogen exchanger 23. Second nitrogen heat exchanger; 24. Nitrogen compressor; 25. LNG heat exchanger; 26. Second liquid air pump; 27. First heater; 32. Second heater; 33. Third heater; 34. Fourth heater; 28. First stage expander; 29. ​​Second stage expander; 30. Third stage expander; 31. Fourth stage expander; 35. Electric motor; 36. First throttle valve; 37. First liquid air pump; 38. Fourth throttle valve; 39. Fifth throttle valve; 40. Sixth throttle valve; 41. Hot water tank; 42. Cold water tank; 43. LNG tank body; 44. First connecting pipe. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0051] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0053] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0054] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0055] The following is combined with Figure 1 The specific structure and working principle of the liquid air energy storage system of the present invention, which couples an LNG and an air separation unit, are described.

[0056] like Figure 1As shown, the liquid air energy storage system coupling the LNG and air separation unit includes an LNG tank 43, an air compressor, a main heat exchanger 13, a nitrogen circulation system, a liquid air storage tank 16, a distillation unit, and a power generation unit. The air compressor compresses and cools the air to obtain ambient temperature, high-pressure air. The main heat exchanger 13 is connected to the air compressor. The nitrogen circulation system is connected to the main heat exchanger 13, the LNG tank 43, and the air compressor. The nitrogen circulation system uses nitrogen as a heat exchange medium to transfer the cold energy of the LNG to the air compressor and the main heat exchanger 13. The main heat exchanger 13 liquefies the ambient temperature, high-pressure air. The liquid air storage tank 16 is connected to the main heat exchanger 13 and is used to store liquid air. The distillation unit is connected to the nitrogen circulation system and the main heat exchanger 13, and the power generation unit is connected to the main heat exchanger 13.

[0057] The liquid air energy storage system coupled with an LNG and air separation unit provided by this invention uses circulating nitrogen as the intermediate heat exchange medium, which matches the temperature range of the LNG vaporization process and the compressed air cooling process, and also isolates the LNG from the compressed air, ensuring system safety. By adjusting the system flow, without affecting the LNG vaporization process, the air separation subsystem can absorb the cold energy of LNG during peak periods, eliminating the need for the LNG-LAES cold storage unit and effectively reducing oxygen production energy consumption. By adjusting the operating load of the air separation subsystem, the combined cooling, power, and power system can effectively cope with the seasonal fluctuations in LNG vaporization, and the system's peak-shaving capacity is enhanced.

[0058] In one embodiment of the present invention, the air compression device includes a multi-stage compressor, a hot water tank 41, an LNG heat exchanger 25, a cold water tank 42, and a multi-stage interstage cooler. The first inlet of the LNG heat exchanger 25 is connected to the outlet of the hot water tank 41, and the second inlet of the LNG heat exchanger 25 is connected to the first outlet of the main heat exchanger 13. The inlet of the cold water tank 42 is connected to the first outlet of the LNG heat exchanger 25. The LNG heat exchanger 25 is used to transfer the cold energy of LNG to the air compression device to reduce the energy consumption during the operation of the compressor. Adjacent compressor stages are connected through corresponding interstage coolers. The inlet of the lowest stage interstage cooler is connected to the atmosphere, and the outlet of the highest stage compressor is connected to the third and fifth inlets of the main heat exchanger 13. The third outlet of the main heat exchanger 13 is connected to the distillation unit through a third throttle valve 17. The inlet of the hot water tank 41 is connected to the outlet of each stage interstage cooler, and the outlet of the cold water tank 42 is connected to the inlet of each stage interstage cooler.

[0059] It should be noted that in this invention, the main heat exchanger 13, LNG heat exchanger 25, subcooler 20, first nitrogen heat exchanger 22 and second nitrogen heat exchanger 23 are all provided with multiple inlets and multiple outlets. The inlets and outlets of each phase are connected in a one-to-one correspondence. For example, the first inlet is connected to the first outlet, and the second inlet is connected to the second outlet.

[0060] In one embodiment of the present invention, the air compression device further includes a multi-stage cooler, with a corresponding cooler provided at the outlet of each stage compressor.

[0061] Specifically, such as Figure 1 As shown, the air compression device includes a first-stage compressor 1, a second-stage compressor 2, a third-stage compressor 3, a fourth-stage compressor 4, a first-stage interstage cooler 5, a second-stage interstage cooler 6, a third-stage interstage cooler 7, a fourth-stage interstage cooler 8, a first-stage cooler 9, a second-stage cooler 10, a third-stage cooler 11, and a fourth-stage cooler 12. The inlet of the first-stage interstage cooler 5 is open to the atmosphere, and the outlet of the first-stage interstage cooler 5 is connected to the inlet of the first-stage compressor 1. The second-stage interstage cooler 6 and the first-stage cooler 9 are located between the first-stage compressor 1 and the second-stage compressor 2. The outlet of the first-stage compressor 1 is connected to the inlet of the second-stage interstage cooler 6 through the first-stage cooler 9, and the outlet of the second-stage interstage cooler 6 is connected to the inlet of the second-stage compressor 2. The third-stage interstage cooler 7 and the second-stage cooler 10 are located between the second-stage compressor 2 and the third-stage compressor 3. The outlet of the second-stage compressor 2 is connected to the inlet of the third-stage interstage cooler 7 through the second-stage cooler 10, and the outlet of the third-stage interstage cooler 7 is connected to the inlet of the third-stage compressor 3. The fourth-stage interstage cooler 8 and the third-stage cooler 11 are located between the third-stage compressor 3 and the fourth-stage compressor 4. The outlet of the third-stage compressor 3 is connected to the inlet of the fourth-stage interstage cooler 8 through the third-stage cooler 11, and the outlet of the fourth-stage interstage cooler 8 is connected to the inlet of the fourth-stage compressor 4. The outlet of the fourth-stage compressor 4 is connected to the third and fifth inlets of the main heat exchanger 13 through the fourth-stage cooler 12.

[0062] The inlet of the hot water tank 41 is connected to the outlets of the first-stage intercooler 5, the second-stage intercooler 6, the third-stage intercooler 7, and the fourth-stage intercooler 8, while the outlet of the cold water tank 42 is connected to the inlet of the first-stage intercooler 5, the second-stage intercooler 6, the third-stage intercooler 7, and the fourth-stage intercooler 8.

[0063] It should be noted that the use of "stage" to define the compressor and interstage cooler in this invention is merely for the purpose of distinguishing each compressor and each interstage cooler for ease of description, and has no substantive meaning.

[0064] In one embodiment of the present invention, the air compression device further includes a first connecting pipe 44. The air inlet of one stage of the multi-stage interstage cooler is connected to one end of the first connecting pipe 44. Specifically, the air inlet of the third stage interstage cooler 7 is connected to one end of the first connecting pipe 44. The other end of the first connecting pipe 44 is connected to the fourth inlet of the main heat exchanger 13, and the fourth outlet of the main heat exchanger 13 is connected to the distillation unit via a cryogenic expander 18. By providing the first connecting pipe 44, the undifferentiated air output from the second-stage compressor 2 can be introduced into the main heat exchanger 13 for cooling, and finally expanded by the cryogenic expander 18 before entering the distillation unit.

[0065] In one embodiment of the present invention, the nitrogen circulation device includes a first nitrogen heat exchanger 22, a second nitrogen heat exchanger 23, and a nitrogen compressor 24. The first inlet of the first nitrogen heat exchanger 22 is connected to the second outlet of the main heat exchanger 13. The LNG tank 43 is connected to the third inlet of the first nitrogen heat exchanger 22 via a first liquid air pump 37, and the third outlet of the first nitrogen heat exchanger 22 is connected to the third inlet of the LNG heat exchanger 25. The first outlet of the second nitrogen heat exchanger 23 is connected to the first inlet of the main heat exchanger 13, and the second inlet of the second nitrogen heat exchanger 23 is connected to the first outlet of the first nitrogen heat exchanger 22. The inlet of the nitrogen compressor 24 is connected to the second outlet of the second nitrogen heat exchanger 23, and the outlet of the nitrogen compressor 24 is connected to the second inlet of the first nitrogen heat exchanger 22. The second outlet of the first nitrogen heat exchanger 22 is connected to the third inlet of the second nitrogen heat exchanger 23, and the third outlet of the second nitrogen heat exchanger 23 is connected to the second inlet of the main heat exchanger 13 via a first throttle valve 36.

[0066] The nitrogen compressor 24, the first nitrogen heat exchanger 22, the second nitrogen heat exchanger 23, and the main heat exchanger 13 constitute a nitrogen circulation pipeline. The nitrogen compressor 24 drives nitrogen to circulate within the nitrogen circulation pipeline. During the vaporization process of liquefied natural gas (LNG), a large amount of cold energy is released. During the circulation process, the nitrogen transfers the low-grade cold energy of the LNG to the first nitrogen heat exchanger 22 and the LNG heat exchanger 25. Part of this low-grade cold energy is supplied to the air compression unit to reduce energy consumption during the compression process, while the other part is output to surrounding plants for use.

[0067] High-grade cold energy is transferred to the main heat exchanger 13 via circulating nitrogen, cooling the compressed air to a low-temperature gaseous state or liquefying it. Using circulating nitrogen as an intermediate heat exchange medium separates liquefied natural gas (LNG) from compressed air, ensuring system safety. Furthermore, the pressure of the circulating nitrogen is changed by the nitrogen compressor 24, ensuring that the nitrogen temperature at the second inlet of the main heat exchanger 13 is lower than the minimum temperature required for the compressed air cooling process, thus efficiently utilizing the high-grade cold energy of the LNG. Part of the liquefied air is stored in the liquid air storage tank 16 and used for expansion power generation during non-peak hours; the other part enters the distillation unit, where liquid oxygen and liquid nitrogen are separated and output. During the energy release process, the liquid air vaporizes and enters the power generation unit for expansion power generation. Simultaneously, to ensure stable operation of the distillation unit, it continues to operate normally during the energy release process, thus fully recovering the cold energy of the LNG during energy release.

[0068] In one embodiment of the present invention, the liquid air energy storage system further includes a liquid expander 14 and a second throttle valve 15. The inlet of the liquid expander 14 is connected to the fifth outlet of the main heat exchanger 13. The inlet of the second throttle valve 15 is connected to the outlet of the liquid expander 14, and the outlet of the second throttle valve 15 is connected to the inlet of the liquid air storage tank 16. Room temperature high-pressure air enters the main heat exchanger 13 and is cooled to liquefaction. The liquid air then enters the liquid expander 14 for expansion, then enters the second throttle valve 15 for throttling, and finally enters the liquid air storage tank 16 for storage.

[0069] In one embodiment of the present invention, the liquid air energy storage system further includes a second liquid air pump 26. The outlet of the liquid air storage tank 16 is connected to the seventh inlet of the main heat exchanger 13 through the second liquid air pump 26, and the seventh outlet of the main heat exchanger 13 is connected to the inlet of the power generation device. When power generation is required, the second liquid air pump 26 pumps the liquid air in the liquid air storage tank 16 to the main heat exchanger 13 to provide cooling energy for the compressed air. After heat exchange between the liquid air and the compressed air, the liquid air is converted into room temperature high-pressure air.

[0070] Furthermore, the outlet of the liquid air storage tank 16 is connected to the sixth inlet of the main heat exchanger 13 through a return gas pipeline, and the sixth outlet of the main heat exchanger 13 is connected to the outside or the storage tank.

[0071] In one embodiment of the present invention, the power generation device includes a multi-stage expander and a plurality of heaters, wherein the outlet of the previous stage expander is connected to the inlet of the next stage expander. Each stage expander has a heater at its inlet, and the inlet of the lowest stage expander is connected to the seventh outlet of the main heat exchanger 13 through a heater.

[0072] Specifically, such as Figure 1As shown, the power generation unit includes a first heater 27, a second heater 32, a third heater 33, a fourth heater 34, a first-stage expander 28, a second-stage expander 29, a third-stage expander 30, and a fourth-stage expander 31. The inlet of the first heater 27 is connected to the seventh outlet of the main heat exchanger 13, and the outlet of the first heater 27 is connected to the inlet of the first-stage expander 28. The second heater 32 is located between the first-stage expander 28 and the second-stage expander 29, and the outlet of the first-stage expander 28 is connected to the inlet of the second-stage expander 29 through the second heater 32. The third heater 33 is located between the second-stage expander 29 and the third-stage expander 30, and the outlet of the second-stage expander 29 is connected to the inlet of the third-stage expander 30 through the third heater 33. The fourth heater 34 is located between the third-stage expander 30 and the fourth-stage expander 31, and the outlet of the third-stage expander 30 is connected to the inlet of the fourth-stage expander 31 through the fourth heater 34. The shafts of the first-stage expander 28, the second-stage expander 29, the third-stage expander 30, and the fourth-stage expander 31 are connected in sequence, and the shaft of the fourth-stage expander 31 is connected to the shaft of the motor 35.

[0073] In one embodiment of the present invention, the distillation apparatus includes a subcooler 20, a high-pressure column 19, and a low-pressure column 21. The fourth outlet of the subcooler 20 is connected to the first inlet of the second nitrogen heat exchanger 23. The first inlet of the high-pressure column 19 is connected to the cryogenic expander 18, and the second inlet of the high-pressure column 19 is connected to the third throttling valve 17. The first outlet of the high-pressure column 19 is connected to the first inlet of the subcooler 20, the second outlet of the high-pressure column 19 is connected to the second inlet of the subcooler 20, and the third outlet of the high-pressure column 19 is connected to the third inlet of the subcooler 20. The low-pressure column 21 is disposed above the high-pressure column 19. The first inlet of the low-pressure column 21 is connected to the first outlet of the subcooler 20 through the fourth throttling valve 38, the second inlet of the low-pressure column 21 is connected to the second outlet of the subcooler 20 through the fifth throttling valve 39, the third inlet of the low-pressure column 21 is connected to the third outlet of the subcooler 20 through the sixth throttling valve 40, and the first outlet of the low-pressure column 21 is connected to the fourth inlet of the subcooler 20.

[0074] The working principle of the liquid air energy storage system of the present invention, which couples LNG and air separation unit:

[0075] In the energy storage process, air is cooled in the first-stage interstage cooler 5 before entering the first-stage compressor 1. The compressed air temperature is higher than room temperature, and it is cooled to room temperature in the first-stage cooler 9, and then cooled to an even lower temperature in the second-stage interstage cooler 6 to reduce the compressor's energy consumption. After four stages of compression and cooling, the room-temperature high-pressure air enters the main heat exchanger 13 for further cooling. A portion of the air is cooled to liquefaction, and the liquid air enters the liquid expander 14 for expansion, then enters the second throttle valve 15 for throttling, and finally enters the liquid air storage tank 16 for storage. The low-temperature air in the liquid air storage tank 16 enters the main heat exchanger 13 through the return gas pipeline to provide cooling energy for the compressed air.

[0076] Two streams of air entering through the third and fifth inlets of the main heat exchanger 13 are cooled within the main heat exchanger 13, then depressurized via the third throttling valve 17 and the cryogenic expander 18 before entering the high-pressure tower 19. After distillation, liquid nitrogen and oxygen-enriched liquid air are obtained at the top and bottom of the high-pressure tower 19. Additionally, a stream of oxygen-deficient liquid air is drawn from the middle of the high-pressure tower 19 and further cooled in the subcooler 20. The liquid nitrogen output from the high-pressure tower 19 is cooled in the subcooler 20 and then throttled by the sixth throttling valve 40. After throttling, a portion is output as product liquid nitrogen, and the other portion enters from the top of the low-pressure tower 21 as reflux. The oxygen-enriched and oxygen-deficient liquid air, subcooled in the subcooler 20, are throttled by the fourth throttling valve 38 and the fifth throttling valve 39 before entering the upper-middle part of the low-pressure tower 21. After distillation, liquid oxygen is obtained at the bottom of the low-pressure tower 21 and output as product liquid oxygen. Sludge nitrogen is generated at the top of the low-pressure tower 21 and enters the subcooler 20 to provide cooling energy for other streams.

[0077] The circulating nitrogen exiting from the second outlet of the main heat exchanger 13 enters the first nitrogen heat exchanger 22 and the second nitrogen heat exchanger 23, where it is cooled by LNG and waste nitrogen. The cooled nitrogen is compressed to high pressure in the nitrogen compressor 24 and then re-enters the first and second nitrogen heat exchangers 22 and 23 for cooling. After being throttled by the first throttle valve 36, the circulating nitrogen has a low temperature, sufficient to cool compressed air. The waste nitrogen, after heat exchange in the second nitrogen heat exchanger 23, enters the main heat exchanger 13 to provide cooling energy for the compressed air. Subsequently, the LNG and waste nitrogen enter the LNG heat exchanger 25 for further heating, with the cooling energy recovered by methanol. A portion of the cooling energy is supplied to the air compressor to reduce compressor energy consumption, while another portion of the low-grade cooling energy is supplied as a product to surrounding plants.

[0078] During the energy release process, the air is divided into two streams. One stream enters the main heat exchanger 13 through the first connecting pipe 44, while the other stream enters the main heat exchanger 13 through the fourth-stage cooler 12. The latter, with a higher pressure, is more easily liquefied. After cooling, the liquid air and cryogenic air are throttled by the third throttle valve 17 and enter the distillation unit through the cryogenic expander 18, respectively. Simultaneously, the liquid air is pressurized by the second liquid air pump 26 and enters the main heat exchanger 13 to provide cooling energy for the compressed air, and is reheated to room temperature. This air is then heated by the first heater 27 and enters the first-stage expander 28. After multiple stages of heating and expansion, the air expands to atmospheric pressure and outputs work, driving the motor 35 to generate electricity. During the energy release process, in addition to the circulating nitrogen and waste nitrogen providing cooling energy for the compressed air, liquid air from the liquid air storage tank 16 also provides cooling energy. Because the compressed air receives more cooling energy, the power consumption of the compression process is reduced.

[0079] The flow rates differ in each stage of the compressor during energy storage and release. During energy storage, three streams of air undergo four stages of compression before entering the main heat exchanger 13. Two streams are cooled and then enter the distillation unit, while the third is liquefied and stored in the liquid air storage tank 16. During energy release, to ensure continuous operation of the distillation unit, the flow rates of the first two streams of air remain constant, but one stream undergoes only two stages of compression. Since flow rate variations affect compressor efficiency, three parallel compressor units are installed in the LNG-LAES-ASU system to compress three streams of air separately. Furthermore, the vaporization rate of liquefied natural gas (LNG) fluctuates seasonally. To address this, the loads of the nitrogen compressor 24 and the distillation unit are adjusted based on the LNG vaporization rate, thereby efficiently utilizing the cold energy of the LNG.

[0080] The liquid air energy storage system coupled with an air separation unit provided by this invention has the following advantages:

[0081] 1. The liquid air energy storage system coupled to the air separation unit provided by the present invention eliminates the cold storage unit of the original energy storage system, avoids the use of large-scale liquid phase cold storage working fluid, and improves the safety of the system.

[0082] 2. The liquid air energy storage system coupled with an air separation unit provided by this invention uses circulating nitrogen as an intermediate heat exchange medium. It utilizes nitrogen expansion and refrigeration cycles to recover high-grade cold energy from liquefied natural gas and improve the quality of this cold energy, matching the temperature range of the compressed air cooling liquefaction process. Simultaneously, nitrogen isolates LNG and compressed air to ensure system safety. Furthermore, the low-grade cold energy of liquefied natural gas is used to cool the interstage air of the compressor, reducing compressor energy consumption and improving system efficiency.

[0083] 3. The liquid air energy storage system coupled with LNG and air separation unit provided by the present invention stores a portion of the liquefied air in liquid air storage tank 16, which is used for expansion power generation during non-off-peak periods, and the remaining portion enters the distillation unit as feed gas, while simultaneously supplementing the cooling capacity of the air separation tower.

[0084] The present invention also provides a liquid air energy storage method coupled with an LNG and an air separation unit. The energy storage method is based on the liquid air energy storage system coupled with an LNG and an air separation unit as described in any of the above embodiments, and includes:

[0085] Step S100: The air compression device compresses the air and cools it to obtain room temperature high-pressure air.

[0086] In step S200, the nitrogen circulation device uses nitrogen as a heat exchange medium to transfer the cold energy of LNG to the air compression device and the main heat exchanger 13, so that the main heat exchanger 13 liquefies the ambient temperature high pressure air, and the liquefied liquid air is stored in the liquid air storage tank 16.

[0087] In step S300, the liquid air output from the liquid air storage tank 16 enters the main heat exchanger 13 to provide cooling energy for the room temperature high pressure air, and the liquid air is restored to room temperature high pressure air.

[0088] In step S100, the power generation device expands and heats the input ambient temperature high pressure air to drive the motor 35 to generate electricity.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid air energy storage system coupling LNG and an air separation unit, characterized in that, include: LNG tank (43); An air compression device, which is used to compress air and cool the air to obtain room temperature high-pressure air; The main heat exchanger (13) is connected to the air compression device; A nitrogen circulation device is connected to the main heat exchanger (13), the LNG tank (43) and the air compression device. The nitrogen circulation device is used to use nitrogen as a heat exchange medium to deliver the cold energy of LNG to the air compression device and the main heat exchanger (13). The main heat exchanger (13) is used to liquefy ambient temperature high-pressure air. A liquid air storage tank (16) is connected to the main heat exchanger (13) and is used to store liquid air. A distillation apparatus, wherein the distillation apparatus is connected to the nitrogen circulation apparatus and the main heat exchanger (13); A power generation device, which is connected to the main heat exchanger (13); The air compression device includes: Multistage compressor; Hot water tank (41); LNG heat exchanger (25), the first inlet of the LNG heat exchanger (25) is connected to the outlet of the hot water tank (41), and the second inlet of the LNG heat exchanger (25) is connected to the first outlet of the main heat exchanger (13); Cold water tank (42), the inlet of which is connected to the first outlet of the LNG heat exchanger (25); The multi-stage intercooler connects two adjacent compressor stages through the corresponding intercooler. The inlet of the lowest stage intercooler is connected to the atmosphere. The outlet of the highest stage compressor is connected to the third and fifth inlets of the main heat exchanger (13). The third outlet of the main heat exchanger (13) is connected to the distillation unit through the third throttle valve (17). The inlet of the hot water tank (41) is connected to the outlet of each stage intercooler. The outlet of the cold water tank (42) is connected to the inlet of each stage intercooler. The nitrogen circulation device includes: The first nitrogen heat exchanger (22) has its first inlet connected to the second outlet of the main heat exchanger (13); the LNG tank (43) is connected to the third inlet of the first nitrogen heat exchanger (22) via the first liquid air pump (37), and the third outlet of the first nitrogen heat exchanger (22) is connected to the third inlet of the LNG heat exchanger (25). The second nitrogen heat exchanger (23) has its first outlet connected to the first inlet of the main heat exchanger (13), and its second inlet connected to the first outlet of the first nitrogen heat exchanger (22). A nitrogen compressor (24) is provided, the inlet of which is connected to the second outlet of the second nitrogen heat exchanger (23), the outlet of which is connected to the second inlet of the first nitrogen heat exchanger (22), the second outlet of the first nitrogen heat exchanger (22) is connected to the third inlet of the second nitrogen heat exchanger (23), and the third outlet of the second nitrogen heat exchanger (23) is connected to the second inlet of the main heat exchanger (13) through a first throttle valve (36). The distillation apparatus includes: Subcooler (20); the fourth outlet of the subcooler (20) is connected to the first inlet of the second nitrogen heat exchanger (23); A high-pressure tower (19) has its first inlet connected to a cryogenic expander (18), its second inlet connected to a third throttle valve (17), its first outlet connected to the first inlet of a subcooler (20), its second outlet connected to the second inlet of a subcooler (20), and its third outlet connected to the third inlet of a subcooler (20). The low-pressure tower (21) is located above the high-pressure tower (19). The first inlet of the low-pressure tower (21) is connected to the first outlet of the subcooler (20) through the fourth throttle valve (38). The second inlet of the low-pressure tower (21) is connected to the second outlet of the subcooler (20) through the fifth throttle valve (39). The third inlet of the low-pressure tower (21) is connected to the third outlet of the subcooler (20) through the sixth throttle valve (40). The first outlet of the low-pressure tower (21) is connected to the fourth inlet of the subcooler (20).

2. The liquid air energy storage system coupled with an LNG and air separation unit according to claim 1, characterized in that, The air compression device further includes: A multi-stage cooler is provided, with a corresponding cooler installed at the outlet of each stage of the compressor.

3. The liquid air energy storage system coupled with an LNG and air separation unit according to claim 1, characterized in that, The air compression device further includes: The first connecting pipe (44) is connected to one end of the air inlet of one stage of the multi-stage intercooler. The other end of the first connecting pipe (44) is connected to the fourth inlet of the main heat exchanger (13). The fourth outlet of the main heat exchanger (13) is connected to the distillation apparatus through a cryogenic expander (18).

4. The liquid air energy storage system coupled with an LNG and air separation unit according to any one of claims 1 to 3, characterized in that, The liquid air energy storage system also includes: A liquid expander (14) is connected at its inlet to the fifth outlet of the main heat exchanger (13). The inlet of the second throttle valve (15) is connected to the outlet of the liquid expander (14), and the outlet of the second throttle valve (15) is connected to the inlet of the liquid air storage tank (16).

5. The liquid air energy storage system coupled with an LNG and air separation unit according to claim 4, characterized in that, The liquid air energy storage system also includes: The second liquid air pump (26) is connected to the seventh inlet of the main heat exchanger (13) through the outlet of the liquid air storage tank (16), and the seventh outlet of the main heat exchanger (13) is connected to the inlet of the power generation device.

6. The liquid air energy storage system coupled with an LNG and air separation unit according to claim 5, characterized in that, The power generation device includes: A multi-stage expander, wherein the outlet of the previous stage expander is connected to the inlet of the next stage expander; Multiple heaters are provided, with one heater installed at the air inlet of each stage of the expander, and the air inlet of the lowest stage expander is connected to the seventh outlet of the main heat exchanger (13) through one of the heaters.

7. A method for storing liquid air coupled with an LNG and air separation unit, said energy storage method being based on the liquid air energy storage system coupled with an LNG and air separation unit as described in any one of claims 1 to 6, characterized in that, include: An air compressor compresses and cools the air to obtain room-temperature, high-pressure air. The nitrogen circulation device uses nitrogen as a heat exchange medium to deliver the cold energy of LNG to the air compression device and the main heat exchanger (13), so that the main heat exchanger (13) liquefies the room temperature high pressure air, and the liquefied liquid air is stored in the liquid air storage tank (16). The liquid air output from the liquid air storage tank (16) enters the main heat exchanger (13) to provide cooling energy for the room temperature high pressure air, and the liquid air is restored to room temperature high pressure air; The power generation device expands and heats the input room-temperature high-pressure air to drive the electric motor to generate electricity.

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