Liquid air energy storage system and method for coupling LNG and air separation device

Abstract

The invention provides a liquid air energy storage system and method for coupling LNG and an air separation device, and relates to the technical field of energy storage. The liquid air energy storage system coupling the LNG and the air separation device comprises an LNG tank body, 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. Circulating nitrogen is adopted as a heat exchange intermediate medium, so that the temperature zones of the liquefied natural gas vaporization process and the compressed air cooling process are matched, the liquefied natural gas is isolated from the compressed air, and the safety of the system is guaranteed. By adjusting the system flow, on the premise that the vaporization process of the liquefied natural gas is not affected, the air separation subsystem can absorb the cold energy of the liquefied natural gas in the peak period, a cold storage unit of the LNG-LAES is omitted, 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 seasonal fluctuation of the vaporization amount of the liquefied natural gas, and the peak regulation capacity of the system is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of energy storage technology, and in particular to a liquid air energy storage system and method for coupling LNG and an air separation unit. Background Art

[0002] The use of renewable energy is an important way to solve environmental problems. It is estimated that by 2030, the proportion of renewable energy in China will reach 30%. However, the volatility and intermittency of renewable energy are not conducive to the stability of the power grid. Energy storage technology can effectively reduce the peak-to-valley difference of the power grid and ensure the stable operation of the power grid. Among them, liquid air energy storage (LAES) has the advantages of high energy density, no geographical restrictions and normal pressure storage. In the energy storage process, the air is compressed and liquefied to store electricity in the form of liquid air. In the energy release process, the liquid air is pressurized and vaporized, enters the expander to drive the turbine to rotate, and drives the generator to generate electricity. The round-trip efficiency of independent liquid air energy storage is low, generally 50% to 60%.

[0003] During the gasification process of liquefied natural gas (LNG), its temperature rises from -162℃ to 15℃, while releasing 830-860kJ / kg of cold energy. By coupling liquid air energy storage with the vaporization process of LNG, the power consumption of the liquid air energy storage system during the charging process can be effectively reduced, thereby improving the round-trip efficiency of the liquid air energy storage system. The air separation unit (ASU) is the cornerstone of heavy industry, but its high production cost restricts 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 way of energy release. The coupling LNG-LAES-ASU multi-generation system can not only effectively utilize the cold energy of LNG, but also cope with the seasonal fluctuations of LNG vaporization by adjusting the load of the air separation unit.

[0004] In the study of coupling LNG and liquid air energy storage, there are two main ways to utilize the cold energy of LNG. The first is to cool the air between the compressor stages. Although it reduces energy consumption, it fails to fully utilize the high-grade cold energy of LNG. The second is to enter the cold box heat exchanger to cool the air and liquefy it, but the liquefied natural gas vaporization temperature zone does not match the air liquefaction temperature zone, resulting in a low liquefaction rate of the air, which in turn affects the round-trip efficiency of the system. In these studies, LNG and air exchange heat in the same heat exchanger, which poses a safety hazard. Due to changes in natural gas demand, the vaporization amount of LNG also fluctuates with the seasons. In the LNG-LAES coupling system, the fluctuation of the vaporization amount of LNG poses a threat to the stable operation of liquid air energy storage. Summary of the invention

[0005] The present invention provides a liquid air energy storage system coupling LNG and an air separation unit, so as to solve the problems of low liquefaction rate and low safety in the existing LNG-LAES coupling system.

[0006] The present invention provides a liquid air energy storage system coupling LNG and an air separation unit, comprising: LNG tank; An air compression device, the air compression device is used to compress the air and cool the air to obtain high-pressure air at room temperature; a main heat exchanger, the main heat exchanger being in communication with the air compression device; A nitrogen circulation device, the 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 transmit the cold energy of the LNG to the air compression device and the main heat exchanger, and the main heat exchanger is used to liquefy the normal temperature and high pressure air; a liquid air storage tank, the liquid air storage tank being in communication with the main heat exchanger and being used for storing liquid air; a distillation device, the distillation device being in communication with the nitrogen circulation device and the main heat exchanger; A power generation device is communicated with the main heat exchanger.

[0007] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the air compression device comprises: Multi-stage compressor; Hot water tank; an LNG heat exchanger, wherein a first inlet of the LNG heat exchanger is communicated with an outlet of the hot water tank, and a second inlet of the LNG heat exchanger is communicated with a first outlet of the main heat exchanger; a cold water tank, the inlet of the cold water tank being in communication with the first outlet of the LNG heat exchanger; A multi-stage interstage cooler, wherein the compressors of two adjacent stages are connected through the corresponding interstage coolers, the air inlet of the lowest-stage interstage cooler is connected to the atmosphere, the air outlet of the highest-stage compressor is connected to the third inlet and the fifth inlet of the main heat exchanger, the third outlet of the main heat exchanger is connected to the distillation device through the third throttle valve, the liquid inlet of the hot water tank is connected to the liquid outlet of each stage of the interstage cooler, and the liquid outlet of the cold water tank is connected to the liquid inlet of each stage of the interstage cooler.

[0008] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the air compression device further comprises: A multi-stage cooler is provided at the air outlet of each stage of the compressor.

[0009] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the air compression device further comprises: A first connecting pipe, wherein the air inlet of one of the interstage coolers of the multi-stage interstage cooler is connected to one end of the first connecting pipe, the other end of the first connecting pipe is connected to the fourth inlet of the main heat exchanger, and the fourth outlet of the main heat exchanger is connected to the distillation device through a low-temperature expander.

[0010] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the nitrogen circulation device comprises: a first nitrogen heat exchanger, wherein a first inlet of the first nitrogen heat exchanger is connected to a second outlet of the main heat exchanger; the LNG tank is connected to a third inlet of the first nitrogen heat exchanger through a first liquid air pump, and the third outlet of the first nitrogen heat exchanger is connected to a third inlet of the LNG heat exchanger; a second nitrogen heat exchanger, wherein a first outlet of the second nitrogen heat exchanger is communicated with a first inlet of the main heat exchanger, and a second inlet of the second nitrogen heat exchanger is communicated with a first outlet of the first nitrogen heat exchanger; a nitrogen compressor, wherein the inlet of the nitrogen compressor is communicated with the second outlet of the second nitrogen heat exchanger, the outlet of the nitrogen compressor is communicated with the second inlet of the first nitrogen heat exchanger, the second outlet of the first nitrogen heat exchanger is communicated with the third inlet of the second nitrogen heat exchanger, and the third outlet of the second nitrogen heat exchanger is communicated with the second inlet of the main heat exchanger through a first throttle valve.

[0011] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the liquid air energy storage system further comprises: a liquid expander, wherein an inlet of the liquid expander is connected to a fifth outlet of the main heat exchanger; A second throttle valve, wherein the inlet of the second throttle valve is connected to the outlet of the liquid expander, and the outlet of the second throttle valve is connected to the inlet of the liquid air storage tank.

[0012] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the liquid air energy storage system further comprises: A second liquid air pump, the liquid outlet of the liquid air storage tank is connected to the seventh inlet of the main heat exchanger through the second liquid air pump, and the seventh outlet of the main heat exchanger is connected to the inlet of the power generation device.

[0013] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the power generation device comprises: A multi-stage expander, wherein the air outlet of the expander of the previous stage is connected to the air inlet of the expander of the next stage; A plurality of heaters are provided at the air inlet of each stage of the expander, and the air inlet of the lowest stage of the expander is connected to the seventh outlet of the main heat exchanger through one of the heaters.

[0014] According to a liquid air energy storage system coupling LNG and an air separation unit provided by the present invention, the distillation unit comprises: A subcooler; a fourth outlet of the subcooler is connected to the first inlet of the second nitrogen heat exchanger; A high-pressure tower, wherein a first inlet of the high-pressure tower is communicated with the low-temperature expander, a second inlet of the high-pressure tower is communicated with the third throttle valve; a first outlet of the high-pressure tower is communicated with a first inlet of the subcooler, a second outlet of the high-pressure tower is communicated with a second inlet of the subcooler, and a third outlet of the high-pressure tower is communicated with a third inlet of the subcooler; A low-pressure tower, wherein the low-pressure tower is arranged on the upper part of the high-pressure tower, the first inlet of the low-pressure tower is connected to the first outlet of the subcooler through a fourth throttle valve, the second inlet of the low-pressure tower is connected to the second outlet of the subcooler through a fifth throttle valve, the third inlet of the low-pressure tower is connected to the third outlet of the subcooler through a sixth throttle valve, and the first outlet of the low-pressure tower is connected to the fourth inlet of the subcooler.

[0015] The present invention also provides a liquid air energy storage method for coupling LNG and an air separation unit. The energy storage method is based on any of the above-mentioned liquid air energy storage systems for coupling LNG and an air separation unit, comprising: The air compressor compresses the air and cools it down to obtain high-pressure air at room temperature; 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 normal temperature and high pressure air, and the liquefied liquid air is stored in the liquid air storage tank; The liquid air outputted from the liquid air storage tank enters the main heat exchanger to provide cold energy for the normal temperature and high pressure air, and the liquid air is restored to the normal temperature and high pressure air; The power generation device expands and heats the input high-pressure air at normal temperature to drive the electric motor to generate electricity.

[0016] The liquid air energy storage system coupled with LNG and an air separation unit provided by the present invention uses circulating nitrogen as a heat exchange intermediate medium, which not only matches the temperature zone of the liquefied natural gas vaporization process and the compressed air cooling process, but also isolates the liquefied natural gas from the compressed air, thereby ensuring the safety of the system. By adjusting the system flow, the air separation subsystem can absorb the cold energy of the liquefied natural gas during peak periods without affecting the liquefied natural gas vaporization process, eliminating the cold storage unit of the LNG-LAES and effectively reducing the energy consumption of oxygen production. By adjusting the operating load of the air separation subsystem, the multi-generation system can effectively cope with the seasonal fluctuations in the amount of liquefied natural gas vaporization, and the system's peak-shaving capacity is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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.

[0018] Figure 1 It is a structural schematic diagram of the liquid air energy storage system coupled with LNG and an air separation unit provided by the present invention.

[0019] Reference numerals: 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 heat 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, 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 DESCRIPTION

[0020] 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.

[0021] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and 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 devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0022] In the description of the embodiments of the present invention, 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 a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0023] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "above" or "below" the 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, the first feature being "above", "above" and "above" the 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. The first feature being "below", "below" and "below" the 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.

[0024] 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 embodiment of the present invention. 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.

[0025] Combine the following Figure 1 The specific structure and working principle of the liquid air energy storage system coupling LNG and an air separation unit of the present invention are described.

[0026] like Figure 1 As shown, the liquid air energy storage system coupling LNG and the air separation unit includes an LNG tank 43, an air compression device, a main heat exchanger 13, a nitrogen circulation device, a liquid air storage tank 16, a distillation device and a power generation device. The air compression device is used to compress the air and cool the air to obtain normal temperature and high pressure air; the main heat exchanger 13 is connected to the air compression device. The 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 transfer 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 the normal temperature and high pressure air. The liquid air storage tank 16 is connected to the main heat exchanger 13, and the liquid air storage tank 16 is used to store liquid air. The distillation device is connected to the nitrogen circulation device and the main heat exchanger 13, and the power generation device is connected to the main heat exchanger 13.

[0027] The liquid air energy storage system coupled with LNG and an air separation unit provided by the present invention uses circulating nitrogen as a heat exchange intermediate medium, which not only matches the temperature zone of the liquefied natural gas vaporization process and the compressed air cooling process, but also isolates the liquefied natural gas from the compressed air, thereby ensuring the safety of the system. By adjusting the system flow, the air separation subsystem can absorb the cold energy of the liquefied natural gas during peak periods without affecting the liquefied natural gas vaporization process, eliminating the cold storage unit of the LNG-LAES and effectively reducing the energy consumption of oxygen production. By adjusting the operating load of the air separation subsystem, the multi-generation system can effectively cope with the seasonal fluctuations in the amount of liquefied natural gas vaporization, and the system's peak-shaving capacity is enhanced.

[0028] 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, wherein 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, and the LNG heat exchanger 25 is used to deliver the cold energy of the LNG to the air compression device to reduce the energy consumption during the operation of the compressor. The adjacent two-stage compressors are connected through the corresponding interstage cooler, the air inlet of the lowest interstage cooler is connected to the atmosphere, the air outlet of the highest compressor is connected to the third inlet and the fifth inlet of the main heat exchanger 13, the third outlet of the main heat exchanger 13 is connected to the distillation device through the third throttle valve 17, the liquid inlet of the hot water tank 41 is connected to the liquid outlet of each interstage cooler, and the liquid outlet of the cold water tank 42 is connected to the liquid inlet of each interstage cooler.

[0029] It should be noted here that in the present invention, the main heat exchanger 13, the LNG heat exchanger 25, the subcooler 20, the first nitrogen heat exchanger 22 and the second nitrogen heat exchanger 23 are all provided with multiple inlets and multiple outlets, and the inlet and outlet of each period are connected one-to-one, for example, the first inlet is connected to the first outlet, and the second inlet is connected to the second outlet.

[0030] In one embodiment of the present invention, the air compression device further includes a multi-stage cooler, and a corresponding cooler is provided at the air outlet of each stage of the compressor.

[0031] Specifically, Figure 1As 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 air inlet of the first-stage interstage cooler 5 is connected to the atmosphere, and the air outlet of the first-stage interstage cooler 5 is connected to the air 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 air outlet of the first-stage compressor 1 is connected to the air inlet of the second-stage interstage cooler 6 through the first-stage cooler 9, and the air outlet of the second-stage interstage cooler 6 is connected to the air 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 air outlet of the second-stage compressor 2 is communicated with the air inlet of the third-stage interstage cooler 7 through the second-stage cooler 10, and the air outlet of the third-stage interstage cooler 7 is communicated with the air 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 air outlet of the third-stage compressor 3 is communicated with the air inlet of the fourth-stage interstage cooler 8 through the third-stage cooler 11, and the air outlet of the fourth-stage interstage cooler 8 is communicated with the air inlet of the fourth-stage compressor 4. The air outlet of the fourth-stage compressor 4 is communicated with the third inlet and the fifth inlet of the main heat exchanger 13 through the fourth-stage cooler 12.

[0032] The liquid inlet of the hot water tank 41 is connected to the liquid outlets of the first interstage cooler 5, the second interstage cooler 6, the third interstage cooler 7 and the fourth interstage cooler 8, and the liquid outlet of the cold water tank 42 is connected to the liquid inlet of the first interstage cooler 5, the second interstage cooler 6, the third interstage cooler 7 and the fourth interstage cooler 8.

[0033] It should be noted here that the term “stage” is used in the present invention to define the compressor and the interstage cooler only for the purpose of distinguishing each compressor and each interstage cooler for the convenience of description and has no substantial meaning.

[0034] In one embodiment of the present invention, the air compression device further includes a first connecting pipe 44, and the air inlet of one of the interstage coolers of the multi-stage interstage cooler is connected to one end of the first connecting pipe 44, specifically, the air inlet of the third 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 device through the low-temperature expander 18. By setting the first connecting pipe 44, the undivided air output by the second-stage compressor 2 can be introduced into the main heat exchanger 13 for cooling, and finally enters the distillation device after being expanded by the low-temperature expander 18.

[0035] 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 through 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 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, 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 through the first throttle valve 36.

[0036] 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 the nitrogen to circulate in the nitrogen circulation pipeline. Liquefied natural gas releases a large amount of cold energy during the vaporization process. During the circulation process, the nitrogen transfers the low-grade cold energy of the liquefied natural gas to the first nitrogen heat exchanger 22 and the LNG heat exchanger 25. Part of the low-grade cold energy is provided to the air compression device to reduce the energy consumption of the compression process, and the other part of the low-grade cold energy is output to the outside and provided to the surrounding factories.

[0037] The high-grade cold energy is transferred to the main heat exchanger 13 through the circulating nitrogen, so that the compressed air is cooled to a low-temperature gas state or liquefied. The circulating nitrogen is used as the intermediate heat exchange medium to separate the liquefied natural gas from the compressed air, thereby ensuring the safety of the system. In addition, the pressure of the circulating nitrogen is changed by the nitrogen compressor 24, so that the temperature of the nitrogen at the second inlet of the main heat exchanger 13 is lower than the lowest temperature of the compressed air cooling process, so as to efficiently utilize the high-grade cold energy of the liquefied natural gas. Part of the liquefied air is stored in the liquid air storage tank 16, which is used for expansion and power generation during non-trough periods, and the other part enters the distillation device, where liquid oxygen and liquid nitrogen are separated and output. During the energy release process, the liquid air vaporizes and enters the power generation device to expand and generate electricity. At the same time, in order to ensure the stable operation of the distillation device, the distillation device operates as usual during the energy release process, so that the cold energy of the liquefied natural gas during the energy release period can be fully recovered.

[0038] 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, and 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. Normal temperature high pressure air enters the main heat exchanger 13 and is cooled to liquefaction, 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.

[0039] In one embodiment of the present invention, the liquid air energy storage system further includes a second liquid air pump 26. The liquid 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. 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 into the main heat exchanger 13 to provide cold energy for the compressed air. After the liquid air exchanges heat with the compressed air, the liquid air is converted into normal temperature and high pressure air.

[0040] Furthermore, the gas outlet of the liquid air storage tank 16 is communicated with the sixth inlet of the main heat exchanger 13 through the return air pipeline, and the sixth outlet of the main heat exchanger 13 is communicated with the outside or the gas storage tank.

[0041] In one embodiment of the present invention, the power generation device includes a multi-stage expander and a plurality of heaters, and the air outlet of the upper stage expander is connected to the air inlet of the lower stage expander. A heater is provided at the air inlet of each stage expander, and the air inlet of the lowest stage expander is connected to the seventh outlet of the main heat exchanger 13 through a heater.

[0042] Specifically, Figure 1As shown, the power generation device 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 rotating 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 rotating shaft of the fourth-stage expander 31 is connected to the rotating shaft of the motor 35 .

[0043] In one embodiment of the present invention, the distillation device includes a subcooler 20, a high-pressure tower 19 and a low-pressure tower 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 tower 19 is connected to the low-temperature expander 18, and the second inlet of the high-pressure tower 19 is connected to the third throttle valve 17; the first outlet of the high-pressure tower 19 is connected to the first inlet of the subcooler 20, the second outlet of the high-pressure tower 19 is connected to the second inlet of the subcooler 20, and the third outlet of the high-pressure tower 19 is connected to the third inlet of the subcooler 20. The low-pressure tower 21 is arranged at the upper part of 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, and the first outlet of the low-pressure tower 21 is connected to the fourth inlet of the subcooler 20.

[0044] Working principle of the liquid air energy storage system coupling LNG and air separation unit of the present invention: In the energy storage process, the air is cooled in the first interstage cooler 5 and then enters the first compressor 1. The compressed air temperature is higher than normal temperature. After being cooled to normal temperature in the first interstage cooler 9, it is cooled to a lower temperature in the second interstage cooler 6 to reduce the energy consumption of the compressor. After four stages of compression and four stages of cooling, the normal temperature high-pressure air enters the main heat exchanger 13 and is further cooled. A part 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 air pipeline to provide cold energy for the compressed air.

[0045] The two streams of air entering through the third inlet and the fifth inlet of the main heat exchanger 13 are cooled in the main heat exchanger 13, and are depressurized by the third throttle valve 17 and the cryogenic expander 18 respectively and enter the high-pressure tower 19. After rectification, liquid nitrogen and oxygen-enriched liquid air are obtained at the top and bottom of the high-pressure tower 19, and an oxygen-depleted liquid air is extracted from the middle of the high-pressure tower 19 and enters the subcooler 20 for further cooling. The liquid nitrogen output from the high-pressure tower 19 is cooled in the subcooler 20, and then throttled by the sixth throttle valve 40. After throttling, a part of it is output as product liquid nitrogen, and the other part enters from the top of the low-pressure tower 21 and serves as reflux liquid. The oxygen-enriched liquid air and the oxygen-depleted liquid air supercooled in the subcooler 20 are throttled by the fourth throttle valve 38 and the fifth throttle valve 39 and enter the middle and upper part of the low-pressure tower 21. After rectification, liquid oxygen is obtained at the bottom of the low-pressure tower 21 and is output as product liquid oxygen. Dirty nitrogen is produced at the top of the low-pressure tower 21 and enters the subcooler 20 to provide cold energy for other streams.

[0046] The circulating nitrogen leaving the second outlet of the main heat exchanger 13 enters the first nitrogen heat exchanger 22 and the second nitrogen heat exchanger 23 to be cooled by LNG and dirty nitrogen. The cooled nitrogen is compressed to high pressure in the nitrogen compressor 24 and enters the first nitrogen heat exchanger 22 and the second nitrogen heat exchanger 23 again to be cooled. After throttling by the first throttle valve 36, the temperature of the circulating nitrogen is relatively low and has the ability to cool the compressed air. After the dirty nitrogen is heat exchanged in the second nitrogen heat exchanger 23, it enters the main heat exchanger 13 to provide cold energy for the compressed air. Subsequently, LNG and dirty nitrogen enter the LNG heat exchanger 25 for further heating, and the cold energy is recovered by methanol. Part of the cold energy is supplied to the air compressor to compress the air to reduce the energy consumption of the compressor, and the other part of the low-grade cold energy is supplied to the surrounding factories as a product.

[0047] During the energy release process, the air is divided into two streams, one part of the air enters the main heat exchanger 13 through the first connecting pipe 44, and the other part of the air enters the main heat exchanger 13 through the fourth-stage cooler 12. The latter has a higher pressure than the former and is easier to liquefy. After cooling, the liquid air and the low-temperature air enter the distillation device through the third throttle valve 17 and the low-temperature expander 18 respectively. At the same time, the liquid air is pressurized by the second liquid air pump 26 and enters the main heat exchanger 13 to provide cold energy for the compressed air, and is reheated to room temperature. This stream of air is heated by the first heater 27 and enters the first-stage expander 28. After multi-stage heating and multi-stage expansion, the air expands to normal pressure and outputs work to the outside, driving the motor 35 to generate electricity. During the energy release process, in addition to the circulating nitrogen and dirty nitrogen providing cold energy for the compressed air, the liquid air from the liquid air storage tank 16 also provides cold energy. Since the cold energy obtained by the compressed air increases, the power consumption of the compression process is reduced.

[0048] The flow rates in each compressor are different during the energy storage process and the energy release process. During the energy storage process, three air streams enter the main heat exchanger 13 after four-stage compression, two of which enter the distillation device after cooling, and the other is stored in the liquid air storage tank 16 after liquefaction. During the energy release process, in order to ensure the continuous operation of the distillation device, the flow rates of the first two air streams remain unchanged, but one of the air is only compressed in two stages. Since the change in flow rate will affect the efficiency of the compressor, in order to ensure the efficient operation of the compressor, LNG-LAES-ASU is equipped with three sets of parallel compressor units, which are compressed to obtain three compressed air respectively. In addition, due to seasonal fluctuations in the vaporization amount of liquefied natural gas. In order to cope with this problem, the load of the nitrogen compressor 24 and the distillation device is adjusted according to the vaporization amount of liquefied natural gas, so as to efficiently absorb the cold energy of liquefied natural gas.

[0049] The liquid air energy storage system coupled with LNG and an air separation unit provided by the present invention has the following advantages: 1. The liquid air energy storage system coupled with LNG and an air separation unit provided by the present invention couples the air separation unit, eliminates the cold storage unit of the original energy storage system, avoids the use of large-scale liquid cold storage medium, and improves the safety of the system.

[0050] 2. The liquid air energy storage system coupled with LNG and air separation unit provided by the present invention uses circulating nitrogen as the intermediate heat exchange medium, and utilizes nitrogen expansion refrigeration cycle to recover high-grade cold energy of liquefied natural gas and improve the quality of cold energy to match the temperature zone of compressed air cooling liquefaction process. At the same time, nitrogen can isolate LNG and compressed air to ensure system safety. In addition, the low-grade cold energy of liquefied natural gas is used to cool the air between compressor stages, reducing the energy consumption of the compressor to improve system efficiency.

[0051] 3. The liquid air energy storage system coupled with LNG and an air separation unit provided by the present invention stores part of the liquefied air in a liquid air storage tank 16, which is used for expansion and power generation during non-peak periods, and the remaining part enters a distillation unit as a feed gas, while supplementing cooling capacity for the air separation tower.

[0052] The present invention further provides a liquid air energy storage method for coupling LNG and an air separation unit. The energy storage method is based on the liquid air energy storage system for coupling LNG and an air separation unit described in any one of the above embodiments, comprising: Step S100, the air compression device compresses the air and cools the air to obtain normal temperature and high pressure air; 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 normal temperature high pressure air, and the liquefied liquid air is stored in the liquid air storage tank 16; Step S300, the liquid air outputted from the liquid air storage tank 16 enters the main heat exchanger 13 to provide cold energy for the normal temperature and high pressure air, and the liquid air is restored to the normal temperature and high pressure air; In step S100, the power generation device expands and heats the input high-pressure air at room temperature to drive the motor 35 to generate electricity.

[0053] 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 air energy storage system coupling LNG and an air separation unit, characterized in that: include: LNG tank (43); An air compression device, the air compression device is used to compress the air and cool the air to obtain high-pressure air at room temperature; A main heat exchanger (13), the main heat exchanger (13) being in communication with the air compression device; a nitrogen circulation device, the nitrogen circulation device being in communication with the main heat exchanger (13), the LNG tank (43) and the air compression device, the nitrogen circulation device being used to use nitrogen as a heat exchange medium to transfer cold energy of the LNG to the air compression device and the main heat exchanger (13), the main heat exchanger (13) being used to liquefy normal temperature and high pressure air; a liquid air storage tank (16), the liquid air storage tank (16) being in communication with the main heat exchanger (13), and the liquid air storage tank (16) being used to store liquid air; a distillation device, the distillation device being in communication with the nitrogen circulation device and the main heat exchanger (13); A power generation device is connected to the main heat exchanger (13).

2. The liquid air energy storage system for coupling LNG and an air separation unit according to claim 1 is characterized in that: The air compression device comprises: Multi-stage compressor; Hot water tank (41); an LNG heat exchanger (25), wherein a first inlet of the LNG heat exchanger (25) is in communication with an outlet of the hot water tank (41), and a second inlet of the LNG heat exchanger (25) is in communication with a first outlet of the main heat exchanger (13); a cold water tank (42), wherein an inlet of the cold water tank (42) is connected to a first outlet of the LNG heat exchanger (25); A multi-stage interstage cooler, wherein the compressors of two adjacent stages are connected via the corresponding interstage coolers, the air inlet of the interstage cooler of the lowest stage is connected to the atmosphere, the air outlet of the compressor of the highest stage is connected to the third inlet and the fifth inlet of the main heat exchanger (13), the third outlet of the main heat exchanger (13) is connected to the distillation device via a third throttle valve (17), the liquid inlet of the hot water tank (41) is connected to the liquid outlet of each interstage cooler, and the liquid outlet of the cold water tank (42) is connected to the liquid inlet of each interstage cooler.

3. The liquid air energy storage system for coupling LNG and an air separation unit according to claim 2 is characterized in that: The air compression device also includes: A multi-stage cooler is provided at the air outlet of each stage of the compressor.

4. The liquid air energy storage system for coupling LNG and an air separation unit according to claim 2, characterized in that: The air compression device also includes: A first connecting pipe (44), wherein an air inlet of one of the interstage coolers of the multi-stage interstage cooler is connected to one end of the first connecting pipe (44), and the other end of the first connecting pipe (44) is connected to a fourth inlet of the main heat exchanger (13), and the fourth outlet of the main heat exchanger (13) is connected to the distillation device via a low-temperature expander (18).

5. The liquid air energy storage system coupling LNG and an air separation unit according to any one of claims 2 to 4, characterized in that: The nitrogen circulation device comprises: a first nitrogen heat exchanger (22), wherein a first inlet of the first nitrogen heat exchanger (22) is connected to a second outlet of the main heat exchanger (13); the LNG tank (43) is connected to a 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 a third inlet of the LNG heat exchanger (25); a second nitrogen heat exchanger (23), wherein a first outlet of the second nitrogen heat exchanger (23) is communicated with a first inlet of the main heat exchanger (13), and a second inlet of the second nitrogen heat exchanger (23) is communicated with a first outlet of the first nitrogen heat exchanger (22); a nitrogen compressor (24), wherein the inlet of the nitrogen compressor (24) is communicated with the second outlet of the second nitrogen heat exchanger (23), the outlet of the nitrogen compressor (24) is communicated with the second inlet of the first nitrogen heat exchanger (22), the second outlet of the first nitrogen heat exchanger (22) is communicated with the third inlet of the second nitrogen heat exchanger (23), and the third outlet of the second nitrogen heat exchanger (23) is communicated with the second inlet of the main heat exchanger (13) via a first throttle valve (36).

6. The liquid air energy storage system for coupling LNG and an air separation unit according to any one of claims 1 to 4, characterized in that: The liquid air energy storage system further comprises: a liquid expander (14), wherein an inlet of the liquid expander (14) is connected to a fifth outlet of the main heat exchanger (13); A second throttle valve (15), wherein 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).

7. The liquid air energy storage system for coupling LNG and an air separation unit according to claim 6, characterized in that: The liquid air energy storage system further comprises: A second liquid air pump (26), wherein the liquid 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.

8. The liquid air energy storage system for coupling LNG and an air separation unit according to claim 7, characterized in that: The power generation device comprises: A multi-stage expander, wherein the air outlet of the expander of the previous stage is connected to the air inlet of the expander of the next stage; A plurality of heaters are provided, one heater being arranged at the air inlet of each stage of the expander, and the air inlet of the lowest stage of the expander is connected to the seventh outlet of the main heat exchanger (13) through one of the heaters.

9. The liquid air energy storage system for coupling LNG and an air separation unit according to claim 5, characterized in that: The distillation device comprises: A subcooler (20); a fourth outlet of the subcooler (20) is in communication with a first inlet of the second nitrogen heat exchanger (23); a high-pressure tower (19), wherein a first inlet of the high-pressure tower (19) is connected to the low-temperature expander (18), and a second inlet of the high-pressure tower (19) is connected to the third throttle valve (17); a first outlet of the high-pressure tower (19) is connected to a first inlet of the subcooler (20), a second outlet of the high-pressure tower (19) is connected to a second inlet of the subcooler (20), and a third outlet of the high-pressure tower (19) is connected to a third inlet of the subcooler (20); A low-pressure tower (21), wherein the low-pressure tower (21) is arranged at the upper part of 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 a fourth throttle valve (38), the second inlet of the low-pressure tower (21) is connected to the second outlet of the subcooler (20) through a fifth throttle valve (39), the third inlet of the low-pressure tower (21) is connected to the third outlet of the subcooler (20) through a sixth throttle valve (40), and the first outlet of the low-pressure tower (21) is connected to the fourth inlet of the subcooler (20).

10. A liquid air energy storage method for coupling LNG and an air separation unit, the energy storage method is based on the liquid air energy storage system for coupling LNG and an air separation unit according to any one of claims 1 to 9, characterized in that: include: The air compressor compresses the air and cools it down to obtain high-pressure air at room temperature; The nitrogen circulation device uses nitrogen as a heat exchange medium to transfer cold energy of LNG to the air compression device and the main heat exchanger (13), so that the main heat exchanger (13) liquefies the normal 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 cold energy for the normal temperature and high pressure air, and the liquid air is restored to normal temperature and high pressure air; The power generation device expands and heats the input high-pressure air at normal temperature to drive the electric motor to generate electricity.

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