Cold energy air separation system based on liquid air energy storage

Abstract

The invention relates to a cold energy air separation system based on liquid air energy storage, comprising: an air pretreatment unit comprising an air filter, an air compressor, a first cooler and an air purification system which are sequentially connected in series; the rectifying unit comprises a rectifying tower, a main cold box, a first heat exchanger and an argon rectifying system, a gas outlet of the air purifying system is connected with a gas inlet of the main cold box, a gas outlet of the main cold box is connected with a gas inlet of a lower tower of the rectifying tower, and a nitrogen outlet in the top of the lower tower of the rectifying tower is connected with a gas inlet of the argon rectifying system; another nitrogen outlet of the rectifying tower is connected with a gas inlet of the first heat exchanger, and a liquid nitrogen inlet of the first heat exchanger is connected with a liquid nitrogen outlet of the LNG cold box; the cooling capacity supply unit is used for providing cooling capacity for the system; and the energy storage unit comprises a liquid air storage tank connected with the air compressor and is used for providing liquid air for the air compressor. According to the system, refrigeration is conducted in a compression expansion throttling mode when no extra cold energy is supplied.

Description

Technical Field

[0001] This invention relates to a cold energy air separation system based on liquid air energy storage, belonging to the field of liquid air energy storage technology. Background Technology

[0002] LNG-based cold energy air separation is a novel air separation technology. The difference between this technology and conventional air separation lies in its use of LNG cold energy to replace the mechanical refrigeration that consumes a large amount of electricity in conventional processes, significantly reducing system energy consumption. The main cost of an air separation unit depends on its energy consumption level. LNG cold energy air separation technology has relatively low energy consumption, and using LNG cold energy to cool and liquefy air can significantly reduce the power consumption of the air separation process. However, in actual operation, the unstable output of LNG from LNG receiving terminals may lead to intermittent shutdowns of the cold energy air separation unit. These shutdowns not only result in decreased sales but may also lead to the loss of long-term customers. Therefore, there is an urgent need for a method to ensure the normal operation of cold energy air separation units even without LNG. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a cold energy air separation system based on liquid air energy storage. This system utilizes liquid air energy storage technology, employing a compression-expansion throttling method for cooling when no additional cold energy supply is available. The generated cooling capacity replaces LNG and is transferred to nitrogen circulation for cooling the air separation unit, enabling operation even without LNG exports. Simultaneously, the liquid air storage system liquefies and stores the cooling capacity of air during off-peak electricity hours at night, transferring this cooling capacity to the high-purity nitrogen that would otherwise be released from the air separation unit throughout the day, thus increasing the daily production of liquid nitrogen from the air separation system.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A cold energy air separation system based on liquid air energy storage includes: The air pretreatment unit includes an air filter, an air compressor, a first cooler, and an air purification system connected in series. The distillation unit includes a distillation column, a main cold box, a first heat exchanger, and an argon distillation system. The outlet of the air purification system is connected to the inlet of the main cold box, the outlet of the main cold box is connected to the inlet of the lower column of the distillation column, the nitrogen outlet at the top of the lower column of the distillation column is connected to the inlet of the argon distillation system, another nitrogen outlet of the distillation column is connected to the inlet of the first heat exchanger, and the liquid nitrogen inlet of the first heat exchanger is connected to the liquid nitrogen outlet of the LNG cold box. The nitrogen exchanges heat with the liquid nitrogen from the LNG cold box in the first heat exchanger and is liquefied before returning to the top of the lower column of the distillation column, thereby completing the transfer of cold energy. In the cooling supply unit, when LNG provides cooling capacity, liquid nitrogen from the LNG cold box is compressed and further cooled and throttled into pressurized liquid nitrogen in the first subcooler. A portion of the pressurized liquid nitrogen returns to the first subcooler and the LNG cold box as a cooling source. The remaining pressurized liquid nitrogen enters the main cold box, is throttled, and then enters the first heat exchanger to exchange heat with the pressurized nitrogen extracted from the bottom of the distillation column. After being vaporized, it enters the main cold box for reheating and then returns to the first nitrogen booster, which is connected to the LNG cold box. When no LNG provides cooling capacity, the required cooling capacity of the system is transferred from liquid air to nitrogen. The nitrogen in the main cold box exchanges heat with liquid air in the second liquid air-nitrogen heat exchanger and condenses into liquid nitrogen. After being supplied with circulating pressure by the liquid nitrogen pump, it enters the second liquid separator and finally enters the liquid nitrogen storage tank. The energy storage unit includes a liquid air tank connected to an air compressor for supplying liquid air to the air compressor.

[0006] The cold energy air separation system based on liquid air energy storage preferably includes two adsorbers arranged in parallel.

[0007] The aforementioned cold energy air separation system based on liquid air energy storage preferably has an adsorber with a double-bed structure, with activated alumina at the bottom and molecular sieve at the top. When one unit is running, the other unit is regenerating, and the regeneration gas source is the main cold box that transports waste nitrogen.

[0008] Preferably, the liquid air energy storage-based cold energy air separation system further includes a second heat exchanger in the distillation unit. The second heat exchanger is connected to the distillation column and the argon distillation system. Part of the nitrogen gas generated in the distillation column is subcooled and throttled by the second heat exchanger and then sent to the top of the upper column of the distillation column as the upper column reflux liquid to participate in the upper column distillation.

[0009] Preferably, in the liquid air energy storage-based cold energy air separation system, the second heat exchanger is also connected to the main cold box, which is connected to the first nitrogen booster. Low-pressure pure nitrogen is obtained from the top of the distillation column, and after being reheated to a certain temperature by the second heat exchanger and the main cold box, it is sent to the first nitrogen booster as the raw nitrogen for liquid nitrogen products. A portion of low-temperature, low-pressure nitrogen is drawn from the distillation column, pressurized by the third nitrogen booster, and then liquefied by the liquid air from the cold energy supply unit in the first liquid air-nitrogen heat exchanger. This liquefied nitrogen is then sent to the liquid nitrogen storage tank as product liquid nitrogen. Liquid oxygen is drawn from the bottom of the middle layer of the distillation column, subcooled by the second heat exchanger, and then sent out of the main cold box as product liquid oxygen.

[0010] Preferably, the energy storage unit of the cold energy air separation system based on liquid air energy storage includes an air compression cooling component, a molecular sieve, an air cold box, and a liquid air storage tank connected in series, with the liquid air storage tank connected to the air compressor.

[0011] The aforementioned cold energy air separation system based on liquid air energy storage preferably includes an air compression cooling component comprising a first air compressor, a first air cooler, a second air compressor, and a second air cooler connected in series.

[0012] The aforementioned cold energy air separation system based on liquid air energy storage preferably stores liquid air at night. During the energy storage stage, air enters from the first air compressor, is cooled by the first air cooler, and then enters the molecular sieve. After being dehydrated and decarbonized in the molecular sieve, the air enters the second air compressor, is cooled by the second air cooler, and then enters the air cold box. One part of the air entering the air cold box is drawn through an air expander to provide cooling, while the other part is directly cooled into liquid and then depressurized through a liquid air throttle valve for further cooling before entering the air separator for gas-liquid separation. The separated gas flows back to the air cold box to provide cooling before entering the second air compressor, and the separated liquid enters the liquid air storage tank for storage.

[0013] Preferably, in the liquid air energy storage-based cold energy air separation system, the liquid air releases energy during the day. When LNG provides cooling capacity, during the energy release phase, the liquid air is pumped from the liquid air storage tank into the first liquid air-nitrogen heat exchanger to exchange heat with the high-purity nitrogen gas released from the top of the distillation column. After heat exchange, the liquid air releases cooling capacity and becomes air, returning to the air compressor. After heat exchange, the high-purity nitrogen gas absorbs cooling capacity and becomes liquid nitrogen, entering the liquid nitrogen storage tank. During the day, liquid air releases energy. When there is no LNG to provide cooling, during the energy release phase, liquid air is pumped from the liquid air storage tank into the second liquid air-nitrogen heat exchanger to exchange heat with nitrogen. After releasing cooling energy and becoming air, the liquid air further releases cooling energy to ethylene glycol in the ethylene glycol cooler before returning to the air compressor. Nitrogen condenses into liquid nitrogen and enters the liquid nitrogen storage tank.

[0014] Preferably, in the liquid air energy storage-based cold energy air separation system, an argon fraction gas is drawn from the lower part of the distillation column and sent to the argon distillation system for distillation to reduce the oxygen content. The oxygen-rich liquid air drawn from the supercooled column is throttled and sent into the system as the first cold source. Liquid nitrogen drawn from the middle of the distillation column is supercooled by a second heat exchanger as the second cold source. Pressurized nitrogen drawn from the top of the lower part of the distillation column is used as a heat source to evaporate the liquid argon and liquefy the nitrogen. After full distillation to produce argon, 99.999% pure liquid argon is obtained. Finally, the liquid argon is drawn from the argon distillation system into the liquid argon storage tank as the product liquid argon.

[0015] The present invention has the following advantages due to the adoption of the above technical solutions: 1. The cold energy air separation system of the present invention has the functions of air separation and liquid air supplementation, making full use of the function of liquid air energy storage for off-peak cooling to supplement the problem of insufficient cold energy air separation cooling caused by LNG cold energy fluctuations.

[0016] 2. The cold energy air separation system of the present invention is suitable for air separation systems near LNG receiving terminals. It improves the utilization rate of LNG cold energy at the receiving terminal by utilizing LNG cold energy, and promotes the balance of the power system by using a liquid air energy storage system to regulate the peak-valley difference of the nearby power system. At the same time, it increases the output of air separation products by simultaneously utilizing LNG cold energy utilization and liquid air energy storage technology.

[0017] 3. This invention utilizes liquid air energy storage technology to store cold energy, solving the cold energy supply problem for air separation when LNG exports are insufficient or unstable. By using liquid air energy storage for off-peak cold storage, the production of liquid nitrogen from air separation is increased. Simultaneously, the liquid air enables the cascaded utilization of cold energy, providing cooling for the nitrogen cycle and then for the ethylene glycol cycle. This invention allows for a smooth switch between LNG cold energy supply and non-LNG cold energy supply, and can be implemented on existing air separation projects without altering the original air separation process. Attached Figure Description

[0018] Figure 1 A flowchart of a cold energy air separation system based on liquid air energy storage provided in an embodiment of the present invention; The attached figures are labeled as follows: 1-Air filter, 2-Air compressor, 3-First cooler, 4-Adsorber, 5-First heater; 11-First nitrogen booster, 12-Second nitrogen booster, 13-LNG cold box, 14-First subcooler, 15-First throttle valve; 21-First air compressor, 22-First air cooler, 23-Molecular sieve, 24-Second air compressor, 25-Second air cooler, 26-Air cold box, 27-Air expander, 28-Liquid air throttle valve, 29-Air separator; 31-Distillation column, 32-Main cold box, 33-Second separator, 34-Third throttle valve, 35-First heat exchanger, 36-Liquid nitrogen storage tank, 37-Liquid oxygen storage tank, 38-Second heat exchanger; 41-Argon distillation system, 42-Liquid argon storage tank, 43-Fourth throttle valve, 44-Fifth throttle valve; 51-Liquid air storage tank, 52-Liquid air pump, 53-Third nitrogen booster, 54-First liquid air-nitrogen heat exchanger, 55-Second liquid air-nitrogen heat exchanger, 56-Ethylene glycol cooler, 57-Liquid nitrogen pump. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. 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.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," "third," "fourth," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0021] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "above," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure.

[0022] LNG-based cold energy air separation is a novel air separation technology. The difference between this technology and conventional air separation lies in its use of LNG cold energy to replace the mechanical refrigeration that consumes a large amount of electricity in conventional processes, significantly reducing system energy consumption. The main cost of an air separation unit depends on its energy consumption level. LNG cold energy air separation technology has relatively low energy consumption, and using LNG cold energy to cool and liquefy air can significantly reduce the power consumption of the air separation process. However, in actual operation, the unstable output of LNG from LNG receiving terminals may lead to intermittent shutdowns of the cold energy air separation unit. These shutdowns not only result in decreased sales but may also lead to the loss of long-term customers. Therefore, there is an urgent need for a method to ensure the normal operation of cold energy air separation units even without LNG.

[0023] To address the aforementioned technical problems, this invention provides a cold energy air separation system based on liquid air energy storage. This system utilizes liquid air energy storage technology, employing a compression-expansion throttling method for cooling when no additional cold energy supply is available. The generated cooling capacity replaces LNG and is transferred to nitrogen circulation for cooling the air separation unit, enabling operation even without LNG exports. Simultaneously, the liquid air storage system liquefies and stores cooling capacity during off-peak electricity hours at night, transferring this cooling capacity to the high-purity nitrogen that would otherwise be released from the air separation unit throughout the day, thus increasing the daily production of liquid nitrogen from the air separation system.

[0024] like Figure 1 As shown, the cold energy air separation system based on liquid air energy storage involved in this invention includes: The air pretreatment unit includes an air filter 1, an air compressor 2, a first cooler 3, and an air purification system connected in series. The distillation unit includes a distillation column 31, a main cold box 32, a first heat exchanger 35, and an argon distillation system 41. The outlet of the air purification system is connected to the inlet of the main cold box 32, and the outlet of the main cold box 32 is connected to the lower column inlet of the distillation column 31. The nitrogen outlet at the top of the lower column of the distillation column 31 is connected to the inlet of the argon distillation system 41. Another nitrogen outlet of the distillation column 31 is connected to the inlet of the first heat exchanger 35. The liquid nitrogen inlet of the first heat exchanger 35 is connected to the liquid nitrogen outlet of the LNG cold box 13. Nitrogen exchanges heat with liquid nitrogen from the LNG cold box 13 in the first heat exchanger 35 and is liquefied before returning to the top of the lower column of the distillation column 31, thus completing the transfer of cooling capacity. The cooling supply unit, when LNG provides cooling capacity, supplies cooling from the LNG cold box... The liquid nitrogen in 13 is compressed and further cooled and throttled into pressurized liquid nitrogen in the first subcooler 14. A portion of the pressurized liquid nitrogen returns to the first subcooler 14 and the LNG cold box 13 as a cold source. The remaining pressurized liquid nitrogen enters the main cold box 32 and is throttled before entering the first heat exchanger 35 to exchange heat with the pressurized nitrogen extracted from the bottom of the distillation column 31. After being vaporized, it enters the main cold box 32 for reheating and then returns to the first nitrogen booster 11. The first nitrogen booster 11 is connected to the LNG cold box 13. When there is no LNG to provide cooling, the cooling required by the system is transferred from liquid air to nitrogen. The nitrogen in the main cold box 32 exchanges heat with liquid air in the second liquid air-nitrogen heat exchanger 55 and condenses into liquid nitrogen. After being provided with circulating pressure by the liquid nitrogen pump 57, it enters the second liquid separator 33 and finally enters the liquid nitrogen storage tank 36. The energy storage unit includes a liquid air storage tank 51 connected to the air compressor 2, which is used to supply liquid air to the air compressor 2.

[0025] Specifically, the specific workflow of the cold energy air separation system of the present invention is as follows: 1. Filtration, compression, precooling, and purification: The raw material process air is drawn in through the intake port, enters the air filter 1 to remove dust and mechanical impurities, and then passes through the inlet silencer before entering the air compressor 2 for compression. The compressed air is cooled by the first cooler 3 and then sent to the air purification system. The cooling medium between the compressor stages and the final stage is an aqueous solution of ethylene glycol. The air purification system adsorbs moisture, carbon dioxide, and some hydrocarbons. The adsorber 4 in the air purification system consists of two vertical containers with a double-bed structure. The bottom of the adsorption container is activated alumina, and the top is a molecular sieve. When one container is running, the other is regenerating. The regeneration air source is waste nitrogen from the cold box that has been heated by the first heater 5.

[0026] Air distillation: Clean process air from the air purification system enters the main cold box 32 within the cold box. After being cooled to near its dew point by the returning gas, it enters the bottom of the lower column of distillation column 31 to participate in the lower column distillation. In the lower column of distillation column 31, the rising gas and the falling liquid are in full contact. After heat and mass transfer, the nitrogen concentration in the rising gas gradually increases, and the oxygen content in the falling liquid gradually increases. Pressurized nitrogen is obtained at the top of the lower column of distillation column 31. A small portion of the pressurized nitrogen is extracted as a heat source for the argon distillation system 41. Another portion of the pressurized nitrogen is extracted and enters the first heat exchanger 35 to exchange heat with the pressurized liquid nitrogen from the LNG cold box 13. After being liquefied, the liquid nitrogen returns to the top of the lower column of distillation column 31, thus completing the transfer of cooling capacity. The remaining nitrogen enters the middle layer of distillation column 31 and is condensed into liquid nitrogen. Except for a portion used as reflux liquid in the lower column of distillation column 31, the remaining liquid nitrogen is subcooled and throttled in the second heat exchanger 38 and sent to the top of the upper column of distillation column 31 as reflux liquid, participating in the distillation in the upper column of distillation column 31. Simultaneously with the condensation of nitrogen, the liquid oxygen in the middle layer of distillation column 31 is vaporized, serving as the rising gas for the distillation in the upper column of distillation column 31. The oxygen-enriched liquid air generated at the bottom of the lower section of distillation column 31 is subcooled by the second heat exchanger 38 and then throttled by the fourth throttling valve 43 before being sent to the middle section of the upper section of distillation column 31 to participate in the distillation process. After distillation in the upper section of distillation column 31, low-pressure nitrogen, impure nitrogen, and oxygen are obtained. A small amount of liquid nitrogen is extracted from the top of the upper section of distillation column 31 and sent out of the cold box as product liquid nitrogen. Liquid oxygen is extracted from the bottom of the middle section of distillation column 31, subcooled by the second heat exchanger 38, and then sent out of the cold box as product liquid oxygen. Low-pressure pure nitrogen is obtained from the top of the distillation column 31. After being reheated to a certain temperature by the second heat exchanger 38 and the main cold box 32, it is sent to the first nitrogen booster 11 as the raw nitrogen for liquid nitrogen products. A portion of the low-temperature, low-pressure nitrogen extracted from the middle section is pressurized by the third nitrogen booster 53 and then liquefied by the liquid air from the liquid air cooling unit in the first liquid air-nitrogen heat exchanger 54. This liquefied nitrogen is then sent to the liquid nitrogen storage tank 36 as product liquid nitrogen. In the upper part of the distillation column 31, waste nitrogen is obtained. After being reheated by the second heat exchanger 38 and the main cold box 32, it is sent out of the cold box. A portion of it is used as regeneration gas for the purification system, and the remainder is vented. Medium-pressure liquid nitrogen from the LNG cold box 13 is throttled by the third throttle valve 34 and enters the second liquid separator 32 for gas-liquid separation. This liquid nitrogen is then sent to the liquid nitrogen storage tank 36 as product liquid nitrogen.

[0027] Cooling supply: When LNG provides cooling capacity, the required cooling capacity of the unit is transferred from LNG to liquid nitrogen, which comes from the LNG cold box 13. The high-pressure liquid nitrogen, after being compressed, liquefied, and subcooled in the first subcooler 14, is throttled to medium-pressure liquid nitrogen. Part of it returns to the first subcooler 14 and the LNG cold box 13; part of it is throttled into pressurized liquid nitrogen through the first throttling valve 15 and returns to the first subcooler 14 and the LNG cold box 13 as a cooling source; the remainder enters the main cold box 32, is throttled, and then enters the first heat exchanger 35, where it exchanges heat with the pressurized nitrogen extracted from the lower column of the distillation column 31 and is vaporized. After being reheated in the main cold box 32, it returns to the inlet of the first nitrogen booster 11, transferring the cooling capacity from LNG to the air separation system.

[0028] When there is no LNG to provide cooling, the cooling required by the unit is transferred to nitrogen by liquid air. The nitrogen comes from the main cold box 32. In the main cold box, the nitrogen exchanges heat with liquid air in the second liquid air-nitrogen heat exchanger 55 and condenses into liquid nitrogen. After being provided with circulation pressure by the liquid nitrogen pump 57, it enters the second liquid distribution tank 33 and then enters the liquid nitrogen storage tank 36.

[0029] When LNG cooling capacity is available, off-peak electricity is used at night to liquefy additional liquid air for cooling storage. After releasing cooling capacity using liquid air throughout the day, additional high-purity nitrogen is liquefied for further cooling. Therefore, the liquid air-based cold energy air separation system has the function of storing cooling capacity. When LNG cooling capacity is unavailable, off-peak electricity is used at night to liquefy additional liquid air for cooling storage. After releasing cooling capacity using liquid air throughout the day, nitrogen is circulated for further cooling. Therefore, the liquid air-based cold energy air separation system has the function of providing backup cooling energy when LNG cooling capacity is unavailable. In summary, the liquid air-based cold energy air separation system has one energy storage line and two energy release lines. The energy release lines can supplement the cooling capacity of the cold energy air separation system regardless of the availability of LNG.

[0030] When there is no LNG cooling capacity, the cooling energy of the liquid air is utilized in a cascade manner. The high-grade cooling capacity of the liquid air is transferred to the nitrogen cycle through a liquid air-nitrogen heat exchanger. The nitrogen cycle, after liquefaction, provides cooling capacity to the distillation column and then circulates. The remaining low-grade cooling capacity of the liquid air is sent to the air compressor interstage cooler, final stage cooler, oil cooler, and motor cooler via ethylene glycol.

[0031] Energy storage: Liquid air is stored at night. During the storage phase, air enters from the first air compressor 21, is cooled by the first air cooler 22, and then enters the molecular sieve 23. After being dehydrated and decarbonized in the molecular sieve 23, the air enters the second air compressor 24, is cooled by the second air cooler 25, and then enters the air cold box 26. One part of the air entering the air cold box 26 is drawn through the air expander 27 to provide cooling, and the other part is directly cooled into liquid and then depressurized and further cooled by the liquid air throttle valve 28 before entering the air separator for gas-liquid separation. The separated gas flows back to the air cold box 26 to provide cooling for the cold box and then enters the inlet of the second air compressor 25. The separated liquid enters the liquid air storage tank 51 for storage.

[0032] During the daytime, liquid air releases energy. When LNG provides cooling, during the energy release phase, liquid air is pumped from liquid air storage tank 51 through liquid air pump 52 and exchanged with high-purity nitrogen that should have been vented from the top of the tower in the first liquid air-nitrogen heat exchanger 54. Before the heat exchange, the high-purity nitrogen is pressurized by the third nitrogen booster 53. After the heat exchange, the liquid air releases cooling energy and becomes air, returning to the inlet of air compressor 2. After the heat exchange, the high-purity nitrogen absorbs cooling energy and becomes liquid nitrogen, which enters liquid nitrogen storage tank 36.

[0033] During the daytime, liquid air releases energy. When there is no LNG to provide cooling, during the energy release phase, liquid air is pumped from liquid air storage tank 51 through liquid air pump 52 and exchanged with nitrogen in the second liquid air-nitrogen heat exchanger 55. After releasing cooling energy and becoming air, the liquid air further releases cooling energy to ethylene glycol in ethylene glycol cooler 56 and then returns to the inlet of air compressor 2. After condensing into liquid nitrogen, it enters the second liquid separator 33 and then the liquid nitrogen storage tank 36 after being provided with circulation pressure by liquid nitrogen pump 57.

[0034] Argon extraction: Argon extraction employs a full distillation argon production technology. To produce argon, an argon fraction is drawn from an appropriate position at the bottom of the upper part of the distillation column 31 and fed into the argon distillation system 41 for distillation to reduce the oxygen content. The oxygen-rich liquid air drawn from the supercooled column is throttled by the fifth throttle valve 44 and fed into the system as the first cold source. Liquid nitrogen drawn from the middle of the distillation column 31 is supercooled by the second heat exchanger 38 as the second cold source. Pressurized nitrogen drawn from the top of the lower part of the distillation column 31 is used as the heat source to evaporate the liquid argon, while the nitrogen is liquefied. After full distillation argon production, 99.999% Ar pure liquid argon is obtained and drawn from the argon distillation system 41 into the liquid argon storage tank 42 as the product liquid argon.

[0035] LNG / NG transportation: A portion of the high-pressure, cryogenic LNG from the receiving terminal's booster pump is transported via pipeline to the air separation zone, serving as a cold source in the LNG cold box 13 of the LNG cold energy recovery cold box system. A portion of this LNG is directly vaporized and reheated to above 1°C before entering the user's pipeline network. The remaining LNG is drawn from the central plate section of LNG cold box 13 and used as a cold source by the first cooler 3, transferring its high-temperature cooling capacity to ethylene glycol. It then vaporizes and reheats to above 1°C before being transported via pipeline to the LNG receiving terminal's NG pipeline network. The LNG / NG transport can be quickly isolated from the receiving terminal via valves, and multiple manual valves ensure the safety of the LNG receiving terminal. Due to the peak-shaving characteristics of the LNG receiving terminal, the LNG supply is discontinuous.

[0036] Ethylene glycol circulating cooling system: The ethylene glycol aqueous solution, cooled by LNG, is used as a cooling medium and fed into the interstage cooler, final stage cooler, oil cooler, and motor cooler of air compressor 2; as well as the interstage cooler, final stage cooler, and oil cooler of the first nitrogen booster compressor 11, and the oil cooler and motor cooler of the second nitrogen booster compressor 12. During startup, the cryogenic LNG directly exchanges heat with the ethylene glycol aqueous solution. Under normal operating conditions, the cryogenic cooling capacity of the LNG is absorbed by the circulating nitrogen, and the high-temperature cooling capacity of the LNG is absorbed by the ethylene glycol system. In the absence of LNG supply, the circulating nitrogen absorbs the cryogenic cooling capacity of the liquid air, and the ethylene glycol system absorbs the high-temperature cooling capacity of the liquid air.

[0037] Product allocation: Low-pressure nitrogen: The low-pressure nitrogen gas from the upper column of distillation column 31 is reheated to a certain temperature by the second heat exchanger 38 and the main cold box 32. A portion of the nitrogen gas is sent to the inlet of the first nitrogen booster 11, and the remaining nitrogen gas, after being pressurized, is cooled to liquid nitrogen by the liquid air in the liquid air storage tank 51 in the first liquid air-nitrogen heat exchanger 54 and then enters the liquid nitrogen storage tank 36. Waste nitrogen: Waste nitrogen from the upper column of distillation column 31 is reheated by the second liquid air heat exchanger 38 and the main cold box 32 and then sent out of the cold box. A portion is used as regeneration gas for the purification system, and the rest is vented. Liquid oxygen: Liquid oxygen is drawn from the middle of distillation column 31, subcooled by the second heat exchanger 38, and then sent out of the cold box into the liquid oxygen storage tank 37. Liquid nitrogen: A portion of the liquid nitrogen is drawn from the top of the upper column of distillation column 31 and sent out. The remaining liquid nitrogen is throttled by the medium-pressure subcooled liquid nitrogen from the LNG cold box 13 and then enters the liquid nitrogen storage tank 36. Liquid argon: Liquid argon is output through the cold box and enters the liquid argon storage tank 42. Circulating nitrogen: Circulating pressurized nitrogen from the LNG cold box 13 is reheated by the first heat exchanger 35 and the main cold box 32 before being sent out of the cold box and returned to the first nitrogen booster 11. Pressurized nitrogen: A portion of pressurized nitrogen is extracted from the lower column of the distillation column 31. When LNG provides cooling, it is liquefied through the first heat exchanger 35 and returned to the lower column of the distillation column 31, completing the transfer of cooling capacity. When no LNG provides cooling, the liquid air in the liquid air storage tank 51 is cooled into liquid nitrogen by the second liquid air-nitrogen heat exchanger 55 and enters the second separator 33.

[0038] This invention uses liquid air as the medium to supplement the cooling capacity of the air separation system. The air separation system and the liquid air cooling unit use pressurized nitrogen circulation to transfer cooling capacity. The circulating nitrogen does not participate in distillation, resulting in good safety performance of the air separation system. When there is LNG cooling capacity, part of the liquid nitrogen product comes directly from the liquid nitrogen in the LNG cold box and is subcooled, another part comes from the air separation unit, and a third part comes from the recovery of vented pure nitrogen. When there is no LNG cooling capacity, there is no liquid nitrogen production at all, only liquid oxygen is produced.

[0039] In this invention, the liquid air cooling unit is shared during the energy storage stage, while the two lines are configured separately during the release stage. That is, when there is LNG cooling capacity and when there is no LNG cooling capacity, the liquid air cooling pipelines are two completely different lines that do not conflict with each other, making startup and normal operation easier and operation more stable.

[0040] This invention enables continuous operation of the air separation unit even when LNG supply is unstable; air separation operation can be smoothly switched between LNG supply interruptions and supply interruptions; the system is suitable for retrofit projects, without altering the original air separation process and operation. Through technical upgrades, air separation operating efficiency can be improved, output value and economic benefits can be increased, while ensuring air separation operating safety.

[0041] 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 cold energy air separation system based on liquid air energy storage, characterized in that, include: The air pretreatment unit includes an air filter (1), an air compressor (2), a first cooler (3), and an air purification system connected in series. The distillation unit includes a distillation column (31), a main cold box (32), a first heat exchanger (35), and an argon distillation system (41). The outlet of the air purification system is connected to the inlet of the main cold box (32). The outlet of the main cold box (32) is connected to the inlet of the lower column of the distillation column (31). The nitrogen outlet at the top of the lower column of the distillation column (31) is connected to the inlet of the argon distillation system (41). Another nitrogen outlet of the distillation column (31) is connected to the inlet of the first heat exchanger (35). The liquid nitrogen inlet of the first heat exchanger (35) is connected to the liquid nitrogen outlet of the LNG cold box (13). The nitrogen exchanges heat with the liquid nitrogen from the LNG cold box (13) in the first heat exchanger (35) and is liquefied before returning to the top of the lower column of the distillation column (31), thereby completing the transfer of cold energy. In the cooling supply unit, when LNG provides cooling capacity, liquid nitrogen from the LNG cold box (13) is compressed and further cooled and throttled into pressurized liquid nitrogen in the first subcooler (14). A portion of the pressurized liquid nitrogen returns to the first subcooler (14) and the LNG cold box (13) as a cold source. The remaining pressurized liquid nitrogen enters the main cold box (32), is throttled, and then enters the first heat exchanger (35) to exchange heat with the pressurized nitrogen extracted from the bottom of the distillation column (31). After being vaporized, it enters the main cold box (32) for reheating and then returns to the first nitrogen booster (11). The first nitrogen booster (11) is connected to the LNG cold box (13). When no LNG provides cooling capacity, the cooling capacity required by the system is transferred to nitrogen by liquid air. Nitrogen in the main cold box (32) exchanges heat with liquid air in the second liquid air-nitrogen heat exchanger (55) and condenses into liquid nitrogen. After being supplied with circulating pressure by the liquid nitrogen pump (57), it enters the second liquid separator (33) and finally enters the liquid nitrogen storage tank (36). The energy storage unit includes a liquid air tank (51) connected to the air compressor (2) for supplying liquid air to the air compressor (2).

2. The cold energy air separation system based on liquid air energy storage according to claim 1, characterized in that, The air purification system includes two adsorbers arranged in parallel (4).

3. The cold energy air separation system based on liquid air energy storage according to claim 2, characterized in that, The adsorber (4) has a double-bed structure with activated alumina at the bottom and molecular sieve at the top. When one is running, the other is regenerating. The regeneration gas source is the main cold box (32) that transports waste nitrogen.

4. The cold energy air separation system based on liquid air energy storage according to claim 1, characterized in that, The distillation unit also includes a second heat exchanger (38), which is connected to the distillation column (31) and the argon distillation system (41) respectively. Part of the nitrogen generated by the distillation column (31) is subcooled and throttled by the second heat exchanger (38) and sent to the top of the upper column of the distillation column (31) as the upper column reflux liquid to participate in the upper column distillation of the distillation column (31).

5. The cold energy air separation system based on liquid air energy storage according to claim 4, characterized in that, The second heat exchanger (38) is also connected to the main cold box (32), which is connected to the first nitrogen booster (11). Low-pressure pure nitrogen is obtained from the top of the distillation column (31), and after being reheated to a certain temperature by the second heat exchanger (38) and the main cold box (32), it is sent to the first nitrogen booster (11) as the raw material nitrogen for liquid nitrogen products. A portion of low-temperature and low-pressure nitrogen is drawn from the distillation column (31), and after being boosted by the third nitrogen booster (53), it is liquefied by the liquid air from the cold supply unit in the first liquid air nitrogen heat exchanger (54) and sent to the liquid nitrogen storage tank (36) as product liquid nitrogen. Liquid oxygen is drawn from the bottom of the middle layer of the distillation column (31), and after being subcooled by the second heat exchanger (38), it is sent out of the main cold box (32) as product liquid oxygen.

6. The cold energy air separation system based on liquid air energy storage according to claim 1, characterized in that, The energy storage unit includes an air compression cooling assembly, a molecular sieve (23), an air cold box (26), and a liquid air storage tank (51) connected in series. The liquid air storage tank (51) is connected to the air compressor (2).

7. The cold energy air separation system based on liquid air energy storage according to claim 6, characterized in that, The air compression cooling assembly includes a first air compressor (21), a first air cooler (22), a second air compressor (24), and a second air cooler (25) connected in series.

8. The cold energy air separation system based on liquid air energy storage according to claim 7, characterized in that, Liquid air is used for energy storage at night. During the energy storage stage, the air enters from the first air compressor (21), is cooled by the first air cooler (22), and then enters the molecular sieve (23). The air is dehydrated and decarbonized in the molecular sieve (23) and then enters the second air compressor (24). After being cooled by the second air cooler (25), it enters the air cold box (26). One part of the air entering the air cold box (26) is drawn through the air expander (27) to provide cooling, and the other part is directly cooled into liquid and then depressurized through the liquid air throttle valve (28) for further cooling before entering the air separator for gas-liquid separation. The separated gas flows back to the air cold box (26) to provide cooling before entering the second air compressor (25). The separated liquid enters the liquid air storage tank (51) for storage.

9. The cold energy air separation system based on liquid air energy storage according to claim 8, characterized in that, During the daytime, liquid air releases energy. When LNG provides cooling, during the energy release phase, liquid air is pumped from the liquid air storage tank (51) into the first liquid air-nitrogen heat exchanger (54) to exchange heat with the high-purity nitrogen gas released from the top of the distillation column (31). After heat exchange, the liquid air releases cooling energy and becomes air, returning to the air compressor (2). After heat exchange, the high-purity nitrogen gas absorbs cooling energy and becomes liquid nitrogen, entering the liquid nitrogen storage tank (36). During the daytime, liquid air releases energy. When there is no LNG to provide cooling, during the energy release phase, liquid air is pumped from the liquid air storage tank (51) into the second liquid air-nitrogen heat exchanger (55) to exchange heat with nitrogen. After the liquid air releases cooling energy and becomes air, it further releases cooling energy to ethylene glycol in the ethylene glycol cooler (56) and then returns to the air compressor (2). Nitrogen condenses into liquid nitrogen and enters the liquid nitrogen storage tank (36).

10. The cold energy air separation system based on liquid air energy storage according to claim 1, characterized in that, An argon fraction gas is drawn from the lower part of the upper column (31) and sent to the argon distillation system (41) for distillation to reduce the oxygen content. The oxygen-rich liquid air drawn from the lower column (31) is throttled and sent into the system as the first cold source. The liquid nitrogen drawn from the middle of the distillation column (31) is subcooled by the second heat exchanger (38) as the second cold source. The pressurized nitrogen drawn from the top of the lower column (31) is used as the heat source to evaporate the liquid argon. At the same time, the nitrogen is liquefied. After full distillation to produce argon, 99.999% pure liquid argon is obtained. Finally, the liquid argon is drawn from the argon distillation system (41) and sent to the liquid argon storage tank (42) as the product liquid argon.

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