Cold energy air separation system based on mixed refrigerant copious cooling

Abstract

The invention relates to a cold energy air separation system based on mixed refrigerant copious cooling. The cold energy air separation system comprises an air pretreatment unit, a first cooling unit and a second cooling unit. The air pretreatment unit comprises 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 mixed refrigerant deep cooling unit comprises a mixed refrigerant compressor, a mixed refrigerant cooler and a mixed refrigerant heat exchanger which are sequentially connected in series, and the mixed refrigerant heat exchanger is connected with the LNG cold box; the energy storage unit comprises a liquid air storage tank connected with the air filter and used for providing air for the air filter.

Description

Technical Field

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

[0002] LNG cold energy-based 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 air separation, 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, due to the expansion of LNG receiving terminals and the increase in storage tanks, the BOG evaporation rate increases, leading to a rise in LNG export temperature. This may cause a reduction in cold energy air separation production, necessitating a method to maintain normal production even under elevated LNG temperatures. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a cold energy air separation system based on mixed refrigerant deep cooling. It employs mixed refrigerant refrigeration technology and uses mixed refrigerant compression and throttling to achieve refrigeration when the LNG cold energy supply is insufficient. The generated cooling capacity can lower the temperature of the LNG, enabling the cold energy air separation system to operate even without an increase in LNG temperature.

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

[0005] A cold energy air separation system based on mixed refrigerant deep cryogenics 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 lower column inlet 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. The mixed refrigerant cryogenic unit includes a mixed refrigerant compressor, a mixed refrigerant cooler, and a mixed refrigerant heat exchanger connected in series. The mixed refrigerant heat exchanger is connected to the LNG cold box and is used to provide cooling for the LNG. An energy storage unit includes a liquid air tank connected to the air filter for supplying air to the air filter.

[0006] Preferably, the air purification system of the cold energy air separation system based on mixed refrigerant cryogenics includes two adsorbers arranged in parallel.

[0007] Preferably, in the cold energy air separation system based on mixed refrigerant deep cryogenics, the adsorber has 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 regenerated, and the regeneration gas source is the waste nitrogen supplied by the main cold box.

[0008] Preferably, in the cold energy air separation system based on mixed refrigerant deep cryogenics, the distillation system further includes a second heat exchanger. The second heat exchanger is connected to the distillation column and the argon distillation system, respectively. Part of the nitrogen gas generated by 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 of the distillation column.

[0009] Preferably, in the cold energy air separation system based on mixed refrigerant cryogenics, the second heat exchanger is also connected to the main cold box, and the main cold box 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 the low-temperature, low-pressure nitrogen is extracted and vented.

[0010] Preferably, in the deep cryogenic system based on mixed refrigerant, the distillation unit further includes a second separating tank and a liquid nitrogen storage tank. The two ends of the second separating tank are respectively connected to the LNG cold box and the first heat exchanger. Impure nitrogen is obtained at the top of the distillation column. The impure nitrogen is reheated by the second heat exchanger and the main cold box and then sent out. A portion of it is used as regeneration gas for the air purification system, and the remainder is vented. The liquid nitrogen from the LNG cold box enters the second separating tank for gas-liquid separation and is sent to the liquid nitrogen storage tank as product liquid nitrogen.

[0011] Preferably, in the cold energy air separation system based on mixed refrigerant cryogenics, the distillation unit further includes a first subcooler, the two ends of which are respectively connected to the LNG cold box and the second liquid separator.

[0012] The cold energy air separation system based on deep cryogenic mixing of refrigerants, preferably, includes a first-stage refrigerant compressor and a second-stage refrigerant compressor connected in series.

[0013] The cold energy air separation system based on deep cryogenic mixing of refrigerants, preferably, includes a first refrigerant heat exchanger and a second refrigerant heat exchanger.

[0014] Preferably, in the cold energy air separation system based on mixed refrigerant deep cryogenics, the energy storage unit further includes a first liquid distribution tank, a liquid air pump, and an air expander. The liquid air storage tank, the liquid air pump, the air expander, and the first liquid distribution tank are connected in series. The first liquid distribution tank is connected to the air filter.

[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 mixed refrigerant supplementation, making full use of the mixed refrigerant refrigeration function to supplement the problem of insufficient cold energy air separation cooling caused by LNG cold energy fluctuations.

[0016] 2. The system of the present invention is an air separation system suitable for use near LNG receiving terminals. It improves the utilization rate of LNG cold energy at the receiving terminal by utilizing LNG cold energy, further improves the quality of LNG cold energy by adopting mixed refrigerant technology, and increases the output of air separation products by simultaneously utilizing LNG cold energy utilization and mixed refrigerant refrigeration technology.

[0017] 3. This invention utilizes mixed refrigerant refrigeration technology to improve the quality of cold energy, solving the problem of cold energy supply in air separation when the LNG export temperature rises. By lowering the LNG temperature, the production of liquid nitrogen in the air separation is increased. Simultaneously, the cold energy of LNG is utilized in a cascade manner, providing cooling for the nitrogen cycle and then for the ethylene glycol cycle. This invention can be implemented in existing air separation projects without altering the original air separation process. This invention demonstrates excellent performance and has high application and promotion value. Attached Figure Description

[0018] Figure 1 A flowchart of a cold energy air separation system based on deep cryogenic mixing of refrigerants; 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-stage mixed refrigerant compressor; 22-Second-stage mixed refrigerant compressor; 23-Mixed refrigerant cooler; 24-First mixed refrigerant heat exchanger; 25-Second mixed refrigerant heat exchanger; 26-Mixed refrigerant throttle valve; 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. 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 cold energy-based 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 air separation, 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, due to the expansion of LNG receiving terminals and the increase in storage tanks, the BOG evaporation rate increases, leading to a rise in LNG export temperature. This may cause a reduction in cold energy air separation production, necessitating a method to maintain normal production even under elevated LNG temperatures.

[0023] To address the aforementioned technical issues, this invention provides a cold energy air separation system based on mixed refrigerant deep cooling. It employs mixed refrigerant refrigeration technology and uses mixed refrigerant compression and throttling to refrigerate when LNG cold energy supply is insufficient. The generated cooling capacity can lower the temperature of LNG, enabling the cold energy air separation system to operate even without an increase in LNG temperature.

[0024] like Figure 1 As shown, the cold energy air separation system based on mixed refrigerant deep cryogenics 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. 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. The mixed refrigerant cryogenic unit includes a mixed refrigerant compressor, a mixed refrigerant cooler 23, and a mixed refrigerant heat exchanger connected in series. The mixed refrigerant heat exchanger is connected to the LNG cold box 13 to provide cooling for the LNG. The energy storage unit includes a liquid air tank connected to the air filter 1 for supplying air to the air filter 1.

[0025] Furthermore, the air purification system includes two adsorbers 4 arranged in parallel. 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, which delivers polluted nitrogen.

[0026] Furthermore, the distillation system also includes a second heat exchanger 38, which is connected to both the distillation column 31 and the argon distillation system 41. A portion of the nitrogen produced in the distillation column 31 is subcooled and throttled by the second heat exchanger 38 before being sent to the top of the upper column of the distillation column 31 as reflux liquid, participating in the upper column distillation of the distillation column 31. 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 obtained from the top of the upper column of the distillation column 31 is reheated to a certain temperature by the second heat exchanger 38 and the main cold box 32 before being sent to the first nitrogen booster 11 as raw nitrogen for liquid nitrogen products. A portion of the low-temperature, low-pressure nitrogen is extracted and vented.

[0027] Furthermore, the distillation unit also includes a second separating tank 33 and a liquid nitrogen storage tank 36. The two ends of the second separating tank 33 are connected to the LNG cold box 13 and the first heat exchanger 35, respectively. Impure nitrogen is obtained at the upper column of the distillation column 31. The impure nitrogen is reheated by the second heat exchanger 38 and the main cold box 32 and then sent out. Part of it is used as regeneration gas for the air purification system, and the rest is vented. The liquid nitrogen from the LNG cold box 13 enters the second separating tank 33 for gas-liquid separation and is sent to the liquid nitrogen storage tank 36 as product liquid nitrogen.

[0028] Furthermore, the distillation unit also includes a first subcooler 14, the two ends of which are connected to the LNG cold box 13 and the second liquid separator 33, respectively.

[0029] Furthermore, the mixed refrigerant compressor includes a first-stage mixed refrigerant compressor 21 and a second-stage mixed refrigerant compressor 22 connected in series; the mixed refrigerant heat exchanger includes a first mixed refrigerant heat exchanger 24 and a second mixed refrigerant heat exchanger 25.

[0030] Furthermore, the energy storage unit also includes a first liquid distribution tank, a liquid air pump, and an air expander. The liquid air storage tank, the liquid air pump, the air expander, and the first liquid distribution tank are connected in series. The first liquid distribution tank is connected to the air filter 1.

[0031] A second aspect of the present invention provides a process flow for the above-mentioned cold energy air separation system, as follows: 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.

[0032] 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 in the upper column of distillation column 1, 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 column of distillation column 31 is subcooled by the second heat exchanger 38 and throttled by the fourth throttle valve 43 before being sent to the middle section of the upper column of distillation column 31 to participate in the distillation. After distillation in the upper column 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 column 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 sent out of the cold box as product liquid oxygen. Low-pressure pure nitrogen is obtained from the top of the upper column of distillation column 31, reheated to a certain temperature by the second heat exchanger 38 and the main cold box 32, and then sent to the first nitrogen booster 11 as the raw material nitrogen for liquid nitrogen products. A portion of the low-temperature, low-pressure nitrogen is extracted from the middle section and vented. In the upper part of the distillation column 31, impure 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. Part of it is used as regeneration gas for the purification system, and the rest is vented. The medium-pressure liquid nitrogen from the LNG cold box 13 is throttled by the third throttle valve 34 and enters the second liquid separator 33 for gas-liquid separation. The product liquid nitrogen is sent to the liquid nitrogen storage tank 36.

[0033] Cooling supply: When the LNG cooling supply is sufficient, the cooling required by 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 bottom of the distillation column 31 and is vaporized. After being reheated, it enters the main cold box 32 and returns to the inlet of the first nitrogen booster 11, transferring the cooling capacity from LNG to the air separation system.

[0034] When the LNG cooling supply is insufficient, the required cooling capacity for the unit is achieved by deep cooling the LNG with a mixed refrigerant, and then transferring the LNG to liquid nitrogen using the same supply method as when the LNG cooling supply is sufficient. The mixed refrigerant is first pressurized by the first-stage mixed refrigerant compressor 21 and the second-stage mixed refrigerant compressor 22, then cooled by the mixed refrigerant cooler 23. It is further cooled in the first mixed refrigerant heat exchanger 24 by the returning lower-temperature mixed refrigerant, and then cooled again in the second mixed refrigerant heat exchanger 25. Finally, it is throttled and cooled by the mixed refrigerant throttling valve 26 and returned to the second mixed refrigerant heat exchanger 25 to provide cooling capacity to reduce the LNG to below -140°C.

[0035] 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 subcooled oxygen-enriched liquid air is then throttled through 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 subcooled through 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.

[0036] 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 the LNG cold box 13 and used as a cold source by the first cooler 3, transferring its high-temperature end cooling energy 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 temperature fluctuates significantly; simultaneously, the expansion of the receiving terminal has led to an increase in the number of LNG storage tanks and a greater BOG evaporation rate, resulting in a significant temperature rise in the LNG export temperature due to the absorption of a large amount of BOG.

[0037] 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 cryogenic cooling capacity of the LNG is absorbed by the ethylene glycol system.

[0038] Product allocation: Low-pressure nitrogen: The low-pressure nitrogen gas from the upper column of distillation column 31 is reheated to a certain temperature via 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 remainder is vented. Sludge nitrogen: Sludge nitrogen from the upper column of distillation column 31 is reheated via 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 remainder is vented. Liquid oxygen: Liquid oxygen is drawn from the middle of distillation column 31, subcooled via the second heat exchanger 38, and then sent out of the cold box, entering the liquid oxygen storage tank 37. Liquid nitrogen: A portion of the liquid nitrogen is drawn from the top of distillation column 31 and sent out. The remaining liquid nitrogen is throttled from 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 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 drawn from the lower column of distillation column 31, liquefied by the first heat exchanger 35, and returned to the lower column of distillation column 31, completing the transfer of cooling capacity.

[0039] The cold energy air separation system based on mixed refrigerant deep cryogenics of the present invention has the following advantages: 1. Using a mixed refrigerant for refrigeration lowers the temperature of LNG and improves the quality of its cold energy. Furthermore, the mixed refrigerant is only used to raise the temperature of the LNG in its cryogenic range (e.g., below -130℃), primarily enhancing the quality of LNG's cold energy rather than increasing its cooling capacity. Therefore, the mixed refrigerant system consumes less power.

[0040] 2. One part of the liquid nitrogen product comes directly from the liquid nitrogen in the LNG cold box and has been subcooled, while the other part comes from the air separation unit. It is flexible in adjustment and has a wide range of applications. If the LNG feed temperature is too high, the mixed refrigerant system can be started at any time to increase the supply of cooling capacity and maintain the stable and economical operation of liquid oxygen and liquid argon production.

[0041] 3. The working fluid is a multi-component mixed refrigerant consisting of C1 to C5 hydrocarbons and N2, etc.

[0042] 4. The cold energy of LNG is utilized in a cascade manner. The mixed refrigerant increases the grade of the LNG's cold energy. The high-grade LNG cold energy is transferred to the nitrogen cycle through the LNG cold box. The nitrogen cycle is compressed, throttled, cooled, and liquefied multiple times in the LNG cold box before providing cooling to the distillation column and then circulating. The remaining low-grade LNG cold energy is sent to the air compressor interstage cooler, final stage cooler, oil cooler, and motor cooler via ethylene glycol.

[0043] 5. A mixed refrigerant is used as the medium for LNG cooling, and nitrogen is used as the medium for heat exchange with LNG. The air separation system and the liquid air cooling unit use pressure nitrogen circulation to transfer cooling capacity. The mixed refrigerant and circulating nitrogen do not come into direct contact, and the circulating nitrogen does not participate in distillation, resulting in good safety performance of the air separation system.

[0044] 6. The mixed refrigerant compressor is configured in stages and uses interstage cooling, which reduces the compressor inlet temperature and thus reduces compressor energy consumption.

[0045] 7. The system can achieve stable operation of the air separation unit even when the LNG supply temperature rises. It is suitable for retrofit projects and does not change the original air separation process and operation. Through technical transformation, the air separation operating efficiency can be improved, output value and economic benefits can be increased, and the safety of air separation operation can be guaranteed.

[0046] 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 deep cryogenic mixing of refrigerants, 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. The mixed refrigerant cryogenic unit includes a mixed refrigerant compressor, a mixed refrigerant cooler (23), and a mixed refrigerant heat exchanger connected in series. The mixed refrigerant heat exchanger is connected to the LNG cold box (13) and is used to provide cooling for LNG. The energy storage unit includes a liquid air tank connected to the air filter (1) for supplying air to the air filter (1).

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

3. The cold energy air separation system based on mixed refrigerant deep cryogenics 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 regenerated. The regeneration gas source is the main cold box (32) which delivers waste nitrogen.

4. The cold energy air separation system based on mixed refrigerant deep cryogenics according to claim 1, characterized in that, The distillation system also includes a second heat exchanger (38), which is connected to the distillation column (31) and the argon distillation system (41). 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 mixed refrigerant deep cryogenics 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 the low-temperature and low-pressure nitrogen is extracted and vented.

6. The cold energy air separation system based on mixed refrigerant deep cryogenics according to claim 5, characterized in that, The distillation unit also includes a second separator (33) and a liquid nitrogen storage tank (36). The two ends of the second separator (33) are connected to the LNG cold box (13) and the first heat exchanger (35) respectively. Impure nitrogen is obtained at the top of the distillation column (31). The impure nitrogen is reheated by the second heat exchanger (38) and the main cold box (32) and then sent out. A portion of it is used as regeneration gas for the air purification system, and the rest is vented. The liquid nitrogen from the LNG cold box (13) enters the second separator (33) for gas-liquid separation and is sent to the liquid nitrogen storage tank (36) as product liquid nitrogen.

7. The cold energy air separation system based on mixed refrigerant deep cryogenics according to claim 5, characterized in that, The distillation unit also includes a first subcooler (14), the two ends of which are connected to the LNG cold box (13) and the second liquid separator (33), respectively.

8. The cold energy air separation system based on mixed refrigerant deep cryogenics according to claim 1, characterized in that, The mixed refrigerant compressor includes a first-stage mixed refrigerant compressor (21) and a second-stage mixed refrigerant compressor (22) connected in series.

9. The cold energy air separation system based on mixed refrigerant deep cryogenics according to claim 1, characterized in that, The mixed refrigerant heat exchanger includes a first mixed refrigerant heat exchanger (24) and a second mixed refrigerant heat exchanger (25).

10. The cold energy air separation system based on mixed refrigerant deep cryogenics according to claim 1, characterized in that, The energy storage unit also includes a first liquid distribution tank, a liquid air pump and an air expander. The liquid air storage tank, the liquid air pump, the air expander and the first liquid distribution tank are connected in series. The first liquid distribution tank is connected to the air filter (1).

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