Liquid air separation device for preparing high-purity liquid oxygen by utilizing nitrogen circulation

Abstract

The utility model discloses a liquid air separation device for preparing high-purity liquid oxygen by utilizing nitrogen circulation, which comprises an air pretreatment system, an outer circulation cooling system and a rectification system, the external circulation cooling system comprises an air precooler with the air inlet end connected with the air outlet end of the air compressor, a main heat exchanger used for cooling air at the air outlet end of the air purifier, a nitrogen circulation supercharger connected with the main heat exchanger, and a high-temperature nitrogen expansion machine connected with the air outlet end of the nitrogen circulation supercharger. And the low-temperature nitrogen expansion machine is connected with the gas outlet end of the high-temperature nitrogen expansion machine. Nitrogen generated at the rear end is conveyed to the front end through the external circulation cooling system to be subjected to expansion cooling and heat exchange with air, the temperature of the nitrogen generated at the rear end is lower than that of existing air before expansion, the cooling range is reduced, energy loss is reduced, the refrigeration effect is fully achieved, and the service life of the air conditioner is prolonged. And the great requirement of the full-liquid air separation device on the cooling capacity is well met.

Description

Technical Field

[0001] The utility model relates to the technical field of air separation equipment, and particularly relates to a liquid air separation device for producing high-purity liquid oxygen by using nitrogen circulation. Background Art

[0002] High-purity oxygen is an important industrial raw material and is widely used in industries such as metallurgy, non-ferrous metals, electronics, medical treatment, and aerospace. To meet its increasing demand, it is necessary to increase the output of high-purity oxygen. Currently, an air separation device is generally used to further produce high-purity liquid oxygen while producing low-purity liquid oxygen. This can not only effectively increase the output of liquid products but also has the advantages of high purity of liquid oxygen products and convenient transportation.

[0003] An air separation device uses air as raw material and consumes electric energy to produce different gases. Therefore, the energy consumption of liquid air separation equipment is crucial for users. Currently, the general air separation device uses air expansion refrigeration, and air separation refrigeration mainly relies on the temperature change during the compression and expansion of air to achieve the refrigeration effect. The compressor consumes a large amount of electric energy when compressing air, and although the expander can release heat during the expansion process, the energy conversion efficiency of the entire process is not 100%, so there will be some energy losses.

[0004] How to provide a liquid air separation device that can reduce the power consumption of the expander and compressor and reduce the power loss of the air separation device is a technical problem that urgently needs to be solved now. Summary of the Utility Model

[0005] The purpose of the utility model is to provide a liquid air separation device for producing high-purity liquid oxygen by using nitrogen circulation, so as to solve the problem that the existing air separation device has large power loss and is not conducive to energy conservation and emission reduction in the background art.

[0006] To achieve the above purpose, the utility model provides a liquid air separation device for producing high-purity liquid oxygen by using nitrogen circulation, which includes an air pretreatment system, an external circulation cooling system, and a rectification system; the air pretreatment system includes an air compressor, an air purifier connected to the air outlet end of the air compressor, and a self-cleaning air filter arranged on the air inlet end of the air compressor. The air outlet end of the air purifier enters the rectification system after being cooled by the external circulation cooling system; the external circulation cooling system includes an air precooler with an air inlet end connected to the air outlet end of the air compressor, a main heat exchanger for cooling the air at the air outlet end of the air purifier, a nitrogen circulation booster connected to the main heat exchanger, a high-temperature nitrogen expander connected to the air outlet end of the nitrogen circulation booster, and a low-temperature nitrogen expander connected to the air outlet end of the high-temperature nitrogen expander.

[0007] Optionally, the liquid oxygen rectification system includes a lower column and a subcooler; the gas at the outlet end of the air purifier enters the lower end of the lower column after passing through the main heat exchanger. The upper end of the lower column is connected to the inlet end of the nitrogen circulation booster through a pipeline via the main heat exchanger. The outlet end of the nitrogen circulation booster is connected to a high-temperature nitrogen expander, and the outlet end of the high-temperature nitrogen expander is connected to the main heat exchanger and a low-temperature nitrogen expander. The outlet end of the low-temperature nitrogen expander is in communication with the lower column.

[0008] Optionally, a first circulation pipe and a second circulation pipe are provided at the outlet end of the low-temperature nitrogen expander. The first circulation pipe is in communication with the lower column, and a second cooler is provided on the first circulation pipe. The first circulation pipe is in communication with the lower column after passing through the main heat exchanger. The second circulation pipe is connected to the inlet end of the nitrogen circulation booster, and a third circulation pipe connected to the inlet end of the low-temperature nitrogen expander is provided on the main heat exchanger.

[0009] Optionally, the liquid oxygen rectification system further includes a main condenser-evaporator provided on the lower column, an upper column provided on the main condenser-evaporator, a first crude argon column in two-way communication with the lower part of the upper column, a second crude argon column connected to the top of the first crude argon column, a high-purity oxygen column connected to the inlet end of the first crude argon column, and a pure argon column connected to the first crude argon column.

[0010] Optionally, a nitrogen outlet pipe and a precooling conduit are provided at the upper end of the upper column. The nitrogen outlet pipe exports nitrogen through the main heat exchanger, and the precooling conduit is in communication with the air purifier and the air precooler through the main heat exchanger.

[0011] Optionally, a high-purity oxygen evaporator is provided in the high-purity oxygen column, and both the inlet end and the outlet end of the high-purity oxygen evaporator are in communication with the upper part of the lower column; a crude argon condenser is provided at the top of the second crude argon column, and a pure argon condenser is provided at the top of the pure argon column. The inlet ends of the pure argon condenser and the crude argon condenser are connected to a pure argon evaporator, and the inlet end of the pure argon evaporator is in communication with the bottom of the lower column 31; a lower column return pipe of the main condenser-evaporator in communication with the upper part of the lower column, an upper column return pipe passing through the subcooler and in communication with the upper end of the upper column, and a liquid nitrogen outlet pipe passing through the subcooler.

[0012] Optionally, the bottom end of the lower column is connected to the pure argon evaporator through a pipeline via the subcooler.

[0013] Optionally, the middle part of the first crude argon column is in two-way communication with the top of the high-purity oxygen column through a pipeline, and a high-purity liquid oxygen outlet pipe is provided at the bottom of the high-purity oxygen column; a liquid oxygen outlet pipe is provided at the bottom of the main condenser-evaporator.

[0014] Optionally, a liquid argon pump is connected to the bottom end of the second crude argon column, and the outlet end of the liquid argon pump is in communication with the middle part of the first crude argon column.

[0015] Optionally, the outlet end of the crude argon condenser is connected to the pure argon column, and a liquid argon discharge pipe is provided at the bottom of the pure argon column.

[0016] Compared with the prior art, the present utility model provides a liquid air separation device for producing high-purity liquid oxygen with nitrogen circulation, having the following beneficial effects:

[0017] The liquid air separation device for producing high-purity liquid oxygen with nitrogen circulation connects a high-temperature nitrogen expander and a low-temperature nitrogen expander in series through an external circulation cooling system, transports the nitrogen generated at the rear end to the front end for expansion and cooling, exchanges heat with air, and the temperature of the nitrogen generated at the rear end is lower than the temperature of the existing air before expansion, reducing the cooling range, thereby reducing energy consumption, and fully exerting the refrigeration effect, well meeting the great demand for cold energy of the all-liquid air separation device. Description of the Drawings

[0018] Figure 1 is a schematic connection diagram of the overall structure of the present utility model.

[0019] Reference numerals in the figure: 1. Air pretreatment system; 11. Air compressor; 12. Air purifier; 13. Self-cleaning air filter; 2. External circulation cooling system; 21. Air precooler; 22. Main heat exchanger; 23. Nitrogen circulation booster; 24. High-temperature nitrogen expander; 241. First cooler; 25. Low-temperature nitrogen expander; 251. First circulation pipe; 252. Second circulation pipe; 253. Third circulation pipe; 254. Second cooler; 3. Rectification system; 31. Lower column; 32. Subcooler; 33. Main condenser-evaporator; 331. Lower column reflux pipe; 332. Upper column reflux pipe; 333. Liquid nitrogen discharge pipe; 334. Liquid oxygen discharge pipe; 34. Upper column; 341. Nitrogen discharge pipe; 342. Precooling conduit; 35. First crude argon column; 36. Second crude argon column; 361. Crude argon condenser; 362. Liquid argon pump; 37. High-purity oxygen column; 371. High-purity oxygen evaporator; 372. High-purity liquid oxygen discharge pipe; 38. Pure argon column; 381. Pure argon condenser; 382. Liquid argon discharge pipe; 39. Pure argon evaporator. Detailed Embodiments

[0020] The following is a detailed description in combination with the drawings and specific embodiments. Many specific details are set forth in the following description in order to fully understand the present utility model. However, the present utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present utility model. Therefore, the present utility model is not limited by the specific embodiments disclosed below.

[0021] A liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to the present application can be applicable to occasions such as liquid air separation of air, and of course can also be used in other similar application scenarios. A liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation will be described in detail below.

[0022] Refer to the appendix Figure 1 As shown in the figure, a schematic structural diagram of a preferred embodiment of a liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to the present application is shown. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation includes an air pretreatment system 1, an external circulation cooling system 2, and a rectification system 3; among them, the air pretreatment system 1 includes an air compressor 11, an air purifier 12 connected to the air outlet end of the air compressor 11, a self-cleaning air filter 13 provided at the air inlet end of the air compressor 11, and the air outlet end of the air purifier 12 enters the rectification system 3 after being cooled by the external circulation cooling system 2.

[0023] In the present utility model, through the setting of the air compressor 11, the external air is sucked and pressurized, so that the air can enter the rectification system 3 for rectification and separation of the air after being cooled by the external circulation cooling system 2; through the setting of the air purifier 12, the air can be purified, and H2O, CO2, N2O and harmful trace hydrocarbons in the air can be removed; through the setting of the self-cleaning air filter 13, the dust in the air can be removed to ensure the purity of the air for subsequent separation.

[0024] Refer to the appendix Figure 1 As shown in the figure, in the present utility model, the external circulation cooling system 2 includes an air precooler 21 with an air inlet end connected to the air outlet end of the air compressor 11, a main heat exchanger 22 for cooling the air at the air outlet end of the air purifier 12, a nitrogen circulation booster 23 connected to the main heat exchanger 22, a high-temperature nitrogen expander 24 connected to the air outlet end of the nitrogen circulation booster 23, and a low-temperature nitrogen expander 25 connected to the air outlet end of the high-temperature nitrogen expander 24; among them, the gas at the air outlet end of the air purifier 12 enters the lower end of the lower column 31 after passing through the main heat exchanger 22, the upper end of the lower column 31 is connected to the air inlet end of the nitrogen circulation booster 23 through a pipeline passing through the main heat exchanger 22, the air outlet end of the nitrogen circulation booster 23 is connected to the high-temperature nitrogen expander 24, the air outlet end of the high-temperature nitrogen expander 24 is connected to the main heat exchanger 22 and the low-temperature nitrogen expander 25, and the air outlet end of the low-temperature nitrogen expander 25 is connected to the lower column 31.

[0025] With the provision of the air precooler 21, the present utility model can precool the air, reducing the heat exchange requirements of the subsequent high-temperature nitrogen expander 24 and low-temperature nitrogen expander 25, reducing the power consumption of the high-temperature nitrogen expander 24 and low-temperature nitrogen expander 25, reducing energy consumption, and ensuring that the air can be cooled to the required temperature to guarantee the effect of subsequent air separation; with the provision of the main heat exchanger 22, it is used to cool the air through heat exchange; with the provision of the high-temperature nitrogen expander 24, the temperature of nitrogen can be initially reduced, providing a more suitable starting temperature for the subsequent low-temperature expansion process. This helps to improve the energy conversion efficiency of the entire system, reduce unnecessary energy losses. At the same time, the rapid temperature change will generate thermal stress inside the material, which may cause material deformation or damage. The slow cooling process through the high-temperature expander first can reduce the generation of this thermal stress and protect the materials and structure of the low-temperature expander from damage; with the provision of the low-temperature nitrogen expander 25, it is used to rapidly cool the nitrogen so that the nitrogen can cool the air through heat exchange; by extracting the nitrogen in the rear rectification system 3 to the front for cooling again, compared with directly using the gas at normal temperature for heat exchange, this method can effectively reduce the cooling range, thereby effectively reducing energy losses, saving energy, and using the nitrogen in the lower column 31. Compared with the nitrogen in the upper column 34, the purity of the nitrogen in the lower column is reduced. While carrying out the nitrogen external circulation, the distillation of the lower column 31 can be further carried out to improve the purity of the nitrogen entering the upper column 34.

[0026] Refer to the appendix Figure 1 As shown, in the present utility model, a first cooler 241 is provided between the outlet end of the high-temperature nitrogen expander 24 and the inlet end of the low-temperature nitrogen expander 25; a first circulation pipe 251 and a second circulation pipe 252 are provided at the outlet end of the low-temperature nitrogen expander 25. The first circulation pipe 251 is connected to the lower column 31. A second cooler 254 is provided on the first circulation pipe 251. After passing through the main heat exchanger 22, the first circulation pipe 251 is connected to the lower column 31. After passing through the main heat exchanger 22, the second circulation pipe 252 is connected to the inlet of the nitrogen circulation booster 23. A third circulation pipe 253 is provided on the main heat exchanger 22, and this third circulation pipe 253 is connected to the inlet end of the low-temperature nitrogen expander 25.

[0027] The first cooler 241 in the present utility model is a cooler for the high-temperature expander boost end, and the second cooler 254 is a cooler for the low-temperature expander boost end; with the provision of the first circulation pipe 251, the nitrogen after heat exchange can be re-transported into the lower column 31; with the provision of the second circulation pipe 252 and the third circulation pipe 253, the nitrogen can be circulated for refrigeration heat exchange; it should be particularly noted that the outlet end of the high-temperature nitrogen expander 24 can also be connected to the inlet end of the high-temperature nitrogen expander 24 for circulation, and the connection position is in front of the inlet of the nitrogen circulation booster 23.

[0028] Refer to the appendix Figure 1 As shown, in the present utility model, a nitrogen gas outlet pipe 341 and a precooling conduit 342 are provided at the upper end of the upper column 34. Among them, the nitrogen gas outlet pipe 341 exports nitrogen gas through the main heat exchanger 22, and the precooling conduit 342 is connected to the air purifier 12 and the air precooler 21 through the main heat exchanger 22. By precooling part of the nitrogen gas in the upper column 34 with air, the present utility model can effectively reduce the subsequent cooling degree and energy consumption. Moreover, the demand for nitrogen gas products is lower than that for liquid nitrogen products. Therefore, using part of the nitrogen gas for air precooling will not affect the overall requirement.

[0029] Refer to the appendix Figure 1 As shown, in the present utility model, the liquid oxygen rectification system 3 includes a lower column 31, a subcooler 32, a main condenser-evaporator 33 provided on the lower column 31, an upper column 34 provided on the main condenser-evaporator 33, a first crude argon column 35 in two-way communication with the lower part of the upper column 34, a second crude argon column 36 connected to the top of the first crude argon column 35, a high-purity oxygen column 37 connected to the inlet end of the first crude argon column 35, a pure argon column 38 connected to the first crude argon column 35, and a pure argon evaporator 39 connected to the bottom of the lower column 31. It should be particularly noted that the lower column 31, the upper column 34, the first crude argon column 35, the second crude argon column 36, the pure argon column 38, and the high-purity oxygen column 37 are all structured packing columns with good rectification effect and large operating flexibility; the main heat exchanger 22, the main condenser-evaporator 33, the subcooler 32, the high-purity oxygen evaporator 371, the crude argon condenser 361, the pure argon evaporator 39, and the pure argon condenser 381 are all plate-fin heat exchangers with good heat exchange effect.

[0030] In the present utility model, through the setting of the main condenser-evaporator 33, nitrogen gas is cooled to form liquid nitrogen. Then, part of the liquid nitrogen is returned to the lower column as reflux liquid, and part of the liquid nitrogen is throttled and branched after being subcooled by the subcooler. One branch is used as liquid nitrogen product, and the other branch is sent to the top of the upper column as the upper column reflux liquid; by connecting the lower column 31 and the first crude argon column 35, the oxygen-rich liquid air at the bottom of the lower column 31 is obtained, and after being subcooled by the subcooler 32, it is sent to the pure argon evaporator 39 for heat exchange; through the settings of the first crude argon column 35, the second crude argon column 36, and the pure argon column 38, argon gas can be separated to obtain liquid argon.

[0031] Refer to the appendix Figure 1As shown, in the present utility model, a high-purity oxygen evaporator 371 is provided inside the high-purity oxygen tower 37. The inlet end and the outlet end of the high-purity oxygen evaporator 371 are both connected to the upper part of the lower tower 31; a crude argon condenser 361 is provided at the top of the crude argon tower II 36, and a pure argon condenser 381 is provided at the top of the pure argon tower 38. The inlet ends of the pure argon condenser 381 and the crude argon condenser 361 are connected to a pure argon evaporator 39, and the inlet end of the pure argon evaporator 39 is connected to the bottom of the lower tower 31; the lower tower return pipe 331 of the main condenser-evaporator 33 connected to the upper part of the lower tower 31, the upper tower return pipe 332 passing through the subcooler 32 and connected to the upper end of the upper tower 34, and the liquid nitrogen outlet pipe 333 passing through the subcooler 32.

[0032] The setting of the high-purity oxygen evaporator 371 in the present utility model exchanges heat with the evaporated high-purity oxygen to form liquid oxygen products; through the setting of the crude argon condenser 361, it is used to condense and reflux part of the argon gas, and part of the argon gas is condensed and then transported to the pure argon tower 38 for rectification; through the setting of the pure argon condenser 381, it is used to condense the rising gas in the pure argon tower to form pure argon liquid; through the setting of the liquid nitrogen outlet pipe 333, the liquid nitrogen products can be exported and collected.

[0033] Refer to the appendix Figure 1 As shown, in the present utility model, the bottom end of the lower tower 31 is connected to the pure argon evaporator 39 through the subcooler 32 by a pipeline; the middle part of the crude argon tower I 35 is bidirectionally connected to the top end of the high-purity oxygen tower 37 through a pipeline, and a high-purity liquid oxygen outlet pipe 372 is provided at the bottom of the high-purity oxygen tower 37; a liquid oxygen outlet pipe 334 is provided at the bottom of the main condenser-evaporator 33.

[0034] In the present utility model, by connecting the lower tower 31 with the pure argon evaporator 39, the oxygen-rich liquid air in the lower tower 31 can exchange heat with the gas in the pure argon evaporator 39 after passing through the subcooler 32, and then exchange heat with the rising gas in the pure argon condenser 381 and the crude argon condenser 361; through the setting of the high-purity liquid oxygen outlet pipe 372, high-purity liquid oxygen can be exported; through the setting of the liquid oxygen outlet pipe 334, the liquid oxygen products with a purity lower than that of the high-purity liquid oxygen in the main condenser-evaporator 33 can be exported.

[0035] Refer to the appendix Figure 1 As shown, in the present utility model, a liquid argon pump 362 is connected to the bottom end of the crude argon tower II 36, and the outlet end of the liquid argon pump 362 is connected to the middle part of the crude argon tower I 35; the outlet end of the crude argon condenser 361 is connected to the pure argon tower 38, and a liquid argon outlet pipe 382 is provided at the bottom of the pure argon tower 38.

[0036] With the arrangement of the liquid argon pump 362, the utility model is used to pressurize and transport the liquid argon fraction in the second crude argon tower 36 into the first crude argon tower 35 or reflux it to the second crude argon tower 36; with the arrangement of the liquid argon outlet pipe 382, the liquid argon product in the pure argon tower 38 can be exported.

[0037] Refer to the appendix Figure 1 As shown, the usage process of the utility model is as follows:

[0038] First, the air compressor 11 starts to operate, sucking in external air from the intake end of the air compressor 11, allowing the air to enter the air compressor 11 for pressurization after passing through the self-cleaning air filter 13, and then discharging it from the outlet end of the air compressor 11. After passing through the air pre-cooler 21 and the air purifier 12, it then exchanges heat in the main heat exchanger 22 and enters the bottom of the lower column 31. At the top of the lower column 31, nitrogen is obtained. A part of the nitrogen is extracted and sent to the high-purity oxygen evaporator 371 for heat exchange and enters the main heat exchanger 22. A part of the nitrogen is condensed by the main condenser-evaporator 33 to obtain liquid nitrogen. A part of the liquid nitrogen returns to the lower column 31 through the lower column reflux pipe 331. A part of the liquid nitrogen is sub-cooled by the sub-cooler 32 and then throttled and branched. One way is to export the liquid nitrogen product through the liquid nitrogen outlet pipe 333, and the other way is to reflux to the top of the upper column through the upper column reflux pipe 332; at the bottom of the lower column 31, oxygen-rich liquid air is obtained. It is first sub-cooled by the sub-cooler 32 and then sent to the pure argon evaporator 39 for heat exchange, and then sent to the pure argon condenser 381 and the crude argon condenser 361 for heat exchange; at the top of the upper column 34, nitrogen is obtained. The nitrogen obtained from the upper column 34 and the nitrogen generated by the throttling of the liquid nitrogen in the sub-cooler 32 first exchange heat in the sub-cooler 32 and then are reheated in the main heat exchanger 22 and exported as nitrogen products through the nitrogen outlet pipe 341; at the upper part of the upper column 34, waste nitrogen is obtained. It first exchanges heat in the sub-cooler 32 and then is reheated in the main heat exchanger 22. A part is sent to the air purifier 12 as a regeneration gas, and a part is sent to the air pre-cooler 21 to pre-cool the air; the liquid oxygen product is extracted from the bottom of the main condenser-evaporator 33 and exported after being sub-cooled by the liquid oxygen outlet pipe 334 through the sub-cooler 32; a stream of argon fraction is drawn from the lower part of the upper column 34 and sent to the first crude argon column 35 for rectification. Crude argon gas is obtained at the top of the first crude argon column 35 and then sent to the bottom of the second crude argon column 36 for further rectification; a liquid argon fraction is obtained at the bottom of the second crude argon column 36, sent to the liquid argon pump 362 for pressurization and then sent to the upper part of the first crude argon column 35 or refluxed to the second crude argon column 36 for re-rectification. A part of the crude argon gas is condensed by the crude argon condenser 361 and used as the reflux liquid of the second crude argon column 36. The rest is drawn from the top of the second crude argon column 36 and sent to the pure argon column 38. Most of the rising gas is condensed by the pure argon condenser 381 and used as the reflux liquid of the pure argon column 38. After the rectification of the pure argon column, liquid argon is obtained at the bottom of the pure argon column 38 and exported through the liquid argon outlet pipe 382; in addition, an oxygen-rich liquid is drawn from the middle of the first crude argon column 35 and sent as a reflux liquid to the top of the high-purity oxygen column 37. A stream of nitrogen is drawn from the top of the lower column 31 and used as the heat source of the high-purity oxygen evaporator 371 to exchange heat with the evaporated high-purity oxygen. The condensed liquid nitrogen returns to the top of the lower column 31. The oxygen-rich gas at the top of the high-purity oxygen column 37 returns to the middle of the first crude argon column 35. High-purity liquid oxygen is obtained at the bottom of the high-purity oxygen column 37, and then the high-purity liquid oxygen product is exported through the high-purity liquid oxygen outlet pipe 372.

[0039] The above embodiments are illustrative of the present application and not restrictive thereof. Any solution obtained by simply transforming the present application falls within the protection scope of the present application.

Claims

1. A liquid air separation unit for producing high-purity liquid oxygen by circulating nitrogen, characterized in that: It comprises an air pretreatment system (1), an external circulation cooling system (2) and a distillation system (3); The air pretreatment system (1) comprises an air compressor (11), an air purifier (12) connected to the air outlet of the air compressor (11), and a self-cleaning air filter (13) arranged on the air inlet of the air compressor (11); the air outlet of the air purifier (12) is cooled by the external circulation cooling system (2) and then enters the distillation system (3); The external circulation cooling system (2) comprises an air precooler (21) whose air inlet end is connected to the air outlet end of the air compressor (11), a main heat exchanger (22) for cooling air at the air outlet end of the air purifier (12), a nitrogen circulation booster (23) connected to the main heat exchanger (22), a high-temperature nitrogen expander (24) connected to the air outlet end of the nitrogen circulation booster (23), and a low-temperature nitrogen expander (25) connected to the air outlet end of the high-temperature nitrogen expander (24).

2. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 1, characterized in that: The liquid oxygen distillation system (3) comprises a lower tower (31) and a subcooler (32); The gas at the outlet end of the air purifier (12) passes through the main heat exchanger (22) and enters the lower end of the lower tower (31). The upper end of the lower tower (31) is connected to the inlet end of the nitrogen circulation booster (23) through a pipeline via the main heat exchanger (22). The outlet end of the nitrogen circulation booster (23) is connected to the high-temperature nitrogen expander (24). The outlet end of the high-temperature nitrogen expander (24) is connected to the main heat exchanger (22) and the low-temperature nitrogen expander (25). The outlet end of the low-temperature nitrogen expander (25) is connected to the lower tower (31).

3. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 1 or 2, characterized in that: A first cooler (241) is provided between the gas outlet end of the high-temperature nitrogen expander (24) and the gas inlet end of the low-temperature nitrogen expander (25); A first circulation pipe (251) and a second circulation pipe (252) are provided at the gas outlet end of the cryogenic nitrogen expander (25); the first circulation pipe (251) is connected to the lower tower (31); a second cooler (254) is provided on the first circulation pipe (251); the first circulation pipe (251) is connected to the lower tower (31) after passing through the main heat exchanger (22); the second circulation pipe (252) is connected to the gas inlet end of the nitrogen circulation booster (23); and a third circulation pipe (253) connected to the gas inlet end of the cryogenic nitrogen expander (25) is provided on the main heat exchanger (22).

4. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 2, characterized in that: The liquid oxygen distillation system (3) further comprises a main condenser evaporator (33) arranged on the lower tower (31), an upper tower (34) arranged on the main condenser evaporator (33), a crude argon first tower (35) bidirectionally connected to the lower part of the upper tower (34), a crude argon second tower (36) connected to the top of the crude argon first tower (35), a high-purity oxygen tower (37) connected to the air inlet end of the crude argon first tower (35), and a pure argon tower (38) connected to the crude argon first tower (35).

5. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 4, characterized in that: A nitrogen outlet pipe (341) and a precooling pipe (342) are provided at the upper end of the upper tower (34). The nitrogen outlet pipe (341) outlets nitrogen through the main heat exchanger (22), and the precooling pipe (342) is connected to the air purifier (12) and the air precooler (21) through the main heat exchanger (22).

6. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 4, characterized in that: A high-purity oxygen evaporator (371) is provided in the high-purity oxygen tower (37), and the air inlet and air outlet of the high-purity oxygen evaporator (371) are both connected to the upper part of the lower tower (31); A crude argon condenser (361) is provided at the top of the second crude argon tower (36), and a pure argon condenser (381) is provided at the top of the pure argon tower (38). The gas inlet ends of the pure argon condenser (381) and the crude argon condenser (361) are connected to a pure argon evaporator (39), and the gas inlet end of the pure argon evaporator (39) is connected to the bottom of the lower tower (31); The lower tower reflux pipe (331) of the main condenser evaporator (33) is connected to the upper part of the lower tower (31), passes through the upper tower reflux pipe (332) connected to the upper end of the upper tower (34) through the cooler (32), and passes through the liquid nitrogen outlet pipe (333) of the cooler (32).

7. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 6, characterized in that: The bottom end of the lower tower (31) is connected to the pure argon evaporator (39) via a pipeline through a cooler (32).

8. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 4 or 6, characterized in that: The middle of the crude argon tower (35) is bidirectionally connected to the top of the high-purity oxygen tower (37) through a pipeline, and a high-purity liquid oxygen outlet pipe (372) is provided at the bottom of the high-purity oxygen tower (37); A liquid oxygen outlet pipe (334) is provided at the bottom of the main condenser evaporator (33).

9. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 4 or 6, characterized in that: The bottom end of the crude argon second tower (36) is connected to a liquid argon pump (362), and the outlet end of the liquid argon pump (362) is connected to the middle of the crude argon first tower (35).

10. The liquid air separation device for producing high-purity liquid oxygen by nitrogen circulation according to claim 6, characterized in that: The outlet end of the crude argon condenser (361) is connected to the pure argon tower (38), and a liquid argon outlet pipe (382) is provided at the bottom of the pure argon tower (38).

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