Process and system for producing oxygen-enriched and high-purity oxygen

Abstract

The present application relates to the field of three-tower low-temperature rectification, and provides a process and system for preparing oxygen-enriched gas and high-purity oxygen, the system comprising a purification system, a pressurized expansion system and a rectification system; the rectification system comprising a low-temperature cold box heat exchanger, a low-pressure nitrogen column, a supercooler, a low-pressure nitrogen column condenser, a high-pressure nitrogen column, an upper column and a high-purity oxygen column; the system and equipment of the present application are stable and safe, and can produce oxygen-enriched gas with a purity of 80%-85%, high-purity oxygen with a purity of 99.999%, pressurized nitrogen and liquid nitrogen at the same time; and can be applied in the fields of metal smelting, solid waste recovery, new energy manufacturing, oxygen-enriched combustion and the like.

Description

Technical Field

[0001] This invention relates to the field of three-tower cryogenic distillation, and more particularly to a process and system for producing oxygen-enriched and high-purity oxygen. Background Technology

[0002] In the field of iron and steel smelting, oxygen top-blown converter steelmaking, bottom-blown converter steelmaking, and oxygen side-blown converter steelmaking all require a large amount of oxygen. A large amount of oxygen is also needed in the smelting of non-ferrous metals and in the recycling and reuse of scrap metals.

[0003] Existing oxygen production processes only produce oxygen-enriched gas, while the electronics industry, which requires fine processing, needs high-purity 5N oxygen, high-purity nitrogen, etc., and existing oxygen production processes cannot meet their gas needs.

[0004] Therefore, there is an urgent need for a process and system that can produce oxygen-enriched gas, as well as 5N high-purity oxygen, high-purity nitrogen, liquid oxygen, and liquid nitrogen products. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a process and system for producing oxygen-enriched and high-purity oxygen.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A first aspect of the present invention is to provide a system for producing oxygen-enriched and high-purity oxygen, comprising: a purification system, a pressurization and expansion system, and a distillation system;

[0008] The outlet of the purification system is connected to the first inlet of the distillation system, the booster end of the pressurization and expansion system, and the inlet of the circulating booster unit; the first outlet of the pressurization and expansion system is connected to the second inlet of the distillation system; the first outlet of the circulating booster unit is connected to the third inlet of the distillation system; and the second outlet of the circulating booster unit is connected to the fourth inlet of the distillation system.

[0009] The distillation system includes: a low-temperature cold box heat exchanger, a low-pressure nitrogen tower, a subcooler, a low-pressure nitrogen tower condenser, a high-pressure nitrogen tower, an upper tower, and a high-purity oxygen tower; the first outlet of the low-temperature cold box heat exchanger is connected to the first inlet at the bottom of the low-pressure nitrogen tower; the first outlet at the top of the low-pressure nitrogen tower is connected to the first inlet in the middle of the upper tower; the second outlet at the bottom of the low-pressure nitrogen tower is connected to the first inlet of the low-pressure nitrogen tower condenser; the third and fourth outlets of the low-temperature cold box heat exchanger are respectively connected to the first inlet and the second inlet at the bottom of the high-pressure nitrogen tower; the first outlet at the top of the high-pressure nitrogen tower passes through the low-temperature cold box heat exchanger... The high-pressure nitrogen tower is connected to the first nitrogen outlet. The second outlet at the bottom of the high-pressure nitrogen tower, after passing through the subcooler, is connected to the second inlet in the middle of the upper tower. The second outlet at the bottom of the high-pressure nitrogen tower is also connected to the inlet of the high-purity oxygen tower. The outlet at the bottom of the high-purity oxygen tower is connected to the second oxygen outlet. The second outlet of the low-temperature cold box heat exchanger is connected to the first inlet of the pressurization and expansion system. The second outlet of the pressurization and expansion system is connected to the third inlet in the middle of the upper tower. The first outlet at the top of the upper tower is connected to the second nitrogen outlet. The first outlet at the bottom of the upper tower is connected to the first oxygen outlet. The second outlet at the bottom of the upper tower is connected to the third inlet at the top of the high-pressure nitrogen tower.

[0010] All connections are pipe connections.

[0011] Preferably, it also includes: a filtration system, a compression system, a precooling system, and a circulating water system;

[0012] The outlet of the filtration system is connected to the inlet of the compression system, the outlet of the compression system is connected to the first inlet of the precooling system, and the first outlet of the precooling system is connected to the inlet of the purification system.

[0013] All connections are pipe connections.

[0014] Preferably, a chiller unit is connected in a pipeline between the first outlet of the pressurization and expansion system and the second inlet of the distillation system.

[0015] Preferably, the circulating booster unit includes two boosters connected in series; the second discharge port of the circulating booster unit is located between the two boosters, and the first discharge port of the circulating booster unit is located at one end near the distillation system.

[0016] Preferably, the low-pressure nitrogen tower condenser is connected by a pipeline between the first discharge port at the top of the low-pressure nitrogen tower and the first inlet port in the middle of the upper tower; the subcooler is connected by a pipeline between the second discharge port at the bottom of the low-pressure nitrogen tower and the first inlet port of the low-pressure nitrogen tower condenser; and the first discharge port of the low-pressure nitrogen tower condenser is connected by a pipeline to the second inlet port at the top of the low-pressure nitrogen tower.

[0017] Preferably, a third condenser is connected in a pipeline between the third outlet of the low-temperature cold box heat exchanger and the first inlet at the bottom of the high-pressure nitrogen tower.

[0018] Preferably, the subcooler and the cryogenic cold box heat exchanger are sequentially connected by pipelines between the first discharge port at the top of the upper tower and the second nitrogen output port.

[0019] Preferably, a third condenser and the low-temperature cold box heat exchanger are sequentially connected by a pipeline between the first discharge port at the bottom of the upper tower and the first oxygen output port.

[0020] Preferably, a cryogenic pump and a high-purity oxygen liquid storage tank are connected by a pipeline between the discharge port at the bottom of the high-purity oxygen tower and the second oxygen output port.

[0021] A second aspect of the present invention is to provide a process for producing oxygen-enriched and high-purity oxygen, using the above-described system, the steps of which include:

[0022] S1. Air is sequentially passed through the filtration system, the compression system, and the precooling system before being delivered to the purification system for purification.

[0023] S2. The purified gas is divided into three streams;

[0024] S2-1. The first gas stream is delivered to the low-pressure nitrogen tower for condensation and evaporation after passing through the low-temperature cold box heat exchanger. The low-pressure liquid nitrogen obtained from the top of the low-pressure nitrogen tower enters the upper tower for rectification. The oxygen-enriched liquid air obtained from the bottom of the low-pressure nitrogen tower is throttled by the subcooler and enters the condenser of the low-pressure nitrogen tower. The gas after the oxygen-enriched liquid air is evaporated is delivered to the middle of the upper tower for rectification.

[0025] S2-2, The second stream of gas is supplied to the circulating booster unit and pressurized to 4 bar. A portion of the gas is drawn from the pipeline between the two boosters and then supplied to the bottom of the high-pressure nitrogen tower via the low-temperature cold box heat exchanger. The medium-pressure air at the end of the circulating booster unit exchanges heat with the pressurized oxygen-rich liquid via the low-temperature cold box heat exchanger. The liquid air obtained from the heat exchange is throttled and then supplied to the bottom of the high-pressure nitrogen tower for distillation. The high-purity liquid nitrogen obtained at the top of the high-pressure nitrogen tower is subcooled by the subcooler and then supplied to the top of the upper tower for further distillation.

[0026] S2-3. The third gas is pressurized at the pressurization end of the pressurization and expansion system, then cooled by the chiller and heated by the low-temperature cold box heat exchanger before re-entering the pressurization and expansion system for expansion. The expanded low-temperature gas is then transported to the middle of the upper column for distillation. The high-purity nitrogen obtained at the top of the upper column is reheated by the subcooler and the low-temperature cold box heat exchanger before being transported to the second nitrogen outlet. The oxygen-enriched liquid with a purity of 80%-85% extracted from the bottom of the upper column is divided into two lines. The first line is pressurized by a liquid pump and then reheated to room temperature by the low-temperature cold box heat exchanger before being transported to the first oxygen outlet. The second line transports the oxygen-enriched liquid to the top of the high-purity oxygen tower. After heat exchange and evaporation in the reboiler at the bottom of the high-purity oxygen tower, 5N-grade high-purity liquid oxygen is obtained at the bottom of the high-purity oxygen tower. This liquid is then transported by the low-temperature pump to the high-purity oxygen liquid storage tank and then to the second oxygen outlet.

[0027] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0028] The system equipment of this invention is stable and safe, and produces a variety of products. It can simultaneously produce oxygen-enriched gas with a purity of 80%-85%, high-purity oxygen with a purity of 99.999%, pressurized nitrogen, and liquid nitrogen. It can be applied to metal smelting, solid waste recycling, new energy manufacturing, oxygen-enriched combustion, and other fields. Attached Figure Description

[0029] Figure 1 This is a flowchart of a system for preparing oxygen-enriched and high-purity oxygen in one embodiment of the present invention.

[0030] The reference numerals in the figure include:

[0031] Filtration system 1; Compression system 2; Precooling system 3; Purification system 4; Circulating water system 5; Pressurization and expansion system 6; Distillation system 7; Circulating booster unit 8; First nitrogen outlet 9; Second nitrogen outlet 10; First oxygen outlet 11; Second oxygen outlet 13; Chiller unit 14; Cryogenic pump 15; High-purity oxygen liquid storage tank 16; Cryogenic cold box heat exchanger E1; Subcooler E2; Low-pressure nitrogen tower T1; High-pressure nitrogen tower T2; Upper tower T3; High-purity oxygen tower T4; Low-pressure nitrogen tower condenser K1; Third condenser K3; Reboiler K4. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0035] Example

[0036] like Figure 1 As shown, this embodiment provides a system for producing oxygen-enriched and high-purity oxygen, including: a filtration system 1, a compression system 2, a precooling system 3, a purification system 4, a circulating water system 5, a pressurization and expansion system 6, and a distillation system 7.

[0037] The discharge port of the filtration system 1 is connected to the inlet of the compression system 2, and the discharge port of the compression system 2 is connected to the first inlet of the precooling system 3; the first discharge port of the precooling system 3 is connected to the inlet of the purification system 4, and the discharge port of the purification system 4 is connected to the first inlet of the distillation system 7, the booster end of the pressurization and expansion system 6, and the inlet of the circulating booster unit 8; the first discharge port of the pressurization and expansion system 6 is connected to the second inlet of the distillation system 7, and the pressurization and expansion system 6... A chiller unit 14 is connected between the first discharge port of the expansion system 6 and the second inlet of the distillation system 7; the circulating booster unit 8 includes two boosters connected in series; the second discharge port of the circulating booster unit 8 is located between the two boosters, and the first discharge port of the circulating booster unit 8 is located at one end close to the distillation system 7; the first discharge port of the circulating booster unit 8 is connected to the third inlet of the distillation system 7, and the second discharge port of the circulating booster unit 8 is connected to the fourth inlet of the distillation system 7;

[0038] The distillation system 7 includes: a low-temperature cold box heat exchanger E1, a low-pressure nitrogen tower T1, a subcooler E2, a low-pressure nitrogen tower condenser K1, a high-pressure nitrogen tower T2, an upper tower T3, and a high-purity oxygen tower T4; the first outlet of the low-temperature cold box heat exchanger E1 is connected to the first inlet at the bottom of the low-pressure nitrogen tower T1; the first outlet at the top of the low-pressure nitrogen tower T1 is connected to the first inlet in the middle of the upper tower T3; the low-pressure nitrogen tower condenser K1 is connected between the first outlet at the top of the low-pressure nitrogen tower T1 and the first inlet in the middle of the upper tower T3; and the second outlet at the bottom of the low-pressure nitrogen tower T1 is connected to the high-pressure nitrogen tower T4. The first inlet of the tower condenser K1 is connected to the subcooler E2, which is connected between the second outlet at the bottom of the low-pressure nitrogen tower T1 and the first inlet of the low-pressure nitrogen tower condenser K1. The first outlet of the low-pressure nitrogen tower condenser K1 is connected to the second inlet at the top of the low-pressure nitrogen tower T1. The third outlet and the fourth outlet of the low-temperature cold box heat exchanger E1 are respectively connected to the first and second inlets at the bottom of the high-pressure nitrogen tower T2. The third outlet of the low-temperature cold box heat exchanger E1 is connected to the first inlet at the bottom of the high-pressure nitrogen tower T2. The high-pressure nitrogen tower T2 has a three-condenser K3; its first outlet at the top is connected to the first nitrogen outlet 9 via the low-temperature cold box heat exchanger E1; its second outlet at the bottom is connected to the second inlet in the middle of the upper tower T3 via the subcooler E2; and its second outlet at the bottom is also connected to the inlet of the high-purity oxygen tower T4; the outlet at the bottom of the high-purity oxygen tower T4 is connected to the second oxygen outlet 13; a low-temperature pump 15 and a high-purity oxygen liquid storage tank 16 are connected between the outlet at the bottom of the high-purity oxygen tower T4 and the second oxygen outlet 13; the low-temperature cold box heat exchanger... The second outlet of the heat exchanger E1 is connected to the first inlet of the pressurization and expansion system 6, and the second outlet of the pressurization and expansion system 6 is connected to the third inlet in the middle of the upper tower T3; the first outlet at the top of the upper tower T3 is connected to the second nitrogen outlet 10, and the subcooler E2 and the low-temperature cold box heat exchanger E1 are connected sequentially between the first outlet at the top of the upper tower T3 and the second nitrogen outlet 10; the first outlet at the bottom of the upper tower T3 is connected to the first oxygen outlet 11, and the second outlet at the bottom of the upper tower T3 is connected to the third inlet at the top of the high-pressure nitrogen tower T2;

[0039] All connections are pipe connections.

[0040] The process flow is as follows: After the air is filtered by the filtration system 1 to remove dust and impurities, it is sent to the compression system 2 for compression. The compressed gas is then sent to the precooling system 3 to lower the temperature of the gas to about 17°C before it is sent to the purification system 4 for purification. The purified gas is then divided into three streams.

[0041] The first gas stream is directly transported to the low-pressure nitrogen tower T1 after passing through the low-temperature cold box heat exchanger E1 for condensation and evaporation. The low-pressure liquid nitrogen obtained from the top of the low-pressure nitrogen tower T1 enters the upper tower T3 for rectification. The oxygen-enriched liquid air obtained from the bottom of the low-pressure nitrogen tower T1 is throttled by the cooler E2 and enters the low-pressure nitrogen tower condenser K1 to provide cooling for the top of the low-pressure nitrogen tower T1. The gas after the oxygen-enriched liquid air is evaporated is transported to the middle of the upper tower T3 for rectification in the upper tower T3.

[0042] The second gas stream is delivered to the circulating booster unit 8 and pressurized to 4 bar. Part of the gas is drawn out from the pipeline between the two boosters and delivered to the bottom of the high-pressure nitrogen tower T2 after passing through the low-temperature cold box heat exchanger E1. The medium-pressure air at the end of the circulating booster unit 8 exchanges heat with the pressurized oxygen-rich liquid through the low-temperature cold box heat exchanger E1. The liquid air obtained from the heat exchange is throttled and delivered to the bottom of the high-pressure nitrogen tower T2 for distillation. The high-purity liquid nitrogen obtained at the top of the high-pressure nitrogen tower T2 is subcooled by the cooler E2 and then delivered to the top of the upper tower T3 for distillation.

[0043] The third gas is pressurized at the pressurization end of the pressurization and expansion system 6, then cooled by the chiller unit 14 and heated by the low-temperature cold box heat exchanger E1 before entering the pressurization and expansion system 6 again for expansion. The expanded low-temperature gas is then transported to the middle of the upper tower T3 for distillation. The high-purity nitrogen obtained from the top of the upper tower T3 is reheated by the cooler E2 and the low-temperature cold box heat exchanger E1 before being transported to the second nitrogen outlet 10. The oxygen-enriched liquid with a purity of 80%-85% extracted from the bottom of the upper tower T3 is divided into two lines. The first line is pressurized by the liquid pump and then reheated to room temperature by the low-temperature cold box heat exchanger E1 before being transported to the first oxygen outlet 11. The second line transports the oxygen-enriched liquid to the top of the high-purity oxygen tower T4. After heat exchange and evaporation in the reboiler K4 at the bottom of the high-purity oxygen tower T4, 5N-grade high-purity liquid oxygen is obtained in the bottom of the high-purity oxygen tower T4. It is then transported by the low-temperature pump 15 to the high-purity oxygen liquid storage tank 16 and then to the second oxygen outlet 13.

[0044] In summary, the system equipment of this invention is stable and safe, and offers a variety of products. It can simultaneously produce oxygen-enriched gas with a purity of 80%-85%, high-purity oxygen with a purity of 99.999%, pressurized nitrogen, and liquid nitrogen. It can be applied to fields such as metal smelting, solid waste recycling, new energy manufacturing, and oxygen-enriched combustion.

[0045] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for producing oxygen-enriched and high-purity oxygen, characterized in that, include: Purification system (4), pressurization and expansion system (6), and distillation system (7); The distillation system (7) includes: a low-temperature cold box heat exchanger (E1), a low-pressure nitrogen tower (T1), a subcooler (E2), a low-pressure nitrogen tower condenser (K1), a high-pressure nitrogen tower (T2), an upper tower (T3), and a high-purity oxygen tower (T4). The outlet of the purification system (4) is connected to the first inlet of the low-temperature cold box heat exchanger (E1) of the distillation system (7), the pressurization end of the pressurization expansion system (6), and the inlet of the circulating pressurizer (8); the first outlet of the pressurization expansion system (6) is connected to the second inlet of the low-temperature cold box heat exchanger (E1) of the distillation system (7); the first outlet of the circulating pressurizer (8) is connected to the third inlet of the low-temperature cold box heat exchanger (E1) of the distillation system (7), and the second outlet of the circulating pressurizer (8) is connected to the fourth inlet of the low-temperature cold box heat exchanger (E1) of the distillation system (7); The first outlet of the low-temperature cold box heat exchanger (E1) is connected to the first inlet at the bottom of the low-pressure nitrogen tower (T1); the first outlet at the top of the low-pressure nitrogen tower (T1) is connected to the first inlet in the middle of the upper tower (T3); the second outlet at the bottom of the low-pressure nitrogen tower (T1) is connected to the first inlet of the low-pressure nitrogen tower condenser (K1); the third outlet and the fourth outlet of the low-temperature cold box heat exchanger (E1) are respectively connected to the first inlet and the second inlet at the bottom of the high-pressure nitrogen tower (T2); the first outlet at the top of the high-pressure nitrogen tower (T2) is connected to the first nitrogen outlet (9) after passing through the low-temperature cold box heat exchanger (E1); the second outlet at the bottom of the high-pressure nitrogen tower (T2) is connected to the first nitrogen outlet (9) after passing through the low-temperature cold box heat exchanger (E1); The supercooler (E2) is connected to the second inlet in the middle of the upper tower (T3), and the second outlet at the bottom of the high-pressure nitrogen tower (T2) is also connected to the inlet of the high-purity oxygen tower (T4); the outlet at the bottom of the high-purity oxygen tower (T4) is connected to the second oxygen outlet (13); the second outlet of the low-temperature cold box heat exchanger (E1) is connected to the first inlet of the pressurization expansion system (6), and the second outlet of the pressurization expansion system (6) is connected to the third inlet in the middle of the upper tower (T3); the first outlet at the top of the upper tower (T3) is connected to the second nitrogen outlet (10), the first outlet at the bottom of the upper tower (T3) is connected to the first oxygen outlet (11), and the second outlet at the bottom of the upper tower (T3) is connected to the third inlet at the top of the high-pressure nitrogen tower (T2); The low-pressure nitrogen tower condenser (K1) is connected by a pipeline between the first discharge port at the top of the low-pressure nitrogen tower (T1) and the first inlet port in the middle of the upper tower (T3); the subcooler (E2) is connected by a pipeline between the second discharge port at the bottom of the low-pressure nitrogen tower (T1) and the first inlet port of the low-pressure nitrogen tower condenser (K1); the first discharge port of the low-pressure nitrogen tower condenser (K1) is connected by a pipeline to the second inlet port at the top of the low-pressure nitrogen tower (T1). All connections are pipe connections.

2. The system according to claim 1, characterized in that, Also includes: The system includes a filtration system (1), a compression system (2), a precooling system (3), and a circulating water system (5). The outlet of the filtration system (1) is connected to the inlet of the compression system (2), the outlet of the compression system (2) is connected to the first inlet of the precooling system (3), and the first outlet of the precooling system (3) is connected to the inlet of the purification system (4). All connections are pipe connections.

3. The system according to claim 1, characterized in that, A chiller unit (14) is connected by a pipeline between the first outlet of the pressurization expansion system (6) and the second inlet of the distillation system (7).

4. The system according to claim 1, characterized in that, The circulating booster unit (8) includes two boosters connected in series; the second outlet of the circulating booster unit (8) is located between the two boosters, and the first outlet of the circulating booster unit (8) is located at one end near the distillation system (7).

5. The system according to claim 1, characterized in that, A third condenser (K3) is connected by a pipeline between the third outlet of the low-temperature cold box heat exchanger (E1) and the first inlet at the bottom of the high-pressure nitrogen tower (T2).

6. The system according to claim 1, characterized in that, The subcooler (E2) and the low-temperature cold box heat exchanger (E1) are sequentially connected by pipelines between the first discharge port at the top of the upper tower (T3) and the second nitrogen output port (10).

7. The system according to claim 1, characterized in that, The first outlet at the bottom of the upper tower (T3) and the first oxygen outlet (11) are connected in sequence by a third condenser (K3) and the low-temperature cold box heat exchanger (E1).

8. The system according to claim 1, characterized in that, A cryogenic pump (15) and a high-purity oxygen liquid storage tank (16) are connected by a pipeline between the discharge port at the bottom of the high-purity oxygen tower (T4) and the second oxygen output port (13).

9. A process for producing oxygen-enriched and high-purity oxygen, employing the system described in any one of claims 1-8, characterized in that the steps... include: S1. Air passes through the filtration system (1), the compression system (2), and the precooling system (3) in sequence, and is then transported to the purification system (4) for purification. S2. The purified gas is divided into three streams; S2-1. The first gas stream is transported to the low-pressure nitrogen tower (T1) after passing through the low-temperature cold box heat exchanger (E1) for condensation and evaporation. The low-pressure liquid nitrogen obtained from the top of the low-pressure nitrogen tower (T1) enters the upper tower (T3) for rectification. The oxygen-enriched liquid air obtained from the bottom of the low-pressure nitrogen tower (T1) is throttled by the subcooler (E2) and enters the low-pressure nitrogen tower condenser (K1). The gas after the oxygen-enriched liquid air is evaporated is transported to the middle of the upper tower (T3) for rectification in the upper tower (T3). S2-2, The second gas is delivered to the circulating booster unit (8) and pressurized to 4 bar. Part of the gas is extracted from the pipeline between the two boosters and delivered to the bottom of the high-pressure nitrogen tower (T2) after passing through the low-temperature cold box heat exchanger (E1). The medium-pressure air at the end of the circulating booster unit (8) exchanges heat with the pressurized oxygen-rich liquid through the low-temperature cold box heat exchanger (E1). The liquid air obtained by heat exchange is delivered to the bottom of the high-pressure nitrogen tower (T2) after throttling for distillation in the high-pressure nitrogen tower (T2). The high-purity liquid nitrogen obtained at the top of the high-pressure nitrogen tower (T2) is subcooled by the subcooler (E2) and delivered to the top of the upper tower (T3) to participate in distillation. S2-3, the third gas is supplied to the pressurization end of the pressurization expansion system (6) for pressurization, and then cooled by the chiller unit (14) and heat exchanged by the low-temperature cold box heat exchanger (E1) before entering the pressurization expansion system (6) again for expansion; the expanded low-temperature gas is supplied to the middle of the upper column (T3) for distillation; the high-purity nitrogen obtained from the top of the upper column (T3) is reheated by the subcooler (E2) and the low-temperature cold box heat exchanger (E1) before being supplied to the second nitrogen outlet (10); the gas extracted from the bottom of the upper column (T3) The oxygen-enriched liquid with a purity of 80%-85% is divided into two lines. The first line is pressurized by a liquid pump and then reheated to room temperature by the low-temperature cold box heat exchanger (E1) and delivered to the first oxygen outlet (11). The second line delivers the oxygen-enriched liquid to the top of the high-purity oxygen tower (T4), and after heat exchange and evaporation in the reboiler (K4) at the bottom of the high-purity oxygen tower (T4), 5N-grade high-purity liquid oxygen is obtained in the bottom of the high-purity oxygen tower (T4), and is delivered to the high-purity oxygen liquid storage tank (16) by a low-temperature pump (15) and delivered to the second oxygen outlet (13).

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