A liquid air separation unit for the production of high-purity liquid oxygen

Abstract

This utility model discloses a liquid air separation unit for the production of high-purity liquid oxygen, belonging to the field of cryogenic air separation technology. The unit includes an air pretreatment section, a circulating nitrogen compressor, a circulating air compressor, and a cryogenic separation cold box. The air pretreatment section receives raw air, removes impurities, dries it, and then transfers it to the cryogenic separation cold box for distillation and purification. The cryogenic separation cold box contains a main heat exchanger, a lower column, a main condenser-evaporator, an upper column, a demethanizer, and a high-purity oxygen column. By setting up a nitrogen circulation loop, a heat source of nitrogen is provided to the high-purity oxygen column evaporator, and a cold source of liquid nitrogen is provided to the high-purity oxygen column condenser. This meets the high heat load requirements of the high-purity oxygen column evaporator and condenser, reduces the nitrogen extraction rate of the lower column, improves the distillation effect, reduces the amount of raw air, increases the oxygen extraction rate, reduces the unit's production cost and energy consumption, and improves the overall profitability of the unit.

Description

Technical Field

[0001] This utility model belongs to the field of cryogenic air separation technology, specifically relating to a liquid air separation device for the production of high-purity liquid oxygen. Background Technology

[0002] With the continuous advancement of industrialization, the demand for high-purity oxygen products continues to grow. According to the standard GB / T14599-2008 "Pure Oxygen, High-Purity Oxygen and Ultra-Purity Oxygen," high-purity oxygen refers to high-purity gaseous and liquid oxygen produced through air separation, water electrolysis, or other processes, with an oxygen (O2) volume fraction ≥ 99.999%. This high-purity oxygen is a high-end industrial product, widely used in integrated circuits, photovoltaic panels, and other technological fields, as well as other industries with high oxygen purity requirements.

[0003] Currently, the main method for producing high-purity liquid oxygen is cryogenic separation technology. This technology uses low-temperature technology to separate different components in the air, and uses low-temperature distillation to separate oxygen, nitrogen, argon, etc. In the existing technology, the process for producing high-purity liquid oxygen is mainly divided into the following two types: (1) Based on a large-scale air separation project with argon, a single-tower distillation process is adopted. A high-purity oxygen tower is set up in the cold box. Oxygen free of impurities such as hydrocarbons and nitrous oxide is extracted from the lower section of the argon tower as raw material gas, and then sent to the high-purity oxygen tower for distillation to produce high-purity oxygen; (2) Without an air separation project with argon, a double-tower distillation process is adopted. Oxygen or liquid oxygen is extracted from the main cold box as raw material gas and sent to high-purity oxygen tower I to remove components with a higher boiling point than oxygen and high-purity oxygen tower II to remove components with a lower boiling point than oxygen.

[0004] Both of the above processes produce high-purity oxygen simultaneously with ordinary oxygen (O2 purity ≥ 99.6%), nitrogen, argon, and other products. To meet the production demands of high-purity liquid oxygen, nitrogen at the top of the lower column or positively flowing air is typically used as the heat source for the high-purity oxygen tower evaporator. The higher the proportion of high-purity liquid oxygen in the total liquid oxygen product (high-purity liquid oxygen + ordinary liquid oxygen), the greater the amount of nitrogen at the bottom column or positively flowing air required, resulting in higher energy consumption for the air separation unit. Therefore, how to reduce the energy consumption of the air separation unit while meeting the production requirements of high-purity liquid oxygen has become a pressing technical problem to be solved. Utility Model Content

[0005] The purpose of this invention is to address the shortcomings of the existing technology and provide a liquid air separation device for the production of high-purity liquid oxygen.

[0006] The specific technical solution adopted in this utility model is as follows:

[0007] This utility model provides a liquid air separation device for the production of high-purity liquid oxygen, including an air pretreatment section, a circulating nitrogen compressor, a circulating air compressor, and a cryogenic separation cold box; the air pretreatment section receives raw material air, removes impurities and dries it, and then transfers it to the cryogenic separation cold box for distillation and purification;

[0008] The cryogenic separation cold box is equipped with a main heat exchanger, a lower tower, a main condenser-evaporator, an upper tower, a demethanizer, and a high-purity oxygen tower. The main condenser-evaporator is located between the lower and upper towers. A demethanizer condenser is installed at the top of the demethanizer. A high-purity oxygen condenser is installed at the top of the high-purity oxygen tower, and a high-purity oxygen evaporator is installed at the bottom. The circulating nitrogen compressor realizes a nitrogen circulation loop, providing heat source nitrogen to the high-purity oxygen evaporator and cold source liquid nitrogen to the high-purity oxygen condenser.

[0009] Preferably, the air pretreatment section includes an air filter, a raw material air compressor, an air cooling tower, and an adsorber connected in sequence.

[0010] Furthermore, the air pretreatment section is also equipped with a water-cooling tower for pre-cooling the compressed air and cooling the cooling water.

[0011] Preferably, the nitrogen circulation loop is configured as follows:

[0012] The compressed air outlet of the circulating air compressor is divided into two branches. One branch is connected to the first hot-side inlet of the main heat exchanger via a pipeline. The first hot-side outlet of the main heat exchanger is connected to the expansion end of the hot-end turbo expander, the first cold-side inlet of the main heat exchanger, and the first cold-side outlet of the main heat exchanger via pipelines, before returning to the circulating air compressor. The other branch is connected to the booster end of the hot-end turbo expander, the booster end of the cold-end turbo expander, and the second hot-side inlet of the main heat exchanger via pipelines. The second hot-side outlet of the main heat exchanger is divided into two branches. One branch is connected to the lower tower, and the other branch is connected to the expansion end of the cold-end turbo expander, the second cold-side inlet of the main heat exchanger, and the second cold-side outlet of the main heat exchanger via pipelines, before returning to the circulating air compressor. The expansion end of the cold-end turbo expander is also provided with a pipeline connected to the lower tower.

[0013] The nitrogen outlet of the lower column is connected to the condenser-side inlet of the high-purity oxygen tower evaporator via a pipeline; the oxygen-enriched liquid air outlet at the bottom of the lower column is connected to the evaporator side of the demethanizer condenser after passing through a subcooler; the oxygen-enriched air outlet at the top of the demethanizer condenser is connected to the upper column via a pipeline; the oxygen outlet at the bottom of the upper column is connected to the demethanizer via a pipeline; the oxygen outlet at the top of the demethanizer is connected to the demethanizer condenser; the liquid oxygen outlet of the demethanizer condenser is divided into two branches, one branch is connected to the high-purity oxygen tower via a pipeline, and the other branch returns to the demethanizer;

[0014] The nitrogen outlet at the top of the high-purity oxygen tower condenser is connected to the condenser-side inlet of the high-purity oxygen tower evaporator via a pipeline that passes sequentially through the third cold-side inlet of the main heat exchanger, the third cold-side outlet of the main heat exchanger, the circulating nitrogen compressor, the third hot-side inlet of the main heat exchanger, and the third hot-side outlet of the main heat exchanger. The liquid nitrogen outlet of the high-purity oxygen tower evaporator is connected to the evaporation-side inlet of the high-purity oxygen tower condenser via a pipeline that passes through a subcooler. The high-purity liquid oxygen outlet of the high-purity oxygen tower bottom is connected to the cryogenic separation cold box via a pipeline.

[0015] Furthermore, both the upper and lower towers are packed towers.

[0016] Furthermore, both the demethanizing tower and the high-purity oxygen tower are packed towers.

[0017] Compared with the prior art, this utility model has the following advantages:

[0018] This invention adds a circulating nitrogen compressor to the process flow of a liquid air separation unit with a high proportion of high-purity liquid oxygen, forming the following circulation loop: pressurized nitrogen is drawn from the lower column and sent to the high-purity oxygen evaporator for condensation into liquid nitrogen; the liquid nitrogen is vaporized as a cold source for the high-purity oxygen condenser; the vaporized nitrogen is reheated by the main heat exchanger and then sent to the circulating nitrogen compressor for compression; the pressurized nitrogen is cooled by the main heat exchanger and then returned to the lower column. This improvement effectively reduces the amount of pressurized nitrogen drawn from the lower column, improves the distillation effect, reduces the consumption of feedstock air, and thus reduces the operating energy consumption of the unit, providing strong process support for liquid air separation units with a high proportion of high-purity oxygen. Attached Figure Description

[0019] Figure 1 This is an overall flow diagram of a liquid air separation unit for producing high-purity liquid oxygen provided in this embodiment;

[0020] Figure 2 This is a schematic diagram of the air pretreatment section provided in this embodiment;

[0021] Figure 3 This is a schematic diagram of the internal process of the cryogenic separation cold box provided in this embodiment;

[0022] In the diagram: 1. Air filter; 2. Raw material air compressor; 3. Air cooling tower; 4. Water cooling tower; 5. Adsorber; 6. Circulating nitrogen compressor; 7. Circulating air compressor; 8. Hot-end booster turbine expander; 9. Cold-end booster turbine expander; 10. Cryogenic separation cold box; 11. Main heat exchanger; 12. Lower tower; 13. Main condenser evaporator; 14. Upper tower; 15. Demethanizer tower; 16. Demethanizer tower condenser; 17. High-purity oxygen tower evaporator; 18. High-purity oxygen tower; 19. High-purity oxygen tower condenser; 20. Subcooler. Detailed Implementation

[0023] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0024] like Figure 1 As shown in the figure, as a preferred embodiment of this utility model, this embodiment provides a liquid air separation unit for the production of high-purity liquid oxygen, including an air pretreatment section, a circulating nitrogen compressor 6, a circulating air compressor 7, and a cryogenic separation cold box 10. The air pretreatment section receives raw material air, removes impurities and dries it, and then transfers it to the cryogenic separation cold box 10 for distillation and purification.

[0025] like Figure 2 As shown, the air pretreatment section provided in this embodiment includes an air filter 1, a raw material air compressor 2, an air cooling tower 3, a water cooling tower 4, and an adsorber 5. The air is first filtered by the self-cleaning air filter 1, then enters the raw material air compressor 2 for pressurization, then is pre-cooled by the air cooling tower 3, and finally is dried by the adsorber 5 before being sent to the cryogenic separation cold box 10.

[0026] like Figure 3 As shown, the cryogenic separation cold box 10 provided in this embodiment is equipped with a main heat exchanger 11, a lower tower 12, a main condenser-evaporator 13, an upper tower 14, a demethanizer 15, and a high-purity oxygen tower 18. The main condenser-evaporator 13 is located between the lower tower 12 and the upper tower 14. A demethanizer condenser 16 is installed at the top of the demethanizer 15. A high-purity oxygen tower condenser 19 is installed at the top of the high-purity oxygen tower 18, and a high-purity oxygen tower evaporator 17 is installed at the bottom. A circulating nitrogen compressor 6 realizes a nitrogen circulation loop, providing heat source nitrogen for the high-purity oxygen tower evaporator 17 and cold source liquid nitrogen for the high-purity oxygen tower condenser 19.

[0027] The specific settings for the nitrogen circulation loop are as follows:

[0028] The compressed air outlet of the circulating air compressor 7 is divided into two branches. One branch is connected to the first hot side inlet of the main heat exchanger 11 through a pipeline. The first hot side outlet of the main heat exchanger 11 is connected to the expansion end of the hot end booster turbine expander 8, the first cold side inlet of the main heat exchanger 11, and the first cold side outlet of the main heat exchanger 11 through a pipeline and then returns to the circulating air compressor 7. The other branch is connected to the booster end of the hot end booster turbine expander 8, the booster end of the cold end booster turbine expander 9, and the second hot side inlet of the main heat exchanger 11 through a pipeline.

[0029] The second hot-side outlet of the main heat exchanger 11 is divided into two branches. One branch is connected to the inlet at the bottom of the lower tower 12, and the other branch is connected to the expansion end of the cold-end booster turbine expander 9. Then it is divided into two branches. One branch passes through the second cold-side inlet and the second cold-side outlet of the main heat exchanger 11 and returns to the circulating air compressor 7. The other branch is connected to the inlet at the bottom of the lower tower 12.

[0030] Nitrogen and oxygen are separated in the lower column 12. The nitrogen outlet of the lower column 12 is connected to the condenser-side inlet of the high-purity oxygen tower evaporator 17 via a pipeline. The oxygen-enriched liquid air outlet at the bottom of the lower column 12 is connected to the evaporation side of the demethanizer condenser 16 after passing through the subcooler 20. The oxygen-enriched air outlet at the top of the demethanizer condenser 16 is connected to the upper column 14 via a pipeline. The oxygen outlet at the bottom of the upper column 14 is connected to the demethanizer 15 via a pipeline. The nitrogen obtained from the upper column 14 passes through the subcooler 20 and the main heat exchanger 11 in sequence before exiting the cryogenic separation cold box 10.

[0031] In the apparatus provided in this embodiment, the oxygen outlet at the top of the demethanizer 15 is connected to the demethanizer condenser 16; the liquid oxygen outlet of the demethanizer condenser 16 is divided into two branches, one branch is connected to the high-purity oxygen tower 18 through a pipeline, and the other branch returns to the demethanizer 15.

[0032] The nitrogen outlet at the top of the high-purity oxygen tower condenser 19 is connected to the condensing side inlet of the high-purity oxygen tower evaporator 17 via a pipeline, passing sequentially through the third cold side inlet of the main heat exchanger 11, the third cold side outlet of the main heat exchanger 11, the circulating nitrogen compressor 6, the third hot side inlet of the main heat exchanger 11, and the third hot side outlet of the main heat exchanger 11. The liquid nitrogen outlet of the high-purity oxygen tower evaporator 17 is connected to the evaporating side inlet of the high-purity oxygen tower condenser 19 via a pipeline, passing through the subcooler 20. The high-purity liquid oxygen outlet of the high-purity oxygen tower 18 bottom is connected to the cryogenic separation cold box 10 via a pipeline.

[0033] It should be noted that in this embodiment, the upper tower 14, lower tower 12, demethanizer 15, and high-purity oxygen tower 18 are all packed towers. This invention does not impose specific limitations on the specific type of packed tower; those skilled in the art can select appropriate temperature, pressure distribution, and packing type based on actual operating conditions.

[0034] Next, this embodiment provides a method for producing high-purity liquid oxygen using the above-mentioned liquid air separation unit, the specific steps of which are as follows:

[0035] S1: The raw air is filtered, compressed, cooled and purified in the air pretreatment section to obtain purified air, which is then combined with the reflux expansion air from the cryogenic separation cold box 10. After being compressed by the circulating air compressor 7, it is divided into two streams: one stream of purified air is cooled by the main heat exchanger 11 and then enters the expansion end of the hot-end booster turbine expander 8 for expansion and cooling. The expanded air is then reheated by the main heat exchanger 11 and returns to the circulating air compressor 7. The other stream of purified air is successively pressurized and cooled by the booster end of the hot-end booster turbine expander 8 and the booster end of the cold-end booster turbine expander 9 before entering the main heat exchanger 11. After being cooled by the main heat exchanger 11, it is divided into two streams: one stream of high-pressure liquid air is throttled and enters the lower column 12 to participate in distillation, and the other stream of high-pressure air enters the expansion end of the cold-end booster turbine expander 9 for expansion and cooling. Part of the expanded air is reheated by the main heat exchanger 11 and returns to the circulating air compressor 7, while the remaining expanded air enters the lower column 12 to participate in distillation.

[0036] S2: Expanded air and high-pressure liquid air enter the lower column 12 for rectification, separating into nitrogen at the top and oxygen-enriched liquid air at the bottom; the oxygen-enriched liquid air is cooled by the subcooler 20 and enters the evaporation side of the demethanizer condenser 16, where it evaporates into oxygen-enriched air, which then enters the upper column 14 for further rectification; during the evaporation of the oxygen-enriched liquid air, the oxygen at the top of the demethanizer 15 enters the demethanizer condenser 16 and is liquefied into liquid oxygen, a portion of which is refluxed back to the demethanizer 15 for rectification to remove components with a boiling point higher than oxygen, and the remaining liquid oxygen enters the high-purity oxygen column 18;

[0037] S3: After being pressurized by the circulating nitrogen compressor 6, the high-pressure nitrogen is cooled by the main heat exchanger 11 and then merges with the nitrogen at the top of the lower tower 12 before entering the condensation side of the high-purity oxygen tower evaporator 17. After condensation, liquid nitrogen is obtained. The liquid nitrogen is cooled by the subcooler 20 and then enters the evaporation side of the high-purity oxygen tower condenser 19. The nitrogen obtained from evaporation is reheated by the main heat exchanger 11 and then returned to the circulating nitrogen compressor 6. While the nitrogen in the high-purity oxygen tower evaporator 17 is condensing, the liquid oxygen in the bottom of the high-purity oxygen tower 18 is vaporized on the evaporation side of the high-purity oxygen tower evaporator 17. The oxygen obtained after vaporization is used as the rising gas in the high-purity oxygen tower 18 for distillation to remove components with a boiling point lower than oxygen, thus obtaining high-purity liquid oxygen.

[0038] The above embodiments are merely preferred solutions of this utility model, and are not intended to limit this utility model. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this utility model. Therefore, all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of this utility model.

Claims

1. A liquid air separation unit for producing high-purity liquid oxygen, characterized in that, It includes an air pretreatment section, a circulating nitrogen compressor (6), a circulating air compressor (7), and a cryogenic separation cold box (10); the air pretreatment section receives raw material air, removes impurities and dries it, and then transfers it to the cryogenic separation cold box (10) for distillation and purification; The cryogenic separation cold box (10) is equipped with a main heat exchanger (11), a lower tower (12), a main condenser-evaporator (13), an upper tower (14), a demethanizer (15), and a high-purity oxygen tower (18). The main condenser-evaporator (13) is located between the lower tower (12) and the upper tower (14). A demethanizer condenser (16) is installed at the top of the demethanizer (15). A high-purity oxygen tower condenser (19) is installed at the top of the high-purity oxygen tower (18), and a high-purity oxygen tower evaporator (17) is installed at the bottom. The circulating nitrogen compressor (6) realizes a nitrogen circulation loop, providing heat source nitrogen to the high-purity oxygen tower evaporator (17) and cold source liquid nitrogen to the high-purity oxygen tower condenser (19).

2. The liquid air separation unit for producing high-purity liquid oxygen according to claim 1, characterized in that, The air pretreatment section includes an air filter (1), a raw material air compressor (2), an air cooling tower (3), and an adsorber (5) connected in sequence.

3. The liquid air separation unit for producing high-purity liquid oxygen according to claim 2, characterized in that, The air pretreatment section is also equipped with a water-cooled tower (4) for cooling the cooling water.

4. The liquid air separation unit for producing high-purity liquid oxygen according to claim 1, characterized in that, The nitrogen circulation loop is specifically configured as follows: The compressed air outlet of the circulating air compressor (7) is divided into two branches. One branch is connected to the first hot-side inlet of the main heat exchanger (11) via a pipeline. The first hot-side outlet of the main heat exchanger (11) is connected to the expansion end of the hot-end booster turbine expander (8), the first cold-side inlet of the main heat exchanger (11), and the first cold-side outlet of the main heat exchanger (11) via pipelines, and then returns to the circulating air compressor (7). The other branch is connected to the booster end of the hot-end booster turbine expander (8) and the cold-end booster turbine expander (8) via pipelines. The pressure boosting end of the flat expander (9) and the second hot side inlet of the main heat exchanger (11); the second hot side outlet of the main heat exchanger (11) is divided into two branches, one branch is connected to the lower tower (12), and the other branch is connected to the expansion end of the cold end booster turbine expander (9), the second cold side inlet of the main heat exchanger (11), and the second cold side outlet of the main heat exchanger (11) in sequence through a pipeline and then returned to the circulating air compressor (7); the expansion end of the cold end booster turbine expander (9) is also provided with a pipeline connected to the lower tower (12); The nitrogen outlet of the lower tower (12) is connected to the condenser side inlet of the high-purity oxygen tower evaporator (17) via a pipeline; the oxygen-enriched liquid air outlet at the bottom of the lower tower (12) is connected to the evaporation side of the demethanizer condenser (16) after passing through the subcooler (20); the oxygen-enriched air outlet at the top of the demethanizer condenser (16) is connected to the upper tower (14) via a pipeline; the oxygen outlet at the bottom of the upper tower (14) is connected to the demethanizer (15) via a pipeline; the oxygen outlet at the top of the demethanizer (15) is connected to the demethanizer condenser (16); the liquid oxygen outlet of the demethanizer condenser (16) is divided into two branches, one branch is connected to the high-purity oxygen tower (18) via a pipeline, and the other branch returns to the demethanizer (15); The nitrogen outlet at the top of the high-purity oxygen tower condenser (19) is connected to the condensing side inlet of the high-purity oxygen tower evaporator (17) via a pipeline through the third cold side inlet of the main heat exchanger (11), the third cold side outlet of the main heat exchanger (11), the circulating nitrogen compressor (6), the third hot side inlet of the main heat exchanger (11), and the third hot side outlet of the main heat exchanger (11). The liquid nitrogen outlet of the high-purity oxygen tower evaporator (17) is connected to the evaporating side inlet of the high-purity oxygen tower condenser (19) via a pipeline through the subcooler (20). The high-purity liquid oxygen outlet of the high-purity oxygen tower (18) bottom is connected to the cryogenic separation cold box (10) via a pipeline.

5. The liquid air separation unit for producing high-purity liquid oxygen according to claim 4, characterized in that, Both the upper tower (14) and the lower tower (12) are packed towers.

6. The liquid air separation unit for producing high-purity liquid oxygen according to claim 4, characterized in that, Both the demethanizer (15) and the high-purity oxygen tower (18) are packed towers.

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