A device and method for producing high-purity nitrogen and ultra-pure oxygen by flash exhaust low-temperature supercharging cycle

Abstract

This invention discloses an apparatus and method for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas through low-temperature pressurization and recirculation. The apparatus includes an air compressor, a purification system, and a cold box. The cold box includes a main heat exchanger, an expander, a distillation column, a flash evaporation column, an oxygen column, an ultrapure oxygen column, a pressure reducing valve, and a jet evaporator. The purpose of this invention is to overcome the problems of low extraction rate and high energy consumption in existing single-tower distillation processes, and the inability of conventional oxygen products to meet the purity requirements of ultrapure oxygen. By utilizing low-temperature pressurization and recirculation of flash evaporation waste gas to recover the nitrogen component and its compression work, energy consumption in nitrogen production is reduced. Multi-stage distillation technology is used to simultaneously produce high-purity nitrogen and ultrapure oxygen without increasing energy consumption. This invention provides an economical and reasonable apparatus and method for obtaining high-purity nitrogen and ultrapure oxygen through cryogenic separation, which features low energy consumption, low investment, small footprint, and high energy efficiency.

Description

Technical Field

[0001] This invention relates to the field of air separation, and more particularly to an apparatus and method for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas through low-temperature pressurization and circulation. Background Technology

[0002] With the development of high-tech industries, high-purity gases are widely used in various fields such as the research and production of large-scale integrated circuits (e.g., chips), the smelting and processing of high-purity metals, and the solar photovoltaic industry. Electronic gases, in particular, play a crucial role in the chip industry, directly impacting chip yield and production costs, leading to continuously rising demand. The demand for electronic gases is primarily for high-purity nitrogen, but there is also a demand for other gases such as ultra-pure oxygen. The key characteristic of these gases is the requirement for high purity and stability.

[0003] To remove impurities in nitrogen, high-purity nitrogen produced by cryogenic distillation is typically required, which is then introduced into a purifier for further purification. If traditional or existing cryogenic distillation equipment is used to produce high-purity nitrogen, the traditional single-tower distillation process suffers from low extraction rates and high energy consumption. The dual-tower distillation process involves high investment and complex operation.

[0004] Oxygen obtained through conventional cryogenic distillation contains impurities such as argon, nitrous oxide, carbon dioxide, and hydrocarbons, which do not meet the requirements for electronic-grade oxygen. Further purification is typically required, increasing energy consumption and occupying more industrial land. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide an apparatus and method for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas through low-temperature pressurization and circulation. Nitrogen distillation uses a single distillation column with waste gas circulation. An additional flash evaporation column is added to recover flash evaporation waste gas with a nitrogen content >80%. The flash evaporation waste gas is then recovered through low-temperature pressurization at the pressurization end of an expander and circulated back into the lower part of the distillation column to recover its nitrogen components and compressive work to produce high-purity nitrogen. Simultaneously, an oxygen tower and an ultrapure oxygen tower are added to obtain qualified ultrapure oxygen using a multi-stage distillation method.

[0006] The technical solution of this invention is implemented as follows: An apparatus for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas via low-temperature pressurization and circulation includes an air compressor, a purification system, and a cold box. The cold box includes a main heat exchanger, an expander, a distillation column, a flash evaporation column, an oxygen column, an ultrapure oxygen column, a pressure reducing valve, and a jet evaporator. Evaporators are installed in the lower parts of the flash evaporation column, the oxygen column, and the ultrapure oxygen column, while a condenser is installed in the upper part of the ultrapure oxygen column. The air compressor is connected to the purification system via a first pipeline. The gas outlet of the purification system is connected to a second pipeline, which is connected to the distillation column after passing through the main heat exchanger. The liquid outlet at the bottom of the distillation column is connected to the flash evaporation column via a third pipeline. The gas outlet at the top of the distillation column is connected to pipes four, five, seven, and sixteen. Pipe four extends to the outside of the cold box after passing through the main heat exchanger. Pipe five is connected to the evaporator at the bottom of the oxygen tower. The liquid outlet of the evaporator in the oxygen tower is connected to pipe six, which is connected to the top of the distillation column. Pipe seven is connected to the evaporator at the bottom of the flash evaporator. The liquid outlet of the evaporator in the flash evaporator is connected to pipe eight, which is connected to the top of the distillation column. The liquid outlet at the bottom of the flash evaporator is connected to pipe nine, which connects to the upper part of the oxygen tower after passing through the pressure reducing valve. The gas outlet at the top of the oxygen tower is connected to pipe ten. Pipeline 10 connects to the expansion end of the expander after passing through the main heat exchanger, and the jet evaporator is installed on pipeline 10. Pipeline 11 connects to the outlet of the expansion end of the expander, and pipeline 11 connects to the purification system after passing through the main heat exchanger. The gas phase outlet of the flash evaporator is connected to the pressurization end of the expander through pipeline 12. Pipeline 13 connects to the outlet of the pressurization end of the expander, and pipeline 13 connects to the lower part of the distillation column after passing through the main heat exchanger. The gas outlet of the lower part of the oxygen tower is connected to the middle part of the ultrapure oxygen tower through pipeline 14. The liquid outlet at the bottom of the oxygen tower is connected to the jet evaporator through pipeline 15. The sixteenth pipe is connected to the evaporator at the bottom of the ultrapure oxygen tower. The outlet of the evaporator at the bottom of the ultrapure oxygen tower is connected to the seventeenth pipe, which is connected to the condenser at the top of the ultrapure oxygen tower. The liquid outlet of the evaporator at the bottom of the oxygen tower is connected to the condenser at the top of the ultrapure oxygen tower via the eighteenth pipe. The gas outlet of the condenser at the top of the ultrapure oxygen tower is connected to the expansion end outlet of the expander via the twentieth pipe. The gas outlet at the top of the ultrapure oxygen tower is connected via the nineteenth and twentieth pipes. The gas outlet at the bottom of the ultrapure oxygen tower is connected to the twenty-first pipe, which extends to the outside of the cold box after passing through the main heat exchanger.

[0007] Furthermore, the distillation column is a sieve tray column or a structured packed column with a theoretical number of 35 to 50 trays or a corresponding actual number of 45 to 65 trays.

[0008] Furthermore, the flash tower is a sieve plate tower with a theoretical number of 2 to 8 trays or a corresponding actual number of 4 to 10 trays.

[0009] Furthermore, the oxygen tower is a sieve tray tower or a structured packed tower with a theoretical number of 20 to 30 trays or a corresponding actual number of 25 to 45 trays.

[0010] Furthermore, the ultrapure oxygen tower is a sieve tray tower or a structured packed tower with a theoretical number of 20 to 30 trays or a corresponding actual number of 25 to 45 trays.

[0011] Furthermore, the expander is a turbine expander.

[0012] A method for producing high-purity nitrogen and ultrapure oxygen using the above-mentioned apparatus, the process of which is as follows: After compression and purification, the air enters the main heat exchanger, is cooled by the reflux gas, and then enters the distillation column. Pure nitrogen is obtained at the top of the distillation column. A portion of this nitrogen, as a product, is reheated in the main heat exchanger and sent out of the cold box. A second portion of the nitrogen enters the oxygen tower evaporator, is liquefied, and then enters the distillation column as reflux. A third portion enters the flash evaporator, is condensed and liquefied, and then replenishes the distillation column as reflux. A fourth portion of the nitrogen enters the bottom evaporator of the ultrapure oxygen tower, is condensed and liquefied, and then throttled and depressurized before entering the top condenser of the ultrapure oxygen tower. After evaporation, it is finally replenished into the twentieth pipeline as regeneration waste gas. The oxygen-rich liquid air at the bottom of the distillation column enters the flash evaporator for flashing. The liquid at the bottom of the flash evaporator has a high oxygen content; after being depressurized and throttled by a pressure reducing valve, it enters the oxygen tower as reflux. The gas phase at the top of the oxygen tower enters the main heat exchanger for partial reheating and is used as expansion waste gas. The gas enters the expansion end of the expander, providing cooling for the entire unit. After expansion, the waste gas is reheated by the main heat exchanger and then enters the purification system as regeneration gas for the adsorbent. The top gas phase of the flash evaporator has a high nitrogen content and enters the expansion end for pressurization. After being cooled by the main heat exchanger, it enters the lower part of the distillation column for direct recycling of its nitrogen components. The liquid at the bottom of the oxygen tower is vaporized by the waste gas at the top of the oxygen tower through the jet evaporator and enters the main heat exchanger to recover its cooling capacity. Pure oxygen is drawn from the middle of the oxygen tower and sent to the middle of the ultrapure oxygen tower. The heat source for the evaporator of the ultrapure oxygen tower comes from the pressurized nitrogen at the top of the distillation column. After liquefaction and depressurization, it is sent to the condenser at the top of the ultrapure oxygen tower as a cooling source. Part of the supplementary cooling source for the condenser of the ultrapure oxygen tower comes from the liquid nitrogen liquefied in the evaporator at the bottom of the oxygen tower. Ultrapure oxygen is drawn from the bottom of the ultrapure oxygen tower, reheated by the main heat exchanger, and then sent out of the cold box as a product.

[0013] Furthermore, the operating pressure of the distillation column is 0.4~1.5 MPa. The operating pressure of the oxygen column is 0.2~0.8 MPa. The operating pressure of the ultrapure oxygen column is 0.2~0.8 MPa. The operating pressure of the flash distillation column is 0.3~1.2 MPa.

[0014] The positive effects of the technical solution of the present invention are as follows: This application utilizes the flash gas exiting the top of the flash distillation tower (existing processes directly discharge it into the cold box as waste gas). High-nitrogen flash gas is recovered through low-temperature pressurization at the expander's booster end, and then recycled into a distillation tower to recover its nitrogen components and recover compression work to produce high-purity nitrogen. Compared to traditional single-tower low-temperature distillation processes: nitrogen extraction rate is increased by 10-15%, energy consumption is reduced by 10-15%; the air compressor and purification system are smaller in scale than in single-tower processes; the distillation section has a more complex structure; and the overall investment is only slightly higher than that of single-tower low-temperature distillation processes. High-purity nitrogen and ultra-pure oxygen are produced simultaneously without additional energy consumption.

[0015] Therefore, this process not only minimizes investment and land occupation, reduces energy consumption and production costs, but also saves human resources and investment, making it scientific and rational. This invention is of great significance for improving economic efficiency and plays a positive role in saving social resources and creating a low-carbon, environmentally friendly society. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the device for producing high-purity nitrogen from flash evaporation waste gas at low temperature and pressure.

[0017] The diagram is labeled as follows: 1. Air compressor; 2. Purification system; 3. Main heat exchanger; 4. Turbine expander expansion end; 5. Turbine expander pressurization end; 6. Distillation column; 7. Flash evaporator; 8. Pressure reducing valve; 9. Oxygen tower; 10. Ultrapure oxygen tower; 11. Jet evaporator; 12. Flash evaporator; 13. Oxygen tower evaporator; 14. Ultrapure oxygen tower evaporator; 15. Ultrapure oxygen tower condenser; 16. Cold box; 101. First pipe; 102. Second pipe; 103. Third pipe; 104. Pipeline 4; Pipeline 5; Pipeline 6; Pipeline 7; Pipeline 8; Pipeline 9; Pipeline 100; Pipeline 111; Pipeline 112; Pipeline 12; Pipeline 13; Pipeline 14; Pipeline 15; Pipeline 16; Pipeline 16; Pipeline 17; Pipeline 18; Pipeline 19; Pipeline 120; Pipeline 20; Pipeline 21. Detailed Implementation

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] Purification systems are very versatile technologies, and there are many types, such as TSA or PSA technologies. This patent does not specify any particular type.

[0020] Example 1 A device for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas through low-temperature pressurization and circulation, such as... Figure 1As shown, the system includes an air compressor 1, a purification system 2, and a cold box 16. The cold box includes a main heat exchanger 3, turbine expanders 4 and 5, a distillation column 6, a flash distillation column 7, a pressure reducing valve 8, an oxygen column 9, an ultrapure oxygen column 10, and a jet evaporator 11. Evaporators are installed in the lower parts of the flash distillation column 7, oxygen column 9, and ultrapure oxygen column 10. A condenser 15 is installed in the upper part of the ultrapure oxygen column 10. The air compressor 1 is connected to the purification system 2 via a first pipe 101. The gas outlet of the purification system 2 is connected to the distillation column 6 via a second pipe 102, passing through the main heat exchanger 3. The liquid outlet at the bottom of the distillation column 6 is connected to the flash distillation column 7 via a third pipe 103. The gas outlet at the top of column 6 is connected to the fourth pipe 104, the fifth pipe 105, the seventh pipe 107, and the sixteenth pipe 116. The fourth pipe 104 extends to the outside of the cold box 16 after passing through the main heat exchanger 3. The fifth pipe 105 is connected to the evaporator 13 at the bottom of the oxygen column 9. The liquid outlet of the evaporator 13 in the oxygen column 9 is connected to the sixth pipe 106, which is connected to the top of the distillation column 6. The seventh pipe 107 is connected to the evaporator 12 at the bottom of the flash column 7. The liquid outlet of the evaporator 12 in the flash column 7 is connected to the eighth pipe 108, which is connected to the top of the distillation column 6. The liquid outlet at the bottom of the flash column 7 is connected to the ninth pipe. Pipeline 109, the ninth pipe, is connected to the oxygen tower 9 after passing through the pressure reducing valve 8. The gas outlet at the top of the oxygen tower 9 is connected to the tenth pipe 110. Pipeline 110 is connected to the expansion end 4 of the turbine expander after passing through the main heat exchanger 3. The jet evaporator 11 is installed on the tenth pipe 110. The outlet of the expansion end 4 of the turbine expander is connected to the eleventh pipe 111. Pipeline 111 is connected to the purification system 2 after passing through the main heat exchanger 3. The gas phase outlet of the flash tower 7 is connected to the pressurization end 5 of the turbine expander through the twelfth pipe 112. The outlet of the pressurization end 5 of the turbine expander is connected to the thirteenth pipe 113. Pipeline 113 is connected to the main heat exchanger 3. The gas outlet of the lower part of the oxygen tower 9 is connected to the middle part of the ultrapure oxygen tower 10 through the fourteenth pipe 114; the liquid outlet at the bottom of the oxygen tower 9 is connected to the jet evaporator 11 through the fifteenth pipe 115, and is injected into the tenth pipe 110, passing through the main heat exchanger 3 and then connected to the expansion end 4 of the turbine expander; the sixteenth pipe 116 is connected to the evaporator 14 at the bottom of the ultrapure oxygen tower 10, and after liquefaction, it is sent to the condenser 15 at the top of the ultrapure oxygen tower 10 through the seventeenth pipe 117; the liquid drawn from the evaporator 13 at the bottom of the oxygen tower 9 is sent to the condenser 15 at the top of the ultrapure oxygen tower 10 through the eighteenth pipe 118.The gas outlet of the condenser 15 at the top of the ultrapure oxygen tower 10 is connected to the outlet of the expansion end 4 of the turbine expander via the twentieth pipe 120. The gas at the top of the ultrapure oxygen tower 10 is connected to the nineteenth pipe 119, which is connected to the twentieth pipe 120. This allows the condensed gas at the top of the ultrapure oxygen tower 10 to be reheated by the main heat exchanger 3 via the eleventh pipe 111 before entering the purification system 2. The gas outlet at the bottom of the ultrapure oxygen tower 10 is connected to the twenty-first pipe 121, which extends from the main heat exchanger 3 to the outside of the cold box 16, thus delivering the ultrapure oxygen product.

[0021] The working process of the above device is as follows: The compressed air from air compressor 1 has an exhaust pressure of 0.63 MPaA. After compression and purification, the air contains 20.95% oxygen, 78.118% nitrogen, and 0.993% argon. The remainder consists of trace impurities such as carbon dioxide, hydrocarbons, nitrous oxide, carbon monoxide, hydrogen, and other rare gases. The pressure is 0.615 MPaA, and the temperature is 15°C. This air enters the main heat exchanger 3 and is cooled to near its liquefaction temperature (-172°C) by the reflux gas before entering the distillation column 6. The distillation column 6 operates at a pressure of 0.6 MPaA, has 50 theoretical plates, and uses a structured packed column. Nitrogen gas with a purity >99.99% is obtained at the top of distillation column 6. A portion of this nitrogen gas is reheated to 13°C in the main heat exchanger 3 and then exits the cold box 16. The nitrogen product has a purity >99.99%, and the pressure exiting the cold box 16 is >0.57 MPaA. It can be further compressed for use as needed. The second portion of nitrogen gas enters evaporator 13 within oxygen tower 9 and is liquefied. The third portion enters evaporator 12 within flash tower 7 and is condensed and liquefied. Both the second and third portions of liquefied nitrogen gas maintain a pressure of 0.6 MPaA and a saturated liquid temperature of -176.9℃. After condensation, they are combined and used as reflux to supplement distillation tower 6. The fourth portion enters evaporator 14 within ultrapure oxygen tower 10 and is condensed and liquefied. At the bottom of distillation tower 6, oxygen-enriched liquid air at 0.6 MPaA is obtained, containing 36.2% oxygen and 62.3% nitrogen. This oxygen-enriched liquid air enters flash tower 7 for flash evaporation. The operating pressure of flash tower 7 is 0.39 MPaA, as high as possible to fully utilize the pressure energy of the flash evaporation waste gas. The theoretical number of trays in flash tower 7 is set at 5, using a sieve tray tower to save costs. After flash evaporation, the heavy oxygen components are further enriched at the bottom of flash tower 7. The bottom liquid has an oxygen content of 44.5%, a pressure of 0.392 MPaA, and a saturated liquid temperature of -177.5℃. However, the enrichment of heavy components is not limited to oxygen; other impurities also accumulate here, such as argon content >1.8%, hydrocarbon content >50ppm, carbon dioxide content >0.5ppm, and nitrous oxide content >0.2ppm. The oxygen-enriched liquid at the bottom of flash tower 7 is reduced and throttled to 0.245MPaA via pressure reducing valve 8, and then enters the top of oxygen tower 9 as feed liquid at -183.3℃. The top gaseous flash exhaust gas from flash tower 7 has a nitrogen content as high as 81.5%, an oxygen content of 17.5%, and the remainder being impurities such as argon, and maintains a relatively high pressure of 0.39MPaA. Flash exhaust gas with a saturated gas temperature of -178.4℃ is collected from the condenser 15 at the top of flash tower 7. This flash exhaust gas is first reheated to -174℃ by the main heat exchanger 3 before entering the turboexpander pressurization end and being pressurized to 0.605MPaA, higher than the operating pressure of distillation tower 6. After pressurization, the temperature is -155.3℃. After pressurization, the exhaust gas is cooled to near saturation temperature (-173℃) by the main heat exchanger 3 before entering the lower part of the distillation column 6 for direct recycling of its nitrogen components. The oxygen tower 9 operates at a pressure of 0.245 MPaA and is a structured packed tower with 30 theoretical plates.The top gas phase of oxygen tower 9 is a saturated gas with a main component of 42.4% oxygen, 55.5% nitrogen, and 2% argon, at a pressure of 0.245 MPaA. It enters the main heat exchanger 3 and is partially reheated to -169°C. This gas then enters the expansion end 4 of the turbine expander as expansion waste gas, providing cooling for the entire unit. After expansion, the waste gas pressure is 0.125 MPaA and the temperature is -183.6°C. After being reheated to 13°C by the main heat exchanger 3, it enters the purification system 2 as regeneration gas for the adsorbent. The components of the regeneration waste gas are all from air, with a carbon dioxide content of 500 ppm as the main desorption medium. It is directly discharged into the atmosphere at a safe high point. In the liquid oxygen at the bottom of oxygen tower 9, heavy components such as hydrocarbons are further concentrated. For operational safety, this is promptly extracted and vaporized by the waste gas in the jet evaporator 11, heated to -180°C, and then enters the main heat exchanger 3 to recover its cooling capacity. Pure oxygen is extracted from the middle and lower parts of oxygen tower 9 and enters the middle part of the ultrapure oxygen tower 10 as its feed gas. At this point, the heavy components in the oxygen have been removed, but the light components such as argon, nitrogen, and hydrogen still do not meet the requirements for ultrapure oxygen. The ultrapure oxygen tower 10 operates at a pressure of 0.24 MPaA and is a structured packed tower with 20 theoretical plates. The heat source for the lower evaporator 14 of the ultrapure oxygen tower 10 comes from the pressurized nitrogen at the top of the distillation column 6, which is the aforementioned fourth part, liquefied to a pressure of 0.6 MPaA and a temperature of -176.9℃. This portion of liquid nitrogen, after throttling and depressurization, is sent to the upper condenser 15 of the ultrapure oxygen tower 10 as a cold source. Part of the supplementary cold source for the condenser 15 comes from the liquid nitrogen liquefied in the lower evaporator 13 of the oxygen tower 9. The two streams of liquid nitrogen are combined and controlled at a pressure of 0.15 MPaA and a temperature of -192℃. A small amount of light component waste gas is drawn from the top of the ultrapure oxygen tower 10, with its main components controlled to be 60% oxygen and 40% argon. Light component waste gas is collected in the nitrogen vapor produced by condenser in ultrapure oxygen tower 10 at a pressure of 0.15 MPaA and a temperature of -192℃. This nitrogen vapor is then collected in the expanded waste gas and reheated to 12℃ via main heat exchanger 3, serving as regeneration gas for purification system 2. Ultrapure oxygen with a purity ≥99.9999% and a pressure of 0.24 MPaA is drawn from the lower part of ultrapure oxygen tower 10. This ultrapure oxygen is reheated to 12℃ via main heat exchanger 3 and sent out as product from cold box 16 at a pressure of 0.23 MPaA. It can be bottled or compressed for use as needed. The yield of ultrapure oxygen depends primarily on demand, with an extraction rate of <10%.

[0022] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A device for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas through low-temperature pressurization and circulation, characterized in that: The system includes an air compressor, a purification system, and a cold box. The cold box includes a main heat exchanger, an expander, a distillation column, a flash distillation column, an oxygen tower, an ultrapure oxygen tower, a pressure reducing valve, and a jet evaporator. Evaporators are installed in the lower parts of the flash distillation column, the oxygen tower, and the ultrapure oxygen tower, and a condenser is installed in the upper part of the ultrapure oxygen tower. The air compressor is connected to the purification system via a first pipe. The gas outlet of the purification system is connected to a second pipe, which is connected to the distillation column after passing through the main heat exchanger. The liquid outlet at the bottom of the distillation column is connected to the flash distillation column via a third pipe. The gas outlet at the top of the distillation column is connected to a fourth pipe... Pipes five, seven, and sixteen; pipe four extends to the outside of the cold box after passing through the main heat exchanger; pipe five connects to the evaporator at the bottom of the oxygen tower; the liquid outlet of the evaporator in the oxygen tower is connected to pipe six, which connects to the top of the distillation column; pipe seven connects to the evaporator at the bottom of the flash tower; the liquid outlet of the evaporator in the flash tower is connected to pipe eight, which connects to the top of the distillation column; the liquid outlet at the bottom of the flash tower is connected to pipe nine, which connects to the upper part of the oxygen tower after passing through the pressure reducing valve; the gas outlet at the top of the oxygen tower is connected to pipe ten, which connects to the main heat exchanger... The expander is connected to the expansion end of the expander, and the jet evaporator is located on the tenth pipe; the outlet of the expander's expansion end is connected to the eleventh pipe, which is connected to the purification system after passing through the main heat exchanger; the gas phase outlet of the flash evaporator is connected to the pressurization end of the expander through the twelfth pipe; the outlet of the pressurization end of the expander is connected to the thirteenth pipe, which is connected to the lower part of the distillation column after passing through the main heat exchanger; the gas outlet of the lower part of the oxygen tower is connected to the middle part of the ultrapure oxygen tower through the fourteenth pipe; the liquid outlet at the bottom of the oxygen tower is connected to the jet evaporator through the fifteenth pipe, and the sixteenth pipe... The gas outlet of the evaporator at the bottom of the ultrapure oxygen tower is connected to the 17th pipe, which is connected to the condenser at the top of the ultrapure oxygen tower. The liquid outlet of the evaporator at the bottom of the oxygen tower is connected to the condenser at the top of the ultrapure oxygen tower via the 18th pipe. The gas outlet of the condenser at the top of the ultrapure oxygen tower is connected to the expansion end outlet of the expander via the 20th pipe. The gas outlet at the top of the ultrapure oxygen tower is connected via the 19th and 20th pipes. The gas outlet at the bottom of the ultrapure oxygen tower is connected to the 21st pipe, which extends to the outside of the cold box after passing through the main heat exchanger.

2. The apparatus for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas by low-temperature pressurization and circulation according to claim 1, characterized in that: The distillation column is a sieve tray column or a structured packed column with a theoretical number of 35 to 50 trays or a corresponding actual number of 45 to 65 trays.

3. The apparatus for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas by low-temperature pressurization and circulation according to claim 1, characterized in that: The flash tower is a sieve plate tower with a theoretical number of 2 to 8 trays or a corresponding actual number of 4 to 10 trays.

4. The apparatus for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas by low-temperature pressurization and circulation according to claim 1, characterized in that: The oxygen tower is a sieve tray tower or a structured packed tower with a theoretical number of 20 to 30 trays or a corresponding actual number of 25 to 45 trays.

5. The apparatus for producing high-purity nitrogen and ultrapure oxygen from flash evaporation waste gas by low-temperature pressurization and circulation according to claim 1, characterized in that: The ultrapure oxygen tower is a sieve tray tower or a structured packed tower with a theoretical number of 20-30 trays or a corresponding actual number of 25-45 trays.

6. A method for producing high-purity nitrogen and ultrapure oxygen using the apparatus according to any one of claims 1 to 5, characterized in that: The process is as follows: After compression and purification, the air enters the main heat exchanger and is cooled by the reflux gas before entering the distillation column. Pure nitrogen is obtained at the top of the distillation column. Part of the nitrogen is sent out of the cold box after being reheated by the main heat exchanger as nitrogen product. The second part of the nitrogen enters the oxygen tower evaporator and is liquefied, then enters the distillation column as reflux liquid. The third part of the nitrogen enters the flash evaporator and is condensed and liquefied, then enters the distillation column as reflux liquid. The fourth part of the nitrogen enters the bottom evaporator of the ultrapure oxygen tower and is condensed and liquefied, then enters the top condenser of the ultrapure oxygen tower after being throttled and depressurized. After being evaporated, it is finally added to the twentieth pipeline as regeneration waste gas. The oxygen-rich liquid air at the bottom of the distillation column enters the flash evaporator for flashing. The liquid at the bottom of the flash evaporator has a high oxygen content. After being depressurized and throttled by the pressure reducing valve, it enters the oxygen tower as reflux liquid. The gas phase at the top of the oxygen tower is partially reheated in the main heat exchanger and enters the expansion end of the expander as expansion waste gas, providing cooling for the entire unit. After being reheated by the main heat exchanger, the expanded waste gas enters the purification system as regeneration gas for the adsorbent. The gas phase at the top of the flash evaporator has a high nitrogen content and is pressurized at the booster end of the expander. After being cooled by the main heat exchanger, it enters the lower part of the distillation column for direct recycling of its nitrogen components. The liquid at the bottom of the oxygen tower is vaporized by the waste gas at the top of the oxygen tower through the jet evaporator and enters the main heat exchanger to recover its cooling capacity. Pure oxygen is drawn from the middle of the oxygen tower and fed into the middle of the ultrapure oxygen tower. The heat source for the evaporator of the ultrapure oxygen tower comes from the pressurized nitrogen at the top of the distillation column. After liquefaction, the nitrogen is depressurized and sent to the condenser at the top of the ultrapure oxygen tower as a cold source. Part of the supplementary cold source for the condenser of the ultrapure oxygen tower comes from the liquid nitrogen liquefied in the evaporator at the bottom of the oxygen tower. Ultrapure oxygen is drawn from the lower part of the ultrapure oxygen tower, reheated by the main heat exchanger, and then sent out of the cold box as a product.

7. The method for producing high-purity nitrogen and ultrapure oxygen according to claim 6, characterized in that: The distillation column operates at a pressure of 0.4~1.5 MPa.

8. The method for producing high-purity nitrogen and ultrapure oxygen according to claim 6, characterized in that: The working pressure of the oxygen tower is 0.2~0.8 MPa.

9. The method for producing high-purity nitrogen and ultrapure oxygen according to claim 6, characterized in that: The ultrapure oxygen tower operates at a pressure of 0.2~0.8 MPa.

10. The method for producing high-purity nitrogen and ultrapure oxygen according to claim 6, characterized in that: The working pressure of the flash evaporator is 0.3~1.2 MPa.

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