Liquid pressurizing and cold returning type air separation device

Abstract

Pure liquid nitrogen, liquid air or dirty liquid nitrogen generated by a rectifying tower of the air separation device is subjected to secondary pressurization through a hydraulic pump and then enters a main heat exchanger or a recooling device to recover cold energy, and high-pressure gas formed by heat absorption and gasification enters a high-pressure expansion machine to expand and do work; exhaust gas of the high-pressure expansion machine enters the rectifying tower to provide cold energy required by air separation, and pure nitrogen, waste nitrogen and pure oxygen which are discharged from the rectifying tower and are subjected to cold energy recovery through the main heat exchanger are output. The purposes of energy conservation and consumption reduction of the air separation device are achieved through the processes of primary pressurization of the compressor, secondary pressurization of the hydraulic pump, cold returning, gasification and expansion.

Description

Technical Field

[0001] This invention relates to an air separation unit, and more particularly to an air separation unit that uses a hydraulic pump for pressurization and recooling vaporization, belonging to the field of air separation technology. Background Technology

[0004] With the increasing demand for air separation products from industries such as steel metallurgy, chemicals, and especially coal chemicals, oxygen generators have developed towards large-scale and ultra-large-scale models. Domestic ultra-large oxygen generators have reached the 90,000 m³ / h level. New technologies and processes for oxygen production are constantly emerging, and the oxygen consumption per unit has decreased from over 3 kW·h / m³O₂ to around 0.37 kW·h / m³O₂. The products of oxygen generators are no longer limited to gaseous oxygen; they now produce both gaseous and liquid products, including pure oxygen, pure nitrogen, pure argon, and rare gas extraction. The development of oxygen production technology and oxygen generators has consistently focused on safety, intelligence, energy saving, simplified processes, and reduced investment. A typical process employs the Lachmann principle, where expanded air is blown into the upper column, or nitrogen extracted from the lower column or the top of the condenser-evaporator is used. A portion of this nitrogen is reheated via a switching heat exchanger before being combined and fed into the turbine expander. The expanded nitrogen is then drawn off as product nitrogen, or it is combined with waste nitrogen, reheated in a switching heat exchanger to recover cooling, and then vented. Because nitrogen is drawn from the lower column, the condensation rate in the condenser-evaporator is reduced, thus decreasing the amount of liquid fed into the upper column and utilizing the distillation potential. This nitrogen expansion process has been adopted in large-scale low-pressure air separation units abroad. Both air and nitrogen expansion methods aim to reduce the liquid fraction in the upper column, thereby reducing the temperature difference between the gas and liquid during distillation and utilizing the upper column's distillation potential, making the low-pressure air separation unit more efficient.

[0005] Chinese Patents 201310029678.8 - An air separation unit for isobaric separation of oxygen and nitrogen (Authorization Announcement No.: CN103148676B; Authorization Announcement Date: 2016.03.30), 201310030247.3 - An air separation unit for isobaric separation of oxygen and nitrogen (Authorization Announcement No.: CN103148677B; Authorization Announcement Date: 2015.06.10), and 201310030923.7 - An air separation unit for isobaric separation of oxygen and nitrogen. The paper (Authorization Announcement No.: CN103162512B; Authorization Announcement Date: 2015.06.10) proposes an external circulation liquid pressurized recirculation cooling system based on a new theoretical foundation. This system replenishes the cooling capacity required for gas separation in an air separation unit and compensates for the cooling losses of the air separation unit. This cooling system requires a separate refrigerant storage tank to construct a cooling circulation loop for the refrigerant. The material balance and energy balance organization of the external circulation cooling system are relatively complex, and the rationality of the process flow has not yet been experimentally verified.

[0006] Therefore, it is worthwhile for practitioners in the air separation industry to conduct in-depth research and exploration on how to explore new air separation units that are more practical, easier to implement, and energy-saving and consumption-reducing, based on existing mature air separation process units. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the above-mentioned technologies by proposing a liquid-pressurized and recooled air separation unit. Utilizing the characteristic of liquids approaching incompressibility during pressurization, a hydraulic pump is used for secondary pressurization and recooling. Essentially, this increases the inlet pressure of the expander in the Capiché cycle, thereby improving the expander's cooling capacity and saving most of the gas compression power consumption during the secondary pressurization process entering the expander, thus achieving the goal of energy saving and consumption reduction in the air separation unit.

[0008] The objective of this invention is achieved through the following measures:

[0009] A liquid-pressurized recirculating air separation unit, characterized in that: the air separation unit includes a compressor 3, a purifier 6, a main heat exchanger 8, a distillation column, a hydraulic pump 11, and a high-pressure expander 13.

[0010] Air 1 is compressed by compressor 3 and then enters purifier 6 to remove moisture, carbon dioxide, hydrocarbons, etc. It then passes through main heat exchanger 8 and enters distillation column. The low-temperature pure nitrogen and low-temperature pure oxygen produced in the distillation column are cooled by a cooler before entering main heat exchanger 8 to cool the compressed air from purifier 6. Pure liquid nitrogen, liquid air, or sludge nitrogen produced in the distillation column are pressurized by hydraulic pump 11 and then enter main heat exchanger 8. After absorbing heat and vaporizing in main heat exchanger 8, they enter high-pressure expander 13 to expand and perform work. The exhaust gas from high-pressure expander 13 enters the distillation column to provide the cooling required for distillation. The low-temperature pure nitrogen and low-temperature pure oxygen produced in the distillation column recover the cooling energy through main heat exchanger 8 to form pure nitrogen 22 and pure oxygen 24, which are then output.

[0011] Alternatively, air 1 is compressed by compressor 3 and then enters purifier 6 to remove moisture, carbon dioxide, hydrocarbons, etc. It then enters distillation column via cooler 7 and main heat exchanger 8. The low-temperature pure nitrogen and low-temperature pure oxygen produced in distillation column enter main heat exchanger 8 to cool the compressed air sent from purifier 6. The pure liquid nitrogen, liquid air, or sludge liquid nitrogen produced in distillation column is pressurized by hydraulic pump 11 and enters cooler 7. After absorbing heat and vaporizing in cooler 7, it enters high-pressure expander 13 to expand and do work. The exhaust gas of high-pressure expander 13 enters distillation column to provide the cooling required for distillation. The low-temperature pure nitrogen and low-temperature pure oxygen produced in distillation column recover the cooling capacity through main heat exchanger 8 and are output as pure nitrogen 22, sludge nitrogen 23, and pure oxygen 24.

[0012] The distillation column includes a lower column 10, a condenser-evaporator 14, an upper column 20, and a subcooler.

[0013] Air 1 enters the lower column 10 via compressor 3, purifier 6, and main heat exchanger 8. Liquid air generated in the lower column 10 passes through a cooler and liquid air throttling valve 17 before entering the upper column 20. Nitrogen drawn from the upper part of the lower column 10 is cooled by condenser-evaporator 14 to form liquid nitrogen; part of this liquid nitrogen returns to the lower column 10, while the other part passes through a cooler and pure liquid nitrogen throttling valve 21 before entering the upper column 20. Liquid oxygen generated in the lower part of the upper column 20 is vaporized by condenser-evaporator 14, and the resulting oxygen returns to the upper column 20. Low-temperature pure oxygen drawn from the lower part of tower 20 is cooled by the main heat exchanger 8 to form pure oxygen 24, which is then output. Low-temperature pure nitrogen drawn from the top of upper tower 20 is cooled by the cooler and the main heat exchanger 8 to form pure nitrogen 22, which is then output. Liquid air, sludge nitrogen, or pure liquid nitrogen drawn from the condenser-evaporator 14 of lower tower 10 is pumped by hydraulic pump 11 into the main heat exchanger 8 to absorb heat and vaporize. The resulting gas is then expanded by high-pressure expander 13 and enters lower tower 10 or upper tower 20.

[0014] Alternatively, air 1 enters the lower column 10 via compressor 3, purifier 6, cooler 7, and main heat exchanger 8. The liquid air produced in the lower column 10 passes through the cooler and liquid air throttle valve 17 before entering the upper column 20. Nitrogen drawn from the upper part of the lower column 10 is cooled by condenser-evaporator 14 to form liquid nitrogen; part of this liquid nitrogen returns to the lower column 10, while the other part passes through the cooler and pure liquid nitrogen throttle valve 21 before entering the upper column 20. Liquid oxygen produced in the lower part of the upper column 20 is vaporized by condenser-evaporator 14, and the resulting oxygen returns to the upper column 20. 0. Low-temperature pure oxygen drawn from the lower part of the upper tower 20 is discharged as pure oxygen 24 after the main heat exchanger 8 recovers the cold energy. Low-temperature pure nitrogen drawn from the top of the upper tower 20 is discharged as pure nitrogen 22 after the cooler and the main heat exchanger 8 recover the cold energy. Liquid air, sludge liquid nitrogen or pure liquid nitrogen drawn from the condenser evaporator 14 of the lower tower 10 enters the return cooler 7 through the hydraulic pump 11 to absorb heat and vaporize. The generated gas enters the high-pressure expander 13 for expansion and then enters the lower tower 10 or the upper tower 20.

[0015] The subcooler includes a liquid air subcooler 16 and a liquid nitrogen subcooler 18, as shown in the attached diagram. Figure 1 To be continued Figure 3 The dashed box containing the liquid air subcooler 16 and the liquid nitrogen subcooler 18 is shown. The liquid air subcooler 16 and the liquid nitrogen subcooler 18 can be independent cold exchangers or they can be combined together to form an integrated cold exchanger.

[0016] The waste nitrogen drawn from the lower tower 10 enters the upper tower 20 through the liquid nitrogen subcooler 18 and the waste nitrogen throttling valve 19. The low-temperature waste nitrogen gas drawn from the upper tower 20 recovers its cold energy through the liquid nitrogen subcooler 18 and the main heat exchanger 8, and the resulting waste nitrogen gas 23 is output.

[0017] A liquefaction unit 9 is provided: low-temperature pure nitrogen gas drawn from the upper column 20 is processed by the liquid air subcooler 16, liquefaction unit 9, and main heat exchanger 8 to recover its cooling capacity and form pure nitrogen gas 22; or low-temperature pure oxygen gas drawn from the upper column 20 is processed by the liquefaction unit 9 and main heat exchanger 8 to recover its cooling capacity and form pure oxygen gas 24. Air 1 enters the lower column 10 via compressor 3, purifier 6, main heat exchanger 8, and liquefaction unit 9.

[0018] Alternatively, the low-temperature pure nitrogen gas drawn from the upper column 20 can be converted into pure nitrogen gas 22 after the cold energy is recovered by the liquid air subcooler 16, liquefier 9, and main heat exchanger 8. Or, the low-temperature pure oxygen gas drawn from the upper column 20 can be converted into pure oxygen gas 24 after the cold energy is recovered by the liquefier 9 and main heat exchanger 8. Air 1 enters the lower column 10 through the compressor 3, purifier 6, cooler 7, main heat exchanger 8, and liquefier 9.

[0019] A thermostat 4 is provided: Air 1 enters the purifier 6 via the compressor 3 and thermostat 4. The low-temperature liquid output from the hydraulic pump 11 absorbs heat and vaporizes through the main heat exchanger 8 or the cooler 7, and then enters the high-pressure expander 13 via the thermostat 4.

[0020] A precooler 5 is provided: air 1 enters the purifier 6 via compressor 3 and precooler 5.

[0021] The braking device 12 driven by the high-pressure expander 13 includes a fan, a liquid booster pump, an air compressor, and a generator.

[0022] When the braking device 12 driven by the high-pressure expander 13 is a gas compressor, the low-temperature liquid output from the hydraulic pump 11 absorbs heat and vaporizes through the main heat exchanger 8 or the cooler 7, and then enters the high-pressure expander 13 after being pressurized by the braking device 12.

[0023] An air cooler 25 is provided: the low-temperature liquid output from the hydraulic pump 11 absorbs heat and vaporizes through the main heat exchanger 8 or the return cooler 7, is pressurized and heated by the braking device 12, and is cooled by the air cooler 25 before entering the high-pressure expander 13.

[0024] A filter 2 is provided: air 1 passes through filter 2 to remove solid dust and other contaminants before entering compressor 3.

[0025] The "high pressure" in the high-pressure expander 13 is relative to the fully low-pressure expander in the Kapitza cycle.

[0026] The recooler 7 adopts a partitioned heat exchange method.

[0027] The precooler 5 is used to reduce the air temperature entering the purifier 6.

[0028] The subcooler is used to subcool the liquid entering the upper column 20, thereby reducing vaporization losses.

[0029] In practical applications, the liquid air subcooler 16, liquid nitrogen subcooler 18, and liquefaction unit 9 can be integrated into a single design. A multi-flow plate-fin heat exchanger can be used to integrate the liquid nitrogen and liquid air channels into one device, forming an integrated composite heat exchanger.

[0030] When using a pressurized turbine expander for refrigeration and molecular sieve adsorption for purification, the cooling capacity regulation function of the liquefier 9 can be shared by the main heat exchanger 8 and the subcooler.

[0031] The purifier 6 is used to remove moisture, carbon dioxide, hydrocarbons such as acetylene, etc. from compressed air.

[0032] The purifier 6 includes a molecular sieve purifier, an alumina purifier, a silica gel purifier, an activated carbon purifier, a catalytic converter, a stone regenerator, etc., which, individually or in combination, remove components in compressed air that are harmful to gas separation.

[0033] The main function of the precooler 5 is to reduce the temperature of compressed air from 80℃~120℃ to 8℃~15℃ to meet the purification temperature requirements of the purifier 6, and further recover the cooling capacity of the return gas. The main types include: nitrogen-water precooler (which uses the return waste nitrogen to exchange heat with the compressed air to reduce the air temperature), water cooling tower (which uses the cooling capacity of the return waste nitrogen to cool the cooling water to form a closed-loop circulating water system), shell and tube precooler (cooling water flows inside the tube and air flows outside the tube, and heat exchange occurs through the tube wall), Freon / ammonia refrigeration precooler, etc., which play a role in cooling, removing water and impurities, saving energy and reducing consumption, and protection (preventing high temperature air from directly entering the molecular sieve, avoiding damage to the molecular sieve performance, and stabilizing the operating conditions of the subsequent distillation column, etc.).

[0034] The main function of the thermostat 4 is to regulate the inlet air temperature of the high-pressure expander 13 and ensure that the outlet air of the high-pressure expander 13 is within a safe humidity range.

[0035] An air cooler 25 is installed between the booster-type high-pressure expander 13 and the braking device 12 to regulate the inlet air temperature and outlet air humidity of the high-pressure expander 13 and enhance the cooling capacity of the expanded gas.

[0036] To prevent cavitation when the hydraulic pump 11 draws in liquid at saturation temperature, the liquid drawn in by the hydraulic pump 11 can be subcooled using low-temperature pure nitrogen or low-temperature pure oxygen drawn from the upper tower 20.

[0037] The air separation unit of the present invention adopts the startup method of the existing all-low-pressure air separation unit, or injects liquid air or liquid nitrogen into the lower column of the rectification column, and injects liquid air or liquid nitrogen into the condensing evaporator 14 of the rectification column. First, start the compressor to convey compressed air into the purifier, the main heat exchanger, and the rectification column, and then start the hydraulic pump to output liquid air or liquid nitrogen, which enters the main heat exchanger 8 or the regenerative heat exchanger 7 to absorb heat and gasify, and then enters the high-pressure expander 13 to expand and refrigerate, entering the cooling and liquid accumulation stage, so as to achieve the purpose of rapid startup.

[0038] For parts not described in detail in this disclosure, reference can be made to books such as "Principles and Calculations of All-Low-Pressure Oxygen Generators" (First Edition, First Printing, December 1976, Mechanical Industry Press, Unified Book Number: 15033·4305), "Oxygen Generation Technology" (Second Edition, 9th Printing, August 2009, Metallurgical Industry Press, Unified Book Number: ISBN978-7-5024-4963-6), "Cryogenic Handbook" (Volume I, First Edition, First Printing, September 1973, Fuel Chemical Industry Press, Unified Book Number: 15063·Internal 566 (Chemistry-71)), "Cryogenic Handbook" (Volume II, First Edition, First Printing, July 1979, Chemical Industry Press, Unified Book Number: 15063·3014), "Synthetic Ammonia Engineering" (First Volume, Second Edition, First Printing, July 1978, Petroleum Chemical Industry Press, Unified Book Number: 15063·Chemistry 330), etc.

[0039] For equipment not described in the present invention, such as the standby system, pipelines, instruments, valves, insulation, bypass with adjustment function, automatic control equipment, etc., well-known and mature technologies are used for matching.

[0040] The present invention has the following advantages compared with the prior art:

[0041] 1. The present invention retains the advantages of the Kapitza cycle operating at all-low pressure. By using a hydraulic pump to re-pressurize the liquid air, pure liquid nitrogen or dirty liquid nitrogen drawn from the rectification column, and utilizing the characteristic that the liquid is nearly an incompressible fluid when the pressure is increased, compared with the gas compression pressurization method, a large amount of pressurization power consumption can be saved, that is, a large amount of power consumption required for pressurizing the part of the gas entering the high-pressure expander is saved. Then, its cold energy is used to cool the compressed air, and the gas generated by the liquid air absorbing heat and gasifying enters the high-pressure expander to expand and refrigerate again, which is equivalent to retaining the advantages of the Claude cycle and the Heyland cycle, where the inlet pressure of the expander is high and the refrigeration capacity of expansion is large, thus forming a brand-new liquid pressurization and regenerative cooling type air separation process including the advantages of the Kapitza cycle, the Claude cycle and the Heyland cycle. Moreover, the liquid fraction entering the upper column is reduced, and the temperature difference between gas and liquid during rectification in the upper column is reduced, making the process setting of the entire device more reasonable. Compared with the existing air separation process, it is expected to save 5% to 12% of energy. This disclosure can be regarded as an air separation technology of milestone significance after the advent of the "Kapitza cycle" and all-low-pressure oxygen generators;

[0042] 2. Compared with the external circulation cooling system provided by existing Chinese patents such as 201310029678.8 - an air separation device for isobaric separation to produce oxygen and nitrogen, 201310030247.3 - an air separation device for isobaric separation to produce oxygen and nitrogen, and 201310030923.7 - an air separation device for isobaric separation to produce oxygen and nitrogen, the present invention adopts an internal circulation liquid pressurization and recooling type air separation process, which makes material balance and energy balance organization easier. Based on the existing successfully operating full low-pressure air separation process, a hydraulic pump, a recooler and a high-pressure section expander are added to form a new type of high and low pressure composite air separation device;

[0043] 3. This invention can be used to build new air separation units or to modify existing air separation units with expanders. That is, by adding hydraulic pumps, coolers, and high-pressure expanders to the existing expanders, the process can be updated and modified. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the process flow of a liquid pressurized and recooled air separation unit according to the present invention (pure liquid nitrogen pressurization).

[0045] Figure 1 In the middle, 1-Air, 2-Filter, 3-Compressor, 4-Thermostat, 5-Precooler, 6-Purifier, 7-Recooler, 8-Main Heat Exchanger, 9-Liquefier, 10-Lower Tower, 11-Hydraulic Pump, 12-Braking Equipment, 13-High Pressure Expander, 14-Condenser Evaporator, 15-Non-condensable Gas, 16-Liquid Air Subcooler, 17-Liquid Air Throttling Valve, 18-Liquid Nitrogen Subcooler, 19-Sludge Liquid Nitrogen Throttling Valve, 20-Upper Tower, 21-Pure Liquid Nitrogen Throttling Valve, 22-Pure Nitrogen, 23-Sludge Nitrogen, 24-Pure Oxygen, 25-Air Cooler.

[0046] Figure 2 This is a schematic diagram of the process flow of a liquid-pressurized recooling type air separation unit (liquid-air pressurization) according to the present invention.

[0047] Figure 2 In the middle, 1-Air, 2-Filter, 3-Compressor, 4-Thermostat, 5-Precooler, 6-Purifier, 7-Recooler, 8-Main Heat Exchanger, 9-Liquefier, 10-Lower Tower, 11-Hydraulic Pump, 12-Braking Equipment, 13-High Pressure Expander, 14-Condenser Evaporator, 15-Non-condensable Gas, 16-Liquid Air Subcooler, 17-Liquid Air Throttling Valve, 18-Liquid Nitrogen Subcooler, 19-Sludge Liquid Nitrogen Throttling Valve, 20-Upper Tower, 21-Pure Liquid Nitrogen Throttling Valve, 22-Pure Nitrogen, 23-Sludge Nitrogen, 24-Pure Oxygen, 25-Air Cooler.

[0048] Figure 3This is a schematic diagram of the process flow of a liquid pressurization and recooling type air separation unit (sewage liquid nitrogen pressurization) according to the present invention.

[0049] Figure 3 In the middle, 1-Air, 2-Filter, 3-Compressor, 4-Thermostat, 5-Precooler, 6-Purifier, 7-Recooler, 8-Main Heat Exchanger, 9-Liquefier, 10-Lower Tower, 11-Hydraulic Pump, 12-Braking Equipment, 13-High Pressure Expander, 14-Condenser Evaporator, 15-Non-condensable Gas, 16-Liquid Air Subcooler, 17-Liquid Air Throttling Valve, 18-Liquid Nitrogen Subcooler, 19-Sludge Liquid Nitrogen Throttling Valve, 20-Upper Tower, 21-Pure Liquid Nitrogen Throttling Valve, 22-Pure Nitrogen, 23-Sludge Nitrogen, 24-Pure Oxygen, 25-Air Cooler. Detailed Implementation

[0050] The present disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] Example 1:

[0052] As attached Figure 1 As shown, a liquid-pressurized recirculating air separation unit includes a compressor 3, a purifier 6, a main heat exchanger 8, a distillation column, a hydraulic pump 11, and a high-pressure expander 13.

[0053] The distillation column includes a lower column 10, a condenser-evaporator 14, an upper column 20, and a subcooler.

[0054] Air 1 enters the lower column 10 via filter 2, compressor 3, thermostat 4, precooler 5, purifier 6, and main heat exchanger 8. Liquid air generated in the lower column 10 passes through a cooler and liquid air throttling valve 17 before entering the upper column 20. Nitrogen gas drawn from the upper part of the lower column 10 is cooled by a condenser-evaporator 14 to form liquid nitrogen; part of this liquid nitrogen returns to the lower column 10, while the other part passes through a cooler and pure liquid nitrogen throttling valve 21 before entering the upper column 20. Liquid oxygen generated in the lower part of the upper column 20 is vaporized by condenser-evaporator 14 after absorbing heat. The generated oxygen returns to the upper column 20. The low-temperature pure oxygen drawn from the lower part of the upper column 20 recovers its cooling capacity through the main heat exchanger 8, forming pure oxygen 24 which is output. The low-temperature pure nitrogen drawn from the top of the upper column 20 recovers its cooling capacity through the cooler and the main heat exchanger 8, forming pure nitrogen 22 which is output. The pure liquid nitrogen drawn from the condenser-evaporator 14 is pressurized by the hydraulic pump 11 and then enters the main heat exchanger 8 to absorb heat and vaporize. The resulting gas then enters the high-pressure expander 13 for expansion and then enters the lower column 10 or the upper column 20.

[0055] Alternatively, air 1 passes through filter 2, compressor 3, thermostat 4, precooler 5, purifier 6, recooler 7, and main heat exchanger 8 before entering lower tower 10. The liquid air generated in lower tower 10 passes through a cooler and liquid air throttling valve 17 before entering upper tower 20. Nitrogen gas drawn from the upper part of lower tower 10 is cooled by condenser-evaporator 14 to form liquid nitrogen; part of this returns to lower tower 10, and the other part passes through a cooler and pure liquid nitrogen throttling valve 21 before entering upper tower 20. Liquid oxygen generated in the lower part of upper tower 20 passes through condenser-evaporator 1... 4. The oxygen produced by heat absorption and vaporization returns to the upper tower 20. The low-temperature pure oxygen drawn from the lower part of the upper tower 20 recovers its cold energy through the main heat exchanger 8 and forms pure oxygen 24 for output. The low-temperature pure nitrogen drawn from the top of the upper tower 20 recovers its cold energy through the cooler and the main heat exchanger 8 and forms pure nitrogen 22 for output. The pure liquid nitrogen drawn from the condenser evaporator 14 enters the return cooler 7 through the hydraulic pump 11 to absorb heat and vaporize. The gas produced enters the high-pressure expander 13 for expansion and then enters the lower tower 10 or the upper tower 20.

[0056] The subcooler includes a liquid air subcooler 16 and a liquid nitrogen subcooler 18. The liquid air subcooler 16 and the liquid nitrogen subcooler 18 can be independent cold exchangers or they can be combined together to form an integrated cold exchanger.

[0057] The waste nitrogen drawn from the lower tower 10 enters the upper tower 20 through the liquid nitrogen subcooler 18 and the waste nitrogen throttling valve 19. The low-temperature waste nitrogen gas drawn from the upper tower 20 recovers its cold energy through the liquid nitrogen subcooler 18 and the main heat exchanger 8, and the resulting waste nitrogen gas 23 is output.

[0058] A liquefier 9 is provided: low-temperature pure nitrogen gas drawn from the upper column 20 is cooled by a liquid-air subcooler 16, liquefier 9, and main heat exchanger 8 to form pure nitrogen gas 22; or low-temperature pure oxygen gas drawn from the upper column 20 is cooled by a liquefier 9 and main heat exchanger 8 to form pure oxygen gas 24. Air 1 enters the lower column 10 via compressor 3, purifier 6, main heat exchanger 8, and liquefier 9.

[0059] Alternatively, the low-temperature pure nitrogen gas drawn from the upper column 20 can be recycled through the liquid-air subcooler 16, liquefier 9, and main heat exchanger 8 to form pure nitrogen gas 22, or the low-temperature pure oxygen gas drawn from the upper column 20 can be recycled through the liquefier 9 and main heat exchanger 8 to form pure oxygen gas 24. Air 1 enters the lower column 10 through the filter 2, compressor 3, thermostat 4, precooler 5, purifier 6, cooler 7, main heat exchanger 8, and liquefier 9.

[0060] The braking device 12 driven by the high-pressure expander 13 includes a fan, a liquid booster pump, an air compressor, and a generator.

[0061] When the braking device 12 driven by the high-pressure expander 13 is a gas compressor, the low-temperature liquid output from the hydraulic pump 11 absorbs heat and vaporizes through the main heat exchanger 8 or the cooler 7, and is pressurized by the braking device 12 before entering the high-pressure expander 13.

[0062] An air cooler 25 is provided: the low-temperature liquid output from the hydraulic pump 11 absorbs heat and vaporizes through the main heat exchanger 8 or the return cooler 7, is pressurized and heated by the braking device 12, and is cooled by the air cooler 25 before entering the high-pressure expander 13.

[0063] The "high pressure" in the high-pressure expander 13 is relative to the fully low-pressure expander in the Kapitza cycle.

[0064] The recooler 7 adopts a partitioned heat exchange method.

[0065] The precooler 5 is used to reduce the air temperature entering the purifier 6.

[0066] The subcooler is used to subcool the liquid entering the upper column 20, thereby reducing vaporization losses.

[0067] In practical applications, the liquid air subcooler 16, liquid nitrogen subcooler 18, and liquefaction unit 9 can be integrated into a single design. A multi-flow plate-fin heat exchanger can be used to integrate the liquid nitrogen and liquid air channels into one device, forming an integrated composite heat exchanger.

[0068] When using a pressurized turbine expander for refrigeration and molecular sieve adsorption for purification, the cooling capacity regulation function of the liquefier 9 can be shared by the main heat exchanger 8 and the subcooler.

[0069] The purifier 6 is used to remove moisture, carbon dioxide, hydrocarbons, etc. from compressed air.

[0070] The purifier 6 uses a molecular sieve purifier to remove components in compressed air that are harmful to gas separation.

[0071] The main function of the precooler 5 is to reduce the temperature of compressed air from 80℃~120℃ to 8℃~15℃ to meet the purification temperature requirements of the purifier 6, and further recover the cooling capacity of the return gas. The main types include: nitrogen-water precooler (which uses the return waste nitrogen to exchange heat with the compressed air to reduce the air temperature), water cooling tower (which uses the cooling capacity of the return waste nitrogen to cool the cooling water to form a closed-loop circulating water system), shell and tube precooler (cooling water flows inside the tube and air flows outside the tube, and heat exchange occurs through the tube wall), Freon / ammonia refrigeration precooler, etc., which play a role in cooling, removing water and impurities, saving energy and reducing consumption, and protection (preventing high temperature air from directly entering the molecular sieve, avoiding damage to the molecular sieve performance, and stabilizing the operating conditions of the subsequent distillation column, etc.).

[0072] The main function of the thermostat 4 is to regulate the inlet air temperature of the high-pressure expander 13 and ensure that the outlet air of the high-pressure expander 13 is within a safe humidity range.

[0073] An air cooler 25 is installed between the booster-type high-pressure expander 13 and the braking device 12 to regulate the inlet air temperature and outlet air humidity of the high-pressure expander 13 and enhance the cooling capacity of the expanded gas.

[0074] Non-condensable gas 15, such as argon, in the condenser-evaporator 14 can be discharged periodically.

[0075] The air separation unit of the present invention adopts the start-up method of the existing low-pressure air separation unit, or injects liquid air or liquid nitrogen into the lower column of the distillation column, or injects liquid air or liquid nitrogen into the condenser-evaporator of the distillation column. First, the compressor is started to deliver compressed air into the purifier, the main heat exchanger, and the distillation column. Then, the hydraulic pump is started to output liquid air or liquid nitrogen, which enters the main heat exchanger 8 or the cooler 7 to absorb heat and vaporize. Then, it enters the high-pressure expander 13 for expansion and refrigeration, and enters the cooling and liquid accumulation stage.

[0076] Equipment not described in this invention, such as backup systems, pipelines, instruments, valves, insulation, bypasses with regulating functions, and automatic control equipment, shall be equipped with known and mature technologies.

[0077] Example 2:

[0078] As attached Figure 2 As shown, the liquid air drawn from the lower tower 10 is pressurized by the hydraulic pump 11, and then enters the high-pressure expander 13 through the main heat exchanger 8 or the cooler 7 and the temperature controller 4. The rest is the same as in Example 1.

[0079] Example 3:

[0080] As attached Figure 3 As shown, the nitrogen from the waste liquid drawn from the middle of the lower tower 10 is pressurized by the hydraulic pump 11, and then enters the high-pressure expander 13 through the main heat exchanger 8 or the cooler 7 and the temperature controller 4. The rest is the same as in Example 1.

[0081] Equipment not described in this invention, such as backup systems, pipelines, instruments, valves, insulation, and bypasses with regulating functions, shall be equipped with well-known and mature technologies.

[0082] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of this disclosure, and these changes also fall within the protection scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims of this application.

Claims

1. A liquid-pressurized and recooled air separation unit, characterized in that: The air separation unit includes a compressor, a purifier, a main heat exchanger, a distillation column, a hydraulic pump, and a high-pressure expander. Air is compressed by a compressor and then enters a purifier, followed by a main heat exchanger before entering a distillation column. The low-temperature pure nitrogen and oxygen produced in the distillation column enter the main heat exchanger to cool the compressed air from the purifier. Pure liquid nitrogen, liquid air, or sludge nitrogen produced in the distillation column is pressurized by a hydraulic pump and then enters the main heat exchanger. After absorbing heat and vaporizing in the main heat exchanger, it enters a high-pressure expander to expand and perform work. The exhaust gas from the high-pressure expander enters the distillation column, where pure nitrogen and pure oxygen are output after absorbing heat and heating up in the main heat exchanger. Alternatively, air is compressed by a compressor and enters a purifier, then passes through a cooler and a main heat exchanger before entering a distillation column. The low-temperature pure nitrogen and low-temperature pure oxygen produced in the distillation column enter the main heat exchanger to cool the compressed air sent from the purifier. The pure liquid nitrogen, liquid air, or sludge produced in the distillation column is pressurized by a hydraulic pump and enters a cooler. After absorbing heat and vaporizing in the cooler, it enters a high-pressure expander to expand and do work. The exhaust gas from the high-pressure expander enters the distillation column, and the pure nitrogen and pure oxygen that are heated by absorbing heat in the main heat exchanger are output.

2. The air separation unit according to claim 1, characterized in that: The distillation column includes a lower column, a condenser-evaporator, an upper column, and a subcooler. Air enters the lower column after passing through the compressor, purifier, and main heat exchanger. Liquid air generated in the lower column passes through a cooler and a liquid air throttling valve into the upper column. Nitrogen gas drawn from the upper part of the lower column is cooled by a condenser-evaporator to form liquid nitrogen; part of this liquid nitrogen returns to the lower column, while the other part passes through a cooler and a pure liquid nitrogen throttling valve into the upper column. Liquid oxygen generated in the lower part of the upper column is vaporized by a condenser-evaporator, and the resulting oxygen returns to the upper column. Low-temperature pure oxygen drawn from the lower part of the upper column is discharged after its cooling capacity is recovered by the main heat exchanger. Low-temperature pure nitrogen gas drawn from the top of the upper column is discharged after its cooling capacity is recovered by a cooler and the main heat exchanger. Liquid air, sludge-liquid nitrogen, or pure liquid nitrogen drawn from the lower column are pressurized by a hydraulic pump and then vaporized by the main heat exchanger. The resulting gas is then expanded by a high-pressure expander and enters either the lower or upper column. Alternatively, air enters the lower tower via a compressor, purifier, cooler, and main heat exchanger. Liquid air generated in the lower tower passes through a cooler and a liquid air throttle valve into the upper tower. Nitrogen drawn from the upper part of the lower tower is cooled by a condenser-evaporator to form liquid nitrogen. Part of the liquid nitrogen returns to the lower tower, while the other part passes through a cooler and a pure liquid nitrogen throttle valve into the upper tower. Liquid oxygen generated in the lower part of the upper tower absorbs heat and vaporizes in the condenser-evaporator, and the resulting oxygen returns to the upper tower. Low-temperature pure oxygen drawn from the lower part of the upper tower recovers its cooling capacity in the main heat exchanger before being output. Low-temperature pure nitrogen drawn from the top of the upper tower recovers its cooling capacity in the cooler and main heat exchanger before being output. Liquid air, sludge liquid nitrogen, or pure liquid nitrogen drawn from the lower tower is pressurized by a hydraulic pump and enters the cooler to absorb heat and vaporize. The resulting gas is expanded in a high-pressure expander and then enters the lower or upper tower.

3. The air separation unit according to claim 2, characterized in that: The subcooler includes a liquid air subcooler and a liquid nitrogen subcooler. The liquid air subcooler and the liquid nitrogen subcooler are independent cold exchangers, or they can be combined together to form an integrated cold exchanger.

4. The air separation unit according to claim 2, characterized in that: The waste nitrogen drawn from the lower tower enters the upper tower through the liquid nitrogen subcooler and the waste nitrogen throttling valve. The low-temperature waste nitrogen gas drawn from the upper tower is discharged after recovering its cooling capacity through the liquid nitrogen subcooler and the main heat exchanger.

5. The air separation unit according to claim 2, characterized in that: A liquefaction unit is provided: the low-temperature pure nitrogen gas drawn from the upper column is discharged after recovering its cooling capacity via a liquid air subcooler, liquefaction unit, and main heat exchanger; or the low-temperature pure oxygen gas drawn from the upper column is discharged after recovering its cooling capacity via a liquefaction unit and main heat exchanger. Air enters the lower column via a compressor, purifier, main heat exchanger, and liquefaction unit, or air enters the lower column via a compressor, purifier, cooler, main heat exchanger, and liquefaction unit.

6. The air separation unit according to claim 1, characterized in that: It is equipped with a temperature controller: air enters the purifier through the compressor and temperature controller, and the low-temperature liquid output from the hydraulic pump absorbs heat and vaporizes through the main heat exchanger or cooler, and then enters the high-pressure expander through the temperature controller.

7. The air separation unit according to claim 1, characterized in that: It is equipped with a precooler: air enters the purifier after passing through the compressor and precooler.

8. The air separation unit according to claim 1, characterized in that: When the braking device driven by the high-pressure expander is a gas compressor, the low-temperature liquid output from the hydraulic pump absorbs heat and vaporizes through the main heat exchanger or cooler, and after being pressurized by the braking device, it enters the high-pressure expander.

9. The air separation unit according to claim 8, characterized in that: An air cooler is provided: the low-temperature liquid output from the hydraulic pump absorbs heat and vaporizes through the main heat exchanger or return cooler, and then enters the high-pressure expander after being pressurized by the braking equipment and cooled by the air cooler.

10. The air separation unit according to claim 2, characterized in that: The air separation unit adopts the start-up method of the existing low-pressure air separation unit, or injects liquid air or liquid nitrogen into the lower column of the distillation column, or injects liquid air or liquid nitrogen into the condenser-evaporator of the distillation column. First, the compressor is started to deliver compressed air into the purifier, main heat exchanger, and distillation column. Then, the hydraulic pump is started to output liquid air or liquid nitrogen, which enters the main heat exchanger or cooler to absorb heat and vaporize. Then, it enters the high-pressure expander for expansion and refrigeration, and enters the cooling and liquid accumulation stage.

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