Air separation device using mixed refrigerant for cooling

Abstract

The utility model relates to an air separation device utilizing mixed refrigerants for cooling. The device comprises a first compressor, a second compressor, a three-stage compressor, a water cooling tower, a high-pressure rectifying tower, a low-pressure rectifying tower, a first dehydrating tower, a second dehydrating tower, a main heat exchanger, a subcooler, a second heat exchanger, a built-in heat exchanger at the bottom of the low-pressure rectifying tower, a refrigerant buffer tank, a first gas-liquid separator and a second gas-liquid separator. Compared with an existing air separation process and device, the energy consumption can be greatly reduced, the total energy consumption can be reduced by about 20% or above, and the method has the advantages of being efficient and saving energy.

Description

Technical Field

[0001] The utility model relates to an air separation device which utilizes mixed refrigerant to supply cooling. Background Art

[0002] The main components of air are nitrogen and oxygen, and there are also some gases such as CO2 and Ar, which exist in the air in a molecular state. The low-temperature method is used to liquefy, separate and purify the air. The components in the air mixture are separated by utilizing the different evaporation temperatures of each component, thereby obtaining high-purity nitrogen, high-purity oxygen, liquid nitrogen, liquid oxygen or some rare gas products.

[0003] Large and medium-sized all-liquid air separation units generally adopt a high-low temperature double expansion refrigeration process, which has many moving equipment and complex processes. Utility Model Content

[0004] In view of the problems existing in the above-mentioned prior art, the utility model provides a new all-liquid air separation process and device using a mixed refrigerant to provide cooling capacity, which has a simple process and greatly reduces energy consumption.

[0005] According to the first aspect of the utility model, there is provided an air separation device using a mixed refrigerant for refrigeration, comprising a first compressor, a second compressor, a three-stage compressor, a water cooling tower, a high-pressure distillation tower, a low-pressure distillation tower, a first dehydration tower, a second dehydration tower, a main heat exchanger, a subcooler, a second heat exchanger, a built-in heat exchanger at the bottom of the low-pressure distillation tower, a refrigerant buffer tank, a first gas-liquid separator, and a second gas-liquid separator;

[0006] The air intake pipe is connected to the inlet of the first compressor, the outlet pipe of the first compressor is connected to the lower inlet of the water cooling tower, the circulating water pipe is divided into two branches, the first branch of the circulating water pipe is connected to the lower tower inlet of the water cooling tower (i.e., the lower tower inlet), the second branch of the circulating water pipe is connected to the first heat exchange channel of the second heat exchanger (for heat exchange with the dirty nitrogen drawn from the main heat exchanger), and the outlet pipe of the first heat exchange channel of the second heat exchanger is connected to the upper tower inlet of the water cooling tower (i.e., the upper tower inlet);

[0007] The outlet pipeline at the top of the water cooling tower is switchably connected to the gas inlet of the first dehydration tower and the second dehydration tower through a valve. The first dehydration tower and the second dehydration tower are intermittently operated adsorption towers. When one tower is adsorbing impurities in the air, the other tower is back-blown and regenerated by low-temperature polluted nitrogen from the distillation system.

[0008] The outlet pipelines of the first dehydration tower and the second dehydration tower (equipped with corresponding valves) merge into a purified air pipeline, and the purified air pipeline branches into a first purified air branch and a second purified air branch. The first purified air branch is connected to the first heat exchange channel of the main heat exchanger, and the outlet pipeline of the first heat exchange channel, i.e., the low-temperature and low-pressure air pipeline, is connected to the feed inlet of the low-pressure distillation tower (the feed inlet of the low-pressure distillation tower T2 is located in the middle and upper part of the low-pressure distillation tower, for example, the position of the 25th to 32nd tower plates), and a second compressor is arranged on the second purified air branch. The second purified air branch is connected to the second heat exchange channel of the main heat exchanger, and the outlet pipeline of the second heat exchange channel, i.e., the low-temperature and high-pressure air pipeline, is connected to the lower inlet of the high-pressure distillation tower;

[0009] The bottom outlet of the high-pressure distillation tower is connected to the first heat exchange channel of the subcooler through an oxygen-rich liquid air pipeline, the outlet pipeline of the first heat exchange channel of the superheater is connected to an inlet of the low-pressure distillation tower after passing through a first throttle valve (the inlet of the low-pressure distillation tower is located at the upper part of the low-pressure distillation tower, for example, the 10th to 20th tower plate position), the upper outlet of the high-pressure distillation tower is connected to the inlet of the internal heat exchanger located at the bottom of the low-pressure distillation tower through a high-purity nitrogen pipeline, the outlet pipeline of the internal heat exchanger at the bottom of the low-pressure distillation tower is divided into a first liquid nitrogen branch after being led out from the low-pressure distillation tower and returns to the top of the high-pressure distillation tower, the second liquid nitrogen branch is connected to the second heat exchange channel of the subcooler, the outlet pipeline of the second heat exchange channel of the subcooler is divided into two routes, the first subcooled liquid nitrogen pipeline is connected to another inlet (top inlet) of the low-pressure distillation tower after passing through a second throttle valve, and the second subcooled liquid nitrogen pipeline is connected to a liquid nitrogen storage tank;

[0010] The low-pressure distillation tower leads out the first high-purity nitrogen pipeline, the dirty nitrogen pipeline, the liquid argon pipeline, the high-purity oxygen pipeline, and the liquid oxygen pipeline from different tray positions (for example, the top, the upper part, the middle upper part, the middle part, and the bottom in sequence); there are differences in the boiling points of components such as O2, N2, Ar, and CO2. When the mixed liquid composed of substances with different boiling points absorbs heat and partially evaporates, the low-boiling point component will evaporate more, and when the mixed steam releases heat and partially condenses, the high-boiling point component will condense more. The separation effect is achieved by continuous evaporation and condensation on the multi-layer trays. In the present application, the nitrogen purity of the high-purity nitrogen is usually >99.99%, the argon content in the liquid argon is usually >99.999%, the oxygen content in the liquid oxygen is usually >99.99%, the nitrogen content in the dirty nitrogen is usually 84~88%, and the oxygen content in the high-purity oxygen is usually >99.95%, by volume.

[0011] Furthermore, the top is the 1st to 3rd tower plates, preferably the 1st tower plate, the upper part is the 12th to 17th tower plates, the upper middle part is the 28th to 36th tower plates, the middle part is the 40th to 50th tower plates, the bottom is the 80th to 85th tower plates, preferably the 82nd tower plate, and the total number of tower plates is 80 to 85, preferably 82.

[0012] Furthermore, the first high-purity nitrogen pipeline is connected to the third heat exchange channel of the subcooler, the outlet pipeline of the third heat exchange channel of the subcooler is connected to the third heat exchange channel of the main heat exchanger, and the outlet pipeline of the third heat exchange channel of the main heat exchanger, that is, the second high-purity nitrogen pipeline, is connected to the high-purity nitrogen storage tank or the high-purity nitrogen user; the liquid argon pipeline is connected to the liquid argon storage tank or the liquid argon user; the liquid oxygen pipeline is sent to the liquid oxygen storage tank or the liquid oxygen user; the dirty nitrogen pipeline is connected to the fourth heat exchange channel of the subcooler, and the outlet pipeline of the fourth heat exchange channel of the subcooler is connected to the fourth heat exchange channel of the main heat exchanger, and the fourth heat exchange channel of the main heat exchanger is connected to the fourth heat exchange channel of the main heat exchanger. The outlet pipeline is divided into two routes. The first dirty nitrogen branch can be switched to connect the regeneration gas inlet of the first dehydration tower and the second dehydration tower (the regeneration gas outlet pipelines of the first dehydration tower and the second dehydration tower are connected to the plant vent main pipe for direct venting), the second dirty nitrogen branch is connected to the second heat exchange channel of the second heat exchanger (the outlet pipeline of the second heat exchange channel of the second heat exchanger is connected to the plant vent main pipe for direct venting), the high-purity oxygen pipeline is connected to the eighth heat exchange channel of the main heat exchanger, and the outlet of the eighth heat exchange channel of the main heat exchanger, i.e. the high-purity oxygen pipeline, is connected to the oxygen storage tank or oxygen user.

[0013] Furthermore, the refrigerant outlet pipeline of the refrigerant buffer tank is connected to the inlet of the three-stage compressor, the gas-liquid mixed refrigerant pipeline is drawn out from the second stage of the compressor (the second stage is compressed to a pressure of 0.5~1.8MPa) and connected to the inlet of the first gas-liquid separator, the gas phase outlet pipeline of the first gas-liquid separator is connected to the third-stage inlet of the three-stage compressor, the third-stage outlet of the three-stage compressor is connected to the inlet of the second gas-liquid separator through the gas-liquid mixed flow pipeline, the gas phase outlet pipeline of the second gas-liquid separator is connected to the fifth heat exchange channel of the main heat exchanger, and the fifth heat exchange channel of the main heat exchanger is connected to the sixth heat exchange channel of the main heat exchanger through the first refrigerant flow pipeline and the third throttle valve. The outlet of the sixth heat exchange channel of the main heat exchanger leads to a first mixed refrigerant logistics pipeline, the first liquid phase pipeline led from the bottom of the first gas-liquid separator and the second liquid phase pipeline led from the bottom of the second gas-liquid separator merge into a mixed refrigerant main pipe and then connect to the seventh heat exchange channel of the main heat exchanger, the second refrigerant logistics pipeline leads to the outlet of the seventh heat exchange channel of the main heat exchanger, the second refrigerant logistics pipeline is connected to the eighth heat exchange channel of the main heat exchanger after passing through the fourth throttle valve, the second mixed refrigerant logistics pipeline leads to the outlet of the eighth heat exchange channel of the main heat exchanger, the second mixed refrigerant logistics pipeline merges with the first mixed refrigerant logistics pipeline and then connects to the inlet of the refrigerant buffer tank. The liquid phase outlet pipeline of the refrigerant buffer tank goes to the refrigerant storage tank outside the boundary area for supplying refrigerant replenishment logistics.

[0014] Furthermore, the refrigerant supplementary flow pipeline, the second mixed refrigerant flow pipeline and the first mixed refrigerant flow pipeline are combined into a feed main pipe of the refrigerant buffer tank.

[0015] Furthermore, the regeneration gas outlet pipelines of the first dehydration tower and the second dehydration tower are connected to the plant vent main for direct discharge, the second dirty nitrogen branch is connected to the second heat exchange channel of the second heat exchanger, and the outlet pipeline of the second heat exchange channel of the second heat exchanger is connected to the plant vent main for direct discharge.

[0016] According to a second aspect of the utility model, there is provided an air separation process for providing refrigeration using a mixed refrigerant, the process comprising the following steps:

[0017] Air purification part:

[0018] The air is first compressed to 0.05~0.3MPa by the raw gas compressor and enters the water cooling tower. In the lower tower, it is countercurrently contacted with circulating water (circulating water temperature is about 28~32℃, circulating water is sprayed by nozzles, and the volume flow ratio of circulating water to air can be 1:80~160 (Nm³ / h) / t) to remove most of the water-soluble harmful substances such as NH3, HCL, SO2, NO2, etc., and then in the upper tower, it is countercurrently contacted with chilled water (chilled water temperature is about 6~30℃, chilled water is sprayed by nozzles, and the volume flow ratio of chilled water to air can be 1:500~600 (Nm³ / h) / t) to transfer heat and mass and be cooled to 7~30℃, and then enters the dehydration tower (the dehydration tower can be filled with any one or more commercially purchased dehydration molecular sieves (3A, 4A, 5A, 13X, etc.)) to remove moisture, CO2, etc. in the air;

[0019] The circulating water (which can come from the plant's circulating water system) is divided into two routes. One route directly enters the lower tower of the water-cooled tower, and the other route is cooled to 6~30℃ in the heat exchanger after heat exchange with the low-temperature polluted nitrogen from the low-pressure distillation tower and the main heat exchanger and enters the upper tower of the water-cooled tower. The flow ratio of one route to the other is generally 1:3~8;

[0020] The air drawn from the top of the water-cooling tower enters the dehydration tower, which is an intermittently operated adsorption tower. While one tower is adsorbing impurities in the air, the other tower is back-blown and regenerated by the low-temperature dirty nitrogen gas from the distillation system.

[0021] Heat exchange distillation part:

[0022] The purified air from the dehydration tower is divided into two routes (the volume ratio of one route to the other route can be 1:0.17~0.43). One route is compressed to 0.3~3MPa by the compressor and then cooled to -120~-175℃ in the main heat exchanger to obtain low-temperature and high-pressure air, which enters the high-pressure distillation tower for distillation (the operating conditions of the high-pressure distillation tower: pressure 0.5~2MPa, temperature -183~-110℃), and the other route is cooled to -140~-90℃ in the main heat exchanger to obtain low-temperature and low-pressure air, which enters the low-pressure distillation tower (the operating conditions of the low-pressure distillation tower: pressure 0.05~0.15MPa, temperature is -195~-178℃) for distillation;

[0023] Oxygen-rich liquid air is extracted from the lower part of the high-pressure distillation tower, and is supercooled to -180~-193℃ in the supercooler, and is further cooled to -175~-198℃ after throttling before entering the low-pressure distillation tower; high-purity nitrogen is extracted from the upper part of the high-pressure distillation tower and enters the internal heat exchanger at the bottom of the low-pressure distillation tower, and is cooled to liquid nitrogen by the liquid oxygen at the bottom and is divided into two paths (the volume ratio of one path to the other path can be 1.5~1.9:1), one path of liquid nitrogen enters the top of the high-pressure distillation tower as reflux liquid, and the other path of liquid nitrogen is supercooled to -180~-193℃ in the supercooler and is divided into two branches (the volume ratio of one branch to the other branch can be 65~75:1), one branch of supercooled liquid nitrogen is further cooled to -175~-198℃ after throttling before entering the low-pressure distillation tower (upper or top), and the other branch of supercooled liquid nitrogen is sent to the liquid nitrogen storage tank as a product;

[0024] The low-pressure distillation tower extracts high-purity nitrogen, dirty nitrogen, liquid argon, high-purity oxygen, and liquid oxygen from different tray positions (for example, the top (for example, the 1st to 3rd trays, preferably the 1st tray), the upper part (for example, the 12th to 17th trays), the upper middle part (for example, the 28th to 36th trays), the middle part (for example, the 40th to 50th trays), and the bottom (for example, the 80th to 85th trays, preferably the 82nd tray), and the total number of trays is 80-85, preferably 82). The high-purity nitrogen passes through the cooler, After the main heat exchanger recovers cold energy step by step, it becomes high-purity nitrogen at 15~30℃ and is sent to the high-purity nitrogen storage tank; liquid argon is sent to the liquid argon storage tank or liquid argon users; liquid oxygen is sent to the liquid oxygen storage tank or liquid oxygen users; after the dirty nitrogen gas recovers cold energy step by step through the cooler and the main heat exchanger, its temperature is increased to 5~30℃ and it is divided into two paths, one path enters the dehydration system as the regeneration gas of the dehydration tower, and the other path enters the heat exchanger to cool the circulating water. The high-purity oxygen is sent to the oxygen storage tank or oxygen users after heat exchange through the main heat exchanger.

[0025] Refrigeration system:

[0026] The refrigerant from the refrigerant buffer tank enters the three-stage compressor, and the gas-liquid mixed refrigerant is drawn out from the second stage of the compressor (the second stage is compressed to a pressure of 0.5~1.8MPa). After the gas-liquid separation in the first gas-liquid separator, the gas phase enters the third stage and continues to be compressed to 1.8~5MPa to obtain a gas-liquid mixed flow. After the gas-liquid mixed flow passes through the second gas-liquid separator for gas-liquid separation, the gas phase is cooled by the main heat exchanger and cooled to -100~-158℃. After being drawn out from the main heat exchanger, it is throttled by the throttle valve and cooled to a mixed refrigerant flow of -100~-188℃. The mixed refrigerant flow enters the cold box (main heat exchanger) for heat exchange to obtain the first mixed flow. Combined refrigerant logistics; the liquid phase drawn from the bottom of the first gas-liquid separator and the liquid phase drawn from the bottom of the second gas-liquid separator are combined and then cooled to -5~-30℃ by the main heat exchanger. After being drawn out from the main heat exchanger, they are throttled and cooled to -20~-50℃ by the throttle valve, and then enter the cold box for heat exchange to obtain the second mixed refrigerant logistics. The first mixed refrigerant logistics and the second mixed refrigerant logistics are combined and enter the refrigerant buffer tank for gas-liquid separation. The gas phase enters the circulation compressor (almost no liquid phase, in special cases, the liquid phase is re-vaporized or sent to the torch for combustion as the working conditions change), and the liquid phase goes to the refrigerant storage tank outside the boundary area to supply the refrigerant replenishment logistics. The 0.1-0.5MPa logistics from the refrigerant tank area is the refrigerant replenishment logistics, which is replenished according to the working conditions and losses of the refrigerant circulation system.

[0027] The refrigerant in the mixed refrigerant circulation system is a multi-component mixture, which can be combined and proportioned according to different product requirements. The adjustment range is wide, and the refrigerant components and composition are flexible and changeable. The refrigerant molar composition can be in the following range: CH4 (0.05-0.20), C2H4 (0.10-0.20), C3H8 (0.01-0.15), i-C5H 10 (0.01~0.13), N2 (0.40~0.65).

[0028] Advantages of this application:

[0029] This application is a brand-new process technology. Compared with the existing air separation process and equipment, the energy consumption can be greatly reduced, and the total energy consumption can be reduced by more than about 20%, which has the advantages of high efficiency and energy saving;

[0030] The air (raw gas) is pressurized, cooled by heat exchange, cryogenically distilled, and reheated to recover cold energy to obtain separated nitrogen (liquid, gas) and oxygen (liquid, gas). The mixed refrigerant and the air medium undergo heat exchange in the heat exchange cooling section to achieve the conditions required for cryogenic distillation.

[0031] The cryogenic distillation is divided into a high-pressure tower and a low-pressure tower. The high-pressure tower separates liquid nitrogen and oxygen-enriched air. The oxygen-enriched air is separated in the low-pressure tower to obtain liquid oxygen. The cooling capacity required by the low-pressure tower can be provided by the throttled oxygen-enriched air and the reflux liquid nitrogen provided by the high-pressure tower. The dirty nitrogen gas discharged from the low-pressure tower is recovered by the heat exchanger.

[0032] If it is necessary to produce some nitrogen and oxygen at the same time, the heat exchanger can be used to gasify liquid oxygen and liquid nitrogen to recover cold energy, reduce the amount of circulating refrigerant, and reduce energy consumption;

[0033] The refrigerant in the mixed refrigerant circulation system is a multi-component mixture, which can be combined and proportioned according to different product requirements. The adjustment range is wide, and the refrigerant components and composition are flexible and changeable. The refrigerant molar composition can be in the following range: CH4 (0.05-0.20), C2H4 (0.10-0.20), C3H8 (0.01-0.15), i-C5H 10 (0.01~0.13), N2 (0.40~0.65). BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of an air separation device that uses a mixed refrigerant to provide cooling according to the utility model.

[0035] Description of reference numerals:

[0036] C1-first compressor; C2-second compressor; C3-third compressor; T1-high-pressure distillation tower; T2-low-pressure distillation tower; T3-water cooling tower; T4-first dehydration tower; T5-second dehydration tower; E1-main heat exchanger; E2-subcooler; E3-second heat exchanger; E4-built-in heat exchanger at the bottom of low-pressure distillation tower; V1-refrigerant buffer tank; V2-first gas-liquid separator; V3-second gas-liquid separator;

[0037] L0-air inlet pipeline; L1-first compressor outlet pipeline; L2-purified air pipeline; L3-first purified air branch; L4-second purified air branch; L5-low-temperature low-pressure air pipeline; L6-low-temperature high-pressure air pipeline; L7-oxygen-enriched liquid air pipeline; L8-first heat exchange channel outlet pipeline of subcooler; L9-high-purity nitrogen pipeline; L10-low-pressure distillation tower bottom internal heat exchanger outlet pipeline; L11-second liquid nitrogen branch; L12-first liquid nitrogen branch; L13-second heat exchange channel of subcooler outlet pipeline of the main heat exchanger; L14-first subcooled liquid nitrogen pipeline; L15-second subcooled liquid nitrogen pipeline; L16-first high-purity nitrogen pipeline; L17-export pipeline of the third heat exchange channel of the subcooler; L18-second high-purity nitrogen pipeline; L19-liquid argon pipeline; L20-liquid oxygen pipeline; L21-dirty nitrogen pipeline; L22-export pipeline of the fourth heat exchange channel of the subcooler; L23-export pipeline of the fourth heat exchange channel of the main heat exchanger; L24-first dirty nitrogen branch; L25-second dirty nitrogen branch; L26-second heat exchange The outlet pipeline of the second heat exchange channel of the heat exchanger; L27-regeneration gas outlet pipeline; L29-circulating water pipeline; L30-the second branch of the circulating water pipeline; L31-the outlet pipeline of the first heat exchange channel of the second heat exchanger; L32-the first branch of the circulating water pipeline; L33-the outlet pipeline at the bottom of the water cooling tower; L34-refrigerant replenishment logistics pipeline; L35-feed main pipe; L36-refrigerant outlet pipeline; L37-gas-liquid mixed refrigerant pipeline; L38-gas phase outlet pipeline of the first gas-liquid separator; L39-the first liquid phase pipeline L 39; L40-gas-liquid mixed flow pipeline; L41-second liquid phase pipeline; L42-gas phase outlet pipeline of the second gas-liquid separator; L43-mixed refrigerant main pipe; L44-second refrigerant logistics pipeline; L45-first mixed refrigerant logistics pipeline; L46-second mixed refrigerant logistics pipeline; L47-first refrigerant logistics pipeline; L48-merging pipe; L49-high-purity oxygen pipeline; L50-water cooling tower top outlet pipeline; L51-high-purity oxygen pipeline; L52-refrigerant buffer tank liquid phase outlet pipeline. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings.

[0039] like Figure 1 As shown, an air separation device using a mixed refrigerant for cooling includes a first compressor C1, a second compressor C2, a three-stage compressor C3, a water-cooling tower T3, a high-pressure distillation tower T1, a low-pressure distillation tower T2, a first dehydration tower T4, a second dehydration tower T5, a main heat exchanger E1, a subcooler E2, a second heat exchanger E3, a built-in heat exchanger E4 at the bottom of the low-pressure distillation tower, a refrigerant buffer tank V1, a first gas-liquid separator V2, and a second gas-liquid separator V3.

[0040] The air intake pipe L0 is connected to the inlet of the first compressor C1, and the first compressor outlet pipe L1 is connected to the lower inlet of the water cooling tower T3.

[0041] The circulating water pipeline L29 is divided into two branches. The first branch L32 of the circulating water pipeline is connected to the inlet of the lower tower (lower section of the tower) of the water cooling tower T3, the second branch L30 of the circulating water pipeline is connected to the first heat exchange channel of the second heat exchanger E3 (for heat exchange with the dirty nitrogen drawn out from the main heat exchanger), and the outlet pipeline L31 of the first heat exchange channel of the second heat exchanger is connected to the inlet of the upper tower (upper section of the tower) of the water cooling tower T3.

[0042] The outlet pipe L50 at the top of the water-cooling tower is switchably connected to the gas inlets of the first dehydration tower T4 and the second dehydration tower T5 through a valve. The first dehydration tower T4 and the second dehydration tower T5 are intermittently operated adsorption towers. When one tower adsorbs impurities in the air, the other tower is back-blown and regenerated by the low-temperature contaminated nitrogen gas from the distillation system.

[0043] The outlet pipes (equipped with corresponding valves) of the first dehydration tower T4 and the second dehydration tower T5 merge into a purified air pipeline L2, and the purified air pipeline L2 branches into a first purified air branch L3 and a second purified air branch L4. The first purified air branch L3 is connected to the first heat exchange channel of the main heat exchanger E1, and the outlet pipe of the first heat exchange channel, i.e., the low-temperature and low-pressure air pipeline L5, is connected to the feed port of the low-pressure distillation tower T2 (the middle and upper part of the low-pressure distillation tower, for example, the position of the 25th to 32nd plates), and the second compressor C2 is arranged on the second purified air branch L4. The second purified air branch L4 is connected to the second heat exchange channel of the main heat exchanger E1, and the outlet pipe of the second heat exchange channel, i.e., the low-temperature and high-pressure air pipeline L6, is connected to the lower inlet of the high-pressure distillation tower T1.

[0044] The bottom outlet of the high-pressure distillation tower T1 is connected to the first heat exchange channel of the subcooler E2 through the oxygen-rich liquid air pipeline L7, and the outlet pipeline L8 of the first heat exchange channel of the subcooler is connected to an inlet of the low-pressure distillation tower T2 (the upper part of the low-pressure distillation tower, for example, the 10th to 20th tower plate position) after passing through the first throttle valve XV1. The upper outlet of the high-pressure distillation tower T1 is connected to the inlet of the built-in heat exchanger E4 at the bottom of the low-pressure distillation tower through the high-purity nitrogen pipeline L9. The inlet pipeline L10 is led out from the low-pressure distillation tower and is divided into a first liquid nitrogen branch L12 to return to the top of the high-pressure distillation tower T1. The second liquid nitrogen branch L11 is connected to the second heat exchange channel of the subcooler E2. The outlet pipeline L13 of the second heat exchange channel of the subcooler is divided into two routes. The first subcooled liquid nitrogen pipeline L14 is connected to another inlet (top inlet, for example, located at the 1st to 10th tower plate position) of the low-pressure distillation tower T2 after passing through the second throttle valve XV2. The second subcooled liquid nitrogen pipeline L15 is connected to the liquid nitrogen storage tank.

[0045] The low-pressure distillation tower T2 respectively draws out a first high-purity nitrogen pipeline L16, a dirty nitrogen pipeline L21, a liquid argon pipeline L19, a high-purity oxygen pipeline L51, and a liquid oxygen pipeline L20 from different tray positions (for example, in order, the top (for example, the 1st to 3rd trays, preferably the 1st tray), the upper part (for example, the 12th to 17th trays), the middle upper part (for example, the 28th to 36th trays), the middle part (for example, the 40th to 50th trays), and the bottom (for example, the 80th to 85th trays, preferably the 82nd tray), with a total number of trays of 80-85, preferably 82). There are differences in the boiling points of components such as O2, N2, Ar, and CO2. When a mixed liquid composed of substances with different boiling points absorbs heat and partially evaporates, the low-boiling-point component will evaporate more, and when the mixed vapor releases heat and partially condenses, the high-boiling-point component will condense more. The separation effect is achieved by continuous evaporation and condensation on multi-layer tower plates. In this application, the nitrogen purity of high-purity nitrogen is usually >99.99%, the argon content in liquid argon is usually >99.999%, the oxygen content in liquid oxygen is usually >99.99%, the nitrogen content in contaminated nitrogen is usually 84~88%, and the oxygen content in high-purity oxygen is usually >99.95%, by volume.

[0046] The first high-purity nitrogen pipeline L16 is connected to the third heat exchange channel of the subcooler, and the outlet pipeline L17 of the third heat exchange channel of the subcooler is connected to the third heat exchange channel of the main heat exchanger E1. The outlet pipeline of the third heat exchange channel of the main heat exchanger, i.e., the second high-purity nitrogen pipeline L18 is connected to the high-purity nitrogen storage tank (not shown in the figure) or the high-purity nitrogen user; the liquid argon pipeline L19 is connected to the liquid argon storage tank (not shown in the figure) or the liquid argon user; the liquid oxygen pipeline L20 is sent to the liquid oxygen storage tank (not shown in the figure) or the liquid oxygen user; the dirty nitrogen pipeline L21 is connected to the fourth heat exchange channel of the subcooler E2, and the outlet pipeline L22 of the fourth heat exchange channel of the subcooler is connected to the fourth heat exchange channel of the main heat exchanger, the fourth heat exchange channel of the main heat exchanger The outlet pipeline L23 of the heat exchange channel is divided into two routes. The first dirty nitrogen branch L24 can be switchably connected to the regeneration gas inlet of the first dehydration tower T4 and the second dehydration tower T5 (the regeneration gas outlet pipeline L27 of the first dehydration tower T4 and the second dehydration tower T5 is connected to the plant vent main pipe for direct venting), the second dirty nitrogen branch L25 is connected to the second heat exchange channel of the second heat exchanger (the outlet pipeline L26 of the second heat exchange channel of the second heat exchanger is connected to the plant vent main pipe for direct venting), the high-purity oxygen pipeline L51 is connected to the eighth heat exchange channel of the main heat exchanger E1, and the outlet of the eighth heat exchange channel of the main heat exchanger E1, i.e., the high-purity oxygen pipeline L49, is connected to the oxygen storage tank or oxygen user.

[0047] The refrigerant outlet pipeline L36 of the refrigerant buffer tank V1 is connected to the inlet of the three-stage compressor C3, the gas-liquid mixed refrigerant pipeline L37 leading out from the second stage of the compressor is connected to the inlet of the first gas-liquid separator V2, the gas phase outlet pipeline L38 of the first gas-liquid separator is connected to the third-stage inlet of the three-stage compressor, the third-stage outlet of the three-stage compressor is connected to the inlet of the second gas-liquid separator V3 through the gas-liquid mixed flow pipeline L40, the gas phase outlet pipeline L42 of the second gas-liquid separator is connected to the fifth heat exchange channel of the main heat exchanger E1, the fifth heat exchange channel of the main heat exchanger E1 is connected to the sixth heat exchange channel of the main heat exchanger through the first refrigerant flow pipeline L47 and the third throttle valve XV03, and the outlet of the sixth heat exchange channel of the main heat exchanger leads out the first The mixed refrigerant logistics pipeline L45, the first liquid phase pipeline L39 led out from the bottom of the first gas-liquid separator V2 and the second liquid phase pipeline L41 led out from the bottom of the second gas-liquid separator V3 merge into a mixed refrigerant main pipe L43 and then connected to the seventh heat exchange channel of the main heat exchanger, the second refrigerant logistics pipeline L44 is led out from the outlet of the seventh heat exchange channel of the main heat exchanger, the second refrigerant logistics pipeline L44 is connected to the eighth heat exchange channel of the main heat exchanger after passing through the fourth throttle valve XV04, the second mixed refrigerant logistics pipeline L46 is led out from the outlet of the eighth heat exchange channel of the main heat exchanger, the second mixed refrigerant logistics pipeline L46 merges with the first mixed refrigerant logistics pipeline L45 (merging pipe L48) and then connected to the inlet of the refrigerant buffer tank V1.

[0048] Furthermore, the refrigerant supplementary flow pipeline L34 merges with the second mixed refrigerant flow pipeline L46 and the first mixed refrigerant flow pipeline L45 into a merging pipe L48 to form a feed main pipe L35 of the refrigerant buffer tank V1.

[0049] Air purification part:

[0050] Air, preferably filtered and dust-removed air, is first compressed to 0.05~0.3MPa by the raw gas compressor C1, enters the water-cooling tower T3, and is countercurrently contacted with circulating water (circulating water temperature is about 28~32℃, circulating water is sprayed by nozzles, and the volume flow ratio of circulating water to air is 1:80~160 (Nm³ / h) / t) in the lower tower to remove most of the water-soluble harmful substances such as NH3, HCL, SO2, NO2, etc., and then is countercurrently contacted with chilled water (chilled water temperature is about 6~30℃, chilled water is sprayed by nozzles, and the volume flow ratio of chilled water to air is 1:500~600 (Nm³ / h) / t) in the upper tower to transfer heat and mass and be cooled to 7~30℃, and then enters the dehydration tower T4 / T5 (the dehydration tower is filled with commercially purchased dehydration molecular sieves (3A, 4A, 5A, 13X, etc.)) to remove moisture, CO2, etc. in the purified air.

[0051] The circulating water (which can come from the plant's circulating water system) is divided into two routes. One route directly enters the lower tower of the water-cooled tower T3, and the other route is cooled to 6~30℃ after heat exchange with the low-temperature polluted nitrogen from the low-pressure distillation tower T2 and the main heat exchanger E1 in the heat exchanger E3 and enters the upper tower of the water-cooled tower T3. The flow ratio of one route to the other is generally 1:3~8).

[0052] The air drawn from the upper part of the water-cooling tower enters the dehydration tower. The dehydration tower T4 / T5 is an intermittently operated adsorption tower. When one tower is adsorbing impurities in the air, the other tower is back-blown and regenerated by the low-temperature dirty nitrogen gas from the distillation system.

[0053] Heat exchange distillation part:

[0054] The purified air from the dehydration tower T4 / C5 is divided into two routes (the volume ratio of one route to the other route can be 1:0.17~0.43). One route is compressed to 0.3~3MPa by the compressor C2 and then cooled to -120~-175℃ in the main heat exchanger E1 to obtain low-temperature and high-pressure air, which enters the high-pressure distillation tower T1 for distillation (the operating conditions of the high-pressure distillation tower: pressure 0.5~2MPa, temperature -183~-110℃). The other route is cooled to -140~-90℃ in the main heat exchanger E1 to obtain low-temperature and low-pressure air, which enters the low-pressure distillation tower T2 (the operating conditions of the low-pressure distillation tower: pressure 0.05~0.15MPa, temperature -195~-178℃) for distillation.

[0055] Oxygen-rich liquid air is extracted from the lower part of the high-pressure distillation tower T1, and is supercooled to -180~-193℃ in the supercooler E2. It is throttled by the first throttle valve XV1 and further cooled to -175~-198℃ before entering the low-pressure distillation tower T2. High-purity nitrogen is extracted from the upper part of the high-pressure distillation tower T1 and enters the heat exchanger E4 at the bottom of the low-pressure distillation tower T2. It is cooled into liquid nitrogen by the liquid oxygen at the bottom of the low-pressure distillation tower T2 and then divided into two paths (the volume ratio of one path to the other is 1.5~ 1.9:1), one branch of liquid nitrogen enters the top of the high-pressure distillation tower T1 as reflux liquid, and the other branch of liquid nitrogen is subcooled to -180~-193℃ in the subcooler E2 and then divided into two branches (the volume ratio of one branch to the other branch is 65~75:1). The subcooled liquid nitrogen in one branch is further cooled to -175~-198℃ by throttling valve XV2 and then enters the low-pressure distillation tower T2 (upper or top), and the other branch of subcooled liquid nitrogen is taken as a product to the liquid nitrogen storage tank.

[0056] The low-pressure distillation tower T2 extracts high-purity nitrogen, dirty nitrogen, liquid argon, high-purity oxygen, and liquid oxygen from different tray positions (e.g., top (e.g., tray 1), upper (e.g., trays 12 to 17), upper middle (e.g., trays 28 to 36), middle (e.g., trays 40 to 50), and bottom (e.g., tray 82)). After the high-purity nitrogen recovers the cold energy step by step through the cooler E2 and the main heat exchanger E1, it becomes high-purity nitrogen at 15 to 30°C and is sent to the high-purity nitrogen storage tank; the liquid argon is sent to the liquid argon storage tank; the liquid oxygen is sent to the liquid oxygen storage tank; after the dirty nitrogen recovers the cold energy step by step through the cooler E2 and the main heat exchanger E1, the temperature is increased to 5 to 30°C and is divided into two paths, one path enters the dehydration system as the dehydration tower regeneration gas, and the other path enters the heat exchanger E3 to cool the circulating water, and the high-purity oxygen is sent to the oxygen storage tank after heat exchange through the main heat exchanger E1.

[0057] Refrigeration system:

[0058] The refrigerant from the refrigerant buffer tank V1 enters the three-stage compressor C3, and the gas-liquid mixed refrigerant is drawn out from the second stage of the compressor (the second stage is compressed to a pressure of 0.5~1.8MPa). After the gas-liquid separation in the first gas-liquid separator V2, the gas phase enters the third stage and continues to be compressed to 1.8~5MPa to obtain a gas-liquid mixed flow. After the gas-liquid mixed flow passes through the second gas-liquid separator V3 for gas-liquid separation, the gas phase is cooled by the main heat exchanger E1 and cooled to -100~-158℃. After being drawn out from the main heat exchanger and throttled by the throttle valve, the mixed refrigerant flow is cooled to -100~-188℃. The mixed refrigerant flow enters the cold box for heat exchange. The first mixed refrigerant logistics is obtained; the liquid phase drawn from the bottom of the first gas-liquid separator V2 and the liquid phase drawn from the bottom of the second gas-liquid separator V3 are combined and then cooled to -5~-30℃ by the main heat exchanger E1, and then throttled by the throttle valve to -20~-50℃ after being drawn from the main heat exchanger E1, and then enter the cold box for heat exchange to obtain the second mixed refrigerant logistics. The first mixed refrigerant logistics and the second mixed refrigerant logistics are combined and enter the refrigerant buffer tank V1 for gas-liquid separation, and the gas phase enters the circulation compressor. The liquid phase outlet pipeline of the refrigerant buffer tank is L52, which goes to the refrigerant storage tank outside the boundary area to supply the refrigerant supplementary logistics. The 0.1-0.5MPa logistics from the refrigerant tank area is the refrigerant supplementary logistics, which is supplemented according to the working conditions and losses of the refrigerant circulation system.

[0059] The purpose of this patent is to propose a new process technology, which can significantly reduce energy consumption compared to existing processes, and the total energy consumption can be reduced by about 20% or more, with the advantages of high efficiency and energy saving.

[0060] The preferred embodiments of the present invention are described in detail above. However, it should be understood that the above description is only for illustrative purposes and does not constitute any limitation on the scope of the present invention. A person of ordinary skill in the art may make substitutions or changes to certain features of the present invention without departing from the spirit and scope of the present invention, and such substitutions or changes shall be deemed to fall within the scope of protection of the claims of the present invention.

Claims

1. An air separation unit using mixed refrigerant for cooling, characterized in that: It includes a first compressor (C1), a second compressor (C2), a three-stage compressor (C3), a high-pressure distillation tower (T1), a low-pressure distillation tower (T2), a water-cooling tower (T3), a first dehydration tower (T4), a second dehydration tower (T5), a main heat exchanger (E1), a subcooler (E2), a second heat exchanger (E3), a built-in heat exchanger (E4) at the bottom of the low-pressure distillation tower, a refrigerant buffer tank (V1), a first gas-liquid separator (V2), and a second gas-liquid separator (V3); The air intake pipe (L0) is connected to the inlet of the first compressor (C1), and the first compressor outlet pipe (L1) is connected to the lower inlet of the water cooling tower (T3); The circulating water pipeline (L29) is divided into two branches, the first branch (L32) of the circulating water pipeline is connected to the lower tower inlet of the water cooling tower (T3), the second branch (L30) of the circulating water pipeline is connected to the first heat exchange channel of the second heat exchanger (E3), and the outlet pipeline (L31) of the first heat exchange channel of the second heat exchanger is connected to the upper tower inlet of the water cooling tower (T3); The outlet pipeline (L50) at the top of the water cooling tower is switchably connected to the gas inlets of the first dehydration tower (T4) and the second dehydration tower (T5) through a valve. The first dehydration tower (T4) and the second dehydration tower (T5) are intermittently operated adsorption towers. When one tower is adsorbing impurities in the air, the other tower is back-blown and regenerated by low-temperature contaminated nitrogen gas from the distillation system. The outlet pipelines of the first dehydration tower (T4) and the second dehydration tower (T5) merge into a purified air pipeline (L2), the purified air pipeline (L2) branches into a first purified air branch (L3) and a second purified air branch (L4), the first purified air branch (L3) is connected to the first heat exchange channel of the main heat exchanger (E1), the outlet pipeline of the first heat exchange channel, i.e., the low-temperature and low-pressure air pipeline (L5), is connected to the feed inlet of the low-pressure distillation tower (T2), the second purified air branch (L4) is provided with a second compressor (C2), the second purified air branch (L4) is connected to the second heat exchange channel of the main heat exchanger (E1), and the outlet pipeline of the second heat exchange channel, i.e., the low-temperature and high-pressure air pipeline (L6), is connected to the lower inlet of the high-pressure distillation tower (T1); The bottom outlet of the high-pressure distillation tower (T1) is connected to the first heat exchange channel of the subcooler (E2) through an oxygen-rich liquid air pipeline (L7), the outlet pipeline (L8) of the first heat exchange channel of the subcooler is connected to an inlet of the low-pressure distillation tower (T2) after passing through a first throttle valve (XV1), the upper outlet of the high-pressure distillation tower (T1) is connected to the inlet of the built-in heat exchanger (E4) at the bottom of the low-pressure distillation tower through a high-purity nitrogen pipeline (L9), and the outlet pipeline of the built-in heat exchanger at the bottom of the low-pressure distillation tower is connected to the inlet of the built-in heat exchanger (E4) at the bottom of the low-pressure distillation tower. (L10) is drawn out from the low-pressure distillation tower and is divided into a first liquid nitrogen branch (L12) and returns to the top of the high-pressure distillation tower (T1). The second liquid nitrogen branch (L11) is connected to the second heat exchange channel of the subcooler (E2). The outlet pipeline (L13) of the second heat exchange channel of the subcooler is divided into two paths. The first subcooled liquid nitrogen pipeline (L14) is connected to the other inlet of the low-pressure distillation tower (T2) after passing through the second throttle valve (XV2). The second subcooled liquid nitrogen pipeline (L15) is connected to the liquid nitrogen storage tank. The low-pressure distillation tower (T2) leads out the first high-purity nitrogen pipeline (L16), the dirty nitrogen pipeline (L21), the liquid argon pipeline (L19), the high-purity oxygen pipeline (L51), and the liquid oxygen pipeline (L20) from different tower plate positions.

2. The air separation device using mixed refrigerant for refrigeration according to claim 1, characterized in that: The first high-purity nitrogen pipeline (L16) is connected to the third heat exchange channel of the subcooler, and the outlet pipeline (L17) of the third heat exchange channel of the subcooler is connected to the third heat exchange channel of the main heat exchanger (E1). The outlet pipeline of the third heat exchange channel of the main heat exchanger, i.e., the second high-purity nitrogen pipeline (L18) is connected to the high-purity nitrogen storage tank or the high-purity nitrogen user; the liquid argon pipeline (L19) is connected to the liquid argon storage tank or the liquid argon user; the liquid oxygen pipeline (L20) is sent to the liquid oxygen storage tank or the liquid oxygen user; the dirty nitrogen pipeline (L21) is connected to the fourth heat exchange channel of the subcooler (E2), and the outlet pipeline of the fourth heat exchange channel of the subcooler (L22) is connected to the fourth heat exchange channel of the main heat exchanger (E1), the outlet pipeline (L23) of the fourth heat exchange channel of the main heat exchanger is divided into two branches, the first dirty nitrogen branch (L24) can be switched to connect the regeneration gas inlet of the first dehydration tower (T4) and the second dehydration tower (T5), the second dirty nitrogen branch (L25) is connected to another heat exchange channel of the heat exchanger (E3), the high-purity oxygen pipeline (L51) is connected to the eighth heat exchange channel of the main heat exchanger (E1), and the outlet of the eighth heat exchange channel of the main heat exchanger (E1), i.e., the high-purity oxygen pipeline (L49), is connected to the oxygen storage tank or oxygen user.

3. The air separation device using mixed refrigerant for refrigeration according to claim 1 or 2, characterized in that: The refrigerant outlet pipeline (L36) of the refrigerant buffer tank (V1) is connected to the inlet of the three-stage compressor (C3), the gas-liquid mixed refrigerant pipeline (L37) leading out from the second stage of the compressor is connected to the inlet of the first gas-liquid separator (V2), the gas phase outlet pipeline (L38) of the first gas-liquid separator is connected to the third-stage inlet of the three-stage compressor, the third-stage outlet of the three-stage compressor is connected to the inlet of the second gas-liquid separator (V3) through the gas-liquid mixed flow pipeline (L40), the gas phase outlet pipeline (L42) of the second gas-liquid separator is connected to the fifth heat exchange channel of the main heat exchanger (E1), the fifth heat exchange channel of the main heat exchanger (E1) is connected to the sixth heat exchange channel of the main heat exchanger through the first refrigerant flow pipeline (L47) and the third throttle valve (XV3), and the outlet of the sixth heat exchange channel of the main heat exchanger A first mixed refrigerant logistics pipeline (L45) is led out, a first liquid phase pipeline (L39) led out from the bottom of the first gas-liquid separator (V2) and a second liquid phase pipeline (L41) led out from the bottom of the second gas-liquid separator (V3) are combined into a mixed refrigerant main pipeline (L43) and then connected to the seventh heat exchange channel of the main heat exchanger, a second refrigerant logistics pipeline (L44) is led out from the outlet of the seventh heat exchange channel of the main heat exchanger, the second refrigerant logistics pipeline (L44) is connected to the eighth heat exchange channel of the main heat exchanger after passing through a fourth throttle valve (XV4), a second mixed refrigerant logistics pipeline (L46) is led out from the outlet of the eighth heat exchange channel of the main heat exchanger, the second mixed refrigerant logistics pipeline (L46) is combined with the first mixed refrigerant logistics pipeline (L45) and then connected to the inlet of the refrigerant buffer tank (V1).

4. The air separation device using mixed refrigerant for refrigeration according to claim 3, characterized in that: The refrigerant supplementary flow pipeline (L34) merges with the second mixed refrigerant flow pipeline (L46) and the first mixed refrigerant flow pipeline (L45) to form a main feed pipeline (L35) of the refrigerant buffer tank (V1).

5. The air separation device using mixed refrigerant for refrigeration according to claim 1 or 2, characterized in that: The regeneration gas outlet pipeline (L27) of the first dehydration tower (T4) and the second dehydration tower (T5) is connected to the plant vent main pipe for direct discharge, the second dirty nitrogen branch (L25) is connected to the second heat exchange channel of the second heat exchanger, and the outlet pipeline (L26) of the second heat exchange channel of the second heat exchanger is connected to the plant vent main pipe for direct discharge.

6. The air separation device using mixed refrigerant for refrigeration according to claim 1 or 2, characterized in that: The first high-purity nitrogen pipeline (L16), the dirty nitrogen pipeline (L21), the liquid argon pipeline (L19), the high-purity oxygen pipeline (L51), and the liquid oxygen pipeline (L20) are led out from the top, the upper part, the upper middle part, the middle part, and the bottom respectively.

7. The air separation device using mixed refrigerant for refrigeration according to claim 6, characterized in that: The top is at the 1st to 3rd tower plates, the upper part is at the 12th to 17th tower plates, the upper middle part is at the 28th to 36th tower plates, the middle part is at the 40th to 50th tower plates, and the bottom is at the 80th to 85th tower plates. The total number of tower plates is 80 to 85.

Images