Air separation device and a producing method of nitrogen

Abstract

This invention provides an air separation device comprising a crude argon distillation column and a pure argon distillation column, capable of recovering nitrogen from gas exported from the condensation section of a pure argon distillation column. The air separation device 1 includes: a first distillation column 2; a first condensation section 3; a second distillation column 4; a third distillation column 5; a second condensation section 6; a fourth distillation column; a third condensation section 8; and a reflux pipe L81 for returning gas exported from the third condensation section 8 to the second distillation column 4. It also includes: a branch pipe L811 branching from the reflux pipe L81; and a control unit C8 that, from the start of a predetermined period after the third condensation section 8 is activated, controls the opening and closing of valves in a manner that supplies gas exported from the third condensation section 8 to the branch pipe L811, and after the predetermined period has elapsed, controls the opening and closing of valves in a manner that supplies gas exported from the third condensation section 8 to the reflux pipe L81.

Description

Technical Field

[0001] This disclosure relates to air separation equipment, and more particularly to air separation equipment equipped with crude argon distillation columns and pure argon distillation columns. Prior Technology

[0002] Previously, the process of transferring oxygen-rich liquid containing argon extracted from an air separation unit to an argon distillation column to extract high-purity argon liquid products was already underway. Patent documents 1 and 2 have disclosed an air separation device comprising a first distillation column, a second distillation column, a crude argon distillation column, and a pure argon distillation column, wherein the first distillation column comprises a first condenser and the crude argon distillation column comprises a second condenser. Patent documents 3, 4, and 5 have disclosed an air separation device comprising a first distillation column, a second distillation column, and a crude argon distillation column, wherein the first distillation column comprises a first condenser and the crude argon distillation column comprises a second condenser.

[0003] While patent documents 1 and 2 include a pure argon distillation column, they do not describe the exhaust gas used in the pure argon distillation column. None of patent documents 3-5 include an air separation device for the pure argon distillation column. [Existing Technical Documents] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent No. 6557763 [Patent Document 2] Japanese Patent Application Publication No. 2021-110466 [Patent Document 3] Japanese Patent No. 6440232 [Patent Document 4] U.S. Patent Publication No. 2019 / 0293347 [Patent Document 5] Japanese Patent Application Publication No. 2004-251569 Summary of the Invention

[0005] [The problem to be solved]

[0006] In air separation units that simultaneously produce high-purity nitrogen and high-purity argon, argon is generated at high purity from the feed gas (containing argon, oxygen, and nitrogen) supplied to the pure argon distillation column, while nitrogen is present in its exhaust gas. In cases where the pure argon distillation column can operate independently of other distillation columns (starting and stopping), the piping becomes complex (narrow pipes, dead-end pipe paths). As a result, there is a risk of contamination in the air separation unit. Therefore, there are still concerns regarding the recovery of nitrogen from the exhaust gas. On the other hand, there is a need to recover nitrogen contained in the gas extracted from the condensation section of a pure argon distillation column. In view of the above facts, this disclosure aims to provide an air separation device comprising a crude argon distillation column and a pure argon distillation column, which can recover nitrogen from the gas exported from the condensation section of the pure argon distillation column, and a method for recovering nitrogen from the gas exported from the condensation section of the pure argon distillation column. [Solutions]

[0007] The air separation device (1) disclosed herein includes: First distillation column (2), feed air is introduced; The first condensation section (3) condenses the nitrogen gas discharged from the top (25) of the aforementioned first distillation column (2); The second distillation column (4) (to the upper distillation section (44) or the intermediate distillation section (43)) introduces nitrogen-containing liquid discharged from the upper section (23) or the top (25) of the aforementioned first distillation column (2); The third distillation column (5) introduces argon-containing oxygen-rich material (which may be gaseous, liquid, or a gas-liquid mixture) extracted from the lower section (42) or intermediate section (43) of the aforementioned second distillation column (4). The second condensation section (6) condenses the gas discharged from the top (55) of the aforementioned third distillation column (5); The fourth distillation column (7) introduces argon-rich material (which may be gaseous, liquid, or a gas-liquid mixture) extracted from the rectification section (53) (from the middle section to the top section) or the top (55) of the aforementioned third distillation column (5). The third condensation section (8) introduces gas exported from the top (75) of the aforementioned fourth distillation column (7); and The reflux piping (L81) allows the gas (containing nitrogen gas) exported from the aforementioned third condensation section (8) to reflux back to the aforementioned second distillation column (4) (the intermediate distillation section (43) or the upper distillation section (44)). The third distillation column can also be called a crude argon distillation column, and the fourth distillation column can also be called a pure argon distillation column.

[0008] The first condensation section (3) can also be located above the first distillation column (2). The second condensation section (6) can also be located above the third distillation column (5). The third condensation section (8) can also be located above the fourth distillation column (7).

[0009] Feed air can also be introduced from the warm end of the main heat exchanger (E1), through the cold end, and introduced to the bottom (21) of the first distillation column (high pressure column (2)). Feed air can also be treated in the air purification section to remove impurities before being introduced into the main heat exchanger (E1). Alternatively, a branch pipe (L811) can be provided that branches off from the aforementioned return pipe (L81). Valves may also be installed on the return piping (L81) and / or the branch piping (L811). Valves (three-way valves) may also be installed at the branch locations. It may also have a control unit (C8) that controls the opening and closing of the valve by conveying the gas exported from the third condensation unit (8) to the branch pipe (L811) for a predetermined period of time starting from the drive of the third condensation unit (8), and controls the opening and closing of the valve by conveying the gas exported from the third condensation unit (8) to the return pipe (L81) after the predetermined period has elapsed.

[0010] The air separation unit (1) may also include a reboiler (9) for introducing nitrogen-containing liquid (LIN) discharged from the upper section of the aforementioned first distillation column (2). A discharge pipe (L91) may also be provided in the reboiler (9) for discharging liquid argon (high-purity argon liquid) from the lower part of the reboiler (9). The reboiler (9) may be located at the lower part of the fourth distillation column (7) or outside the column. An inlet pipe (L92) may also be provided to introduce the gas discharged from the aforementioned reboiler (9) into the aforementioned third condensation section (8). A pressure reducing means (V4) may also be provided in the inlet pipe (L92). The oxygen-enriched liquid drawn from the bottom (21) of the first distillation column (2) can also be introduced into the upper section or top of the third distillation column (5), or the second condensation section (6). The third distillation column (5) can be divided into two or more columns, or it can be a single column. The second distillation column (4) can be divided into two or more columns, or it can be a single column.

[0011] A secondary cooler (E2) may also be installed, with its input: The nitrogen-containing liquid is discharged from the upper section (23) or the top (25) of the aforementioned first distillation column (2) and introduced into the second distillation column (4); The oxygen-enriched liquid is drawn from the bottom (21) of the first distillation column (2) and introduced into the upper section or top of the third distillation column (5), the second condensation section (6), or the additional distillation column (5a); High-purity nitrogen gas is drawn from the top (45) of the aforementioned second distillation column (4); The exhaust gas discharged from the upper or middle section of the aforementioned second distillation column (4); and The exhaust gas (i.e., the nitrogen-containing liquid after use) flowing through the aforementioned branch pipe (L811) Two or more of them exchange heat with each other.

[0012] The control unit (C8) can also be used as a control device for the air separation device. The control unit (C8) can also be composed of dedicated devices, information processing devices (e.g., cloud servers, local servers, general-purpose computers, etc.), devices for the coordinated operation of software and hardware (memory, processor), firmware, etc.

[0013] The method disclosed herein for recovering nitrogen from exhaust gas used in the condensation section of a pure argon distillation column includes: In an air separation device comprising a first distillation column (high-pressure distillation column), a second distillation column (low-pressure distillation column), a crude argon distillation column, a pure argon distillation column, a first condensation section, a second condensation section, a third condensation section, and a reboiler, nitrogen is recovered from the gas by refluxing the gas exiting the third condensation section back to the second distillation column. The gas exported from the aforementioned third condensation section is based on the nitrogen-containing liquid (LIN) gas exported from the upper section of the aforementioned first distillation column and introduced into the aforementioned third condensation section through the aforementioned reboiler. The above method can also be used. Includes: a control step that prevents the gas exported from the third condensation section from flowing back during a predetermined period after the start of the drive, and then causes the gas exported from the third condensation section to flow back to the second distillation column after the predetermined period has elapsed.

[0014] (Effects of the invention) By refluxing the gas from the third condensation section (8) to the second distillation column (4), impurities in the gas can be purified (removed) and nitrogen can be recovered in the second distillation column (4), thereby increasing the nitrogen recovery rate. Furthermore, the gas driven at the start of the third condensation section (8) is not transported to the second distillation column for processing, and the distillation of the gas can be carried out after the second distillation column (4) is operating stably. Simple Explanation of the Diagram

[0015] [Figure 1] Figure 1 shows the air separation device of Embodiment 1. Implementation

[0016] The following describes several embodiments of the present invention. These embodiments are merely examples illustrating the present invention. The present invention is not limited to any of the following embodiments, and includes various modifications implemented within the scope of the invention without altering its essence. Furthermore, not all of the components described below are essential components of the present invention.

[0017] (Implementation Type 1) Figure 1 illustrates the air separation device 1 of Embodiment 1. The air separation device 1 includes: a main heat exchanger (E1), a first distillation column (high-pressure distillation column) 2, a second distillation column (low-pressure distillation column) 4, a third distillation column (first crude argon distillation column) 5, a fourth distillation column 7 (pure argon distillation column), a first condensation section 3, a second condensation section 6, a third condensation section 8, a reboiler 9, and a secondary cooler E2. The first distillation column 2 is called a high-pressure distillation column because distillation is carried out at a higher pressure than that of the second distillation column 4. The second distillation column 4 is sometimes referred to as a low-pressure distillation column.

[0018] (High-pressure distillation column) The feed air is introduced into the bottom 21 of the first distillation column 2 or the lower section of the distillation section 23 via the main heat exchanger E1 and piping L1. The feed air is separated into an oxygen-enriched liquid and a nitrogen-containing liquid LIN in the first distillation column 2. The first condensation section (nitrogen condenser) 3 condenses (liquefies) the nitrogen gas drawn from the top 25 of the first distillation column 2 via pipe L25c, returning it to the first distillation column 2. A portion of the oxygen drawn from the top of the first condensation section (nitrogen condenser) 3 is transported to the bottom 41 of the second distillation column 4 or the lower distillation section 42. Another portion drawn from the top of the first condensation section 3 is introduced into the main heat exchanger E1 via pipe L32 and its branch pipe L321, where it can be removed as product oxygen after heat exchange. Furthermore, it is introduced into the main heat exchanger E1 via branch pipe L322 of pipe L32, and discharged as waste gas after heat exchange. Valves may also be installed on either or both of branch pipes L321 and L322. The oxygen-enriched liquid is discharged from the bottom 21 of the first distillation column 2 via pipe L21, and after heat exchange in the auxiliary cooler E2, it is introduced into the rectification section or top of the third distillation column 5. A valve V2 is installed on pipe L21 to function as a flow control valve or an on / off gate valve. Nitrogen-containing liquid (LIN) is discharged from the top 25 of the first distillation column 2 via pipe L25b, and after heat exchange in the auxiliary cooler E2, it is introduced into the upper section of the second distillation column 44. A valve V1 is installed on piping L25b, which functions as a flow control valve or an on / off gate valve. Valve V1 can also be controlled by the control unit C8. In addition, nitrogen-containing liquid (LIN) is discharged from the top 25 of the first distillation column 2 via pipe L25a and introduced into the reboiler 9. A valve V3 is installed on pipe L25a, which functions as a flow control valve, an on / off gate valve, or a pressure regulating valve. Details regarding the nitrogen-containing liquid (LIN) supplied to the reboiler 9 will be described later.

[0019] (Low-pressure distillation column) The nitrogen-containing liquid (LIN) introduced into the upper section 44 of the second distillation column 4 is distilled in the second distillation column 4. The high-purity oxygen liquid discharged from the bottom 41 of the second distillation column 4 is transported to the first condensation section 3. Argon-containing oxygen-rich material (which may be gaseous, liquid, or a gas-liquid mixture) is discharged from the lower section 42 or intermediate section 43 of the second distillation column 4 via pipe L42 and introduced into the bottom 51 or lower section 53 of the third distillation column 5 (the first crude argon distillation column).

[0020] High-purity nitrogen (GAN) is drawn from the top 45 of the second distillation column 4 via pipe L45, and after heat exchange in the auxiliary cooler E2, it is introduced into the main heat exchanger E1, and discharged as product nitrogen (Nitrogen) after heat exchange.

[0021] It is led out from the upper section of the second distillation column 44 or the intermediate distillation section 43 via the piping L43, and after heat exchange in the auxiliary cooler E2, it is introduced into the main heat exchanger E1 and discharged as exhaust gas after heat exchange. In this embodiment, the exhaust gas introduced into the main heat exchanger E1 via pipe L322 and pipe L43 (pipe L43 is also the confluence of pipe L811 from the third condensation section 8) leaves from the middle of the main heat exchanger E1 and is transported to the expansion turbine ET. After being used for turbine drive, it returns to the main heat exchanger E1 and is discharged as exhaust gas.

[0022] (Crude argon distillation column) The third distillation column 5 distills the argon-containing oxygen-enriched material to obtain an argon-enriched product. The argon-enriched product (which may be gaseous, liquid, or a gas-liquid mixture) is discharged from the upper section 53 or the top 55 of the third distillation column 5 via pipe L55 and introduced into the distillation section 73 of the fourth distillation column 7 (pure argon distillation column). The argon-containing oxygen-enriched distillate is discharged from the bottom 51 of the third distillation column 5 via pipe L51 and returned to the lower section 42 or the intermediate section 43 of the second distillation column 4. The argon-containing oxygen-enriched distillate gas (argon) is discharged from the top 55 of the third distillation column 5 via pipe L52 and transported to the second condensation section 6, where it is condensed (liquefied) and returned to the top 55. The oxygen-enriched distillate, which is discharged from the lower part of the second condensation section 6 via pipe L61, is introduced into the intermediate distillation section 43 of the second distillation column 4. The gas from the oxygen-enriched distillate discharged from the top of the second condensation section 6 is introduced into the intermediate distillation section 43 of the second distillation column 4 via pipe L62.

[0023] (Pure argon distillation column) The fourth distillation column 7 is introduced into the distillation section 73 of the third distillation column 5 or the top of the column 55 to carry out distillation. The argon-rich material (which may be gaseous, liquid or gas-liquid mixture) is introduced into the distillation section 73 for distillation. The third condensation section 8 introduces argon gas exported from the top 75 of the fourth distillation column 7. The condensed argon liquid in the third condensation section 8 returns to the fourth distillation column 7. The argon liquid stored at the bottom 71 of the fourth distillation column 7 is fed to the reboiler 9. Gas from the reboiler 9 is introduced into the fourth distillation column 7. Nitrogen-containing liquid (LIN) is introduced from the top 25 of the first distillation column 2 via pipe L25a as cooling energy for the reboiler 9. The pressure on pipe L25a is regulated and supplied via valve 3. The nitrogen-containing liquid (LIN) undergoing heat exchange in the reboiler 9 is then transported to the third condensation section 8 via inlet pipe L92. A pressure reducing valve V4 is installed on inlet pipe L92. The nitrogen-containing liquid (LIN) introduced to the third condensation section 8 is utilized as cooling energy there. From the top of the third condensation section 8, gas (nitrogen-containing gas) is transported via reflux pipe L81 to the intermediate distillation section 43 or the upper distillation section 44 of the second distillation column 4. Liquid argon (high-purity liquid argon LAr) can be taken out as product argon liquid from the bottom of reboiler 9 via outlet pipe L91.

[0024] In this embodiment, a branch pipe L811 is provided, branching from the return pipe L81. A gate valve V8 is provided on the return pipe L81, and a gate valve V7 is provided on the branch pipe L811. Control unit C8, starting from the start of the third condensation unit 8, controls the opening of gate valve V7 and closing of gate valve V8 to supply nitrogen-containing liquid (LIN) from the third condensation unit 8 to branch pipe L811 for a predetermined period. After the predetermined period, it controls the opening of gate valve V8 and closing of gate valve V7 to supply nitrogen-containing liquid (LIN) from the third condensation unit 8 to return pipe L81. "Predetermined period" is, for example, the time until stable operation, which can be set through test runs, experience, etc. "Predetermined period" also refers to the time until the nitrogen concentration in return pipe L81 reaches 99% or higher purity, as measured by a nitrogen concentration measuring unit (not shown). A specific time for the "predetermined period" is, for example, 12 hours. Branch pipe L811 merges with pipe L43, and after heat exchange in the auxiliary cooler E2, it is introduced into the main heat exchanger E1 and discharged as exhaust gas after heat exchange.

[0025] (Other implementation methods) (1) The oxygen-enriched liquid discharged from the bottom 21 of the first distillation column 2 can also be introduced into the intermediate distillation section 43 of the second distillation column 4 after heat exchange in the auxiliary cooler E2. (2) The auxiliary cooler is optional. (3) The main heat exchanger E1 is optional. Alternatively, a purification device for purifying the raw material air can be installed upstream of the main heat exchanger E1. (4) Each distillation column may also be equipped with thermometers, pressure gauges, liquid level gauges, etc. (5) Thermometers, pressure gauges, flow meters, and various valves (e.g., pressure regulating valves, flow regulating valves, gate valves) may also be installed in each piping. (6) The expansion turbine ET may also be omitted. (7) Alternatively, there may be no branch piping L811 and valve V7. (8) Control unit C8 can control all of various valves (gate valve V7, gate valve V8, etc.), or in other implementations, control units for each valve can be set up corresponding to their respective valves. Alternatively, control unit C8 can control each control unit, and each control unit can control various valves.

[0026] (Example) Simulations have confirmed that, in the configuration shown in Figure 1, compared to the comparative example where recirculation is not performed using recirculation pipe L81 and pipe L811 is used as the exhaust outlet, the nitrogen recovery rate is increased by 1% to 2% in the embodiment where recirculation is performed using recirculation pipe L81.

[0027] 1: Air separation device 2: First distillation column (high-pressure distillation column) 21: Base of the tower 23: Distillation Section 25: Top of the tower 3: First Condensation Section 4: Second distillation column (low-pressure distillation column) 41: Base of the tower 42: Lower distillation section 43: Intermediate Distillation Section 44: Upper distillation section 45: Top of the tower 5: Third distillation column (crude argon distillation column) 51: Base of the tower 53: Distillation Section 55: Top of the tower 6: Second Condensation Section 7: Fourth Distillation Column (Pure Argon Distillation Column) 71: Base of the tower 73: Distillation Section 75: Top of the tower 8: Third Condensation Section 9: Reboiler C8: Control Department E1: Main heat exchanger E2: Auxiliary Cooler ET: Expansion Turbine GAN: High-purity nitrogen gas L1:Piping L21:Piping L25a:Piping L25b:Piping L25c:Piping L32:Piping L321: Branch piping L322: Branch piping L42:Piping L43:Piping L45:Piping L51:Piping L52:Piping L55:Piping L61:Piping L62:Piping L81: Return piping L811: Branch piping L91: Outbound piping L92: Piping Inlet LAr: High-purity liquid argon LIN: Nitrogen-containing liquid V1: Valve V2: Valve V3: Valve V4: Stress Relief Methods V7: Gate Valve V8: Gate valve

Claims

1. An air separation apparatus comprising: a first distillation column for introducing feed air; a first condensation section for condensing nitrogen gas discharged from the top of the first distillation column; a second distillation column for introducing nitrogen-containing liquid discharged from the upper section or top of the rectification section of the first distillation column; a third distillation column for introducing argon-containing oxygen-rich material discharged from the lower section or intermediate section of the second distillation column; a second condensation section for condensing gas discharged from the top of the third distillation column; a fourth distillation column for introducing argon-rich material discharged from the rectification section or top of the third distillation column; a third condensation section for introducing gas discharged from the top of the fourth distillation column; and a reflux piping for refluxing gas discharged from the third condensation section back to the second distillation column. The branch pipe branches off from the aforementioned return pipe; and the control unit controls the opening and closing of the valve in a manner that supplies gas from the aforementioned third condensation unit to the aforementioned branch pipe for a predetermined period starting from the start of the drive of the aforementioned third condensation unit, and controls the opening and closing of the aforementioned valve in a manner that supplies gas from the aforementioned third condensation unit to the aforementioned return pipe after the predetermined period has elapsed.

2. A nitrogen recovery method for recovering nitrogen from a gas discharged from a third condensation section of a fourth distillation column, comprising: a first distillation column having a feedstock air introduced; a second distillation column having a nitrogen-containing liquid discharged from the upper section or top of the distillation section of the first distillation column; a third distillation column having an argon-containing oxygen-enriched compound discharged from the lower section or intermediate section of the second distillation column; a fourth distillation column having an argon-enriched compound discharged from the distillation section or top of the third distillation column; a first condensation section for condensing nitrogen gas discharged from the top of the first distillation column; a second condensation section for condensing gas discharged from the top of the third distillation column; and a third distillation column having an argon-enriched compound discharged from the lower section or intermediate section of the second distillation column; a fourth distillation column having a feedstock air introduced; a first condensation section for condensing nitrogen gas discharged from the top of the first distillation column; a second condensation section for condensing nitrogen gas discharged from the top of the third distillation column; and a third distillation column having a feedstock air introduced; a fourth distillation column having a feedstock air introduced; a second condensation section having a feedstock air introduced; a third distillation column having a feedstock air introduced; a third distillation column having a feedstock air introduced; a fourth distillation column ... The process of recovering nitrogen from the gas in the third condensation section of the distillation column and the air separation device of the reflux piping that refluxes the gas from the third condensation section back to the second distillation column; and the process of controlling the start of the drive to reflux the gas from the third condensation section back to the second distillation column after a predetermined period of time has elapsed, without refluxing the gas from the third condensation section.

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