Air separation device

Abstract

This air separation system is optimized for the mass production of nitrogen and argon, enabling efficient management of cold temperatures and mass balance by using two or more expansion turbines with different operating conditions, even when recovering large quantities of product oxygen. [Solution] The air separation apparatus comprises a main heat exchanger 1, an intermediate pressure rectification column 2, a low pressure rectification column 4, a crude argon column 5, a nitrogen condenser 3, a crude argon condenser 6, a first expansion turbine 9, and a second expansion turbine 8. The first expansion turbine 9 introduces the oxygen gas flow discharged from the low pressure rectification column 4 or the nitrogen condenser 3 into the main heat exchanger 1, discharges it from the first intermediate section, and then expands it. The second expansion turbine 8 discharges a portion of the raw material air that is discharged from the first intermediate section or from the second intermediate section which is on the warmer end side of the first intermediate section, and which is at the same temperature as or higher than the temperature of the oxygen gas flow discharged from the first intermediate section.

Description

[Technical Field]

[0001] This invention relates to an air separation apparatus, specifically a cryogenic air separation apparatus for producing nitrogen, argon, and oxygen. [Background technology]

[0002] To meet the demands of industries that use large amounts of nitrogen and argon (e.g., the semiconductor industry), cryogenic air separators have been developed that optimize nitrogen intensity while producing argon by designing the low-pressure rectification column of a compound rectification process air separation unit to a relatively high pressure of about 2 to 5 barA. In cryogenic air separators, to balance the heat balance of the apparatus, raw material air, nitrogen, oxygen-containing fluid, etc., are expanded in an expansion turbine to generate cold. Patent document 1 expands the raw material air in an expansion turbine, Patent document 2 expands the nitrogen in an expansion turbine, and Patent documents 3 and 4 expand the oxygen-containing fluid in an expansion turbine.

[0003] In particular, to maximize nitrogen recovery, it is desirable to introduce as much raw air as possible into the rectification column for nitrogen recovery. Therefore, it is desirable to use a gas that does not contribute to rectification, i.e., the gas after rectification separation, for generating cold. In the processes described in Patent Documents 3 and 4, cold is generated by expanding an oxygen-containing fluid discharged from a low-pressure rectification column. The expanded oxygen-containing fluid is used for the regeneration treatment of the purification column, which removes water and CO2 from the raw air. The flow rate required for this regeneration treatment is, for example, about 10% to 20% of the flow rate of the raw air.

[0004] In addition to nitrogen and argon, there may also be a demand for oxygen gas. In this case, it is more efficient to supply oxygen gas at high pressure from the low-pressure rectification column than to expand it in an expansion turbine and then recompress it before supplying it. However, in this case, the oxygen flow expanded in the expansion turbine decreases by the amount of oxygen gas demand, which reduces the cold generated in the expansion turbine and creates a problem in maintaining the overall heat balance of the air separation unit.

[0005] Reference 2 discloses a combination of a nitrogen turbine for expanding nitrogen and an oxygen turbine for expanding oxygen. While it is conceivable to operate the nitrogen turbine to maintain the overall heat balance of the air separation unit when the oxygen turbine load decreases, this does not solve the problem of the decrease in the oxygen flow rate, which is expanded by the oxygen turbine and used for regeneration in the refining column. Maintaining the oxygen turbine load or increasing the flow rate by mixing nitrogen into the oxygen stream for the regeneration of refined sugar would waste the energy expended to separate nitrogen and oxygen, which is undesirable, especially during steady-state operation.

[0006] Patent Document 4 discloses a configuration in which the oxygen flow and a portion of the raw material air flow merge at the inlet of the expansion turbine via an expansion valve, thereby increasing the expansion turbine flow. However, the expansion valve cannot efficiently generate cold. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Patent Publication No. 2022 / 058043 [Patent Document 2] U.S. Patent No. 11,933,538 [Patent Document 3] International Patent Publication No. 2023 / 030679 [Patent Document 4] U.S. Patent Publication No. 2020 / 318898 [Overview of the project] [Problems that the invention aims to solve]

[0008] This disclosure provides an air separation system optimized for the mass production of nitrogen and argon, which can efficiently manage cold temperatures and mass balance by using two or more expansion turbines with different operating conditions, even when recovering large quantities of product oxygen. [Means for solving the problem]

[0009] The air separation apparatus of this disclosure (A1, A2, A11, A21, B1, C1, C2) comprises a main heat exchanger (1) for cooling raw material air, a high-pressure rectification column (2) for introducing and rectifying the cooled raw material air, a low-pressure rectification column (4) for introducing and rectifying a portion of the fluid rectified in the high-pressure rectification column (2), a crude argon column (5) for introducing and rectifying a portion of the fluid rectified in the low-pressure rectification column (4), a nitrogen condenser (3) for introducing and condensing a portion of the fluid discharged from the high-pressure rectification column (5), a crude argon condenser (6) for introducing and condensing a portion of the fluid discharged from the crude argon column (5), a first expansion turbine (9), and a second expansion turbine (8). In the air separation apparatus (A1, A2, A11, A21, B1, C1, C2), the first expansion turbine (9) may expand the oxygen gas flow (after heat exchange in the subcooler (7)) that is led out from the low-pressure rectification column (4) or nitrogen condenser (3) (upper gas phase of the refrigerant storage section 32) and led out from the first intermediate section (1a) into the main heat exchanger (1). The expanded oxygen gas flow may be reintroduced into the main heat exchanger (1) and removed as waste gas.

[0010] In the aforementioned air separation devices (A1, A2, A11, A21, B1, C1, C2), the second expansion turbine (8) may expand a portion of the raw material air that is led out from the first intermediate section (1a) of the main heat exchanger (1) or from the second intermediate section (1b) on the warmer end side of the first intermediate section (1a), and whose temperature is the same as or higher than the temperature of the oxygen gas flow led out from the first intermediate section (1a). That is, it is preferable that the inlet temperature of the second expansion turbine is equal to or higher than the inlet temperature of the first expansion turbine. A portion of the expanded raw air may merge with the oxygen gas flow expanded in the first expansion turbine (9), and be reintroduced to the main heat exchanger (1) from the third intermediate section (1c), which is on the colder end side of the first intermediate section (1a), and removed as exhaust gas. In the air separation device (A11), at least a portion of the raw material air expanded by the second expansion turbine (8) may merge with the oxygen gas flow before being expanded by the first expansion turbine (9).

[0011] The air separation device (A2, A21) further includes a first air booster (81) that boosts a part of the raw material air before it is introduced into the main heat exchanger (1). A part of the boosted raw material air is introduced into the main heat exchanger (1), and may be led out from the first intermediate part (1a) or the second intermediate part (1b) on the warmer side than the first intermediate part (1a), and expanded by the second expansion turbine (8). In the air separation device (A21), at least a part of the raw material air expanded by the second expansion turbine (8) may be expanded by the first expansion turbine (9) after merging with the oxygen gas stream. The first air booster (81) may be driven by the second expansion turbine (8).

[0012] The air separation device (B1) further includes an air booster (81) that boosts a part of the raw material air before it is introduced into the main heat exchanger (1). A part of the boosted raw material air is introduced into the main heat exchanger (1), and may be led out from the first intermediate part (1a) or the second intermediate part (1b) on the warmer side than the first intermediate part (1a), and expanded by the second expansion turbine (8). A part of the raw material air expanded by the second expansion turbine (8) may be introduced into the rectification section of the low-pressure rectification column (4) (or the gas phase or rectification section of the crude argon condenser (6)) after heat exchange in the sub-cooler (7). Also, a part of the expanded raw material air may merge with the gas stream expanded by the first expansion turbine (9) and be re-introduced into the main heat exchanger (1) and taken out as waste gas. In the air separation device (B1), after merging the low-pressure nitrogen-containing gas stream led out from the rectification section (42) of the low-pressure rectification column (4) and heat-exchanged in the sub-cooler (7) with the oxygen gas stream led out from the nitrogen condenser (3) (the gas phase of the refrigerant storage section 32) and heat-exchanged in the sub-cooler (7), it may be introduced into the main heat exchanger (1). Note that the rectification section (42) may be composed of an upper rectification section (423), an intermediate rectification section (422), and a lower rectification section (421). The first air booster (81) may be driven by the second expansion turbine (8).

[0013] The air separation device (C1) further includes a second air booster (15) that pressurizes a portion of the raw material air before it is introduced into the main heat exchanger (1). The second expansion turbine (8) introduces a portion of the raw material air pressurized by the second air booster (15) into the main heat exchanger (1), and expands it after it is discharged from the first intermediate section (1a) or the second intermediate section (1b) which is on the warmer end side of the first intermediate section (1a). A portion of the raw material air expanded by the second expansion turbine (8) may be introduced into the high-pressure rectification column (2) (the lower or bottom part of the rectification section). Alternatively, a portion of the expanded raw material air may merge with the gas flow expanded by the first expansion turbine (9) and be introduced back into the main heat exchanger (1) and removed as waste gas.

[0014] The air separation device (C2) may include a second air booster (15) that pressurizes a portion of the raw material air before it is introduced into the main heat exchanger (1), and a first air booster (81) that further pressurizes a portion of the raw material air pressurized by the second air booster (15). The second expansion turbine (8) may introduce a portion of the raw material air pressurized by the second air booster (15) and the first air booster (81) into the main heat exchanger (1), and expand after being discharged from the first intermediate section (1a) or the second intermediate section (1b) on the warmer end side of the first intermediate section (1a). A portion of the raw material air expanded by the second expansion turbine (8) may be introduced into the high-pressure rectification column (2) (the lower rectification section or bottom). Alternatively, a portion of the expanded raw material air may merge with the gas flow expanded by the first expansion turbine (9) and be introduced back into the main heat exchanger (1) and removed as waste gas. The air separation device (C2) may also include a liquid transfer pump (18) for sending liquid oxygen discharged from the nitrogen condenser (3) to the main heat exchanger (1).

[0015] The air separation devices (A1, A2, A11, A21, B1, C1, C2) further include a rectification section (65) above the crude argon condenser (6), and oxygen-enriched liquid supplied from the high-pressure rectification column (2) (the bottom 21) may be supplied to the upper part of the rectification section (65). Alternatively, oxygen-enriched gas may be discharged from above the rectification section (65) and introduced into the low-pressure rectification column (4). Furthermore, the oxygen-enriched liquid (refrigerant liquid) concentrated in the crude argon condenser (6) may be introduced below the oxygen-enriched gas introduction section of the low-pressure rectification column (4).

[0016] The oxygen concentration of the oxygen gas flow introduced into the first expansion turbine (9) is preferably 20% to 100%, and more preferably 80% to 100%.

[0017] The aforementioned air separation devices (A1, A2, A11, A21, B1, C1, C2) are A main heat exchanger (1) from which feed air is introduced from the hot end and discharged from the cold end, The raw material air discharged from the cold end of the main heat exchanger (1) is introduced into the high-pressure rectification column (2) at its bottom (21), A vapor flow is introduced from the upper part (23) of the aforementioned high-pressure rectification column (2) into a nitrogen condenser (3) that condenses the vapor and discharges it as reflux liquid. A low-pressure rectification column (4) is formed in which oxygen-enriched liquid discharged from the bottom (21) of the high-pressure rectification column (2) is introduced into its rectification section (42), and / or oxygen-enriched gas discharged from the gas phase of the refrigerant storage section (32) of the nitrogen condenser (3) is introduced into its bottom (41). The raw material air introduced into the main heat exchanger (1) is led out from the second intermediate section (1b), and then expanded and cooled by a second expansion turbine (8). The system may also include a first expansion turbine (9) that introduces oxygen-enriched gas, which is discharged from the gas phase of the refrigerant storage section (32) of the nitrogen condenser (3), into the main heat exchanger (1), discharges it from the first intermediate section (1a), and then expands and cools it. The raw material air may have been pre-pressurized to a predetermined pressure and may be in a state from which impurities such as foreign matter and water have been removed.

[0018] The aforementioned air separation devices (A1, A2, A11, A21, B1, C1, C2) are The oxygen-containing fluid discharged from the rectification section (42) of the low-pressure rectification column (4) is introduced into the crude argon column (5) at its bottom (51), The system may also include a crude argon condenser (6) into which a vapor flow is introduced from the upper part (53) of the crude argon column (5), condensed, and discharged as reflux liquid. The aforementioned air separation devices (A1, A2, A11, A21, B1, C1, C2) are The system may include a subcooler (7) into which oxygen-enriched liquid discharged from the bottom (21) of the high-pressure rectification column (2) is introduced, cooled, and then discharged, and / or into which nitrogen gas discharged from the top (23) of the high-pressure rectification column (2) is introduced, cooled in the nitrogen condenser (3), and / or into which nitrogen gas discharged from the top (43) of the low-pressure rectification column (4) is introduced, heated, and then discharged.

[0019] The aforementioned air separation devices (A1, A2, A11, A21, B1, C1, C2) are A feed air line (L1) for introducing feed air to the high-pressure rectification column (2) via the main heat exchanger (1), A raw material air branch line (L11, L3211) is branched from the raw material air line (L1) in the main heat exchanger (1), and is led out from the first intermediate section (1a) or the second intermediate section (1b) on the hot end side of the first intermediate section (1a) of the main heat exchanger (1), sending a portion of the raw material air to the second expansion turbine (8), and sending a portion of the expanded raw material air back to the main heat exchanger (1) (by combining it with the oxygen gas flow expanded in the first expansion turbine (9) and sending it back from the third intermediate section (1c) on the cold end side of the first intermediate section (1a)) to be removed as waste gas. An oxygen enriched liquid piping line (L21) for introducing the oxygen enriched liquid discharged from the bottom (21) of the high-pressure rectification column (2) to the rectification section (42) of the low-pressure rectification column (4) via the subcooler (7), A branch piping line (L211) of the oxygen enriched liquid piping line (L21) is branched downstream from the subcooler (7) and is used to introduce the oxygen enriched liquid into the crude argon condenser (6) (the upper part of the refrigerant storage section (61) or the rectification section (65) of the crude argon condenser (6)), A steam flow piping line (L23) for introducing the steam flow discharged from the upper part (23) of the high-pressure rectification column (2) into the nitrogen condenser (3) for cooling, A liquid nitrogen branch piping line (L231) branches off from the steam flow piping line (L23) downstream of the nitrogen condenser (3), and a portion of the liquid nitrogen is discharged and introduced to the upper part (43) of the low-pressure rectification column (4) via the subcooler (7), A vapor flow is drawn out from the gas phase of the refrigerant storage section (32) of the nitrogen condenser (3) and introduced to the lower or bottom (41) of the rectification section of the low-pressure rectification column (4), and the oxygen-enriched liquid is refluxed through an oxygen reflux line (L32), An oxygen extraction line (L321) is branched from the oxygen reflux line (L32), introduced to the main heat exchanger (1) via the subcooler (7), heated, and then discharged to be extracted as oxygen gas (GO2). A waste gas extraction line (L3211) is branched from the oxygen extraction line (L321) in the main heat exchanger (1), led out from the first intermediate section (1a), and introduced back into the main heat exchanger (1) via the second expansion turbine (9) from the third intermediate section (1c), which is on the colder end side of the first intermediate section (1a) of the main heat exchanger (1), and led out from the hot end to be extracted as waste gas. An oxygen-containing fluid piping line (L421) is led out from the rectification section (42) of the low-pressure rectification column (4) and introduced into the bottom (51) of the crude argon column (5), A nitrogen gas piping line (L43) is led out from the upper part (43) of the low-pressure rectification column (4) and is taken out as nitrogen gas (GN2) via the subcooler (7) and the main heat exchanger (1), A bottom fluid piping line (L51) is provided from the bottom (51) of the crude argon column (5) and is used to introduce bottom fluid below the outlet position of the oxygen-containing fluid piping line (L421) of the rectification section (42) of the low-pressure rectification column (4), The argon reflux line (L53) introduces the vapor flow from the upper part (53) of the crude argon column (5) into the crude argon condenser (6) and returns the cooled reflux liquid, An argon extraction line (L531) is branched off from the aforementioned argon reflux line (L53) to extract liquefied argon, A refrigerant liquid piping line (L61) for introducing the oxygen-enriched liquid discharged from the refrigerant storage section (61) of the crude argon condenser (6) to the intermediate rectification section (422) of the low-pressure rectification column (4), A crude argon condenser piping line (L62) is used to introduce crude argon condenser liquid into the intermediate rectification section (422) of the low-pressure rectification column (4), which is located above the refrigerant liquid piping line (L61) and is led out from the upper gas phase (62) or rectification section (56) of the crude argon condenser (6). It may also be equipped with.

[0020] In an alternative embodiment, the exhaust gas extraction line (L3211) may be a piping line that branches off from the oxygen extraction line (L321) downstream of the subcooler (7) and upstream of the main heat exchanger (1), is introduced into the main heat exchanger (1), is led out from the first intermediate section (1a), and is introduced back into the main heat exchanger (1) via the first expansion turbine (9) from the third intermediate section (1c) on the colder end side of the first intermediate section (1a) of the main heat exchanger (1), is heated, and then led out to be extracted as exhaust gas.

[0021] Instead of the oxygen extraction line (L321), a second oxygen extraction line (L31) may be provided to extract the refrigerant (oxygen-enriched liquid) from the refrigerant storage section (32) of the nitrogen condenser (3) as liquefied oxygen (LOX) or oxygen gas (GO2) via the main heat exchanger (1).

[0022] The fluid introduced from the rectification section (42) of the low-pressure rectification column (4) to the crude argon column (5) is called the oxygen-containing fluid, and the liquid discharged from a point lower than the raw material air introduction stage (for example, the bottom of the high-pressure rectification column) is called the oxygen-enriched liquid. The oxygen-containing fluid may be a liquid or a gas-liquid mixture.

[0023] The aforementioned air separation devices (A1, A2, A11, A21, B1, C1, C2) are Various measuring instruments such as flow rate meters, pressure meters, temperature meters, and liquid level meters, Control valves, gate valves and other types of valves, Piping that connects each element, It may have.

[0024] (Effects and Benefits) (1) In an air separation apparatus for producing nitrogen, argon, and oxygen, cold is generated by expanding an oxygen gas stream with a higher oxygen concentration than air in an expansion turbine (first expansion turbine), and furthermore, in order to obtain more cold, a portion of the raw air is expanded in an expansion turbine (second expansion turbine). In addition, at least a portion of the outlet flow of the second expansion turbine is combined with the oxygen gas stream discharged from the low-pressure rectification column and expanded in the first expansion turbine. This makes it possible to compensate for the amount of cold generated by the first expansion turbine, which decreases as the amount of product oxygen gas discharged increases, to increase the oxygen-containing flow that regenerates the purification column that removes water and CO2 from the raw air, and by utilizing the pressure of the raw air for cold generation, a larger amount of cold can be generated and supplied to the air separation apparatus. (2) The excess cooling makes it easier to produce liquefied products (liquid nitrogen, liquid argon, liquid oxygen, etc.) from the air separation unit. (3) In a configuration equipped with an air booster, a portion of the raw material air is compressed to high pressure in the air booster, then expanded in a second expansion turbine and supplied to the high-pressure rectification column. As a result, the raw material air expanded in the second expansion turbine is separated into nitrogen, argon, and oxygen in the high-pressure and low-pressure rectification columns, and then supplied to the first expansion turbine to generate cold. In other words, since cold is generated using the gas after rectification separation, which does not contribute to rectification, the recovery rate of the product gas can be maximized. [Brief explanation of the drawing]

[0025] [Figure 1A] This is a diagram showing the air separation device of Embodiment 1. [Figure 1B]This figure shows a modified air separation device according to Embodiment 1. [Figure 2A] This is a diagram showing an air separation device according to Embodiment 2. [Figure 2B] This figure shows a modified air separation device according to Embodiment 2. [Figure 3] This is a diagram showing the air separation device of Embodiment 3. [Figure 4] This is a diagram showing the air separation device of Embodiment 4. [Figure 5] This is a diagram showing the air separation device of Embodiment 5. [Modes for carrying out the invention]

[0026] Some embodiments of the present disclosure are described below. The embodiments described below illustrate examples of the present disclosure. The present disclosure is not limited to the embodiments described below and includes various modifications that do not alter the essence of the present disclosure. Not all of the configurations described below are essential to the present disclosure. Upstream and downstream are based on the flow direction of the fluid (liquid, gas).

[0027] (Embodiment 1) The air separation apparatus A1 of Embodiment 1 will be described with reference to Figure 1A. The air separation apparatus A1 comprises a main heat exchanger 1, a high-pressure rectification column 2, a low-pressure rectification column 4, a crude argon column 5, a nitrogen condenser 3, a crude argon condenser 6, a first expansion turbine 9 (oxygen turbine), and a second expansion turbine 8 (air turbine).

[0028] The main heat exchanger 1 cools the raw material air introduced from the hot end and discharges it from the cold end. The cooled raw material air is introduced to the high-pressure rectification column 2 via the raw material air piping line L1. The high-pressure rectification column 2 comprises a bottom section 21, a rectification section 22, and an upper section 23. The raw material air piping line L1 is connected to the bottom section 21. The oxygen-enriched liquid stored in the bottom section 21 is sent via the oxygen-enriched liquid piping line L21, after heat exchange in the subcooler 7, to the intermediate rectification section 422 and the upper rectification section 423 of the low-pressure rectification column 4. After heat exchange in the subcooler 7, a portion of the oxygen-enriched liquid is introduced to the upper section of the crude argon condenser 6 via the oxygen-enriched liquid branch piping line L211. The nitrogen gas (vapor flow) discharged from the upper section 23 is introduced to the nitrogen condenser 3 via the vapor flow piping line L23, where it is cooled and returned to the upper section 23 as liquefied nitrogen (reflux). The liquefied nitrogen branch piping line L231 branches off from the steam flow piping line L23 downstream of the nitrogen condenser 3, and is a piping line that leads out a portion of the liquefied nitrogen and introduces it to the upper part 43 of the low-pressure rectification column 4 via the subcooler 7. The oxygen enrichment liquid piping line L21 is equipped with a gate valve V1, and the liquefied nitrogen branch piping line L231 is equipped with a gate valve V2.

[0029] The nitrogen condenser 3 is located above the upper part 23 of the high-pressure rectification section 2. In the nitrogen condenser 3, nitrogen gas (vapor flow) discharged from the upper part 23 of the high-pressure rectification column 2 is introduced via the vapor flow piping line L23, and is cooled (condensed) and liquefied by heat exchange with the oxygen-enriched liquid, which is the refrigerant. The liquefied liquid nitrogen returns to the upper part 23 of the high-pressure rectification column 2 as reflux liquid.

[0030] A vapor flow from the upper gas phase of the refrigerant storage section 32 of the nitrogen condenser 3 is led out via the oxygen reflux line L32 and introduced into the lower or bottom 41 of the lower rectification section 421 of the low-pressure rectification column 4, where the oxygen-enriched liquid is refluxed back into the refrigerant storage section 32. The oxygen extraction line L321 branches off from the oxygen reflux line L32 and is introduced to the main heat exchanger 1 via the subcooler 7, where it is heated and led out, and extracted as oxygen gas GO2.

[0031] The low-pressure rectification column 4 comprises a bottom section 41, a lower rectification section 421, an intermediate rectification section 422, an upper rectification section 423, and an upper section 43. The oxygen-containing fluid discharged from between the lower rectification section 421 and the intermediate rectification section 422 of the low-pressure rectification column 4 is introduced to the bottom section 51 of the crude argon column 5 via the oxygen-containing fluid piping line L421. The nitrogen gas piping line L43 is a line that extracts nitrogen gas discharged from the upper section 43 as the product nitrogen gas GN2 via the subcooler 7 and then the main heat exchanger 1.

[0032] The crude argon column 5 comprises a bottom section 51, a rectification section 52, and an upper section 53. The bottom fluid piping line L51 is led out from the bottom section 51 of the crude argon column 5 and is a line for introducing bottom fluid below the outlet position of the oxygen-containing fluid piping line L421 between the lower rectification section 421 and the intermediate rectification section 422 of the low-pressure rectification column 4. The argon reflux line L53 is a line for introducing the vapor flow from the upper section 53 of the crude argon column 5 to the crude argon condenser 6 and returning the cooled reflux liquid. The argon extraction line L531 is branched off from the argon reflux line L53 and is a line for extracting liquefied argon.

[0033] The crude argon condenser 6 receives the vapor flow from the upper part of the crude argon column 5, condenses it, and discharges it as reflux liquid. The oxygen-enriched liquid discharged from the refrigerant storage section 61 of the crude argon condenser 6 is introduced via the refrigerant liquid piping line L61 between the intermediate rectification section 422 and the upper rectification section 423 of the low-pressure rectification column 4. The crude argon condenser piping line L62 is a line for discharging the vapor flow from the upper gas phase 62 of the crude argon condenser 6 and introducing it between the intermediate rectification section 422 and the upper rectification section 423 of the low-pressure rectification column 4, which is above the refrigerant liquid piping line L61.

[0034] The subcooler 7 exchanges heat between the oxygen-enriched liquid discharged from the bottom 21 of the high-pressure rectification column 2, the liquefied nitrogen discharged from the top 23 of the high-pressure rectification column 2 and condensed in the nitrogen condenser 3, the vapor flow discharged from the nitrogen condenser 3, and the nitrogen gas discharged from the top 43 of the low-pressure rectification column 4.

[0035] The first expansion turbine 9 expands an oxygen gas flow having a higher oxygen concentration than air, generating cold. In this embodiment 1, the first expansion turbine 9 introduces an oxygen gas flow, which is drawn from the upper gas phase of the refrigerant storage section 32 of the nitrogen condenser 3 and has undergone heat exchange in the subcooler 7, into the main heat exchanger 1, where it is drawn out from the first intermediate section 1a and then expands. The expanded oxygen gas flow is introduced back into the main heat exchanger 1 and removed as waste gas. The waste gas extraction line L3211 branches off from the oxygen extraction line L321 within the main heat exchanger 1, is drawn out from the first intermediate section 1a, passes through the first expansion turbine 9, is introduced again from the cold end side of the main heat exchanger 1, and is drawn out from the hot end to be extracted as waste gas. The oxygen concentration of the oxygen gas flow introduced into the first expansion turbine 9 is preferably 20% to 100%, and more preferably 80% to 100% or more.

[0036] The second expansion turbine 8 expands a portion of the raw material air to generate cold. In this embodiment 1, the second expansion turbine 8 branches off from the raw material air line 1 in the main heat exchanger 1 and expands a portion of the raw material air that is led out from the second intermediate section 1b, which is on the warmer side of the first intermediate section 1a of the main heat exchanger 1. The expanded portion of the raw material air is combined with the oxygen gas flow expanded by the first expansion turbine 9 and sent back to the main heat exchanger 1 from the third intermediate section 1c, which is on the colder side of the first intermediate section 1a, and is removed as waste gas. The raw material air branch line L11 branches off from the raw material air line L1 in the main heat exchanger 1 and is led out from the second intermediate section 1b, which is on the warmer side of the first intermediate section 1a of the main heat exchanger 1. This line sends a portion of the raw material air to the second expansion turbine 8 and combines a portion of the expanded raw material air with the oxygen gas flow expanded by the first expansion turbine 9. After the merger, a portion of the raw air, along with the oxygen gas flow, is sent to the main heat exchanger 1 from the third intermediate section 1c (which is on the colder end side than the first intermediate section 1a) via the waste gas extraction line L3211, and is extracted as waste gas.

[0037] (Modification 1 of Embodiment 1) The air separation device A11 of the modified example 1 will be explained using Figure 1B. Reference numerals that are the same as those in Embodiment 1 have the same function, so their explanation may be omitted. The air separation device A11 is equipped with a second raw material air branch line L111 that branches off from the raw material air branch line L11 downstream of the second expansion turbine 8 and sends to the first expansion turbine 9. The second raw material air branch line L111 merges with the exhaust gas extraction line L3211, and sends a portion of the raw material air to the first expansion turbine 9 along with the oxygen gas flow, where they are both expanded. A gate valve V3 is provided in the raw material air branch line L11 downstream of the second expansion turbine 8, before it merges with the exhaust gas extraction line L3211. By closing the gate valve V3 and opening the gate valve V31 on the second raw material air branch line L111, a portion of the raw material air can be sent to the first expansion turbine 9. By opening the gate valve V3 and closing the gate valve V31 on the second raw material air branch line L111, a portion of the raw material air can be merged into the exhaust gas extraction line L3211.

[0038] (Embodiment 2) The air separation device A2 of Embodiment 3 will be described using Figure 2A. Reference numerals that are the same as those in Embodiment 1 (Figure 1A) have the same function, so their explanation may be omitted. The air separation device A2 includes a first air booster 81 that pressurizes a portion of the raw material air before it is introduced into the main heat exchanger 1. The first air booster 81 is installed in the raw material air branch line L11, which is branched off from the raw material air line 1 before it is sent to the main heat exchanger 1. The pressurized raw material air is introduced from the hot end of the main heat exchanger 1 via the raw material air branch line L11 and is led out from the second intermediate section 1b on the hot end side of the first intermediate section 1a. The led out raw material air is sent to the second expansion turbine 8, and the expanded raw material air is joined to the exhaust gas extraction line L3211. The first air booster 81 is driven by the second expansion turbine 8.

[0039] (Modification 2 of Embodiment 2) The air separation device A21 of the modified example 2 will be explained using Figure 2B. The reference numerals are the same as those in Embodiment 2 (Figure 2A) and have the same function, so their explanation may be omitted. The air separation device A21 is equipped with a second raw material air branch line L111 that branches off from the raw material air branch line L11 downstream of the second expansion turbine 8 and sends to the first expansion turbine 9. The second raw material air branch line L111 merges with the exhaust gas extraction line L3211 and sends a portion of the raw material air to the first expansion turbine 9 along with the oxygen gas flow, where they are both expanded. A gate valve V3 is provided in the raw material air branch line L11 downstream of the second expansion turbine 8, before it merges with the exhaust gas extraction line L3211. By closing the gate valve V3 and opening the gate valve V31 on the second raw material air branch line L111, a portion of the raw material air can be sent to the first expansion turbine 9. By opening the gate valve V3 and closing the gate valve V31 on the second raw material air branch line L111, a portion of the raw material air can be merged into the exhaust gas extraction line L3211.

[0040] (Embodiment 3) The air separation device B1 of Embodiment 3 will be described with reference to Figure 3. Reference numerals that are the same as those in Embodiment 2 (Figure 2A) have the same function, and therefore their explanation may be omitted. The exhaust gas extraction line L3211 branches off from the oxygen extraction line L321, which is downstream of the subcooler 7 and upstream of the main heat exchanger 1, and is introduced into the main heat exchanger 1, where it is led out from the first intermediate section 1a. The exhaust gas extraction line L3211 then functions as a piping line for extraction as exhaust gas, being introduced back into the main heat exchanger (1) via the second expansion turbine 9 from the third intermediate section 1c, which is on the cold end side of the first intermediate section 1a of the main heat exchanger 1, and led out from the hot end. Furthermore, the low-pressure column outlet line L423 is a line that connects the low-pressure nitrogen-containing gas discharged from the upper rectification section 423 of the low-pressure rectification column 4 to the waste gas extraction line L3211 before it is introduced to the main heat exchanger 1 via the subcooler 7. The raw air branch line L11 is introduced via a subcooler 7 between the intermediate rectification section 422 and the upper rectification section 423 of the low-pressure rectification column 4. This configuration allows a portion of the pressurized and expanded raw air to be sent to the low-pressure rectification column 4, in addition to being removed as waste gas. Furthermore, branch line L111, which branches off from the raw air branch line L11, merges with the waste gas removal line L3211 via a gate valve V3.

[0041] (Embodiment 4) The air separation device C1 of Embodiment 4 will be described with reference to Figure 4. Reference numerals that are the same as those in Embodiment 1 (Figure 1A) have the same function, and therefore their description may be omitted. The air separation device C1 includes a second air booster 15 that pressurizes a portion of the raw material air before it is introduced into the main heat exchanger 1. The second air booster 15 is provided in the raw material air branch line L11. A portion of the pressurized raw material air is sent via the raw material air branch line L11 to the bottom 21 of the high-pressure rectification column 2 through the main heat exchanger 1. A gate valve V4 is provided in the raw material air branch line L11. The branch line L11a branches off from the raw material air branch line L11 in the main heat exchanger 1, is led out from the second intermediate section 1b on the hot end side of the first intermediate section 1a, and sends a portion of the pressurized raw material air to the second expansion turbine 8. A portion of the expanded raw material air is sent to the bottom 21 of the high-pressure rectification column 2 via the branch line L11a. In addition, the branch line L11b, which branches off from the branch line L11a, merges with the exhaust gas extraction line L3211 via the gate valve V3.

[0042] A rectification section 65 is provided in the upper gas phase 62 of the refrigerant storage section 61 above the crude argon condenser 6. The crude argon condenser piping line L62 is a line for introducing the vapor flow from the upper part of the rectification section 65 of the crude argon condenser 6 to the area between the intermediate rectification section 422 and the upper rectification section 423 of the low-pressure rectification column 4, which is above the refrigerant liquid piping line L61.

[0043] (Embodiment 5) The air separation device C2 of Embodiment 5 will be described with reference to Figure 5. Reference numerals that are the same as those in Embodiment 4 (Figure 4) have the same function, and therefore their explanation may be omitted. The branch line L11a branches off from the raw material air branch line L11 after the second air booster 15 and upstream of the main heat exchanger 1, and sends a portion of the pressurized raw material air to the first air booster 81. A portion of the further pressurized raw material air is introduced to the main heat exchanger 1 via the branch line L11a, and is led out from the second intermediate section 1b on the hot end side of the first intermediate section 1a and sent to the second expansion turbine 8. A portion of the expanded raw material air is sent to the bottom 21 of the high-pressure rectification column 2 via the branch line L11a. In addition, the branch line L11b, which branches off from the branch line L11a, merges with the exhaust gas extraction line L3211 via the gate valve V3. In this embodiment 5, the exhaust gas extraction line L3211 branches off from the oxygen reflux line L32, is introduced to the main heat exchanger 1 via the subcooler 7, is led out from the first intermediate section 1a, and sends an oxygen gas flow to the first expansion turbine 9. Furthermore, the second oxygen extraction line L31 is a line for introducing the refrigerant (oxygen-enriched liquid) from the refrigerant storage section 32 of the nitrogen condenser 3 to the main heat exchanger 1 via the liquid transfer pump 18, heating it, and extracting it as oxygen gas (GO2).

[0044] By exchanging heat in the main heat exchanger 1 between the high-pressure raw air obtained from the second air booster 15 and the liquefied oxygen supplied from the lower part of the low-pressure rectification column 4 and pressurized by the liquid transfer pump 18, it is possible to obtain a high-pressure oxygen gas equivalent in amount to the high-pressure raw air while liquefying the high-pressure raw air. Therefore, the oxygen compressor required to raise the oxygen gas pressure above the pressure of the low-pressure rectification column 4 can be reduced. Alternatively, a portion of the raw air supplied from the first air booster 81 may be heat-exchanged with liquefied oxygen in the main heat exchanger 1. Since the outlet pressure of the first air booster 81 is higher than the outlet pressure of the second air booster 15, it is suitable for obtaining oxygen gas at a higher pressure by evaporation of liquefied oxygen. When the raw air is liquefied, the vapor flow in the high-pressure rectification column 2 is reduced, decreasing the separation efficiency of the high-pressure rectification column 2. For example, the argon concentration in the oxygen-enriched liquid decreases, reducing argon recovery. To solve this problem, a rectification section 65 is provided at the top of the crude argon condenser 6 to which the oxygen enrichment liquid is supplied, thereby concentrating the argon in the oxygen enrichment liquid, and introducing the concentrated liquid into the low-pressure rectification column 4. This prevents a decrease in the argon recovery rate.

[0045] A rectification section 65 is provided in the upper gas phase 62 of the refrigerant storage section 61 above the crude argon condenser 6. The crude argon condenser piping line L62 is a line for introducing the vapor flow from the upper part of the rectification section 65 of the crude argon condenser 6 to the area between the intermediate rectification section 422 and the upper rectification section 423 of the low-pressure rectification column 4, which is above the refrigerant liquid piping line L61.

[0046] (Example 1) The results of the physical simulation of the air separation device A1 of Embodiment 1 are shown. The raw air is introduced into the main heat exchanger 1 at 1051 Nm3 / h, 9.4 barA, and 20°C, of ​​which 1000 Nm3 is used. 3 The 51 Nm³ of 51 Nm³ is cooled to -162°C before being introduced into the high-pressure rectification column 2. 3 The gas is cooled to -55°C and then expanded to 1.4 barA in the second expansion turbine 8. The second expansion turbine 8 generates 1.43 kW of cold. The nitrogen gas that accumulates in the upper part 23 of the high-pressure rectification column 2 is liquefied by the nitrogen condenser 4, producing 426 Nm³ of liquid nitrogen. 3 The oxygen is supplied to the upper part 43 of the low-pressure rectification column 4. All or part of the oxygen-enriched liquid that accumulates at the bottom 21 of the high-pressure rectification column 2 is supplied to the crude argon condenser 6 of the crude argon column 5, and then supplied to the intermediate rectification section 422 of the low-pressure rectification column 4. Nitrogen gas is released from the upper part 43 of the low-pressure rectification column 4 at a rate of 781 Nm³. 3 The output is derived at / h, 2.7 barA, -187℃, and then heated to 18℃ in the main heat exchanger 1 before being derived. Argon-containing flow (oxygen-containing fluid) of 296 Nm³ discharged from the intermediate rectification section 422 of the low-pressure rectification column 4. 3 / h is introduced into crude argon column 5 and purified, and 8.0 Nm³ is extracted from the top of crude argon column 53. 3 / h of liquefied argon is recovered. From the bottom 41 of the low-pressure rectification column 4, oxygen gas is released at 211 Nm³. 3 The result was derived at / h, 2.8 barA, -172℃, of which 105 Nm 3 The oxygen gas at / h is heated to 18°C ​​in the main heat exchanger 1 before being discharged as product oxygen gas. Other oxygen at 106Nm3 / h is heated to -115°C in the main heat exchanger 1, then expanded to 1.4 barA in the first expansion turbine 9, and reintroduced into the main heat exchanger 1. In the first expansion turbine 9, 0.8 kW of cold is generated.

[0047] In the above configuration, in order to derive approximately half of the oxygen gas separated by the air separation device A1 as product oxygen gas, the amount of cold generated in the first expansion turbine 9 is reduced by half and becomes insufficient in the conventional method. However, by expanding a part (about 5%) of the raw air in the second expansion turbine 8, the heat balance can be maintained. The cold generated in the second expansion turbine 8 cools the warm end side of the main heat exchanger 1, so that the first expansion turbine 9 can be configured to optimize the cooling of the cold end side of the main heat exchanger 1. Further, since the operating conditions of the second expansion turbine 8 are at a higher temperature and a higher expansion ratio than those of the first expansion turbine 9, the amount of cold generated per unit volume flow rate can be increased.

[0048] (Example 2) The results of the physical simulation of the air separation device A11 of the modification 1 of the embodiment 1 are shown. The raw air is introduced into the main heat exchanger 1 at 1050 Nm 3 / h, 9.4 barA, 20°C, and among them, 1000 Nm 3 / h is cooled to -162°C and then introduced into the high-pressure rectification column 2. The other 50 Nm 3 / h is cooled to -55°C and then expanded to 2.8 barA in the second expansion turbine 8. In the second expansion turbine 8, 1.04 kW of cold is generated. The nitrogen gas accumulated in the upper part 23 of the high-pressure rectification column 2 is liquefied by the nitrogen condenser 3, and 426 Nm of liquefied nitrogen 3 / h is supplied to the upper part 43 of the low-pressure rectification column 4. All or part of the oxygen-enriched liquid accumulated at the bottom 21 of the high-pressure rectification column 2 is supplied to the intermediate rectification section 422 of the low-pressure rectification column 4 after being supplied to the crude argon condenser 6 of the crude argon column 5. From the upper part 43 of the low-pressure rectification column 4, nitrogen gas is derived at 781 Nm 3 / h, 2.7 barA, -187°C, heated to 18°C in the main heat exchanger 1 and then derived. Argon-containing flow (oxygen-containing fluid) of 296 Nm³ discharged from the intermediate rectification section 422 of the low-pressure rectification column 4. 3 / h is introduced into crude argon column 5 and purified, and 8.0 Nm³ is extracted from the upper part 53 of crude argon column 5. 3 / h of liquefied argon is recovered. From the bottom 41 of the low-pressure rectification column 4, oxygen gas is released at 211 Nm³. 3 The result was derived at / h, 2.8 barA, -172℃, of which 105 Nm 3 The oxygen gas at / h is heated to 18°C ​​in the main heat exchanger 1 before being discharged as product oxygen gas. Other oxygen gases: 106Nm 3 The water is heated to -115°C in the main heat exchanger 1, then merges with the outlet flow of the second expansion turbine 8, expands to 1.4 barA in the first expansion turbine 9, and is reintroduced to the main heat exchanger 1. In the first expansion turbine 9, 1.18 kW of cold is generated.

[0049] The above configuration maintains the heat balance by mixing a portion of the raw material air expanded in the second expansion turbine 8 with oxygen gas before expanding it in the first expansion turbine 9. This allows for the maintenance of a highly efficient operating point without reducing the load of the first expansion turbine 9, even when the amount of product oxygen gas fluctuates, and as a result, the amount of raw material air expanded in the second expansion turbine 8 can be reduced by about 2%.

[0050] (Example 3) The results of the physical simulation of the air separation device B1 of Embodiment 3 are shown. The raw material air expanded by the second expansion turbine 8 is introduced into the low-pressure rectification column 4 for separation before being supplied to the first expansion turbine 9. At this time, the outlet flow of the second expansion turbine 8 needs to be at a pressure and temperature that can be supplied to the low-pressure rectification column 4, and a higher expansion ratio is required, so a first air booster 81 is applied to pressurize the raw material air expanded by the power obtained from the second expansion turbine 8. At this time, the first air booster 81 pressurizes the air from 9.4 barA to 15.1 barA, then it is cooled in the main heat exchanger 1, and after being discharged from the main heat exchanger 1 at -115°C, it is cooled to 2.8 barA and -170°C by the second expansion turbine 8. When expanded raw material air is introduced into the low-pressure rectification column 4, the reflux liquid may decrease relatively, which may reduce the purity of the nitrogen gas. In such cases, the purity of the product nitrogen gas can be maintained by dischargeing the nitrogen-containing gas from the rectification stage at or above the raw material air supply position in the low-pressure rectification column 4. The nitrogen-containing gas may be mixed with oxygen gas and then expanded in the first expansion turbine 9.

[0051] In the above configuration, oxygen and argon from the raw material air supplied to the low-pressure rectification column 4 are condensed by liquid nitrogen descending from the upper part 43 of the low-pressure rectification column 4. Therefore, even when the raw material air is expanded, oxygen and argon can be recovered.

[0052] (Example 4) The results of the physical simulation of the air separation device C1 of Embodiment 4 are shown. Raw material air 1000 Nm 3 / h, 9.4 barA, 20℃, of which 910 Nm 3 The 90 Nm³ of heat is introduced into the main heat exchanger, cooled to -162°C, and then introduced into the high-pressure rectification column. 3 The air at / h is pressurized to 40 barA in the second air booster 15, then cooled to -110°C, and then expanded to 9.4 barA in the second expansion turbine 8 before being introduced into the high-pressure rectification column 2. The second expansion turbine 8 generates 1.2 kW of cold air. The nitrogen gas that accumulates in the upper part 23 of the high-pressure rectification column 2 is liquefied by the nitrogen condenser 3, producing 426 Nm³ of liquid nitrogen. 3The oxygen is supplied to the upper part 43 of the low-pressure rectification column 4. All or part of the oxygen-enriched liquid that accumulates at the bottom 21 of the high-pressure rectification column 2 is supplied to the crude argon condenser 6 of the crude argon column 5, and then supplied to the intermediate rectification section 422 of the low-pressure rectification column 4. Nitrogen gas is released from the upper part 43 of the low-pressure rectification column 4 at a rate of 781 Nm³. 3 The output is derived at / h, 2.7 barA, -187℃, and then heated to 18℃ in the main heat exchanger 1 before being derived. Argon-containing flow (oxygen-containing fluid) of 296 Nm³ discharged from the intermediate rectification section 422 of the low-pressure rectification column 4. 3 / h is introduced into crude argon column 5 and purified, and 8.0 Nm³ is extracted from the upper part 53 of crude argon column 5. 3 / h of liquefied argon is recovered. From the bottom 41 of the low-pressure rectification column 4, oxygen gas is released at 211 Nm³. 3 The result was derived at / h, 2.8 barA, -172℃, of which 105 Nm 3 The oxygen gas at / h is heated to 18°C ​​in the main heat exchanger 1 before being discharged as product oxygen gas. Other oxygen at 106Nm 3 The heat per hour is heated to -115°C in the main heat exchanger 1, then expanded to 1.4 barA in the first expansion turbine 9, and reintroduced to the main heat exchanger 1. The first expansion turbine 9 generates 0.8 kW of cold.

[0053] In the above configuration, a portion of the raw material air is pressurized in the second air booster 15 and then expanded in the second expansion turbine 8 to the pressure of the high-pressure rectification column 2, thereby generating cold air, so that all of the raw material air is introduced into the high-pressure rectification column 2. By doing so, all of the raw material air contributes to rectification, increasing the rectification efficiency and improving the oxygen recovery rate, which in turn increases the load on the first expansion turbine 9 and consequently reduces the consumption of raw material air. Furthermore, the high-pressure raw material air can also be used to generate high-pressure product gases by evaporating liquid nitrogen, liquid air, or liquid argon that have been pressurized by a pump. For example, liquid oxygen discharged from the low-pressure rectification column 4 can be pressurized by a pump, and heat exchange can be performed with the high-pressure raw material air inside the main heat exchanger 1 to discharge high-pressure oxygen gas.

[0054] (Another embodiment) (1) Unless otherwise specified, pressure regulators, flow rate control devices, etc. may be installed in each piping line, and pressure regulation or flow rate regulation may be performed. (2) Although not specifically stated, control valves, gate valves, etc. may be installed on each line. (3) Unless otherwise specified, each tower may be equipped with a pressure regulator, a temperature measuring device, etc., and pressure regulation or temperature regulation may be performed. [Explanation of Symbols]

[0055] 1 heat exchanger 2. High-pressure rectification column 3. Nitrogen condenser 4. Low-pressure rectification column 5. Crude Argon Tower 6. Crude Argon Condenser 8. Second expansion turbine 9. First expansion turbine

Claims

1. An air separation apparatus comprising a main heat exchanger for cooling raw material air, a high-pressure rectification column for introducing and rectifying the cooled raw material air, a low-pressure rectification column for introducing and rectifying a portion of the fluid rectified in the high-pressure rectification column, a crude argon column for introducing and rectifying a portion of the fluid rectified in the low-pressure rectification column, a nitrogen condenser for introducing and condensing a portion of the fluid discharged from the high-pressure rectification column, a crude argon condenser for introducing and condensing a portion of the fluid discharged from the crude argon column, a first expansion turbine, and a second expansion turbine, The first expansion turbine introduces the oxygen gas flow, which is discharged from the low-pressure rectification column or the nitrogen condenser, into the main heat exchanger and then expands after being discharged from the first intermediate section. The second expansion turbine is led out from the first intermediate section of the main heat exchanger or from the second intermediate section on the warmer end side of the first intermediate section, and expands a portion of the raw air that is at the same temperature as or higher than the temperature of the oxygen gas flow led out from the first intermediate section. Air separation device.

2. The system further includes a first air booster that pressurizes a portion of the raw air before it is introduced into the main heat exchanger. An air separation apparatus according to claim 1, wherein a portion of the pressurized raw material air is introduced to the main heat exchanger, is discharged from the first intermediate section or the second intermediate section on the warmer end side of the first intermediate section, is expanded by the second expansion turbine, and the first air booster is driven by the second expansion turbine.

3. At least a portion of the raw material air expanded by the second expansion turbine merges with the oxygen gas flow and is then expanded by the first expansion turbine. The air separation device according to claim 1.

4. The system further includes a first air booster that pressurizes a portion of the raw air before it is introduced into the main heat exchanger. A portion of the pressurized raw air is introduced into the main heat exchanger, exited from the first intermediate section or the second intermediate section on the warmer side of the first intermediate section, and expanded by the second expansion turbine; the first air booster is driven by the second expansion turbine; A portion of the raw material air expanded by the second expansion turbine is introduced into the low-pressure rectification column or crude argon condenser. The air separation device according to claim 1.

5. The system includes a second air booster that pressurizes a portion of the raw air before it is introduced into the main heat exchanger. The second expansion turbine introduces a portion of the raw air pressurized by the second air booster into the main heat exchanger, and after it is discharged from the first intermediate section or the second intermediate section on the warmer end side of the first intermediate section, it expands. A portion of the raw material air expanded by the second expansion turbine is introduced into the high-pressure rectification column. The air separation device according to claim 1.

6. The system includes a second air booster that pressurizes a portion of the raw material air before it is introduced into the main heat exchanger, and a first air booster driven by the second expansion turbine that further pressurizes a portion of the raw material air pressurized by the second air booster. The air separation apparatus according to claim 1, wherein the second expansion turbine introduces a portion of the raw material air pressurized by the second air booster and the first air booster to the main heat exchanger, and expands after being discharged from the first intermediate section or the second intermediate section on the warmer end side of the first intermediate section.

7. The air separation apparatus according to any one of claims 1 to 6, further comprising a liquid transfer pump for sending liquid oxygen discharged from the nitrogen condenser to the main heat exchanger.

8. The air separation apparatus according to any one of claims 1 to 6, further comprising a subcooler for cooling the oxygen-enriched liquid discharged from the high-pressure rectification column or the liquid nitrogen discharged from the nitrogen condenser.

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