Air separation method and air separation device

Abstract

An object of the present invention is to provide an air separation method and an air separation device that can improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate. The air separation method includes: a high-pressure separation step for separating high-pressure raw air; a turbine air production step for producing middle-pressure turbine air; a turbine air compression step for producing high-pressure turbine air; a turbine air adiabatic expansion step for producing low-pressure turbine air; a low-pressure separation step for separating the low-pressure turbine air; an argon separation step for separating the argon-enriched liquefied oxygen; an argon condensation step for producing liquified argon and low-pressure oxygen gas; a high-pressure nitrogen condensation step for producing high-pressure liquefied nitrogen and middle-pressure oxygen gas; and a product argon leading out step for leading out a product argon, wherein, in the turbine air compression step, the middle-pressure turbine air is compressed using energy generated by the turbine air adiabatic expansion step, and wherein the air separation method further includes a raw air bypass step in which a part of the high-pressure raw air is separated, decompressed, and mixed with the high-pressure turbine air.

Description

TECHNICAL FIELD

[0001] The present invention relates to an air separation method and air separation device.BACKGROUND ART

[0002] Conventionally, as a method for industrially producing oxygen or nitrogen, a method (air separation method) in which oxygen or nitrogen is produced by low-temperature distillation using air as a raw material and an apparatus (air separation device) used therein are generally known.

[0003] For example, Patent Document 1 proposes an air separation method using an air separation device including a high-pressure column, a low-pressure column, an argon column, an indirect heat-exchanger that performs indirect heat-exchange between low-pressure liquefied oxygen in the bottom portion of the low-pressure column and argon gas in the top portion of the argon column, and an indirect heat-exchanger that performs indirect heat-exchange between middle-pressure liquefied oxygen in the bottom portion of the argon column and high-pressure nitrogen gas in the top portion of the high-pressure column. According to Patent Document 1, it is possible to recover more product high-pressure nitrogen gas while maintaining or improving the argon recovery rate, and it is possible to reduce the power consumption of the entire device including the power for pumping the product gas.

[0004] In addition, FIG. 1 of Patent Document 1 discloses a device in which high-pressure oxygen-enriched liquified air led out from a bottom portion of a high-pressure column is decompressed and then vaporized in an indirect heat-exchanger to produce middle-pressure oxygen-enriched air, which is then compressed in a turbine blower and adiabatically expanded in an expansion turbine, and supplied into a low-pressure column. According to Patent Document 1, as described above, by using oxygen-enriched air by the expansion turbine, the oxygen concentration of the air supplied into the low-pressure column is increased, and the argon recovery rate is also improved, compared to a case where a part of the raw air is used by the expansion turbine.

[0005] Generally, a cryogenic air separation device such as that disclosed in Patent Document 1 requires an expansion turbine to produce cold as described above, and as the amount of liquid product increases, the amount of cold required also increases, so the processing flow rate of the expansion turbine increases. On the other hand, in the case of a general air separation device configured to supply air adiabatically expanded by the expansion turbine into a low-pressure column, if the flow rate of the low-pressure air produced by the expansion turbine (low-pressure turbine air) increases too much, the argon recovery rate tends to decrease due to the decrease in the ascending gas in the bottom portion of the low-pressure column.

[0006] As a means for suppressing the decrease in the argon recovery rate, Patent Document 2 discloses a method for optimizing the flow rate of the low-pressure turbine air which is supplied into an upper column by mixing a part or all of the low-pressure turbine air with a return low-temperature gas generated in the upper column for recovery.PRIOR ART DOCUMENTSPatent DocumentsPatent Document 1: Japanese Patent No. 6155515

[0008] Patent Document 2: Japanese Examined Patent Application, Second Publication No. Sho 60-44587SUMMARY OF INVENTIONProblem to be Solved by the Invention

[0009] The air separation device disclosed in Patent Document 1 is capable of recovering more product high-pressure nitrogen gas while maintaining or improving the argon recovery rate, and is also capable of reducing the power consumption of the entire device. On the other hand, the air separation device disclosed in Patent Document 1 has a lower pressure at an inlet of the expansion turbine and a smaller expansion ratio than when raw air is used as the processing fluid for the expansion turbine, so that the processing volume is greater even when the same amount of cold is generated. For this reason, the air separation device of Patent Document 1 has a problem in that, particularly when the amount of liquid product is large and the amount of cold required to operate the air separation device is large, the amount of fluid to be processed by the expansion turbine becomes excessive, and the argon recovery rate drops significantly.

[0010] In the case of an air separation device in which a part of raw air is used for the expansion turbine, it is possible to suppress a decrease in the argon recovery rate by optimizing the amount of the low-pressure turbine air, for example, by the method disclosed in Patent Document 2. However, when oxygen-enriched air is used for the expansion turbine, since a part of the oxygen-enriched air, which is richer in oxygen and argon components than those of raw air, is not supplied into the low-pressure column, and is recovered (released to the atmosphere) as a return gas, there is a problem in that it actually becomes a factor that reduces the oxygen recovery rate and the argon recovery rate.

[0011] The present invention has been made in consideration of the above problems, and has an object to provide an air separation method and an air separation device that can improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate.Means for Solving the Problem

[0012] In order to solve the above problem, the inventors have conducted extensive research into a device in which middle-pressure turbine air, which is oxygen-enriched air, is produced by decompressing high-pressure oxygen-enriched liquified air led out from the bottom portion of a high-pressure column, vaporizing it by indirect heat-exchange, and then compressed by a turbine blower, adiabatically expanded by an expansion turbine, and then supplied into a low-pressure column. As a result, they discovered that by separating a part of the raw air and mixing it with high-pressure turbine air, which is oxygen-enriched air, at the inlet of the expansion turbine, it is possible to reduce the flow rate of the fluid to be processed by the expansion turbine while maintaining the amount of cold being generated, or increase the amount of cold being generated while maintaining the flow rate of the fluid to be processed by the expansion turbine.

[0013] It has been found that this makes it possible to improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate, and thus the present invention has been completed.

[0014] That is, in order to solve the above problems, the following air separation methods and air separation devices are provided.

[0015] [1] An air separation method, including: a high-pressure separation step in which high-pressure raw air which has been obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon is cooled and then low-temperature distilled to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a turbine air production step in which middle-pressure oxygen-enriched liquified air which has been obtained by decompressing the high-pressure oxygen-enriched liquefied air is vaporized to produce middle-pressure turbine air; a turbine air compression step in which the middle-pressure turbine air which has been heated is compressed to produce high-pressure turbine air; a turbine air adiabatic expansion step in which the high-pressure turbine air is adiabatically expanded to produce low-pressure turbine air and generate cold required for an air separation operation; a low-pressure separation step in which the low-pressure turbine air is low-temperature distilled to separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen; an argon separation step in which the argon-enriched liquefied oxygen which has been pressurized is low-temperature distilled at a pressure higher than that in the low-pressure separation step to separate it into argon gas and middle-pressure liquefied oxygen; an argon condensation step in which by indirect heat-exchange between the argon gas and the low-pressure liquefied oxygen, the argon gas is liquefied to produce liquified argon and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas; a high-pressure nitrogen condensation step in which by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure liquefied oxygen, the high-pressure nitrogen gas is liquefied to produce high-pressure liquified nitrogen, and the middle-pressure liquefied oxygen is vaporized to produce middle-pressure oxygen gas; and a product argon leading out step in which at least one of a part of the argon gas, the argon gas not liquefied in the argon condensation step, and a part of the liquefied argon is led out as a product, wherein, in the turbine air compression step, the middle-pressure turbine air is compressed using energy generated by the turbine air adiabatic expansion step, and wherein the air separation method further includes a raw air bypass step in which a part of the high-pressure raw air is separated, decompressed, and mixed with the high-pressure turbine air.

[0016] [2] The air separation method according to [1], wherein, in the turbine air production step, by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure oxygen-enriched liquified air, the high-pressure nitrogen gas is liquefied to produce high-pressure liquefied nitrogen, and the middle-pressure oxygen-enriched liquified air is vaporized to produce the middle-pressure turbine air.

[0017] [3] The air separation method according to [1], wherein, in the turbine air production step, by indirect heat-exchange between high-pressure nitrogen-enriched air produced in the intermediate stage of the high-pressure separation step and the middle-pressure oxygen-enriched liquified air, the high-pressure nitrogen-enriched air is liquefied to produce high-pressure nitrogen-enriched liquefied air, and the middle-pressure oxygen-enriched liquified air is vaporized to produce the middle-pressure turbine air.

[0018] [4] The air separation method according to [1], wherein, in the turbine air production step, by indirect heat-exchange between the high-pressure raw air and the middle-pressure oxygen-enriched liquefied air, the high-pressure raw air is liquified to produce high-pressure liquefied air, and the middle-pressure oxygen-enriched liquefied air is vaporized to produce the middle-pressure turbine air.

[0019] [5] The air separation method according to any of [1] to [4], wherein, in the raw air bypass step, a flow rate of the high-pressure raw air which has been separated from the high-pressure raw air is indirectly adjusted by controlling the pressure after decompression.

[0020] [6] An air separation device, including: a high-pressure column in which high-pressure raw air which has been obtained by compressing, pre-cooling, purifying and cooling air containing oxygen, nitrogen, and argon is low-temperature distilled to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a turbine air-evaporator in which middle-pressure oxygen-enriched liquefied air which has been obtained by decompressing the high-pressure oxygen-enriched liquefied air is evaporated to produce middle-pressure turbine air; a turbine blower in which the middle-pressure turbine air which has been heated is compressed to produce high-pressure turbine air; an expansion turbine in which the high-pressure turbine air is adiabatically expanded to produce low-pressure turbine air and generate cold required for an air separation operation; a low-pressure column in which the low-pressure turbine air is low-temperature distilled to separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen; an argon column in which the argon-enriched liquefied oxygen which has been pressurized is low-temperature distilled at a pressure higher than that of the low-pressure column to separate it into argon gas and middle-pressure liquefied oxygen; an argon condenser in which the argon gas is liquefied to produce liquefied argon and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas by indirect heat-exchange between the argon gas and the low-pressure liquefied oxygen; a high-pressure nitrogen condenser in which the high-pressure nitrogen gas is liquefied to produce high-pressure liquefied nitrogen and the middle-pressure liquefied oxygen is vaporized to produce middle-pressure oxygen gas by indirect heat-exchange between the high-pressure nitrogen gas and middle-pressure liquefied oxygen; and lines which lead out at least one of a part of the argon gas, the argon gas which has not been liquefied in the argon condenser and the liquefied argon in the argon condenser as product argon gas or product liquefied argon, wherein the turbine blower is driven by rotational energy generated by the expansion turbine, and wherein the air separation device further includes a raw air bypass which separates a part of the high-pressure raw air, after decompression of the high-pressure raw air, then mixes with the high-pressure turbine.

[0021] [7] The air separation device according to [6], wherein the turbine air evaporator liquefies the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizes the middle-pressure oxygen-enriched liquified air to produce the middle-pressure turbine air by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure oxygen-enriched liquified air.

[0022] [8] The air separation device according to [6], wherein the turbine air evaporator liquefies high-pressure nitrogen-enriched air which has been produced in a middle section of the high-pressure column to produce high-pressure nitrogen-enriched liquefied air, and vaporizes the middle-pressure oxygen-enriched liquified air to produce the middle-pressure turbine air, by indirect heat-exchange between the high-pressure nitrogen-enriched air and the middle-pressure oxygen-enriched liquified air.

[0023] [9] The air separation device according to [6], wherein the turbine air evaporator liquefies the high-pressure raw air to produce high-pressure liquefied air, and vaporizes the middle-pressure oxygen-enriched liquefied air to produce the middle-pressure turbine air, by indirect heat-exchange between the high-pressure raw air and the middle-pressure oxygen-enriched liquefied air.

[0024]

[10] The air separation device according to any one of [6] to [9], wherein the air separation device further includes a raw air bypass valve which is provided on the raw air bypass line and which can indirectly adjust a flow rate of the high-pressure raw air which has been separated from the high-pressure raw air by controlling the pressure of the high-pressure raw air after decompression.Effects of the Invention

[0025] As described above, the air separation method according to the present invention includes the turbine air production step in which the middle-pressure turbine air is produced, and the turbine air compression step in which the high-pressure turbine air is produced, and further includes the raw air bypass step in which a part of the high-pressure raw air is separated, decompressed, and mixed with the high-pressure turbine air. In this way, by separating a part of the high-pressure raw air and mixing it with the high-pressure turbine air, which is oxygen-enriched air, it is possible to reduce the flow rate of the fluid to be processed by the expansion turbine while maintaining the amount of cold being generated, or increase the amount of cold being generated while maintaining the flow rate of fluid to be processed by the expansion turbine 24.

[0026] The air separation device the present invention is an air separation device in which the high-pressure oxygen-enriched liquified air led out from the bottom portion of the high-pressure column is decompressed, vaporized by the indirect heat-exchange to produce the middle-pressure turbine air, which is the oxygen-enriched air, and the middle-pressure turbine air is compressed by the turbine blower, then adiabatically expanded by the expansion turbine and supplied into the low-pressure column, wherein the air separation device further includes the raw air bypass line which mixes a part of the high-pressure raw air which has been decompressed with the high-pressure turbine air. By providing such a raw air bypass line, similar to the air separation method above, it is possible to reduce the flow rate of the fluid to be processed by the expansion turbine while maintaining the amount of cold being generated, or increase the amount of cold being generated while maintaining the flow rate of the fluid to be processed by the expansion turbine.

[0027] Therefore, it is possible to improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate, as with the air separation method above.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a schematic diagram showing an air separation method and an air separation device according to one embodiment of the present invention, and is a system diagram showing the general configuration of the entire air separation device.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, an air separation method and air separation device, which are one embodiment of the present invention, will be described below with reference to FIG. 1.

[0030] Note that the drawings used in the following description may show characteristic parts in an enlarged or simplified form for the sake of making the features easier to understand. Furthermore, the materials exemplified in the following description are merely examples, although the present invention is not limited thereto. Appropriate modifications can be made within the scope of the present invention.<Air Separation Device>

[0031] The following is a detailed description of an air separation device that can be used in the operation of the air separation method of the present embodiment.

[0032] FIG. 1 is a system diagram showing the entire schematic configuration of an air separation device 10 of the present embodiment.

[0033] In the description of the present embodiment, “low pressure” refers to a pressure that is equal to or lower than the operating pressure of the low-pressure column 18, which will be described in detail later, and is equal to or lower than 400 kPaA. In addition, “middle-pressure” refers to a pressure that is equal to or lower than the pressure of the fluid having the highest pressure among middle-pressure oxygen gas produced by vaporization in a high-pressure nitrogen condenser H2 and middle-pressure turbine air produced by vaporization in the turbine air-evaporator H3, and is higher than the operating pressure of the low-pressure column. Furthermore, “high pressure” refers to a pressure that is higher than the pressure of fluid having the highest pressure among the middle-pressure oxygen gas produced by vaporization in the high-pressure nitrogen condenser H2 and the middle-pressure turbine air produced by vaporization in the turbine air-evaporator H3.

[0034] As shown in FIG. 1, the air separation device 10 of the present embodiment includes a main air compressor 11, an air precooler 12, an air purifier 13, a booster air compressor 14, a booster air compressor aftercooler 15, a main heat-exchanger 16, a high-pressure column 17, a low-pressure column 18, an argon column 19, an outer cylinder 20 of a turbine air-evaporator, a subcooler 21, a turbine blower 22, a turbine blower aftercooler 23, an expansion turbine 24, a liquefied oxygen pump 25, an argon-enriched liquefied oxygen pump 26, an argon condenser H1, a high-pressure nitrogen condenser H2, a turbine air-evaporator H3, lines L1, L2, L4-L6, L8-L18, L20-L24, L31-L35, L51, L52, L71, L72, L191, and L192, and valves V1-V8. The air separation device 10 of the present embodiment further includes a raw air bypass line L25 and a raw air bypass valve V9.

[0035] The main air compressor 11 is provided on the line L1. The main air compressor 11 is connected with a raw air supply source, not shown, that supplies air (raw air) containing oxygen, nitrogen, and argon, and the air precooler 12 through the line L1. The main air compressor 11 compresses air containing oxygen, nitrogen, and argon. The air (raw air) compressed by the main air compressor 11 is transported into the air precooler 12 through the line L1.

[0036] One end of the line L1 is connected to the raw air supply source not shown, and the other end is connected to a bottom portion of the high-pressure column 17. A part of the line L1 passes through the main heat-exchanger 16. Through the line L1, air from the raw air supply source not shown is compressed by the main air compressor 11, precooled by the air precooler 12, and purified by the air purifier 13 to produce high-pressure raw air, the generated high-pressure raw air is cooled by the main heat-exchanger 16 and then supplied into the high-pressure column 17.

[0037] The air precooler 12 is provided on the line L1 located between the main air compressor 11 and the air purifier 13. The air precooler 12 is connected to the main air compressor 11 and the air purifier 13 through the line L1. The air precooler 12 removes the compression heat of the air compressed by the main air compressor 11. The air from which the compression heat has been removed by the air precooler 12 is supplied into the air purifier 13 through the line L1.

[0038] The air purifier 13 is provided on the line L1 located between the air precooler 12 and a branching position of the line L2. The air purifier 13 is connected to the air precooler 12 and the main heat-exchanger 16 through the line L1. The air purifier 13 removes impurities, specifically, water and carbon dioxide, contained in the air from which the heat of compression has been removed by the air precooler 12, to produce high-pressure raw air. The high-pressure raw air from which impurities have been removed by the air purifier 13 is supplied into a bottom portion of the high-pressure column 17 through the line L1 and the main heat-exchanger 16, and is also supplied into the booster air compressor 14 through the line L2 branched off from the line L1, and is further supplied into the line L51 through the raw air bypass line L25 branched off from the line L1.

[0039] The line L2 is branched off from the line L1 located between the air purifier 13 and the main heat-exchanger 16, and one end of the line L2 is connected to the lower portion of the high-pressure column 17. A part of the line L2 passes through the main heat-exchanger 16, and the valve V4 is provided on the line L2. Through the line L2, a part of the high-pressure raw air which has been purified in the air purifier 13 is compressed in the booster air compressor 14, pre-cooled in the booster air compressor aftercooler 15, cooled in the main heat-exchanger 16, decompressed by the valve V4, and then supplied into the high-pressure column 17.

[0040] The booster air compressor 14 is provided on the line L2 located between the branch point of the line L2 from the line L1 and the booster air compressor aftercooler 15. The booster air compressor 14 further compresses a part of the high-pressure raw air from which the impurities have been removed to produce pressurized raw air. The pressurized raw air which has been compressed by the booster air compressor 14 is transported into the booster air compressor aftercooler 15 through the line L2.

[0041] The booster air compressor aftercooler 15 is provided on the line L2 located downstream of the booster air compressor 14. The booster air compressor aftercooler 15 removes heat of compression from the pressurized raw air compressed by the booster air compressor 14. The pressurized raw air cooled by the booster air compressor aftercooler 15 passes through the line L2, the main heat-exchanger 16, and the valve V4 to become high-pressure raw liquefied air, and is supplied into the lower portion of the high-pressure column 17.

[0042] The valve V4 is provided on the line L2 located between the main heat-exchanger 16 and the high-pressure column 17. The valve V4 decompresses the pressurized raw air cooled by the booster air compressor aftercooler 15 and the main heat-exchanger 16 to produce high-pressure raw liquefied air.

[0043] The main heat-exchanger 16 is installed so that a part of the lines L1, L2, L5, L51, L8, L13, L14, L16, and L20 pass through it. The main heat-exchanger 16 performs indirect heat-exchange between high-temperature fluid flowing through the lines L1, L2, and L51 and low-temperature fluid flowing through the lines L5, L8, L13, L14, L16, and L20 to cool the high-temperature fluids and heat the low-temperature fluids.

[0044] The high-pressure column 17 is connected to the lines L1, L2, and L72. The high-pressure column 17 performs low-temperature distillation on a part of the high-pressure raw air which is obtained by compressing, pre-cooling, purifying, and cooling air containing oxygen, nitrogen, and argon and supplied from the line L1, the high-pressure raw liquefied air which is supplied from the line L2, and high-pressure liquefied nitrogen which is supplied from the line L72, to separate them into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air.

[0045] In the high-pressure column 17, the high-pressure nitrogen gas is concentrated in the upper portion of the high-pressure column 17, and the high-pressure oxygen-enriched liquified air is concentrated in the lower portion of the high-pressure column 17 by the low-temperature distillation.

[0046] One end of the line L71 is connected to the top portion of the high-pressure column 17, and the other end is connected to the liquefaction passage inlet of the high-pressure nitrogen condenser H2. The line L71 supplies the high-pressure nitrogen gas concentrated in the upper portion of the high-pressure column 17 into the high-pressure nitrogen condenser H2.

[0047] The high-pressure nitrogen condenser H2 is housed in the bottom portion of the argon column 19, a liquefaction passage inlet thereof is connected to the line L71 and a liquefaction passage outlet thereof is connected to the line L72. The high-pressure nitrogen condenser H2 performs indirect heat-exchange between the high-pressure nitrogen gas supplied from the line L71 and the middle-pressure liquefied oxygen in the bottom portion of the argon column 19, thereby liquefying the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen, and vaporizing the middle-pressure liquefied oxygen to produce middle-pressure oxygen gas.

[0048] The line L8 is branched off from the line L71. A part of the line L8 passes through the main heat-exchanger 16. The line L8 is a line for recovering a part of the high-pressure nitrogen gas as product high-pressure nitrogen gas (HPGN2) after heat recovery in the main heat-exchanger 16.

[0049] One end of the line L72 is connected to the liquefaction passage outlet of the high-pressure nitrogen condenser H2, and the other end is connected to the top portion of the high-pressure column 17. The line L72 supplies the high-pressure liquefied nitrogen produced in the high-pressure nitrogen condenser H2 into the high-pressure column 17.

[0050] The line L9 is branched off from the line L72 and connected to the top portion of the low-pressure column 18. A part of the line L9 passes through the subcooler 21, and is provided with the valve V6. Through the line L9, a part of the high-pressure liquefied nitrogen produced in the high-pressure nitrogen condenser H2 is cooled in the subcooler 21, the pressure thereof is reduced by the valve V6, and then supplied into the low-pressure column 18.

[0051] The valve V6 is provided on the line L9 located between the low-pressure column 18 and the subcooler 21. The valve V6 decompresses the high-pressure liquefied nitrogen flowing through the line L9.

[0052] The line L10 is branched off from the line L9. The line L10 is a line for recovering a part of the high-pressure liquefied nitrogen as product high-pressure liquefied nitrogen (HPLN2).

[0053] One end of the line L11 is connected to the middle or lower portion of the high-pressure column 17, and the other end is connected to the middle or upper portion of the low-pressure column 18. A part of the line L11 passes through the subcooler 21, and the valve V7 is provided. The line L11 leads out a part of fluid descending in the middle or lower portion of the high-pressure column 17. Through the line 11, the fluid is cooled in the subcooler 21, decompressed by the valve V7, and supplied into the low-pressure column 18.

[0054] The valve V7 is provided on the line L11 located between the low-pressure column 18 and the subcooler 21. The valve V7 decompresses the fluid flowing through the line L11.

[0055] One end of the line L4 is connected to the bottom portion of the high-pressure column 17, and the other end is connected to the outer cylinder 20 of the turbine air-evaporator H3. The valve V1 is provided on the line LA. Through the line LA, the high-pressure oxygen-enriched liquified air which has been led out from the high-pressure column 17 is decompressed by the valve V1 to produce middle-pressure oxygen-enriched liquified air and the middle-pressure oxygen-enriched liquified air is supplied into the outer cylinder 20 of the turbine air-evaporator H3.

[0056] The valve V1 is provided on the line L4. The valve V1 decompresses the high-pressure oxygen-enriched liquified air flowing through the line LA to produce the middle-pressure oxygen-enriched liquified air.

[0057] As shown by the dashed line in FIG. 1, it is also possible to lead out a part of the high-pressure oxygen-enriched liquified air through line L12 branched off from the line L4, cool it in the subcooler 21, decompressed by the valve V3, and then supply it to the low-pressure column 18.

[0058] One end of the line L31 is connected to the upper portion of the high-pressure column 17, and the other end is connected to the liquefaction passage inlet of the turbine air-evaporator H3. The line L31 leads out the high-pressure nitrogen gas concentrated in the upper portion of the high-pressure column 17 and supplies it into the turbine air-evaporator H3.

[0059] Instead of leading out the high-pressure nitrogen gas from the upper portion of the high-pressure column 17 through the line L31, it is also possible to lead out a part of the high-pressure raw air through the line L33 branched from the line L1 and supply it into the turbine air-evaporator H3, as shown by the dashed line in FIG. 1, or to lead out the high-pressure nitrogen-enriched air ascending in the middle or lower portion of the high-pressure column 17 through the line L34, one end of which is connected to the middle or lower portion of the high-pressure column 17, and supply it into the turbine air-evaporator H3.

[0060] The outer cylinder 20 of the turbine air-evaporator H3 is connected to the one end of the line L4, and houses the turbine air-evaporator H3 inside. The outer cylinder 20 of the turbine air-evaporator H3 can store the middle-pressure oxygen-enriched liquified air supplied from the line L4.

[0061] The turbine air-evaporator H3 is housed in the outer cylinder 20, and its liquefaction passage inlet is connected to one end of the line L31. The turbine air-evaporator H3 performs indirect heat-exchange between the high-pressure nitrogen gas supplied from the line L31 and the middle-pressure oxygen liquefied air supplied from the line L4, thereby liquefying the high-pressure nitrogen gas supplied from the line L31 to produce high-pressure liquefied nitrogen, and vaporizing the middle-pressure oxygen-enriched liquified air supplied from the line L4 and stored inside the outer cylinder 20 of the turbine air evaporator H3 to produce middle-pressure turbine air.

[0062] One end of the line L32 is connected to the liquefaction passage outlet of the turbine air-evaporator H3, and the other end is connected to the upper portion of the low-pressure column 18. A part of the line L32 passes through the subcooler 21, and is provided with the valve V5. Through the line L32, the high-pressure liquefied nitrogen generated in the turbine air-evaporator H3 is cooled in the subcooler 21, decompressed by the valve V5, and then supplied into the low-pressure column 18.

[0063] In the present embodiment, as shown by the dashed line in FIG. 1, it is also possible to provide the line L35 that is branched off from the line L32 located between the liquefaction passage outlet of the turbine air-evaporator H3 and the subcooler 21, and has one end connected to the upper portion of the high-pressure column 17. The line L35 supplies all or a part of the high-pressure liquefied nitrogen flowing through the line L32 into the high-pressure column 17.

[0064] The valve V5 is provided on the line L32 located between the low-pressure column 18 and the subcooler 21. The valve V5 decompresses the high-pressure liquefied nitrogen flowing through the line L32.

[0065] One end of the line L5 is connected to the gas outlet of the outer cylinder 20 of the turbine air-evaporator H3, and the other end is connected to the turbine blower 22. A part of the line L5 passes through the main heat-exchanger 16.

[0066] Through the line L5, the middle-pressure turbine air generated in the turbine air-evaporator H3 housed inside the outer cylinder 20 is supplied into the turbine blower 22 after heat recovery in the main heat-exchanger 16.

[0067] The turbine blower 22 is connected to one end of the line L5. The turbine blower 22 further compresses the middle-pressure turbine air transported through the line L5 to produce high-pressure turbine air. The turbine blower 22 is rotationally driven by the rotational energy generated by the expansion turbine 24 described later.

[0068] One end of the line L51 is connected to the turbine blower 22, and the other end is connected to the expansion turbine 24. In the illustrated example, the line L51 is provided with the turbine blower aftercooler 23, and a part of the line L51 passes through the main heat-exchanger 16. Through the line L51, the high-pressure turbine air compressed by the turbine blower 22 is supplied into the expansion turbine 24 after being cooled by the turbine blower aftercooler 23 and the main heat-exchanger 16.

[0069] The turbine blower aftercooler 23 is provided on the line L51 located between the turbine blower 22 and the main heat-exchanger 16. The turbine blower aftercooler 23 removes heat of compression of the high-pressure turbine air compressed by the turbine blower 22.

[0070] The expansion turbine 24 is connected to one end of the line L51. The expansion turbine 24 adiabatically expands the high-pressure turbine air that has passed through the turbine blower aftercooler 23 and the main heat-exchanger 16 to produce the cold needed to operate the device, and also produces the low-pressure turbine air.

[0071] The expansion turbine 24 uses the rotational energy generated by the expansion turbine 24 to rotate the turbine blower 22.

[0072] One end of the line L52 is connected to the outlet of the expansion turbine 24, and the other end is connected to the middle part of the low-pressure column 18. The line L52 supplies the low-pressure turbine air generated by the expansion turbine 24 into the middle portion of the low-pressure column 18.

[0073] One end of line L6 is connected to the liquid outlet of the outer cylinder 20 of the turbine air evaporator H3, and the other end is connected to the middle portion of the low-pressure column 18. The valve V2 is provided on the line L6. The line L6 supplies the middle-pressure oxygen-enriched liquified air that is not vaporized in the turbine air-evaporator H3 housed inside the outer cylinder 20 into the low-pressure column 18 after reducing the pressure by the valve V2.

[0074] The valve V2 is provided on the line L6. The valve V2 decompress the fluid flowing through the line L6.

[0075] To the low-pressure column 18, one end of the line L9, the line L32, the line L11, the line L52, and the line L6 is connected, and the low-pressure column 18 houses the argon condenser H1 in the lower portion thereof. The low-pressure column 18 performs low-temperature distillation on the fluid decompressed by the valve V5, the valve V6, the valve V2, and the valve V7, the low-pressure turbine air obtained by adiabatic expansion by the expansion turbine 24, and the low-pressure oxygen gas obtained by vaporization in the argon condenser H1, and separates them into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen.

[0076] One end of the line L13 is connected to the top portion of the low-pressure column 18, and a part of the line L13 passes through the subcooler 21 and the main heat-exchanger 16. The line L13 is a line for recovering the low-pressure nitrogen gas concentrated in the upper portion of the low-pressure column 18 as product low-pressure nitrogen gas (LPGN 2) after heat recovery by the subcooler 21 and the main heat-exchanger 16.

[0077] The argon condenser H1 is provided in the bottom portion of the low-pressure column 18, and a liquefaction passage inlet thereof is connected to the line L191. The argon condenser H1 liquefies the argon gas to produce liquefied argon by indirect heat-exchange between the argon gas supplied from the line L191 and the low-pressure liquefied oxygen in the bottom portion of the low-pressure column 18, and vaporizes the low-pressure liquefied oxygen to produce low-pressure oxygen gas.

[0078] One end of the line L18 is connected to the middle portion of the low-pressure column 18, and the other end is connected to the middle portion or the lower portion of the argon column 19. The argon-enriched liquefied oxygen pump 26 is provided on the line L18. Through the line L18, the argon-enriched liquefied oxygen which has been concentrated in the middle portion of the low-pressure column 18 is pressurized by the argon-enriched liquefied oxygen pump 26, and supplied into the argon column 19.

[0079] The argon-enriched liquefied oxygen pump 26 is provided on the line L18. The argon-enriched liquefied oxygen pump 26 pressurizes the argon-enriched liquefied oxygen led out from the low-pressure column 18 into the line L18.

[0080] To the argon column 19, one end of the lines L18 and L192 is connected, and the argon column 19 houses the high-pressure nitrogen condenser H2 in the bottom portion thereof. The argon column 19 separates the argon-enriched liquefied oxygen pressurized by the argon-enriched liquefied oxygen pump 26 and the liquefied argon supplied from the line L192 into argon gas and middle-pressure liquefied oxygen by low-temperature distillation at a pressure higher than that of the low-pressure column 18.

[0081] One end of the line L191 is connected to the top portion of the argon column 19, and the other end is connected to the liquefaction passage inlet of the argon condenser H1. The line L191 supplies argon gas concentrated in the upper portion of the argon column 19 into the argon condenser H1.

[0082] One end of the line L192 is connected to the liquefaction passage outlet of the argon condenser H1, and the other end is connected to the top portion of the argon column 19. The line L192 supplies liquefied argon generated in the argon condenser H1 into the argon column 19.

[0083] One end of the line L15 is connected to the bottom portion of the low-pressure column 18, and the other end is connected to one end of the line L23 and one end of the line L16. The line L15 is a line for supplying low-pressure liquefied oxygen in the bottom portion of the low-pressure column 18 into the line L16.

[0084] The line L17 is branched off from the line L15. The line L17 is a line for recovering a part of the low-pressure liquefied oxygen flowing through the line L15 as product low-pressure liquefied oxygen (LPLO2).

[0085] One end of the line L23 is connected to the bottom portion of the argon column 19, and the other end is connected to one end of the line L15 and one end of the line L16. The line 23 is provided with the valve V8. The line L23 is a line for supplying middle-pressure liquefied oxygen in the bottom portion of the argon column 19 into the line L16.

[0086] The valve V8 is provided on the line L23. The valve V8 decompresses the middle-pressure liquefied oxygen flowing through the line L23.

[0087] The line L24 is branched off from the line L23. The line L24 is a line for recovering a part of the middle-pressure liquefied oxygen flowing through the line L23 as product middle-pressure liquefied oxygen (MPLO2).

[0088] One end of the line L16 is connected to one end of the line L15 and the line L23. Part of the line L16 passes through the main heat-exchanger 16, and the liquefied oxygen pump 25 is provided on the line L16. The line L16 is a line for pressurizing the fluid supplied by the liquefied oxygen pump 25, recovering the heat in the main heat-exchanger 16, and recovering it as product high-pressure oxygen gas (HPGO2).

[0089] The liquefied oxygen pump 25 is provided on the line L16 located upstream of the main heat-exchanger 16. The liquefied oxygen pump 25 pressurizes the fluid supplied into the line L16.

[0090] The line L20 is branched off from the line L191, and a part of it passes through the main heat-exchanger 16. The line L20 is a line for recovering a part of the argon gas flowing through the line L191 as product argon gas (GAR) after heat recovery in the main heat-exchanger 16.

[0091] Note that, as shown by the dashed line in FIG. 1, one end of the line L21 may be connected to the liquefaction passage outlet of the argon condenser H1. In this case, the line L21 merges with the line 20, and argon gas that is not liquefied in the argon condenser H1 is recovered as product argon gas (GAR) after heat recovery in the main heat-exchanger 16.

[0092] The line L22 is branched off from the line L192. The line L22 is a line for recovering a part of the liquefied argon flowing through the line L192 as product liquefied argon (LAR).

[0093] The subcooler 21 is positioned so that a part of the line L14, the line L13, the line L11, the line L32, and the line L9 pass through it. The subcooler 21 heats the low-temperature fluid flowing through line L13 by indirect heat-exchange with the high-temperature fluid flowing through lines L11, L32, and L9, and cools each high-temperature fluid.

[0094] Note that the combination of low-temperature fluid and high-temperature fluid in the subcooler 21 is not limited to this embodiment.

[0095] One end of the line L14 is connected to the upper portion of the low-pressure column 18, and a part of the line L14 passes through the subcooler 21 and the main heat-exchanger 16. The line L14 is a line for recovering the low-purity low-pressure nitrogen gas concentrated in the upper portion of the low-pressure column 18 as waste nitrogen gas WGN2 after heat recovery by the subcooler 21 and the main heat-exchanger 16.

[0096] One end of the raw air bypass line L25 is connected to the downstream side of the air purifier 13 in the line L1, and the other end is connected to the upstream side of the main heat-exchanger 16 in the line L51, and provided with the raw air bypass valve V9. The raw air bypass line L25 is branched off from the line L1. Through the line L1, a part of the high-pressure raw air from the line L1 is separated, decompressed by the raw air bypass valve V9, and then mixed with the high-pressure turbine air flowing through the line 51. The raw air bypass valve V9 is provided on the raw air bypass line L25 located upstream of the main heat-exchanger 16. The raw air bypass valve V9 reduces the pressure of the high-pressure raw air flowing through the raw air bypass line L25. More specifically, the raw air bypass valve V9 can indirectly adjust the flow rate of the high-pressure raw air through the raw air bypass line L25 by controlling the pressure after decompression of the high-pressure raw air branched off from the line L1.

[0097] In the present embodiment, the raw air bypass valve V9 can be an automatic valve, and the raw air bypass valve V9 can be operated using a flow rate regulator not shown so that the flow rate meter not shown installed in the raw air bypass line L25 matches the set value. In addition, a pressure regulator not shown can be used to operate the set value of the flow rate regulator so that the indicated value of a pressure gauge not shown provided in the inlet system of the expansion turbine 24 matches a target value, thereby indirectly controlling the flow rate.

[0098] In the present embodiment, the air separation device 10 has been described as having lines L20 and L22 for leading out the product argon gas (GAR) or the product liquefied argon (LAR) as an example, but it is sufficient to have at least one of the lines L20 and L22.

[0099] Although not shown in FIG. 1, for example, when product low-pressure oxygen gas (LPGO2) is recovered, a product lead-out line is provided, one end of which is connected to the bottom portion of the low-pressure column 18 and a part of which passes through the main heat-exchanger 16. In this case, the product lead-out line not shown recovers the low-pressure oxygen gas in the low-pressure column 18 as product low-pressure oxygen gas (LPGO2) after heat recovery in the main heat-exchanger 16.

[0100] Furthermore, for example, when product middle-pressure oxygen gas (MPGO2) is recovered, a product lead-out line not shown is provided, one end of which is connected to the bottom portion of the argon column 19 and a part of which passes through the main heat-exchanger 16. In this case, the product lead-out line recovers the middle-pressure oxygen gas from the argon column 19 as product middle-pressure oxygen gas (MPGO2) after heat recovery in the main heat-exchanger 16.

[0101] In addition, in the case where the product high-pressure oxygen gas (HPGO2) is not recovered, and product low-pressure oxygen gas (LPGO2), product middle-pressure oxygen gas (MPGO2), product middle-pressure liquefied oxygen (MPLO2), product low-pressure liquefied oxygen (LPLO2), and the like are recovered, the line L16, the liquefied oxygen pump 25, the booster air compressor 14, the booster air compressor aftercooler 15, the line L2, and the valves V4 and V8 can be removed from the air separation device 10.

[0102] The air separation device 10 of the present embodiment includes: the high-pressure column 17 in which the high-pressure raw air which has been obtained by compressing, pre-cooling, purifying and cooling air containing oxygen, nitrogen, and argon is low-temperature distilled to separate it into the high-pressure nitrogen gas and the high-pressure oxygen-enriched liquefied air; the turbine air-evaporator H3 in which the middle-pressure oxygen-enriched liquefied air which has been obtained by decompressing is vaporized to produce the middle-pressure turbine air; the turbine blower 22 in which the middle-pressure turbine air which has been heated is compressed to produce the high-pressure turbine air; the expansion turbine 24 in which the high-pressure turbine air is adiabatically expanded to produce the low-pressure turbine air and generate the cold required for an air separation operation; the low-pressure column 18 in which the low-pressure turbine air is low-temperature distilled to separate it into the low-pressure nitrogen gas, the low-pressure liquefied oxygen, and the argon-enriched liquefied oxygen; the argon column 19 in which the argon-enriched liquefied oxygen which has been pressurized is low-temperature distilled at a pressure higher than that of the low-pressure column 18 to separate it into the argon gas and the middle-pressure liquefied oxygen; the argon condenser H1 in which the argon gas is liquefied to produce the liquefied argon and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas by indirect heat-exchange between the argon gas and the low-pressure liquefied oxygen; the high-pressure nitrogen condenser H2 in which the high-pressure nitrogen gas is liquefied to produce the high-pressure liquefied nitrogen and the middle-pressure liquefied oxygen is vaporized to produce the middle-pressure oxygen gas by indirect heat-exchange between the high-pressure nitrogen gas and middle-pressure liquefied oxygen; and the lines L20 and L21 which lead out at least one of a part of the argon gas, the argon gas that is not liquefied in the argon condenser H1 and the liquefied argon in the argon condenser H1 as the product argon gas (GAR) or the product liquefied argon (LAR). The air separation device 10 of the present embodiment uses rotational energy generated by the expansion turbine 24 to rotate the turbine blower 22. The air separation device 10 of the present embodiment further includes the raw air bypass line L25 in which a part of the high-pressure raw air is decompressed and mixed with the high-pressure turbine air.

[0103] According to the air separation device 10 of the present embodiment having the configurations above, for example, even when the flow rates of the product middle-pressure liquefied oxygen (MPLO2), the product low-pressure liquefied oxygen (LPLO2), the product high-pressure liquefied nitrogen (HPLN2), and the like are large and a large amount of cold is required for operation, since a part of the high-pressure raw air is supplied into the expansion turbine 24 through the line L51 which serves as the inlet of the expansion turbine 24, it is possible to relatively reduce the flow rate of the turbine blower 22 and increase the compression ratio, thereby suppressing an increase in the processing amount caused by increasing the expansion ratio of the expansion turbine 24. As a result, the flow rate of the low-pressure turbine air supplied into the low-pressure column 18 can be reduced, making it possible to improve the argon recovery rate.

[0104] On the other hand, in the case where a part or the entire amount of the low-pressure turbine air is recovered (released to the atmosphere) without being supplied into the low-pressure column as in Patent Document 2, the flow rate of the low-pressure turbine air supplied into the low-pressure column is optimized, and the argon recovery rate can be improved. However, the oxygen contained in the low-pressure turbine air that is not supplied into the low-pressure column cannot be recovered as a product, so the oxygen recovery rate decreases. In contrast, by using the air separation device 10 of the present embodiment, the entire amount of the low-pressure turbine air can be supplied into the low-pressure column 18 and used as the raw material for the low-pressure column 18, so the decrease in the oxygen recovery rate can be suppressed.<Air Separation Method>

[0105] The air separation method of the present embodiment will be described below in detail, taking as an example a method of performing air separation using the air separation device 10 shown in FIG. 1.

[0106] Note that in the following explanation, as with the explanation of the air separation device 10 of the present embodiment described above, the explanation will be given with reference to FIG. 1, and a detailed explanation of the configuration of the air separation device 10 already explained will be omitted.

[0107] Air containing oxygen, nitrogen, and argon is supplied into the line L1. The air is compressed by the main air compressor 11, the heat of compression is removed by the air precooler 12. Impurities contained in the air, specifically water, carbon dioxide, and the like are removed by the air purifier 13, resulting in the high-pressure raw air.

[0108] A part of the high-pressure raw air from which the impurities have been removed in the air purifier 13 is cooled by the main heat-exchanger 16 and supplied into the high-pressure column 17.

[0109] A part of the remaining high-pressure raw air from which impurities have been removed in the air purifier 13 is further pressurized by the booster air compressor 14 provided on the line L2 branched off from the line L1 to become the pressurized raw air. The heat of compression of the pressurized raw air is removed by the booster air compressor aftercooler 15. Then, the pressurized raw air is cooled by the main heat-exchanger 16, then decompressed by the valve V4 to become the high-pressure raw liquefied air, and supplied into the high-pressure column 17.

[0110] In the main heat-exchanger 16, high-temperature fluids flowing through the lines L1, L2, and L51 are indirectly heat-exchanged with low-temperature fluids flowing through the lines L5, L8, L13, L14, L16, and L20, so that the high-temperature fluids are cooled and the low-temperature fluids are heated.

[0111] In the high-pressure column 17, the high-pressure raw air introduced through the line L1, the high-pressure raw liquefied air introduced through the line L2, and the high-pressure liquefied nitrogen introduced through the line L72 are separated by low-temperature distillation into the high-pressure nitrogen gas in the upper portion of the high-pressure column 17 and the high-pressure oxygen-enriched liquefied air in the lower portion of the high-pressure column 17 (high-pressure separation step).

[0112] The high-pressure nitrogen gas in the top portion of the high-pressure column 17 is introduced through the line L71 into the high-pressure nitrogen condenser H2 housed in the bottom portion of the argon column 19.

[0113] The high-pressure nitrogen gas supplied into the high-pressure nitrogen condenser H2 through the line L71 liquefies and becomes the high-pressure liquefied nitrogen and vaporizes the middle-pressure liquefied oxygen in the bottom portion of the argon column 19 to produce the middle-pressure oxygen gas by indirect heat-exchange with the middle-pressure liquefied oxygen in the bottom portion of the argon column 19 (high-pressure nitrogen condensation step).

[0114] A part of the high-pressure nitrogen gas led out into the line L71 is led out into the line L8 branched off from the line L71, and, after heat recovery in the main heat-exchanger 16, is recovered as the product high-pressure nitrogen gas (HPGN2).

[0115] The high-pressure liquefied nitrogen produced in the high-pressure nitrogen condenser H2 is introduced into the top portion of the high-pressure column 17 through the line L72.

[0116] A part of the high-pressure liquefied nitrogen introduced into the line L72 is introduced into the line L9, cooled in the subcooler 21, decompressed by the valve V6, and then introduced into the top portion of the low-pressure column 18.

[0117] A part of the high-pressure liquefied nitrogen in the line L9 is introduced into the line L10 and recovered as the product high-pressure liquefied nitrogen (HPLN2).

[0118] The high-pressure oxygen-enriched liquified air in the bottom portion of the high-pressure column 17 is led out into the line LA, decompressed by the valve V1 to become the middle-pressure oxygen-enriched liquified air, and supplied into the outer cylinder 20 of the turbine air evaporator H3.

[0119] A part of the high-pressure nitrogen gas concentrated in the upper portion of the high-pressure column 17 is led out from the upper portion of the high-pressure column 17 into the line L31 and introduced into the turbine air evaporator H3.

[0120] The high-pressure nitrogen gas supplied into the turbine air evaporator H3 through the line L31 liquefies and becomes the high-pressure liquefied nitrogen by indirect heat-exchange with the middle-pressure oxygen-enriched liquified air supplied into the outer cylinder 20 of the turbine air evaporator H3 through the line L4, and also vaporizes the middle-pressure oxygen-enriched liquified air supplied into the outer cylinder 20 of the turbine air evaporator H3 through the line L4 to produce the middle-pressure turbine air (turbine air production step).

[0121] Note that the fluid introduced into the turbine air-evaporator H3 through the line L31 can be a part of the high-pressure raw air (L33) or a part of the high-pressure nitrogen-enriched air ascending in the middle or lower portion of the high-pressure column 17 (L34) instead of the high-pressure nitrogen gas concentrated in the upper portion of the high-pressure column 17, as shown by the dashed lines in FIG. 1.

[0122] Even in this case, a part of the high-pressure raw air or a part of the high-pressure nitrogen-enriched air is liquefied in the turbine air-evaporator H3, and becomes the high-pressure liquefied air or the high-pressure nitrogen-enriched liquefied air.

[0123] By changing the fluid as described above, the fluid temperature on the condensation side in the turbine air-evaporator H3 rises and the fluid temperature on the evaporation side also rises, so that the pressure of the middle-pressure turbine air generated in the turbine air-evaporator H3 increases, which results in an advantageous effect of allowing a larger expansion ratio by the expansion turbine 24, which will be described below.

[0124] In the present embodiment, as shown by the dashed line in FIG. 1, it is also possible to lead all or a part of the fluid liquefied in the turbine air-evaporator H3 into the line L35 branched off from the line L32 and supply it into the high-pressure column 17.

[0125] The high-pressure liquefied nitrogen produced in the turbine air-evaporator H3 is led out into the line L32, cooled in the subcooler 21, decompressed by the valve V5, and then introduced into the upper portion of the low-pressure column 18.

[0126] The middle-pressure turbine air generated in the turbine air-evaporator H3 is led out into the line L5, thermally recovered to room temperature in the main heat-exchanger 16, and then compressed by the turbine blower 22 (turbine air compression step).

[0127] In the turbine air compression step, the middle-pressure turbine air is compressed using energy generated in the turbine air adiabatic expansion step, the details of which will be described later. That is, in the turbine air compression step, the turbine blower 22 is rotationally driven by the expansion turbine 24, and the middle-pressure turbine air is compressed.

[0128] The high-pressure turbine air compressed by the turbine blower 22 is led out into the line L51, the heat of compression is removed in the turbine blower aftercooler 23, further cooled in the main heat-exchanger 16, and then introduced into the expansion turbine 24.

[0129] The high-pressure turbine air introduced into the expansion turbine 24 is decompressed to the operating pressure of the low-pressure column 18 by adiabatic expansion, and after generating the cold required to operate the air separation device, becomes the low-pressure turbine air and is led out into the line L52 (turbine air adiabatic expansion step).

[0130] The energy generated by the turbine air adiabatic expansion step is used in the turbine air compression step described above to compress the middle-pressure turbine air.

[0131] In the air separation method of the present embodiment, a part of the high-pressure raw air is introduced from the line L1 into the raw air bypass line L25, and depressurized by the raw air bypass valve V9, and mixed with the high-pressure turbine air flowing through the line 51 (raw air bypass step).

[0132] As a result, the flow rate of the turbine blower 22 becomes relatively smaller than the flow rate of the expansion turbine 24, and the outlet pressure of the turbine blower 22 increases, so the expansion ratio of the expansion turbine 24 increases. This makes it possible to increase the amount of cold generated per unit processing volume by the expansion turbine 24.

[0133] Furthermore, as the flow rate of the raw air bypass line L25 increases, the pressure of the high-pressure turbine air increases, so it becomes possible to adjust the pressure of the high-pressure turbine air by the flow rate of the raw air bypass line L25. The pressure of the high-pressure turbine air is set to be equal to or lower than the pressure of the high-pressure raw air or the pressure of the high-pressure column 17.

[0134] In the raw air bypass step, for example, the raw air bypass valve V9 controls the pressure after decompression of the high-pressure raw air flowing through the line 2 branched off from the line L1, thereby indirectly adjusting the flow rate of the high-pressure raw air in the raw air bypass line L25.

[0135] The raw air bypass line L25 and the raw air bypass valve V9 can also be used when the air separation device 10 is started up. In such a case, when the air separation device 10 is started up to cool each piece of equipment such as the high-pressure column 17, the low-pressure column 18, and the argon column 19 from an initial state at room temperature to a steady state at low temperature, the high-pressure raw air in the line L1 can be supplied into the expansion turbine 24 through the raw air bypass line L25 without passing through the high-pressure column 17. This makes it possible to produce a low-temperature fluid by adiabatic expansion by the expansion turbine 24, making it possible to efficiently cool the equipment.

[0136] The low-pressure turbine air led out into the line L52 is introduced into the middle portion of the low-pressure column 18 as a raw material for the low-pressure column 18.

[0137] The middle-pressure oxygen-enriched liquified air that is supplied into the outer cylinder 20 of the turbine air evaporator H3 and is not vaporized in the turbine air-evaporator H3 is led out into the line L6, depressurized by the valve V2, and introduced into the middle portion of the low-pressure column 18 as the raw material for the low-pressure column 18.

[0138] In the low-pressure column 18, the fluid decompressed by the valve V5, the fluid decompressed by the valve V7, the fluid decompressed by the valve V6, the fluid decompressed by the valve V2, the low-pressure turbine air obtained by adiabatic expansion by the expansion turbine 24, and the low-pressure oxygen gas obtained by vaporization in the argon condenser H1 are separated by low-temperature distillation into the low-pressure nitrogen gas in the upper portion of the low-pressure column 18, the low-pressure liquefied oxygen in the lower portion of the low-pressure column 18, and the argon-enriched liquefied oxygen in the middle portion of the low-pressure column 18 (low-pressure separation step).

[0139] The low-pressure nitrogen gas in the top portion of the low-pressure column 18 is led out into the line L13, heat thereof is recovered by the subcooler 21 and the main heat-exchanger 16, and then recovered as the product low-pressure nitrogen gas (LPGN2).

[0140] The low-purity low-pressure nitrogen gas ascending the upper portion of the low-pressure column 18 is led out into the line L14, heat thereof is recovered by the subcooler 21 and the main heat-exchanger 16, and then recovered as the waste nitrogen gas WGN2.

[0141] In the subcooler 21, the high-temperature fluids flowing through the lines L11, L32, and L9 and the low-temperature fluids flowing through the lines L13 and L14 are indirectly heat-exchanged to cool the high-temperature fluids and heat the low-temperature fluids, but the combination of high-temperature and low-temperature fluids is not limited to this embodiment.

[0142] In the argon condenser H1 housed in the bottom portion of the low-pressure column 18, the low-pressure liquefied oxygen in the bottom portion of the low-pressure column 18 vaporizes and becomes the low-pressure oxygen gas, and liquefies the argon gas in the top portion of the argon column 18 to produce the liquefied argon by indirect heat-exchange with the argon gas in the top portion of the argon column 19 (argon condensation step).

[0143] The low-pressure liquefied oxygen that is not vaporized in the argon condenser H1 is led out into the line L15, mixed with the middle-pressure liquefied oxygen that has been depressurized by the valve V8 and introduced into the line L16.

[0144] The fluid introduced into line L16 is pressurized by the liquefied oxygen pump 25 to the required pressure according to the product specifications, and becomes the high-pressure liquefied oxygen. All the high-pressure liquefied oxygen is vaporized in the main heat-exchanger 16, and heat is recovered so as to be room temperature, recovered as the product high-pressure oxygen gas (HPGO2).

[0145] A part of the low-pressure liquefied oxygen led out into the line L15 is introduced into the line L17 branched off from the line L15, and recovered as the product low-pressure liquefied oxygen (LPLO2).

[0146] The argon-enriched liquefied oxygen concentrated in the middle portion of the low-pressure column 18 is led out into the line L18 and pressurized by an argon-enriched liquefied oxygen pump 26 to a pressure required for sending the argon-enriched liquefied oxygen into the argon column 19, which has a higher operating pressure than the low-pressure column 18, and then introduced into the middle portion or lower portion of the argon column 19.

[0147] Depending on the positional relationship between the low-pressure column 18 and the argon column 19, it may be possible to send the argon-enriched liquefied oxygen from the low-pressure column 18 into the argon column 19 by utilizing the liquid head caused by the difference in liquid level height, without using the argon-enriched liquefied oxygen pump 26. In this case, the argon-enriched liquefied oxygen pump 26 is not required.

[0148] In the argon column 19, the argon-enriched liquefied oxygen supplied through the line L18, the liquefied argon supplied through the line L192, and the middle-pressure oxygen gas obtained by vaporization in the high-pressure nitrogen condenser H2 are separated by low-temperature distillation into the argon gas in the upper portion of the argon column 19 and the middle-pressure liquefied oxygen in the lower portion of the argon column 19 (argon separation step).

[0149] The argon gas in the upper portion of the argon column 19 is introduced into the argon condenser H1 through the line L191.

[0150] The argon gas introduced into the argon condenser H1 liquefies and becomes liquefied argon by indirect heat-exchange with the low-pressure liquefied oxygen in the bottom portion of the low-pressure column 18, and also vaporizes the low-pressure liquefied oxygen to produce low-pressure oxygen gas (argon condensation step).

[0151] The liquefied argon produced in the argon condensation step is introduced into the top portion of the argon column 19 through the line L192.

[0152] A part of the argon gas in line L191 is led out into the line L20 branched off from the line L191, heat is recovered so as to be room temperature in the main heat-exchanger 16, and recovered as the product argon gas (GAR) (product argon leading out step).

[0153] Also, as shown by the dashed line in FIG. 1, the argon gas that is not liquefied in the argon condenser H1 may be led out into the line L21, passed through the line 20, and heat thereof is recovered so as to be room temperature in the main heat-exchanger 16, and then recovered as the product argon gas (GAR).

[0154] A part of the liquefied argon flowing through the line L192 is led out into the line L22 branched off from the line the L192, and recovered as the product liquefied argon (LAR) (product argon leading out steps).

[0155] The middle-pressure liquefied oxygen in the bottom portion of the argon column 19 vaporizes and becomes the middle-pressure oxygen gas by indirect heat-exchange with the high-pressure nitrogen gas supplied from the top portion of the high-pressure column 17 in the high-pressure nitrogen condenser H2 housed in the bottom portion of the argon column 19, and also liquefies the high-pressure nitrogen gas to produce the high-pressure liquefied nitrogen (high-pressure nitrogen condensation step).

[0156] The middle-pressure liquefied oxygen that is not vaporized in the high-pressure nitrogen condenser H2 is led out into the line L23, depressurized by the valve V8, and mixed with the low-pressure liquefied oxygen in the line L15.

[0157] A part of the middle-pressure liquefied oxygen led out into the line L23 is led out into the line L24 branched off from the line L23, and recovered as the product middle-pressure liquefied oxygen (MPLO2).

[0158] Although not shown in FIG. 1, the other end of the line L15 having one end connected to the bottom portion of the low-pressure column 18 may be connected to the bottom portion of the argon column 19. In this case, through the line L15, the low-pressure liquefied oxygen led out from the bottom portion of the low-pressure column 18 is pressurized by a liquid head due to the difference in liquid level or a pump not shown installed in the line L15 to produce pressurized liquefied oxygen, and supplied into the bottom portion of the argon column 19. The pressurized liquefied oxygen supplied from the line L15 is mixed with the middle-pressure liquefied oxygen in the bottom portion of the argon column 19, is led out into the line L23, and recovered as the product high-pressure oxygen gas (HPGO2) through the line L16. In this case, the valve V8 installed in the line L23 is not necessary.

[0159] Although not shown in FIG. 1, the other end of the line L23 having one end connected to the bottom portion of the argon column 19 may be connected to the lower portion of the low-pressure column 18. In this case, through the line L23, the middle-pressure liquefied oxygen led out from the bottom portion of the argon column 19 is decompressed by the valve V8 to produce decompressed liquefied oxygen, supplied into the lower portion of the low-pressure column 18. The decompressed liquefied oxygen supplied from the line L23 is mixed with the low-pressure liquefied oxygen in the bottom portion of the low-pressure column 18, led out into the line L15, and recovered as the product high-pressure oxygen gas (HPGO2) through the line L16.

[0160] Also, although not shown in FIG. 1, some or all of the high-pressure raw liquefied air introduced into the high-pressure column 17 through the line L2 may be supplied into the middle or upper portion of the low-pressure column 18.

[0161] In addition, the raw air bypass line L25 may be branched off from the line 1 passing through the main heat-exchanger 16, or from the line 1 located at the outlet of the main heat-exchanger 16, and merged with the line 51 at the inlet of the expansion turbine 24. In this case, it is possible to bypass and supply a part of the high-pressure raw air cooled in the main heat-exchanger 16 in the line L1 into the inlet of the expansion turbine 24.

[0162] The concentration of argon contained in the product argon gas (GAR) and the product liquefied argon (LAR) is, for example, 50% or more, and preferably 95% or more.

[0163] In addition to the case where argon gas and liquefied argon are recovered as products as described above, there are cases where argon purification equipment not shown is installed in the downstream stage to remove impurities such as oxygen and nitrogen components.

[0164] Even if the product argon gas (GAR) or the product liquefied argon (LAR) is not required, argon gas may be recovered for the purpose of improving the oxygen recovery rate if the purity of product high-pressure oxygen gas (HPGO2) or product liquefied oxygen (LPLO2, MPLO2, and the like) is high, for example when the oxygen concentration is 98% or more.

[0165] Although not shown in FIG. 1, when the product low-pressure oxygen gas (LPGO2) is recovered, the low-pressure oxygen gas is led out from the bottom portion of the low-pressure column 18, heat thereof is recovered so as to be room temperature in the main heat-exchanger 16, and then recovered as a product.

[0166] When the product middle-pressure oxygen gas (MPGO2) is recovered, the middle-pressure oxygen gas is led out from the bottom portion of the argon column 19, heat thereof is recovered so as to be room temperature in the main heat-exchanger 16, and then recovered as a product.

[0167] When the product low-pressure oxygen gas (LPGO2) and / or the product middle-pressure oxygen gas (MPGO2) are recovered, the flow rate balance can be adjusted by introducing the low-pressure liquefied oxygen in the bottom portion of the low-pressure column 18 into the bottom portion of the argon column 19 through a line not shown, or by introducing the middle-pressure liquefied oxygen in the bottom portion of the argon column 19 into the bottom portion of the low-pressure column 18 through a line not shown.

[0168] The air separation method in the present embodiment includes: the high-pressure separation step in which high-pressure raw air obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon is cooled and then low-temperature distilled to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; the turbine air production step in which the middle-pressure oxygen-enriched liquified air which has been obtained by decompressing is vaporized to produce middle-pressure turbine air; the turbine air compression step in which the middle-pressure turbine air is heated and then compressed to produce the high-pressure turbine air; the turbine air adiabatic expansion step in which the high-pressure turbine air is adiabatically expanded to produce the low-pressure turbine air and generate cold required for an air separation operation; the low-pressure separation step in which the low-pressure turbine air is low-temperature distilled to separate it into the low-pressure nitrogen gas, the low-pressure liquefied oxygen, and the argon-enriched liquefied oxygen; the argon separation step in which the argon-enriched liquefied oxygen is pressurized, and then low-temperature distilled at a pressure higher than that in the low-pressure separation step to separate it into the argon gas and the middle-pressure liquefied oxygen; the argon condensation step in which by indirect heat-exchange between the argon gas and the low-pressure liquefied oxygen, the argon gas is liquefied and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas; the high-pressure nitrogen condensation step in which by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure liquefied oxygen, the high-pressure nitrogen gas is liquefied to produce high-pressure liquified nitrogen, and the middle-pressure liquefied oxygen is vaporized to produce the middle-pressure oxygen gas; and the product argon leading out step in which at least one of a part of the argon gas, the argon gas not liquefied in the argon condensation step, and a part of the liquefied argon is led out as a product, wherein, in the turbine air compression step, the middle-pressure turbine air is compressed using energy generated by the turbine air adiabatic expansion step, and wherein the air separation method further includes a raw air bypass step in which a part of the high-pressure raw air is separated, decompressed, and mixed with the high-pressure turbine air.

[0169] According to the air separation method of the present embodiment, similarly to the air separation device above, even when the flow rates of the product middle-pressure liquefied oxygen (MPLO2), the product low-pressure liquefied oxygen (LPLO2), the product high-pressure liquefied nitrogen (HPLN2), and the like are large and a large amount of cold is required for operation, by bypassing and supplying a part of the high-pressure raw air into the line L51 which serves as the inlet of the expansion turbine 24, it is possible to relatively reduce the flow rate of the turbine blower 22 and increase the compression ratio, thereby suppressing an increase in the processing amount caused by increasing the expansion ratio of the expansion turbine 24. As a result, the flow rate of the low-pressure turbine air supplied into the low-pressure column 18 can be reduced, making it possible to improve the argon recovery rate.

[0170] In addition, as in Patent Document 2, when a part or all of the low-pressure turbine air is recovered (released to the atmosphere) without being supplied into the low-pressure column, the flow rate of the low-pressure turbine air supplied into the low-pressure column is optimized, and the argon recovery rate can be improved. However, since the oxygen contained in the low-pressure turbine air that is not supplied into the low-pressure column cannot be recovered as a product, the oxygen recovery rate decreases. In contrast, by using the air separation device 10 of the present embodiment, the entire amount of the low-pressure turbine air can be supplied into the low-pressure column 18 and used as the raw material for the low-pressure column 18, so that the decrease in the oxygen recovery rate can be suppressed.

[0171] As described above, the high-pressure column 17, the low-pressure column 18, and the argon column 19 are thermally integrated by each step, and therefore the operating pressures of the distillation columns increase in the order of the low-pressure column 18, the argon column 19, and the high-pressure column 17.Other Embodiments

[0172] Examples of an air separation method and air separation device according to the present invention have been explained in the above embodiments. However, the present invention is not limited to the embodiments above. Each configuration and their combination in the embodiments above is an example, and additions, omissions, substitutions, and other modifications of the configuration are possible within the scope of the spirit of the present invention.Effects

[0173] As described above, the air separation method of the present embodiment includes the turbine air production step that generates the middle-pressure turbine air, the turbine air compression step that generates the high-pressure turbine air, and further includes the raw air bypass step that decompresses a part of the high-pressure raw air and mixes it with the high-pressure turbine air. In this way, by separating a part of the high-pressure raw air and mixing it with the high-pressure turbine air, which is the oxygen-enriched air, it is possible to reduce the amount of flow rate of fluid to be processed by the expansion turbine 24 while maintaining the amount of cold being generated, or increase the amount of cold being generated while maintaining the amount of flow rate of fluid to be processed by the expansion turbine 24.

[0174] Therefore, it is possible to improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate.

[0175] The air separation device 10 of the present embodiment is an air separation device in which the high-pressure oxygen-enriched liquified air led out from the bottom portion of the high-pressure column 17 is decompressed, vaporized by the indirect heat-exchange to produce the middle-pressure turbine air, which is the oxygen-enriched air, and the middle-pressure turbine air is compressed by the turbine blower 22, then adiabatically expanded by the expansion turbine 24 and supplied into the low-pressure column 18, wherein the air separation device further includes the raw air bypass line L25 that decompresses a part of the high-pressure raw air, and mixes it with the high-pressure turbine air. By providing such a raw air bypass line L25, similar to the air separation method above, it is possible to reduce the flow rate of the fluid to be processed by the expansion turbine 24 while maintaining the amount of cold being generated, or increase the amount of cold being generated while maintaining the flow rate of the fluid to be processed by the expansion turbine 24.

[0176] Therefore, it is possible to improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate, as with the air separation method above.EXAMPLES

[0177] The air separation method and air separation device of the present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples and can be modified as appropriate without departing from the gist of the present invention.Example

[0178] In Example, a simulator manufactured by Taiyo Nippon Sanso Corporation (this simulator is the same as that actually used to design the air separation device) was used to perform a simulation using the air separation device 10 shown in FIG. 1.

[0179] In the simulation in the present Example, under the conditions in which the flow rate of high-pressure raw air was set to 100, product low-pressure nitrogen gas (LPGN2) with a flow rate of 24.1, pressure of 117 kPaA, and oxygen concentration of 0.1 ppm or less, product high-pressure nitrogen gas (HPGN2) with a flow rate of 9.8, pressure of 800 kPaA or more, and oxygen concentration of 0.1 ppm or less, product low-pressure liquefied nitrogen (LPLN2) with a flow rate of 2.2 and oxygen concentration of 0.1 ppm or less were recovered, and the recoverable flow rates of product high-pressure oxygen gas (HPGO2) with a pressure of 3120 kPaA and an oxygen concentration of 99.6% or more, and product argon gas (GAR) with an oxygen concentration of 1.5% or less were calculated. The flow rate of high-pressure raw air flowing through the raw air bypass line L25 was set to 6.1.

[0180] The simulation conditions and results of Example are shown in Table 1. The following Table 1 shows the simulation conditions and the simulation results of the example and the Comparative Example described later. In Table 1, the values in parentheses are calculated values obtained by simulation.TABLE 1Simulation conditions and calculation resultsComparativeExampleExampleHigh-pressureFlow rate100.0100.0raw airPressure (kPaA)846846Oxygen concentration  21%  21%Raw air bypassFlow rate6.10ExpansionFlow rate(28.7)(30.0)turbineInlet pressure (kPaA)(662)(613)Outlet pressure(kPaA)138138LPGN2Flow rate24.124.1Pressure (kPaA)117117Oxygen concentration<0.1ppm<0.1ppmHPGN2Flow rate9.89.8Pressure (kPaA)805805Oxygen concentration<0.1ppm<0.1ppmLPLN2Flow rate2.22.2Oxygen concentration<0.1ppm<0.1ppmHPGO2Flow rate(19.2)(19.2)Pressure (kPaA)31203120Oxygen concentration>99.6%>99.6%GARFlow rate(0.62)(0.50)Pressure (kPaA)291291Oxygen concentration <1.5% <1.5%Recovery ratio of oxygen(92%)(92%)Recovery ratio of argon(67%)(54%)Comparative Example

[0181] In the Comparative Example, a simulation was performed under the same conditions as those in the example above, except that the raw air bypass line L25 shown in FIG. 1 was not used, that is, the flow rate of the high-pressure raw air in the raw air bypass line L25 was set to 0 (zero), and the results are shown in Table 1 above.Evaluation Results of Example and Comparative Example

[0182] As shown in the simulation results in Table 1, in Example where a simulation was performed using an air separation device 10 provided with the raw air bypass line L25 as shown in FIG. 1 and a part of the high-pressure raw air was passed through the raw air bypass line L25 at a flow rate of 6.1, the outlet pressure of the turbine blower 22 driven by the expansion turbine 24, that is, the inlet pressure of the expansion turbine 24 increased, the expansion ratio of the expansion turbine 24 increased, and the processing volume of the expansion turbine 24 decreased. As a result, in Example, the amount of the low-pressure turbine air supplied into the low-pressure column 18 decreased, and conversely, the flow rates of the middle-pressure oxygen gas and the low-pressure oxygen gas generated in the high-pressure nitrogen condenser and argon condenser increased. As a result, it was confirmed that the flow rate of the product argon gas (GAR) increased while maintaining the flow rate of the product high-pressure oxygen gas (HPGO2). Specifically, in Example, the flow rate of the product high-pressure oxygen gas (HPGO2) was maintained at 19.2, while the flow rate of the product argon gas (GAR) was obtained at 0.62.

[0183] On the other hand, in Comparative Example where the simulation was performed under conditions where the high-pressure raw air was not flowing through the raw air bypass line L25, it was confirmed that the outlet pressure of the turbine blower 22 driven by the expansion turbine 24, that is, the inlet pressure of the expansion turbine 24, was lower than in Example, and therefore the expansion ratio of the expansion turbine 24 also decreased and the throughput increased. As a result, in Comparative Example, the amount of the low-pressure turbine air supplied into the low-pressure column 18 increased to 30.0 compared to Example, resulting in the flow rate of the product high-pressure oxygen gas (HPGO2) being maintained at 19.2 while reducing the flow rate of the product argon gas (GAR) to 0.50.

[0184] From the results of Examples described above, it was confirmed that the air separation method including the raw air bypass step, and the air separation device 10 provided with the raw air bypass line L25 according to the present invention are capable of improving the argon recovery rate while maintaining or suppressing a decrease in the oxygen recovery rate.INDUSTRIAL APPLICABILITY

[0185] The air separation method and air separation device of the present invention are capable of improving the argon recovery rate while maintaining or suppressing a decrease in the oxygen recovery rate, and are therefore extremely suitable for various applications in which oxygen or nitrogen is produced industrially.EXPLANATION OF SYMBOLS10 air separation device

[0187] 11 main air compressor

[0188] 12 air precooler

[0189] 13 air purifier

[0190] 14 booster air compressor

[0191] 15 booster air compressor aftercooler

[0192] 16 main heat-exchanger

[0193] 17 high-pressure column

[0194] 18 low-pressure column

[0195] 19 argon column

[0196] 20 outer cylinder of the turbine air evaporator

[0197] 21 subcooler

[0198] 22 turbine blower

[0199] 23 turbine blower aftercooler

[0200] 24 expansion turbine

[0201] 25 liquefied oxygen pump

[0202] 26 argon-enriched liquefied oxygen pump

[0203] H1 argon condenser

[0204] H2 high-pressure nitrogen condenser

[0205] H3 turbine air evaporator

[0206] L1, L2, L4-L6, L8-L18, L20-L24, L31-L35, L51, L52, L71, L72, L191, L192 lines

[0207] L25 raw air bypass line

[0208] V1-V8 valves

[0209] V9 raw air bypass valve

Claims

1. An air separation method, comprising:a high-pressure separation step in which high-pressure raw air which has been obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon is cooled and then low-temperature distilled to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air;a turbine air production step in which middle-pressure oxygen-enriched liquified air which has been obtained by decompressing the high-pressure oxygen-enriched liquefied air is vaporized to produce middle-pressure turbine air;a turbine air compression step in which the middle-pressure turbine air which has been heated is compressed to produce high-pressure turbine air;a turbine air adiabatic expansion step in which the high-pressure turbine air is adiabatically expanded to produce low-pressure turbine air and generate cold required for an air separation operation;a low-pressure separation step in which the low-pressure turbine air is low-temperature distilled to separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen;an argon separation step in which the argon-enriched liquefied oxygen which has been pressurized is low-temperature distilled at a pressure higher than that in the low-pressure separation step to separate it into argon gas and middle-pressure liquefied oxygen;an argon condensation step in which by indirect heat-exchange between the argon gas and the low-pressure liquefied oxygen, the argon gas is liquefied to produce liquified argon and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas;a high-pressure nitrogen condensation step in which by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure liquefied oxygen, the high-pressure nitrogen gas is liquefied to produce high-pressure liquified nitrogen, and the middle-pressure liquefied oxygen is vaporized to produce middle-pressure oxygen gas; anda product argon leading out step in which at least one of a part of the argon gas, the argon gas not liquefied in the argon condensation step, and a part of the liquefied argon is led out as a product,wherein, in the turbine air compression step, the middle-pressure turbine air is compressed using energy generated by the turbine air adiabatic expansion step, andwherein the air separation method further comprises a raw air bypass step in which a part of the high-pressure raw air is separated, decompressed, and mixed with the high-pressure turbine air.

2. The air separation method according to claim 1,wherein, in the turbine air production step, by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure oxygen-enriched liquified air, the high-pressure nitrogen gas is liquefied to produce high-pressure liquefied nitrogen, and the middle-pressure oxygen-enriched liquified air is vaporized to produce the middle-pressure turbine air.

3. The air separation method according to claim 1,wherein, in the turbine air production step, by indirect heat-exchange between high-pressure nitrogen-enriched air produced in the intermediate stage of the high-pressure separation step and the middle-pressure oxygen-enriched liquified air, the high-pressure nitrogen-enriched air is liquefied to produce high-pressure nitrogen-enriched liquefied air, and the middle-pressure oxygen-enriched liquified air is vaporized to produce the middle-pressure turbine air.

4. The air separation method according to claim 1,wherein, in the turbine air production step, by indirect heat-exchange between the high-pressure raw air and the middle-pressure oxygen-enriched liquefied air, the high-pressure raw air is liquified to produce high-pressure liquefied air, and the middle-pressure oxygen-enriched liquefied air is vaporized to produce the middle-pressure turbine air.

5. The air separation method according to claim 1,wherein, in the raw air bypass step, a flow rate of the high-pressure raw air which has been separated from the high-pressure raw air is indirectly adjusted by controlling the pressure after decompression.

6. An air separation device, comprising:a high-pressure column in which high-pressure raw air which has been obtained by compressing, pre-cooling, purifying and cooling air containing oxygen, nitrogen, and argon is low-temperature distilled to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air;a turbine air-evaporator in which middle-pressure oxygen-enriched liquefied air which has been obtained by decompressing the high-pressure oxygen-enriched liquefied air is vaporized to produce middle-pressure turbine air;a turbine blower in which the middle-pressure turbine air which has been heated is compressed to produce high-pressure turbine air;an expansion turbine in which the high-pressure turbine air is adiabatically expanded to produce low-pressure turbine air and generate cold required for an air separation operation;a low-pressure column in which the low-pressure turbine air is low-temperature distilled to separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen;an argon column in which the argon-enriched liquefied oxygen which has been pressurized is low-temperature distilled at a pressure higher than that of the low-pressure column to separate it into argon gas and middle-pressure liquefied oxygen;an argon condenser in which the argon gas is liquefied to produce liquefied argon and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas by indirect heat-exchange between the argon gas and the low-pressure liquefied oxygen;a high-pressure nitrogen condenser in which the high-pressure nitrogen gas is liquefied to produce high-pressure liquefied nitrogen and the middle-pressure liquefied oxygen is vaporized to produce middle-pressure oxygen gas by indirect heat-exchange between the high-pressure nitrogen gas and middle-pressure liquefied oxygen; andlines which lead out at least one of a part of the argon gas, the argon gas which has not been liquefied in the argon condenser and the liquefied argon in the argon condenser as product argon gas or product liquefied argon,wherein the turbine blower is driven by rotational energy generated by the expansion turbine, andwherein the air separation device further comprises a raw air bypass which separates a part of the high-pressure raw air, after decompression of the high-pressure raw air, then mixes with the high-pressure turbine air.

7. The air separation device according to claim 6,wherein the turbine air evaporator liquefies the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizes the middle-pressure oxygen-enriched liquified air to produce the middle-pressure turbine air by indirect heat-exchange between the high-pressure nitrogen gas and the middle-pressure oxygen-enriched liquified air.

8. The air separation device according to claim 6,wherein the turbine air evaporator liquefies high-pressure nitrogen-enriched air which has been produced in a middle section of the high-pressure column to produce high-pressure nitrogen-enriched liquefied air, and vaporizes the middle-pressure oxygen-enriched liquified air to produce the middle-pressure turbine air, by indirect heat-exchange between the high-pressure nitrogen-enriched air and the middle-pressure oxygen-enriched liquified air.

9. The air separation device according to claim 6,wherein the turbine air evaporator liquefies the high-pressure raw air to produce high-pressure liquefied air, and vaporizes the middle-pressure oxygen-enriched liquefied air to produce the middle-pressure turbine air, by indirect heat-exchange between the high-pressure raw air and the middle-pressure oxygen-enriched liquefied air.

10. The air separation device according to claim 6,wherein the air separation device further includes a raw air bypass valve which is provided on the raw air bypass line and which can indirectly adjust a flow rate of the high-pressure raw air which has been separated from the high-pressure raw air by controlling the pressure of the high-pressure raw air after decompression.

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