JP2024104492A - Air separation method and air separation apparatus - Google Patents

Abstract

[Problem] To provide an air separation method and an air separation apparatus capable of improving the argon recovery rate while maintaining or suppressing a decrease in the oxygen recovery rate. [Solution] The air separation method and the air separation apparatus include a high-pressure separation step for separating high-pressure feed air, a turbine air generation step for generating intermediate-pressure turbine air, a turbine air compression step for generating high-pressure turbine air, a turbine air adiabatic expansion step for generating low-pressure turbine air, a low-pressure separation step for separating the low-pressure turbine air, an argon separation step for separating argon-enriched liquefied oxygen, an argon condensation step for generating liquefied argon and low-pressure oxygen gas, a high-pressure nitrogen condensation step for generating high-pressure liquefied nitrogen and medium-pressure oxygen gas, and a product argon extraction step for extracting argon, and the turbine air compression step compresses the intermediate-pressure turbine air using energy generated by the turbine air adiabatic expansion step, and further includes a feed air bypass step for branching off a portion of the high-pressure feed air and joining it with the high-pressure turbine air after decompression. [Selected Figure] Figure 1

Description

The present invention relates to an air separation method and an air separation device.

Conventionally, methods for industrially producing oxygen and nitrogen have generally been known that involve low-temperature distillation using air as a raw material (air separation method), and the equipment used for this (air separation unit).

For example, the following Patent Document 1 proposes an air separation method using an air separation unit 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 at the bottom of the low-pressure column and argon gas at the top of the argon column, and an indirect heat exchanger that performs indirect heat exchange between medium-pressure liquefied oxygen at the bottom of the argon column and high-pressure nitrogen gas at the top 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 unit, including the power for pumping the product gas.

Furthermore, FIG. 1 of Patent Document 1 discloses an apparatus in which high-pressure oxygen-enriched liquefied air drawn from the bottom of the high-pressure column is reduced in pressure and then vaporized in an indirect heat exchanger to generate medium-pressure oxygen-enriched air, which is then compressed in a turbine blower and adiabatically expanded in an expansion turbine before being supplied to the low-pressure column. According to Patent Document 1, as described above, by using oxygen-enriched air in the expansion turbine, the oxygen concentration of the air supplied to the low-pressure column is increased compared to when a portion of the feed air is used in the expansion turbine, and the argon recovery rate is further improved.

Generally, in a cryogenic air separation unit such as that disclosed in Patent Document 1, an expansion turbine is required to generate refrigeration as described above, and as the amount of liquid product increases, the amount of refrigeration required also increases, so the processing flow rate of the expansion turbine increases. On the other hand, in the case of a typical air separation unit that is configured to supply air adiabatically expanded by an expansion turbine to the low-pressure tower, if the flow rate of the low-pressure turbine air increases too much, the argon recovery rate tends to decrease due to a decrease in the ascending gas at the bottom of the low-pressure tower.

As a means of suppressing the above-mentioned decrease in argon recovery rate, Patent Document 2 discloses optimizing the flow rate of low-pressure turbine air supplied to the upper tower by merging some or all of the low-pressure turbine air with the return low-temperature gas generated in the upper tower and recovering it.

Patent No. 6155515 Special Publication No. 60-44587

The air separation unit disclosed in Patent Document 1 is said to be capable of recovering a larger amount of product high-pressure nitrogen gas while maintaining or improving the argon recovery rate, and is also said to be capable of reducing the power consumption of the entire unit. On the other hand, the air separation unit disclosed in Patent Document 1 has a lower inlet pressure and smaller expansion ratio for the expansion turbine compared to when feed air is used as the processing fluid for the expansion turbine, so that the processing volume is larger even when the same amount of refrigeration is generated. For this reason, the air separation unit of Patent Document 1 has a problem in that the expansion turbine volume becomes excessive, and the argon recovery rate is significantly reduced, especially when the amount of liquid product is large and the amount of refrigeration required to operate the air separation unit is large.

Here, in an air separation unit that uses a portion of the feed air in the expansion turbine, it is possible to optimize the amount of low-pressure turbine air by, for example, the method disclosed in Patent Document 2, and prevent a decrease in the argon recovery rate. However, when oxygen-enriched air is used in the expansion turbine, a portion of the oxygen-enriched air, which is richer in oxygen and argon components than the feed air, is not supplied to the low-pressure tower, but is instead recovered (released to the atmosphere) as feedback gas, which can be a factor in reducing the oxygen and argon recovery rates.

The present invention has been made in consideration of the above problems, and aims to provide an air separation method and air separation apparatus that can improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate.

In order to solve the above problems, the inventors have conducted extensive research into an apparatus that generates oxygen-enriched medium-pressure turbine air by reducing the pressure of high-pressure oxygen-enriched liquefied air drawn out from the bottom of the high-pressure column and vaporizing it through indirect heat exchange, and then compressing this medium-pressure turbine air with a turbine blower and then adiabatically expanding it with an expansion turbine to supply it to the low-pressure column. As a result, they have discovered that by branching off a portion of the feed air and merging it with the high-pressure turbine air, which is oxygen-enriched air at the inlet of the expansion turbine, it is possible to reduce the amount of refrigeration generated while maintaining the amount of refrigeration, or to increase the amount of refrigeration generated while maintaining the amount of refrigeration generated by the expansion turbine. They have discovered 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 have completed the present invention.

That is, in order to solve the above problem, according to the invention of claim 1, there is provided a high-pressure separation process in which high-pressure feed air obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon is cooled and then subjected to low-temperature distillation to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a turbine air generation process in which the medium-pressure oxygen-enriched liquefied air obtained by reducing the pressure of the high-pressure oxygen-enriched liquefied air is vaporized to generate medium-pressure turbine air; a turbine air compression process in which the medium-pressure turbine air is heated and then compressed to generate high-pressure turbine air; a turbine air adiabatic expansion process in which the high-pressure turbine air is adiabatically expanded to generate low-pressure turbine air and generate the cold necessary for air separation operation; a low-pressure separation process 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 process in which the argon-enriched liquefied oxygen is pressurized and then subjected to low-temperature distillation at a pressure higher than that of the low-pressure separation process to separate it into argon gas and medium-pressure liquefied oxygen; The method includes an argon condensation step in which the argon gas is liquefied to produce liquefied argon by indirect heat exchange between the argon gas and the low-pressure liquefied oxygen, and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas; a high-pressure nitrogen condensation step in which the high-pressure nitrogen gas is liquefied to produce high-pressure liquefied nitrogen by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen, and the medium-pressure oxygen is vaporized to produce medium-pressure oxygen gas; and a product argon extraction step in which at least one of a portion of the argon gas, the argon gas not liquefied in the argon condensation step, and a portion of the liquefied argon is extracted as a product. The turbine air compression step compresses the medium-pressure turbine air using the energy generated by the turbine air adiabatic expansion step, and further includes a feed air bypass step in which a portion of the high-pressure feed air is branched off and merged with the high-pressure turbine air after decompression.

According to the invention of claim 2, the air separation method described in claim 1 is provided, characterized in that the turbine air generation process liquefies the high-pressure nitrogen gas by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied nitrogen, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air.

According to the invention of claim 3, the air separation method described in claim 1 is provided, characterized in that the turbine air generation process liquefies the high-pressure nitrogen-enriched air generated in an intermediate stage of the high-pressure separation process by indirect heat exchange between the high-pressure nitrogen-enriched air and the medium-pressure oxygen-enriched liquefied air to generate high-pressure nitrogen-enriched liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air.

According to the invention of claim 4, the air separation method described in claim 1 is provided, characterized in that the turbine air generation process liquefies the high-pressure feed air by indirect heat exchange between the high-pressure feed air and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air.

According to the invention of claim 5, there is provided an air separation method according to any one of claims 1 to 4, characterized in that the feed air bypass process indirectly adjusts the flow rate of the high-pressure feed air branched off from the high-pressure feed air by controlling the pressure after reduction.

In addition, in order to solve the above problem, according to the invention of claim 6, there is provided a high-pressure tower which cools the high-pressure feed air obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon, and then performs low-temperature distillation to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a turbine air evaporator which vaporizes the medium-pressure oxygen-enriched liquefied air obtained by reducing the pressure of the high-pressure oxygen-enriched liquefied air to generate medium-pressure turbine air; a turbine blower which warms the medium-pressure turbine air and then compresses it to generate high-pressure turbine air; an expansion turbine which adiabatically expands the high-pressure turbine air to generate low-pressure turbine air and generates the cold required for air separation operation; a low-pressure tower which performs low-pressure distillation of the low-pressure turbine air to separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen; an argon tower which pressurizes the argon-enriched liquefied oxygen and then performs low-temperature distillation at a pressure higher than that of the low-pressure tower to separate it into argon gas and medium-pressure liquefied oxygen; The air separation unit has an argon condenser that liquefies the argon gas to produce liquefied argon by indirect heat exchange between the gas and the low-pressure liquefied oxygen and vaporizes the low-pressure liquefied oxygen to produce low-pressure oxygen gas, a high-pressure nitrogen condenser that indirectly exchanges heat between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen to liquefy the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizes the medium-pressure liquefied oxygen to produce medium-pressure oxygen gas, and a product argon discharge line that extracts at least one type of argon as a product from among a portion of the argon gas, the argon gas that was not liquefied in the argon condenser, and a portion of the liquefied argon, and the turbine blower is driven to rotate by using the rotational energy generated by the expansion turbine, and includes a feed air bypass line that branches off a portion of the high-pressure feed air and merges it with the high-pressure turbine air after decompression.

According to the invention of claim 7, the turbine air evaporator liquefies the high-pressure nitrogen gas by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied nitrogen, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air. The air separation unit according to claim 6 is characterized in that the turbine air evaporator liquefies the high-pressure nitrogen gas by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air.

According to the invention of claim 8, the air separation unit according to claim 6 is provided, characterized in that the turbine air evaporator liquefies the high-pressure nitrogen-enriched air produced in the intermediate stage of the process in the high-pressure column by indirect heat exchange between the high-pressure nitrogen-enriched air and the medium-pressure oxygen-enriched liquefied air to produce high-pressure nitrogen-enriched liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to produce the medium-pressure turbine air.

According to the invention of claim 9, the air separation unit according to claim 6 is provided, characterized in that the turbine air evaporator liquefies the high-pressure feed air by indirect heat exchange between the high-pressure feed air and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air.

According to the invention of claim 10, there is provided an air separation unit according to any one of claims 6 to 9, further comprising a feed air bypass valve on the feed air bypass line, which is capable of indirectly adjusting the flow rate of the high-pressure feed air branched off from the high-pressure feed air by controlling the pressure after reduction.

As described above, the air separation method according to the present invention includes a turbine air generating step for generating intermediate pressure turbine air, a turbine air compressing step for generating high pressure turbine air, and a feed air bypass step for reducing the pressure of a portion of the high pressure feed air and merging it with the high pressure turbine air. In this manner, by branching off a portion of the high pressure feed air and merging it with the high pressure turbine air, which is oxygen-enriched air, it is possible to reduce the amount of refrigeration processed by the expansion turbine while maintaining the amount of refrigeration generated, or to increase the amount of refrigeration generated while maintaining the amount of refrigeration processed by the expansion turbine.
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.

In addition, according to the air separation unit of the present invention, in the apparatus configuration in which high-pressure oxygen-enriched liquefied air discharged from the bottom of the high-pressure column is depressurized and then vaporized by indirect heat exchange to generate medium-pressure turbine air, which is oxygen-enriched air, and this is compressed by a turbine blower and then adiabatically expanded by an expansion turbine to supply to the low-pressure column, a configuration is further adopted which includes a feed air bypass line for depressurizing a portion of the high-pressure feed air before it is merged with the high-pressure turbine air. By providing such a feed air bypass line, it is possible to reduce the amount of refrigeration generated while maintaining the amount of refrigeration generated, or to increase the amount of refrigeration generated while maintaining the amount of refrigeration generated by the expansion turbine.
Therefore, similarly to the above, it is possible to improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate.

FIG. 1 is a schematic diagram for explaining an air separation method and an air separation apparatus according to an embodiment of the present invention, and is a system diagram showing a schematic configuration of the entire air separation apparatus.

An air separation method and an air separation unit according to one embodiment of the present invention will now be described with reference to FIG.
In addition, the drawings used in the following description may show characteristic parts in an enlarged or simplified form for the sake of convenience in order to make the characteristics easier to understand. Furthermore, the materials and the like exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented within the scope of the present invention.

<Air separation unit>
An air separation unit that can be used in the operation of the air separation method of this embodiment will be described in detail below.
FIG. 1 is a system diagram showing an overall schematic configuration of an air separation unit 10 of the present embodiment.
In the description of this embodiment, "low pressure" refers to a pressure that is equal to or lower than the operating pressure of the low-pressure column 18, the details of which will be described later, and is equal to or lower than 400 kPaA. Also, "medium pressure" refers to a pressure that is equal to or lower than the pressure of the fluid having the highest pressure among the medium-pressure oxygen gas produced by vaporization in the high-pressure nitrogen condenser H2 and the medium-pressure turbine air produced by vaporization in the turbine air evaporator H3, and is higher than the operating pressure of the low-pressure column 18. Also, "high pressure" refers to a pressure that is higher than the pressure of the fluid having the highest pressure among the medium-pressure oxygen gas produced by vaporization in the high-pressure nitrogen condenser H2 and the medium-pressure turbine air produced by vaporization in the turbine air evaporator H3.

As shown in FIG. 1, the air separation unit 10 of this embodiment has an air compressor 11, an air precooler 12, an air purifier 13, an air booster 14, an air booster aftercooler 15, a main heat exchanger 16, a high-pressure tower 17, a low-pressure tower 18, an argon tower 19, a turbine air evaporator outer casing 20, 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, L192, and valves V1-V8. The air separation unit 10 of this embodiment is further generally configured to include a feed air bypass line L25 and a feed air bypass valve V9.

The air compressor 11 is provided on line L1 and is connected to a raw air supply source (not shown) that supplies air (raw air) containing oxygen, nitrogen, and argon, and to the air precooler 12 via line L1. The air compressor 11 compresses the air containing oxygen, nitrogen, and argon. The air (raw air) compressed by the air compressor 11 is transported to the air precooler 12 via line L1.

One end of line L1 is connected to a feed air supply source (not shown), and the other end is connected to the bottom of high-pressure tower 17. A portion of line L1 passes through main heat exchanger 16. Line L1 compresses air from a feed air supply source (not shown) in air compressor 11, precools it in air precooler 12, and purifies it in air purifier 13 to generate high-pressure feed air, which is cooled in main heat exchanger 16 and then supplied to high-pressure tower 17.

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

The air purifier 13 is provided on line L1 located between the air precooler 12 and the branching position of line L2. The air purifier 13 is connected to the air precooler 12 and the main heat exchanger 16 via 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 generate high-pressure feed air. The high-pressure feed air from which the impurities have been removed by the air purifier 13 is supplied to the bottom of the high-pressure tower 17 via line L1 and the main heat exchanger 16, and is also supplied to the air booster 14 via line L2 branched off from line L1, and is further supplied to line L51 via the feed air bypass line L25 branched off from line L1.

Line L2 branches off from line L1, which is located between air purifier 13 and main heat exchanger 16, and one end is connected to the lower part of high-pressure tower 17. A part of line L2 passes through main heat exchanger 16, and line L2 is provided with valve V4. Line L2 compresses a part of the high-pressure feed air purified by air purifier 13 in air booster 14, pre-cools it in air booster aftercooler 15, cools it in main heat exchanger 16, and reduces the pressure in valve V4 before supplying it to high-pressure tower 17.

The air booster 14 is provided on line L2, which is located between the branch point of line L2 from line L1 and the air booster aftercooler 15. The air booster 14 further compresses a portion of the high-pressure feed air from which impurities have been removed to generate compressed feed air. The compressed feed air compressed by the air booster 14 is transported to the air booster aftercooler 15 via line L2.

The air booster aftercooler 15 is provided in line L2 located downstream of the air booster 14. The air booster aftercooler 15 removes the heat of compression from the pressurized feed air compressed by the air booster 14. The pressurized feed air cooled by the air booster aftercooler 15 becomes high-pressure liquefied feed air via line L2, main heat exchanger 16, and valve V4, and is supplied to the bottom of the high-pressure tower 17.

Valve V4 is provided in line L2 located between the main heat exchanger 16 and the high-pressure column 17. Valve V4 reduces the pressure of the pressurized feed air cooled by the air booster aftercooler 15 and the main heat exchanger 16 to generate high-pressure feed liquefied air.

The main heat exchanger 16 is positioned so that a portion 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 the high-temperature fluid flowing through the lines L1, L2, and L51 and the low-temperature fluid flowing through the lines L5, L8, L13, L16, and L20 to cool each high-temperature fluid and heat each low-temperature fluid.

The high-pressure column 17 is connected to lines L1, L2, and L72. The high-pressure column 17 performs low-temperature distillation on a portion of the high-pressure feed air obtained by compressing, pre-cooling, purifying, and cooling air containing oxygen, nitrogen, and argon, as well as the high-pressure feed liquefied air supplied from line L2 and the high-pressure liquefied nitrogen supplied from line L72, to separate them into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air.
In the high pressure column 17, the high pressure nitrogen gas is concentrated in the upper part of the high pressure column 17 and the high pressure oxygen-enriched liquefied air is concentrated in the lower part of the high pressure column 17 by the above-mentioned low temperature distillation.

One end of line L71 is connected to the top of high-pressure tower 17, and the other end is connected to the liquefaction passage inlet of high-pressure nitrogen condenser H2. Line L71 supplies high-pressure nitrogen gas concentrated at the top of high-pressure tower 17 to high-pressure nitrogen condenser H2.

The high-pressure nitrogen condenser H2 is housed at the bottom of the argon tower 19, with a liquefaction passage inlet connected to line L71 and a liquefaction passage outlet connected to line L72. The high-pressure nitrogen condenser H2 liquefies the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizes the medium-pressure liquefied oxygen to produce medium-pressure oxygen gas by indirect heat exchange between the high-pressure nitrogen gas supplied from line L71 and the medium-pressure liquefied oxygen located at the bottom of the argon tower 19.

The line L8 is a line branched off from the line L71. A portion of the line L8 passes through the main heat exchanger 16. The line L8 is a line for recovering a portion of the high-pressure nitrogen gas as product high-pressure nitrogen gas (HPGN ₂ ) after heat recovery in the main heat exchanger 16.

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 of the high-pressure column 17. The line L72 supplies the high-pressure liquefied nitrogen produced in the high-pressure nitrogen condenser H2 to the high-pressure column 17.
The line L9 is a line branched off from the line L72 and connected to the top of the low-pressure column 18. A portion of the line L9 passes through the subcooler 21, and a valve V6 is provided in the path. The line L9 cools a portion of the high-pressure liquefied nitrogen produced in the high-pressure nitrogen condenser H2 in the subcooler 21, reduces the pressure in the valve V6, and then supplies the cooled portion to the low-pressure column 18.
The valve V6 is provided in a line L9 located between the low-pressure column 18 and the subcooler 21. The valve V6 reduces the pressure of the high-pressure liquefied nitrogen flowing through the line L9.
The line L10 is a line 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 (HPLN ₂ ).
One end of the line L11 is connected to an intermediate or lower portion of the high-pressure column 17, and the other end is connected to an intermediate or upper portion of the low-pressure column 18. A portion of the line L11 passes through a subcooler 21, and a valve V7 is provided on the path of the line L11. The line L11 extracts a portion of the fluid descending from the intermediate or lower portion of the high-pressure column 17, cools it in the subcooler 21, reduces the pressure through the valve V7, and then supplies it to the low-pressure column 18.
The valve V7 is provided in a line L11 located between the low-pressure column 18 and the subcooler 21. The valve V7 reduces the pressure of the fluid flowing through the line L11.

One end of the line L4 is connected to the bottom of the high-pressure column 17, and the other end is connected to the turbine air evaporator outer casing 20. A valve V1 is provided on the path of the line L4. The line L4 reduces the pressure of the high-pressure oxygen-enriched liquefied air extracted from the high-pressure column 17 by the valve V1, generates medium-pressure oxygen-enriched liquefied air, and supplies it to the turbine air evaporator outer casing 20.
The valve V1 is provided in the line L4. The valve V1 reduces the pressure of the high-pressure oxygen-enriched liquefied air flowing through the line L4 to generate medium-pressure oxygen-enriched liquefied air.
As shown by a dashed line in FIG. 1, it is also possible to extract a portion of the high-pressure oxygen-enriched liquefied air through a line L12 branched off from the line L4, cool it in a subcooler 21, reduce the pressure through a valve V3, and then supply it to the low-pressure column 18.

One end of the line L31 is connected to the upper part 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 extracts the concentrated high-pressure nitrogen gas at the upper part of the high-pressure column 17 and supplies it to the turbine air evaporator H3.
Incidentally, instead of extracting high pressure nitrogen gas from the upper part of the high pressure column 17 through line L31, it is also possible to extract a part of the high pressure feed air through line L33 branched off from line L1 and supply it to the turbine air evaporator H3, as shown by the dashed line in FIG. 1, or to extract the high pressure nitrogen-enriched air ascending through the intermediate or lower part of the high pressure column 17 through line L34, one end of which is connected to the intermediate or lower part of the high pressure column 17, and supply it to the turbine air evaporator H3.

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

The turbine air evaporator H3 is housed in the turbine air evaporator outer cylinder 20, and its liquefaction passage inlet is connected to one end of line L31. The turbine air evaporator H3 liquefies the high-pressure nitrogen gas supplied from line L31 to generate high-pressure liquefied nitrogen by indirect heat exchange between the high-pressure nitrogen gas supplied from line L31 and the medium-pressure oxygen-enriched liquefied air supplied from line L4, and vaporizes the medium-pressure oxygen-enriched liquefied air supplied from line L4 and stored inside the turbine air evaporator outer cylinder 20 to generate medium-pressure turbine air.

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 part of the low-pressure column 18. A part of the line L32 passes through the subcooler 21, and a valve V5 is provided in the path. The line L32 cools the high-pressure liquefied nitrogen produced in the turbine air evaporator H3 in the subcooler 21, reduces the pressure in the valve V5, and then supplies it to the low-pressure column 18.
1, it is also possible to provide a line L35 which 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 part 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 to the high-pressure column 17.

Valve V5 is provided in the path of line L32 located between low pressure column 18 and subcooler 21. Valve V5 reduces the pressure of the high pressure liquefied nitrogen flowing through line L32.

One end of the line L5 is connected to the gas outlet of the turbine air evaporator outer cylinder 20, and the other end is connected to the turbine blower 22. A portion of the line L5 passes through the main heat exchanger 16.
The line L5 supplies the intermediate pressure turbine air generated in the turbine air evaporator H3 housed inside the turbine air evaporator outer casing 20 to the turbine blower 22 after heat recovery in the main heat exchanger 16.

The turbine blower 22 is connected to one end of the line L5. The turbine blower 22 further compresses the intermediate pressure turbine air transported via the line L5 to generate high pressure turbine air. The turbine blower 22 is rotationally driven using the rotational energy generated by the expansion turbine 24 described below.

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 a turbine blower aftercooler 23, and a portion of the line passes through the main heat exchanger 16. The line L51 supplies the high-pressure turbine air compressed by the turbine blower 22 to the expansion turbine 24 after being cooled by the turbine blower aftercooler 23 and the main heat exchanger 16.

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

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 generate the cold necessary for the operation of the device, and also generates low-pressure turbine air.
The expansion turbine 24 uses the rotational energy generated by the expansion turbine 24 to rotate the turbine blower 22 .

One end of 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 tower 18. Line L52 supplies the low-pressure turbine air generated by the expansion turbine 24 to the middle part of the low-pressure tower 18.

One end of the line L6 is connected to the liquid outlet port of the turbine air evaporator outer cylinder 20, and the other end is connected to an intermediate portion of the low-pressure tower 18. A valve V2 is provided in the path of the line L6. The line L6 supplies the medium-pressure oxygen-enriched liquefied air contained inside the turbine air evaporator outer cylinder 20 that has not been vaporized in the turbine air evaporator H3 to the low-pressure tower 18 after reducing the pressure by the valve V2.
The valve V2 is provided in the path of the line L6. The valve V2 reduces the pressure of the fluid flowing through the line L6.

The low-pressure tower 18 is connected to one end of line L9, one end of line L32, one end of line L11, one end of line L52, and one end of line L6, and contains an argon condenser H1 at its bottom. The low-pressure tower 18 performs low-temperature distillation on the fluid depressurized by valve V5, the fluid depressurized by valve V6, the fluid depressurized by valve V2, the fluid depressurized by valve V7, the low-pressure turbine air obtained by adiabatic expansion in 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.

One end of the line L13 is connected to the top of the low-pressure column 18, and a portion 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 part 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.

An argon condenser H1 is provided at the bottom of the low-pressure column 18, and its liquefaction passage inlet is connected to line L191. The argon condenser H1 liquefies the argon gas to produce liquefied argon by indirect heat exchange between the argon gas supplied from line L191 and the low-pressure liquefied oxygen located at the bottom of the low-pressure column 18, and vaporizes the low-pressure liquefied oxygen to produce low-pressure oxygen gas.

One end of line L18 is connected to the middle part of low pressure column 18, and the other end is connected to the middle part or lower part of argon column 19. Line L18 is provided with an argon-enriched liquefied oxygen pump 26. Line L18 supplies argon-enriched liquefied oxygen concentrated in the middle part of low pressure column 18 to argon column 19 after pressurizing it with argon-enriched liquefied oxygen pump 26.

The argon-enriched liquefied oxygen pump 26 is provided in the path of line L18. The argon-enriched liquefied oxygen pump 26 pressurizes the argon-enriched liquefied oxygen discharged from the low-pressure column 18 to line L18.

The argon tower 19 is connected to one end of the lines L18 and L192, and contains a high-pressure nitrogen condenser H2 at its bottom. The argon tower 19 performs low-temperature distillation on the argon-enriched liquefied oxygen pressurized by the argon-enriched liquefied oxygen pump 26 and the liquefied argon supplied from the line L192 at a pressure higher than that of the low-pressure tower 18, thereby separating the argon gas and the medium-pressure liquefied oxygen.

One end of the line L191 is connected to the top 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 the argon gas concentrated in the upper part of the argon column 19 to the argon condenser H1.
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 of the argon column 19. The line L192 supplies the liquefied argon produced in the argon condenser H1 to the argon column 19.
One end of the line L15 is connected to the bottom 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 located at the bottom of the low-pressure column 18 to the line L16.

The line L17 is a line branched off from the line L15. The line L17 is a line for recovering a portion of the low-pressure liquefied oxygen flowing through the line L15 as product low-pressure liquefied oxygen (LPLO ₂ ).
One end of the line L23 is connected to the bottom 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. A valve V8 is provided in the path of the line L23. The line L23 is a line for supplying the medium-pressure liquefied oxygen located at the bottom of the argon column 19 to the line L16.
The valve V8 is provided in the line L23. The valve V8 reduces the pressure of the medium-pressure liquefied oxygen flowing through the line L23.
The line L24 is a line branched off from the line L23. The line L24 is a line for recovering a portion of the medium pressure liquefied oxygen flowing through the line L23 as product medium pressure liquefied oxygen (MPLO ₂ ).

One end of the line L16 is connected to one end of the line L15 and one end of the line L23. A part of the line L16 passes through the main heat exchanger 16, and a liquefied oxygen pump 25 is provided in the path of the line L16. The line L16 is a line for pressurizing the fluid supplied to the line L16 by the liquefied oxygen pump 25, recovering heat in the main heat exchanger 16, and recovering the fluid as product high-pressure oxygen gas (HPGO ₂ ).
The liquefied oxygen pump 25 is provided in a line L16 located upstream of the main heat exchanger 16. The liquefied oxygen pump 25 pressurizes the fluid supplied to the line L16.

The line L20 is a line branched off from the line L191, and a portion of the line L20 passes through the main heat exchanger 16. The line L20 is a line for recovering a portion of the argon gas flowing through the line L191 as product argon gas (GAR) after heat recovery in the main heat exchanger 16.
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 recovers the argon gas that was not liquefied in the argon condenser H1 as product argon gas (GAR) after heat recovery in the main heat exchanger 16.
The line L22 is a line branched off from the line L192. The line L22 is a line for recovering a portion of the liquefied argon flowing through the line L192 as product liquefied argon (LAR).

The supercooler 21 is disposed so that a part of the line L14, a part of the line L13, a part of the line L11, a part of the line L32, and a part of the line L9 pass through it. The supercooler 21 performs indirect heat exchange between the low-temperature fluid flowing through the line L13 and the high-temperature fluid flowing through the line L11, the line L32, and the line L9 to warm the low-temperature fluid and cool the high-temperature fluids.
However, the combination of the low-temperature fluid and the high-temperature fluid in the supercooler 21 is not limited to this.

One end of the line L14 is connected to the upper part 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 part of the low-pressure column 18 as waste nitrogen gas _WGN2 after heat recovery by the subcooler 21 and the main heat exchanger 16.

One end of the feed air bypass line L25 is connected to the line L1 downstream of the air purifier 13, and the other end is connected to the line L51 upstream of the main heat exchanger 16, with a feed air bypass valve V9 provided in the path. The feed air bypass line L25 branches off a portion of the high-pressure feed air from the line L1, and after reducing the pressure of the feed air by the feed air bypass valve V9, the feed air bypass line L25 merges with the high-pressure turbine air flowing through the line 51.
The feed air bypass valve V9 is provided on the route of the feed air bypass line L25 located upstream of the main heat exchanger 16. The feed air bypass valve V9 reduces the pressure of the high-pressure feed air flowing through the feed air bypass line L25. More specifically, the feed air bypass valve V9 is configured to be able to indirectly adjust the flow rate of the high-pressure feed air in the feed air bypass line L25 by controlling the pressure of the high-pressure feed air branched off from the line L1 after it has been reduced in pressure.

In this embodiment, the feed air bypass valve V9 is an automatic valve, and a flow regulator (not shown) can be used to operate the feed air bypass valve V9 so that the value indicated by a flow meter (not shown) installed in the feed air bypass line L25 matches the set value. In addition, a pressure regulator (not shown) can be used to indirectly control the flow rate by manipulating the set value of the flow regulator so that the value indicated by a pressure gauge (not shown) installed in the inlet system of the expansion turbine 24 matches the target value.

In the air separation unit 10 of this embodiment, as an example, a case has been described in which the unit has lines L20 and L22 for extracting product argon gas (GAR) or product liquefied argon (LAR), but it is sufficient to have at least one of lines L20 and L22.

1, for example, when product low-pressure oxygen gas (LPGO ₂ ) is recovered, a product discharge line is provided whose one end is connected to the bottom of the low-pressure column 18 and whose part passes through the main heat exchanger 16. In this case, the product discharge line (not shown) recovers the low-pressure oxygen gas from the low-pressure column 18 as product low-pressure oxygen gas (LPGO ₂ ) after heat recovery in the main heat exchanger 16.
Furthermore, for example, when product medium-pressure oxygen gas ( _MPGO2 ) is recovered, a product discharge line (not shown) is provided, one end of which is connected to the bottom of the argon column 19 and a part of which passes through the main heat exchanger 16. In this case, this product discharge line recovers the medium-pressure oxygen gas from the argon column 19 as product medium-pressure oxygen gas ( _MPGO2 ) after heat recovery in the main heat exchanger 16.

In addition, if product high pressure oxygen gas (HPGO ₂ ) is not recovered instead of recovering product low pressure oxygen gas (LPGO ₂ ), product medium pressure oxygen gas (MPGO ₂ ), product medium pressure liquefied oxygen (MPLO ₂ ), product low pressure liquefied oxygen (LPLO ₂ ), etc., line L16, liquefied oxygen pump 25, air booster 14, air booster aftercooler 15, line L2, and valves V4 and V8 can be excluded from the components.

The air separation unit 10 of this embodiment includes a high-pressure tower 17 that cools the high-pressure feed air obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon, and then performs low-temperature distillation to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a turbine air evaporator H3 that vaporizes the medium-pressure oxygen-enriched liquefied air obtained by reducing the pressure of the high-pressure oxygen-enriched liquefied air to generate medium-pressure turbine air; a turbine blower 22 that warms the medium-pressure turbine air and then compresses it to generate high-pressure turbine air; an expansion turbine 24 that adiabatically expands the high-pressure turbine air to generate low-pressure turbine air and generates the cold required for air separation operation; a low-pressure tower 18 that performs low-pressure distillation of the low-pressure turbine air to separate it into low-pressure nitrogen gas, low-pressure liquefied oxygen, and argon-enriched liquefied oxygen; and a turbine air evaporator H4 that compresses the argon-enriched liquefied oxygen and then releases it from the low-pressure tower 18. the argon column 19 performing low-temperature distillation at a pressure as high as possible to separate the argon gas and the medium-pressure liquefied oxygen; an argon condenser H1 liquefying the argon gas to produce liquefied argon by indirect heat exchange between the argon gas and the low-pressure liquefied oxygen and vaporizing the low-pressure liquefied oxygen to produce low-pressure oxygen gas; a high-pressure nitrogen condenser H2 performing indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen to liquefy the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizing the medium-pressure liquefied oxygen to produce medium-pressure oxygen gas; and lines L20, L21 which are product argon discharge lines for extracting at least one type of argon from a portion of the argon gas, the argon gas not liquefied in the argon condenser, and a portion of the liquefied argon as product argon gas (GAR) or product liquefied argon (LAR). In this embodiment of the air separation unit 10, the turbine blower 22 uses the rotational energy generated by the expansion turbine 24 to rotate the turbine blower 22, and further includes a feed air bypass line L25 that branches off a portion of the high-pressure feed air and merges it with the high-pressure turbine air after decompression.

According to the air separation unit 10 of this embodiment, by being provided with the above-mentioned configuration, even when, for example, the flow rates of product medium pressure liquefied oxygen (MPLO ₂ ), product low pressure liquefied oxygen (LPLO ₂ ), product high pressure liquefied nitrogen (HPLN ₂ ), etc. are high and a large amount of refrigeration is required for operation, it is possible to relatively reduce the flow rate of the turbine blower 22 and increase the compression ratio by bypassing a portion of the high pressure feed air to the line L51 which serves as the inlet of the expansion turbine 24, thereby preventing an increase in the throughput caused by increasing the expansion ratio of the expansion turbine 24. As a result, the flow rate of the low pressure turbine air supplied to the low pressure column 18 can be reduced, making it possible to improve the argon recovery rate.

On the other hand, in the case of a configuration in which some or all of the low-pressure turbine air is recovered (released into the atmosphere) without being supplied to the low-pressure tower, as in Patent Document 2 mentioned above, the flow rate of the low-pressure turbine air supplied to the low-pressure tower is optimized and the argon recovery rate can be improved, but the oxygen recovery rate decreases because the oxygen component contained in the low-pressure turbine air that is not supplied to the low-pressure tower cannot be recovered as a product. In contrast, by using the air separation unit 10 of this embodiment, the entire amount of low-pressure turbine air can be supplied to the low-pressure tower 18 and used as a feedstock for the low-pressure tower 18, thereby suppressing a decrease in the oxygen recovery rate.

<Air separation method>
The air separation method of this embodiment will be described in detail below by taking as an example a method of performing air separation using the air separation unit 10 shown in FIG.
In the following explanation, similar to the explanation of the air separation unit 10 of this embodiment described above, the explanation will be made with reference to FIG. 1, and detailed explanation of the configuration of the air separation unit 10 already explained will be omitted.

Air containing oxygen, nitrogen, and argon is supplied to a line L1. This air is compressed by an air compressor 11, the heat of compression is removed by an air precooler 12, and impurities contained in the air, specifically, for example, water and carbon dioxide, are removed by an air purifier 13 to produce high-pressure feed air.
A portion of the high-pressure feed air from which the impurities have been removed in the air purifier 13 is cooled in the main heat exchanger 16 and supplied to the high-pressure column 17.

The remaining part of the high-pressure feed air from which impurities have been removed in the air purifier 13 is further pressurized by the air booster 14 installed in line L2 branched off from line L1 to become pressurized feed air. The compressed feed air has heat of compression removed by the air booster aftercooler 15, is cooled in the main heat exchanger 16, and is then reduced in pressure by valve V4 to become high-pressure liquefied feed air, which is then supplied to the high-pressure column 17.

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

In the high-pressure column 17, the high-pressure feed air introduced via line L1, the high-pressure liquefied feed air introduced via line L2, and the high-pressure liquefied nitrogen introduced via line L72 are separated by low-temperature distillation into high-pressure nitrogen gas located at the top of the high-pressure column 17 and high-pressure oxygen-enriched liquefied air located at the bottom (high-pressure separation process).

The high pressure nitrogen gas located at the top of the high pressure column 17 is introduced via line L71 into a high pressure nitrogen condenser H2 housed at the bottom of the argon column 19.
The high-pressure nitrogen gas supplied to the high-pressure nitrogen condenser H2 via line L71 liquefies itself to become high-pressure liquefied nitrogen through indirect heat exchange with the medium-pressure liquefied oxygen located at the bottom of the argon column 19, and also vaporizes the medium-pressure liquefied oxygen located at the bottom of the argon column 19 to produce medium-pressure oxygen gas (high-pressure nitrogen condensation process).

A part of the high pressure nitrogen gas discharged to the line L71 is discharged to a line L8 branched off from the line L71, and after heat recovery in the main heat exchanger 16, is recovered as product high pressure nitrogen gas (HPGN ₂ ).

High pressure liquefied nitrogen produced in high pressure nitrogen condenser H2 is introduced into the top of high pressure column 17 via line L72.
A portion of the high pressure liquefied nitrogen discharged to the line L72 is discharged to the line L9, cooled in the subcooler 21, and introduced into the top of the low pressure column 18 after being reduced in pressure through the valve V6.
A portion of the high pressure liquefied nitrogen in line L9 is discharged to line L10 and recovered as product high pressure liquefied nitrogen (HPLN ₂ ).

The high-pressure oxygen-enriched liquefied air located at the bottom of the high-pressure column 17 is discharged to a line L4, where it is depressurized at a valve V1 to become medium-pressure oxygen-enriched liquefied air, which is then supplied to the turbine air evaporator outer casing 20.
A portion of the high pressure nitrogen gas concentrated in the upper portion of the high pressure column 17 is discharged from the upper portion of the high pressure column 17 to a line L31 and introduced into the turbine air evaporator H3.

The high-pressure nitrogen gas supplied to the turbine air evaporator H3 via line L31 liquefies itself to become high-pressure liquefied nitrogen through indirect heat exchange with the medium-pressure oxygen-enriched liquefied air supplied to the turbine air evaporator outer casing 20 via line L4, and vaporizes the medium-pressure oxygen-enriched liquefied air supplied to the turbine air evaporator outer casing 20 via line L4 to generate medium-pressure turbine air (turbine air generation process).

The fluid introduced into the turbine air evaporator H3 via line L31 may be a part of the high-pressure feed air (line L33) or a part of the high-pressure nitrogen-enriched air rising in the middle or lower part of the high-pressure column 17 (line L34), instead of the high-pressure nitrogen gas concentrated in the upper part of the high-pressure column 17, as shown by the dashed lines in FIG. 1.
Even in this case, a portion of the high pressure feed air or a portion of the high pressure nitrogen-enriched air is liquefied in the turbine air evaporator H3 to become high pressure liquefied air or high pressure nitrogen-enriched liquefied air, respectively.

By changing the fluid as described above, the fluid temperature on the condensation side in the turbine air evaporator H3 increases, and the fluid temperature on the evaporation side also increases, so the pressure of the medium-pressure turbine air generated in the turbine air evaporator H3 increases, which has the advantage of making it possible to increase the expansion ratio in the expansion turbine 24, which will be described later.

In addition, in this embodiment, as shown by the dashed line in Figure 1, it is also possible to discharge all or part of the fluid liquefied in the turbine air evaporator H3 to line L35 branched off from line L32 and supply it to the high-pressure column 17.

The high-pressure liquefied nitrogen produced in the turbine air evaporator H3 is discharged to a line L32, cooled in a subcooler 21, and reduced in pressure through a valve V5, before being introduced into the upper part of the low-pressure column 18.
The intermediate-pressure turbine air generated in the turbine air evaporator H3 is discharged to a line L5, and is subjected to heat recovery to room temperature in the main heat exchanger 16, and then compressed by the turbine blower 22 (turbine air compression process).
In the turbine air compression process, the intermediate-pressure turbine air is compressed using energy generated in a turbine air adiabatic expansion process, the details of which will be described later. That is, in the turbine air compression process, the turbine blower 22 is rotationally driven by the expansion turbine 24 to compress the intermediate-pressure turbine air.

The high-pressure turbine air compressed and generated by the turbine blower 22 is discharged to a line L51, has heat of compression removed in the turbine blower aftercooler 23, and is further cooled in the main heat exchanger 16 before being introduced into the expansion turbine 24.
The high-pressure turbine air introduced into the expansion turbine 24 is reduced in pressure by adiabatic expansion to near the operating pressure of the low-pressure column 18, and after generating the refrigeration necessary to operate the equipment, becomes low-pressure turbine air and is discharged to line L52 (turbine air adiabatic expansion process).
The energy generated by the turbine air adiabatic expansion process is utilized in the above-mentioned turbine air compression process to compress the intermediate-pressure turbine air.

Here, in the air separation method of this embodiment, a portion of the high-pressure feed air is branched off from line L1 by feed air bypass line L25, and after being reduced in pressure by feed air bypass valve V9, it is merged with the high-pressure turbine air circulating through line 51 (feed air bypass process).
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, increasing the expansion ratio of the expansion turbine 24. This makes it possible to increase the amount of refrigeration generated per unit throughput in the expansion turbine 24.
Since the pressure of the high-pressure turbine air increases with an increase in the flow rate of the feed air bypass line L25, it becomes possible to adjust the pressure of the high-pressure turbine air by adjusting the flow rate of the feed 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 feed air or the pressure of the high-pressure column 17.

In the feed air bypass step, for example, the feed air bypass valve V9 controls the pressure after reduction of the high-pressure feed air branched off from the line L1, thereby indirectly adjusting the flow rate of the high-pressure feed air in the feed air bypass line L25.
The feed air bypass line L25 and the feed air bypass valve V9 can also be used during start-up of the air separation unit 10. In this case, when the air separation unit 10 is started up and each device such as the high-pressure column 17, the low-pressure column 18, the argon column 19, etc. is cooled from an initial state at room temperature to a low-temperature steady state, the high-pressure feed air in the line L1 can be supplied to the expansion turbine 24 via the feed air bypass line L25 without passing through the high-pressure column 17. This allows a low-temperature fluid to be produced by adiabatic expansion in the expansion turbine 24, making it possible to efficiently cool the unit.

The low-pressure turbine air discharged to line L52 is introduced into the middle of low-pressure column 18 as a feedstock for low-pressure column 18.

The medium-pressure oxygen-enriched liquefied air that is supplied to the turbine air evaporator outer cylinder 20 and is not vaporized in the turbine air evaporator H3 is discharged to line L6, depressurized by valve V2, and then introduced into the middle of the low-pressure tower 18 as the feedstock for the low-pressure tower 18.

In the low-pressure tower 18, the fluid depressurized by valve V5, the fluid depressurized by valve V7, the fluid depressurized by valve V6, the fluid depressurized by valve V2, the low-pressure turbine air obtained by adiabatic expansion in 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 low-pressure nitrogen gas located at the top of the low-pressure tower 18, low-pressure liquefied oxygen located at the bottom of the low-pressure tower 18, and argon-enriched liquefied oxygen located in the middle of the low-pressure tower 18 (low-pressure separation process).

The low-pressure nitrogen gas located at the top of the low-pressure column 18 is discharged to a line L13, and after heat recovery by the subcooler 21 and the main heat exchanger 16, is recovered as product low-pressure nitrogen gas (LPGN ₂ ).
The low-purity low-pressure nitrogen gas rising in the upper part of the low-pressure column 18 is discharged to line L14, and after heat recovery in the subcooler 21 and the main heat exchanger 16, is recovered as waste nitrogen gas WGN _2. In the subcooler 21, each high-temperature fluid is cooled and each low-temperature fluid is heated by indirect heat exchange between the high-temperature fluid flowing in line L11, line L32, and line L9 and the low-temperature fluid flowing in line L13 and line L14, but the combination of the high-temperature fluid and the low-temperature fluid is not limited to this.
The low-pressure liquefied oxygen located at the bottom of the low-pressure column 18 vaporizes into low-pressure oxygen gas through indirect heat exchange with argon gas at the top of the argon column 19 in the argon condenser H1 housed at the bottom of the low-pressure column 18, and at the same time liquefies the argon gas to produce liquefied argon (argon condensation process).

The low-pressure liquefied oxygen that was not vaporized in the argon condenser H1 is discharged to a line L15, where it merges with the medium-pressure liquefied oxygen whose pressure has been reduced by a valve V8, and is introduced into a line L16.
The fluid introduced into line L16 is pressurized to the required pressure according to the product specifications by the liquefied oxygen pump 25 to become high-pressure liquefied oxygen. The high-pressure liquefied oxygen is entirely vaporized in the main heat exchanger 16, and after heat recovery to room temperature, it is recovered as product high-pressure oxygen gas (HPGO ₂ ).
A portion of the low-pressure liquefied oxygen discharged to line L15 is discharged to line L17 branched off from line L15 and recovered as product low-pressure liquefied oxygen (LPLO ₂ ).

The argon-enriched liquefied oxygen concentrated in the middle of the low-pressure column 18 is discharged to line L18 and pressurized by the argon-enriched liquefied oxygen pump 26 to the pressure required to send the liquid to the argon column 19, which has a higher operating pressure than the low-pressure column 18, and then introduced into the middle or lower part of the argon column 19.

Depending on the relative positions of the low-pressure tower 18 and the argon tower 19, it may be possible to send argon-enriched liquefied oxygen from the low-pressure tower 18 to the argon tower 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.

In the argon tower 19, the argon-enriched liquefied oxygen supplied via line L18, the liquefied argon supplied via line L192, and the medium-pressure oxygen gas obtained by vaporization in the high-pressure nitrogen condenser H2 are separated by low-temperature distillation into argon gas located at the top of the argon tower 19 and medium-pressure liquefied oxygen located at the bottom of the argon tower 19 (argon separation process).

The argon gas located at the top of the argon column 19 is introduced into an argon condenser H1 via a line L191.
The argon gas introduced into the argon condenser H1 liquefies itself to become liquefied argon through indirect heat exchange with the low-pressure liquefied oxygen located at the bottom of the low-pressure column 18, and at the same time, the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas (argon condensation process).
The liquefied argon produced by the argon condensation step is introduced into the top of the argon column 19 via line L192.
A portion of the argon gas in line L191 is discharged to line L20 branched off from line L191, and after heat recovery to room temperature in the main heat exchanger 16, is recovered as product argon gas (GAR) (product argon discharge process).

In addition, as shown by the dashed line in FIG. 1, argon gas that is not liquefied in the argon condenser H1 may be discharged to a line L21, and after heat recovery to room temperature in the main heat exchanger 16, may be recovered as product argon gas (GAR).
A portion of the liquefied argon flowing through line L192 is discharged to line L22 branched off from line L192 and recovered as product liquefied argon (LAR) (product argon discharge step).

The medium-pressure liquefied oxygen located at the bottom of the argon column 19 vaporizes into medium-pressure oxygen gas through indirect heat exchange with the high-pressure nitrogen gas supplied from the top of the high-pressure column 17 in the high-pressure nitrogen condenser H2 contained at the bottom of the argon column 19, and at the same time liquefies the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen (high-pressure nitrogen condensation process).
The medium-pressure liquefied oxygen that has not been vaporized in the high-pressure nitrogen condenser H2 is discharged to a line L23, and after being reduced in pressure by a valve V8, it joins with the low-pressure liquefied oxygen in a line L15.
A portion of the medium pressure liquefied oxygen discharged to the line L23 is discharged to a line L24 branched off from the line L23 and recovered as product medium pressure liquefied oxygen (MPLO ₂ ).

Although not shown in FIG. 1, one end of the line L15 connected to the bottom of the low-pressure column 18 may be connected to the lower part of the argon column 19 at the other end. In this case, the line L15 pressurizes the low-pressure liquefied oxygen discharged from the bottom of the low-pressure column 18 by a liquid head due to a difference in liquid level or a pump (not shown) installed in the line L15 to generate pressurized liquefied oxygen, which is supplied to the lower part of the argon column 19. The pressurized liquefied oxygen supplied from the line L15 is merged with the medium-pressure liquefied oxygen located at the bottom of the argon column 19, discharged to the line L23, and recovered as product high-pressure oxygen gas (HPGO ₂ ) via the line L16. In this case, the valve V8 installed in the line L23 is not necessary.
1, one end of a line L23 connected to the bottom of the argon column 19 may be connected to the lower part of the low-pressure column 18 at the other end. In this case, the line L23 reduces the pressure of the medium-pressure liquefied oxygen discharged from the bottom of the argon column 19 via a valve V8 to generate reduced-pressure liquefied oxygen and supplies it to the lower part of the low-pressure column 18. The reduced-pressure liquefied oxygen supplied from the line L23 merges with the low-pressure liquefied oxygen located at the bottom of the low-pressure column 18, is discharged to a line L15, and is recovered as a product high-pressure oxygen gas (HPGO ₂ ) via a line L16.

Although not shown in FIG. 1, a part or all of the high-pressure liquefied feed air introduced into the high-pressure column 17 via line L2 may be supplied to the middle or upper part of the low-pressure column 18.
In addition, the feed air bypass line L25 may branch off from the middle of the main heat exchanger 16 of line L1 or from the outlet of the main heat exchanger 16 of line L1 and merge with the inlet of the expansion turbine 24 of line L51. In this case, it is possible to bypass and supply a part of the high-pressure feed air cooled in the main heat exchanger 16 of line L1 to the inlet of the expansion turbine 24.

The concentration of argon contained in the product argon gas (GAR) and the concentration of argon contained in the product liquefied argon (LAR) are, for example, 50% or more, and preferably 95% or more.
In addition to being recovered as a product as described above, argon gas and liquefied argon may be provided with an argon purification facility (not shown) in a downstream stage to remove impurities such as oxygen and nitrogen components.
Even when product argon gas (GAR) or product liquefied argon (LAR) is not required, if the purity of product high pressure oxygen gas ( _HPGO2 ) or product liquefied oxygen ( _LPLO2 , _MPLO2 , etc.) is high, for example, if the oxygen concentration is 98% or more, argon gas may be recovered in order to improve the oxygen recovery rate.

Although not shown in FIG. 1, when product low-pressure oxygen gas (LPGO ₂ ) is recovered, the low-pressure oxygen gas is discharged from the bottom of the low-pressure column 18, and is recovered as a product after being subjected to heat recovery to room temperature in the main heat exchanger 16.
When medium pressure oxygen gas product (MPGO ₂ ) is recovered, the medium pressure oxygen gas is discharged from the bottom of the argon column 19, and is recovered as a product after being cooled to room temperature in the main heat exchanger 16 .

When product low-pressure oxygen gas (LPGO ₂ ) and/or product medium-pressure oxygen gas (MPGO ₂ ) are recovered, the flow rate balance can be adjusted by introducing low-pressure liquefied oxygen from the bottom of the low-pressure tower 18 to the bottom of the argon tower 19 via a line not shown, or by introducing medium-pressure liquefied oxygen from the bottom of the argon tower 19 to the bottom of the low-pressure tower 18 via a line not shown.

The air separation method of this embodiment includes a high-pressure separation process in which high-pressure feed air obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon is cooled and then subjected to low-temperature distillation to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air; a turbine air generation process in which the medium-pressure oxygen-enriched liquefied air obtained by reducing the pressure of the high-pressure oxygen-enriched liquefied air is vaporized to generate medium-pressure turbine air; a turbine air compression process in which the medium-pressure turbine air is heated and then compressed to generate high-pressure turbine air; a turbine air adiabatic expansion process in which the high-pressure turbine air is adiabatically expanded to generate low-pressure turbine air and generate the cold necessary for air separation operation; a low-pressure separation process 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; and an adiabatic separation process in which the argon-enriched liquefied oxygen is pressurized and then subjected to low-temperature distillation at a pressure higher than that in the low-pressure separation process to separate it into argon gas and medium-pressure liquefied oxygen. The turbine air compression process includes a argon separation process, an argon condensation process in which argon gas is liquefied to produce liquefied argon by indirect heat exchange between argon gas and low-pressure liquefied oxygen, and low-pressure oxygen gas is produced by vaporizing the low-pressure liquefied oxygen, a high-pressure nitrogen condensation process in which high-pressure nitrogen gas is liquefied to produce high-pressure liquefied nitrogen by indirect heat exchange between high-pressure nitrogen gas and medium-pressure liquefied oxygen, and medium-pressure oxygen gas is produced by vaporizing the medium-pressure liquefied oxygen, and a product argon extraction process in which at least one of a portion of the argon gas, the argon gas not liquefied in the argon condensation process, and a portion of the liquefied argon is extracted as a product. The turbine air compression process compresses the medium-pressure turbine air using the energy generated by the turbine air adiabatic expansion process, and further includes a feed air bypass process in which a portion of the high-pressure feed air is branched off and merged with the high-pressure turbine air after decompression.

According to the air separation method of the present embodiment, by providing a method including the above-mentioned steps, even when, for example, the flow rates of product medium pressure liquefied oxygen (MPLO ₂ ), product low pressure liquefied oxygen (LPLO ₂ ), product high pressure liquefied nitrogen (HPLN ₂ ), etc. are high and a large amount of refrigeration is required for operation, by bypassing a portion of the high pressure feed air to 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 preventing an increase in the expansion ratio of the expansion turbine 24 and an increase in the throughput. This makes it possible to reduce the flow rate of the low pressure turbine air supplied to the low pressure column 18, thereby improving the argon recovery rate.

In addition, as in Patent Document 2 mentioned above, when some or all of the low-pressure turbine air is recovered (released into the atmosphere) without being supplied to the low-pressure tower, the flow rate of the low-pressure turbine air supplied to the low-pressure tower is optimized and the argon recovery rate can be improved, but the oxygen recovery rate decreases because the oxygen component contained in the low-pressure turbine air not supplied to the low-pressure tower cannot be recovered as a product. In contrast, by using the air separation unit 10 of this embodiment, the entire amount of low-pressure turbine air can be supplied to the low-pressure tower 18 and used as a feedstock for the low-pressure tower 18, thereby suppressing a decrease in the oxygen recovery rate.

As mentioned above, the high pressure column 17, the low pressure column 18, and the argon column 19 are thermally integrated by each process, so the operating pressure of each distillation column increases in the order of low pressure column 18, argon column 19, and high pressure column 17.

<Other forms>
Although an example of the air separation method and air separation apparatus according to the present invention has been described above using the embodiments, the present invention is not limited to the above-mentioned embodiments. Each configuration and their combination in the above-mentioned embodiments is an example, and addition, omission, substitution, and other modifications of the configuration are possible within the scope of the gist of the present invention.

<Action and effect>
As described above, the air separation method of the present embodiment includes a turbine air generating step for generating intermediate pressure turbine air, a turbine air compressing step for generating high pressure turbine air, and further includes a feed air bypass step for reducing the pressure of a portion of the high pressure feed air and merging it with the high pressure turbine air. In this manner, by branching off a portion of the high pressure feed air and merging it with the high pressure turbine air, which is oxygen-enriched air, it is possible to reduce the throughput of the expansion turbine 24 while maintaining the amount of refrigeration generated, or to increase the amount of refrigeration generated while maintaining the throughput of the expansion turbine 24.
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.

Moreover, according to the air separation unit 10 of this embodiment, in the apparatus configuration in which the high-pressure oxygen-enriched liquefied air drawn out from the bottom of the high-pressure column 17 is depressurized and then vaporized by indirect heat exchange to generate medium-pressure turbine air, which is oxygen-enriched air, and this is compressed by the turbine blower 22 and then adiabatically expanded by the expansion turbine 24 to supply to the low-pressure column 18, a configuration is further adopted which includes a feed air bypass line L25 for depressurizing a portion of the high-pressure feed air and then merging it with the high-pressure turbine air. By providing such a feed air bypass line L25, it is possible to reduce the throughput of the expansion turbine 24 while maintaining the amount of refrigeration generated, or to increase the amount of refrigeration generated while maintaining the throughput of the expansion turbine 24, as described above.
Therefore, similarly to the above, it is possible to improve the argon recovery rate while maintaining the oxygen recovery rate or suppressing a decrease in the oxygen recovery rate.

The air separation method and air separation apparatus of the present invention will be described 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 spirit and scope of the present invention.

<Example>
In the examples, a simulation was carried out using air separation unit 10 shown in FIG. 1 using a simulator manufactured by Taiyo Nippon Sanso Corporation (this simulator is the same as that used when actually designing air separation units).

In the simulation in this embodiment, the flow rate of the high pressure feed air was set to 100, and the conditions for recovering product low pressure nitrogen gas (LPGN ₂ ) 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 (HPGN ₂ ) with a flow rate of 9.8, pressure of 800 kPaA or more, and oxygen concentration of 0.1 ppm or less, and product low pressure liquefied nitrogen (LPLN ₂ ) with a flow rate of 2.2 and oxygen concentration of 0.1 ppm or less were set to calculate the recoverable flow rates of product high pressure oxygen gas (HPGO ₂ ) with a pressure of 3120 kPaA and oxygen concentration of 99.6% or more, and product argon gas (GAR) with an oxygen concentration of 1.5% or less. The flow rate of the high pressure feed air flowing through the feed air bypass line L25 was set to 6.1.

The simulation conditions and results of the above embodiment are shown in Table 1 below. Table 1 below is a table showing a list of the simulation conditions and simulation results of the embodiment and the comparative example described below. In addition, in Table 1 below, values in parentheses are calculated values obtained by simulation.

Comparative Example
In the comparative example, a simulation was carried out under the same conditions as in the above example, except for the case where the feed air bypass line L25 shown in FIG. 1 was not used, i.e., the flow rate of the high-pressure feed air in the feed air bypass line L25 was set to 0 (zero), and the results are shown in Table 1 above.

<Evaluation Results of Examples and Comparative Examples>
As shown in the simulation results in Table 1, in an example where a simulation was performed using an air separation unit 10 equipped with a feed air bypass line L25 as shown in Figure 1 and a part of the high-pressure feed air was passed through the feed 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, i.e., the inlet pressure of the expansion turbine 24, increased, the expansion ratio of the expansion turbine 24 increased, and the throughput of the expansion turbine 24 decreased. As a result, in the example, the amount of low-pressure turbine air supplied to the low-pressure tower 18 decreased, and conversely, the flow rates of the medium-pressure oxygen gas and low-pressure oxygen gas generated in the high-pressure nitrogen condenser and the argon condenser increased, and as a result, it was confirmed that the flow rate of the product argon gas (GAR) increased while the flow rate of the product high-pressure oxygen gas (HPGO ₂ ) was maintained. Specifically, in the example, the flow rate of the product high-pressure oxygen gas (HPGO ₂ ) was maintained at 19.2, and the flow rate of the product argon gas (GAR) was obtained at 0.62.

On the other hand, in the comparative example where the simulation was performed under the condition that high pressure feed air was not flowing through the feed air bypass line L25, it was confirmed that the outlet pressure of the turbine blower 22 driven by the expansion turbine 24, i.e., the inlet pressure of the expansion turbine 24, was lower than in the example, and therefore the expansion ratio of the expansion turbine 24 was also lowered and the throughput was increased. As a result, in the comparative example, the amount of low pressure turbine air supplied to the low pressure tower 18 was increased to 30.0 compared to the example, and as a result, 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 reduced to 0.50.

From the results of the examples described above, it has been confirmed that the air separation method of the present invention equipped with a feed air bypass process, and the air separation unit 10 of the present invention equipped with a feed air bypass line L25, are capable of improving the argon recovery rate while maintaining or suppressing a decrease in the oxygen recovery rate.

The air separation method and air separation apparatus of the present invention can improve argon recovery while maintaining or suppressing a decrease in oxygen recovery, and is therefore highly suitable for various applications in which oxygen and nitrogen are produced industrially.

LIST OF SYMBOLS 10: Air separation unit 11: Air compressor 12: Air precooler 13: Air purifier 14: Air booster 15: Air booster aftercooler 16: Main heat exchanger 17: High pressure column 18: Low pressure column 19: Argon column 20: Turbine air evaporator outer cylinder 21: Subcooler 22: Turbine blower 23: Turbine blower aftercooler 24: Expansion turbine 25: Liquefied oxygen pump 26: Argon-enriched liquefied oxygen pump H1: Argon condenser H2: High pressure nitrogen condenser H3: Turbine air evaporator L1, L2, L4-L6, L8-L18, L20-L24, L31-L35, L51, L52, L71, L72, L191, L192: Line L25: Feed air bypass line V1-V8: Valve V9: Feed air bypass valve

Claims (10)

A high-pressure separation process in which high-pressure feed air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon is cooled and then subjected to low-temperature distillation to separate it into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air;
a turbine air generating step of vaporizing medium-pressure oxygen-enriched liquefied air obtained by reducing the pressure of the high-pressure oxygen-enriched liquefied air to generate medium-pressure turbine air;
a turbine air compression step of heating the intermediate pressure turbine air and then compressing it to generate high pressure turbine air;
a turbine air adiabatic expansion step of adiabatically expanding the high-pressure turbine air to generate low-pressure turbine air and generate refrigeration necessary for air separation operation;
a low pressure separation step for cryogenically distilling the low pressure turbine air and separating 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 is pressurized and then subjected to low-temperature distillation at a pressure higher than that of the low-pressure separation step to separate the argon-enriched liquefied oxygen into argon gas and medium-pressure liquefied oxygen;
an argon condensation step in which the argon gas is liquefied to produce liquefied argon by indirect heat exchange between the argon gas and the low-pressure liquefied oxygen, and the low-pressure liquefied oxygen is vaporized to produce low-pressure oxygen gas;
a high-pressure nitrogen condensation step of liquefying the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizing the medium-pressure liquefied oxygen to produce medium-pressure oxygen gas by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen;
and a product argon extraction step of extracting at least one type of argon as a product from among a portion of the argon gas, the argon gas not liquefied in the argon condensation step, and a portion of the liquefied argon,
the turbine air compression process compresses the intermediate-pressure turbine air using the energy generated by the turbine air adiabatic expansion process;
The air separation method further comprises a feed air bypass step of branching off a portion of the high pressure feed air and, after reducing the pressure, allowing it to merge with the high pressure turbine air. The air separation method according to claim 1, characterized in that the turbine air generation process liquefies the high-pressure nitrogen gas by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied nitrogen, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air. The air separation method according to claim 1, characterized in that the turbine air generation process liquefies the high-pressure nitrogen-enriched air generated in an intermediate stage of the high-pressure separation process by indirect heat exchange between the high-pressure nitrogen-enriched air and the medium-pressure oxygen-enriched liquefied air to generate the high-pressure nitrogen-enriched liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air. The air separation method according to claim 1, characterized in that the turbine air generation process liquefies the high-pressure feed air by indirect heat exchange between the high-pressure feed air and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air. The air separation method according to any one of claims 1 to 4, characterized in that the feed air bypass process indirectly adjusts the flow rate of the high-pressure feed air branched off from the high-pressure feed air by controlling the pressure after decompression. A high-pressure column that compresses, pre-cools, and refines air containing oxygen, nitrogen, and argon, cools the high-pressure feed air, and then performs low-temperature distillation to separate the air into high-pressure nitrogen gas and high-pressure oxygen-enriched liquefied air;
a turbine air evaporator for vaporizing medium-pressure oxygen-enriched liquefied air obtained by reducing the pressure of the high-pressure oxygen-enriched liquefied air to generate medium-pressure turbine air;
a turbine blower that warms the intermediate pressure turbine air and then compresses it to generate high pressure turbine air;
an expansion turbine that adiabatically expands the high-pressure turbine air to generate low-pressure turbine air and generates refrigeration necessary for air separation operation;
a low pressure column for cryogenically distilling the low pressure turbine air and separating it into low pressure nitrogen gas, low pressure liquefied oxygen, and argon-enriched liquefied oxygen;
an argon column for compressing the argon-enriched liquefied oxygen and then subjecting it to low-temperature distillation at a pressure higher than that of the low-pressure column to separate it into argon gas and medium-pressure liquefied oxygen;
an argon condenser for liquefying the argon gas to produce liquefied argon and vaporizing the low-pressure liquefied oxygen 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 that indirectly exchanges heat between the high-pressure nitrogen gas and the medium-pressure liquefied oxygen to liquefy the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporizes the medium-pressure liquefied oxygen to produce medium-pressure oxygen gas;
a product argon discharge line for extracting at least one of a portion of the argon gas, the argon gas not liquefied in the argon condenser, and a portion of the liquefied argon as a product,
The turbine blower is rotationally driven by using rotational energy generated in the expansion turbine,
The air separation unit further comprises a feed air bypass line for branching off a portion of the high pressure feed air and for joining the high pressure turbine air after reduction in pressure. The air separation unit according to claim 6, characterized in that the turbine air evaporator liquefies the high-pressure nitrogen gas to generate high-pressure liquefied nitrogen by indirect heat exchange between the high-pressure nitrogen gas and the medium-pressure oxygen-enriched liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air. The air separation unit according to claim 6, characterized in that the turbine air evaporator liquefies the high-pressure nitrogen-enriched air produced in an intermediate stage of the process in the high-pressure column by indirect heat exchange between the high-pressure nitrogen-enriched air and the medium-pressure oxygen-enriched liquefied air to produce the high-pressure nitrogen-enriched liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to produce the medium-pressure turbine air. The air separation unit according to claim 6, characterized in that the turbine air evaporator liquefies the high-pressure feed air by indirect heat exchange between the high-pressure feed air and the medium-pressure oxygen-enriched liquefied air to generate high-pressure liquefied air, and vaporizes the medium-pressure oxygen-enriched liquefied air to generate the medium-pressure turbine air. The air separation unit according to any one of claims 6 to 9, further comprising a feed air bypass valve on the feed air bypass line, which is capable of indirectly adjusting the flow rate of the high-pressure feed air branched off from the high-pressure feed air by controlling the pressure after decompression.

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