JP2003028568A - Method and apparatus for separating air - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for separating air capable of separating air to ensure energy saving upon collecting nitrogen and oxygen. SOLUTION: Stock air RA is cooled by heat exchange with an oxygen distillation passage 53 on an air condensation passage 51 and is partially liquefied to separate nitrogen rich air of gas phase and oxygen rich air of liquid phase (1). The nitrogen rich air is distilled on a nitrogen distillation passage 52 while being cooled by heat exchange with the oxygen distillation passage 53 to separate product middle pressure nitrogen MGN where nitrogen is concentrated and nitrogen contents with low nitrogen concentration (2). The nitrogen contents and the foregoing oxygen rich air are distilled in a distillation tower 6 to separate product low pressure nitrogen GN where nitrogen is concentrated and coarse oxygen where oxygen is concentrated (3). The coarse oxygen is distilled on the oxygen distillation passage 53 while being heated by heat exchange with the passages 51, 52 to separate product liquefied oxygen GO where oxygen is concentrated (4).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an air separation method and apparatus for separating nitrogen and oxygen by cryogenic distillation of air.

[0002]

2. Description of the Related Art A double distillation column consisting of a high pressure column and a low pressure column is used to produce nitrogen, oxygen, etc. by low temperature distillation of air. In recent years, an air separation method utilizing a heat exchange type distillation apparatus has been proposed in order to suppress the power consumption when performing air separation and reduce the manufacturing cost. For example, Japanese Patent No. 2833594 discloses a method for producing medium purity oxygen (oxygen concentration 85 to 99%) using a heat exchange type distillation apparatus. In the method disclosed herein, a plate fin heat exchanger in which two passages are arranged so that heat can be exchanged is used as a heat exchange type distillation apparatus. In this method, the raw material air is fed to the first heat exchange type distillation apparatus first.
Distill in the passage to collect a low-boiling nitrogen-rich gas phase product from the upper portion of the passage and a high-boiling oxygen-rich liquid phase product from the lower portion of the passage. In the second passage, the oxygen-rich liquid-phase product is distilled while heat-exchanged with the raw material air in the first passage, the nitrogen-rich gas-phase product is collected from the upper portion of the passage, and product oxygen is obtained from the lower portion of the passage. Obtainable. In addition, JP-A-8
No. 36499 also discloses an air separation method using a heat exchange type distillation apparatus. In this method, the raw material air is distilled in the first passage of the heat exchange type distillation apparatus, the gas phase product rich in nitrogen is led out from the upper portion of the passage, and this is condensed,
A part thereof is introduced into the second passage as a reflux liquid, and a product having an oxygen concentration of 70% or more is collected from the lower portion of the second passage.

[0003]

However, in the conventional air separation method, in order to improve the heat exchange efficiency and obtain a product with sufficient purity, it is necessary to make the raw material air have a high pressure. Therefore, there is a problem that power consumption increases. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air separation method and device that can improve heat exchange efficiency and reduce power consumption.

[0004]

The air separation method of the present invention comprises a heat exchange type distillation apparatus comprising an air condensing passage, a nitrogen distillation passage, and an oxygen distillation passage capable of exchanging heat with these passages. (1) After compressing the raw material air by using a distillation column, the raw material air is cooled by heat exchange with the oxygen distillation passage in the air condensing passage to be partially liquefied, and the gas phase nitrogen-enriched air and liquid A phase-separated from the oxygen-enriched air of the phase, and (2) the nitrogen-enriched air is distilled while cooling in the nitrogen distillation passage by heat exchange with the oxygen distillation passage, and a nitrogen concentrate enriched in nitrogen; Nitrogen-containing substances with a lower nitrogen concentration than this are separated, and the nitrogen concentrate is recovered as product intermediate-pressure nitrogen,
(3) Nitrogen-containing material and the oxygen-enriched air are distilled in a distillation column to separate nitrogen-enriched product low-pressure nitrogen and oxygen-enriched crude oxygen, and recover product low-pressure nitrogen,
(4) In the oxygen distillation passage, crude oxygen is distilled while being heated by heat exchange with the air condensing passage and the nitrogen distillation passage, and the product liquefied oxygen enriched with oxygen is separated and the product liquefied oxygen is recovered. Is characterized by. In the air separation method of the present invention, the gas-liquid mixed nitrogen concentrate separated by the nitrogen distillation passage can be gas-liquid separated, and the liquid phase portion can be introduced into the distillation column. In the present invention, a part of the nitrogen concentrate separated by the nitrogen distillation passage can be liquefied by heat exchange with crude oxygen and introduced into the distillation column. In the present invention, a part of the compressed raw material air is further compressed, and the product liquefied oxygen can be vaporized by heat exchange with the obtained secondary compressed raw material air. In the present invention, after compressing a part of the nitrogen concentrate separated by the nitrogen distillation passage, it is adiabatically expanded, and the power obtained during the adiabatic expansion can be used to compress the nitrogen concentrate.

The air separation apparatus of the present invention comprises an air compressor for compressing raw material air, a main heat exchanger for cooling the compressed raw material air, a heat exchange type distillation apparatus for distilling the cooled raw material air, The heat exchange type distillation apparatus is provided with a distillation column for further distilling the distillate that has passed through the heat exchange type distillation apparatus, and the heat exchange type distillation apparatus has an air condensation passage, a nitrogen distillation passage, and an oxygen distillation passage capable of heat exchange with these passages. The air condensing passage is provided with the raw material air,
Partial liquefaction by cooling by heat exchange with the oxygen distillation passage,
Gas phase nitrogen-enriched air and liquid phase oxygen-enriched air are made available, and a nitrogen distillation passage distills the nitrogen-enriched air while cooling it by heat exchange with the oxygen distillation passage. To obtain product medium-pressure nitrogen, which is a nitrogen concentrate enriched with nitrogen, and a nitrogen-containing substance having a lower nitrogen concentration than the product, and the distillation column uses the nitrogen-containing substance and the oxygen-enriched substance. It is made possible to distill air to obtain nitrogen-enriched product low-pressure nitrogen and oxygen-enriched crude oxygen, and an oxygen distillation passage is used to remove the crude oxygen from the air condensation passage and the nitrogen distillation passage. It is characterized in that product liquefied oxygen enriched with oxygen can be obtained by distillation while heating by heat exchange. The air separation device of the present invention includes a gas-liquid separator for separating a nitrogen concentrate in a gas-liquid mixed state separated by a nitrogen distillation passage into a gas-liquid separator, and a liquid phase portion separated by the gas-liquid separator is a distillation column. It can be configured to be introduced into. The air separation device of the present invention is provided with a condenser for liquefying a part of the nitrogen concentrate separated by the nitrogen distillation passage by heat exchange with crude oxygen, and the liquid phase portion obtained by this condenser is used in a distillation column. It is also possible to adopt a configuration that can be introduced into. The air separation device of the present invention vaporizes product liquefied oxygen using a secondary compressor that further compresses a part of the raw material air compressed by the air compressor, and the secondary compressed raw material air that is compressed by this compressor. It is also possible to adopt a configuration including an oxygen evaporator that allows The air separation device of the present invention,
It is also possible to employ a configuration provided with a booster pump that boosts the product liquefied oxygen.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing a first embodiment of an air separation device of the present invention. The air separation device 10 shown here is an air compressor 1 for compressing raw material air RA.
And an air precooler 2 that removes the compression heat of the compressed raw material air, and impurities (water content, etc.) in the raw material air that has passed through the air precooler 2.
A purifier 3 for removing (carbon dioxide, etc.), a main heat exchanger 4 for cooling the raw material air that has passed through the purifier 3, a heat exchange type distillation apparatus 5 for distilling the raw material air that has passed through the main heat exchanger 4, A distillation column 6 for further distilling the distillate passed through the exchangeable distillation apparatus 5,
Expansion turbine 7, gas-liquid separators 8 and 9, and supercooler 11
And the booster 13 are major components. Also, reference numeral 1
Reference numeral 5 indicates a cold storage tank.

The heat exchange type distillation apparatus 5 includes an air condensing passage 51.
, A nitrogen distillation passage 52, and an oxygen distillation passage 53 capable of exchanging heat with the passages 51, 52. As the heat exchange type distillation apparatus 5, a plate fin type heat exchanger can be used. FIG. 2 shows an example of a plate fin type heat exchanger that can be used as the heat exchange type distillation apparatus 5. The plate fin type heat exchanger 20 shown here is
Inside the box-shaped hermetically sealed exterior body 21, upper circulation spaces 25, 25 in which a fluid circulates and lower circulation spaces 26, 26 are provided.

The distribution spaces 25 and 26 are divided into a first flow path 23 and a second flow path 24 by a plurality of partition walls 22. The first flow path 23 and the second flow path 24 are alternately provided from one side of the circulation spaces 25, 26 to the other side. In this heat exchanger 20, the first flow passage 23a of the lower circulation space 26 is the air condensing passage 51, and the first flow passage 23b of the upper circulation space 25 is the nitrogen distillation passage 52. The second flow path 24 serves as an oxygen distillation passage 53.

In the heat exchange type distillation apparatus 5 of the illustrated example,
Although the passages 51 to 53 are integrated and integrated in the exterior body 21, the heat exchange distillation apparatus may be divided into two in the present invention. That is, the oxygen distillation passage is divided into an upper passage and a lower passage, and a first heat exchange type distillation section having the upper passage and the nitrogen distillation passage and a second heat exchange type distillation section having the lower passage and the air condensation passage. It is also possible to use a heat exchange type distillation apparatus equipped with and. It is preferable that the booster 13 be configured to be able to be driven by using the power obtained during adiabatic expansion in the expansion turbine 7.

Next, the first embodiment of the air separation method of the present invention will be described by taking the case of using this air separation device 10 as an example. First, the raw material air RA such as the atmosphere is compressed by the air compressor 1 (for example, compressed to about 400 kPa) and cooled to the room temperature by the air precooler 2, and then the water and carbon dioxide in the raw material air are purified by the purifier 3. The impurities of are removed by adsorption.

Next, the raw material air that has passed through the purifier 3 is partially liquefied in the main heat exchanger 4 by heat exchange with a low-temperature fluid such as product low-pressure nitrogen and product liquefied oxygen, which will be described later, to about -178 ° C. After that, through the pipe line L1, the air condensing passage 5
1 Introduce to the top. The introduced raw material air descends in the air condensing passage 51 while being cooled by exchanging heat with the fluid (crude oxygen described later) in the oxygen distillation passage 53. The raw material air becomes a gas-liquid mixed state due to partial liquefaction and is introduced into the gas-liquid separator 8 from the lower part of the passage 51 through the pipe line L2, and in the gas-liquid separator 8, the gas-phase nitrogen-enriched air and the liquid phase Is separated into oxygen-enriched air.

The liquid-phase oxygen-enriched air is discharged from the lower part of the gas-liquid separator 8, passes through the line L3 and the subcooler 11,
After the pressure is reduced by the pressure reducing valve V1 of the line L4, it is introduced into the lower part of the distillation column 6. On the other hand, the gas-phase nitrogen-enriched air is discharged from the upper portion of the gas-liquid separator 8 and introduced into the lower portion of the nitrogen distillation passage 52 through the pipe line L5.

In the process of rising in the nitrogen distillation passage 52, this nitrogen-enriched air is heat-exchanged with the fluid (crude oxygen) in the oxygen distillation passage 53 to be distilled while being cooled, and nitrogen is concentrated in the gas phase. To do. The resulting nitrogen concentrate (for example, a nitrogen concentration of 9
8% or more, oxygen content 2% or less), the nitrogen distillation passage 52
Is led out from the upper part of the pipe through the line L6 and introduced into the gas-liquid separator 9. When the nitrogen concentrate is in a gas-liquid mixed state, the nitrogen concentrate is gas-liquid separated by the gas-liquid separator 9,
The separated liquid phase portion is supplied from the lower part of the gas-liquid separator 9 to the pipe line L.
7. After passing through the supercooler 11 and the pipe L8, the pressure is reduced by the pressure reducing valve V2 and supplied to the upper portion of the distillation column 6.

The nitrogen concentrate in the gas phase is discharged from the upper part of the gas-liquid separator 9 and recovered as medium pressure nitrogen MGN through the line L9 and the main heat exchanger 4. A part of this nitrogen concentrate is introduced into the booster 13 through the line L16 to increase its pressure, then adiabatically expanded by the expansion turbine 7 to a low temperature, and introduced into the main heat exchanger 4 through the line L17. It As a result, the raw material air can be efficiently cooled.
The nitrogen concentrate that has passed through the main heat exchanger 4 is discharged as an exhaust gas WG. When boosting the pressure of the nitrogen concentrate with the booster 13, it is preferable to drive the booster 13 using the power obtained when the expansion turbine 7 adiabatically expands the nitrogen concentrate. Thereby, power efficiency can be improved.

In the process of distilling the nitrogen-enriched air in the nitrogen distillation passage 52, the nitrogen concentration in the liquid phase becomes low, and a liquid nitrogen-containing substance having a low nitrogen concentration is obtained. This nitrogen content is
Derived from the lower part of the nitrogen distillation passage 52 by a pipe line L14,
It is introduced into the subcooler 11 through the pipe line L3, decompressed by the pressure reducing valve V1 of the pipe line L4, and supplied to the lower part of the distillation column 6.

In the distillation column 6, the liquid phase product introduced from the upper part and the nitrogen-containing substance and oxygen-enriched air introduced from the lower part are distilled, and in the process nitrogen is concentrated in the gas phase, Oxygen is concentrated in the liquid phase. The gas phase product (for example, a nitrogen concentration of 98% or more and an oxygen content of 2% or less) is led out from the upper part of the distillation column 6 and is passed through the line L10, the subcooler 11, and the line L11 to the main heat exchanger 4. After being introduced and heated here, it is recovered as the product low-pressure nitrogen GN.

On the other hand, crude oxygen, which is a liquid-phase oxygen concentrate, is
It is led out from the lower part of the distillation column 6 and introduced into the oxygen distillation passage 53 through a pipe line L12. This crude oxygen passes through the oxygen distillation passage 5
In the process of descending 3, the raw material air in the air condensing passage 51,
And is heated by exchanging heat with the nitrogen-enriched air in the nitrogen distillation passage 52. In this process, distillation raises the concentration of nitrogen in the gas phase and the concentration of oxygen in the liquid phase. As a result, a gas-phase nitrogen-containing gas and a liquid-phase oxygen concentrate (for example, an oxygen concentration of 95% or more) which is product liquefied oxygen are obtained. The nitrogen-containing gas is reintroduced from the upper part of the oxygen distillation passage 53 to the lower part of the distillation column 6 through the line L15.

On the other hand, the product liquefied oxygen is passed through the oxygen distillation passage 53.
Is introduced into the main heat exchanger 4 from the lower part of the pipe through the line L13,
It is vaporized by heat exchange with the raw material air and is recovered as gaseous product liquefied oxygen GO. The product liquefied oxygen can be recovered by increasing the pressure by increasing the pressure by the pressure increasing pump 12.

In the air separation method of this embodiment, since the heat exchange type distillation apparatus 5 having the air condensing passage 51, the nitrogen distillation passage 52 and the oxygen distillation passage 53 and the distillation column 6 are used,
The heat exchange between the feed air, the nitrogen-enriched air, and the crude oxygen can be efficiently performed. Therefore, the pressure of the raw material air compressed by the air compressor 1 can be set low. For example, the raw material air pressure of about 500 kPa required in the conventional method can be set to about 400 kPa.
Therefore, power consumption can be significantly reduced. For example, it is possible to save energy by about 20% as compared with the case of using a conventional air separation device equipped with a double distillation column.

In the present invention, a part of the raw material air from the purifier 3 is secondarily compressed by the secondary compressor 14 using the line L18 shown by the broken line in FIG. 400k
It can also be introduced into the distillation column 6 through Pa) and the line L3. In this case, the pressure of the raw material air in the air compressor 1 can be further lowered (for example, about 350 kPa).
Therefore, the power consumption can be further reduced.

Next, a second embodiment of the air separation device of the present invention will be described. FIG. 3 shows a second embodiment of the air separation device of the present invention.
3 is a system diagram showing an embodiment of FIG. The air separation device 30 shown here is a condenser 31 for cooling and liquefying a part of the nitrogen concentrate discharged from the nitrogen distillation passage 52 through the line L6.
1 is provided, an oxygen evaporator 32 for vaporizing product liquefied oxygen by heat exchange with raw material air is provided, and a gas-liquid separator 9 is not provided. Different from 10.

The condenser 31 is capable of liquefying the nitrogen concentrate by heat exchange with the crude oxygen discharged from the distillation column 6. The oxygen evaporator 32 is compressed by the secondary compressor 14 and is capable of vaporizing the product liquefied oxygen by heat exchange with the secondary compressed raw material air that has passed through the main heat exchanger 4.

Next, a second embodiment of the air separation method of the present invention will be described by taking the case of using this air separation device 30 as an example. The raw material air is compressed by the air compressor 1 (for example, pressure is about 350 kPa), cooled to room temperature by the air precooler 2, impurities are removed by the purifier 3, and the heat exchange type distillation apparatus 5 is passed through the line L1. Is introduced into the air condensing passage 51. After passing through the purifier 3, a part of the raw material air is introduced into the secondary compressor 14 and compressed to 450 to 500 kPa, cooled by the main heat exchanger 4, and cooled by the line L18a to the oxygen evaporator 32. Will be introduced to. Here, the oxygen distillation passage 5
By heat exchange with the product liquefied oxygen from 3, the raw material air is liquefied, and the line L18b, the line L3, the supercooler 11,
It is introduced into the lower part of the distillation column 6 via the line L4.

In the nitrogen distillation passage 52, the nitrogen-enriched air is distilled, the gas-phase nitrogen concentrate is discharged from the line L6, and is recovered as the product intermediate-pressure nitrogen MGN through the line L9. A portion of this nitrogen concentrate is introduced into condenser 31 via line L31. The nitrogen concentrate introduced into the condenser 31 is liquefied by heat exchange with the crude oxygen from the distillation column 6, and the liquefied product is fed from the lower part of the condenser 31 through the line L32, the supercooler 11, and the line L8. It is then introduced into the upper part of the distillation column 6. When the nitrogen concentrate introduced into the condenser 31 is in a gas-liquid mixed state, the nitrogen concentrate is gas-liquid separated in the condenser 31, and the separated liquid phase part is condensed with the liquefaction product in the condenser 31. Is introduced into the upper part of the distillation column 6 from the lower part of. Therefore, the nitrogen concentrate in the gas-liquid mixed state can be gas-liquid separated without using the gas-liquid separator 9, and the device cost required for the gas-liquid separator 9 can be reduced.

The crude oxygen obtained by the distillation in the distillation column 6 is introduced into the condenser 31 through the line L12a, exchanges heat with the nitrogen concentrate, and then introduced into the oxygen distillation line 53 through the line L12b. Distillation gives product liquefied oxygen enriched with oxygen.

The product liquefied oxygen is introduced into the oxygen evaporator 32 through the line L13a, vaporized by heat exchange with the raw material air, and then recovered through the line L13b and the main heat exchanger 4. Product liquefied oxygen is the booster pump 1 installed in the line L13a.
Alternatively, the pressure may be increased by using 2, and then the oxygen vaporizer 32 may be vaporized and recovered. In this case, high-pressure product liquefied oxygen can be recovered.

In the air separation method of this embodiment, as in the method of the first embodiment, by using the heat exchange type distillation apparatus 5 and the distillation column 6, the feed air, the nitrogen-enriched air and the crude oxygen are separated. The heat exchange between them can be efficiently performed, and the pressure of the raw material air can be set low. Therefore, power consumption can be significantly reduced.

[0028]

As described above, in the air separation method of the present invention, the heat exchange type distillation apparatus having the air condensing passage, the nitrogen distillation passage and the oxygen distillation passage and the distillation column are used. The heat exchange between the nitrogen-enriched air and the crude oxygen can be efficiently performed. Therefore, the pressure of the raw material air can be set low. Therefore, power consumption can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of an air separation device of the present invention.

FIG. 2 is a partial cutaway view showing a plate fin type heat exchanger usable as a heat exchange type distillation apparatus in the air separation apparatus shown in FIG.

FIG. 3 is a system diagram showing a second embodiment of the air separation device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Air compressor, 4 ... Main heat exchanger, 5 ... Heat exchange type distillation apparatus, 6 ... Distillation tower, 7 ... Expansion turbine, 8, 9 ...
Gas-liquid separator, 10, 30 ... Air separator, 13 ... Booster, 14 ... Secondary compressor, 20 ... Plate fin type heat exchanger (heat exchange type distillation apparatus), 31 ... -Condenser, 32 ... Oxygen evaporator, 51 ... Air condensing passage, 52 ... Nitrogen distillation passage, 53 ... Oxygen distillation passage, RA ... Raw material air, MGN ...
Product medium pressure nitrogen, GN ... Product low pressure nitrogen, GO ... Product liquefied oxygen

Continued front page    (72) Inventor Hiroshi Kawakami             1-16-7 Nishi-Shimbashi, Minato-ku, Tokyo Japan Acid             Inside the corporation F-term (reference) 4D047 AA08 AB01 AB02 CA09 DA05                       DA14 DA17 EA03

Claims (10)

[Claims] 1. An air separation method for separating oxygen and nitrogen by cryogenic distillation of air, the heat exchange comprising an air condensing passage, a nitrogen distillation passage, and an oxygen distillation passage capable of exchanging heat with these passages. (1) After compressing the raw material air using a type distillation apparatus and a distillation column, the raw material air is cooled in the air condensation passage by heat exchange with the oxygen distillation passage to be partially liquefied, and vapor phase nitrogen is obtained. The enriched air and the liquid-phase oxygen-enriched air are separated, and (2) the nitrogen-enriched air is distilled while being cooled by heat exchange with the oxygen distillation passage in the nitrogen distillation passage to concentrate nitrogen. A nitrogen concentrate and a nitrogen-containing substance having a lower nitrogen concentration are separated, and the nitrogen concentrate is recovered as product intermediate-pressure nitrogen. (3) The nitrogen-containing substance and the oxygen-enriched air are distilled in a distillation column. , Nitrogen-enriched products low-pressure nitrogen and oxygen Condensed crude oxygen is separated and product low-pressure nitrogen is recovered, and (4) crude oxygen is distilled while being heated in the oxygen distillation passage by heat exchange with the air condensing passage and the nitrogen distillation passage, and oxygen is concentrated. A method for separating air, characterized in that the product liquefied oxygen is separated and the product liquefied oxygen is recovered. 2. The air separation method according to claim 1, wherein the nitrogen concentrate in a gas-liquid mixed state separated by the nitrogen distillation passage is gas-liquid separated, and the liquid phase portion is introduced into the distillation column. 3. The air separation method according to claim 1, wherein a part of the nitrogen concentrate separated by the nitrogen distillation passage is liquefied by heat exchange with crude oxygen and introduced into the distillation column. 4. The air separation method according to claim 1, wherein a part of the compressed raw material air is further compressed, and the product liquefied oxygen is vaporized by heat exchange with the obtained secondary compressed raw material air. Method. 5. The method according to claim 5, wherein a part of the nitrogen concentrate separated by the nitrogen distillation passage is compressed and then adiabatically expanded, and the power obtained during the adiabatic expansion is used to compress the nitrogen concentrate. The air separation method according to claim 1. 6. An air separation apparatus for separating oxygen and nitrogen by cryogenic distillation of air, an air compressor for compressing raw material air, a main heat exchanger for cooling compressed raw material air, and a cooled raw material. A heat exchange type distillation apparatus for distilling air and a distillation column for further distilling the distillate passed through the heat exchange type distillation apparatus are provided, and the heat exchange type distillation apparatus has an air condensing passage, a nitrogen distillation passage, and these passages. A heat-exchangeable oxygen distillation passage is provided, and an air condensing passage cools the raw material air by heat exchange with the oxygen distillation passage to partially liquefy it, so that gas-phase nitrogen-enriched air and liquid-phase oxygen-enriched air are enriched. A product which is a nitrogen concentrate enriched with nitrogen, wherein the nitrogen distillation passage distills this nitrogen-enriched air while cooling by heat exchange with the oxygen distillation passage to obtain nitrogen. Medium pressure nitrogen and lower nitrogen concentration A nitrogen column is made available to obtain a nitrogen-containing material, and a distillation column distills the nitrogen-containing material and the oxygen-enriched air to produce a product containing low-pressure nitrogen enriched with nitrogen and crude oxygen enriched with oxygen. In order to obtain an oxygen-enriched product liquefied oxygen, the oxygen distillation passage distills the crude oxygen while heating it by heat exchange with the air condensation passage and the nitrogen distillation passage. Air separation device characterized by being. 7. A gas-liquid separator for gas-liquid separating the nitrogen concentrate in a gas-liquid mixed state separated by the nitrogen distillation passage, and the liquid phase part separated by this gas-liquid separator can be introduced into the distillation column. The air separation device according to claim 6, wherein the air separation device is configured as follows. 8. A condenser for liquefying a part of the nitrogen concentrate separated by the nitrogen distillation passage by heat exchange with crude oxygen, and introducing the liquid phase portion obtained by this condenser into a distillation column. 7. The air separation device according to claim 6, wherein the air separation device is capable of being operated. 9. A secondary compressor for further compressing part of raw material air compressed by an air compressor, and oxygen evaporation for vaporizing product liquefied oxygen using the secondary compressed raw material air compressed by this compressor. The air separation device according to claim 6, further comprising: 10. The air separation device according to claim 6, further comprising a booster pump for boosting the product liquefied oxygen.