JP2006071190A - Oxygen producing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for efficiently producing pressure liquefied oxygen and oxygen gas by utilizing discharged fluid and by-product fluid in a nitrogen producing process without affecting the primary nitrogen producing process. <P>SOLUTION: This oxygen producing device comprises (1) extracting a part of oxygen-rich liquefied air of a nitrogen producing device from a nitrogen rectifying tower or a nitrogen rectifying tower condenser, and introducing the same to an intermediate stage of a sub-rectifying tower 8 having a reboiler 9 at its lower part, (2) forming the liquefied air in the reboiler 9 by introducing the compressed air to the lower reboiler 9 of the sub-rectifying tower, returning a part of the liquefied air to the nitrogen rectifying tower, and supplying the rest to a part of the sub-rectifying tower 8 as reflux liquid, and (3) producing oxygen from the lower part of the sub-rectifying tower 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oxygen production apparatus, and is particularly useful for efficiently producing oxygen gas and liquefied oxygen using exhaust fluid and by-product fluid in a nitrogen production process.

  Conventionally, a cryogenic air separation plant has been widely known as an oxygen production apparatus. Generally, a plurality of distillation towers are used to sequentially increase separation efficiency and produce mainly nitrogen, oxygen and argon as final products. Yes. On the other hand, the demand for nitrogen including a semiconductor process is much larger than that of oxygen or the like, and a nitrogen production apparatus is often used because of the balance between the amount used in the market and the production amount. In a nitrogen production apparatus, mainly air is used as a raw material, nitrogen gas and liquefied nitrogen are efficiently produced via a compression / purification process, and a clean gas rich in oxygen is discharged as waste gas.

  However, even in factories or regions where the demand for nitrogen is the primary factor, demand for oxygen may appear in the vicinity of existing nitrogen production equipment, and the waste gas from the above nitrogen production equipment can be used effectively. Oxygen production equipment has been installed, or oxygen production equipment has been installed by using a separate raw material air, such as a room temperature separation method or a cryogenic separation method.

  As an example of a method using an existing nitrogen production apparatus, as illustrated in FIG. 4, as illustrated in FIG. 4, a sub-condenser (reboiler) 7 that incorporates a sub-condenser (reboiler) 7 that heats raw material air and liquefied oxygen to exchange heat. A rectifying column 8 is provided, and a part of the liquefied air of the condenser 5 is led to the sub-rectifying column 8 and a part of the raw material air is led to the sub-condenser (reboiler) 7 so that a small amount of oxygen is obtained. A method A for collecting gas and liquefied oxygen has been proposed (see, for example, Patent Document 1).

  Further, as illustrated in FIG. 5, a sub rectifying column 3 having an evaporator (reboiler) 7 is provided at the bottom, and the tower condensing evaporator is provided at the top of the column from the bottom of the single rectifying column 1 for producing nitrogen. 2 is connected by a conduit so that a part of the liquefied air supplied to 2 is supplied, and one end of an evaporator (reboiler) 7 at the bottom of the sub rectifying column 3 is air below the single rectifying column 1. A method B for collecting oxygen gas and liquefied oxygen by connecting the supply conduit and the other end of the supply conduit to a liquid air conduit introduced into the condensing evaporator 2 for a single fractionator via a valve has been proposed. (For example, refer to Patent Document 2).

Further, as illustrated in FIG. 6, the entire amount of the raw material air after removing moisture and carbon dioxide in the raw material air is introduced into the nitrogen rectifying column 10 to be cooled and liquefied, and the product from the nitrogen rectifying column 10 is The nitrogen rich liquid air obtained in the nitrogen rectifying tower 10 is used as a cold heat source for the nitrogen condenser 14, and the generated oxygen rich air is used as the reboiler 24 of the oxygen rectifying tower 20. A method for producing oxygen while maintaining a nitrogen recovery rate by using oxygen-rich liquid air produced by condensation as a heating source, as an oxygen raw material and a reflux liquid of the oxygen rectification column 20 C has been proposed (see, for example, Patent Document 3).
JP 54-163797 A Japanese Utility Model Publication No. 55-140990 Japanese Patent No. 3203181

  However, the installation of a new oxygen production apparatus has a large economic burden, and oxygen gas or nitrogen gas produced as a by-product from both the existing nitrogen production apparatus and the new oxygen production apparatus will be discarded. A very large loss including energy will occur.

  Moreover, even when an oxygen production apparatus is incidentally installed in the nitrogen production apparatus, there are some problems with the conventional method as described above.

In other words, both the method A and the method B are the raw material air of the nitrogen production apparatus, and the method C is the waste gas from the condensing evaporator (condenser) of the nitrogen rectification column, and the reboiling of the oxygen rectification column The oxygen-rich liquefied air is depressurized until it matches the liquefaction temperature, and as a result, the operating pressure of the oxygen rectification column is lowered and the pressure of the generated oxygen gas is lowered.
In addition, when an oxygen production apparatus is newly added to an existing nitrogen production apparatus, it is not easy to make a modification that does not affect the capacity of the nitrogen production apparatus.

  Accordingly, an object of the present invention is to efficiently use the exhaust fluid and by-product fluid in the nitrogen production process, and efficiently produce pressurized oxygen gas and liquefied oxygen gas without affecting the original nitrogen production process. It is to provide an apparatus for performing.

  As a result of intensive studies, the present inventors have found that the above object can be achieved by an oxygen production apparatus shown below, and have completed the present invention.

  The present invention is an oxygen production apparatus, and (1) a sub-rectification tower having a reboiler at the bottom by extracting a part of the oxygen-rich liquefied air of the nitrogen production apparatus from a nitrogen rectification column or a nitrogen rectification column condenser (2) Compressed air is introduced into the lower reboiler of the sub rectifying column to generate liquefied air in the reboiler, a part thereof is returned to the nitrogen rectifying column, and the rest is returned to the sub rectifying column. (3) Oxygen is produced from the lower part of the sub-rectification column.

  In other words, the present invention is not simply a combination of a nitrogen production apparatus and an oxygen production apparatus, but uses both surplus parts and matches the gas-liquid state or temperature and pressure required by both parties at that time. The aim is to create a highly efficient nitrogen / oxygen production system. A sub rectification column (oxygen rectification column) is installed in the nitrogen rectification column, and a part of oxygen-rich liquefied air (hereinafter referred to as “R / L”) by-produced by the nitrogen production apparatus as a raw material is used as the sub rectification column. In addition to being introduced into the intermediate stage, separately pressurized air is introduced into the reboiler at the bottom of the sub rectification column, and a part of the liquefied liquid air (the amount equivalent to the R / L) is returned to the nitrogen rectification column and the rest is sub-refined. By supplying a reflux liquid to the top of the distillation column, oxygen can be efficiently produced without affecting the original nitrogen production apparatus.

  Specifically, R / L (a low concentration component for the nitrogen production apparatus), which is a by-product, is supplied from the nitrogen production apparatus to the sub rectification column. By receiving the supply of liquefied air (for nitrogen production equipment, a higher concentration component than the above R / L), the production volume of the nitrogen production equipment can be increased. At the same time, R / L (high concentration component for oxygen production apparatus) is supplied to the sub rectification column, and a part of the liquefied air is refluxed, so that the oxygen production apparatus has high concentration oxygen in a small number of stages. Can be manufactured. As described above, according to the present invention, it is possible to simultaneously use raw materials, by-products and the like for both processes in the production of nitrogen and the production of oxygen in a complementary manner.

  The present invention is the above oxygen production apparatus, wherein the nitrogen-enriched gas from the top of the sub rectification column is merged with the raw air for the oxygen production apparatus, or a part of the raw air of the nitrogen rectification tower or the recycle air It is characterized by merging with a part of.

  When air is used as a raw material, from the standpoint of mass balance, oxygen-rich by-products from the nitrogen production device become oxygen production raw materials, and nitrogen-rich by-products from the oxygen production device become nitrogen production raw materials. It is preferable that the amount of introduced air and the amount of exhausted exhaust gas can be reduced. More ideally, a highly efficient nitrogen / oxygen production system can be configured by matching the state of the supply source at the time of such reflux with the gas-liquid state or temperature and pressure required by the supply destination. . In the present invention, the nitrogen-enriched gas in the cooled / pressurized state from the top of the sub rectification column is merged with compressed air as a raw material or recycled air also used as a raw material, thereby improving the yield of nitrogen. In addition, it is possible to produce an excellent effect that the addition of the raw material air in the treatment process can be reduced in terms of energy. Therefore, it is possible to provide an apparatus for efficiently producing oxygen without affecting the original nitrogen production process. Here, the recycle air (RA) is used in this specification including the case where the oxygen content is 21 Vol% or less.

  The present invention is the above oxygen production apparatus, characterized in that a part of the oxygen-rich liquefied air is compressed by a pressurizing means and supplied to the sub rectification column.

  As described above, it has been difficult for an oxygen production apparatus added to a conventional nitrogen production apparatus to meet the demand for pressurized oxygen. In the present invention, as described above, by supplying the R / L from the nitrogen rectification column to the sub rectification column in a pressurized state, the rectification is performed efficiently, and the pressurized oxygen gas or It becomes possible to produce liquefied oxygen. Here, the R / L from the nitrogen rectification column is used as a raw material, but it is in a somewhat pressurized state, but for further pressurization, as in the present invention, it is compressed by a pressurizing means, It is preferable to supply to the sub rectification column.

  The present invention is the above oxygen production apparatus, wherein a part of liquefied oxygen is extracted from the lower part of the sub rectification column and then evaporated to produce oxygen gas.

  When only oxygen gas is produced, hydrocarbons and the like may concentrate and explode in the lower part of the sub rectification column. This is prevented by extracting a part of the liquefied oxygen from the lower part of the sub rectification column. By utilizing this cooling of liquefied oxygen for heat exchange with the raw materials or intermediate products, it becomes possible to produce oxygen gas with higher energy efficiency.

  As described above, according to the present invention, not only a combination of a nitrogen production device and an oxygen production device, but also a surplus portion is used in both, and the gas liquid state or temperature and pressure required by both at that time are used. Therefore, it is possible to configure a highly efficient nitrogen / oxygen production system. In other words, it is possible to provide an apparatus that efficiently uses the exhaust fluid and by-product fluid in the nitrogen production process and efficiently produces pressurized oxygen without affecting the original nitrogen production process.

  In particular, when an oxygen production process is added to an existing nitrogen production apparatus, it is possible to provide a highly efficient oxygen production apparatus with almost no modification of the nitrogen production apparatus. ing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration example of an oxygen production apparatus 1 using a nitrogen production process according to the present invention. The nitrogen production process N and the oxygen production process P are configured to be coupled mainly by an R / L supply path from the nitrogen production process N and a liquefied air supply path from the oxygen production process P. For example, the present invention can be applied when an oxygen production process P is attached to an existing nitrogen production process N.

  In the nitrogen production process N, the air supplied in the pressurized state by the raw material air supply means (MAC) 1 and supplied through the raw material air purification means (APU) 2 is recycled from the compression means (RAC) 4 described later. It introduce | transduces into the air separation means 3 with air, and produces | generates high purity nitrogen (GN2). Also, waste gas (WG) is generated and recycle air is returned. At this time, R / L is taken out from the air separation means 3 and supplied to the oxygen production process P as a raw material for oxygen production. Part of the recycle air (indicated by G. Air) is supplied to the oxygen production process P as a reheater heat source, and the other recycles as a recycle raw material for nitrogen production, so that it joins with the raw air processed by the APU 2 above. Is done. About WG, it introduce | transduces into a heat exchange means (not shown), is returned to normal temperature, is discharged | emitted after being utilized for the regeneration gas of APU2.

  On the other hand, in the oxygen production process P, the supplied R / L is compressed by the pressurizing means 5 and introduced into the cold box 6 as a raw material, and after a predetermined treatment step, high purity oxygen gas (GO2) and high purity are introduced. Liquefied oxygen (not shown) is generated. G. Air is supplied to the cold box 6 after compression by the compression means 7 together with the recycle air (RA) returned from the oxygen production process P. At this time, nitrogen-rich liquefied air (L. Air) with 21% or less oxygen generated as a by-product is returned to the nitrogen production process P as a supplement to R / L and recycle air. In FIG. 1, mechanical means such as a pressurizing pump is illustrated as the pressurizing means 5. However, the present invention is not limited to this, and a liquid head, for example, can be used.

  As described above, according to the present apparatus, it is possible to simultaneously use raw materials, by-products and the like for both the nitrogen production process and the oxygen production process.

  Moreover, although the above mentioned separately about the raw material in each process, a product, and a by-product, it is also possible to grasp this as an air separation process in which both were integrated. That is, in terms of the product manufacturing process, nitrogen is extracted by the air separation means 3 from the raw air compressed and purified by the MAC1 and APU2 in the first process. In the second step, the residue is compressed by the pressurizing means 5 and then the oxygen is extracted by the cold box 6, and the remainder is returned to the air separating means 3 again. This makes it possible to use the raw material very efficiently. Recycled air can also be effectively utilized by combining the nitrogen production process RAC4 and the oxygen production process RAC7 well.

  FIG. 1 shows a case where a part of the high-pressure recycle air of the nitrogen production process N is used as a supplementary gas for the recycle air of the oxygen production process P. Depending on the relationship between the product nitrogen and product oxygen pressures, a portion of the low pressure recycle air of the nitrogen production process N can be utilized. In addition, a part of the raw material air of the nitrogen production process N may be used, or a new raw material air compression means and a raw material air purification means for the oxygen production process P may be added, and the processed compressed air may be used with these. Is possible.

Details of one embodiment of the oxygen production apparatus according to the present invention are illustrated in FIG. A high recovery type nitrogen producing apparatus of existing (eg, high purity nitrogen production 15,000Nm ³ / hr), and the oxygen production process P (for example, high purity oxygen production 3,000Nm ³ /hr,0.5MPaA ) Will be described as an example.

(1) R / L of about 3,625 Nm ³ / hr with an oxygen concentration of about 80.8%, for example, supplied from the nitrogen production process N is compressed to 0.53 MPaA by a booster pump, Introducing to the middle stage of the distillation column 8).

(2) A reboiler 9 is installed at the bottom of the sub rectifying column 8 and the G. About 7,000 Nm ³ / hr of air (RA, recycle gas with oxygen of 21% or less) containing Air is supplied as a heat source for the reboiler 9. The RA is pressurized to about 1.52 MPaA by the compression means 7 (high pressure RA), cooled to the vicinity of the dew point (DP) through the heat exchanger 10 (corresponding to 10a and 10b in FIG. 2), and then the reboiler 9 To be introduced. This is used to evaporate the bottom liquid (liquid acid) in the reboiler 9 of the sub rectifying column 8, and liquefies itself, generating high-pressure liquefied air of about 7,000 Nm ³ / hr.

(3) About 4,072 Nm ³ / hr in the high-pressure liquefied air is a cold source L.L. corresponding to R / L. It returns to the nitrogen production process N as Air. The remaining about 2,928 Nm ³ / hr is supplied to the top of the sub rectifying column 8 as a reflux liquid.

(4) In the sub rectifying column 8, the reflux liquid at the top of the column and the R / L introduced into the intermediate stage flow down in the column and come into gas-liquid contact with the rising vapor from the bottom of the sub rectifying column 8. As a result, liquid oxygen is produced at the bottom of the column. At this time, about 3,107 Nm ³ / hr of 95% oxygen gas and about 50 Nm ³ / hr of hydrocarbon liquefied 97.5% oxygen such as hydrocarbons are taken out from the bottom of the sub rectifying column 8. Further, from the top of the sub rectification column 8, medium pressure recycle air of about 3,396 Nm ³ / hr is taken out.

  (5) The oxygen gas and liquefied oxygen are heated to room temperature by the heat exchanger 10 (corresponding to 10a and 10b in FIG. 2) that counter-flows with the high pressure RA, and are supplied as GO2. Similarly, medium-pressure air is also heated to room temperature by the heat exchanger 10a, and is recycled as part of the RA in this system. On the other hand, FIG. 2 illustrates a method in which the high-pressure RA branches into two flow paths, radiates heat in the heat exchangers 10a and 10b, cools, and then joins again to be introduced into the reboiler 9.

  (6) By the above, the oxygen production apparatus of this invention can form the combination which functions very efficiently with the existing nitrogen production apparatus.

Approximating the required power of this apparatus based on the exemplified numerical values, the power consumption in the compression means 7 is 391 kW (RA of 7,000 Nm ³ / h is compressed from 0.5 MPaA to 1.52 MPaA). Pressure pump) power consumption of 1 kW or less, raw material air (G. Air) compression power of 417 kW (compressing 3,604 Nm ³ / h from atmospheric pressure to 1 MPaA) total of about 809 kW, and the basic unit of pure oxygen base This is about 0.27 kW / Nm ³ . Usually, the electric power required for an oxygen separator of this size is said to be 0.45 to 0.5 kW / Nm ³ . Therefore, this numerical value in the present apparatus is much lower than that of a normal apparatus and shows an advantage in spite of including power for compressing oxygen to 0.53 MPaA.

  Next, FIG. 3 shows another configuration example of the oxygen production apparatus using the nitrogen production process according to the present invention. A case where this oxygen production process P is applied to a new nitrogen production apparatus will be described as an example.

  Basically, it is the same as that of the first embodiment except that a specific example of the nitrogen production process is clearly shown and the main heat exchanger and the like are integrated. Based on FIG. 3, an oxygen production apparatus according to the present invention will be described focusing on differences from the above-described configuration example 1.

  The raw material air is dedusted by a filter (not shown), compressed to about 1 MPaA by MAC 1a, impurities are removed by a room temperature purification unit (not shown), joined with recycle air, and a refrigerant described later in heat exchanger 10a. The liquid is cooled to substantially the liquefaction temperature by indirect heat exchange, and supplied to the lower part of the medium pressure rectification section A of the nitrogen rectification column 12.

  The raw material air supplied to the intermediate pressure rectification section A rises in the intermediate pressure rectification section A and counterflows with the reflux liquid mainly composed of liquid nitrogen flowing down from above to make gas-liquid contact. As a result, oxygen in the gas phase dissolves in the reflux liquid, while nitrogen in the reflux liquid is vaporized and released into the gas phase. As a result, nitrogen gas accumulates in the upper part of the intermediate pressure rectification part A, and liquid air accumulates in the lower part of the intermediate pressure rectification part A. The liquid air is taken out, expanded to about 0.4 MPaA, and then supplied to the upper part of the auxiliary rectifying unit B as a reflux liquid.

  A part of the nitrogen gas accumulated in the upper part of the intermediate pressure rectification part A is supplied from the intermediate pressure rectification part A, introduced into the heat exchanger 10a, and heat-exchanged with the raw air to become room temperature. Supplied as low-pressure product nitrogen gas GN2.

  The remaining nitrogen gas accumulated in the upper portion of the intermediate pressure rectification section A is introduced into the nitrogen condenser 13, cooled by indirect heat exchange with oxygen-rich liquid air (R / L) as a refrigerant, and condensed liquid nitrogen. Is returned as reflux.

  In the auxiliary rectification section B, rectification is performed based on the liquid air, and an oxygen-rich liquid R / L is generated at the bottom. A part of the refrigerant is introduced into the nitrogen condenser 13 as a refrigerant and is evaporated by itself. A part of the vaporized oxygen-rich gas becomes ascending steam in the tower. Further, the remaining part is taken out from the lower part of the auxiliary rectification part B, heated to an intermediate temperature, and then supplied to the expansion turbine ET. The oxygen-rich gas exiting the expansion turbine ET is heated by the heat exchanger 10a, used as a part of the cold source of this process, and then used as a regeneration means for a room temperature purification unit (not shown).

  Recycled air is returned from the top of auxiliary rectification section B. Recycled air is introduced into the heat exchanger 10a, where it is used to cool the raw material air as a refrigerant, returned to room temperature, compressed by the compression means 4, and then branched. One of the branched air is combined with the raw material air as described above, and the remaining recycle air is further compressed by the compression means 7 together with the recycle air returned from the top of the oxygen rectification column 8 described later, and the oxygen rectification column 8 The lower reboiler 9 is supplied.

  A part of R / L used as a refrigerant in the nitrogen rectification column 12 is taken out, further compressed to about 0.53 MPaA by the pressurizing means 5, and then supplied to the intermediate stage of the oxygen rectification column 8. . In the oxygen rectification column 8, it flows down as a reflux liquid, and a low boiling point component is released by contact with a gas rising from below and countercurrent gas-liquid, and the oxygen concentration is increased and accumulated in the lower part of the oxygen rectification column 8. A reboiler 9 is installed in the lower part of the oxygen rectification column 8, and the RA is compressed and introduced as a heating source. Then, the liquid accumulated in the lower portion of the oxygen rectifying column 8 is heated, and components having a boiling point lower than oxygen (argon, carbon monoxide, nitrogen, etc.) are selectively vaporized together with oxygen to raise the oxygen rectifying column 8. .

  The high pressure RA used as a heat source for the reboiler 9 is condensed by the reboiler 9 to form high pressure liquefied air. This is taken out from the reboiler 9 and branched, and one is introduced into the upper part of the oxygen rectification column 8 and becomes the reflux liquid of the oxygen rectification column 8. The other is returned to the nitrogen fractionator 12 as a cold source corresponding to R / L.

  As a result, nitrogen gas containing a component having a boiling point lower than that of oxygen accumulates in the upper portion of the oxygen rectifying column 8, and oxygen gas and liquid oxygen accumulate in the lower portion of the oxygen rectifying column 8. The nitrogen gas that has accumulated in the upper part of the oxygen rectification column 8 is discharged from the top of the column, introduced into the heat exchanger 10a as a refrigerant, and then used as recycle air. On the other hand, the oxygen gas accumulated in the lower part of the oxygen rectification column 8 is heat-exchanged by the heat exchanger 10a and returned to room temperature. The liquid oxygen is vaporized in the sub heat exchanger 10b, merges with the oxygen gas, and is supplied to the user as the product oxygen gas GO2.

  As described above, the oxygen production apparatus of the present invention can be applied not only when it is attached to an existing nitrogen production facility but also when a new oxygen / nitrogen production apparatus is installed. It is also applicable to the replacement of the oxygen production line.

  In the above description, the case of using a double rectification column using air recycling as a nitrogen production process has been described. However, the present invention can also be used for other processes such as a single rectification column. In this case, R / L is extracted from the condenser of the nitrogen rectification column and delivered to the oxygen production process P. Air can be returned to the condenser of the nitrogen rectification column after expansion.

  The oxygen production apparatus of the present invention can be used regardless of existing or new installation. In the description of the embodiment, a numerical example of generation of low-purity oxygen is shown, but the present invention is not limited to this. Moreover, it can be said that the combined nitrogen production process has a high degree of freedom and is highly versatile.

Explanatory drawing which shows the example of 1 structure of the oxygen production apparatus using the nitrogen production process which concerns on this invention Explanatory drawing showing details of the above configuration example Explanatory drawing which shows the other structural example of the oxygen production apparatus using the nitrogen production process which concerns on this invention Explanatory drawing which shows the 1st structural example of the oxygen manufacturing apparatus using the nitrogen manufacturing process which concerns on a prior art. Explanatory drawing which shows the 2nd structural example of the oxygen manufacturing apparatus using the nitrogen manufacturing process which concerns on a prior art. Explanatory drawing which shows the 3rd structural example of the oxygen manufacturing apparatus using the nitrogen manufacturing process which concerns on a prior art.

Explanation of symbols

1, 1a Raw material air supply means (MAC)
2 Raw material air purification means (APU)
3 Air separation means 4, 7 Compression means 5 Pressurization means 6 Cold box 8 Sub rectification tower (oxygen rectification tower)
9 Reboiler 10a, 10b Heat exchanger 11a, 11b Regulating valve 12 Nitrogen fractionator 13 Nitrogen condenser N Nitrogen production process P Oxygen production process

Claims (4)

(1) A part of the oxygen-rich liquefied air of the nitrogen production apparatus is extracted from the nitrogen rectification column or nitrogen rectification column condenser and introduced into the intermediate stage of the sub rectification column having a reboiler at the bottom. (2) Compressed air is introduced into the lower reboiler of the sub rectification column to generate liquefied air in the reboiler, a part thereof is returned to the nitrogen rectification column, and the remainder is returned to the sub rectification column. An oxygen production apparatus characterized in that it is supplied to the top as a reflux liquid and (3) produces oxygen from the lower part of the sub rectification column.   The nitrogen-enriched gas from the top of the sub rectifying column is merged with the raw air for an oxygen production apparatus, or is merged with a part of the raw air of the nitrogen rectifying column or a part of the recycle air. Item 2. The oxygen production apparatus according to Item 1.   The oxygen production apparatus according to claim 1 or 2, wherein a part of the oxygen-rich liquefied air is compressed by a pressurizing means and supplied to the sub rectification column. The oxygen production apparatus according to any one of claims 1 to 3, wherein a part of liquefied oxygen is extracted from the lower part of the sub rectification column and then evaporated to produce oxygen gas.

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