JP7588271B1 - Nitrogen production method and nitrogen production device - Google Patents

Abstract

The present invention aims to provide a nitrogen production technology capable of efficiently producing nitrogen gas at a relatively high pressure over a wide range (e.g., 7 to 15 barA) while simultaneously producing a relatively large amount of argon.
[Solution] A nitrogen production apparatus is provided which comprises a high-pressure tower that distills high-pressure, low-temperature feed air obtained by cooling feed air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by pressurizing medium-pressure liquefied nitrogen, and separates the high-pressure nitrogen gas and high-pressure liquefied air, a medium-pressure tower that distills medium-pressure, low-temperature feed air obtained by adiabatic expansion of a portion of the feed air, and separates the medium-pressure nitrogen gas and medium-pressure liquefied air, a low-pressure tower, an argon tower, a nitrogen condenser, an argon condenser, a product nitrogen outlet line, and a product argon outlet line.
[Selected Figure] Figure 1

Description

The present invention relates to a nitrogen production method and a nitrogen production device.

In recent years, there has been an increasing demand for argon in addition to large amounts of relatively high-pressure (e.g., 7 barA or higher) nitrogen gas in nitrogen production equipment for semiconductor factories.

According to Patent Document 1, high-pressure nitrogen gas is produced from feed air in the first and second fractionation towers, and small amounts of oxygen and argon are produced in the downstream oxygen and argon towers.

According to Patent Document 2, the first to fourth rectification towers can be used to co-produce oxygen and argon in addition to nitrogen gas at 9 to 12 barA. For example, nitrogen gas at 9 to 12 barA can be produced by the first rectification tower, and the fluid vaporized in the condenser of the first rectification tower can be supplied to a double rectification system (second to fourth rectification towers) to co-produce high-purity oxygen and argon. Furthermore, the amount of nitrogen gas produced in the first rectification tower can be increased (i.e., the nitrogen recovery rate can be improved) by pressurizing the liquefied nitrogen produced in the second rectification tower incorporated in the double rectification system with a pump and returning it to the first rectification tower.

Patent No. 7329714 International Publication No. 2020/169257

However, although the nitrogen production device disclosed in Patent Document 1 is capable of producing nitrogen gas at a relatively high pressure while simultaneously producing high-purity oxygen and argon, the argon recovery rate is low, with the amount of argon remaining at approximately 0.5% of the amount of nitrogen gas.

In addition, the air separation unit disclosed in Patent Document 2 is capable of producing high-purity oxygen and argon while simultaneously producing nitrogen gas at a relatively high pressure. However, since the reflux liquid for the first fractionator is produced in a condenser installed at the top of the first fractionator, the operating pressure of the first fractionator is restricted, and it is difficult to operate it outside the range of 9 to 12 barA.
In other words, in the air separation unit disclosed in Patent Document 2, the pressure of the liquefied nitrogen gas is limited depending on the pressure of the fluid vaporizing in the condenser of the first fractionator, so the operating pressure of the first fractionator cannot be lowered below 9 barA.
Therefore, when the required pressure of the product nitrogen gas is lower than 9 barA, the nitrogen gas produced in the first rectification column must be depressurized, which is inefficient. Also, when the pressure of the product nitrogen gas is higher than 12 barA, operations such as depressurizing the gas fluid vaporized in the condenser of the first rectification column are required, which is inefficient.

There has been a demand for a nitrogen production technology that can efficiently produce nitrogen gas at a relatively high and wide range of pressures (e.g., 7 to 15 barA) while simultaneously producing a relatively large amount of argon, but there has been no effective or suitable technology available.

In order to solve the above problems, the present invention provides the following means.
[1] A high-pressure separation process in which high-pressure low-temperature feed air obtained by cooling feed air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by pressurizing medium-pressure liquefied nitrogen are distilled to separate them into high-pressure nitrogen gas and high-pressure liquefied air; a medium-pressure separation process in which medium-pressure low-temperature feed air obtained by adiabatic expansion of a portion of the feed air is distilled to separate them into medium-pressure nitrogen gas and medium-pressure liquefied air; and a low-pressure separation process in which low-pressure liquefied air obtained by reducing the pressure of at least one of the high-pressure liquefied air and the medium-pressure liquefied air is distilled to separate them into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas; a nitrogen condensation step of indirectly exchanging heat between the medium-pressure nitrogen gas and the liquefied oxygen to liquefy the medium-pressure nitrogen gas to produce the medium-pressure liquefied nitrogen and vaporizing the liquefied oxygen to produce oxygen gas; an argon condensation step of liquefying the argon gas to produce liquefied argon; a product nitrogen extraction step of extracting the high-pressure nitrogen gas as a product; and a product argon extraction step of extracting a portion of the argon gas or the liquefied argon as a product.
[2] The nitrogen production method according to [1], characterized in that in the high-pressure separation step, the high-pressure low-temperature feed air and the high-pressure liquefied nitrogen are distilled to separate, in addition to the high-pressure nitrogen gas and the high-pressure liquefied air, high-pressure argon-enriched liquefied air having a higher argon concentration than the high-pressure liquefied air, and the low-pressure argon-enriched liquefied air obtained by reducing the pressure of the high-pressure argon-enriched liquefied air is used as part of the raw material for the low-pressure separation step.
[3] The method for producing nitrogen according to [1], characterized in that in the medium-pressure separation step, the medium-pressure low-temperature feed air is distilled to separate, in addition to the medium-pressure nitrogen gas and the medium-pressure liquefied air, medium-pressure argon-enriched liquefied air having a higher argon concentration than the medium-pressure liquefied air, and the low-pressure argon-enriched liquefied air obtained by reducing the pressure of the medium-pressure argon-enriched liquefied air is used as part of the feed for the low-pressure separation step.
[4] The nitrogen production method according to [2], characterized in that in the low-pressure separation step, the low-pressure argon-enriched liquefied air is supplied below the low-pressure liquefied air.
[5] The nitrogen production method according to [3], characterized in that in the low-pressure separation step, the low-pressure argon-enriched liquefied air is supplied below the low-pressure liquefied air.
[6] A high-pressure column which distills high-pressure low-temperature feed air obtained by cooling feed air obtained by compressing, precooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by pressurizing medium-pressure liquefied nitrogen, and separates them into high-pressure nitrogen gas and high-pressure liquefied air, a medium-pressure column which distills medium-pressure low-temperature feed air obtained by adiabatic expansion of a part of the feed air, and separates them into medium-pressure nitrogen gas and medium-pressure liquefied air, a low-pressure column which distills low-pressure liquefied air obtained by reducing the pressure of at least one of the high-pressure liquefied air and the medium-pressure liquefied air, and separates them into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas, and a nitrogen condenser that performs indirect heat exchange between the medium-pressure nitrogen gas and the liquefied oxygen to liquefy the medium-pressure nitrogen gas to produce the medium-pressure liquefied nitrogen and vaporizes the liquefied oxygen to produce oxygen gas; an argon condenser that liquefies the argon gas to produce liquefied argon; a product nitrogen outlet line for discharging the high-pressure nitrogen gas as a product; and a product argon outlet line for discharging a portion of the argon gas or the liquefied argon as a product.
[7] The nitrogen production apparatus according to [6], characterized in that in the high-pressure column, the high-pressure low-temperature feed air and the high-pressure liquefied nitrogen are distilled to separate, in addition to the high-pressure nitrogen gas and the high-pressure liquefied air, high-pressure argon-enriched liquefied air having a higher argon concentration than the high-pressure liquefied air, and the low-pressure argon-enriched liquefied air obtained by reducing the pressure of the high-pressure argon-enriched liquefied air is introduced into the low-pressure column.
[8] The nitrogen production apparatus according to [6], characterized in that in the medium pressure column, the medium pressure low temperature feed air is distilled to separate, in addition to the medium pressure nitrogen gas and the medium pressure liquefied air, medium pressure argon-enriched liquefied air having a higher argon concentration than the medium pressure liquefied air, and the low pressure argon-enriched liquefied air obtained by reducing the pressure of the medium pressure argon-enriched liquefied air is introduced into the low pressure column.
[9] The nitrogen production apparatus according to [7], characterized in that in the low pressure column, the inlet of the low pressure argon-enriched liquefied air is located lower than the inlet of the low pressure liquefied air.
[10] The nitrogen production apparatus according to [8], characterized in that in the low pressure column, the inlet of the low pressure argon-enriched liquefied air is located lower than the inlet of the low pressure liquefied air.

The present invention makes it possible to efficiently produce nitrogen gas at relatively high and wide pressure ranges (e.g., 7 to 15 barA) while simultaneously producing relatively large amounts of argon.

1 is a diagram showing a nitrogen production apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram showing a nitrogen production apparatus according to a second embodiment of the present invention.

[First embodiment]
<Nitrogen production apparatus 100>
A nitrogen producing apparatus 100 according to a first embodiment of the present invention will be described with reference to the drawings.
1 is a system diagram of a nitrogen production apparatus 100 to which the nitrogen production method of the present invention is applied. In the following description, high pressure, medium pressure, low pressure, high temperature, and low temperature indicate relative differences in pressure and temperature in each embodiment, and do not specify a pressure range or a temperature range.

As shown in FIG. 1, the nitrogen production system 100 of this embodiment includes an air compressor 1, an air precooler 2, an air purifier 3, a high-pressure tower 4, a medium-pressure tower 5, a low-pressure tower 6, an argon tower 7, a nitrogen condenser 8, an argon condenser 9, an argon condenser outer cylinder 10, a main heat exchanger 11, a subcooler 12, an expansion turbine 13, and a liquefied nitrogen pump 14.

The air compressor 1, air precooler 2, and air purifier 3 are devices that compress, precool, and purify air containing oxygen, nitrogen, and argon.

The high-pressure column 4 is a fractionation column that performs low-temperature distillation of the high-pressure low-temperature feed air B and high-pressure liquefied nitrogen C to separate them into high-pressure nitrogen gas, high-pressure liquefied air, and high-pressure argon-enriched liquefied air.

The medium pressure tower 5 is a fractionation tower that performs low-temperature distillation of the medium pressure low-temperature feed air E and medium pressure liquefied nitrogen F to separate them into medium pressure nitrogen gas and medium pressure liquefied air.

The low-pressure tower 6 is a fractionation tower that performs low-pressure liquefied air J, M, low-pressure argon-enriched liquefied air L, low-pressure liquefied air O, low-pressure air P, argon-enriched liquefied oxygen Q, and oxygen gas obtained by vaporization in the nitrogen condenser 8 by low-temperature distillation to separate the air, argon-enriched oxygen gas, and liquefied oxygen.

The argon tower 7 is a fractionation tower that performs low-temperature distillation of argon-enriched oxygen gas S and liquefied argon T to separate them into argon gas and argon-enriched liquefied oxygen.

The nitrogen condenser 8 is housed at the bottom of the low-pressure tower 6 and is a heat exchanger that performs indirect heat exchange between the medium-pressure nitrogen gas G introduced into the nitrogen condenser 8 and the liquefied oxygen accumulated at the bottom of the low-pressure tower 6.

The argon condenser 9 is housed in the argon condenser outer cylinder 10 and is a heat exchanger that liquefies the argon gas U introduced into the argon condenser 9 to produce liquefied argon.

The main heat exchanger 11 and the subcooler 12 are devices that perform heat exchange between the fluids introduced therein and discharge the fluids after heat exchange.
The expansion turbine 13 is a device that adiabatically expands a portion of the feed air A cooled in the main heat exchanger 11 to generate the cold required to operate the apparatus and also produces medium-pressure low-temperature feed air E.
The liquefied nitrogen pump 14 is a device that pressurizes a portion of the medium-pressure liquefied nitrogen F liquefied in the nitrogen condenser 8 to produce high-pressure liquefied nitrogen C.

<Nitrogen production method>
Next, a nitrogen production method using the nitrogen production apparatus 100 of this embodiment will be described.
Air AIR containing oxygen, nitrogen, and argon is introduced from the atmosphere into line L1, compressed by air compressor 1, precooled by air precooler 2, and purified by air purifier 3 to obtain feed air A. The obtained feed air A is then cooled in main heat exchanger 11 to obtain high-pressure, low-temperature feed air B.

[High-pressure separation process]
In the high pressure separation step, the high pressure low temperature feed air B introduced via line L1 and the high pressure liquefied nitrogen C introduced via line L8 are subjected to low temperature distillation in the high pressure column 4 to separate them into high pressure nitrogen gas, high pressure liquefied air, and high pressure argon-enriched liquefied air. Note that the high pressure argon-enriched liquefied air has a higher argon concentration than the high pressure liquefied air.

[Product development process]
In the product discharge step, the high pressure nitrogen gas D discharged from the top of the high pressure column 4 via the line L2 is heated to room temperature in the main heat exchanger 11 and then recovered as product nitrogen gas (GN).

A portion of the feed air A cooled in the main heat exchanger 11 is led to line L5 and introduced into the expansion turbine 13 for expansion. The medium-pressure low-temperature feed air E obtained by the expansion is then introduced into the bottom of the medium-pressure tower 5.

[Medium pressure separation process]
In the medium pressure separation step, the medium pressure low temperature feed air E introduced into the medium pressure tower 5 via line L5 and the medium pressure liquefied nitrogen F introduced via line L7 are subjected to low temperature distillation in the medium pressure tower 5 to separate them into medium pressure nitrogen gas and medium pressure liquefied air.
Then, medium pressure nitrogen gas G is discharged from the top of the medium pressure column 5 into a line L6.
In addition, medium-pressure liquefied air H is discharged from the bottom of the medium-pressure column 5 through a line L9.

High-pressure liquefied air I discharged from the high-pressure column 4 to line L3 is introduced into the subcooler 12. After being cooled in the subcooler 12, the pressure is reduced through valve V1 to obtain low-pressure liquefied air J.

In addition, the high-pressure argon-enriched liquefied air K discharged from the high-pressure column 4 to the line L4 is cooled by the subcooler 12. After being cooled by the subcooler 12, the pressure is reduced through the valve V2 to obtain the low-pressure argon-enriched liquefied air L.
Here, by positioning the outlet position of the line L4 connected to the high pressure column 4 higher than the outlet position of the line L3, the recovery rate of argon can be increased.

In addition, the medium-pressure liquefied air H discharged from the medium-pressure column 5 to the line L9 is cooled by the subcooler 12. After being cooled by the subcooler 12, the pressure is reduced by the valve V3 to obtain the low-pressure liquefied air M.
A portion of the medium pressure liquefied air H discharged to the line L9 is introduced into a line L10 branched off from the line L9, and the pressure is reduced by a valve V4 to obtain low pressure liquefied air N.

[Low pressure separation process]
In the low-pressure separation step, low-pressure liquefied air J, M introduced via line L3 and line L9, low-pressure argon-enriched liquefied air L introduced via line L4, low-pressure liquefied air O introduced via line L11, low-pressure air P introduced via line L12, argon-enriched liquefied oxygen Q introduced via line L19, and oxygen gas obtained by vaporization in the nitrogen condenser 8 are low-temperature distilled in the low-pressure column 6 to separate them into nitrogen-enriched air, argon-enriched oxygen gas, and liquefied oxygen.

Here, the argon recovery rate can be increased by positioning the connection position of line L4, which connects to low-pressure column 6, lower than the connection position of lines L3 and L9.

Next, the nitrogen-enriched air R discharged from the top of the low-pressure column 6 through a line L14 is heated in a subcooler 12, and then heated to room temperature in a main heat exchanger 11, and then recovered as waste gas (WG).
Also, argon-enriched oxygen gas S is discharged from the middle of the low-pressure column 6 to a line L15.

[Argon separation process]
In the argon separation step, argon-enriched oxygen gas S introduced through line L15 and liquefied argon T introduced through line L17 are subjected to low-temperature distillation in argon column 7 to separate them into argon gas and argon-enriched liquefied oxygen.

Argon gas U is discharged from the top of the argon column 7 through a line L16.
Also, argon-enriched liquefied oxygen Q is discharged from the bottom of the argon column 7 through a line L19.

[Nitrogen condensation process]
In the nitrogen condensation step, the medium-pressure nitrogen gas G is introduced via line L6 into a nitrogen condenser 8 housed in the bottom of the low-pressure column 6, and indirect heat exchange is performed between the medium-pressure nitrogen gas G and the liquefied oxygen accumulated in the bottom of the low-pressure column 6. Specifically, the medium-pressure nitrogen gas G is liquefied to produce medium-pressure liquefied nitrogen F, and the liquefied oxygen is vaporized to produce oxygen gas.

The medium-pressure liquefied nitrogen F liquefied in the nitrogen condenser 8 is discharged to line L7. A portion of the medium-pressure liquefied nitrogen F discharged to line L7 is then branched off to line L8 and pressurized by the liquefied nitrogen pump 14 to obtain high-pressure liquefied nitrogen C.

In this embodiment, there is no condenser to liquefy the high-pressure nitrogen gas separated in the high-pressure column 4 to generate reflux liquid, and the high-pressure liquefied nitrogen C obtained by boosting the pressure with the liquefied nitrogen pump 14 becomes the reflux liquid for the high-pressure column 4. This has the advantage that the operating pressure of the high-pressure column 4, i.e., the pressure of the feed air, can be set to a certain degree of arbitrariness depending on the required pressure of the product nitrogen gas.

A portion of the oxygen gas vaporized in the nitrogen condenser 8 becomes the ascending gas in the low-pressure column 6, and the remainder is discharged to a line L20.
The oxygen gas V discharged to the line L20 is depressurized by the valve V8 and then merges with the nitrogen-enriched air R in the line L14.

Although not shown, the oxygen gas V discharged to the line L20 can be heated to room temperature in the main heat exchanger 11 and recovered as product oxygen gas.
The liquefied oxygen W that is not vaporized in the nitrogen condenser 8 is discharged from the bottom of the low-pressure column 6 through a line L21 and recovered as product liquefied oxygen (LO).

[Argon condensation process]
In the argon condensation step, argon gas U is liquefied to generate liquefied argon T. Specifically, argon gas U is introduced into the argon condenser 9 housed in the argon condenser outer cylinder 10 via the line L16, and low-pressure liquefied air N is introduced into the argon condenser outer cylinder 10 via the line L10, and the argon gas U and the low-pressure liquefied air N are indirectly heat exchanged to liquefy the argon gas U to generate liquefied argon T, and the low-pressure liquefied air N is vaporized to generate low-pressure air. As another form, the argon condenser 9 may not be housed in the argon condenser outer cylinder 10. In this case, the low-pressure liquefied air N is directly introduced into the argon condenser 9 and vaporized by indirect heat exchange with the argon gas U to generate low-pressure air X.

[Product argon extraction process]
In the product argon discharge step, liquefied argon T liquefied in the argon condenser 9 is discharged to a line L17.
A portion of the liquefied argon T discharged to the line L17 is branched off to a line L18, vaporized in the main heat exchanger 11, and heated to room temperature before being recovered as product argon gas (GAR).
Although not shown, a portion of the argon gas U in the line L16 may be branched off and heated to room temperature in the main heat exchanger 11, and then recovered as product argon gas (GAR).

The low pressure air X vaporized in the argon condenser 9 is led out to a line L12, and after being depressurized by a valve V6, is introduced into the low pressure column 6 as low pressure air P.
In addition, a portion of the low pressure air X led out to the line L12 is branched off to a line L13, and after being decompressed by a valve V7, is merged with the nitrogen-enriched air R in a line L14.
In addition, the low-pressure liquefied air Y in the argon condenser outer cylinder 10 that has not been vaporized in the argon condenser 9 is led to a line L11, and after being depressurized by a valve V5, is supplied to the low-pressure column 6 as low-pressure liquefied air O.

As described above, in this embodiment, when producing product nitrogen gas of 7 to 15 barA, there is no need to unnecessarily reduce the pressure of the gas fluid, and product nitrogen gas and argon can be produced efficiently.

Second Embodiment
<Nitrogen production apparatus 100A>
Next, a nitrogen producing apparatus 100A according to a second embodiment of the present invention will be described with reference to the drawings. Descriptions of parts similar to those of the first embodiment will be omitted.
In the first embodiment, the line L4 is connected to the middle part of the high pressure column 4, and the high pressure argon-enriched liquefied air K is discharged from the high pressure column 4 to the line L4.
In contrast, in this embodiment, the line L4 is not provided, and instead, a line L22 is connected to the middle part of the medium pressure column 5. Then, medium pressure argon-enriched liquefied air K' is discharged from the medium pressure column 5 to the line L22. Note that the medium pressure argon-enriched liquefied air K' has a higher argon concentration than the medium pressure liquefied air.

<Nitrogen production method>
Next, a nitrogen production method using the nitrogen production apparatus 100A of the second embodiment will be described with reference to Fig. 2. This embodiment is a modified example of the first embodiment, and the description of the same parts as those of the first embodiment will be omitted.

[Medium pressure separation process]
In this embodiment, in the medium pressure separation step, the medium pressure low temperature feed air E introduced into the medium pressure column 5 via line L5 and the medium pressure liquefied nitrogen F introduced via line L7 are low temperature distilled in the medium pressure column 5 to separate medium pressure nitrogen gas, medium pressure liquefied air, and medium pressure argon-enriched liquefied air.

Then, instead of delivering the high pressure argon-enriched liquefied air K from the middle of the high pressure column 4 to the line L4, in this embodiment, the medium pressure argon-enriched liquefied air K' is delivered from the middle of the medium pressure column 5 to the line L22.
The medium-pressure argon-enriched liquefied air K' delivered to the line L22 is cooled in the subcooler 12 and reduced in pressure through the valve V9, and then introduced into the low-pressure column 6 as low-pressure argon-enriched liquefied air L'.
Here, by positioning the connection position of the line L22 connected to the low pressure column 6 lower than the connection position of the line L3 and the line L9, the recovery rate of argon can be increased.

In the nitrogen production method of this embodiment, similarly to the first embodiment, there is no condenser for liquefying the high-pressure nitrogen gas separated in the high-pressure column 4 to generate a reflux liquid, and the high-pressure liquefied nitrogen obtained by boosting the pressure with the liquefied nitrogen pump 14 serves as the reflux liquid for the high-pressure column 4. This has the advantage that the operating pressure of the high-pressure column 4, i.e., the pressure of the feed air, can be set somewhat arbitrarily depending on the required pressure of the product nitrogen gas.
As a result, also in this embodiment, when producing product nitrogen gas of 7 to 15 barA, there is no need to unnecessarily reduce the pressure of the gas fluid, and product nitrogen gas and argon can be produced efficiently.

The present invention has been described above based on the above embodiment examples, but the present invention is not limited to the above embodiment, and can be embodied in various forms without departing from the spirit of the present invention.
For example, the high pressure liquefied air separated in the high pressure column 4 can be depressurized by a valve and then supplied to the bottom of the medium pressure column 5. In the above embodiment, the low pressure liquefied air N obtained by depressurizing the medium pressure liquefied air H drawn out from the bottom of the medium pressure column 5 is used as the fluid for indirect heat exchange with the argon gas U in the argon condensation step, but low pressure liquefied air obtained by depressurizing the high pressure liquefied air I drawn out from the bottom of the high pressure column 4 may also be used.
As a modification of the second embodiment, the high pressure argon-enriched liquefied air can be extracted from the middle of the high pressure column 4 and introduced into the middle of the medium pressure column 5 after reducing the pressure with a valve.

The present invention will be described in detail below with reference to examples and comparative examples.
<Example>
A simulation of the nitrogen production system 100 of the present invention shown in FIG. 1 was carried out using a simulator used in the design of an actual system.
In carrying out the simulation, the flow rate of the feed air was set to 100, and calculations were performed under conditions for recovering the maximum amounts of product nitrogen gas GN (oxygen concentration 1 ppm or less, pressure 9.4 barA) and product argon gas GAR (oxygen concentration 1.5% or less, nitrogen concentration 0.5% or less).
The results are shown in Table 1.

According to the results of this simulation, it was possible to recover product nitrogen gas GN at a flow rate of 40 from raw air with a flow rate of 100, and at the same time recover product argon gas GAR at a flow rate of 0.5.

As is clear from the above results, the nitrogen production method and nitrogen production apparatus of the present invention can recover a large amount (e.g., 40% or more of the air volume) of product nitrogen gas at a relatively high pressure (e.g., 7 barA or more), while at the same time recovering a large amount of product argon (e.g., 1% or more of the product nitrogen gas volume).
In addition, nitrogen gas over a wide range of pressures (eg, 7 to 15 barA) can be produced without using a nitrogen compressor.

1: Air compressor, 2: Air precooler, 3: Air purifier, 4: High pressure tower, 5: Medium pressure tower, 6: Low pressure tower, 7: Argon tower, 8: Nitrogen condenser, 9: Argon condenser, 10: Argon condenser outer cylinder, 11: Main heat exchanger, 12: Subcooler, 13: Expansion turbine, 14: Liquid nitrogen pump

Claims (10)

a high-pressure separation step in which high-pressure low-temperature feed air obtained by cooling feed air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by pressurizing medium-pressure liquefied nitrogen are distilled to separate them into high-pressure nitrogen gas and high-pressure liquefied air;
a medium pressure separation step of distilling the medium pressure low temperature feed air obtained by adiabatic expansion of a portion of the feed air and separating the medium pressure nitrogen gas and medium pressure liquefied air;
a low-pressure separation step in which low-pressure liquefied air obtained by reducing the pressure of at least one of the high-pressure liquefied air and the medium-pressure liquefied air is distilled to separate the low-pressure liquefied air into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas;
an argon separation step of distilling the argon-enriched oxygen gas to separate it into argon gas and argon-enriched liquefied oxygen;
a nitrogen condensation step in which the medium-pressure nitrogen gas is indirectly heat-exchanged with the liquefied oxygen to liquefy the medium-pressure nitrogen gas to produce the medium-pressure liquefied nitrogen and the liquefied oxygen to produce oxygen gas;
an argon condensation step of liquefying the argon gas to produce liquefied argon;
a product nitrogen discharge step of discharging the high-pressure nitrogen gas as a product;
and a product argon discharge step of discharging a portion of the argon gas or the liquefied argon as a product. In the high-pressure separation step, the high-pressure low-temperature feed air and the high-pressure liquefied nitrogen are distilled to separate, in addition to the high-pressure nitrogen gas and the high-pressure liquefied air, high-pressure argon-enriched liquefied air having an argon concentration higher than that of the high-pressure liquefied air;
2. The method for producing nitrogen according to claim 1, wherein said high pressure argon-enriched liquefied air is depressurized to obtain low pressure argon-enriched liquefied air, which is used as a part of the raw material for said low pressure separation step. In the medium-pressure separation step, the medium-pressure low-temperature feed air is distilled to separate, in addition to the medium-pressure nitrogen gas and the medium-pressure liquefied air, medium-pressure argon-enriched liquefied air having an argon concentration higher than that of the medium-pressure liquefied air;
2. The method for producing nitrogen according to claim 1, wherein the low-pressure argon-enriched liquefied air obtained by reducing the pressure of the medium-pressure argon-enriched liquefied air is used as a part of the raw material for the low-pressure separation step. The method for producing nitrogen according to claim 2, characterized in that in the low-pressure separation process, the low-pressure argon-enriched liquefied air is supplied below the low-pressure liquefied air. The nitrogen production method according to claim 3, characterized in that in the low-pressure separation process, the low-pressure argon-enriched liquefied air is supplied below the low-pressure liquefied air. a high-pressure column for distilling high-pressure low-temperature feed air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by pressurizing medium-pressure liquefied nitrogen, thereby separating the high-pressure nitrogen gas and high-pressure liquefied air;
a medium pressure column that distills the medium pressure low temperature feed air obtained by adiabatic expansion of a portion of the feed air and separates it into medium pressure nitrogen gas and medium pressure liquefied air;
a low pressure column for distilling the low pressure liquefied air obtained by reducing the pressure of at least one of the high pressure liquefied air and the medium pressure liquefied air to separate the low pressure liquefied air into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas;
an argon column for distilling the argon-enriched oxygen gas to separate it into argon gas and argon-enriched liquefied oxygen;
a nitrogen condenser that performs indirect heat exchange between the medium-pressure nitrogen gas and the liquefied oxygen to liquefy the medium-pressure nitrogen gas to produce the medium-pressure liquefied nitrogen and vaporize the liquefied oxygen to produce oxygen gas;
an argon condenser for liquefying the argon gas to produce liquefied argon;
a product nitrogen discharge line for discharging the high-pressure nitrogen gas as a product;
a product argon outlet line for outletting a portion of the argon gas or the liquefied argon as a product. In the high-pressure column, the high-pressure low-temperature feed air and the high-pressure liquefied nitrogen are distilled to separate, in addition to the high-pressure nitrogen gas and the high-pressure liquefied air, high-pressure argon-enriched liquefied air having an argon concentration higher than that of the high-pressure liquefied air;
7. The nitrogen producing apparatus according to claim 6, wherein the high pressure argon-enriched liquefied air is reduced in pressure to obtain low pressure argon-enriched liquefied air, which is introduced into the low pressure column. In the medium pressure column, the medium pressure low temperature feed air is distilled to separate, in addition to the medium pressure nitrogen gas and the medium pressure liquefied air, medium pressure argon-enriched liquefied air having an argon concentration higher than that of the medium pressure liquefied air;
7. The nitrogen production system according to claim 6, wherein the medium-pressure argon-enriched liquefied air is reduced in pressure to obtain low-pressure argon-enriched liquefied air, which is introduced into the low-pressure column. The nitrogen production apparatus according to claim 7, characterized in that in the low-pressure column, the inlet of the low-pressure argon-enriched liquefied air is located lower than the inlet of the low-pressure liquefied air. The nitrogen production apparatus according to claim 8, characterized in that in the low-pressure column, the inlet of the low-pressure argon-enriched liquefied air is located lower than the inlet of the low-pressure liquefied air.

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