Nitrogen production method and nitrogen production device

Abstract

The purpose of the present invention is to provide nitrogen production technology with which it is possible to generate a relatively large amount of argon while efficiently generating nitrogen gas having a relatively high and wide pressure range (for example, 7-15 barA). The present invention provides a nitrogen production device characterized by comprising: a high-pressure column (4) that distills high-pressure low-temperature feed air (B) obtained by cooling feed air (A) produced by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen (C) obtained by increasing the pressure of intermediate-pressure liquefied nitrogen (F), to separate the same into high-pressure nitrogen gas (D) and high-pressure liquefied air (I); a medium-pressure column (5) that distills medium-pressure low-temperature feed air (E) obtained by adiabatically expanding a portion of the feed air (A) to separate the same into medium-pressure nitrogen gas (G) and medium-pressure liquefied air (H); a low-pressure column (6); an argon column (7); a nitrogen condenser (8); an argon condenser (9); a product nitrogen lead-out line; and a product argon lead-out line.

Description

Nitrogen production method and nitrogen production device

[0001] The present invention relates to a nitrogen production method and a nitrogen production apparatus.

[0002] In recent years, there has been an increasing demand for argon in addition to a large amount of nitrogen gas at a relatively high pressure (for example, 7 barA or more) in nitrogen production equipment for semiconductor factories.

[0003] According to Patent Document 1, high-pressure nitrogen gas is produced from feed air in a first fractionator and a second fractionator, and small amounts of oxygen and argon are produced in a downstream oxygen tower and argon tower.

[0004] According to Patent Document 2, the first to fourth rectification columns 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 column, and the fluid vaporized in the condenser of the first rectification column can be supplied to a double rectification system (second to fourth rectification columns) to co-produce high-purity oxygen and argon. Furthermore, the amount of nitrogen gas produced in the first rectification column can be increased (i.e., the nitrogen recovery rate can be improved) by pressurizing the liquefied nitrogen produced in the second rectification column incorporated in the double rectification system with a pump and returning it to the first rectification column.

[0005] Patent No. 7329714 International Publication No. 2020 / 169257

[0006] However, although the nitrogen production apparatus 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.

[0007] Furthermore, the air separation unit disclosed in Patent Document 2 is capable of producing nitrogen gas at a relatively high pressure while simultaneously producing high-purity oxygen and argon. However, because a reflux liquid for the first rectification column is produced in a condenser installed at the top of the first rectification column, the operating pressure of the first rectification column is restricted, making it difficult to operate outside the range of 9 to 12 barA. In other words, the air separation unit disclosed in Patent Document 2 restricts the pressure of the nitrogen gas to be liquefied depending on the pressure of the fluid vaporized in the condenser of the first rectification column, so the operating pressure of the first rectification column 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. Furthermore, 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.

[0008] Thus, there has been a demand for a nitrogen production technology that can efficiently produce 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, but no effective and suitable technology has been available.

[0009] In order to solve the above problems, the present invention provides the following means: [1] 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 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 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 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 and produce the medium-pressure liquefied nitrogen and vaporize 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], wherein 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 depressurizing the high-pressure argon-enriched liquefied air is used as part of the feed for the low-pressure separation step. [3] The nitrogen production method according to [1], wherein 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 depressurizing 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], wherein in the low-pressure separation step, the low-pressure argon-enriched liquefied air is supplied below the low-pressure liquefied air.[5] The method for producing nitrogen according to [3], characterized in that in the low-pressure separation step, the low-pressure argon-enriched liquefied air is supplied to a position lower than the low-pressure liquefied air. [6] A method for producing nitrogen comprising: a high-pressure column for distilling 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 separating the high-pressure nitrogen gas and the high-pressure liquefied air; a medium-pressure column for distilling 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 the medium-pressure liquefied air; a low-pressure column for distilling 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 separating the low-pressure liquefied air, liquefied oxygen, and argon-enriched oxygen gas; 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 that liquefies the argon gas to produce liquefied argon; a product nitrogen discharge line through which the high-pressure nitrogen gas is discharged as a product; and a product argon discharge line through which a portion of the argon gas or the liquefied argon is discharged as a product. [7] The nitrogen production apparatus according to [6], wherein the high-pressure column distills the high-pressure low-temperature feed air and the high-pressure liquefied nitrogen 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 depressurizing the high-pressure argon-enriched liquefied air is introduced into the low-pressure column. [8] The nitrogen production apparatus according to [6], wherein the medium-pressure column distills the medium-pressure low-temperature feed air 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 depressurizing the medium-pressure argon-enriched liquefied air is introduced into the low-pressure column. [9] The nitrogen production apparatus according to [7], wherein, in the low-pressure column, an inlet for the low-pressure argon-enriched liquefied air is located lower than the inlet for 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.

[0010] According to the present invention, nitrogen gas can be efficiently produced at relatively high pressures over a wide range (eg, 7-15 barA), while simultaneously producing relatively large amounts of argon.

[0011] 1 is a diagram showing a nitrogen production apparatus according to a first embodiment of the present invention, and FIG. 2 is a diagram showing a nitrogen production apparatus according to a second embodiment of the present invention.

[0012] [First embodiment] <Nitrogen production apparatus 100> A nitrogen production apparatus 100 according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a system diagram of the nitrogen production apparatus 100 to which the nitrogen production method of the present invention is applied. Note that 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.

[0013] 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 column 4, a medium-pressure column 5, a low-pressure column 6, an argon column 7, a nitrogen condenser 8, an argon condenser 9, an argon condenser outer casing 10, a main heat exchanger 11, a subcooler 12, an expansion turbine 13, and a liquefied nitrogen pump 14.

[0014] The air compressor 1, the air precooler 2, and the air purifier 3 are devices that compress, precool, and purify air containing oxygen, nitrogen, and argon.

[0015] The high-pressure column 4 is a fractionator that performs low-temperature distillation of the high-pressure low-temperature feed air B and the high-pressure liquefied nitrogen C to separate them into high-pressure nitrogen gas, high-pressure liquefied air, and high-pressure argon-enriched liquefied air.

[0016] The medium-pressure column 5 is a rectification column that performs cryogenic distillation of the medium-pressure low-temperature feed air E and the medium-pressure liquefied nitrogen F to separate them into medium-pressure nitrogen gas and medium-pressure liquefied air.

[0017] The low-pressure column 6 is a distillation column 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 mixture into nitrogen-enriched air, argon-enriched oxygen gas, and liquefied oxygen.

[0018] The argon column 7 is a fractionation column that performs cryogenic distillation of the argon-enriched oxygen gas S and the liquefied argon T to separate them into argon gas and argon-enriched liquefied oxygen.

[0019] The nitrogen condenser 8 is housed in the bottom of the low-pressure column 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 in the bottom of the low-pressure column 6.

[0020] The argon condenser 9 is housed in an argon condenser outer cylinder 10 and is a heat exchanger that liquefies argon gas U introduced into the argon condenser 9 to produce liquefied argon.

[0021] The main heat exchanger 11 and the subcooler 12 are devices that exchange heat between the fluids introduced and discharge the fluid 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 refrigeration necessary for operating the device and to produce 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.

[0022] <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 introduced from the atmosphere into line L1 is 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.

[0023] [High-pressure separation step] In the high-pressure separation step, high-pressure low-temperature feed air B introduced via line L1 and high-pressure liquefied nitrogen C introduced via line L8 are cryogenically distilled in 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 high-pressure argon-enriched liquefied air has a higher argon concentration than high-pressure liquefied air.

[0024] [Product Discharge Step] 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).

[0025] A portion of the feed air A cooled in the main heat exchanger 11 is led to a line L5 and introduced into an expansion turbine 13 where it is expanded. The medium-pressure low-temperature feed air E obtained by the expansion is then introduced into the bottom of the medium-pressure column 5.

[0026] [Medium-pressure separation step] In the medium-pressure separation step, medium-pressure low-temperature feed air E introduced into the medium-pressure column 5 via line L5 and medium-pressure liquefied nitrogen F introduced via line L7 are cryogenically distilled in the medium-pressure column 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 via line L6. Also, medium-pressure liquefied air H is discharged from the bottom of the medium-pressure column 5 via line L9.

[0027] The high-pressure liquefied air I discharged from the high-pressure column 4 to the line L3 is introduced into the supercooler 12. After being cooled in the supercooler 12, the pressure is reduced through the valve V1 to obtain low-pressure liquefied air J.

[0028] Furthermore, 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 discharge position of the line L4 connected to the high-pressure column 4 above the discharge position of the line L3, the argon recovery rate can be increased.

[0029] Furthermore, the medium-pressure liquefied air H discharged from the medium-pressure column 5 to a line L9 is cooled by a subcooler 12. After being cooled by the subcooler 12, the pressure is reduced by a valve V3 to obtain low-pressure liquefied air M. Furthermore, a portion of the medium-pressure liquefied air H discharged to the line L9 is introduced into a line L10 branched from the line L9, and the pressure is reduced by a valve V4 to obtain low-pressure liquefied air N.

[0030] [Low-pressure separation step] 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 cryogenically distilled in the low-pressure column 6 to separate them into nitrogen-enriched air, argon-enriched oxygen gas, and liquefied oxygen.

[0031] Here, by positioning the connection position of the line L4 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.

[0032] 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 further heated to room temperature in a main heat exchanger 11, and then recovered as waste gas (WG). Also, an argon-enriched oxygen gas S is discharged from the middle of the low-pressure column 6 through a line L15.

[0033] [Argon Separation Step] In the argon separation step, the argon-enriched oxygen gas S introduced via line L15 and the liquefied argon T introduced via line L17 are subjected to low-temperature distillation in the argon column 7 to separate them into argon gas and argon-enriched liquefied oxygen.

[0034] Argon gas U is discharged from the top of the argon column 7 through a line L16, and argon-enriched liquefied oxygen Q is discharged from the bottom of the argon column 7 through a line L19.

[0035] [Nitrogen Condensation Step] In the nitrogen condensation step, medium-pressure nitrogen gas G is introduced via line L6 into nitrogen condenser 8 housed in the bottom of low-pressure column 6, and indirect heat exchange is performed between the medium-pressure nitrogen gas G and liquefied oxygen accumulated in the bottom of 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.

[0036] The medium-pressure liquefied nitrogen F liquefied in the nitrogen condenser 8 is discharged to a line L7. A portion of the medium-pressure liquefied nitrogen F discharged to the line L7 is branched off to a line L8 and pressurized by a liquefied nitrogen pump 14 to obtain high-pressure liquefied nitrogen C.

[0037] In this embodiment, there is no condenser for liquefying the high-pressure nitrogen gas separated in the high-pressure column 4 to produce a reflux liquid, and the high-pressure liquefied nitrogen C obtained by increasing 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 to some degree as desired depending on the required pressure of the product nitrogen gas.

[0038] A portion of the oxygen gas vaporized in the nitrogen condenser 8 becomes an 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 a valve V8 and then merges with the nitrogen-enriched air R in a line L14.

[0039] Although not shown, the oxygen gas V discharged to line L20 can be heated to room temperature in main heat exchanger 11 and recovered as product oxygen gas. Liquefied oxygen W that was not vaporized in nitrogen condenser 8 is discharged from the bottom of low-pressure column 6 to line L21 and recovered as product liquefied oxygen (LO).

[0040] [Argon Condensation Step] In the argon condensation step, argon gas U is liquefied to produce liquefied argon T. Specifically, argon gas U is introduced into the argon condenser 9 housed in the argon condenser outer cylinder 10 via line L16, and low-pressure liquefied air N is introduced into the argon condenser outer cylinder 10 via line L10. The argon gas U and the low-pressure liquefied air N are subjected to indirect heat exchange to liquefy the argon gas U to produce liquefied argon T, and the low-pressure liquefied air N is vaporized to produce low-pressure air. In another embodiment, 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 produce low-pressure air X.

[0041] [Product Argon Discharge Step] In the product argon discharge step, liquefied argon T liquefied in the argon condenser 9 is discharged to line L17. A portion of the liquefied argon T discharged to line L17 is branched to line L18, vaporized in the main heat exchanger 11, heated to room temperature, and recovered as product argon gas (GAR). Although not shown, a portion of the argon gas U in line L16 may be branched, heated to room temperature in the main heat exchanger 11, and recovered as product argon gas (GAR).

[0042] The low-pressure air X vaporized in the argon condenser 9 is discharged to line L12, depressurized by valve V6, and introduced into the low-pressure column 6 as low-pressure air P. A portion of the low-pressure air X discharged to line L12 is branched to line L13, depressurized by valve V7, and then merged with the nitrogen-enriched air R in line L14. The low-pressure liquefied air Y in the argon condenser outer cylinder 10 that was not vaporized in the argon condenser 9 is discharged to line L11, depressurized by valve V5, and then supplied to the low-pressure column 6 as low-pressure liquefied air O.

[0043] 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.

[0044] Second Embodiment <Nitrogen Production Apparatus 100A> Next, a nitrogen production 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, a line L4 was connected to the middle of the high-pressure column 4, and high-pressure argon-enriched liquefied air K was discharged from the high-pressure column 4 to line L4. In contrast, in this embodiment, line L4 is not provided, and instead, a line L22 is connected to the middle of the medium-pressure column 5. Then, medium-pressure argon-enriched liquefied air K' is discharged from the medium-pressure column 5 to line L22. Note that the medium-pressure argon-enriched liquefied air K' has a higher argon concentration than the medium-pressure liquefied air.

[0045] <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 modification of the first embodiment, and the description of the same parts as those of the first embodiment will be omitted.

[0046] [Medium-pressure separation step] 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 cryogenically distilled in the medium-pressure column 5 to separate medium-pressure nitrogen gas, medium-pressure liquefied air, and medium-pressure argon-enriched liquefied air.

[0047] Then, instead of delivering high-pressure argon-enriched liquefied air K from the middle of the high-pressure column 4 to line L4, in this embodiment, medium-pressure argon-enriched liquefied air K' is delivered from the middle of the medium-pressure column 5 to line L22. The medium-pressure argon-enriched liquefied air K' delivered to line L22 is cooled in subcooler 12, depressurized by valve V9, and then introduced into the low-pressure column 6 as low-pressure argon-enriched liquefied air L'. Here, the argon recovery rate can be increased by positioning the connection position of line L22 connected to the low-pressure column 6 lower than the connection position of line L3 and line L9.

[0048] As in the first embodiment, the nitrogen production method of this embodiment does not have a condenser for liquefying the high-pressure nitrogen gas separated in the high-pressure column 4 to produce a reflux liquid, and the high-pressure liquefied nitrogen obtained by pressurizing the high-pressure column 4 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 to a certain degree of discretion depending on the required pressure of the product nitrogen gas. As a result, in this embodiment as well, when producing a product nitrogen gas of 7 to 15 barA, there is no need to unnecessarily depressurize the gas fluid, and product nitrogen gas and argon can be produced efficiently.

[0049] While the present invention has been described above based on the above-mentioned embodiment, it is not limited to the above-mentioned 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 using a valve and then supplied to the bottom of the medium-pressure column 5. In addition, in the above-mentioned embodiment, low-pressure liquefied air N obtained by depressurizing the medium-pressure liquefied air H extracted 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. However, low-pressure liquefied air obtained by depressurizing the high-pressure liquefied air I extracted from the bottom of the high-pressure column 4 may also be used. In addition, as a modification of the second embodiment, high-pressure argon-enriched liquefied air can be extracted from the middle of the high-pressure column 4, depressurized using a valve, and then introduced into the middle of the medium-pressure column 5.

[0050] The present invention will be described in detail below using examples and comparative examples. <Examples> A simulation of the nitrogen production apparatus 100 of the present invention shown in Figure 1 was carried out using a simulator used in the design of an actual machine. In carrying out the simulation, the flow rate of the feed air was set to 100, and calculations were carried out 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.

[0051]

[0052] According to the results of this simulation, product nitrogen gas GN was recovered at a flow rate of 40 from raw air at a flow rate of 100, and at the same time product argon gas GAR was recovered at a flow rate of 0.5.

[0053] As is clear from the above results, the nitrogen production method and nitrogen production apparatus of the present invention can recover a large amount of product nitrogen gas (e.g., 40% or more of the air volume) at a relatively high pressure (e.g., 7 barA or more), while simultaneously recovering a large amount of product argon (e.g., 1% or more of the product nitrogen gas volume). Furthermore, nitrogen gas over a wide range of pressures (e.g., 7 to 15 barA) can be produced without using a nitrogen compressor.

[0054] 1: air compressor, 2: air precooler, 3: air purifier, 4: high-pressure column, 5: medium-pressure column, 6: low-pressure column, 7: argon column, 8: nitrogen condenser, 9: argon condenser, 10: argon condenser outer casing, 11: main heat exchanger, 12: subcooler, 13: expansion turbine, 14: liquefied nitrogen pump

Claims

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 and separated 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 and separated into medium-pressure nitrogen gas and medium-pressure liquefied air; 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 and separated into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas; and an argon separation process in which the argon-enriched oxygen gas is distilled and separated into argon gas and argon-enriched liquefied oxygen. 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 method for producing nitrogen described in claim 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 feed for the low-pressure separation step.

3. The method for producing nitrogen according to claim 1, wherein 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 method for producing nitrogen according to claim 2, wherein in the low-pressure separation step, the low-pressure argon-enriched liquefied air is supplied below the low-pressure liquefied air.

5. A method for producing nitrogen according to claim 3, wherein 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 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 them into high-pressure nitrogen gas and high-pressure liquefied air; a medium-pressure column that distills medium-pressure, low-temperature feed air obtained by adiabatic expansion of a portion of the feed air, and separates them into medium-pressure nitrogen gas and medium-pressure liquefied air; a low-pressure column that 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; an argon column that distills the argon-enriched oxygen gas, and separates it into argon gas and argon-enriched liquefied oxygen; and a nitrogen condenser that indirectly heat exchanges the medium-pressure nitrogen gas with 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. 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 claim 6, wherein the high-pressure column is configured to distill the high-pressure low-temperature feed air and the high-pressure liquefied nitrogen, to separate high-pressure argon-enriched liquefied air having a higher argon concentration than the high-pressure liquefied air in addition to the high-pressure nitrogen gas and the high-pressure liquefied air, and to introduce the low-pressure argon-enriched liquefied air obtained by reducing the pressure of the high-pressure argon-enriched liquefied air into the low-pressure column.

8. The nitrogen production apparatus according to claim 6, wherein the medium-pressure low-temperature feed air is distilled in the medium-pressure column 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 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.

9. The nitrogen production apparatus according to claim 7, wherein the inlet of the low-pressure argon-enriched liquefied air is located lower than the inlet of the low-pressure liquefied air in the low-pressure column.

10. The nitrogen production apparatus according to claim 8, wherein the inlet of the low-pressure argon-enriched liquefied air is located lower than the inlet of the low-pressure liquefied air in the low-pressure column.

Images