Nitrogen production method and nitrogen production apparatus

Abstract

The present invention aims to provide a nitrogen production technology that can efficiently generate nitrogen gas at relatively high and wide pressure ranges (e.g., 7 to 15 bar A) while simultaneously generating a relatively large amount of argon. [Solution] A nitrogen production apparatus is provided, comprising: a high-pressure tower that distills high-pressure low-temperature raw material air obtained by cooling raw material air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquid nitrogen obtained by pressurizing medium-pressure liquid nitrogen, to separate it into high-pressure nitrogen gas and high-pressure liquid air; an intermediate-pressure tower that distills medium-pressure low-temperature raw material air obtained by adiabatically expanding a portion of the raw material air, to separate it into medium-pressure nitrogen gas and medium-pressure liquid 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.

Description

Technical Field

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

Background Art

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

[0003] According to Patent Document 1, high-pressure nitrogen gas can be produced from raw air in a first rectification column and a second rectification column, and a small amount of oxygen and argon can be produced in subsequent oxygen columns and argon columns.

[0004] Also, according to Patent Document 2, using the first to fourth rectification columns, in addition to nitrogen gas at 9 to 12 barA, oxygen and argon can be co-produced. For example, nitrogen gas at 9 to 12 barA can be generated by the first rectification column, and the fluid vaporized in the condenser of the first rectification column can be supplied to a complex rectification system (the second to fourth rectification columns) to co-produce high-purity oxygen and argon. Furthermore, by boosting the pressure of the liquefied nitrogen generated in the second rectification column incorporated in the complex rectification system with a pump and returning it to the first rectification column, the amount of nitrogen gas generated in the first rectification column can be increased (that is, the nitrogen recovery rate can be improved). <所

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the nitrogen production apparatus disclosed in Patent Document 1 is capable of generating nitrogen gas at a relatively high pressure while simultaneously producing high-purity oxygen and argon, but the argon recovery rate is low, and the amount of argon remains at about 0.5% of the amount of nitrogen gas.

[0007] Furthermore, while the air separation apparatus disclosed in Patent Document 2 is capable of generating relatively high-pressure nitrogen gas while simultaneously producing high-purity oxygen and argon, the reflux liquid of the first rectification column is generated in a condenser installed at the top of the first rectification column. This restricts the operating pressure of the first rectification column, making it difficult to operate outside the range of 9 to 12 bar A. In other words, in the air separation apparatus disclosed in Patent Document 2, the pressure of the liquefied nitrogen gas is limited according to 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 bar A. Therefore, if the required pressure of the product nitrogen gas is lower than 9 barA, the nitrogen gas produced in the first rectification column will have to be depressurized, which is inefficient. Also, if the pressure of the product nitrogen gas is higher than 12 barA, operations such as depressurizing the vaporized gas fluid in the condenser of the first rectification column will be necessary, which is also inefficient.

[0008] Thus, there was a need for a nitrogen production technology that could efficiently generate nitrogen gas at relatively high and wide pressure ranges (e.g., 7-15 barA) while simultaneously producing a relatively large amount of argon, but no effective or suitable technology existed. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides the following means. [1] A high-pressure separation step in which raw material air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon is cooled to obtain high-pressure low-temperature raw material air, and high-pressure liquefied nitrogen obtained by increasing the pressure of medium-pressure liquefied nitrogen is distilled to separate it into high-pressure nitrogen gas and high-pressure liquefied air; a medium-pressure separation step in which a portion of the raw material air is adiabatically expanded to obtain medium-pressure low-temperature raw material air, which is distilled to separate it into medium-pressure nitrogen gas and medium-pressure liquefied air; and a low-pressure separation step in which at least one of the high-pressure liquefied air and the medium-pressure liquefied air is depressurized to obtain low-pressure liquefied air, which is distilled to separate it into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas. A method for producing nitrogen, comprising: 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 of indirectly exchanging heat between the medium-pressure nitrogen gas and the liquefied oxygen to liquefy the medium-pressure nitrogen gas and produce 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 raw air and the high-pressure liquefied nitrogen are distilled to separate high-pressure argon-enriched liquefied air, which has 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 the low-pressure argon-enriched liquefied air obtained by depressurizing the high-pressure argon-enriched liquefied air is used as part of the raw materials for the low-pressure separation step. [3] The nitrogen production method according to [1], characterized in that, in the intermediate pressure separation step, the intermediate pressure low temperature raw air is distilled to separate intermediate pressure argon-enriched liquefied air, which has a higher argon concentration than the intermediate pressure liquefied air, in addition to the intermediate pressure nitrogen gas and the intermediate pressure liquefied air, and the low pressure argon-enriched liquefied air obtained by reducing the pressure of the intermediate pressure argon-enriched liquefied air is used as part of the raw material 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 tower that distills high-pressure low-temperature raw material air obtained by cooling raw material air obtained by compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon, and high-pressure liquid nitrogen obtained by pressurizing medium-pressure liquid nitrogen, to separate it into high-pressure nitrogen gas and high-pressure liquid air; an intermediate-pressure tower that distills medium-pressure low-temperature raw material air obtained by adiabatically expanding a portion of the raw material air, to separate it into medium-pressure nitrogen gas and medium-pressure liquid air; a low-pressure tower that distills low-pressure liquid air obtained by depressurizing at least one of the high-pressure liquid air and the intermediate-pressure liquid air, to separate it into nitrogen-enriched air, liquid oxygen, and argon-enriched oxygen gas; and the a A nitrogen production apparatus comprising: an argon column for distilling argon-enriched oxygen gas to separate it into argon gas and argon-enriched liquid oxygen; a nitrogen condenser for indirectly exchanging heat between the medium-pressure nitrogen gas and the liquid oxygen to liquefy the medium-pressure nitrogen gas and produce medium-pressure liquid nitrogen, and vaporize the liquid oxygen to produce oxygen gas; an argon condenser for liquefying the argon gas to produce liquid 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 liquid argon as a product. [7] The nitrogen production apparatus according to [6], characterized in that, in the high-pressure tower, the high-pressure low-temperature raw air and the high-pressure liquefied nitrogen are distilled to separate high-pressure argon-enriched liquefied air, which has 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 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 tower. [8] The nitrogen production apparatus according to [6], characterized in that, in the intermediate pressure column, the intermediate pressure low-temperature raw air is distilled to separate intermediate pressure argon-enriched liquefied air, which has a higher argon concentration than the intermediate pressure liquefied air, in addition to the intermediate pressure nitrogen gas and the intermediate pressure liquefied air, and the intermediate pressure argon-enriched liquefied air is reduced in pressure to obtain low-pressure argon-enriched liquefied air, which is then introduced into the low-pressure column. [9] The nitrogen production apparatus according to [7], characterized in that the introduction section of the low-pressure argon-enriched liquefied air in the low-pressure tower is located below the introduction section of the low-pressure liquefied air.

[10] The nitrogen production apparatus according to [8], characterized in that the introduction section of the low-pressure argon-enriched liquefied air in the low-pressure tower is located below the introduction section of the low-pressure liquefied air. [Effects of the Invention]

[0010] According to the present invention, it is possible to efficiently generate nitrogen gas at relatively high and wide pressures (for example, 7 to 15 bar A) while simultaneously generating a relatively large amount of argon. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a nitrogen production apparatus according to the first embodiment of the present invention. [Figure 2] This figure shows a nitrogen production apparatus according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0012] [First Embodiment] <Nitrogen production equipment 100> A nitrogen production apparatus 100 according to the first embodiment of the present invention will be described with reference to the drawings. Figure 1 is a schematic 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 refer to the relative pressure and temperature differences in each embodiment example, and do not specify pressure ranges or temperature ranges.

[0013] As shown in Figure 1, the nitrogen production apparatus 100 of this embodiment includes an air compressor 1, an air precooler 2, an air purifier 3, a high-pressure tower 4, an intermediate-pressure tower 5, a low-pressure tower 6, an argon tower 7, a nitrogen condenser 8, an argon condenser 9, an argon condenser outer casing 10, a main heat exchanger 11, a supercooler 12, an expansion turbine 13, and a liquefied nitrogen pump 14.

[0014] The air compressor 1, the air pre-cooler 2, and the air purifier 3 are devices for compressing, pre-cooling, and purifying air containing oxygen, nitrogen, and argon.

[0015] The high-pressure column 4 is a rectification column that separates high-pressure nitrogen gas, high-pressure liquefied air, and high-pressure argon-enriched liquefied air by cryogenic distillation of high-pressure low-temperature raw air B and high-pressure liquefied nitrogen C.

[0016] The medium-pressure column 5 is a rectification column that separates medium-pressure nitrogen gas and medium-pressure liquefied air by cryogenic distillation of medium-pressure low-temperature raw air E and medium-pressure liquefied nitrogen F.

[0017] The low-pressure column 6 is a rectification column that separates nitrogen-enriched air, argon-enriched oxygen gas, and liquefied oxygen by cryogenic distillation of 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 vaporized in the nitrogen condenser 8.

[0018] The argon column 7 is a rectification column that separates argon gas and argon-enriched liquefied oxygen by cryogenic distillation of argon-enriched oxygen gas S and liquefied argon T.

[0019] The nitrogen condenser 8 is housed at the bottom of the low-pressure column 6 and is a heat exchanger that indirectly heat-exchanges the medium-pressure nitrogen gas G introduced into the nitrogen condenser 8 and the liquefied oxygen accumulated at the bottom of the low-pressure column 6.

[0020] 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 generate liquefied argon.

[0021] The main heat exchanger 11 and the sub-cooler 12 are devices that perform heat exchange between the introduced fluids and导出 the fluids after heat exchange. The expansion turbine 13 adiabatically expands a part of the raw air A cooled in the main heat exchanger 11 to generate the cold required for the operation of the device and generate medium-pressure low-temperature raw air E. The liquefied nitrogen pump 14 is a device that increases the pressure of a portion of the medium-pressure liquefied nitrogen F liquefied in the nitrogen condenser 8 to produce high-pressure liquefied nitrogen C.

[0022] <Methods for producing nitrogen> Next, a method for producing nitrogen using the nitrogen production apparatus 100 of this embodiment will be described. Air containing oxygen, nitrogen, and argon, introduced from the atmosphere into line L1, is compressed by air compressor 1, pre-cooled by air pre-cooler 2, and purified by air purifier 3 to obtain raw material air A. Then, the obtained raw material air A is cooled by main heat exchanger 11 to obtain high-pressure, low-temperature raw material air B.

[0023] [High-pressure separation process] In the high-pressure separation process, high-pressure low-temperature raw material air B introduced via line L1 and high-pressure liquefied nitrogen C introduced via line L8 are subjected to low-temperature distillation in high-pressure column 4 to separate them into high-pressure nitrogen gas, high-pressure liquefied air, and high-pressure argon-enriched liquefied air. High-pressure argon-enriched liquefied air refers to air with a higher argon concentration than high-pressure liquefied air.

[0024] [Product derivation process] In the product extraction process, the high-pressure nitrogen gas D extracted from the top of the high-pressure tower 4 via 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 raw material air A, cooled in the main heat exchanger 11, is led to line L5 and introduced into the expansion turbine 13 for expansion. The resulting medium-pressure, low-temperature raw material air E is then introduced to the bottom of the medium-pressure tower 5.

[0026] [Intermediate pressure separation process] In the intermediate pressure separation process, the intermediate pressure low-temperature raw material air E introduced into the intermediate pressure column 5 via line L5 and the intermediate pressure liquefied nitrogen F introduced via line L7 are subjected to low-temperature distillation in the intermediate pressure column 5 to separate them into intermediate pressure nitrogen gas and intermediate pressure liquefied air. Then, intermediate-pressure nitrogen gas G is discharged from the top of the intermediate-pressure tower 5 into line L6. Furthermore, medium-pressure liquefied air H is discharged from the bottom of the medium-pressure tower 5 into line L9.

[0027] High-pressure liquefied air I, which is led from high-pressure tower 4 to line L3, is introduced into supercooler 12. After being cooled in supercooler 12, it is depressurized by valve V1 to obtain low-pressure liquefied air J.

[0028] Furthermore, the high-pressure argon-enriched liquefied air K, which is led from the high-pressure tower 4 to line L4, is cooled in the supercooler 12. After cooling in the supercooler 12, it is depressurized by valve V2 to obtain low-pressure argon-enriched liquefied air L. Here, by positioning the outlet of line L4, which connects to the high-pressure tower 4, higher than the outlet of line L3, the argon recovery rate can be increased.

[0029] Furthermore, the medium-pressure liquefied air H that is led from the medium-pressure tower 5 to line L9 is cooled in the supercooler 12. After cooling in the supercooler 12, it is depressurized by valve V3 to obtain low-pressure liquefied air M. Furthermore, a portion of the medium-pressure liquefied air H supplied to line L9 is introduced into line L10, which branches off from line L9, and depressurized by valve V4 to obtain low-pressure liquefied air N.

[0030] [Low-pressure separation process] In the low-pressure separation process, low-pressure liquefied air J and M introduced via lines L3 and 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 separated into nitrogen-enriched air, argon-enriched oxygen gas, and liquefied oxygen by low-temperature distillation in the low-pressure column 6.

[0031] Here, by positioning the connection point of line L4, which connects to the low-pressure tower 6, lower than the connection points of lines L3 and L9, the argon recovery rate can be increased.

[0032] Next, the nitrogen-enriched air R that is led from the top of the low-pressure tower 6 to line L14 is heated in the supercooler 12, and then heated to room temperature in the main heat exchanger 11 before being recovered as waste gas (WG). Furthermore, argon-enriched oxygen gas S is discharged from the middle of the low-pressure tower 6 into line L15.

[0033] [Argon separation process] In the argon separation process, argon-enriched oxygen gas S introduced via line L15 and liquefied argon T introduced via L17 are separated into argon gas and argon-enriched liquefied oxygen by low-temperature distillation in the argon column 7.

[0034] Argon gas U is introduced into line L16 from the top of argon tower 7. Furthermore, argon-enriched liquefied oxygen Q is discharged from the bottom of the argon tower 7 into line L19.

[0035] [Nitrogen condensation process] In the nitrogen condensation process, intermediate-pressure nitrogen gas G is introduced via line L6 into a nitrogen condenser 8 located at the bottom of the low-pressure tower 6, where it is indirectly heat-exchanged with the liquefied oxygen accumulated at the bottom of the low-pressure tower 6. Specifically, the intermediate-pressure nitrogen gas G is liquefied to produce intermediate-pressure liquefied nitrogen F, and the liquefied oxygen is vaporized to produce oxygen gas.

[0036] The medium-pressure liquid nitrogen F liquefied in the nitrogen condenser 8 is led to line L7. Then, a portion of the medium-pressure liquid nitrogen F led to line L7 is branched to line L8, where it is pressurized by the liquid nitrogen pump 14 to obtain high-pressure liquid nitrogen C.

[0037] In this embodiment, there is no condenser for liquefying the high-pressure nitrogen gas separated in the high-pressure tower 4 to produce reflux liquid. Instead, the high-pressure liquefied nitrogen C obtained by pressurizing the liquefied nitrogen pump 14 becomes the reflux liquid in the high-pressure tower 4. Therefore, there is an advantage in that the operating pressure of the high-pressure tower 4, i.e., the pressure of the raw material air, can be set to some extent arbitrarily according to the required pressure of the product nitrogen gas.

[0038] A portion of the oxygen gas vaporized in the nitrogen condenser 8 becomes the rising gas in the low-pressure tower 6, while the remainder is led to line L20. The oxygen gas V supplied to line L20 is depressurized by valve V8 and then merges with the nitrogen-enriched air R in line L14.

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

[0040] [Argon condensation process] In the argon condensation process, argon gas U is liquefied to produce liquefied argon T. Specifically, argon gas U is introduced into the argon condenser 9, which is housed in the argon condenser outer cylinder 10, via line L16. Low-pressure liquefied air N is also introduced into the argon condenser outer cylinder 10 via line L10. The argon gas U and the low-pressure liquefied air N indirectly exchange heat, liquefying the argon gas U to produce liquefied argon T, and vaporizing the low-pressure liquefied air N to produce low-pressure air. In another configuration, the argon condenser 9 may not be housed in the argon condenser outer cylinder 10. In this case, low-pressure liquefied air N is directly introduced into the argon condenser 9 and vaporizes through indirect heat exchange with argon gas U to produce low-pressure air X.

[0041] [Product Argon Derivation Process] In the argon product extraction process, the liquefied argon T, which has been liquefied in the argon condenser 9, is extracted to line L17. Then, a portion of the liquefied argon T that is led out 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 in the diagram, a portion of the argon gas U from line L16 may be branched off and heated to room temperature in the main heat exchanger 11 before being recovered as product argon gas (GAR).

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

[0043] As explained above, in this embodiment, when producing product nitrogen gas at 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 device 100A> Next, a second embodiment of the nitrogen production apparatus 100A of the present invention will be described with reference to the drawings. Parts similar to those of the first embodiment will not be described. In the first embodiment, line L4 was connected to the middle of the high-pressure tower 4, and high-pressure argon-enriched liquefied air K was supplied from the high-pressure tower 4 to line L4. In contrast, in this embodiment, line L4 is not provided; instead, line L22 is connected to the middle of the intermediate pressure tower 5. Intermediate pressure argon-enriched liquefied air K' is then led from the intermediate pressure tower 5 to line L22. Note that intermediate pressure argon-enriched liquefied air K' refers to air with a higher argon concentration than intermediate pressure liquefied air.

[0045] <Methods for producing nitrogen> Next, a nitrogen production method using the nitrogen production apparatus 100A of the second embodiment will be described with reference to Figure 2. This embodiment is a modification of the first embodiment, and the same parts as in the first embodiment will not be explained.

[0046] [Intermediate pressure separation process] In this embodiment, in the intermediate pressure separation process, the intermediate pressure low-temperature raw material air E introduced into the intermediate pressure column 5 via line L5 and the intermediate pressure liquefied nitrogen F introduced via line L7 are subjected to low-temperature distillation in the intermediate pressure column 5 to separate intermediate pressure nitrogen gas and intermediate pressure liquefied air, in addition to the intermediate pressure liquefied air.

[0047] Instead of leading high-pressure argon-enriched liquefied air K from the middle of high-pressure tower 4 to line L4, in this embodiment, intermediate-pressure argon-enriched liquefied air K' is led from the middle of intermediate-pressure tower 5 to line L22. The medium-pressure argon-enriched liquefied air K' that is led out to line L22 is cooled in the supercooler 12 and depressurized by valve V9, and then introduced into the low-pressure tower 6 as low-pressure argon-enriched liquefied air L'. Here, by positioning the connection point of line L22, which connects to the low-pressure tower 6, lower than the connection points of lines L3 and L9, the argon recovery rate can be increased.

[0048] In the nitrogen production method of this embodiment, as in the first embodiment, there is no condenser for liquefying the high-pressure nitrogen gas separated in the high-pressure tower 4 to produce reflux liquid. Instead, the high-pressure liquefied nitrogen obtained by pressurizing the liquefied nitrogen pump 14 becomes the reflux liquid in the high-pressure tower 4. Therefore, there is an advantage in that the operating pressure of the high-pressure tower 4, i.e., the pressure of the raw material air, can be set to some extent arbitrarily according to the required pressure of the product nitrogen gas. As a result, in this embodiment as well, when producing product nitrogen gas at 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.

[0049] Although the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments and can be implemented in various forms without departing from its spirit. For example, the high-pressure liquefied air separated in the high-pressure tower 4 can be reduced in pressure by a valve and then supplied to the bottom of the intermediate-pressure tower 5. Also, in the above embodiment, low-pressure liquefied air N, which is obtained by reducing the pressure of the intermediate-pressure liquefied air H that is led out from the bottom of the intermediate-pressure tower 5, was used as the fluid that indirectly exchanges heat with the argon gas U in the argon condensation process. However, low-pressure liquefied air, which is obtained by reducing the pressure of the high-pressure liquefied air I that is led out from the bottom of the high-pressure tower 4, may also be used. Furthermore, as a modification of the second embodiment, high-pressure argon-enriched liquefied air can be introduced into the middle of the intermediate-pressure tower 5 after being discharged from the middle of the high-pressure tower 4 and depressurized by a valve. [Examples]

[0050] The present invention will be described in detail below using examples and comparative examples. <Examples> Using the simulator used for designing the actual machine, a simulation of the nitrogen production apparatus 100 of the present invention, shown in Figure 1, was performed. In conducting the simulation, the flow rate of the raw air was set to 100, and calculations were performed under conditions that maximized the recovery 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] [Table 1]

[0052] According to these simulation results, it was possible to recover product nitrogen gas (GN) at a flow rate of 40 from raw air at a flow rate of 100, while simultaneously recovering product argon gas (GAR) 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 make it possible to recover a large amount of product nitrogen gas at a relatively high pressure (e.g., 7 bar A or higher) (e.g., 40% or more of the amount of air) while simultaneously recovering a large amount of product argon (e.g., 1% or more of the amount of product nitrogen gas). Furthermore, nitrogen gas can be produced at a wide range of pressures (e.g., 7-15 barA) without the use of a nitrogen compressor. [Explanation of Symbols]

[0054] 1: Air compressor, 2: Air precooler, 3: Air purifier, 4: High-pressure tower, 5: Intermediate-pressure tower, 6: Low-pressure tower, 7: Argon tower, 8: Nitrogen condenser, 9: Argon condenser, 10: Argon condenser outer casing, 11: Main heat exchanger, 12: Supercooler, 13: Expansion turbine, 14: Liquefied nitrogen pump

Claims

1. A high-pressure separation process involves distilling high-pressure nitrogen gas and high-pressure liquefied air by cooling raw material air obtained by compressing, pre-cooling, and purifying raw material air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by increasing the pressure of medium-pressure liquefied nitrogen, thereby separating them into high-pressure nitrogen gas and high-pressure liquefied air. A medium-pressure separation step is performed in which a portion of the aforementioned raw material air is adiabatically expanded to obtain medium-pressure low-temperature raw material air, which is then distilled to separate it into medium-pressure nitrogen gas and medium-pressure liquefied air. A low-pressure separation step is performed in which 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 is distilled to separate it into nitrogen-enriched air, liquefied oxygen, and argon-enriched oxygen gas. The argon separation step involves distilling the argon-enriched oxygen gas to separate it into argon gas and argon-enriched liquefied oxygen. A nitrogen condensation step is performed by indirectly exchanging heat between the medium-pressure nitrogen gas and the liquid oxygen to liquefy the medium-pressure nitrogen gas and produce medium-pressure liquid nitrogen, and by vaporizing the liquid oxygen to produce oxygen gas. An argon condensation step is performed to liquefy the argon gas to produce liquefied argon, A product nitrogen extraction process for extracting the aforementioned high-pressure nitrogen gas as a product, A method for producing nitrogen, characterized by comprising a product argon extraction step of extracting the argon gas or a portion of the liquefied argon as a product.

2. In the high-pressure separation step, the high-pressure low-temperature raw air and the high-pressure liquefied nitrogen are distilled to separate high-pressure argon-enriched liquefied air, which has a higher argon concentration than the high-pressure liquefied air, from the high-pressure nitrogen gas and the high-pressure liquefied air. The nitrogen production method according to claim 1, characterized in that 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 materials for the low-pressure separation step.

3. In the aforementioned intermediate-pressure separation step, the intermediate-pressure low-temperature raw material air is distilled to separate the intermediate-pressure nitrogen gas and the intermediate-pressure liquefied air, and to the intermediate-pressure liquefied air, in addition to the intermediate-pressure liquefied air, which has a higher argon concentration than the intermediate-pressure liquefied air. The nitrogen production method according to claim 1, characterized in that 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 raw materials for the low-pressure separation step.

4. The nitrogen production method according to claim 2, 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.

5. The nitrogen production method according to claim 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 high-pressure tower separates high-pressure nitrogen gas and high-pressure liquefied air by distilling high-pressure liquefied nitrogen, which is obtained by cooling high-pressure low-temperature raw material air obtained by compressing, pre-cooling, and purifying raw material air containing oxygen, nitrogen, and argon, and high-pressure liquefied nitrogen obtained by increasing the pressure of medium-pressure liquefied nitrogen, A medium-pressure column is used to distill the medium-pressure, low-temperature raw material air obtained by adiabatically expanding a portion of the aforementioned raw material air, thereby separating it into medium-pressure nitrogen gas and medium-pressure liquefied air. A low-pressure tower is used to distill 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, separating it 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 liquid oxygen, A nitrogen condenser that indirectly exchanges heat between the aforementioned medium-pressure nitrogen gas and the aforementioned liquid oxygen to liquefy the medium-pressure nitrogen gas and produce the aforementioned medium-pressure liquid nitrogen, and vaporizes the aforementioned liquid oxygen to produce oxygen gas, An argon condenser that liquefies the aforementioned argon gas to produce liquefied argon, A product nitrogen discharge line for dischargering the aforementioned high-pressure nitrogen gas as a product, A nitrogen production apparatus comprising a product argon outlet line for discharging the argon gas or a portion of the liquefied argon as a product.

7. In the aforementioned high-pressure tower, the high-pressure low-temperature raw air and the high-pressure liquefied nitrogen are distilled to separate high-pressure argon-enriched liquefied air, which has a higher argon concentration than the high-pressure liquefied air, in addition to the high-pressure nitrogen gas and the high-pressure liquefied air. The nitrogen production apparatus according to claim 6, characterized in that 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 tower.

8. In the aforementioned intermediate-pressure tower, the intermediate-pressure low-temperature raw material air is distilled to separate intermediate-pressure argon-enriched liquefied air, which has a higher argon concentration than the intermediate-pressure liquefied air, from the intermediate-pressure nitrogen gas and the intermediate-pressure liquefied air. The nitrogen production apparatus according to claim 6, characterized in that 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 tower.

9. The nitrogen production apparatus according to claim 7, characterized in that the introduction section of the low-pressure argon-enriched liquefied air in the low-pressure tower is located below the introduction section of the low-pressure liquefied air.

10. The nitrogen production apparatus according to claim 8, characterized in that the introduction section of the low-pressure argon-enriched liquefied air in the low-pressure tower is located below the introduction section of the low-pressure liquefied air.

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