Nitrogen production method and nitrogen production device

Abstract

The present invention is capable, during normal operation, of generating a large amount of product nitrogen gas while simultaneously generating a small amount of product oxygen gas or product liquefied oxygen. The purpose of the present invention is to provide a nitrogen production technique with which, when liquefied nitrogen is required, it is possible, by switching operating modes, to maintain an amount of product nitrogen gas, while simultaneously producing or increasing liquefied nitrogen, without an increase in power consumption. Provided is a nitrogen production method characterised by including a first separation step, a first condensation step, a second separation step, a second condensation step, an oxygen separation step, an oxygen evaporation step, a product nitrogen derivation step, a product liquefied nitrogen derivation step, and a product oxygen derivation step, wherein, in a first operating mode, at least the oxygen separation step, the oxygen evaporation step and the product oxygen derivation step are performed, and in a second operating mode, the oxygen separation step, the oxygen evaporation step and the product oxygen derivation step are not performed.

Description

Nitrogen production method and nitrogen production apparatus 【0001】 The present invention relates to a nitrogen production method and a nitrogen production apparatus. 【0002】 In recent years, in nitrogen production apparatuses for semiconductor factories, cases where in addition to a large amount of nitrogen gas, a small amount of high-purity oxygen and argon are required have been increasing. 【0003】 According to Patent Document 1, raw air is separated in a first rectification column into a first nitrogen-enriched fluid and a first oxygen-enriched fluid, the first oxygen-enriched fluid is separated in a second rectification column into a second nitrogen-enriched fluid and a second oxygen-enriched fluid, and an oxygen-containing liquid is withdrawn from an intermediate part of the first rectification column or the second rectification column and introduced into the upper part of a third rectification column for separation, so that in addition to product nitrogen, product oxygen can be obtained. 【0004】 According to Patent Document 2, raw air is separated into nitrogen and an oxygen-enriched fluid in a main rectification column and an auxiliary rectification column, a fluid containing oxygen is separated in a separation column, and oxygen can be obtained from the lower part of the separation column. Further, according to Patent Document 3, in addition to nitrogen gas, oxygen and argon can be obtained using a first rectification column, a second rectification column, an oxygen column, and an argon column. 【0005】 U.S. Patent No. 6460373, Japanese Patent Laid-Open No. 11-316080, Patent No. 7329714 【0006】 The nitrogen production apparatuses disclosed in Patent Documents 1 to 3 can generate oxygen while generating nitrogen gas. However, when temporarily storing liquefied nitrogen in a tank for backup of nitrogen gas or the like, if liquefied nitrogen is co-produced, there is a problem that the amount of product nitrogen gas is significantly reduced and the power consumption is significantly increased. Further, when supplying liquefied nitrogen from another site by a tank truck, in addition to the production cost, transportation cost is required, so there is a problem that the cost becomes high. 【0007】 Thus, a nitrogen production technology that can co-produce product nitrogen gas and liquefied nitrogen without significantly reducing the amount of product nitrogen gas or significantly increasing the power consumption by switching the operation mode when liquefied nitrogen is temporarily required while generating nitrogen gas during normal operation has been demanded, but there has been no effective and appropriate one. 【0008】To solve the above problems, the present invention provides the following means. [1] A first separation step in which low-temperature raw material air obtained by cooling raw material air is distilled to separate it into high-pressure nitrogen gas and high-pressure liquefied air; a first condensation step in which the high-pressure nitrogen gas and medium-pressure liquefied air obtained by depressurizing the high-pressure liquefied air are indirectly heat-exchanged to liquefy the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporize the medium-pressure liquefied air to produce medium-pressure air; a second separation step in which the medium-pressure air is distilled to separate it into medium-pressure nitrogen gas and medium-pressure liquefied air; a second condensation step in which the medium-pressure nitrogen gas and low-pressure liquefied air obtained by depressurizing the medium-pressure liquefied air are indirectly heat-exchanged to liquefy the medium-pressure nitrogen gas to produce medium-pressure liquefied nitrogen and vaporize the low-pressure liquefied air to produce low-pressure air; an oxygen separation step in which a portion of the high-pressure liquefied air produced in the first rectification column, or a portion of the medium-pressure liquefied air produced in the second separation step, is distilled to separate it into waste air and liquefied oxygen; A nitrogen production method comprising: an oxygen evaporation step of vaporizing the liquefied oxygen to generate rising gas; a product nitrogen output step of outputting a portion of the high-pressure nitrogen gas as a product; a product liquefied nitrogen output step of outputting either or both of the portion of the high-pressure liquefied nitrogen and / or the portion of the medium-pressure liquefied nitrogen as product liquefied nitrogen; and a product oxygen output step of outputting a portion of the liquefied oxygen or the oxygen gas obtained by vaporizing the liquefied oxygen as a product, wherein the method has at least a first operating mode and a second operating mode in which the amount of product liquefied nitrogen outputted in the product liquefied nitrogen output step is greater than that in the first operating mode, wherein in the first operating mode, at least the oxygen separation step, the oxygen evaporation step, and the product oxygen output step are performed, and in the second operating mode, the oxygen separation step, the oxygen evaporation step, and the product oxygen output step are not performed.[2] The nitrogen production method according to [1], wherein the oxygen separation step includes separating not only the waste air and the liquefied oxygen but also argon-enriched oxygen gas, distilling the argon-enriched oxygen gas to separate it into argon gas and argon-enriched liquefied oxygen, argon condensation step to liquefy the argon gas to produce liquefied argon, and product argon discharge step to discharge a portion of the argon gas or the liquefied argon as a product, wherein the first operating mode further includes the argon separation step, the argon condensation step and the product argon discharge step, and the second operating mode further does not include the argon separation step, the argon condensation step and the product argon discharge step. [3] A nitrogen production method according to [1] or [2], characterized in that it includes a first adiabatic expansion step in which a portion of the low-pressure air is heated and then adiabatically expanded to generate cold in the first operating mode, and a second adiabatic expansion step in which, in addition to the first adiabatic expansion step, another portion of the low-pressure air is heated and then adiabatically expanded to generate cold in the second operating mode. [4] A nitrogen production method according to [3], characterized in that the temperatures of the low-pressure air to be adiabatically expanded in the first adiabatic expansion step and the second adiabatic expansion step are different. [5] A nitrogen production method according to [1] or [2], characterized in that it includes a first adiabatic expansion step in which a portion of the medium-pressure air is heated and then adiabatically expanded to generate cold necessary for the apparatus in the first operating mode, and a second adiabatic expansion step in which, in addition to the first adiabatic expansion step, another portion of the medium-pressure air is heated and then adiabatically expanded to generate cold in the second operating mode. [6] A nitrogen production method according to [5], characterized in that the temperatures of the medium-pressure air to be adiabatically expanded in the first adiabatic expansion step and the second adiabatic expansion step are different.[7] A first rectification column that distills low-temperature raw air obtained by cooling raw air to separate it into high-pressure nitrogen gas and high-pressure liquefied air; a first condenser that indirectly heat exchanges the high-pressure nitrogen gas with medium-pressure liquefied air obtained by reducing the pressure of the high-pressure liquefied air to liquefy the high-pressure nitrogen gas and vaporize the medium-pressure liquefied air to produce medium-pressure air; a second rectification column that distills the medium-pressure air to separate it into medium-pressure nitrogen gas and medium-pressure liquefied air; a second condenser that indirectly heat exchanges the medium-pressure nitrogen gas with low-pressure liquefied air obtained by reducing the pressure of the medium-pressure liquefied air to liquefy the medium-pressure nitrogen gas and vaporize the low-pressure liquefied air to produce low-pressure air; and an oxygen column that distills a portion of the high-pressure liquefied air produced in the first rectification column or a portion of the medium-pressure liquefied air produced in the second separation step to separate it into waste air and liquefied oxygen. A nitrogen production apparatus comprising: an oxygen evaporator that vaporizes the liquefied oxygen in the oxygen tower to generate rising gas; a product nitrogen outlet line that discharges a portion of the high-pressure nitrogen gas as a product; a product liquefied nitrogen outlet line that discharges either or both of the portion of the high-pressure liquefied nitrogen and / or the portion of the medium-pressure liquefied nitrogen as product liquefied nitrogen; a product oxygen outlet line that discharges a portion of the oxygen gas or the liquefied oxygen as a product; a valve provided in a line that introduces a portion of the high-pressure liquefied air or a portion of the medium-pressure liquefied air into the oxygen tower; and a valve provided in a line that introduces a fluid to the oxygen evaporator that exchanges heat with the liquefied oxygen in the oxygen tower. 【0009】 According to the present invention, during normal operation, a large amount of product nitrogen gas can be generated while simultaneously generating a small amount of product oxygen gas or product liquefied oxygen. When liquefied nitrogen is required, the operating mode can be switched to maintain the amount of product nitrogen gas while simultaneously producing or increasing the amount of liquefied nitrogen without increasing power consumption. 【0010】This is a diagram showing a nitrogen production apparatus according to the first embodiment of the present invention. This is a diagram showing a nitrogen production apparatus according to the first embodiment of the present invention. This is a diagram showing a nitrogen production apparatus according to the second embodiment of the present invention. This is a diagram showing a nitrogen production apparatus according to the second embodiment of the present invention. This is a diagram showing a nitrogen production apparatus according to the third embodiment of the present invention. This is a diagram showing a nitrogen production apparatus according to the third embodiment of the present invention. 【0011】 [First Embodiment] <Nitrogen Production Apparatus 1> A nitrogen production apparatus 1 according to the first embodiment of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram of the nitrogen production apparatus 1 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. 【0012】 As shown in Figure 1, the nitrogen production apparatus 1 of this embodiment includes an air compressor 2, an air precooler 3, an air purifier 4, a main heat exchanger 5, a first rectification column 6, a first condenser 7, a second rectification column 8, a second condenser 9, an expansion turbine 10, an oxygen column 11, an oxygen evaporator 12, a liquefied nitrogen pump 13, a liquefied oxygen pump 16, a line L6 for discharging product nitrogen gas, and lines L30 and L31 for discharging product liquefied nitrogen. 【0013】 The air compressor 2, air precooler 3, and air purifier 4 are devices that compress, precool, and purify air containing oxygen, nitrogen, and argon. The main heat exchanger 5 is a device that performs heat exchange between the introduced fluids and discharges the fluid after heat exchange. 【0014】 The first rectification column 6 is a rectification column that separates low-temperature raw material air B into high-pressure nitrogen gas C and high-pressure liquefied air D by low-temperature distillation. The first condenser 7 is a device that indirectly exchanges heat between high-pressure nitrogen gas C and medium-pressure liquefied air E obtained by reducing the pressure of high-pressure liquefied air D. Specifically, the first condenser 7 is a device that liquefies high-pressure nitrogen gas C to produce high-pressure liquefied nitrogen G, and vaporizes medium-pressure liquefied air E to produce medium-pressure air F. 【0015】The second rectification column 8 is a rectification column that separates medium-pressure air F into medium-pressure nitrogen gases H and Q and medium-pressure liquefied air I by low-temperature distillation. The second condenser 9 is a device that indirectly exchanges heat between medium-pressure nitrogen gas H and low-pressure liquefied air J obtained by reducing the pressure of the medium-pressure liquefied air I. Specifically, the second condenser 9 is a device that liquefies medium-pressure nitrogen gas H to produce medium-pressure liquefied nitrogen L, and vaporizes low-pressure liquefied air J to produce low-pressure air K. 【0016】 The expansion turbine 10 is a device that adiabatically expands the introduced gas. The oxygen tower 11 is a rectification column that separates a portion of the medium-pressure liquefied air N discharged from near the bottom of the second rectification column 8 into waste air R and liquefied oxygen M by low-temperature distillation. The oxygen evaporator 12 is a device that exchanges heat between the liquefied oxygen M at the bottom of the oxygen tower 11 and the medium-pressure nitrogen gas Q. Specifically, the oxygen evaporator 12 vaporizes the liquefied oxygen at the bottom of the oxygen tower 11 and liquefies the medium-pressure nitrogen gas Q from the second rectification column 8 to produce medium-pressure liquefied nitrogen X. 【0017】 The liquefied nitrogen pump 13 is a device that increases the pressure of the medium-pressure liquefied nitrogen X supplied from the oxygen evaporator 12. The liquefied oxygen pump 16 is a device that increases the pressure of the liquefied oxygen M supplied from the oxygen tower 11. 【0018】 Next, the pipelines connecting each of the above-mentioned devices will be described. Line L1 is a pipeline (path) that introduces air containing oxygen, nitrogen, and argon introduced from the atmosphere into the first rectification column 6 via the air compressor 2, air precooler 3, air purifier 4, and main heat exchanger 5. The air becomes raw material air A after passing through the air compressor 2, air precooler 3, and air purifier 4, and becomes low-temperature raw material air B after passing through the main heat exchanger 5. 【0019】Line L2, connected to the bottom of the first rectification column, branches into two lines, L15 and L3. Lines L2 and L15 are pipelines that lead the high-pressure liquefied air D from the bottom of the first rectification column 6 to the second rectification column 8. Line L15 has a valve V4 in the middle. Lines L2 and L3 are pipelines that lead the high-pressure liquefied air D from the first rectification column 6 to the first condenser 7. Line L3 has a valve V1 that functions as a pressure reducing valve in the middle. The high-pressure liquefied air D is reduced in pressure by valve V1 to become medium-pressure liquefied air E. 【0020】 Line L4 is a pipeline that introduces high-pressure nitrogen gas C, which is discharged from the top of the first rectification column 6, into the first condenser 7. Line L5 is a pipeline that introduces high-pressure liquefied nitrogen G, which is discharged from the first condenser 7, into the top of the first rectification column 6. 【0021】 Line L6 is a pipeline that supplies high-pressure nitrogen gas C, which is discharged from the top of the first rectification column 6, to the outside of the system as product nitrogen gas GN via the main heat exchanger 5. In Figure 1, line L6 is shown branching off from line L4, but lines L4 and L6 may also be connected separately to the top of the first rectification column 6. Line L7 is a pipeline that introduces medium-pressure air F, which is discharged from the first condenser 7, into the second rectification column 8. 【0022】 Lines L9 and L10 are pipelines that introduce medium-pressure liquefied air I, which is discharged from the bottom of the second rectification column 8, into the second condenser 9. A valve V5, which functions as a pressure reducing valve, is provided downstream of line L9, and line L10 is provided downstream of that. The medium-pressure liquefied air I is reduced in pressure by valve V5 to become low-pressure liquefied air J. Line L11 is a pipeline that introduces medium-pressure nitrogen gas H, which is discharged from the top of the second rectification column 8, into the second condenser 9. 【0023】Line L39 is a pipeline that branches off from line L11 and introduces the medium-pressure nitrogen gas Q discharged from the top of the second rectification column 8 to valve V9, which functions as an on / off valve. Line L40 is located downstream of valve V9. Line L40 is a pipeline that introduces the medium-pressure nitrogen gas Q discharged from valve V9 to the oxygen evaporator 12. Line L12 is a pipeline that introduces the medium-pressure liquefied nitrogen L discharged from the second condenser 9 to the top of the second rectification column 8. 【0024】 Lines L22 and L17 are pipelines that introduce medium-pressure liquefied air N, which is drawn out from near the bottom of the second rectification column 8, to the top of the oxygen column 11. Line L22 is a side-cut line. A valve V3, which functions as an on / off valve, is provided downstream of line L22, and line L17 is provided downstream of valve V3. 【0025】 Line L13 is a pipeline that introduces low-pressure air K, discharged from the second condenser 9, to the expansion turbine 10 via the main heat exchanger 5. Line L14 is a pipeline that discharges fluid discharged from the expansion turbine 10 to the outside of the system as waste gas WG via the main heat exchanger 5. Line L16 is a pipeline that merges with line L14. Lines L16 and L14 are pipelines that supply waste gas WG to the outside of the system via the main heat exchanger 5, using waste air R discharged from the top of the oxygen tower 11. 【0026】 Line L20 is a pipeline that supplies liquefied oxygen M, taken from the oxygen tower 11, to the outside of the system as product high-pressure oxygen gas HPGO via a liquefied oxygen pump 16 and a main heat exchanger 5. The liquefied oxygen M is pressurized into liquefied oxygen Y by the liquefied oxygen pump 16 and heated by the main heat exchanger 5 to become product high-pressure oxygen gas HPGO. 【0027】 Lines L18 and L37 merge and connect to line L19. Lines L18, L19, and L27 are pipelines that introduce medium-pressure liquefied nitrogen X, which is taken from the oxygen evaporator 12, into the upper part of the first rectification column 7 after being pressurized by the liquefied nitrogen pump 13. 【0028】A liquefied nitrogen pump 13 is located downstream of line L19, and line L27 is located downstream of the liquefied nitrogen pump 13. Line L37 is a pipeline that introduces medium-pressure liquefied nitrogen Z, which is supplied from the top of the second rectification column 8, into line L19. 【0029】 Lines L30 and L31 are pipelines branching off from line L12 and supply product liquefied nitrogen LN to the outside of the equipment system. A valve V6, which functions as an on / off valve, is provided between lines L30 and L31. When valve V6 is closed, product liquefied nitrogen cannot be recovered, and when valve V6 is opened, a portion of the medium-pressure liquefied nitrogen L liquefied in the second condenser 9 can be recovered as product liquefied nitrogen LN. Although not shown in the diagram, line L30 may also branch off from line L5. In this case, a portion of the high-pressure liquefied nitrogen G can be recovered as product liquefied nitrogen LN. 【0030】 <Nitrogen Production Method> Next, a nitrogen production method using the nitrogen production apparatus 1 of this embodiment will be described. 【0031】 <<First Operating Mode>> Referring to Figure 1, the first operating mode in which various product gases and product liquefied gases are produced from air using the nitrogen production apparatus 1 will be described. 【0032】 First, air containing oxygen, nitrogen, and argon taken from the atmosphere is introduced into line L1. Then, the air is compressed in air compressor 2, pre-cooled in air pre-cooler 3, and purified in air purifier 4 to obtain raw material air A. Finally, raw material air A is cooled in main heat exchanger 5 to obtain low-temperature raw material air B. 【0033】 [First Separation Process] In the first separation process, low-temperature raw material air B is supplied to the bottom of the first rectification column 6 and separated into high-pressure nitrogen gas C and high-pressure liquefied air D by low-temperature distillation. 【0034】[First Condensation Process] In the first condensation process, a portion of the high-pressure liquefied air D, which is supplied from the bottom of the first rectification column 6 via line L2, is branched off via line L3 and depressurized by valve V1 to obtain medium-pressure liquefied air E. Then, the medium-pressure liquefied air E and the high-pressure nitrogen gas C, which is supplied from the top of the first rectification column 6 via line L4, are indirectly heat-exchanged in the first condenser 7. Specifically, the medium-pressure liquefied air E is vaporized to produce medium-pressure air F, and the high-pressure nitrogen gas C is liquefied to produce high-pressure liquefied nitrogen G. The high-pressure liquefied nitrogen G is introduced to the top of the first rectification column 6 via line L5 and becomes the reflux liquid of the first rectification column 6. 【0035】 [Product Nitrogen Gas Detachment Process] In the product nitrogen gas detachment process, a portion of the high-pressure nitrogen gas C is detached from the top of the first rectification column 6 via line L6, which is the product nitrogen gas detachment line, and after being heated to room temperature in the main heat exchanger 5, it is recovered as product nitrogen gas GN. 【0036】 [Second Separation Process] In the second separation process, medium-pressure air F is supplied to the bottom of the second rectification column 8 via line L7 and separated into medium-pressure nitrogen gases H and Q and medium-pressure liquefied air I by low-temperature distillation. In addition, a portion of the high-pressure liquefied air D that is led out from the bottom of the first rectification column 6 via line L2 is reduced in pressure by valve V4 and supplied to the bottom of the second rectification column 8 via line L15. Although not shown in the diagram, line L15 may also be connected to line L9. In this case, a portion of the high-pressure liquefied air D is reduced in pressure by valve V4 and merged with the medium-pressure liquefied air I from line L9 via line L15. 【0037】 [Second Condensation Process] In the second condensation process, medium-pressure liquefied air I, which is supplied from the bottom of the second rectification column 8 via line L9, is depressurized by valve V5 to obtain low-pressure liquefied air J. Then, the obtained low-pressure liquefied air J and medium-pressure nitrogen gas H, which is supplied from the top of the second rectification column 8 via line L11, are indirectly heat-exchanged in the second condenser 9. Specifically, the low-pressure liquefied air J is vaporized to produce low-pressure air K, and the medium-pressure nitrogen gas H is liquefied to produce medium-pressure liquefied nitrogen L. The medium-pressure liquefied nitrogen L is introduced to the top of the second rectification column 8 via line L12 and becomes the reflux liquid of the second rectification column 8. 【0038】Furthermore, the low-pressure air K discharged from the second condenser 9 via line L13 is introduced into the expansion turbine 10 via the main heat exchanger 5, where it undergoes adiabatic expansion to generate the cold necessary for the nitrogen production device 1 (adiabatic expansion process). It is then introduced into the main heat exchanger 5 via line L14, where it is heated to room temperature before being recovered as waste gas WG. The recovered waste gas WG is used for regenerating the air purifier 4, etc. 【0039】 A portion of the intermediate-pressure liquefied air descending through the second rectification column 8 is extracted via line L22, which is an intermediate-pressure liquefied air side cut line, and after being depressurized by valve V3, is supplied to the top of the oxygen column 11. This supplied intermediate-pressure liquefied air N becomes the raw material for the oxygen separation process (intermediate-pressure liquefied air side cut process). 【0040】 [Oxygen Separation Process] In the oxygen separation process, medium-pressure liquefied air N is separated into waste air R and liquefied oxygen M by low-temperature distillation in the oxygen tower 11. At this time, the liquefied oxygen located at the bottom of the oxygen tower 11 is heated by indirect heat exchange in the oxygen evaporator 12 to obtain rising gas (oxygen evaporation process). Medium-pressure nitrogen gas H, which has been discharged from the top of the second rectification tower 8, is introduced into the oxygen evaporator 12 as medium-pressure nitrogen gas Q via lines L11, L39, valve V9 and line L40, and this indirectly exchanges heat with the liquefied oxygen. The medium-pressure nitrogen gas Q liquefies to become medium-pressure liquefied nitrogen X. 【0041】 [Liquid Nitrogen Supply Process] In the liquid nitrogen supply process, the medium-pressure liquid nitrogen X liquefied in the oxygen evaporator 12 is discharged via line L18, pressurized via the liquid nitrogen pump 13, and then supplied to the top or upper part of the first rectification column 6. 【0042】 [Product Oxygen Derivation Process] In the product oxygen derivation process, the liquefied oxygen at the bottom of the oxygen tower 11 is led to line L20, which is the product oxygen derivation line, and pressurized by the liquefied oxygen pump 16 to produce pressurized liquefied oxygen Y. Then, the pressurized liquefied oxygen Y is vaporized in the main heat exchanger 5 and heated to room temperature. This vaporized gas is recovered as product high-pressure oxygen gas HPGO. Note that product oxygen does not necessarily have to be recovered as a gas; the liquefied oxygen led from the bottom of the oxygen tower 11 may be recovered as product oxygen as is. 【0043】 Further, the waste air R led out from the top of the oxygen tower 11 through the line L16 is merged with the line L14 at the position of the outlet of the expansion turbine 10, heated to room temperature in the main heat exchanger 5, and then recovered as waste gas WG. At this time, it is also possible to recover it as waste gas WG after heating to room temperature in the main heat exchanger 5 without merging with the line L14. 【0044】 [Product Liquid Nitrogen Derivation Process] In the product liquid nitrogen derivation process, the medium-pressure liquefied nitrogen L led out from the second condenser 9 through the line L12 is led out as product liquid nitrogen LN through the line L30 branched from the line L12, the valve V6, and the line L31. When the product liquid nitrogen LN is not supplied, the valve V6 is closed. 【0045】 <<Second Operating Mode>> Next, the second operating mode of the present embodiment will be described with reference to FIG. 2. The description of the parts similar to the first operating mode will be omitted. 【0046】 In the second operating mode, different from the first operating mode, the valves V3 and V9 are closed. Since the valve V3 is closed, the supply of the medium-pressure liquefied air N to the oxygen tower 11 is stopped. Also, since the valve V9 is closed, the supply of the medium-pressure nitrogen gas Q to the oxygen evaporator 12 is stopped. 【0047】 At this time, the amount of the medium-pressure liquefied air N among the medium-pressure liquefied air N and the medium-pressure liquefied air I led out from the second rectification column 8 becomes zero. As a result, the amount of the medium-pressure liquefied air I led out from the bottom of the second rectification column 8 increases, the amount of the low-pressure air K generated in the second condenser 9 increases, and the amount of cold generated in the expansion turbine 10 increases. Thereby, the amount of the extractable product liquid nitrogen LN increases as compared with the first operating mode. 【0048】 As described above, according to the nitrogen production method of the present embodiment, in the first operating mode, a large amount of product nitrogen gas can be generated while simultaneously generating a small amount of product oxygen gas or product liquefied oxygen. And when liquid nitrogen is temporarily required, by switching to the second operating mode, it is possible to co-produce or increase the amount of liquid nitrogen without increasing the consumption power while maintaining the amount of product nitrogen gas. 【0049】 [Second Embodiment] <Nitrogen Production Apparatus 1A> Next, a nitrogen production apparatus 1A of the second embodiment of the present invention will be described with reference to the drawings. The same parts as in the first embodiment will not be described. As shown in Figure 3, the nitrogen production apparatus 1A of this embodiment includes, in addition to the nitrogen production apparatus 1, a first expansion turbine 10A, an argon tower 14, an argon condenser 15, and a second expansion turbine 17. 【0050】 The expansion turbine 10A and the second expansion turbine 17 are devices that adiabatically expand the introduced gas. The argon tower 14 is a tower that separates argon gas S and argon-enriched liquefied oxygen T by low-temperature distillation of argon-enriched oxygen gas V that has been taken out from the middle section of the oxygen tower 11. The argon condenser 15 indirectly exchanges heat between argon gas S and a fluid obtained by reducing the pressure of medium-pressure liquefied air N. Specifically, the argon condenser 15 is a device that liquefies argon gas S to produce liquefied argon W and vaporizes the fluid obtained by reducing the pressure of medium-pressure liquefied air N to produce waste air U. 【0051】 Next, the piping connecting each of the above-mentioned devices will be described. Line L8 is a side-cut line that extracts a portion of the descending liquid from the first rectification column 6 midway, and is a piping line that introduces high-pressure liquefied air O into the middle section of the second rectification column 8. A valve V2 is provided in the middle of line L8. Line L21 is a piping line that supplies oxygen gas P, which has been drawn out from the middle section of the oxygen tower 11, to the outside of the system as product oxygen gas GO through the main heat exchanger 5. 【0052】 Line L23 is a pipeline that introduces argon-enriched oxygen gas V from the middle of the oxygen tower 11 to the bottom of the argon tower 14. Line L24 is a pipeline that introduces argon-enriched liquefied oxygen T from the bottom of the argon tower 14 to the middle of the oxygen tower 11. Line L25 is a pipeline that introduces argon gas S from the top of the argon tower 14 to the argon condenser 15. 【0053】In the first embodiment, line L27 was connected to the top of the first rectification column 6, but in this embodiment, line L27 branches into lines L41 and L42. Line L41 is a pipeline for introducing medium-pressure liquefied nitrogen X into the first rectification column 6. Line L42 is a pipeline for introducing medium-pressure liquefied nitrogen X into the second rectification column 8. 【0054】 Line L32 is a pipeline that branches off from line L13 and is connected to the second expansion turbine 17. A valve V10 is provided in the middle of line L32. Line L33 is also provided downstream of the expansion turbine 17, and line L33 merges with line L16. 【0055】 Line L34 branches off from line L22 and is connected to valve V8. Line L35 is provided downstream of valve V8 and is connected to argon condenser 15. Line L36 is provided downstream of argon condenser 15 and merges with line L16. 【0056】 In the first embodiment, line L37 merged with line L19, but in this embodiment, line L37 is connected to valve V7. Line L38 is provided downstream of valve V7, and line L38 merges with line L19. 【0057】 <Nitrogen Production Method> Next, a nitrogen production method using the nitrogen production apparatus 1A of this embodiment will be described. 【0058】 <<First Operating Mode>> Referring to Figure 3, the process by which various product gases and product liquefied gases are produced from air using the nitrogen production apparatus 1A will be explained. The same parts as in the first embodiment will be omitted from the explanation. 【0059】 In this embodiment, a portion of the high-pressure liquefied air descending through the first rectification column 6 is extracted by a high-pressure liquefied air side cut line L8. This extracted high-pressure liquefied air O is depressurized by a valve V2 and then supplied to the middle section of the second rectification column 8. This high-pressure liquefied air O is used as part of the raw material for the second separation process (high-pressure liquefied air side cut process). 【0060】[Liquid Nitrogen Supply Process] In the liquid nitrogen supply process of this embodiment, the medium-pressure liquid nitrogen X liquefied in the oxygen evaporator 12 is led out from line L18, pressurized by the liquid nitrogen pump 13, and then supplied to the top of the first rectification column 6 or the top of the second rectification column 8 via line L41 or L42. In addition, the medium-pressure liquid nitrogen led out from the top of the second rectification column 8 via line L37 is introduced into line L19 via valve V7 and line L38. 【0061】 [Product Oxygen Derivation Process] In the product oxygen derivation process of this embodiment, similar to the first embodiment, liquefied oxygen M derived from the bottom of the oxygen tower 11 via line L20 is pressurized by the liquefied oxygen pump 16 to produce pressurized liquefied oxygen Y. Then, the pressurized liquefied oxygen Y is vaporized in the main heat exchanger 5 and heated to room temperature before being recovered as product high-pressure oxygen gas HPGO. In addition, in this embodiment, oxygen gas P, which is vaporized in the oxygen evaporator 12 and rising through the oxygen tower 11, is derived via line L21 and heated to room temperature in the main heat exchanger 5 before being recovered as product oxygen gas GO. 【0062】 [Argon Separation Process] In the argon separation process, argon-enriched oxygen gas V is extracted from the middle section of the oxygen column 11 via line L23 and supplied to the bottom of the argon column 14. Using this as raw material, it is separated into argon gas S and argon-enriched liquefied oxygen T by low-temperature distillation. The argon-enriched liquefied oxygen T is extracted from the bottom of the argon column 14 via line L24 and supplied to the middle section of the oxygen column 11. 【0063】 [Argon Condensation Process] In the argon condensation process, medium-pressure liquefied air N, which is discharged from the middle section of the second rectification column 8 via line L22, is introduced into the argon condenser 15 via line L34, valve V8, and line L35. Argon gas S, which is discharged from the top of the argon column 14 via line L25, is also supplied to the argon condenser 15. Then, the fluid obtained by reducing the pressure of the medium-pressure liquefied air N and the argon gas S are indirectly heat exchanged in the argon condenser 15 to liquefy the argon gas S and produce liquefied argon W, and the fluid obtained by reducing the pressure of the medium-pressure liquefied air N is vaporized to produce waste air U. 【0064】Furthermore, liquefied argon W is introduced to the top of the argon column 14 via line L28 to become the reflux liquid of the argon column 14. In addition, waste air U vaporized in the argon condenser 15 is introduced from line L36 to L16. 【0065】 [Product Argon Derivation Process] A portion of the liquefied argon W is branched from line L28 to line L29, which is the product argon derivation line, and recovered as product liquefied argon LAR. 【0066】 In the first operating mode, valve V6 located between lines L30 and L31 is closed, valve V7 located between lines L37 and L38 is closed, and valve V10 located between lines L32 and L33 is closed. 【0067】 <<Second Operating Mode>> Next, the second operating mode of this embodiment will be described with reference to Figure 4. The same parts as the first operating mode will be omitted from the explanation. 【0068】 In the second operating mode, unlike the first operating mode, valves V3, V8, and V9 are closed, and valves V6, V7, and V10 are opened. Specifically, in the second operating mode, valve V3 is closed, so the supply of medium-pressure liquefied air N to the oxygen tower 11 is stopped. Also, valve V8 is closed, so the supply of medium-pressure liquefied air N to the argon condenser 15 is stopped. Furthermore, valve V9 is closed, so the supply of medium-pressure nitrogen gas Q to the oxygen evaporator 12 is stopped. 【0069】 In the second operating mode, no gas is introduced into the oxygen evaporator 12, so liquid nitrogen is not discharged from line L18, and liquid nitrogen is not discharged from line L18 to line L19. Also, since no raw material is supplied to the oxygen tower 11, oxygen separation does not occur in the oxygen tower 11, and product oxygen gas GO and high-pressure product oxygen gas HPGO are not supplied. 【0070】Furthermore, in the second operating mode, since valve V10 is open, low-pressure air K is supplied to the second expansion turbine 17. In the second operating mode, the amount of low-pressure air K produced in the second condenser 9 increases, so in addition to the first expansion turbine 10A, valve V10 can be opened to generate cold in the second expansion turbine 17 as well. Note that the inlet temperature of the second expansion turbine 17 is lower than the inlet temperature of the first expansion turbine 10A. 【0071】 In addition, in the second operating mode, valve V6 is opened to recover a portion of the medium-pressure liquid nitrogen L liquefied in the second condenser 9 as product liquid nitrogen. Even if the amount of low-pressure air adiabatically expanded in the expansion turbine is the same, by dividing the expansion turbine into two units and adiabatically expanding the low-pressure air at different temperatures, the fluid temperature inside the main heat exchanger 5 can be made more uniform, and the amount of cold generated in the expansion turbine can be increased, allowing for the collection of more product liquid nitrogen. As a result, the amount of product liquid nitrogen increases compared to the first operating mode. 【0072】 As described above, according to the nitrogen production method of this embodiment, in the first operating mode, a large amount of product nitrogen gas can be generated while simultaneously generating a small amount of product oxygen gas or product liquefied oxygen. Furthermore, when liquefied nitrogen is temporarily required, by switching to the second operating mode, it is possible to maintain the amount of product nitrogen gas while simultaneously producing or increasing the amount of liquefied nitrogen without increasing power consumption. 【0073】 [Third Embodiment] <Nitrogen Production Apparatus 1B> Next, a nitrogen production apparatus 1B of the third embodiment of the present invention will be described with reference to the drawings. The same parts as in the first embodiment will not be described. As shown in Figure 5, the nitrogen production apparatus 1B of this embodiment is equipped with an expansion turbine 10B instead of an expansion turbine 10. The expansion turbine 10B is supplied with a portion of the medium-pressure air F via line L43 and main heat exchanger 5, and generates the cold necessary for the apparatus. 【0074】Line L44 is a pipeline that introduces high-pressure liquefied air O, which is drawn out from the middle of the first rectification column 6, to the upper part of the oxygen column 11. Line L44 is a side-cut line. Line L44 is also equipped with a valve V11 that functions as an on-off valve. Line L45 is a pipeline that branches off from line L6 and introduces a portion of high-pressure nitrogen gas C to the oxygen evaporator 12. Line L45 is also equipped with a valve V12 that functions as an on-off valve. 【0075】 <Nitrogen Production Method> Next, a nitrogen production method using the nitrogen production apparatus 1B of this embodiment will be described. The same parts as in the first embodiment will be omitted from the explanation. 【0076】 <<First Operating Mode>> Referring to Figure 5, the process by which various product gases and product liquefied gases are produced from air AIR using the nitrogen production apparatus 1B will be explained. In the first operating mode of this embodiment, a portion of the high-pressure liquefied air descending through the first rectification column 6 is extracted by the high-pressure liquefied air side cut line L44. This extracted high-pressure liquefied air O is depressurized by valve V11 and then supplied to the top of the oxygen column 11 (high-pressure liquefied air side cut process). In addition, a portion of the high-pressure nitrogen gas C is branched to line L45 and supplied to the oxygen evaporator 12 via valve V12. In the first operating mode, valve V6, which is located between lines L30 and L31, is closed. 【0077】 <<Second Operating Mode>> Next, the second operating mode of this embodiment will be described with reference to Figure 6. In the second operating mode, unlike the first operating mode, valves V11 and V12 are closed and valve V6 is opened. That is, in the second operating mode, valve V11 is closed, so the supply of high-pressure liquefied air O to the oxygen tower 11 is stopped. Also, since valve V12 is closed, the supply of high-pressure nitrogen gas C to the oxygen evaporator 12 is stopped. 【0078】In the second operating mode, no raw material is supplied to the oxygen tower 11, so oxygen separation does not occur in the oxygen tower 11, and product oxygen gas GO and high-pressure product oxygen gas HPGO are not supplied. In the second operating mode, the amount of high-pressure liquefied air O becomes zero, which increases the amount of high-pressure liquefied air D, and thus increases the amount of medium-pressure air F produced in the first condenser 7. As a result, the amount of medium-pressure air AA branching to line L43 can be increased, and the amount of cold generated in the expansion turbine 10B increases. Consequently, the amount of extractable product liquefied nitrogen LN increases compared to the first operating mode. 【0079】 As described above, the nitrogen production method of this embodiment allows for the generation of a large amount of product nitrogen gas in the first operating mode while simultaneously generating a small amount of product oxygen gas or product liquefied oxygen. Furthermore, when liquefied nitrogen is temporarily required, the second operating mode can be switched to maintain the amount of product nitrogen gas while simultaneously producing or increasing the amount of liquefied nitrogen without increasing power consumption. 【0080】 Although the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments. It can be implemented in various forms without departing from the spirit of the invention. For example, the fluid supplied to the top of the oxygen tower 11, that is, the raw material used for distillation in the oxygen tower 11, can be high-pressure liquefied air supplied from the first rectification tower 6 instead of medium-pressure liquefied air N supplied from the second rectification tower 8. 【0081】 Furthermore, instead of returning the entire amount of high-pressure liquefied nitrogen G extracted from the first condenser 7 to the first rectification column, a portion may be extracted as a product. Also, instead of supplying the medium-pressure liquefied nitrogen Z extracted from the top of the second rectification column 8 to the first or second rectification column 8 after pressurizing it with the liquefied nitrogen pump 13, it may be heated to room temperature in the main heat exchanger and recovered as product medium-pressure nitrogen gas GN. Additionally, argon gas may be extracted as a product from the top of the argon column 14. 【0082】The present invention will be described in detail below using examples and comparative examples. <Examples> A simulation of the nitrogen production apparatus 1A of the present invention shown in Figures 3 and 4 was performed using a simulator used in the design of the actual machine. In performing the simulation, in the first operating mode, the amount of raw material air was set to 100, HPGO (nitrogen concentration 10 ppb or less, argon concentration 10 ppb or less, pressure 11.5 bar A) was recovered at a flow rate of 0.5, LAR (oxygen concentration 1.5% or less, nitrogen concentration 0.5% or less) was recovered at a flow rate of 0.2, while recovering the maximum amount of GN (oxygen concentration 10 ppb or less, pressure 11.5 bar A). In the second operating mode, the amount of raw material air was set to 100, and instead of recovering HPGO and LAR, the same amount of GN and LN as in the first operating mode were recovered at the maximum amount. 【0083】 【0084】 These simulation results confirmed that in the first operating mode, GN was recovered at a flow rate of 52 from a raw material air volume of 100, HPGO at a flow rate of 0.5, and LAR at a flow rate of 0.2. By switching to the second operating mode, GN was recovered at a flow rate of 52 and LN at a flow rate of 2.1 while maintaining a raw material air volume of 100. 【0085】 As is clear from the above results, the nitrogen production method and nitrogen production apparatus of the present invention can produce a large amount of product nitrogen gas during normal operation while simultaneously producing a small amount of product oxygen gas or product liquefied oxygen. When liquefied nitrogen is temporarily needed, the operating mode can be switched to maintain the amount of product nitrogen gas while simultaneously producing or increasing the amount of liquefied nitrogen without increasing power consumption. 【0086】 1, 1A...Nitrogen production equipment, 2...Air compressor, 3...Air precooler, 4...Air purifier, 5...Main heat exchanger, 6...First rectification column, 7...First condenser, 8...Second rectification column, 9...Second condenser, 10, 10A, 10B...Expansion turbine, 11...Oxygen tower, 12...Oxygen evaporator, 13...Liquid nitrogen pump, 14...Argon tower, 15...Argon condenser, 16...Liquid oxygen pump, 17...Second expansion turbine

Claims

1. A first separation step in which low-temperature raw material air obtained by cooling raw material air is distilled to separate it into high-pressure nitrogen gas and high-pressure liquefied air; a first condensation step in which the high-pressure nitrogen gas and medium-pressure liquefied air obtained by depressurizing the high-pressure liquefied air are indirectly heat-exchanged to liquefy the high-pressure nitrogen gas to produce high-pressure liquefied nitrogen and vaporize the medium-pressure liquefied air to produce medium-pressure air; a second separation step in which the medium-pressure air is distilled to separate it into medium-pressure nitrogen gas and medium-pressure liquefied air; a second condensation step in which the medium-pressure nitrogen gas and low-pressure liquefied air obtained by depressurizing the medium-pressure liquefied air are indirectly heat-exchanged to liquefy the medium-pressure nitrogen gas to produce medium-pressure liquefied nitrogen and vaporize the low-pressure liquefied air to produce low-pressure air; an oxygen separation step in which a portion of the high-pressure liquefied air produced in the first rectification column, or a portion of the medium-pressure liquefied air produced in the second separation step, is distilled to separate it into waste air and liquefied oxygen; A nitrogen production method comprising: an oxygen evaporation step of vaporizing the liquefied oxygen to generate rising gas; a product nitrogen output step of outputting a portion of the high-pressure nitrogen gas as a product; a product liquefied nitrogen output step of outputting either or both of the portion of the high-pressure liquefied nitrogen and / or the portion of the medium-pressure liquefied nitrogen as product liquefied nitrogen; and a product oxygen output step of outputting a portion of the liquefied oxygen or the oxygen gas obtained by vaporizing the liquefied oxygen as a product, wherein the method has at least a first operating mode and a second operating mode in which the amount of product liquefied nitrogen outputted in the product liquefied nitrogen output step is greater than that in the first operating mode, wherein in the first operating mode, at least the oxygen separation step, the oxygen evaporation step, and the product oxygen output step are performed, and in the second operating mode, the oxygen separation step, the oxygen evaporation step, and the product oxygen output step are not performed.

2. The nitrogen production method according to claim 1, wherein the oxygen separation step includes separating not only the waste air and the liquefied oxygen but also 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, an argon condensation step of liquefying the argon gas to produce liquefied argon, and a product argon discharge step of discharging a portion of the argon gas or the liquefied argon as a product, the first operating mode further includes the argon separation step, the argon condensation step and the product argon discharge step, and the second operating mode further does not include the argon separation step, the argon condensation step and the product argon discharge step.

3. A method for producing nitrogen according to claim 1 or 2, characterized in that it includes a first adiabatic expansion step in which a portion of the low-pressure air is heated and then adiabatically expanded to generate cold in the first operating mode, and a second adiabatic expansion step in which, in addition to the first adiabatic expansion step, another portion of the low-pressure air is heated and then adiabatically expanded to generate cold in the second operating mode.

4. The nitrogen production method according to claim 3, characterized in that the temperatures of the low-pressure air to be adiabatically expanded in the first adiabatic expansion step and the second adiabatic expansion step are different.

5. A method for producing nitrogen according to claim 1 or 2, characterized in that it includes a first adiabatic expansion step in which a portion of the medium-pressure air is heated and then adiabatically expanded to generate the cold necessary for the apparatus in the first operating mode, and a second adiabatic expansion step in which, in addition to the first adiabatic expansion step, another portion of the medium-pressure air is heated and then adiabatically expanded to generate the cold in the second operating mode.

6. The nitrogen production method according to claim 5, characterized in that the temperatures of the medium-pressure air to be adiabatically expanded in the first adiabatic expansion step and the second adiabatic expansion step are different.

7. A first rectification column that distills low-temperature raw air obtained by cooling raw air to separate it into high-pressure nitrogen gas and high-pressure liquefied air; a first condenser that indirectly heat exchanges the high-pressure nitrogen gas with medium-pressure liquefied air obtained by reducing the pressure of the high-pressure liquefied air to liquefy the high-pressure nitrogen gas and vaporize the medium-pressure liquefied air to produce medium-pressure air; a second rectification column that distills the medium-pressure air to separate it into medium-pressure nitrogen gas and medium-pressure liquefied air; a second condenser that indirectly heat exchanges the medium-pressure nitrogen gas with low-pressure liquefied air obtained by reducing the pressure of the medium-pressure liquefied air to liquefy the medium-pressure nitrogen gas and vaporize the low-pressure liquefied air to produce low-pressure air; and an oxygen column that distills a portion of the high-pressure liquefied air produced in the first rectification column, or a portion of the medium-pressure liquefied air produced in the second separation step, to separate it into waste air and liquefied oxygen. A nitrogen production apparatus comprising: an oxygen evaporator that vaporizes the liquefied oxygen in the oxygen tower to generate rising gas; a product nitrogen outlet line that discharges a portion of the high-pressure nitrogen gas as a product; a product liquefied nitrogen outlet line that discharges either or both of the portion of the high-pressure liquefied nitrogen and / or the portion of the medium-pressure liquefied nitrogen as product liquefied nitrogen; a product oxygen outlet line that discharges a portion of the oxygen gas or the liquefied oxygen as a product; a valve provided in a line that introduces a portion of the high-pressure liquefied air or a portion of the medium-pressure liquefied air into the oxygen tower; and a valve provided in a line that introduces a fluid to the oxygen evaporator that exchanges heat with the liquefied oxygen in the oxygen tower.

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