Air separation unit

Abstract

To provide an air separation unit which generates cold by expanding oxygen gas separated from air, where a heat balance can be maintained without a drop in rare gas and nitrogen recovery rates, by using a nitrogen turbine to supply cold needed for the production of product oxygen or for the production of a liquid product such as liquid nitrogen or liquid argon.SOLUTION: An air separation unit includes: a main heat exchanger 1, a medium-pressure rectification column 2, a low-pressure rectification column 4, a crude argon column 5, a nitrogen condenser 3, a crude argon condenser 6, an oxygen turbine 9, a nitrogen compressor 10, and a nitrogen turbine 8. The nitrogen turbine 8 expands nitrogen gas supplied from the nitrogen compressor 10. The air separation unit includes an inlet temperature of the oxygen turbine 9 that is lower than an inlet temperature of the nitrogen turbine 8.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an air separation unit, for example a cryogenic air separation unit in which nitrogen and rare gases such as argon can be separated. [Background technology]

[0002] When air components are separated into nitrogen, argon, oxygen, etc. by cryogenic air separation, a double rectification system equipped with multiple rectification columns, such as a medium-pressure column, a low-pressure column, and a crude argon column, is used. In particular, when increasing the recovery rate of nitrogen and argon while minimizing the power required for gas compression and optimizing the supply, the pressure of the low-pressure nitrogen gas extracted from the low-pressure rectification column is increased, thereby increasing the inlet pressure of the nitrogen compressor that compresses the low-pressure nitrogen gas and reducing the load on the nitrogen compressor. At this time, the pressure of the low-pressure rectification column is increased, so that the oxygen gas extracted from its bottom can be expanded in an expansion turbine to generate the refrigeration necessary to maintain the heat balance of the air separation unit (e.g., Patent Documents 1 and 2).

[0003] The product gas produced from an air separation unit is required to be supplied in a liquid state for storage and transportation. Known methods for generating refrigeration for gas liquefaction include expanding a portion of the feed air (e.g., Patent Document 3) and recycling and expanding nitrogen gas discharged from a medium-pressure column (e.g., Patent Document 4). However, these methods use a portion of the medium-pressure air introduced into the medium-pressure rectification column or the medium-pressure nitrogen accumulated at the top of the medium-pressure rectification column to evaporate the liquid oxygen accumulated at the bottom of the low-pressure column, which reduces the vapor flow within the rectification column and reduces the recovery of nitrogen or argon. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent Publication No. 2019293347 [Patent Document 2] U.S. Patent Publication No. 2023358468 [Patent Document 3] International Patent Publication No. 2021 / 230911 [Patent Document 4] Japanese Patent Application Publication No. 187086 / 1986 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides an air separation unit that generates refrigeration by expanding oxygen gas separated from air, and that can maintain heat balance by using a nitrogen turbine to supply the refrigeration required for the production of oxygen products and liquid products such as liquefied nitrogen and liquefied argon without reducing the recovery rate of rare gases or nitrogen. [Means for solving the problem]

[0006] The air separation unit of the present disclosure comprises a main heat exchanger (1), a medium-pressure rectification column (2), a low-pressure rectification column (4), a crude argon column (5), a nitrogen condenser (3), a crude argon condenser (6), an oxygen turbine (9), a nitrogen compressor (10), and a nitrogen turbine (8). The nitrogen turbine (8) expands nitrogen gas supplied from the nitrogen compressor (10). The inlet temperature of the oxygen turbine (9) is lower than the inlet temperature of the nitrogen turbine (8). For example, the temperature of the gas discharged from the first intermediate section (1a) of the main heat exchanger (1) and sent to the oxygen turbine (9) is lower than the temperature of the gas discharged from the second intermediate section (1b) of the main heat exchanger (1) and sent to the nitrogen turbine (8). The outlet nozzle position (1a) of the piping connecting the main heat exchanger (1) to the oxygen turbine (9) may be located on the lower temperature side than the outlet nozzle position (1b) of the piping connecting to the nitrogen turbine (8). In addition, a bypass pipe (L431a) may be provided from the nitrogen gas pipe at the warm end of the main heat exchanger (1) to the nitrogen turbine inlet pipe so that the inlet temperature of the nitrogen turbine (8) is higher than the inlet temperature of the oxygen turbine (9). The air separation unit may include a first nitrogen booster (14), which may be driven by an expansion turbine (81). The air separation unit may include a second nitrogen booster (17), which may be driven by the oxygen turbine (9). The air separation unit may be configured such that a portion of the compressed nitrogen gas supplied from the nitrogen compressor (10) is cooled in the main heat exchanger (1) and supplied to the medium pressure rectification column (2). The air separation unit may also include a subcooler (7) for cooling the liquid (e.g., oxygen-enriched liquid) discharged from the medium-pressure rectifier (2) with gas discharged from the low-pressure rectifier (4) or the crude argon condenser (6) (see Figure 6). In the air separation plant, oxygen gas discharged from the gas phase of the refrigerant reservoir 32 of the low-pressure rectification column 4 or the nitrogen condenser 3 may be mixed with nitrogen gas discharged from the low-pressure rectification column 4 or oxygen-enriched gas discharged from the crude argon condenser 6, and then expanded in the oxygen turbine 9. The main heat exchanger 1 may be divided into multiple sections for optimization of the structure according to the design temperature, pressure, and flow rate, or for improving transportability.

[0007] The above-described configuration provides the following advantages: The oxygen turbine (9) constantly generates the refrigeration required to produce the product gas, but the expansion ratio is limited to a maximum of about 2 to 5 times, since it is the ratio between the pressure of the low-pressure rectification column (4) and a low pressure close to atmospheric pressure sufficient to discharge the expanded gas into the atmosphere via the main heat exchanger (1). Nevertheless, the low-temperature gas required for the air separation unit must be supplied, so the inlet temperature of the oxygen turbine (9) is low. On the other hand, the low pressure nitrogen gas (LP GAN) discharged from the main heat exchanger (1) is supplied via a nitrogen compressor (10), the outlet pressure of which can be increased as desired, allowing for a large expansion ratio. In other words, this configuration of the nitrogen compressor (10) and nitrogen turbine (8) is appropriate for supplying the large amount of refrigeration required for liquefying the product gas. However, because the liquefaction of product gas is for storage or transportation, continuous operation is not necessarily required. Therefore, in the air separation unit disclosed herein, the inlet temperature of the oxygen turbine (9) is configured to be lower than that of the nitrogen turbine (9), so that the oxygen turbine (9) serves as a baseload refrigeration source and the nitrogen turbine (8) serves as a variable refrigeration source. This allows the oxygen turbine (9) to supply the refrigeration required for steady gas production, while the nitrogen turbine (8) is operated when additional refrigeration is required, thereby flexibly meeting the demand for product gas and liquid. Furthermore, since the oxygen turbine (9) supplies a lower temperature, the heat balance on the low-temperature side of the main heat exchanger (1) is maintained, allowing the inlet temperature of the nitrogen turbine (9) to be increased, resulting in more efficient supply of refrigeration.

[0008] The air separation units (A1, A2, A3, A4, A5, A6) of the present disclosure are a main heat exchanger (1) into which feed air is introduced from a hot end and discharged from a cold end; a medium-pressure rectification column (2) into whose bottom (21) feed air discharged from the cold end of the main heat exchanger (1) is introduced; a nitrogen condenser (3) into which a vapor stream is introduced from an upper portion (23) of the medium pressure rectification column (2), which is condensed and discharged as reflux; a low-pressure rectification column (4) into whose rectification section (42) an oxygen-enriched liquid withdrawn from the bottom (21) of the medium-pressure rectification column (2) is introduced and / or into whose top (43) a vapor stream withdrawn from the upper section (23) of the medium-pressure rectification column (2) is introduced; an oxygen turbine (9) that performs heat exchange in the main heat exchanger (1) on the oxygen-enriched gas discharged from the gas phase of the refrigerant reservoir (32) of the nitrogen condenser (3), and then expands and cools the gas; a nitrogen turbine (8) in which nitrogen gas discharged from the top (43) of the low-pressure rectification column (4) is heat-exchanged in at least the main heat exchanger (1), compressed to a predetermined pressure in a nitrogen compressor (10), cooled in a cooling device (11), and cooled again in the main heat exchanger (1) before being expanded; The device may also include:

[0009] The air separation units (A1, A2, A3, A4, A5) a crude argon column (5) into whose bottom (51) an oxygen-containing fluid withdrawn from the rectification section (42) of the lower pressure rectification column (4) is introduced; a crude argon condenser (6) into which a vapor stream is introduced from the top of the crude argon column (5), and into which the vapor stream is condensed and discharged as reflux liquid; a subcooler (7) into which an oxygen-enriched liquid withdrawn from the bottom (21) of the medium-pressure rectification column (2) is introduced at its cold end and discharged at its warm end, and / or into which a vapor stream withdrawn from the upper part (23) of the medium-pressure rectification column (2) is introduced at its cold end and discharged at its warm end, and / or into which nitrogen gas withdrawn from the top (43) of the low-pressure rectification column (4) is introduced at its warm end and discharged at its cold end; The device may also include:

[0010] The air separation units (A1, A2, A3, A4, A5, A6) a feed air line (L1) for introducing feed air into the medium-pressure rectification column (2) via the main heat exchanger (1); an oxygen-enriched liquid piping line (L21) for introducing the oxygen-enriched liquid discharged from the bottom (21) of the medium-pressure rectification column (2) into the rectification section (42) of the low-pressure rectification column (4) via the subcooler (7); an oxygen-enriched liquid branch pipe line (L211) branching off from the oxygen-enriched liquid pipe line (L21) at a position downstream of the subcooler (7) and for introducing the oxygen-enriched liquid into a refrigerant reservoir (61) of the crude argon condenser (6); a liquefied nitrogen piping line (L23) for introducing liquefied nitrogen discharged from the upper portion (23) of the medium-pressure rectification column (2) into the top portion (43) of the low-pressure rectification column (4) via the subcooler (7); a liquefied nitrogen branch pipe line (L231) branching off from the liquefied nitrogen pipe line (L23) downstream of the subcooler (7) and discharging a portion of the liquefied nitrogen; a liquefied oxygen extraction line (L31) for extracting the refrigerant (oxygen-enriched liquid) from the refrigerant reservoir (32) of the nitrogen condenser (3) as liquefied oxygen (LOX); an oxygen extraction line (L32) for extracting the refrigerant from the upper gas phase of the refrigerant reservoir (32) of the nitrogen condenser (3), introducing it into the middle of the main heat exchanger (1), warming it, extracting it, expanding it in the oxygen turbine (9), introducing it again into the cold end of the main heat exchanger (1), extracting it from the warm end, and extracting it as oxygen gas; an oxygen-containing fluid piping line (L421) for introducing an oxygen-containing fluid discharged from the rectification section (42) of the low-pressure rectification column (4) into the bottom (51) of the crude argon column (5); a nitrogen gas piping line (L43) leading from the top (43) of the low-pressure rectification column (4) and passing through the subcooler (7) and the main heat exchanger (1) to extract nitrogen gas (GAN); a nitrogen gas branch pipe line (L431) that branches off from the nitrogen gas pipe line (L43) downstream of the heat exchanger (1), is introduced again into the warm end of the main heat exchanger (1), is discharged from an intermediate portion, is expanded in the nitrogen turbine (8), and is then merged into the nitrogen gas pipe line (L43) or is taken out as nitrogen gas via the main heat exchanger (1) again; a crude argon column bottom fluid piping line (L51) for introducing a bottom fluid discharged from the bottom (51) of the crude argon column (5) to a position below the outlet position of the oxygen-containing fluid piping line (L421) of the rectification section (42) of the low-pressure rectification column (4); an argon withdrawal line (L53) for withdrawing the vapor stream or reflux liquid from the upper portion of the crude argon column (5); a crude argon condenser piping line (L62) for introducing the refrigerant from the upper gas phase of the refrigerant reservoir (62) of the crude argon condenser (6) into the rectification section (42) of the low-pressure rectification column (4) above the oxygen-enriched liquid piping line (L21); The device may also include:

[0011] A compressor (10) for compressing nitrogen gas and a cooling device (11) for cooling the compressed nitrogen gas may be provided in the nitrogen gas piping line (L43) between the downstream of the warm end of the main heat exchanger (1) of the nitrogen gas piping line (L43) and the nitrogen gas branch piping line (L431).

[0012] The fluid introduced into the crude argon column (5) from the rectifying section (42) of the lower pressure rectifier (4) is referred to as the oxygen-containing fluid, and the liquid withdrawn from a location below the feed air introduction stage (e.g., the bottom of the nitrogen rectifier) ​​is referred to as the oxygen-enriched liquid. The oxygen-containing fluid may be a liquid or a gas-liquid mixture.

[0013] The air separation unit (A2) a bypass line (L431a) that branches off from the nitrogen gas branch piping line (L431), bypasses the nitrogen gas so as not to be introduced into the main heat exchanger (1), and merges with the nitrogen gas branch piping line (L431); an adjusting valve (V1) for adjusting the amount of nitrogen gas flowing through the bypass line (L431a); The device may also include: The air separation unit (A2) The nitrogen turbine (8) may be provided with a temperature measuring unit (12) for measuring the temperature of the nitrogen gas introduced into the nitrogen turbine (8). The temperature measurement unit (12) may be provided in any of the bypass line (L431a), the nitrogen gas branch piping line (L431), or a line downstream of the junction of the bypass line (L431a) and the nitrogen gas branch piping line (L431). The adjusting valve (V1) may adjust the amount of nitrogen gas circulating through the bypass line (L431a) based on the temperature measured by the temperature measuring unit (12) (for example, when the temperature is maintained within a predetermined temperature range, above or below a threshold value).

[0014] The air separation units (A3, A4, A5) a nitrogen booster (14) provided in the nitrogen gas branch piping line (L431) for increasing the pressure of the nitrogen gas to a predetermined level; a second cooling device (15) for cooling the nitrogen gas pressurized by the nitrogen booster (14); an expansion turbine (81) for expanding the nitrogen gas cooled in the second cooling device (15), introduced back into the main heat exchanger (1), and discharged from the middle; The device may also include:

[0015] According to the above configuration, refrigeration is generated using a nitrogen booster turbine configuration. That is, a portion of the low-pressure nitrogen gas is compressed by the nitrogen compressor (10), and then further pressurized by the booster (14) driven by the expansion turbine (81), and then expanded. This pressure increase process increases the pressure difference in the expansion turbine (81), thereby increasing the amount of refrigeration generated per unit flow rate, and as a result, the molar flow rate of nitrogen required for refrigeration generation can be reduced.

[0016] The air separation units (A4, A5) a recycle nitrogen line (L431b) branching off from the nitrogen gas branch piping line (L431) inside the main heat exchanger (1), leading out from the cold end of the main heat exchanger (1), and for introducing nitrogen gas into the rectification section (22) or the upper part (23) thereof of the medium-pressure rectification column (2); a valve (V2) provided in the recycle nitrogen line (L431b); The device may also include:

[0017] According to the above-described configuration, a portion of the nitrogen gas supplied from the nitrogen compressor (10) is cooled in the main heat exchanger (1) and supplied to the medium-pressure rectification column (2). When producing liquid in an air separation unit, a portion of the feed air is liquefied and introduced into the medium-pressure rectification column (2) or the low-pressure rectification column (4). However, the vapor flow in the rectification column is reduced by the amount of liquefaction, which is detrimental to the product yield. To solve this problem, nitrogen gas can be reintroduced into the medium-pressure rectification column (2), thereby increasing the vapor flow and maintaining the product gas yield.

[0018] The air separation unit (A5) a second nitrogen booster (17) provided in the nitrogen gas branch piping line (L431) upstream of the first nitrogen booster (14) for boosting the nitrogen gas to a predetermined pressure; a second cooling device (18) provided in the nitrogen gas branch piping line (L431) upstream of the first nitrogen booster (14), for cooling the nitrogen gas pressurized by the second nitrogen booster (17); The device may also include: The second nitrogen booster (17) may be driven by the oxygen turbine (9).

[0019] According to the above configuration, the second nitrogen booster (17) is driven by the oxygen turbine (9). That is, a portion of the low-pressure nitrogen gas is compressed by the nitrogen compressor (10), and then further pressurized by the second nitrogen booster (17) driven by the oxygen turbine (9), and then expanded. This pressure increase process increases the pressure difference in the expansion turbine, thereby increasing the amount of refrigeration generated per unit flow rate, and as a result, the molar flow rate of nitrogen required to generate refrigeration can be reduced.

[0020] The subcooler (7) cools the liquid discharged from the medium-pressure rectification column (2) by gas discharged from the low-pressure rectification column (4) or the crude argon condenser (6). This reduces the amount of liquid that evaporates due to reduced pressure when introduced into the low-pressure rectification column (4), and increases the amount of liquid that contributes to the rectification as reflux, thereby improving the rectification efficiency.

[0021] The oxygen gas extracted from the gas phase of the refrigerant reservoir 32 of the nitrogen condenser 3 can be mixed with nitrogen gas and oxygen-enriched liquid before being introduced into the oxygen turbine 9. This increases the gas flow expanding in the oxygen turbine 9, thereby increasing the refrigeration produced and reducing safety risks such as oxygen combustion in the oxygen turbine 9. The liquefied oxygen (LOX) extracted from the refrigerant reservoir 32 can be subcooled in a subcooler 7 (see FIG. 6).

[0022] The air separation units (A1, A2, A3, A4, A5, A6) Various measuring instruments such as flow rate measuring instruments, pressure measuring instruments, temperature measuring instruments, and liquid level measuring instruments, Various valves such as control valves and gate valves, Piping that connects each element; may have [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram showing an air separation unit of a first embodiment. [Figure 2] FIG. 1 is a diagram showing an air separation unit according to a second embodiment. [Figure 3] FIG. 10 is a diagram showing an air separation unit according to a third embodiment. [Figure 4] FIG. 10 is a diagram showing an air separation unit according to a fourth embodiment. [Figure 5] FIG. 10 is a diagram showing an air separation apparatus according to a fifth embodiment. [Figure 6] FIG. 10 is a diagram showing an air separation unit according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Several embodiments of the present disclosure will be described below. The embodiments described below are examples of the present disclosure. The present disclosure is not limited to the following embodiments and includes various modified forms implemented within the scope of the present disclosure. Note that not all of the configurations described below are necessarily essential configurations of the present disclosure. Upstream and downstream are based on the flow direction of the fluid (liquid, gas).

[0025] (Embodiment 1) The first air separation unit A1 of the first embodiment will be described with reference to FIG. The first air separation unit A1 comprises a main heat exchanger (1), a medium-pressure rectification column (2), a low-pressure rectification column (4), a crude argon column (5), a nitrogen condenser (3), a crude argon condenser (6), an oxygen turbine (9), a nitrogen compressor (10), and a nitrogen turbine (8). The main heat exchanger 1 cools the feed air introduced from the hot end and discharges it from the cold end. The cooled feed air is introduced into the medium-pressure rectification column 2 via the feed air piping line L1. The medium-pressure rectification column 2 comprises a bottom section 21, a rectification section 22, and a top section 23. The feed air piping line L1 is connected to the bottom section 21. The oxygen-enriched liquid stored in the bottom portion 21 is sent via the oxygen-enriched liquid piping line L21 to the subcooler 7 for heat exchange, and then sent to the rectification section 42 of the low-pressure rectification column 4. After heat exchange in the subcooler 7, a portion of the oxygen-enriched liquid is introduced into the refrigerant reservoir 61 of the crude argon condenser 6 via the oxygen-enriched liquid branch piping line L211. A portion of the liquefied nitrogen at the top 23 is sent via liquefied nitrogen piping line L23 to the top 43 of the low-pressure rectification column 4 after being heat exchanged in the subcooler 7. The liquefied nitrogen branch piping line L231 is a line that branches off from the liquefied nitrogen piping line L23 downstream of the subcooler 7 and extracts liquefied nitrogen.

[0026] The nitrogen condenser 3 is provided above the top 23 of the medium-pressure rectification section 2. A portion of the nitrogen gas (vapor flow) discharged from the top 23 of the medium-pressure rectification column 2 is introduced into the nitrogen condenser 3 via a reflux piping line, and is cooled (condensed) and liquefied by heat exchange with the oxygen-enriched liquid serving as a refrigerant. The liquefied nitrogen returns to the top 23 of the medium-pressure rectification column 2 as reflux liquid.

[0027] The liquefied oxygen extraction line L31 is a line for extracting the refrigerant (oxygen-enriched liquid) from the refrigerant reservoir 32 of the nitrogen condenser 3 as liquefied oxygen (LOX).

[0028] The low-pressure rectification column 4 comprises a rectification section 42 and a top section 43. The bottom section may also serve as the refrigerant reservoir section 32 of the nitrogen condenser 3. The oxygen-containing fluid discharged from the rectifying section 42 of the low-pressure rectifier 4 is introduced into the bottom 51 of the crude argon column 5 via an oxygen-containing fluid piping line L421.

[0029] The crude argon column 5 comprises a bottom section 51 , a rectifying section 52 and a top section 53 . The crude argon column bottom fluid piping line L51 is a line that is drawn from the bottom 51 of the crude argon column 5 and is used to introduce the bottom fluid below the outlet position of the oxygen-containing fluid piping line L421 of the rectification section 42 of the low-pressure rectification column 4. The argon withdrawal line L53 is a piping line for extracting the vapor flow or reflux liquid (crude argon-containing fluid) from the upper part of the crude argon column 5.

[0030] The crude argon condenser 6 receives the vapor stream from the top of the crude argon column 5, condenses it, and discharges it as reflux liquid. The crude argon condenser piping line L62 is a line leading from the upper gas phase of the refrigerant reservoir 62 of the crude argon condenser 6 and introducing it into the rectification section 42 of the low-pressure rectification column 4 above the oxygen-enriched liquid piping line L21.

[0031] The subcooler 7 receives the oxygen-enriched liquid discharged from the bottom 21 of the medium-pressure rectification column 2 at its warm end and discharges it from its cold end. The subcooler 7 also receives the vapor stream discharged from the upper portion 23 of the medium-pressure rectification column 2 at its warm end and discharges it from its cold end. The subcooler 7 also receives the nitrogen gas discharged from the top 43 of the low-pressure rectification column 4 at its cold end and discharges it from its warm end.

[0032] The oxygen turbine 9 performs heat exchange in the main heat exchanger 1 on the oxygen gas extracted from the gas phase of the refrigerant reservoir 32 of the nitrogen condenser 3, and then expands and cools the oxygen gas. The oxygen extraction line L32 is a line through which oxygen is extracted from the upper gas phase of the refrigerant reservoir 32 of the nitrogen condenser 3, introduced into the middle of the main heat exchanger 1, heated and extracted, expanded in the oxygen turbine 9, introduced again into the cold end of the main heat exchanger 1 and extracted from the warm end, and extracted as product oxygen gas.

[0033] In the nitrogen turbine 8, the nitrogen gas discharged from the top 43 of the low-pressure rectification column 4 is heat exchanged in the subcooler 7 and the main heat exchanger 1, compressed to a predetermined pressure in the nitrogen compressor 10, cooled in the cooling device 11, and cooled again in the main heat exchanger 1 before being expanded. Nitrogen gas discharged from the top 43 of the low-pressure rectification column 4 passes through a nitrogen gas piping line L43, a subcooler 7 and the main heat exchanger 1, and is taken out as low-pressure nitrogen gas. A nitrogen compressor 10 and a cooling device 11 are provided in the nitrogen gas piping line L43 downstream of the warm end of the main heat exchanger 1. The nitrogen gas branch piping line L431 branches off from the nitrogen gas piping line L43 downstream of the cooling device 11, is introduced again from the warm end of the main heat exchanger 1, is discharged from the middle section, is expanded in the nitrogen turbine 8, and joins the nitrogen gas piping line L43.

[0034] In the first embodiment, the inlet temperature of the oxygen turbine 9 is set lower than the inlet temperature of the nitrogen turbine 8, so that the temperature of the gas discharged from the first intermediate section 1a of the main heat exchanger 1 and sent to the oxygen turbine 9 is lower than the temperature of the gas discharged from the second intermediate section 1b of the main heat exchanger 1 and sent to the nitrogen turbine 8. For example, the position (first intermediate section 1a) of the outlet nozzle of the piping connecting the main heat exchanger 1 to the oxygen turbine 9 is positioned on the lower temperature side than the position (second intermediate section 1b) of the outlet nozzle of the piping connected to the nitrogen turbine 8.

[0035] (Embodiment 2) An air separation unit A2 of embodiment 2 will be described using Figure 2. The same reference numerals as those in embodiment 1 have the same functions, and therefore their descriptions may be omitted. The air separation unit A2 includes a bypass line L431a, a control valve V1, and a temperature measurement unit 12. The bypass line L431a is arranged to adjust the heat balance of the main heat exchanger 1, and is a line that branches off from the nitrogen gas branch piping line L431, bypasses it so that it does not enter the main heat exchanger 1, and merges with the nitrogen gas branch piping line L431. The temperature measurement unit 12 measures the temperature of the nitrogen gas introduced into the nitrogen turbine 8. In this embodiment, the temperature measurement unit 12 is provided on the line downstream of the junction of the bypass line L431a and the nitrogen gas branch piping line L431. The regulating valve V1 adjusts the amount of nitrogen gas circulating through the bypass line L431a so that the temperature measured by the temperature measuring unit 12 is higher than the inlet temperature of the oxygen turbine 9 (the temperature value of an installed thermometer not shown).

[0036] To ensure that the inlet temperature of the nitrogen turbine 8 is higher than the inlet temperature of the oxygen turbine 9, a bypass pipe L431a is provided from the nitrogen gas pipe at the warm end of the main heat exchanger 1 to the nitrogen turbine inlet pipe, and is configured to be temperature adjustable.

[0037] (Embodiment 3) An air separation unit A3 of embodiment 3 will be described with reference to Figure 3. The same reference numerals as those in embodiment 1 have the same functions, and therefore their explanations may be omitted. The air separation unit A3 includes a nitrogen booster 14 and a cooling unit 15. The nitrogen booster 14 is provided in the nitrogen gas branch piping line L431 upstream of the main heat exchanger 1, and boosts the nitrogen gas to a predetermined pressure. The second cooling device 15 cools the nitrogen gas pressurized by the nitrogen booster 14 to a predetermined temperature. The expansion turbine 81 expands the nitrogen gas that has been cooled by the second cooling device 15, introduced again from the warm end of the main heat exchanger 1, and discharged from the middle.

[0038] (Embodiment 4) An air separation unit A4 of embodiment 4 will be described with reference to Figure 4. The same reference numerals as those in embodiment 3 have the same functions, and therefore their description may be omitted. The air separation unit A4 is equipped with a recycle nitrogen line L431b. The recycle nitrogen line L431b branches off from the nitrogen gas branch piping line L431 inside the main heat exchanger 1, is led out from the cold end of the main heat exchanger 1, and is a line for introducing nitrogen gas into the rectification section 22 or its upper part 23 of the medium-pressure rectification column 2. Valve V2 is provided in recycled nitrogen line L431b and controls the start and stop of introduction of recycled nitrogen gas and the amount of introduction.

[0039] (Embodiment 5) An air separation unit A5 of embodiment 5 will be described using Figure 5. The same reference numerals as those in embodiment 4 have the same functions, and therefore their descriptions may be omitted. The air separation unit A5 includes a second nitrogen booster 17 and a second cooling unit 18. The second nitrogen booster 17 is provided in the nitrogen gas branch piping line L431 upstream of the first nitrogen booster 14, and boosts the nitrogen gas to a predetermined pressure. The second cooling device 18 is provided in the nitrogen gas branch piping line L431 upstream of the first nitrogen booster 14 and downstream of the second nitrogen booster 17, and cools the nitrogen gas pressurized by the second nitrogen booster 17 to a predetermined temperature. The second nitrogen booster 17 is driven by the oxygen turbine 9 .

[0040] (Embodiment 6) An air separation unit A6 of embodiment 6 will be described using Figure 6. The same reference numerals as those in embodiment 1 have the same functions, and therefore their explanations may be omitted. The air separation unit A6 does not include a crude argon column or a crude argon condenser. The oxygen piping line L31 is a piping line that is introduced into the cold end of the subcooler 7 and led out from the hot end.

[0041] (Example) 10 shows the results of a physical simulation of the air separation unit of the third embodiment. Feed air temperature 20.0℃, pressure 9.4 barA, flow rate 1000Nm 3 / h from the warm end of the main heat exchanger, cooled to -163°C, and introduced into the medium pressure rectification column. The medium pressure rectification column is equipped with a nitrogen condenser at the top, and nitrogen gas at the top is condensed and returned to the top of the medium pressure rectification column. 3 / h is extracted and cooled to -184°C in a subcooler and fed to the top of the low-pressure rectification column. From the bottom of the medium-pressure rectification column, 576 Nm3 of oxygen-enriched liquid with an oxygen concentration of 36.4% is extracted. 3 / h, is cooled to -170°C in a subcooler, and then introduced into the low-temperature side of the intermediate or crude argon condenser of the low-pressure rectification column. Low-pressure nitrogen gas flows from the top of the low-pressure rectification column at a rate of 781 Nm 3 / h and is discharged through the subcooler and main heat exchanger at 18°C ​​and 2.4 barA. Oxygen gas with an oxygen concentration of 99% is discharged from the bottom of the low-pressure rectification column at a rate of 211 Nm 3 / h, is heated to -126°C in the main heat exchanger, and then expanded from 2.5 barA to 1.28 barA in the oxygen turbine. At this time, the oxygen turbine outputs 1.7 kW of work to the outside, and the oxygen gas is cooled to -149°C. The oxygen gas is reintroduced into the main heat exchanger, heated, and then discharged from the warm end of the main heat exchanger. At the bottom of the crude argon column, 299 Nm3 of gas containing 10% argon and 90% oxygen is 3 / h, and is rectified and released from the top of the column at 8 Nm 3 / h of argon is extracted from the bottom of the crude argon column. 3 / h of liquid is returned to the low pressure rectification column. Under these conditions, the pressure is 8 Nm, which is approximately 1% of the pressure of low-pressure nitrogen gas. 3 The refrigeration required to liquefy 1.1kW / h to produce liquefied nitrogen is equivalent to 65% of the refrigeration generated by the oxygen turbine. 3 1 / h of nitrogen gas is cooled to -119°C, expanded to 2.6 barA in the nitrogen turbine, and cooled to -164°C. It then joins with low-pressure nitrogen gas supplied from the subcooler and is introduced into the main heat exchanger. The nitrogen turbine can generate the refrigeration required for the above liquefaction, so the refrigeration balance of the air separation unit can be maintained even when liquefied nitrogen is discharged.

[0042] In the configuration of the above embodiment, the inlet temperature of the oxygen turbine is -126°C, while the inlet temperature of the nitrogen turbine is -119°C, making it possible to discharge at a temperature 7°C higher. In a turbine cycle, expanding gas at a higher temperature allows for a greater amount of work to be sent to the outside, but there is a possibility that the refrigeration required for cooling gas in the low-temperature range may not be supplied. In this embodiment, when baseload refrigeration is supplied by the oxygen turbine and additional refrigeration is required by the nitrogen turbine for liquefying product gas, etc., refrigeration can be efficiently generated by expanding the nitrogen gas at a temperature higher than the inlet temperature of the oxygen turbine due to the synergistic effect with the oxygen turbine. Furthermore, in this configuration, feed air or medium-pressure nitrogen, which contribute to the vapor flow of the medium-pressure rectification column, is not used, so the yields of the product nitrogen and product argon are not affected. For example, when feed air is used as a refrigeration source, about 7% of the feed air is expanded in the expansion turbine due to the generation of refrigeration and does not contribute to the rectification, which affects the yield of nitrogen or argon by about 7%. Therefore, the present embodiment is significantly effective in that it eliminates this effect.

[0043] (Another embodiment) (1) Although not specifically stated, pressure regulators, flow rate controllers, etc. may be installed in each piping line to adjust the pressure or flow rate. (2) Although not specifically stated, control valves, gate valves, etc. may be installed on each line. (3) Although not specifically stated, each tower may be equipped with a pressure regulator, a temperature measuring device, etc., for pressure or temperature regulation. [Explanation of symbols]

[0044] 1 heat exchanger 2 Medium pressure rectification column 3 Nitrogen condenser 4 Low-pressure rectification tower 5. Crude Argon Column 6. Crude Argon Condenser 8 Nitrogen Turbine 9 Oxygen Turbine 10 Nitrogen Compressor 11 Cooling device

Claims

1. a main heat exchanger into which raw air is introduced from a hot end and discharged from a cold end; a medium-pressure rectification column into which feed air discharged from the main heat exchanger is introduced; a nitrogen condenser into which a vapor stream from the medium pressure rectification column is introduced, which condenses the vapor stream, and discharges the vapor stream as reflux; a low-pressure rectification column into which the oxygen-enriched liquid discharged from the medium-pressure rectification column is introduced; an oxygen turbine that expands and cools the oxygen-enriched gas discharged from the nitrogen condenser after heat exchange in the main heat exchanger; a nitrogen turbine in which nitrogen gas discharged from the low-pressure rectification column is heat-exchanged in at least the main heat exchanger, compressed to a predetermined pressure, cooled, and then cooled again in the main heat exchanger, and then expanded; the inlet temperature of the oxygen turbine is lower than the inlet temperature of the nitrogen turbine; Air separation unit.

2. a crude argon column into which the oxygen-containing fluid derived from the lower pressure rectification column is introduced; a crude argon condenser into which the vapor stream from the crude argon column is introduced, and which condenses the vapor stream and discharges it as reflux; 2. The air separation unit of claim 1, comprising:

3. a nitrogen gas piping line leading from the low-pressure rectification column and extracting the nitrogen gas through at least the main heat exchanger; a nitrogen gas branch pipe line that branches off from the nitrogen gas pipe line downstream of the heat exchanger, is introduced again into the warm end of the main heat exchanger, is discharged from an intermediate portion, is expanded in the nitrogen turbine, and is merged into the nitrogen gas pipe line or is taken out as nitrogen gas via the main heat exchanger again; a bypass line that branches off from the nitrogen gas branch piping line, bypasses the nitrogen gas so as not to be introduced into the main heat exchanger, and joins the nitrogen gas branch piping line; an adjusting valve for adjusting the amount of nitrogen gas circulated through the bypass line; Equipped with 10. The air separation unit of claim 1.

4. a nitrogen gas piping line leading from the low-pressure rectification column and extracting the nitrogen gas through at least the main heat exchanger; a nitrogen gas branch pipe line that branches off from the nitrogen gas pipe line downstream of the heat exchanger, is introduced again into the warm end of the main heat exchanger, is discharged from an intermediate portion, is expanded in the nitrogen turbine, and is merged into the nitrogen gas pipe line or is taken out as nitrogen gas via the main heat exchanger again; a nitrogen booster provided in the nitrogen gas branch piping line to boost the nitrogen gas to a predetermined pressure; a second cooling device that cools the nitrogen gas pressurized by the nitrogen booster; Equipped with 10. The air separation unit of claim 1.

5. a recycle nitrogen line branching from the nitrogen gas branch piping line inside the main heat exchanger and leading out from the cold end of the main heat exchanger for introducing nitrogen gas into the medium-pressure rectification column; The air separation unit according to claim 3 or 4, further comprising:

6. a second nitrogen booster provided in the nitrogen gas branch piping line to boost the nitrogen gas to a predetermined pressure; 5. The air separation unit according to claim 3, further comprising a second cooling device provided in the nitrogen gas branch piping line for cooling the nitrogen gas pressurized by the second nitrogen booster.

7. a subcooler into which the oxygen-enriched liquid discharged from the medium pressure rectification column is introduced from a cold end and discharged from a warm end, The air separation unit according to claim 1 or 2, further comprising:

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