Nitrogen generator and nitrogen producing method

Abstract

To provide a nitrogen producing method that uses a pressure boosting expansion process, prevents deterioration of a recovery rate of product nitrogen derived from a first rectification column, and exhibits excellent thermal efficiency in a cascade process of a duplex type rectification column.SOLUTION: A nitrogen producing method that uses a nitrogen generator including a main heat exchanger 1, a first nitrogen rectification column 2, a first nitrogen condenser 3, a second nitrogen rectification column 4, a second nitrogen condenser 5, a first nitrogen booster 71, a first nitrogen expansion turbine 72, and a cooling device 8 includes a step in which part of first nitrogen gas to be derived from the first nitrogen rectification column 2 is introduced to the main heat exchanger 1, and at least part of the derived first product nitrogen is pressurized by the first nitrogen booster 71, is introduced again from a hot end of the main heat exchanger 1 after cooled by the cooling device 8, is derived from an intermediate part of the main heat exchanger 1, and is expanded and cooled by the first nitrogen expansion turbine 72.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitrogen generator and a nitrogen production method, and more particularly to a nitrogen generator and a nitrogen production method intended for producing a large amount of high-purity nitrogen gas, for example, in a cryogenic air separation plant. [Background technology]

[0002] Cryogenic air separation is a well-known method for separating and purifying large amounts of nitrogen from the atmosphere. Among these methods, a double-column rectification system, which has two rectification columns for producing nitrogen, offers the advantage of being able to reduce the column diameter relative to the nitrogen demand compared to a single-column rectification system, which has only one rectification column. This allows for easier transportation of the rectification columns, which reduces construction costs. Therefore, when a large amount of nitrogen is needed and the nitrogen generator is large, a cascade process, which has excellent nitrogen production unit consumption (SPC, Specific Power Consumption), is preferred among double-column rectification systems. This is a process in which two nitrogen rectification columns, each equipped with a nitrogen condenser at the top, supply product nitrogen gas from the top of each nitrogen rectification column.

[0003] To configure a cryogenic air separation process, it is necessary to supply refrigeration so as to maintain a heat-cold balance, and for this purpose, an expansion turbine is used to supply process gas. The process gases used include a portion of the feed air (see, for example, Patent Documents 1 and 2), an oxygen-enriched gas discharged outside the system as a waste gas (see, for example, Patent Document 5), and a portion of the product nitrogen gas (see, for example, Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 5,231,837 [Patent Document 2] U.S. Patent No. 11,674,750 [Patent Document 3] Patent No. 4515225 [Patent Document 4] U.S. Patent No. 5,228,297 [Patent Document 5] Japanese Patent Application Publication No. 2017-72282 Summary of the Invention [Problem to be solved by the invention]

[0005] When part of the feed air is used as a refrigeration source, the expanded feed air must be introduced into a rectification column (e.g., the second rectification column) that operates at a lower pressure than the rectification column (e.g., the first rectification column) into which the undepressurized feed air is introduced. This means that the amount of nitrogen separated in the rectification column into which most of the feed air is introduced decreases, resulting in a decrease in the nitrogen recovery rate of the nitrogen generator.

[0006] In the case of a process for expanding an oxygen-enriched gas, the oxygen-enriched gas extracted from the first nitrogen condenser or the second nitrogen condenser in a cascade process is the target. The oxygen-enriched gas from the first nitrogen condenser can be supplied to the bottom of the second nitrogen rectification column to become the vapor stream of the second nitrogen rectification column, so it is desirable to use it to contribute to the rectification and increase the amount of nitrogen recovered, rather than using it as a refrigeration source. When the nitrogen recovery rate of the nitrogen generator is increased, the pressure of the oxygen-enriched gas extracted from the second nitrogen condenser drops significantly, and a pressure difference sufficient to expand the gas to provide sufficient refrigeration cannot be obtained, making it difficult to use as a primary refrigeration source, especially in nitrogen generators with high nitrogen recovery rates.

[0007] In the case of a nitrogen gas expansion process, a known method uses the pressure difference between a first product nitrogen gas and a second product nitrogen gas to generate refrigeration. The power obtained by the expansion turbine can be used to compress a process gas, such as the product nitrogen gas, or can be converted into electricity, such as by applying a generator.

[0008] However, it is desirable from the viewpoint of thermal efficiency to minimize the amount of pressure reduction required for the product nitrogen gas before supplying it to consumers.

[0009] In view of the above circumstances, the present disclosure provides a nitrogen generator and a nitrogen production method that utilize a pressurized expansion process in a cascade process using a double rectification column, thereby achieving excellent thermal efficiency without reducing the recovery rate of the product nitrogen extracted from the first rectification column. The present invention also provides a nitrogen generator and a nitrogen production method that are excellent in nitrogen recovery rate and thermal efficiency while minimizing the flow rate of the product nitrogen gas used in the pressure boost expansion process. [Means for solving the problem]

[0010] The nitrogen generation apparatus (A1, A2, A3) of the present disclosure includes a main heat exchanger (1), a first nitrogen rectification column (2), a first nitrogen condenser (3), a second nitrogen rectification column (4), a second nitrogen condenser (5), a first nitrogen booster (71), a first nitrogen expansion turbine (72), and a cooling device (8). The first nitrogen booster (71) and the first nitrogen expansion turbine (72) may be configured as a first nitrogen booster turbine (7). The first nitrogen booster (71) may be driven by the first nitrogen expansion turbine (72). The first nitrogen booster (71) introduces a portion of the first nitrogen gas discharged from the top (23) of the first nitrogen rectification column (2) into the main heat exchanger (1), and boosts the pressure of at least a portion of the first product nitrogen gas discharged from the warm end. The cooling device (8) cools the first product nitrogen gas pressurized by the first nitrogen booster (71) to a predetermined temperature (for example, from about 80°C to about 20°C). The first nitrogen expansion turbine (72) expands and cools the first product nitrogen gas, which is cooled by the cooling device (8) and then reintroduced from the warm end of the main heat exchanger (1) and discharged from the middle of the main heat exchanger (1).

[0011] The nitrogen generators (A1, A2, A3) may be equipped with a subcooler (6). The subcooler (6) may be of a structure integrally connected to the main heat exchanger (1) or may be of a separate structure. The subcooler (6) may cool the first oxygen-enriched liquid supplied from the bottom (21) of the first nitrogen rectification column (2) to an intermediate stage of the rectification section (42) of the second nitrogen rectification column (4). The subcooler (6) may cool the first liquefied nitrogen (a part of the reflux liquid which is obtained by condensing the vapor stream from the vapor phase at the top of the first nitrogen rectification column (2) in the first nitrogen condenser (3) and returning to the first nitrogen rectification column (2)) supplied from the first nitrogen condenser (3) to the top (43) or the vapor phase of the second nitrogen rectification column (4). The subcooler (6) may cool the second oxygen-enriched liquid, which is the refrigerant sent from the refrigerant reservoir (31) of the first nitrogen condenser (3) to the refrigerant reservoir (51) of the second nitrogen condenser (5). The subcooler (6) may cool first nitrogen gas (or a portion of the vapor stream) which is a vapor stream sent from the vapor phase at the top of the first nitrogen rectification column (2) to the first nitrogen condenser (3). The cooled first nitrogen gas may be introduced into the cold end of the main heat exchanger (1) and discharged from the warm end as first product nitrogen gas. A portion of the first product nitrogen gas discharged from the warm end may be sent to the first nitrogen booster (71). The subcooler (6) may cool the second nitrogen gas (or a part of the vapor stream) which is the vapor stream sent from the vapor phase at the top of the second nitrogen rectification column (4) to the second nitrogen condenser (5). The cooled second nitrogen gas may be introduced into the cold end of the main heat exchanger (1) and discharged from the warm end as second product nitrogen gas. The subcooler (6) may cool the second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser (5). The cooled second oxygen-enriched gas may be introduced into the cold end of the heat exchanger (1) and discharged from the warm end as waste gas.

[0012] The nitrogen generator (A1, A2) may comprise a second oxygen-enriched gas expansion turbine (9). The second oxygen-enriched gas expansion turbine (9) expands and cools the second oxygen-enriched gas extracted from the vapor phase at the top (43) of the second nitrogen rectification column (4) after it has been cooled in the subcooler (6) and / or the main heat exchanger (1). The expanded and cooled second oxygen-enriched gas may be reintroduced into the main heat exchanger (1) and discharged as waste gas from the warm end.

[0013] The nitrogen production method using the nitrogen generation apparatus (A1, A2, A3) of the present disclosure includes: The method includes the steps of introducing a portion of the first nitrogen gas (a portion of the vapor stream) discharged from the top (23) of the first nitrogen rectification column (2) into the cold end of the main heat exchanger (1) and discharging it from the warm end, and at least a portion of the first product nitrogen gas discharged from the warm end being pressurized in the first nitrogen booster (71) and cooled in the cooling device (8), and then being reintroduced into the warm end of the main heat exchanger (1), discharged from the middle of the main heat exchanger (1), and expanded and cooled in the first nitrogen expansion turbine (72). In this configuration, the refrigerant is reintroduced into the main heat exchanger (1), thereby cooling the main heat exchanger (1) and supplying the refrigeration necessary for operating the nitrogen generator (A1).

[0014] The nitrogen production method includes: The method may further include a step of: expanding and reducing the pressure of the first product nitrogen gas in the first nitrogen expansion turbine (72) and reintroducing it into the main heat exchanger (1); and combining the second nitrogen gas discharged from the top (43) of the second nitrogen rectification column (4) in the main heat exchanger (1); and cooling another substance (e.g., feed air) in the main heat exchanger (1); The method may include a step of cooling another substance (e.g., feed air, etc.) in the main heat exchanger (1) with the first product nitrogen gas expanded and reduced in pressure in the first nitrogen expansion turbine (72) and reintroduced into the main heat exchanger (1), and a step of cooling another substance (e.g., feed air, etc.) in the main heat exchanger (1) with the second product nitrogen gas discharged from the top of the second nitrogen rectification column (4) and introduced into the main heat exchanger (1).

[0015] The nitrogen production method includes: The method may include a step of passing the second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser (5) through the subcooler (6), introducing it into the main heat exchanger (1), discharging it from an intermediate section, expanding and cooling it in a second oxygen-enriched gas expansion turbine (9), and reintroducing the expanded and cooled second oxygen-enriched gas into the main heat exchanger (1) and discharging it from a warm end as waste gas.

[0016] The nitrogen generation apparatus (A1, A2, A3) of the present disclosure includes: a main heat exchanger (1) into which raw air is introduced via a raw air line (L1); a first nitrogen rectification column (2) having a rectification section (22) or a bottom section (21) into which the feed air heat-exchanged in the main heat exchanger (1) is introduced via a feed air line (L1); a first nitrogen condenser (3) that condenses the first nitrogen gas (vapor flow) discharged from the top (23) of the first nitrogen rectification column (2) through a first condensate reflux line (L231) and returns the condensed first nitrogen gas (vapor flow) to the first nitrogen rectification column (2) as a reflux liquid; a first product nitrogen gas line (L23) for introducing the first nitrogen gas (vapor stream) discharged from the top (23) of the first nitrogen rectification column (2) (after passing through a subcooler 6) into at least the cold end of the main heat exchanger (1) and discharging it from the warm end as a first product nitrogen gas; a first product nitrogen branch line (L23a) branching off from the first product nitrogen gas line (L23) at a position downstream of the warm end of the main heat exchanger (1); a first nitrogen booster (71) provided in the first product nitrogen branch line (L23a) for increasing the pressure of the first product nitrogen gas; a cooling device (8) provided in the first product nitrogen branch line (L23a) for cooling the first product nitrogen gas pressurized by the first nitrogen booster (71) to a predetermined temperature; a first nitrogen expansion turbine (72) that introduces the first product nitrogen gas cooled by the cooling device (8) into a warm end of the main heat exchanger (1), discharges it from an intermediate portion, and expands and cools it; a second nitrogen rectification column (4) into which the vapor stream from the first nitrogen condenser (3) is introduced; a second nitrogen condenser (5) for condensing the second nitrogen gas (vapor flow) discharged from the top (43) of the second nitrogen rectification column (4) via a second condensate reflux line (L231) and returning the condensed second nitrogen gas (vapor flow) to the second nitrogen rectification column (4) as reflux liquid; a second product nitrogen gas line (L43) for introducing the second nitrogen gas (vapor stream) discharged from the top (43) of the second nitrogen rectification column (4) (after passing through a subcooler 6) into at least the cold end of the main heat exchanger (1) and discharging it from the warm end as a second product nitrogen gas; The device may also include:

[0017] In the nitrogen generator (A1, A2, A3), The first product nitrogen gas may be used for work in the first nitrogen expansion turbine (72) and then reintroduced into the main heat exchanger (1), merged with the second product nitrogen line (L43), and discharged as second product nitrogen gas. The first product nitrogen branch line (L23a) may merge with the second product nitrogen line (L43) in the main heat exchanger (1).

[0018] The nitrogen generators (A1, A2, A3) are a subcooler (6) connected to the main heat exchanger (1) or separate from the main heat exchanger (1); a first oxygen-enriched liquid line (L21) through which the first oxygen-enriched liquid discharged from the bottom (21) of the first nitrogen rectification column (2) is introduced into the subcooler (6) and then introduced into an intermediate stage of the rectification section (42) of the second nitrogen rectification column (4); a first liquefied nitrogen line (L231a) through which the first liquefied nitrogen condensed in the first nitrogen condenser (3) is introduced into the subcooler (6) and then introduced into the top (43) of the second nitrogen rectification column (4); and a second oxygen-enriched liquid line (L31) through which the second oxygen-enriched liquid discharged from the refrigerant reservoir (31) of the first nitrogen condenser (3) is introduced into the subcooler (6) and then introduced into the refrigerant reservoir (51) of the second nitrogen condenser (5).

[0019] The nitrogen generator (A1) The second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser (5) is introduced into the subcooler (6) and discharged therefrom. The cooled second oxygen-enriched gas is then introduced into the cold end of the main heat exchanger (1) and discharged as a waste gas from the warm end thereof. A first waste gas line (L53) may be provided.

[0020] The nitrogen generator (A2) the waste gas line (L53) is led out from an intermediate portion of the main heat exchanger (1), introduced back into the main heat exchanger (1), and extended so as to exit from the warm end; a second oxygen-enriched gas expansion turbine (9) at a position derived from the intermediate section; The second oxygen-enriched gas may be expanded and cooled in the second oxygen-enriched gas expansion turbine (9) and sent to the main heat exchanger (1) again. The nitrogen generator (A2) The second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser (5) is passed through the subcooler (6), introduced into the main heat exchanger (1), discharged from an intermediate section, and then expanded and cooled in a second oxygen-enriched gas expansion turbine (9). The expanded and cooled second oxygen-enriched gas is then reintroduced into the main heat exchanger (1) and discharged from a warm end as a waste gas. A second waste gas line (L531) may be provided.

[0021] The nitrogen generator (A3) a nitrogen compressor (711) provided in the first product nitrogen branch line (L23a); a third cooling device (81) provided in the first product nitrogen branch line (L23a) for cooling the first product nitrogen gas compressed by the nitrogen compressor (711); a second nitrogen booster (71a) provided in the first product nitrogen branch line (L23a) for increasing the pressure of the first product nitrogen gas cooled in the third cooling device (81); a second cooling device (8a) provided in the first product nitrogen branch line (L23a) for cooling the first product nitrogen gas pressurized by the second nitrogen booster (71a) to a predetermined temperature; a first nitrogen booster (71) provided in the first product nitrogen branch line (L23a) for increasing the pressure of the first product nitrogen gas cooled by the second cooling device (8a); a first cooling device (8) provided in the first product nitrogen branch line (L23a) for cooling the first product nitrogen gas pressurized by the first nitrogen booster (71) to a predetermined temperature; a pressure reducing valve (109) provided in the first product nitrogen branch line (L23a) downstream of the cold end of the main heat exchanger (1); a gas-liquid separator (110) disposed downstream of the pressure reducing valve (109) for separating the gas and liquid components; The device may also include: The nitrogen generator (A3) a second nitrogen expansion turbine (72a) that expands and cools a portion of the first product nitrogen gas that branches off from a first product nitrogen branch line (L23a) upstream of the second nitrogen booster (71a), introduces the first product nitrogen gas from a warm end of the main heat exchanger (1), and discharges the first product nitrogen gas from a first intermediate section (1a); a first nitrogen expansion turbine (72) that expands and cools a portion of the first product nitrogen gas that has been cooled by the first cooling device (8), is introduced into the warm end of the main heat exchanger (1), and is discharged from a second intermediate section (1b) that is closer to the cold end than the first intermediate section (1a); The device may also include: The first product nitrogen branch line (L23a) of the nitrogen generator (A3) is The line may be a line through which the nitrogen passes through a nitrogen compressor (711), a third cooling device (81), a second nitrogen booster (71a), a second cooling device (8a), a first nitrogen booster (71), and a first cooling device (8), and then is introduced into the hot end of the main heat exchanger (1), discharged from the cold end, and then introduced into the gas-liquid separator (110) through a pressure reducing valve (109). The nitrogen generator (A3) a first product nitrogen second branch line (L23b) for branching off from the first product nitrogen branch line (L23a) upstream of the second nitrogen booster (71a) and discharging a part of the first product nitrogen gas, introducing the part into the warm end of the main heat exchanger (1), discharging the part from the first intermediate section (1a), causing the part to work in the second nitrogen expansion turbine (72a), and then introducing the part into the intermediate section of the main heat exchanger (1) again, where the part joins with the second product nitrogen line (L43) in the main heat exchanger (1); a first product nitrogen third branch line (L23c) branching from the first product nitrogen branch line (L23a) inside the main heat exchanger (1) to lead a part of the first product nitrogen gas from a second intermediate section (1b) of the main heat exchanger (1) that is closer to the cold end than the first intermediate section (1a), expand and cool the first product nitrogen gas in the first nitrogen expansion turbine (72), and send the first product nitrogen gas back to the main heat exchanger (1) (or join the second product nitrogen line (L43) upstream of the cold end of the main heat exchanger (1)); The device may also include: The second nitrogen booster (71a) and the second nitrogen expansion turbine (72a) may constitute a second nitrogen booster turbine (7a), and the first nitrogen booster (71) and the first nitrogen expansion turbine (72) may constitute a first nitrogen booster turbine (7).

[0022] The pressure of the first product nitrogen gas may be lower than the pressure of the second product nitrogen gas. The nitrogen generators (A1, A2, A3) are 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

[0023] (Action and effect) (1) Refrigeration can be generated by configuring a first nitrogen booster turbine. A portion of the first product nitrogen gas is boosted to a pressure higher than the pressure of the first product nitrogen gas by the first nitrogen booster, which is driven by the first expansion turbine, and then expanded. This boosting process increases the pressure difference in the first expansion turbine, thereby increasing the amount of refrigeration generated per flow rate, and as a result, reducing the molar flow rate of nitrogen required to generate refrigeration. Furthermore, by obtaining a large pressure difference, when cooling the nitrogen gas to the target temperature, the nitrogen gas can be introduced into the first expansion turbine at a higher temperature, which is advantageous for generating refrigeration. (2) The subcooler function subcools the process liquid with a lower temperature process gas, suppressing the amount of gasification during decompression and increasing the amount of liquid contributing to the rectification process, thereby contributing to an improvement in the nitrogen recovery rate. (3) The second oxygen-enriched gas expansion turbine allows the second oxygen-enriched gas to be used as an auxiliary refrigeration source, thereby reducing the amount of first product nitrogen gas sent to the first nitrogen booster turbine. (4) [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a nitrogen generating apparatus according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a nitrogen generating apparatus according to a second embodiment. [Figure 3] FIG. 10 is a diagram showing a nitrogen generating apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] (Embodiment 1) The nitrogen generator A1 of the first embodiment will be described with reference to FIG. The nitrogen generation apparatus A1 includes a main heat exchanger 1, a first nitrogen rectification column 2, a first nitrogen condenser 3, a second nitrogen rectification column 4, a second nitrogen condenser 5, a subcooler 6, a first nitrogen booster turbine 7, and a cooling device 8. In this embodiment, the subcooler 6 and the main heat exchanger 1 have an integrally connected structure. A separation line is indicated by a dashed dotted line S. The first nitrogen booster turbine 7 includes a first nitrogen booster 71 and a first nitrogen expansion turbine 72, and the first nitrogen booster 71 is driven by the first nitrogen expansion turbine 72.

[0027] 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 nitrogen rectification column 2 via the feed air line L1. The first nitrogen rectification column 2 comprises a bottom section 21, a rectification section 22, and a top section 23. The feed air line L1 is connected to the bottom section 21. The oxygen-enriched liquid stored in the bottom 21 is sent to the subcooler 6 via the first oxygen-enriched liquid line L21, and then sent to the intermediate portion of the rectification section 42 of the second nitrogen rectification column 4.

[0028] The first nitrogen condenser 3 is provided above the top 23. The first nitrogen gas (vapor flow) discharged from the top 23 of the first nitrogen rectifier 2 is introduced into the first nitrogen condenser 3 via the first condensed reflux line L231, and is cooled (condensed) into liquefied nitrogen by heat exchange with the oxygen-enriched liquid. The liquefied nitrogen returns to the top 23 of the first nitrogen rectifier 2 as reflux liquid. The first liquefied nitrogen line L231a branches off from the first condensate reflux line L231. The first liquefied nitrogen line L231a is a line through which the first liquefied nitrogen condensed in the first nitrogen condenser 3 is introduced into the subcooler 6, from which it is discharged and introduced into the top 43 of the second nitrogen rectification column 4. The second oxygen-enriched liquid line L31 is a line that introduces the second oxygen-enriched liquid discharged from the refrigerant reservoir 31 of the first nitrogen condenser 3 to the subcooler 6, and then introduces it into the refrigerant reservoir 51 of the second nitrogen condenser 5.

[0029] The first product nitrogen gas line L23 is a line through which the first nitrogen gas (vapor flow) discharged from the top 23 of the first nitrogen rectification column 2 is introduced into the cold end of the main heat exchanger 1 after passing through the subcooler 6, and discharged from the warm end, thereby being taken out as first product nitrogen. The first product nitrogen gas (vapor flow) discharged from the top 23 of the first nitrogen rectification column 2 is sent to the subcooler 6 via the first product nitrogen gas line L23, discharged from the middle part thereof, introduced into the cold end of the main heat exchanger 1, and discharged from the warm end as high-pressure nitrogen gas. The first nitrogen booster 71 introduces the first product nitrogen gas branched off from the first product nitrogen gas line L23 downstream of the warm end of the main heat exchanger 1 via the first product nitrogen branch line L23a, and pressurizes the first product nitrogen gas.

[0030] The cooling device 8 cools the first product nitrogen pressurized by the first nitrogen booster 71 to a predetermined temperature after being introduced via the first product nitrogen branch line L23a. The cooled first product nitrogen is reintroduced into the warm end of the main heat exchanger 1 and discharged from the intermediate section.

[0031] The first nitrogen expansion turbine 72 expands and cools the first product nitrogen that is discharged from the intermediate portion of the main heat exchanger 1 via the first product nitrogen branch line L23a. The expanded first product nitrogen is again introduced into the intermediate portion of the main heat exchanger 1 via the first product nitrogen branch line L23a and is discharged from the warm end. In FIG. 1, it merges with the second product nitrogen gas line L43 inside the main heat exchanger 1.

[0032] The second nitrogen rectification column 4 receives the vapor stream from the vapor phase of the first nitrogen condenser section 3 and rectifies it. The second nitrogen rectification column 4 comprises a rectification section 42 and a top 43. The second product nitrogen gas line L43 is a line through which the second nitrogen gas (vapor flow) discharged from the top 43 of the second nitrogen rectification column 4 is introduced into the cold end of the main heat exchanger 1 after passing through the subcooler 6, and discharged from the warm end as second product nitrogen. The pressure of the first product nitrogen gas is higher than the pressure of the second product nitrogen gas.

[0033] The second nitrogen condenser 5 is provided above the top 43. The second nitrogen condenser 5 receives the second nitrogen gas (vapor flow) discharged from the top 43 of the second nitrogen rectifier 4 via the second condensate reflux line L431, and cools (condenses) it into liquefied nitrogen by heat exchange with the oxygen-enriched liquid. The liquefied nitrogen returns to the top 43 of the second nitrogen rectifier 4 as reflux liquid. The first waste gas line L53 is a line through which the second oxygen-enriched gas discharged from the gas phase 53 of the second nitrogen condenser 5 is introduced into the subcooler 6 and discharged, and the cooled second oxygen-enriched gas is introduced into the cold end of the main heat exchanger 1 and discharged from the warm end as waste gas.

[0034] (Embodiment 2) The nitrogen generator A2 of the second embodiment will be described with reference to Fig. 2. The same reference numerals as those in the first embodiment have the same functions, and therefore the description thereof may be omitted. The nitrogen generation apparatus A2 includes a main heat exchanger 1, a first nitrogen rectification column 2, a first nitrogen condenser 3, a second nitrogen rectification column 4, a second nitrogen condenser 5, a subcooler 6, a first nitrogen booster turbine 7 (71, 72), a cooling device 8, and a second oxygen-enriched gas expansion turbine 9.

[0035] The second waste gas line L531 is a line through which the second oxygen-enriched gas discharged from the gas phase 53 of the second nitrogen condenser 5 is introduced into the subcooler 6 and discharged, the cooled second oxygen-enriched gas is introduced into the cold end of the main heat exchanger 1, discharged from the intermediate section, sent to the second oxygen-enriched gas expansion turbine 9, expanded and cooled in the second oxygen-enriched gas expansion turbine 9, and the expanded and cooled second oxygen-enriched gas is introduced back into the main heat exchanger 1 and discharged from the warm end as waste gas.

[0036] (Embodiment 3) The nitrogen generator A3 of the third embodiment will be described with reference to Fig. 3. The same reference numerals as those of the first and second embodiments have the same functions, and therefore the description thereof may be omitted. The nitrogen generator A3 includes a nitrogen compressor 711, a third cooling device 81, a first product nitrogen second branch line L23b, a first product nitrogen third branch line L23c, a first nitrogen booster 71, a second nitrogen booster 71a, a first cooling device 8a, a second cooling device 8b, a first nitrogen expansion turbine 72, a second nitrogen expansion turbine 72a, a pressure reducing valve 109, and a gas-liquid separator 110. The subcooler 6 is configured as a body physically separate from the main heat exchanger 1.

[0037] The first product nitrogen branch line L23a is a line that passes through the nitrogen compressor 711, the third cooling device 81, the second nitrogen booster 71a, the second cooling device 8a, the first nitrogen booster 71, and the first cooling device 8, and then introduces the nitrogen from the warm end of the main heat exchanger 1, discharges it from the cold end, and then introduces it into the gas-liquid separator 110 via the pressure reducing valve 109. The first product nitrogen second branch line L23b branches off from the first product nitrogen branch line L23a upstream of the second nitrogen booster 71a to extract a portion of the first product nitrogen gas, introduce it from the warm end of the main heat exchanger 1, extract it from the first intermediate section 1a, perform work in the second nitrogen expansion turbine 72a, and then introduce it back into the intermediate section of the main heat exchanger 1, where it merges with the second product nitrogen line L43 within the main heat exchanger 1. The first product nitrogen third branch line L23c branches off from the first product nitrogen branch line L23a inside the main heat exchanger 1 and extracts a portion of the first product nitrogen gas from the second intermediate section 1b, which is closer to the cold end than the first intermediate section 1a of the main heat exchanger 1, expands and cools the first product nitrogen gas in the first nitrogen expansion turbine 72, and merges with the second product nitrogen line L43 upstream of the cold end of the main heat exchanger 1.

[0038] The first nitrogen booster 71 and the first nitrogen expansion turbine 72 constitute a first nitrogen booster turbine 7, and the second nitrogen booster 71a and the second nitrogen expansion turbine 72a constitute a second nitrogen booster turbine 7a. The nitrogen compressor 711 is provided in the first product nitrogen branch line L23a and pressurizes the first product nitrogen gas to a predetermined pressure. The third cooling device 81 is provided in the first product nitrogen branch line L23a and cools the first product nitrogen gas compressed by the nitrogen compressor 711 to a predetermined temperature. The second nitrogen booster 71a is provided in the first product nitrogen branch line L23a and boosts the first product nitrogen gas cooled in the third cooling device 81 to a predetermined pressure. The second cooling device 8a is provided in the first product nitrogen branch line L23a and cools the first product nitrogen gas boosted in the second nitrogen booster 71a to a predetermined temperature. The first nitrogen booster 71 is provided in the first product nitrogen branch line L23a and boosts the first product nitrogen gas cooled in the second cooling device 8a to a predetermined pressure. The first cooling device 8 is provided in the first product nitrogen branch line L23a and cools the first product nitrogen gas boosted in the first nitrogen booster 71 to a predetermined temperature.

[0039] The pressure reducing valve 109 is provided in the first product nitrogen branch line L23a downstream of the cold end of the main heat exchanger 1, and expands the first product nitrogen gas. The first product nitrogen gas is expanded by the pressure reducing valve 109, becoming a mixture of gas and liquid components, which is sent to the downstream gas-liquid separator 110. The gas-liquid separator 110 separates the mixture into gas and liquid components. The gas component merges with the second product nitrogen line L43 and is introduced again into the main heat exchanger 1. The liquid component can be extracted as liquefied nitrogen.

[0040] The second nitrogen expansion turbine 72a extracts a portion of the first product nitrogen gas that branches off from the first product nitrogen branch line L23a upstream of the second nitrogen booster 71a, introduces it from the warm end of the main heat exchanger 1, and expands and cools the first product nitrogen gas that is extracted from the first intermediate section 1a. The first nitrogen expansion turbine 72 expands and cools a portion of the first product nitrogen gas that is cooled by the first cooling device 8, introduced from the warm end of the main heat exchanger 1, and discharged from the second intermediate section 1b, which is closer to the cold end than the first intermediate section 1a.

[0041] In nitrogen generator A3, at least a portion of the first nitrogen gas product is pressurized in nitrogen compressor 711, then pressurized in first and second nitrogen boosters 71, 71a, cooled in main heat exchanger 1, and then reduced in pressure to the pressure of the second nitrogen gas, where it is liquefied. This liquefied nitrogen stream contains some gas components, so it is introduced into pressure reducing valve 109 and gas-liquid separator 110, where it is separated into liquid and gas. The gas components are combined with the second nitrogen gas stream. The second nitrogen booster 71a is driven by introducing a portion of the compressed nitrogen gas supplied from the nitrogen compressor 711 into the main heat exchanger 1, discharging it at the first intermediate section 1a, and then expanding it through the second nitrogen expansion turbine 72a. The first nitrogen booster 71 is driven by introducing a portion of the nitrogen gas pressurized by the first and second nitrogen boosters 71, 71a into the main heat exchanger 1, discharging it at the second intermediate section 1b, and then expanding it in the first nitrogen expansion turbine 72. To meet the demand for liquefied nitrogen, a nitrogen compressor 711 and a second nitrogen booster turbine (71a, 72a) are combined in addition to the first nitrogen booster turbine (71, 72). To liquefy nitrogen, nitrogen is compressed to supercritical pressure (for example, 50 barA) by the nitrogen compressor 711 and the first and second nitrogen boosters 71, 71a, then cooled in the main heat exchanger 1 and expanded and liquefied by the pressure reducing valve 109. The refrigeration required for liquefaction can be used as a driving force by expanding part of the compressed nitrogen gas in the first and second nitrogen expansion turbines 72, 72a.

[0042] (Example) 3 shows the results of a physical simulation of the nitrogen generating apparatus of the first embodiment. Feed air temperature 20.0℃, pressure 9.9 barA, flow rate 962Nm 3 / h from the warm end of the main heat exchanger 1, cooled to -163.3°C, and introduced into the first nitrogen rectification column 2. The first nitrogen rectification column 2 is equipped with a first nitrogen condenser 3 at its top 23 , which condenses the nitrogen gas at the top 23 and returns it to the top 23 of the first nitrogen rectification column 2 . Part of that liquid nitrogen 52Nm 3 / h is extracted and cooled to -179.2°C in the subcooler 6, and supplied to the top 43 of the second nitrogen rectification column 4. The nitrogen gas accumulated in the top 23 of the first nitrogen rectification column 2 is supplied as the first product nitrogen gas at a rate of 346 Nm 3 / h, heated to 19.0°C in the main heat exchanger 1, and discharged at a pressure of 9.6 barA. From the bottom 21 of the first nitrogen rectification column 2, 564 Nm of the first oxygen-enriched liquid having an oxygen concentration of 35.8% was discharged. 3 / h, is cooled to −168.8° C. in a subcooler 6, and then introduced into the middle of the second nitrogen rectification column 4.

[0043] The second nitrogen rectification column 4 is provided with a second nitrogen condenser 5 at its top 43, which condenses the nitrogen gas at the top 43 and returns it to the top 43 of the second nitrogen rectification column 4. The nitrogen gas accumulated at the top 43 of the second nitrogen rectification column 4 is condensed into 349 Nm3 as second product nitrogen gas. 3 / h, and after cooling the subcooler 6, it is heated to 19.0°C in the main heat exchanger 1 and discharged at a pressure of 4.1 barA. From the bottom of the second nitrogen rectification column 4 (the refrigerant reservoir 31 of the first nitrogen condenser 3), 267 Nm of the second oxygen-enriched liquid having an oxygen concentration of 75.5% was extracted. 3 / h, is cooled to -179.2°C in the subcooler 6, and then introduced into the low-temperature side (refrigerant reservoir 51) of the second nitrogen condenser 5. The second oxygen-enriched liquid is evaporated in the second nitrogen condenser 5 to become a second oxygen-enriched gas, which cools the subcooler 6, is heated to 19.0°C in the main heat exchanger 1, and is then discharged at a pressure of 1.2 barA. 70Nm of the first product nitrogen gas 3 / h is boosted to 14.6 barA in the first nitrogen booster 71, cooled to 35.0°C in the cooling device 8 (aftercooler), and then introduced into the warm end of the main heat exchanger 1, cooled to -78.4°C, expanded to 4.2 barA in the first nitrogen expansion turbine 72, and cooled to -129.6°C before being introduced into the main heat exchanger 1. This expanded nitrogen gas is combined with the second product nitrogen gas and then discharged from the main heat exchanger 1.

[0044] In the configuration of the first nitrogen booster turbine 7, 1.21 kW of refrigeration can be generated by the first nitrogen expansion turbine 71. In the prior art, to generate the same amount of refrigeration, the first product nitrogen gas would need to be expanded to 109 Nm 3 / h and had to be extracted at a temperature of -96.8°C before being expanded. In other words, the amount of product nitrogen gas expanded to generate refrigeration was reduced by 35.8% in this example. This also reduced the power required for recompression in the nitrogen compressor (reducing the number of nitrogen compressors).

[0045] (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. (4) In the first and second embodiments, the main heat exchanger 1 and the subcooler 6 are configured to be connected to each other, but this is not limitative and they may be configured as separate, physically separated units. (5) In the third embodiment, the main heat exchanger 1 and the subcooler 6 are not connected to each other. However, the present invention is not limited to this and they may be connected to each other as in the first and second embodiments. [Explanation of symbols]

[0046] 1 heat exchanger 2. First nitrogen rectification column 3. First nitrogen condenser 4. Second nitrogen rectification column 5 Second nitrogen condenser 6 Subcooler 71 First Nitrogen Booster 72 First nitrogen expansion turbine 8 Cooling device 9. Second oxygen-enriched gas expansion turbine

Claims

1. A method for producing nitrogen using a nitrogen generation apparatus including a main heat exchanger, a first nitrogen rectification column, a first nitrogen condenser, a second nitrogen rectification column, a second nitrogen condenser, a first nitrogen booster, a first nitrogen expansion turbine, and a cooling device, a step of introducing a portion of the first nitrogen gas discharged from the top of the first nitrogen rectification column into a main heat exchanger, and at least a portion of the discharged first product nitrogen gas is pressurized in a first nitrogen booster, cooled in a cooling device, and then reintroduced from the warm end of the main heat exchanger, discharged from the middle of the main heat exchanger, and expanded and cooled in a first nitrogen expansion turbine; Nitrogen production methods.

2. the second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser is passed through a subcooler, introduced into the main heat exchanger, and discharged from an intermediate section thereof, followed by expanding and cooling in a second oxygen-enriched gas expansion turbine; the expanded and cooled second oxygen-enriched gas is then reintroduced into the main heat exchanger and discharged from a warm end thereof as waste gas; The method for producing nitrogen according to claim 1.

3. A nitrogen generation system comprising a main heat exchanger, a first nitrogen rectification column, a first nitrogen condenser, a second nitrogen rectification column, a second nitrogen condenser, a first nitrogen booster, a first nitrogen expansion turbine, and a cooling device, The first nitrogen booster is configured such that a portion of the first nitrogen gas discharged from the top of the first nitrogen rectification column is introduced into a main heat exchanger to boost the pressure of at least a portion of the first product nitrogen gas discharged from a warm end; The cooling device cools the first product nitrogen gas pressurized by the first nitrogen booster to a predetermined temperature, the first nitrogen expansion turbine expands and cools the first product nitrogen, which is cooled by the cooling device and then reintroduced from the warm end of the main heat exchanger and discharged from the middle of the main heat exchanger; Nitrogen generator.

4. a main heat exchanger into which feed air is introduced via a feed air line; a first nitrogen rectification column into which the feed air that has been heat exchanged in the main heat exchanger is introduced via a feed air line; a first nitrogen condenser that condenses the first nitrogen gas discharged from the first nitrogen rectification column and returns the condensed first nitrogen gas to the first nitrogen rectification column as a reflux liquid; a first product nitrogen gas line through which the first nitrogen gas discharged from the first nitrogen rectification column is taken out as first product nitrogen through at least the main heat exchanger; a first product nitrogen branch line branching off from the first product nitrogen gas line at a position downstream of the warm end of the main heat exchanger; a first nitrogen booster provided in the first product nitrogen branch line and configured to increase the pressure of the first product nitrogen; a cooling device provided in the first product nitrogen branch line for cooling the first product nitrogen pressurized by the first nitrogen booster to a predetermined temperature; a first nitrogen expansion turbine that introduces the first product nitrogen gas cooled by the cooling device into a warm end of the main heat exchanger, discharges the first product nitrogen gas from an intermediate section, and expands and cools the first product nitrogen gas; a second nitrogen rectification column into which the vapor stream from the first nitrogen condenser is introduced; a second nitrogen condenser for condensing the second nitrogen gas discharged from the top of the second nitrogen rectification column and returning the condensed second nitrogen gas to the second nitrogen rectification column as reflux; a second product nitrogen gas line through which the second nitrogen gas discharged from the second nitrogen rectification column is introduced into at least the cold end of the main heat exchanger, discharged from the warm end, and taken out as second product nitrogen; Equipped with Nitrogen generator.

5. a subcooler coupled to the main heat exchanger or separate from the main heat exchanger; a first oxygen-enriched liquid line for introducing the first oxygen-enriched liquid discharged from the first nitrogen rectification column into the second nitrogen rectification column via the subcooler; a first liquefied nitrogen line for introducing the first liquefied nitrogen condensed in the first nitrogen condenser into the second nitrogen rectification column via the subcooler; a second oxygen-enriched liquid line that introduces the second oxygen-enriched liquid discharged from the refrigerant reservoir of the first nitrogen condenser into the refrigerant reservoir of the second nitrogen condenser via the subcooler; a first waste gas line for discharging a second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser, cooled through the subcooler, and then discharging the second oxygen-enriched gas as a waste gas through the main heat exchanger; Equipped with The nitrogen generator according to claim 4.

6. a subcooler coupled to the main heat exchanger or separate from the main heat exchanger; a first oxygen-enriched liquid line for introducing the first oxygen-enriched liquid discharged from the first nitrogen rectification column into the second nitrogen rectification column via the subcooler; a first liquefied nitrogen line for introducing the first liquefied nitrogen condensed in the first nitrogen condenser into the second nitrogen rectification column via the subcooler; a second oxygen-enriched liquid line that introduces the second oxygen-enriched liquid discharged from the refrigerant reservoir of the first nitrogen condenser into the refrigerant reservoir of the second nitrogen condenser via the subcooler; a second waste gas line through which the second oxygen-enriched gas discharged from the gas phase of the second nitrogen condenser is passed through the subcooler, introduced into the main heat exchanger, discharged from an intermediate section, and expanded and cooled in a second oxygen-enriched gas expansion turbine, and the expanded and cooled second oxygen-enriched gas is reintroduced into the main heat exchanger and discharged from a warm end as waste gas; The nitrogen generator according to claim 4.

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