JP4150107B2 - Nitrogen production method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for producing nitrogen, and more particularly, a method and apparatus for producing nitrogen that separates nitrogen gas by introducing compressed, purified, and cooled raw material air into a main distillation column and performs low-temperature distillation to collect the product as a product. About.
[0002]
[Prior art and problems to be solved by the invention]
In a nitrogen production system that collects nitrogen gas by low-temperature distillation of raw material air, it is an important technical issue to reduce the production unit of nitrogen while suppressing an increase in equipment, and various methods have been proposed in the past. Has been. As one process for solving this technical problem, a nitrogen production process described in JP-A-3-137484 is known. FIG. 2 shows a system diagram of the nitrogen production process described in the publication. Hereinafter, the procedure for producing nitrogen by the above process will be described with reference to FIG.
[0003]
Feed air introduced from the path 11, the raw material air compressor 1 10kg ^/ cm 2 abs. After being compressed to the extent, it is cooled by the aftercooler 1a. This raw material air is introduced into a pretreatment facility 2 filled with molecular sieves and the like, and impurities such as carbon dioxide and moisture are adsorbed and removed for purification. The refined raw material air passes through the path 12 and is exchanged with the product nitrogen gas and oxygen-enriched air, which will be described later, in the main heat exchanger 3 and cooled to near the dew point temperature. 4 is introduced at the bottom.
[0004]
In the distillation tower 4, low temperature distillation is performed by gas-liquid contact between the gas rising in the tower and the liquid condensed and liquefied by the reboiler / condenser 5 at the top and descending in the tower, and nitrogen gas is sent from the top to the bottom. Each oxygen enriched liquefied air is withdrawn.
[0005]
A part of the nitrogen gas extracted from the top of the tower to the path 14 is heated through the path 16, the supercooler 6, the path 17, and the main heat exchanger 3, and recovered from the path 18 as product nitrogen gas GN. The The remaining nitrogen gas is condensed and liquefied by the reboiler / condenser 5, passes through the path 15, and returned to the distillation column 4 as a reflux liquid.
[0006]
The oxygen-enriched liquefied air extracted from the bottom of the distillation column 4 to the path 19 is cooled by the supercooler 6, then depressurized by the pressure reducing valve 20 a through the path 20, and then passed through the path 21. Then, it is introduced into the reboiler / condenser 5 and vaporized by heat exchange with the nitrogen gas to become oxygen-enriched air. The vaporization pressure at this time is adjusted by the pressure reducing valve 20a so that the temperature difference with the nitrogen gas in the reboiler / condenser 5 is appropriate. The oxygen-enriched air generated in the reboiler / condenser 5 passes through the path 22, is heated by the supercooler 6, and then is branched into two through the path 23. The oxygen-enriched air branched into one path 24 is heated in the main heat exchanger 3 and then introduced into the expansion turbine 8 through the path 25 to expand and generate cold. Cold is recovered by the main heat exchanger 3, becomes room temperature, and is extracted from the path 27 as waste gas WG. At least a part of the waste gas is used as a regeneration gas for the pretreatment facility 2 through the path 28.
[0007]
The oxygen-enriched air branched from the path 23 to the path 29 is compressed by the low-temperature compressor 9, passes through the path 30, is cooled by the main heat exchanger 3, and then passes through the path 31 to the lower part of the distillation column 4. It is circulated and introduced as rising gas in the tower.
[0008]
In this way, a part of the oxygen-enriched air is compressed by a part of the power of the expansion turbine 8 and circulated into the distillation column 4 to improve the nitrogen recovery rate. Further, a part of the power of the expansion turbine 8 is recovered by the power recovery device 10 and is discharged outside the cold box to generate cold.
[0009]
According to such a process, the oxygen-enriched liquefied air extracted from the bottom of the distillation column 4 is vaporized and recirculated and introduced into the lower portion of the distillation column 4 as oxygen-enriched air. Is higher than the oxygen concentration in the raw air. In order to vaporize such oxygen-enriched liquefied air by heat exchange with nitrogen gas by the condenser / reboiler 5, as described above, the pressure must be reduced by the pressure reducing valve 20a to a pressure at which the temperature difference becomes appropriate. Don't be. This vaporization pressure is related to the oxygen concentration in the liquid, and becomes a lower pressure as the oxygen concentration increases. Therefore, since the suction pressure of the low-temperature compressor 9 is lowered, the circulation amount of the oxygen-enriched air is reduced, and it cannot be said that the effect of reducing the nitrogen production basic unit is sufficiently achieved.
[0010]
As another method for improving the basic unit by improving the nitrogen recovery rate, a method described in US Pat. No. 4,848,996 is known. In this method, oxygen-enriched liquefied air extracted from the bottom of the main distillation column is introduced into the top of the auxiliary distillation column. The bottom of the auxiliary distillation column is thermally linked to the top of the main distillation column by a condenser reboiler, and heat exchange occurs between the nitrogen gas at the top of the main distillation column and the oxygen-enriched liquid at the bottom of the auxiliary distillation column. As a result, the nitrogen gas is condensed and supplied to the main distillation column as reflux, and the oxygen-enriched liquid is vaporized and rises in the auxiliary distillation column to be distilled. From the top of the auxiliary distillation column, a gas close to the air component at a pressure higher than the atmospheric pressure is extracted, and after collecting the cold, it is introduced into the intermediate stage of the raw material air compressor as a circulating gas, and the raw material introduced from the outside It is compressed with air and recirculated into the main distillation column.
[0011]
In this way, when all the source air necessary for air separation is compressed from the atmospheric pressure by recompressing and circulating a part of the raw material that has a higher pressure than atmospheric pressure and a component close to air Compared to the above, the production unit of nitrogen is reduced. However, the oxygen-enriched liquefied air extracted from the bottom of the main distillation column has an appropriate temperature difference between the oxygen-enriched liquid having a higher oxygen concentration and nitrogen gas in the condenser / reboiler at the bottom of the auxiliary distillation column. Thus, the pressure of the circulating gas extracted from the top of the auxiliary distillation column is reduced, the pressure of the gas to be circulated to the raw air compressor is reduced, and the circulating gas extracted from the auxiliary distillation column is reduced. Is heated to room temperature and then introduced into the raw air compressor, the pressure loss due to heat exchangers and piping increases, and the amount of circulation decreases accordingly, so the reduction in nitrogen production intensity is not sufficient. .
[0012]
Therefore, the present invention provides a nitrogen production method and apparatus that can suppress the increase in power of the entire process as much as possible and improve the nitrogen recovery rate and reduce the production unit of nitrogen under the condition that equipment is not added as much as possible. It is an object.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the nitrogen production method of the present invention introduces compressed, refined, and cooled raw material air into the main distillation column, performs low-temperature distillation, and separates it into oxygen-enriched liquefied air and nitrogen gas. In the nitrogen production method for collecting nitrogen gas as a product, a part of the oxygen-enriched liquefied air is vaporized by depressurizing and then exchanging heat with the nitrogen gas with a dry-type condenser / reboiler, and rising gas at the bottom of the auxiliary distillation column And the remainder of the oxygen-enriched liquefied air is decompressed and introduced into the top of the auxiliary distillation column as a reflux liquid , and separated into an oxygen-enriched liquid and a nitrogen-enriched gas by distillation in the auxiliary distillation tower. and, wherein the oxygen-enriched liquid to the product oxygen-enriched gas by vaporizing by heat exchange with condenser reboiler of the nitrogen gas and the dry type after decompression, inflating the resulting oxygen-enriched gas Both are characterized by circulating introduced into the main distillation column and compressing the nitrogen-enriched gas.
[0014]
Further, in the nitrogen production method of the present invention, the compressed nitrogen-enriched gas is introduced into the main distillation column from at least one theoretical plate above the introduction position of the raw air introduced into the main distillation column, or the nitrogen The enriched gas is mixed with the raw air before being introduced into the main distillation column. The temperature prior to compressing the nitrogen-enriched gas is in the range of up to the distillation temperature or et ambient temperature of the main distillation column, the oxygen-enriched liquefied air before reducing the pressure derives from the main distillation column And cooling with at least one of the nitrogen gas, the nitrogen-enriched gas, and the oxygen-enriched gas.
[0015]
Nitrogen producing apparatus of the present invention, compressed feed air, purified, the nitrogen producing apparatus for collecting nitrogen by cooling to a low temperature distillation, compression, and the main heat exchanger purified feed air to cooling and cooled A main distillation tower that separates raw material air into nitrogen gas and oxygen- enriched liquefied air by low-temperature distillation, and auxiliary distillation that separates the oxygen-enriched liquefied air into low-temperature distilled and oxygen-enriched liquid and nitrogen-enriched gas a path for introducing the tower, a part of the pre-hexane Mototomi of liquefied air as ascending vapor in the lower part of the auxiliary distillation column pressure was reduced and vaporized, the auxiliary distillation under reduced pressure the remaining portion of the oxygen-enriched liquefied air A path to be introduced as a reflux liquid at the top of the column, the nitrogen gas, the oxygen-enriched liquefied air, and the oxygen-enriched liquid are subjected to heat exchange, and the nitrogen gas is liquefied to produce a reflux liquid of the main distillation column. And oxygen-enriched liquefied air and oxygen-enriched liquid And condenser reboiler dry type for a driving turbine expanding the oxygen-enriched gas produced by vaporizing the oxygen-enriched liquid in the condenser reboiler to generate cold turbine and power generating cold and the nitrogen rich And a circulating compressor for compressing the chemical gas.
[0016]
In addition, the nitrogen producing apparatus of the present invention, the this at least one of said main distillation column and the auxiliary distillation column is packed distillation column, the previous SL condenser reboiler, as vaporizing said oxygen-enriched liquefied air, The oxygen-enriched liquid is divided into components that vaporize and is configured separately. Further, the circulating compressor is of a low temperature specification, and is configured to be coaxially connected to the cold turbine or the drive turbine.
[0017]
In addition, the nitrogen production apparatus of the present invention includes a raw material air introduction path for introducing compressed and purified raw material air to the main distillation column through the main heat exchanger, a pressure reducing valve and the condenser An ascending gas generation path connected to the lower part of the auxiliary distillation column via a reboiler, a reflux liquid introduction path connected to the upper part of the auxiliary distillation column from the lower part of the main distillation column via a pressure reducing valve, and the auxiliary distillation column An oxygen-enriched gas lead-out path connected to the cold turbine and the driving turbine through the main heat exchanger, the heat exchanger from the cold turbine and the driving turbine A nitrogen recovery gas that is led out through a reactor, and a nitrogen-enriched gas that passes through the circulating compressor from the upper part of the auxiliary distillation column and is connected to the lower part of the main distillation column through the main heat exchanger Characterized by comprising a ring introduction path, and wherein the nitrogen-enriched gas circulation introduction path is connected to a lower portion of said main distillation column joined to the feed air introduction path.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a system diagram showing an embodiment of the present invention. Hereinafter, the present invention will be described in more detail based on a process for producing nitrogen by the nitrogen production apparatus.
[0019]
First, the raw material air of 5692 Nm ³ / h passes through the path 61 and is 7.7 kg / cm ² abs. After being compressed to 40 ° C. by the aftercooler 51a, impurities such as carbon dioxide and moisture are adsorbed and removed by the pretreatment facility 52 and purified. The purified raw material air passes through the path 62, is cooled to near the dew point temperature by the main heat exchanger 53, and is then introduced into the lower portion of the main distillation column 54 through the path 63 constituting the raw material air introduction path.
[0020]
In the main distillation column 54, distillation is performed by gas-liquid contact between the gas rising in the column and the liquid condensed in the reboiler / condenser 55 at the top and descending in the column. The nitrogen concentration is from the top and the oxygen concentration is 36 from the bottom. % Oxygen enriched liquefied air is withdrawn.
[0021]
Of the nitrogen gas extracted into the channel 64 at the top of the column, 3000 Nm ³ / h branches to the channel 66 and is heated through the subcooler 56, the channel 67 and the main heat exchanger 53. This nitrogen gas passes through path 68 and is 7.3 kg / cm ² abs. , Extracted at 36 ° C. and recovered as product nitrogen gas GN having an oxygen concentration of 0.1 ppb or less.
[0022]
The remaining nitrogen gas in the path 64 is introduced into the reboiler / condenser 55 and exchanges heat with oxygen-enriched liquefied air extracted from the main distillation column 54 and oxygen-enriched solution extracted from the auxiliary distillation column 57 described later. As a result, the liquid is condensed and returned to the top of the main distillation column 54 from the path 65 as a reflux liquid.
[0023]
The 3844 Nm ³ / h oxygen-enriched liquefied air extracted from the bottom of the main distillation column 54 is cooled by the supercooler 56 through the path 69 and then branches from the path 70 into two paths. The 915 Nm ³ / h oxygen-enriched liquefied air branched into the path 71 constituting the ascending gas generation path is at a pressure (3.6 kg / cm ^{2) at} which an appropriate temperature difference is obtained from the nitrogen gas passing through the reboiler / condenser 55. abs.) is reduced by the pressure reducing valve 71a, and then introduced into the reboiler / condenser 55 through the path 72 and vaporized. This gas passes through the path 73 constituting the rising gas generation path, and is introduced as a rising gas to the lower part of the auxiliary distillation column 57. On the other hand, the oxygen-enriched liquefied air of 2929 Nm ³ / h branched to the path 74 constituting the reflux liquid introduction path after being led out of the supercooler 56 is depressurized to the pressure of the auxiliary distillation column 57 by the pressure reducing valve 74a, and the path 75 To the top of the auxiliary distillation column 57 as a reflux liquid.
[0024]
In the auxiliary distillation column 57, distillation with the rising gas and the reflux liquid is performed, and from the top of the column, a nitrogen-rich gas having a composition close to air of 1152 Nm ³ / h constitutes a route 76 constituting a nitrogen-rich gas circulation introduction route. The oxygen-enriched liquid containing 44% oxygen is extracted from the bottom of the column. The 2692 Nm ³ / h oxygen-enriched liquid extracted from the bottom of the auxiliary distillation column 57 passes through the path 80 and has a pressure (3.3 kg / cm ² abs.), the pressure is reduced by the pressure reducing valve 80a, and then introduced into the reboiler / condenser 55 through the path 81 and vaporized to become an oxygen-enriched gas.
[0025]
This oxygen-enriched gas passes through the path 82 constituting the oxygen-enriched gas lead-out path, is heated by the supercooler 56, and then is heated to -143 ° C by the main heat exchanger 53 through the path 83 To flow out to path 84, where it branches into two paths. The 1008 Nm 3 / h oxygen-enriched gas passing through one path 85 is 1.3 kg / cm 2 abs. The pressure is reduced to a path 86. On the other hand, the remaining oxygen-enriched gas branched into the path 87 is 1.3 kg / cm 2 abs. In the drive turbine 59 connected to the circulating compressor 60 described later. The pressure is then reduced to generate power and lead to the path 88. The oxygen-enriched gas in the path 86 and the path 88 merges into the path 89 constituting the cold recovery path, and the cold is recovered by exchanging heat with the raw air in the main heat exchanger 53, and the temperature is raised to 36 ° C. through the path 90 is withdrawn as waste gas WG, part of it is utilized for the reproduction of pre-treatment facility 52.
[0026]
A path 91 connecting the path 83 constituting the oxygen-enriched gas lead-out path on the introduction side of the cold turbine 58 and the drive turbine 59 and the path 89 constituting the cold recovery path on the lead-out side of the cold turbine 58 and the drive turbine 59. And the valve 91a allows all or part of the oxygen-enriched gas introduced into the turbines 58 and 59 to flow by bypassing the turbines 58 and 59, and when at least one of the turbines 58 and 59 stops, Used when adjusting the flow rate of at least one of the turbines 58 and 59 as required.
[0027]
The nitrogen-enriched gas as the circulating fluid extracted from the top of the auxiliary distillation column 57 to the path 76 constituting the nitrogen-enriched gas circulation introduction path is heated by the supercooler 56 and passes through the path 77 to be circulated and compressed. Compressed by machine 60. The compressed nitrogen-enriched gas passes through a path 78 constituting a nitrogen-enriched gas circulation introduction path, is cooled by the main heat exchanger 53, and then is circulated and introduced into the lower part of the main distillation column 54 through the path 79. The
[0028]
The low-temperature compressor 60 is coaxially connected to the drive turbine 59 described above, and is driven using the power generated by the drive turbine 59.
[0029]
As described above, according to the present embodiment, the nitrogen-enriched gas having a lower oxygen content than the conventional process shown in FIG. 2 is circulated and introduced into the main distillation column 54. The oxygen content in the oxygen-enriched liquefied air extracted is also reduced. Accordingly, when the oxygen-enriched liquefied air is vaporized by the reboiler / condenser 55, the vaporization pressure can be increased by about 0.3 kg / cm ² because the oxygen content is small. As a result, the pressure of the circulating fluid can be made higher than the pressure of the oxygen-enriched gas passing through the path 82 constituting the oxygen-enriched gas lead-out path, and the suction pressure of the nitrogen-enriched gas introduced into the low-temperature compressor 60 is also increased. Since it can be increased, the compression ratio of the circulating compressor 60 can be reduced, the flow rate of the circulating fluid circulated and introduced into the main distillation column 54 can be increased, and the production unit of nitrogen can be reduced.
[0030]
That is, the inlet pressure of the circulating compressor 60 depends on the vaporization pressure in the reboiler / condenser 55 of the fluid introduced therein. This pressure is determined so that the temperature difference from the nitrogen gas through the reboiler / condenser 55 is appropriate and depends on the composition of the fluid. That is, the oxygen-enriched liquefied air extracted from the bottom of the main distillation column 54 has a lower oxygen concentration than that of the oxygen-enriched liquid extracted from the bottom of the auxiliary distillation column 57, and therefore is used when vaporizing with the reboiler / condenser 55. The pressure can be increased. Further, since this vaporized gas is introduced into the auxiliary distillation column 57, the pressure of the circulating fluid extracted from the top of the auxiliary distillation column 57 can be increased. Moreover, since the circulating compressor 60 is driven by the drive turbine 59, the intake amount increases as the inlet pressure increases. This leads to an increase in the circulation rate, and the amount of ascending gas and the amount of descending liquid in the main distillation column 54 is increased. As a result, the product nitrogen recovery rate is increased, and the production unit of nitrogen can be reduced.
[0031]
The condenser reboiler 55 in this embodiment is not a liquid immersion type but a dry type. As in this example, if there are two cold fluids and an immersion condenser reboiler is used, it is necessary to immerse the condenser reboiler in the liquid of the cold fluid, so two condenser reboilers must be installed. Is essential. However, in the case of the dry type, since it is not necessary to immerse in the liquid, it is possible to easily integrate by configuring the flow path of the cold fluid into two flow paths. However, the condenser reboiler 55 may be configured separately from one that vaporizes the oxygen-enriched liquefied air from the main distillation column 54 and one that vaporizes the oxygen-enriched liquid from the auxiliary distillation column 57. Furthermore, in the case of the liquid immersion type, the liquid on the vaporization side is supercooled by the liquid head, and the vaporization pressure must be lowered accordingly, but in the case of the dry type, this is not the case. Can be increased. Furthermore, since the amount of liquid retained is smaller than that of the liquid immersion type, there is an effect of shortening the startup time of the apparatus.
[0032]
In this embodiment, since the nitrogen concentration in the nitrogen-enriched gas extracted from the top of the auxiliary distillation column 57 can be made higher than the nitrogen concentration in the air by the distillation in the auxiliary distillation column 57, this is compressed and circulated to the main distillation column 54. At the time of introduction, it is desirable to supply the rectifying stage of the rising gas in the column having the same composition as the circulating fluid, that is, to supply at least one equilibrium stage, preferably four equilibrium stages, from the feed stage of the feed air. The circulating fluid led out from the circulating compressor 60 to the path 78 may be merged with the raw air in the raw air introduction passage of the main heat exchanger 53. Thereby, since the flow path of the circulating fluid and the flow path of the main heat exchanger 53 can be reduced, the equipment cost can be reduced.
[0033]
In addition, before reducing the pressure of the oxygen-enriched liquefied air extracted from the main distillation column 54, in the supercooler 56, the nitrogen gas from the main distillation column 54, the nitrogen-enriched gas from the auxiliary distillation column 57, and the condenser reboiler 55 are used. By subcooling with the oxygen-enriched gas, the temperature as the cooling source in the condenser reboiler 55 can be lowered, and the flash loss due to the reduced pressure of the reflux liquid introduced into the auxiliary distillation column 57 from the path 75 can be reduced. The rectification efficiency in the auxiliary distillation column 57 can be increased.
[0034]
Further, the compression of the circulating gas in the circulating compressor 60 may be performed at a low temperature distillation temperature as shown in the present embodiment, or the temperature is increased to an appropriate temperature by the main heat exchanger 53 and then compressed. The temperature between the distillation low temperature level and room temperature can be arbitrarily selected according to the design conditions.
[0035]
Further, by using a packing material in at least one of the main distillation column 54 and the auxiliary distillation column 57, the pressure loss of the distillation column can be reduced, so that the nitrogen production unit can be further reduced.
[0036]
According to this embodiment, the nitrogen recovery rate can be about 53%, and the nitrogen power basic unit (the ratio of the total power to the product nitrogen flow rate) can be 0.247 kWh / Nm ³ . Compared with the conventional process of FIG. 2 where the calculation is performed under the same conditions, the power consumption can be reduced by 0.02 kWh / Nm ³ .
[0037]
【The invention's effect】
As described above, according to the present invention, the nitrogen concentration of the circulating gas can be increased by distillation in the auxiliary distillation column, and the amount of gas circulated to the main distillation column can be increased by improving the composition of each gas-liquid. Further, it is possible to improve the nitrogen recovery rate while suppressing the increase in power as much as possible, and to reduce the production unit of nitrogen.
[Brief description of the drawings]
FIG. 1 is a system diagram of a nitrogen production apparatus showing an embodiment of the present invention.
FIG. 2 is a system diagram showing an example of a conventional process.
[Explanation of symbols]
51 ... Raw air compressor, 52 ... Pretreatment equipment, 53 ... Main heat exchanger, 54 ... Main distillation tower, 55 ... Reboiler / condenser, 56 ... Supercooler, 57 ... Auxiliary distillation tower, 58 ... Cold turbine, 59 ... Drive turbine, 60 ... Circulating compressor

Claims (12)

In the nitrogen production method in which the compressed, purified and cooled raw material air is introduced into the main distillation column and subjected to low-temperature distillation, and separated into oxygen-enriched liquefied air and nitrogen gas, and separated nitrogen gas is collected as a product. A part of the liquefied air is decompressed and heat-exchanged with the nitrogen gas and dry type condenser / reboiler to be vaporized and introduced into the lower part of the auxiliary distillation column as a rising gas, and the remaining oxygen-enriched liquefied air is decompressed. And introduced into the top of the auxiliary distillation column as a reflux liquid , and separated into an oxygen-enriched liquid and a nitrogen-enriched gas by distillation in the auxiliary distillation tower, and the oxygen-enriched liquid is dried with the nitrogen gas after drying. the oxygen-enriched gas generated by vaporizing by heat exchange type condenser-reboiler, with inflating the resulting oxygen-enriched gas, said main distillation column by compressing the nitrogen-enriched gas Nitrogen producing method characterized by circulating introduced.   2. The method for producing nitrogen according to claim 1, wherein the compressed nitrogen-enriched gas is introduced into the main distillation column from at least one theoretical stage from the introduction position of the raw air introduced into the main distillation column.   The nitrogen production method according to claim 1, wherein the compressed nitrogen-enriched gas is mixed with raw air before being introduced into the main distillation column. The temperature prior to compressing the nitrogen-rich gas, nitrogen method according to claim 1, wherein the range up to the distillation temperature or et ambient temperature of the main distillation column.   The oxygen-enriched liquefied air that has been led out from the main distillation column and before being depressurized is cooled with at least one of the nitrogen gas, the nitrogen-enriched gas, and the oxygen-enriched gas. The method for producing nitrogen according to 1. Compressed feed air, purified, the nitrogen producing apparatus for collecting nitrogen by cooling to a low temperature distillation, compression, purified feed air and a main heat exchanger for cooling, the cooled feed air to cryogenic distillation nitrogen a main distillation column is separated into a gas and the oxygen-enriched liquefied air, and an auxiliary distillation column for separating the oxygen-enriched liquid and nitrogen-enriched gas the oxygen-enriched liquefied air by cryogenic distillation, prior hexane Mototomi A part of the liquefied liquefied air is decompressed and vaporized and then introduced into the lower part of the auxiliary distillation column as a rising gas, and the remainder of the oxygen-enriched liquefied air is decompressed and introduced to the top of the auxiliary distillation tower as a reflux liquid. Heat exchange between the nitrogen gas, the oxygen-enriched liquefied air and the oxygen-enriched liquid, and liquefying the nitrogen gas to produce a reflux liquid of the main distillation tower, and oxygen-enriched liquefied air and dry-type configuration vaporizing oxygen-enriched liquid Sensor reboiler, a cold turbine that generates cold by expanding the oxygen-enriched gas generated by vaporizing the oxygen-enriched liquid in the condenser reboiler, and a drive turbine that generates power, and compressing the nitrogen-enriched gas A nitrogen production apparatus comprising a circulating compressor.   The nitrogen production apparatus according to claim 6, wherein at least one of the main distillation column and the auxiliary distillation column is a packed distillation column.   The nitrogen production according to claim 6, wherein the condenser reboiler is configured to be separately divided into one that vaporizes the oxygen-enriched liquefied air and one that evaporates the oxygen-enriched liquid. apparatus.   7. The nitrogen production apparatus according to claim 6, wherein the circulating compressor is of a low temperature specification.   The nitrogen production apparatus according to claim 6, wherein the circulating compressor is configured to be coaxially connected to the cold turbine or the driving turbine.   Connected to the lower part of the auxiliary distillation column via the pressure reducing valve and the condenser reboiler from the lower part of the main distillation column, the raw material air introduction path for leading the compressed and purified raw material air to the main distillation column through the main heat exchanger The ascending gas generation path, a reflux liquid introduction path connected to the upper part of the auxiliary distillation column from the lower part of the main distillation column via the pressure reducing valve, and the condenser reboiler from the lower part of the auxiliary distillation column via the pressure reducing valve Passing through the main heat exchanger, the oxygen-enriched gas lead-out path connected to the cold turbine and the drive turbine, the cold recovery path led out from the cold turbine and the drive turbine via a heat exchanger, A nitrogen-enriched gas circulation introduction path that is connected to the lower part of the main distillation column through the main compressor and from the upper part of the auxiliary distillation column. Nitrogen producing apparatus according to claim 6, symptoms.   The nitrogen production apparatus according to claim 11, wherein the nitrogen-enriched gas circulation introduction path joins the raw material air introduction path and is connected to a lower portion of the main distillation column.

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