JPH11351740A - Method and system for producing high purity nitrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce high purity nitrogen in which content of low boiling point components, e.g. hydrogen, is reduced at high yield while suppressing increase of power. SOLUTION: The method for producing high purity nitrogen by subjecting material air to low temperature distillation in a single rectifying column 36 comprises a step for extracting a low boiling point components rich gas from the top of the single rectifying column 36 to a passage 41, a step for extracting high purity nitrogen gas from a part several stages below the top of the single rectifying column 36 to a passage 37, a step for extracting oxygen rich gas from the lower part of the single rectifying column 36 to a passage 48 and reducing the pressure thereof, and a step for liquefying the low boiling point components rich gas and/or the high purity nitrogen gas through heat exchange thereof with the oxygen rich gas in a condenser/evaporator 46 to produce descending liquid of the single rectifying column 36 and producing waste gas by liquefying the oxygen rich gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing high-purity nitrogen. More specifically, the present invention relates to a method and apparatus for producing high-purity nitrogen having a low content of low-boiling components such as hydrogen required in a semiconductor production process. The present invention relates to a high-purity nitrogen production method and apparatus for efficiently producing a high-purity nitrogen with a small increase.

[0002]

2. Description of the Related Art As a method for industrially producing nitrogen, there are many air liquefaction separation methods in which air is used as a raw material, which is compressed, refined, cooled and liquefied, and the composition is distilled at a low temperature by utilizing a boiling point difference. Has been adopted. A nitrogen production apparatus having a single single rectification column utilizing this method has been put to practical use, and the produced nitrogen is used in various industries. In particular, in the semiconductor industry, there is a great demand for high-purity nitrogen having a low boiling point component concentration of ppb order. Low boiling components are hydrogen,
It is a component that has a lower boiling point than nitrogen, such as helium and neon, and is concentrated in nitrogen by low-temperature distillation. Of these, hydrogen is a highly reactive component and must be removed from high-purity nitrogen. There is. Also, carbon monoxide is
Since its boiling point is close to that of nitrogen, it is difficult to separate by low-temperature distillation, and most of it is concentrated in nitrogen. Therefore, it is desirable to remove it before the low-temperature distillation.

[0003] Hydrogen is contained in the raw material air at about several ppm, but by using an oxidation catalyst and an adsorbent, p is reduced.
It can be removed to a trace amount on the order of pb. However, when nitrogen gas is separated by low-temperature distillation, a small amount of hydrogen remaining on the order of ppb in the raw material air is more easily volatilized than nitrogen, and thus accumulates in the nitrogen gas above the single rectification column. It is concentrated more than the concentration in the raw air introduced into the furnace. For example, assuming that the yield of product nitrogen is 50%, the hydrogen in the product nitrogen is concentrated to about twice the concentration in the raw air.

As a process for preventing the concentration of low-boiling components such as hydrogen in nitrogen as described above, a process having the configuration shown in FIG. 8 is known (see Japanese Patent Publication No. 4-12391). In this process, the compressed raw air compressed by the raw air compressor 1 is introduced into the adsorber 2, from which carbon dioxide gas, moisture and the like are removed, and then introduced into the main heat exchanger 4 via the path 3. Where it is cooled to a temperature close to the dew point of the compressed air by performing heat exchange with the cold return gas,
It is introduced into the bottom of the single rectification column 6 via the path 5.

In the single rectification column 6, the introduced air is subjected to low-temperature distillation by utilizing the boiling point difference of the composition, and as the single rectification column 6 moves upward, low boiling components such as nitrogen and hydrogen are reduced. As the boiling point components increase, the concentration of the low boiling point components reaches the maximum concentration at the top of the column. The overhead gas having a large amount of low-boiling components such as hydrogen is extracted to a path 7, and a small amount of the overhead gas is branched to a path 8 as a purge gas, and the temperature is increased by a subcooler 9 or a main heat exchanger 4. After that, it is discharged from the path 10. The remaining overhead gas is introduced into the condensing evaporator 12 from the path 11 and condensed.
After liquefaction, it is refluxed to the top of the single rectification column 6 and becomes a descending liquid in the column.

The descending liquid in the single rectification column 6 is subjected to low-temperature distillation to remove low-boiling components such as hydrogen to a predetermined concentration, and a part thereof is converted into liquefied nitrogen having a low low-boiling component such as hydrogen. 6 is withdrawn from a path 13 connected to the rectification stage part several stages below the top, decompressed by a valve 14, vaporized in a condensing evaporator 12, and cooled by a supercooler 9 or a main heat exchanger 4. The temperature rises,
It is withdrawn from line 15 as product nitrogen gas.

As the remaining descending liquid descends in the single rectification column 6, the oxygen concentration increases by low-temperature distillation, and the oxygen concentration reaches the maximum concentration at the bottom of the column. The oxygen-enriched liquid at the bottom of the column, which is rich in oxygen, is introduced into the subcooler 9 through the path 16, is supercooled, is depressurized by the valve 17, and its boiling point is lowered. It is used as a cold source to liquefy the top gas and vaporizes itself as waste gas. This waste gas is heated in the subcooler 9 and the main heat exchanger 4 via the path 18, is introduced into the expansion turbine 20 via the path 19, expands and cools down, and returns to the main heat exchanger 4 again. After being introduced and collecting the cold, it is discharged from the path 21. An energy discharge mechanism 22 for cooling the inside of the system is attached to the expansion turbine 20.

[0008]

In the above-described process, when the hydrogen content in the product nitrogen gas is introduced into the single rectification column 6 when the hydrogen concentration in the raw air is about 1.0 ppm, for example, It is removed to about 40 ppb by distillation. However, in order to vaporize liquefied nitrogen having a low boiling point component such as hydrogen extracted from the passage 13 and obtain it as product nitrogen gas, the product nitrogen gas is vaporized by heat exchange with a top gas having a similar composition and saturation temperature. I have to do. For this reason, the liquefied nitrogen extracted from the single rectification column 6 is reduced to a pressure at which it can be vaporized by the valve 14 in order to provide a saturation temperature difference with the top gas.

Therefore, the pressure of the obtained product nitrogen gas is reduced by the reduced pressure, and it is necessary to recompress the pressure to the required pressure of the place of use. Therefore, a large power loss due to the reduced pressure is inevitable, and the power consumption is reduced. There was a problem of becoming relatively large.

Accordingly, the present invention provides a high-purity nitrogen production method and apparatus capable of producing high-purity nitrogen that suppresses an increase in power and has a high yield and a low content of low-boiling components such as hydrogen. It is intended to be.

[0011]

According to a first aspect of the present invention, there is provided a method for producing high-purity nitrogen, wherein compressed, purified and cooled raw material air is introduced into a single rectification column to reduce the temperature. By distillation, in a high-purity nitrogen production method of collecting high-purity nitrogen, a step of extracting low-boiling component-enriched gas from the top of the single rectification column, and several stages below the top of the single rectification column A step of extracting high-purity nitrogen gas having a low boiling point component from the rectification stage, a step of extracting an oxygen-enriched liquid from a lower portion of the single rectification column, and reducing the pressure; and a step of extracting the low-boiling-point-enriched gas and / or By performing heat exchange between the high-purity nitrogen gas and the oxygen-enriched liquid after the pressure reduction, a low-boiling component-enriched gas and / or
Or liquefying high-purity nitrogen gas to generate a descending liquid of the single rectification column, and vaporizing the oxygen-enriched liquid to generate waste gas.

A second configuration of the method of the present invention includes a step of extracting a low-boiling component-enriched gas from the top of the single rectification column,
A step of extracting high-purity nitrogen gas having a low boiling point component from the rectification stage several stages below the top of the single rectification column, and a step of extracting an oxygen-enriched liquid from the lower portion of the single rectification column and reducing the pressure. Heat-exchanging the low-boiling component-enriched gas and / or the high-purity nitrogen gas with the oxygen-enriched liquid after the pressure reduction to liquefy the low-boiling component-enriched gas and / or the high-purity nitrogen gas, A step of generating a descending liquid in the single rectification column, a step of vaporizing the oxygen-enriched liquid to generate a circulating gas and a waste gas, and a step of lowering the boiling point from the first or second step of liquefying the low-boiling component-enriched gas. A step of extracting a part of the component-enriched gas as a purge gas, a step of generating power and cold by expanding the waste gas, and a step of compressing the circulating gas and reintroducing it into the single rectification column. It is characterized by having.

Further, the method of the present invention is characterized in that, in the above-mentioned structure, carbon monoxide and hydrogen in the raw material air are removed and then introduced into a single rectification column, and the low-boiling component-enriched gas is liquefied. The obtained liquid is subjected to gas-liquid separation, and the separated liquid is refluxed to the top of the single rectification column, and the separated gas is withdrawn as a purge gas.A part of the waste gas is expanded at an intermediate temperature. A power is generated, at least a part of the remaining part of the waste gas is heated to room temperature, compressed at room temperature, expanded after re-cooling and expanded to generate cold, and the circulating gas is compressed at low temperature and re-cooled to form the unit. Re-introducing into the rectification column, compressing the circulating gas at a low temperature to a primary pressure, raising the temperature to room temperature, compressing the room temperature to a secondary pressure, re-cooling, and re-introducing the single gas into the single rectification column. Compressing the waste gas and the circulating gas Performing using the power generated in the step of expanding the waste gas, performing the room temperature compression of the waste gas using the power obtained in the step of expanding the waste gas to generate cold, the circulating gas Low temperature compression is performed using the power obtained in the step of generating power by expanding the waste gas, and the room temperature compression of the circulating gas is obtained in the step of expanding the waste gas to generate cold. The method is characterized in that it is performed using power, and the purge gas is used as a seal gas for bearing of a turbine or a bearing gas for expanding the waste gas.

Further, the high-purity nitrogen producing apparatus of the present invention comprises, as a first configuration, a high-purity nitrogen for collecting high-purity nitrogen by subjecting compressed, purified and cooled raw material air to low-temperature distillation in a single rectification column. In the manufacturing apparatus, a main heat exchanger for cooling the raw material air by heat exchange with the low-temperature return gas obtained by the low-temperature distillation, and a low-boiling component-enriched gas and a low-boiling component of the cooled raw air by cryogenic distillation. A single rectification column that separates a small amount of high-purity nitrogen gas and an oxygen-enriched liquid, a condensing evaporator that performs heat exchange between the low-boiling component-enriched gas and / or high-purity nitrogen gas and the oxygen-enriched liquid, An expansion turbine that expands waste gas generated by vaporization of the oxygen-enriched liquid in the condensing evaporator to generate cold, and withdraws the low-boiling component-enriched gas from the top of the single rectification column. Liquefying through the condensing evaporator, The low-boiling component-enriched fluid reflux path and / or the high-purity nitrogen gas returned to the top of the rectification column is withdrawn from the top of the single rectification column, liquefied through the condensation evaporator, and liquefied through the top of the single rectification column. A high-purity nitrogen reflux path returning to a position between the tops, and the condensing evaporator from the top of the single rectification column or the low-boiling component-enriched fluid reflux path as part of the low-boiling component-enriched gas as a purge gas. A purge gas path which is taken out from the upstream or downstream of the rectifier and led out through the main heat exchanger, and the condensation and evaporation of the high-purity nitrogen gas as product nitrogen gas from the top of the single rectification column or the high-purity nitrogen reflux path. A product sampling path derived from the upstream of the vessel through the main heat exchanger, and an oxygen-enriched liquid extracted from the bottom of the single rectification column through the main heat exchanger, and led to the condensing evaporator via a pressure reducing valve. Withdrawal route and withdrawal of the oxygen-enriched liquid A waste gas path that is connected to the path and guides the waste gas to the expansion turbine through the main heat exchanger; and a cold recovery path that guides the waste gas expanded and cooled by the expansion turbine through the main heat exchanger. It is characterized by having.

Further, in a second configuration of the apparatus according to the present invention, in addition to the main heat exchanger, the single rectification column, and the condensing evaporator, the condensing evaporator vaporizes the oxygen-enriched liquid. A cold turbine that expands at least a part of the remaining waste gas to generate power by expanding at least a part of the waste gas generated at the condensing evaporator; A low-temperature compressor that compresses a circulating gas produced by vaporization of the liquid at a low temperature, and withdraws the low-boiling-point component-enriched gas from the top of the single rectification column, liquefies it through the condensation evaporator, The low-boiling component-enriched fluid reflux path and / or the high-purity nitrogen gas returned to the top of the rectification column is withdrawn from the top of the single rectification column, liquefied through the condensation evaporator, and liquefied through the top of the single rectification column. A high-purity nitrogen reflux path returning to a position between the tops; A part of the low-boiling component-enriched gas is removed as a purge gas from the top of the single rectification column or from the upstream or downstream of the condensing evaporator in the low-boiling component-enriched fluid reflux path, and the main heat exchanger is removed. And a product derived through the main heat exchanger from the top of the single rectification column or from the upstream of the condensing evaporator in the high-purity nitrogen recirculation path as a high-purity nitrogen gas as product nitrogen gas. A sampling path, an oxygen-enriched liquid extraction path for extracting the oxygen-enriched liquid from the lower portion including the bottom of the single rectification column, and leading the oxygen-enriched liquid to the condensing evaporator via a pressure reducing valve; A waste gas path connected to the outlet path and leading the waste gas to the cold turbine and the drive turbine through the main heat exchanger; and a cold path leading the waste gas expanded by the cold turbine and the drive turbine through the main heat exchanger. Times Path, connected to the oxygen-enriched liquid extraction path, a circulating gas extraction path that guides the circulating gas to the low-temperature compressor, And a circulating gas re-introduction path.

Further, in the apparatus according to the present invention, the condensing evaporator is a dry type heat exchanger in the above-mentioned structure, and is constituted integrally or a block for liquefying a gas having a low boiling point component and a high-purity nitrogen gas. It is configured separately with a block that liquefies, or is separately configured with a block that generates the waste gas and a block that generates the circulating gas, and compresses the waste gas to be introduced into the cold turbine at room temperature. A waste gas compressor, wherein the waste gas path includes a path for guiding waste gas from the middle of the main heat exchanger to the drive turbine, and a path that branches off from the path and passes through the main heat exchanger. Again passing through the main heat exchanger via a gas compressor, being connected to the cold turbine, in place of the low temperature compressor, a primary compressor for compressing the circulating gas to a primary pressure at a low temperature, A secondary compressor for compressing the circulating gas, which has been cold-pressed by the secondary compressor, to a secondary pressure at room temperature, and wherein the circulating gas reintroduction path passes from the primary compressor through the main heat exchanger, and Passing through the main heat exchanger again through the next compressor, being connected to the lower part of the single rectification column, and the oxygen-enriched liquid discharging path is provided with the waste gas from the bottom of the single rectification column. It is characterized by being formed by a path leading to a path and a path leading from the lower part of the single rectification column to the circulation gas extraction path.

[0017]

FIG. 1 is a system diagram showing a first embodiment of the present invention. First, a pressure of 7.
6970 Nm ³ / h of raw air compressed to 6 bar
Is introduced into a purification facility 32 equipped with a catalyst device for adding hydrogen and carbon monoxide in the raw material air to water and carbon dioxide with a catalyst and an adsorption device for adsorbing and removing water and carbon dioxide. Most of carbon monoxide which cannot be removed, most of carbon dioxide gas and moisture are removed, and hydrogen is removed to about 0.1 ppb. The raw material air purified by the purification equipment 32 is introduced into a main heat exchanger 34 via a path 33, and performs heat exchange with various low-temperature return gases described later, so that the temperature -1 close to the dew point temperature of the raw material air.
After being cooled to 68 ° C., the single rectification
Introduced at the bottom.

The feed air introduced into the single rectification column 36 becomes an ascending gas that rises in the column, and low-temperature distillation while ascending the single rectification column 36 increases the nitrogen content, which is a low-boiling component, to increase the nitrogen content. It becomes a rich gas. Then, when reaching a position several steps below the top of the tower, 3000 Nm ³ / h of that part is extracted as a product nitrogen gas to a route 37 constituting a product sampling route.

In cryogenic distillation as described above, nitrogen is
Since the volatility is higher and the latent heat of vaporization is lower than that of oxygen, the rising gas that rises in the tower gradually increases the nitrogen content and the gas amount at the same time. The absolute amount of the low-boiling component of is hardly changed. Therefore, low boiling components such as hydrogen in the rising gas are
The concentration is gradually reduced by being gradually diluted in the rising ascending gas, and falls to about 0.093 ppb at the position of the passage 37 several stages below the top of the tower. That is, the concentration of low-boiling components such as hydrogen contained in the product nitrogen gas extracted to the passage 37 is 0.093 ppb, which is lower than the concentration in the raw material air of about 0.1 ppb.

As described above, the product nitrogen gas extracted from the point where the concentration of the low-boiling component such as hydrogen is minimized to the passage 37 is not depressurized, and is not depressurized.
After the temperature rises through the main heat exchanger 34, it is removed from the path 40.

The rising gas extracted as a part of the product is
Further, the low-boiling components such as hydrogen are further concentrated in the column, and the maximum concentration of the low-boiling components such as hydrogen is about 6.
A low-boiling component-enriched gas containing 7 ppb is produced. The low-boiling-point component-enriched gas is withdrawn from the top of the tower through a path 41, and a small portion 60Nm ³ / h of the gas is branched into a path 42 constituting a purge gas path, and is cooled by a subcooler 38, a path 43, and a main heat exchanger. The gas is discharged as a purge gas from a path 44 via the line.

Most of the low-boiling component-enriched gas in the path 41 is introduced into the condensing evaporator 46 from the path 45 and condensed and liquefied, thereby forming a low-boiling point component-enriched fluid recirculation path 47.
Is refluxed into the single rectification column 36 to form a descending liquid. This descending liquid is rectified with the rising nitrogen gas while descending the upper rectifying section 36a provided at several stages at the top of the tower,
Low boiling components such as hydrogen in the descending liquid are removed.

As the descending liquid descends through the main rectifying section 36b in the middle of the column, the high boiling component, oxygen, increases and the low boiling component decreases, and the low boiling component almost disappears at the bottom of the column. An oxygen-enriched liquid containing no oxygen and having an oxygen concentration of about 37.4% accumulates.

The oxygen-enriched liquid at the bottom of the single rectification column 36 is withdrawn from a path 48 constituting an oxygen-enriched liquid extraction path, is supercooled by a supercooler 38, and is cooled by a pressure reducing valve 49 to about 3 times. After the pressure has been reduced to 0.6 bar, it is introduced into the condensation evaporator 46 and
Heat exchange with the low-boiling-point component-enriched gas introduced from the reactor and evaporates into waste gas.

The generated waste gas passes through a path 50, a subcooler 38, and a path 51 constituting a waste gas path, and passes through the main heat exchanger 34.
After being heated to about −125 ° C.,
, And is introduced into the expansion turbine 53 and expanded to generate cold. The waste gas that has generated the cold is again introduced into the main heat exchanger 34 through a route 54 constituting a cold recovery route,
The cold is collected and discharged from the path 55. At this time,
The power generated by the expansion turbine 53 is dissipated by an energy discharge mechanism 56 attached to the turbine 53, thereby cooling the inside of the system. A path 58 having a valve 57 for adjusting the amount of waste gas introduced into the expansion turbine 53 is provided between the path 51 and the path 54.

Further, 30 Nm ³ / h of the purge gas flowing through the path 44 branches off from the path 44 to the path 59,
The gas is supplied as a bearing sealing gas for the shaft 60 of the expansion turbine 53, or as a bearing gas when the shaft 60 is a bearing.

The bearing seal gas or bearing gas of the expansion turbine 53 as described above needs to be dry and clean. Conventionally, a part of the product nitrogen gas was used. By using a dry and clean purge gas obtained as a by-product as shown in (1), redundant use of product nitrogen gas can be avoided.

As described above, in this embodiment, the product nitrogen gas is collected from the single rectification column 36 at the same pressure without reducing the pressure, so that the power loss due to the decompression of the nitrogen-rich liquid as in the prior art is obtained. Therefore, the power consumption rate is improved as compared with the conventional process.

Further, while a small portion of the low-boiling-point component-enriched gas is led out from the top of the column to the passage 42 as a purge gas,
Since the product nitrogen gas is extracted from the passage 37 several stages below the top of the column, low boiling components such as hydrogen are not concentrated in the product nitrogen gas, and the raw material introduced into the single rectification column 36 is not concentrated. It is possible to obtain high-purity product nitrogen gas having a low boiling point component and a low concentration equivalent to that in the air.

Further, hydrogen and carbon monoxide as impurities are removed from the raw air before the low-temperature distillation by the purification equipment 32 as a catalyst, and a low-boiling component such as hydrogen and a portion containing less carbon monoxide are also used in the low-temperature distillation. Since the product nitrogen is obtained from the above, it is possible to cover performance deterioration such as aging of the catalyst and the adsorbent of the purification equipment 32.

It is preferable to use a dry heat exchanger instead of the immersion type as the condensation evaporator 46. This dry heat exchanger has the advantages that the configuration is simple and the equipment cost can be reduced, the integration and the split configuration can be easily performed, and the start-up time can be shortened because the liquid holding amount is small.

FIG. 2 is a system diagram showing a second embodiment of the present invention. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, a part of the high-purity nitrogen gas having a low concentration of low-boiling components such as hydrogen extracted from the single rectification tower 36 through the passage 37 several stages below the top is transferred from the passage 37 to the passage 61. Into the condensing evaporator 46 and the condensing evaporator 4
After being condensed and liquefied by heat exchange with the oxygen-enriched liquid in step 6, the single rectification column 36 is passed through a path 62 constituting a high-purity nitrogen reflux path.
It is formed so as to be refluxed.

As described above, as the fluid for vaporizing the oxygen-enriched liquid in the condensation evaporator 46, the low-boiling component-enriched gas and the high-purity nitrogen gas extracted from the top of the tower to the passage 41 can be used in combination. Further, it is also possible to use only high-purity nitrogen gas.

The reflux position of the liquefied high-purity nitrogen gas (high-purity liquefied nitrogen) to the single rectification column 36 is a position between the connection position of the passage 37 for extracting the high-purity nitrogen gas and the top of the tower. It can be arbitrarily selected.

FIG. 3 is a system diagram showing a third embodiment of the present invention. In the first embodiment, a part of the waste gas discharged to the outside, that is, the oxygen-enriched gas A part of the gas in which the liquid has been vaporized is used as circulating gas, which is
6 to be recirculated.

The raw material air compressor 31 is compressed to a pressure of 7.6 bar, the purification equipment 32 removes most of water, carbon dioxide and carbon monoxide, and has a hydrogen content reduced to about 0.1 ppb. Raw material air 5915
Nm ³ / h is cooled down to −167 ° C. in the main heat exchanger 34, and then passes through a path 71 from the bottom of the single rectification column 36 to 5 m ³ / h.
It is introduced on the step. In addition, a circulating gas described later is also introduced into the bottom of the single rectification column 36.

Due to the low temperature distillation in the single rectification column 36, these introduced gases increase the nitrogen content, which is a low boiling point component, as the single rectification column 36 moves upward. Further, the liquid condensed in the condensing evaporator 46 becomes a descending liquid, and the liquid descending in the column increases the oxygen content which is a high boiling component as it descends in the column, and the concentration of the low boiling component decreases, An oxygen-enriched liquid having a maximum oxygen concentration of about 43.4% is stored at the bottom of the column as the concentration of low-boiling components such as hydrogen is on the order of nearly zero.

The oxygen-enriched liquid at the bottom of the single rectification column 36 is withdrawn from a path 48 constituting an oxygen-enriched liquid extraction path, and is supercooled by the supercooler 38. Branching in two directions 73. The oxygen-enriched liquid in both paths 72 and 73 is decompressed to about 3.3 bar by pressure reducing valves 74 and 75, respectively, and then heat exchanged with the low-boiling-point component-enriched gas at the top of the single rectification column in the condensation evaporator 46. Is performed, and the waste gas of the path 76 constituting the waste gas path and the circulating gas of the path 77 constituting the circulating gas extraction path are generated.

The temperature of the waste gas in the path 76 is raised to about -142.5 ° C. in the subcooler 38 and the main heat exchanger 34, and thereafter, the waste gas is branched in two directions, a path 78 and a path 79. The waste gas in the path 78 is introduced into the drive turbine 80 and expands, generates power, and is led out to the path 81. The waste gas in the path 79 expands in the cold turbine 82 to generate cold, and
3 is derived. The waste gas derived from both turbines 80 and 82 joins a route 84 constituting a cold recovery route, passes through the main heat exchanger 34, recovers cold, and is discharged from a route 85. An energy discharge mechanism 86 is attached to the cold turbine 82, whereby power is dissipated and the system is cooled.

On the other hand, the circulating gas 1060 Nm ³ / h of the path 77 constituting the circulating gas extraction path passes through the path 86 via the subcooler 38, and is connected to the low-temperature compressor 87 coaxially with the drive turbine 80. Inhaled. This circulating gas is supplied to the single rectification column 3 by the power generated by the expansion of the waste gas in the drive turbine 80 in the low-temperature compressor 87.
Compressed at low temperature to an operating pressure of 6. The circulating gas after compression passes through a route 88 constituting a circulating gas re-introduction route, is cooled to −165.5 ° C. in the main heat exchanger 34, and passes through a route 89.
And is circulated and re-introduced into the single rectification column 36.

The circulating gas re-introduced into the single rectification column 36 is
In addition to functioning to improve the nitrogen yield, this circulating gas is reintroduced to the bottom of the single rectification column 36 in a state where the concentration of low boiling components such as hydrogen is substantially zero, It also serves to dilute the concentration of low-boiling components such as hydrogen in the ascending gas in the tower above the feed air introduction stage.

That is, the circulating gas is reintroduced into the bottom of the single rectification column 36 with a hydrogen concentration of substantially zero,
The hydrogen concentration is gradually increased while ascending 6c, and when it reaches about 0.011 ppb, it merges with the raw air introduced from the path 71. This raw material air is supplied to purification equipment 3
The hydrogen content was removed to about 0.1 ppb in step 2, and the two were combined to reduce the hydrogen concentration to about 0.08 ppb.
It becomes 6 ppb and rises in the tower. The rising gas gradually increases the nitrogen content, which is a low-boiling component, by low-temperature distillation while ascending the main rectification section 36b, and when the nitrogen concentration reaches a specified value, a part of the nitrogen is a few steps from the top of the column. From the position of the lower rectification stage, it is extracted to the path 37 constituting the product sampling path, and after the temperature is raised in the subcooler 38 and the main heat exchanger 34, it is passed as a product high-purity nitrogen gas having a small amount of low-boiling components. Collected from 40.

As described above, during the ascent of the main rectification section 36b, the absolute amount of hydrogen in the ascending gas hardly changes. Since the flow rate increases due to the difference in volatility and latent heat of evaporation, the hydrogen concentration relatively decreases, and the hydrogen concentration in the product nitrogen gas becomes about 0.079 ppb.

The remaining ascending gas, part of which is withdrawn as product nitrogen gas, rises while increasing the hydrogen concentration to the top of the column, and reaches approximately 5.9 ppb at the top of the column. The hydrogen-rich, low-boiling component-enriched gas comprises a small portion of about 60 Nm ^3.
/ H is discharged from the passage 42 as a purge gas, and most of the / h is condensed and liquefied in the condensing evaporator 46,
It is returned to the top of the single rectification tower 36 and descends in the tower.

From the path 42, the subcooler 38 and the main heat exchanger 34
Part of or the entire amount of the purge gas led to the path 44 via the path 90 branches off from the path 90 to the paths 91 and 92, and is about 30 Nm ³ as a bearing seal gas or a bearing gas for the drive turbine 80 and the cold turbine 82, respectively.
/ H.

According to the present embodiment, the circulating gas reintroduced into the single rectification column 36 contains about 56% of nitrogen, while it contains almost no low-boiling components such as hydrogen. By re-introducing 1060 Nm ³ / h of circulating gas into the single rectification column 36, an amount of product nitrogen gas equivalent to introducing 1055 Nm ³ / h of feed air can be obtained, and low-boiling components such as hydrogen can be further reduced. A small amount of high-purity nitrogen gas can be efficiently collected. That is, since the nitrogen yield is higher than in the first embodiment or the like in which the circulating gas is not reintroduced, the required amount of raw material air can be reduced, and hydrogen and the like introduced into the single rectification column 36 together with the raw material air and the like Of the low boiling point components are also reduced. Therefore, a high-purity product nitrogen gas having a lower boiling point component can be obtained more efficiently than in the first embodiment.

As a result, the required purity of high-purity nitrogen becomes even more stringent, and the performance of the purification facility 32 can be covered even when a purity that cannot be achieved by treatment with a catalyst or an adsorbent in the purification facility 32 is required. Can be.

Also, since the compression by the low-temperature compressor 87 necessary for re-introducing the circulating gas into the single rectification column 36 is performed using the power obtained by the expansion of the waste gas in the drive turbine 80. , Power can be used effectively, and the unit consumption can be improved.

In this embodiment, when the oxygen-enriched liquid is vaporized to generate waste gas and circulating gas, the oxygen-enriched liquid is branched and then decompressed and vaporized. The pressure may be reduced by a plurality of pressure reducing valves, and the entire amount may be vaporized by the condensing evaporator 46 before branching to waste gas and circulating gas. Further, the fluid that performs heat exchange with the oxygen-enriched liquid in the condensing evaporator 46 may be both a low-boiling-point-component-enriched gas and a high-purity nitrogen gas, or may be one of them.

FIG. 4 is a system diagram showing a fourth embodiment of the present invention, in which a condensing evaporator is divided into a plurality of blocks. That is, the vaporization of the oxygen-enriched liquid after being extracted from the bottom of the single rectification column 36 to the path 48 and branched into the path 72 and the path 73 and reduced in pressure by the pressure reducing valves 74 and 75 is performed by separate condensation and evaporation. It is formed so as to be performed by the container blocks 101 and 102. A part of the high-purity nitrogen extracted through the passage 37 is introduced into the condensing evaporator block 101 provided on one waste gas side passage by branching to the passage 103, and the condensate provided on the other circulating gas side passage is introduced. Most of the low-boiling-point component-enriched gas extracted through the path 41 is branched into the evaporator block 102 and introduced into the path 104. By forming in this way, the flow rate in each path can be optimized.
It should be noted that it is optional to introduce the high-purity nitrogen and the low-boiling-point component-enriched gas into which of the condensation evaporator blocks.

FIG. 5 is a system diagram showing a fifth embodiment of the present invention. The oxygen-enriched liquid having the maximum oxygen concentration extracted from the bottom of the single rectification column 36 to the path 48 is vaporized in the same manner as described above. This is formed so that circulating gas is obtained by withdrawing the descending liquid several stages above the bottom of the tower into the passage 110 to obtain waste gas. That is, the liquid having a higher nitrogen content than the oxygen-enriched liquid at the bottom of the column is passed through the path 1
10 and vaporized through a subcooler 38, a pressure reducing valve 111, and a condensing evaporator 46 to form a circulating gas. The circulating gas is supplied to the subcooler 38 and the low-temperature compressor 8 as described above.
7. Single rectification column 36 from path 89 through main heat exchanger 34
It is formed so that it is recirculated to the water.

Further, in the present embodiment, the waste gas which has been vaporized by the condensation evaporator 46 and led to the path 112 constituting the waste gas path is supplied to the path 113 and the path 11 in the course of the main heat exchange 34.
4 and the waste gas branched to one path 113 is
In the same manner as described above, after the power is generated by expansion in the drive turbine 80, the exhaust gas is discharged again through the main heat exchange 34, and the waste gas branched to the other path 114 and heated to the normal temperature in the main heat exchange 34 is Compressed by a waste gas compressor 116 coaxially connected to the cold turbine 115,
After removing the heat of compression in the main heat exchanger 34
And cooled to an intermediate temperature, and introduced into the cold turbine 115 through a path 119, where the cold turbine 11
5 to generate the power and cold of the waste gas compressor 116, and finally merge with the waste gas expanded by the drive turbine 80 and discharge it.

As described above, the waste gas is supplied to the waste gas compressor 116.
And then expanded by the cold turbine 115, the expansion ratio in the cold turbine 115 is increased, and the amount of cold generated per unit volume is increased. Therefore, the amount of waste gas for generating cold can be reduced, and , The amount of waste gas supplied to the drive turbine 80 can be increased,
It is possible to increase the amount of circulating gas of the low-temperature compressor 87 driven by, and the nitrogen yield can be further improved.

FIG. 6 is a system diagram showing a sixth embodiment of the present invention, in which the circulating gas is compressed in two stages. As in the third embodiment shown in FIG. 3, the circulating gas vaporized by the condensing evaporator 46 and led to the path 76 is
After being introduced into the primary low-temperature compressor 121 via the subcooler 38 and the path 86 and subjected to primary compression at a low temperature to a primary pressure, it is introduced into the main heat exchanger 34 from a path 122 constituting a circulation gas re-introduction path. The temperature is raised to room temperature, introduced into a secondary room temperature compressor 124 through a path 123, and compressed at room temperature to a secondary pressure substantially equal to the pressure of the single rectification column. The compressed circulating gas is introduced into the main heat exchanger 34 via an after cooler 125 and a path 126, and after being cooled to a predetermined temperature, is introduced into the bottom of the single rectification column 36 from a path 127. At this time, the circulating gas is primarily compressed by the power generated by the drive turbine 80 in the primary low temperature compressor 121, and is secondarily compressed by the power generated by the cold turbine 82 in the secondary room temperature compressor 124.

By thus compressing the circulating gas in two stages, the primary low-temperature compressor 121 connected in pressure series is connected.
And the secondary room-temperature compressor 124 can reduce their respective compression ratios, and can select a compressor having a standard compression ratio and also improve the compression efficiency, so that the amount of circulating gas can be increased, The nitrogen yield can be improved.

As shown in the fifth and sixth embodiments, the power generated by the expansion of the waste gas is effectively used as the compression power of the waste gas and the circulating gas without using the energy discharging mechanism. In addition, the power loss can be suppressed, and the disadvantage that the power consumption when the turbine-generated power is consumed by the energy discharging mechanism as shown in the first to fourth embodiments increases can be improved.

FIG. 7 is a system diagram of a main part showing a seventh embodiment of the present invention, and shows an example in which a purge gas is formed so as to be extracted from a gas-liquid separator. That is, the entire amount of the low-boiling-point component-enriched gas extracted from the top of the single rectification column 36 to the path 41 is introduced into the condensing evaporator 46 to be condensed, and the gas-liquid separator 131 provided at the outlet of the condensing evaporator 46 is provided. And the gas is led to the path 132 as a purge gas,
It is formed so as to be discharged in the same manner as described above.

As described above, the discharge of the purge gas may be performed after the condensing evaporator 46 is drawn out. As shown in each of the above embodiments, the passage 4 connected to the top of the single rectification column 36 is used.
Alternatively, the flow may be performed by branching off from the line 1, and although not shown, a path dedicated to purge gas extraction may be provided at the top of the tower separately from the path 41.

As shown in the second and fourth embodiments,
When a part of the high-purity nitrogen gas is introduced into the condensing evaporator and condensed, instead of extracting to the path 37 and branching, it is necessary to provide dedicated paths for product extraction and condensation. Can be.

In the first embodiment shown in FIG. 1 and the third embodiment shown in FIG. 3 and the conventional example shown in FIG. 8, the raw material air amount and product nitrogen when obtaining the same amount of product nitrogen gas are obtained. Table 1 shows the hydrogen concentration in the gas, the nitrogen yield, and the power consumption unit. Table 1
As is clear from both the examples, the hydrogen concentration in the product nitrogen gas is lower than that of the conventional example due to the use of the purification equipment for removing hydrogen and the like in the pretreatment stage. Also,
By directly extracting the product nitrogen gas from the single rectification column without depressurizing, power loss due to the conventional decompression of liquid nitrogen is eliminated, and the power consumption is improved. In addition, the third
In the embodiment, the oxygen-enriched liquid at the bottom of the single rectification column is vaporized and circulated and reintroduced into the single rectification column, so that the hydrogen concentration in the product nitrogen gas is lower than in the first embodiment, and the nitrogen recovery is reduced. Rates and power consumption have improved.

[0062]

[Table 1]

[0063]

As described above, according to the present invention,
High-purity nitrogen gas having a low concentration of low-boiling components such as hydrogen can be efficiently obtained. In particular, since sampling can be performed at a high pressure, power costs required for recompression can be reduced. In addition, by re-introducing a part of the waste gas that was conventionally discharged into the single rectification column as circulating gas, the hydrogen concentration in the product nitrogen gas can be further reduced, and the nitrogen yield and power generation The unit can be further improved. In addition, by removing hydrogen and the like in the pretreatment stage, the concentration of low-boiling components such as hydrogen can be further reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a first embodiment of the present invention.

FIG. 2 is a system diagram showing a second embodiment of the present invention.

FIG. 3 is a system diagram showing a third embodiment of the present invention.

FIG. 4 is a system diagram showing a fourth embodiment of the present invention.

FIG. 5 is a system diagram showing a fifth embodiment of the present invention.

FIG. 6 is a system diagram showing a sixth embodiment of the present invention.

FIG. 7 is a system diagram showing a seventh embodiment of the present invention.

FIG. 8 is a system diagram showing an example of a conventional high-purity nitrogen production process.

[Explanation of Signs] 31: Raw material air compressor, 32: Purification equipment, 34: Main heat exchanger, 36: Single rectification column, 38: Subcooler, 46: Condensation evaporator, 49: Pressure reducing valve, 53 ... Expansion turbine, 56: Energy discharge mechanism, 80: Drive turbine, 82: Cold turbine, 87: Low temperature compressor, 101, 102: Condensation evaporator block, 115: Cold turbine, 116: Waste gas compressor, 121: Primary low temperature Compressor, 124: Secondary room temperature compressor, 131: Gas-liquid separator

Claims (19)

[Claims] 1. A high-purity nitrogen production method for collecting high-purity nitrogen by introducing compressed, purified, and cooled raw material air into a single rectification column and subjecting it to low-temperature distillation. A step of extracting a boiling component-enriched gas, a step of extracting high-purity nitrogen gas having a low boiling point component from a rectification stage several stages below the top of the single rectification column, and Extracting the oxygen-enriched liquid and reducing the pressure; and performing a heat exchange between the low-boiling-point-enriched gas and / or the high-purity nitrogen gas and the oxygen-enriched liquid after the decompression to obtain a low-boiling-point-enriched gas and And / or liquefying high-purity nitrogen gas to generate a descending liquid of the single rectification column and vaporizing the oxygen-enriched liquid to generate waste gas. Method. 2. A high-purity nitrogen production method for collecting high-purity nitrogen by introducing compressed air, purified and cooled raw material air into a single rectification column and performing low-temperature distillation. A step of extracting a boiling component-enriched gas, a step of extracting high-purity nitrogen gas having a low boiling point component from a rectification stage several stages below the top of the single rectification column, and Extracting the oxygen-enriched liquid and reducing the pressure; and performing a heat exchange between the low-boiling-point-enriched gas and / or the high-purity nitrogen gas and the oxygen-enriched liquid after the decompression to obtain a low-boiling-point-enriched gas and And / or liquefying high-purity nitrogen gas to generate a descending liquid of the single rectification column, and vaporizing the oxygen-enriched liquid to generate a circulating gas and waste gas; Part of the low-boiling-point component-enriched gas from the first or second stage of the liquefaction process Deriving as a purge gas,
A method for producing high-purity nitrogen, comprising: a step of generating power and cold by expanding the waste gas; and a step of compressing and re-introducing the circulating gas into the single rectification column. 3. The method for producing high-purity nitrogen according to claim 1, wherein carbon monoxide and hydrogen among impurities in the raw material air are removed and then introduced into the single rectification column. 4. A liquid obtained when the low-boiling component-enriched gas is liquefied is subjected to gas-liquid separation, and the separated liquid is returned to the top of the single rectification column, and the separated gas is used as the purge gas. 3. The method for producing high-purity nitrogen according to claim 1, wherein the nitrogen is extracted. 5. A part of the waste gas is expanded at an intermediate temperature to generate power, at least a part of the remaining part of the waste gas is heated to room temperature, compressed at room temperature, expanded after re-cooling, and cooled. 3. The method for producing high-purity nitrogen according to claim 2, wherein the circulating gas is compressed at a low temperature, re-cooled, and re-introduced into the single rectification column. 6. The method of claim 1, wherein the circulating gas is compressed to a primary pressure at a low temperature, then heated to room temperature, compressed to a secondary pressure at room temperature, recooled, and reintroduced into the single rectification column. Item 4. The method for producing high-purity nitrogen according to Item 2. 7. The compression of the waste gas and the circulating gas,
The method for producing high-purity nitrogen according to claim 5, wherein the method is performed using power generated in the step of expanding the waste gas. 8. The room temperature compression of the waste gas is performed by using the power obtained in the step of expanding the waste gas to generate cold, and the low temperature compression of the circulating gas is performed by expanding the waste gas. 6. The method for producing high-purity nitrogen according to claim 5, wherein the method is performed using power obtained in the step of generating power. 9. A low-temperature compression of the circulating gas is performed by using power obtained in a step of generating power by expanding the waste gas, and a normal temperature compression of the circulating gas is performed by expanding the waste gas. 7. The method for producing high-purity nitrogen according to claim 6, wherein the method is performed using power obtained in the step of generating cold. 10. The method for producing high-purity nitrogen according to claim 2, wherein the purge gas is used as a seal gas or a bearing gas for a bearing of a turbine for expanding the waste gas. 11. A high-purity nitrogen production apparatus for collecting high-purity nitrogen by subjecting compressed, purified, and cooled raw air to low-temperature distillation in a single rectification column. A main heat exchanger that cools by exchanging heat with gas, and a single heat separator that separates the cooled raw material air into low-boiling component-enriched gas, high-purity nitrogen gas with low low-boiling components and oxygen-enriched liquid by low-temperature distillation A distillation column, a condensing evaporator for heat-exchanging the low-boiling component-enriched gas and / or high-purity nitrogen gas with the oxygen-enriched liquid, and the oxygen-enriched liquid vaporized and generated in the condensing evaporator. An expansion turbine that expands waste gas to generate cold, withdraws the low-boiling component-enriched gas from the top of the single rectification column, liquefies it through the condensing evaporator, and forms a top portion of the single rectification column. A low-boiling component-enriched fluid recirculation path and / or Or a high-purity nitrogen reflux path in which the high-purity nitrogen gas is withdrawn from the top of the single rectification column, liquefied through the condensation evaporator, and returned to a position between the top and the top of the single rectification column; A part of the component-enriched gas is withdrawn as a purge gas from the top of the single rectification column or from the upstream or downstream of the condensing evaporator in the low-boiling component-enriched fluid reflux path and is led through the main heat exchanger. A purge gas path, and a product collection path that is led through the main heat exchanger from the upper part of the single rectification column or the upstream of the condensation evaporator of the high purity nitrogen reflux path as the high purity nitrogen gas as product nitrogen gas. Withdrawing the oxygen-enriched liquid from the bottom of the single rectification column, connected to the oxygen-enriched liquid extraction path leading to the condensation evaporator via a pressure reducing valve, and connected to the oxygen-enriched liquid extraction path, Passing the waste gas through the main heat exchanger Serial and waste gas path for guiding the expansion turbine, the expansion turbine in the expansion to high purity nitrogen production device, characterized in that the waste gas generated cold and a refrigeration recovery path for deriving through the main heat exchanger. 12. A high-purity nitrogen production apparatus for collecting high-purity nitrogen by subjecting compressed, purified, and cooled raw air to low-temperature distillation in a single rectification column. A main heat exchanger that cools by exchanging heat with gas, and a single heat separator that separates the cooled raw material air into low-boiling component-enriched gas, high-purity nitrogen gas with low low-boiling components and oxygen-enriched liquid by low-temperature distillation A distillation column, a condensing evaporator for heat-exchanging the low-boiling component-enriched gas and / or high-purity nitrogen gas with the oxygen-enriched liquid, and the oxygen-enriched liquid vaporized and generated in the condensing evaporator. A cold turbine that expands a part of the waste gas to generate cold, a drive turbine that expands at least a part of the remaining part of the waste gas to generate power, and that the oxygen-enriched liquid is vaporized by the condensation evaporator. Temperature to compress the circulating gas generated by A low-boiling component-enriched gas reflux path for extracting a low-boiling component-enriched gas from the top of the single rectification column, liquefying the gas through the condensing evaporator, and returning the low-boiling component-enriched gas to the top of the single rectification column. And / or a high-purity nitrogen reflux path in which the high-purity nitrogen gas is withdrawn from the top of the single rectification column, liquefied through the condensation evaporator, and returned to a position between the top and the top of the single rectification column; A part of the low-boiling component-enriched gas is withdrawn as a purge gas from the top of the single rectification column or from the upstream or downstream of the condensing evaporator in the low-boiling component-enriched fluid reflux path and passed through the main heat exchanger. A purge gas path to be led out, and a product sampling to be led out from the upper part of the single rectification column as the product nitrogen gas as the product nitrogen gas or from the upstream of the condensation evaporator in the high purity nitrogen reflux path through the main heat exchanger. Route and before The oxygen-enriched liquid is withdrawn from the lower portion including the bottom of the single rectification column, and is connected to an oxygen-enriched liquid extraction path leading to the condensing evaporator via a pressure reducing valve, and is connected to the oxygen-enriched liquid extraction path. A waste gas path that guides the waste gas to the cold turbine and the drive turbine through the main heat exchanger, a cold recovery path that guides waste gas expanded by the cold turbine and the drive turbine through the main heat exchanger, A circulating gas extraction path connected to the oxygen-enriched liquid extraction path and guiding the circulating gas to the low-temperature compressor; and a circulating gas recirculation path that guides the circulating gas compressed by the low-temperature compressor to a lower portion of the single rectification column. An apparatus for producing high-purity nitrogen, comprising an introduction path. 13. The high-purity nitrogen production apparatus according to claim 11, wherein the condensation evaporator is a dry heat exchanger. 14. The apparatus for producing high-purity nitrogen according to claim 11, wherein the condensation evaporator is integrally formed. 15. The condensation evaporator according to claim 11, wherein a block for liquefying the low-boiling component-enriched gas and a block for liquefying the high-purity nitrogen gas are separately provided. 13. The high-purity nitrogen production apparatus according to 12. 16. The high-purity nitrogen producing apparatus according to claim 12, wherein the condensing evaporator is separately provided in a block for generating the waste gas and a block for generating the circulating gas. . 17. A waste gas compressor for compressing waste gas to be introduced into the cold turbine at a normal temperature, wherein the waste gas path includes a path for leading waste gas from the middle of the main heat exchanger to the drive turbine. 13. The high-pressure apparatus according to claim 12, wherein the branch is branched from the path, passes through the main heat exchanger, passes through the waste gas compressor, passes through the main heat exchanger again, and is connected to the cold turbine. Purity nitrogen production equipment. 18. A primary compressor for compressing the circulating gas to a primary pressure at a low temperature instead of the low-temperature compressor, and a secondary compression for compressing the circulating gas compressed at a low temperature by the primary compressor to a secondary pressure at a normal temperature. And the circulation gas re-introduction path passes from the primary compressor through the main heat exchanger, passes through the secondary compressor again through the main heat exchanger, and is located at a lower part of the single rectification column. 2. The device according to claim 1, wherein
2. The high-purity nitrogen producing apparatus according to 2. 19. The oxygen-enriched liquid extraction path includes a path from the bottom of the single rectification column to the waste gas path, and a path from the lower part of the single rectification column to the circulating gas extraction path. The high-purity nitrogen producing apparatus according to claim 12, wherein the apparatus is formed by: