JPH1062062A - Nitrogen production method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen manufacturing method and a nitrogen manufacturing device capable of collecting the nitrogen gas of super-high purity at high pressure while the yield and consumption unit of the product are improved. SOLUTION: A part of the raw air is introduced into a low pressure tower 31 in a low pressure condition, the nitrogen gas separated in a tower top part is liquefied in a condenser 48, the obtained liquefied nitrogen is boosted by a liquefied nitrogen pump 33 to be introduced into a top part of a high pressure tower 32 as the circulating liquid, the raw air in the high pressure condition is introduced into a bottom part of the high pressure tower 32, and the nitrogen gas in the tower top part obtained through distillation in the high pressure tower 32 is collected as the product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and apparatus for producing nitrogen, and more particularly, to a method and apparatus for producing ultra-high-purity nitrogen by subjecting compressed, purified, and cooled raw air to cryogenic liquefaction and rectification.

[0002]

2. Description of the Related Art In recent years, demand for ultra-high purity nitrogen in semiconductor factories has been increasing. As an apparatus for producing this ultra-high purity nitrogen, a nitrogen production apparatus as shown in FIG. 3 is used. This nitrogen production apparatus obtains ultra-high-purity nitrogen gas by cryogenic liquefaction rectification and separation of air in a rectification tower. The air is compressed to a pressure higher than the pressure of product nitrogen gas by an air compressor 1. The raw material air is introduced into the adsorber 3 through the after cooler 2 and is purified by removing impurities such as moisture and carbon dioxide contained therein, and then liquefied by heat exchange with product nitrogen or the like in the main heat exchanger 4. It is cooled to near the point and introduced into the lower part of the rectification column 6 from the path 5.

The raw material air introduced into the rectification column 6 is separated into nitrogen gas at the top of the column and oxygen-enriched liquefied air at the bottom of the column by a well-known cryogenic liquefaction rectification separation operation. The nitrogen gas in the upper part of the column branches after being led out to the path 7, and the nitrogen gas branched to the path 8 is cooled to the normal temperature by cooling the raw material air in the main heat exchanger 4, and then is discharged from the path 9. Collected as product nitrogen gas. The nitrogen gas branched from the path 7 to the path 10 is introduced into the condenser 11 to be condensed and liquefied. The nitrogen gas is returned to the top of the rectification tower 6 via the path 12 and becomes a reflux liquid of the rectification tower 6.

[0004] The oxygen-enriched liquefied air at the bottom of the column is passed through a path 1
3, after being reduced to an intermediate pressure by the pressure reducing valve 14,
The oxygen-enriched liquefied air branched into the path 15 and the path 16 and introduced into the path 15 is introduced into the condenser 11, and serves as a cooling source for liquefying the nitrogen gas. Become air. The oxygen-enriched air led out of the condenser 11 merges with the path 16 and then passes through the path 17 through the path 1
8 and a route 19. The oxygen-enriched air introduced into the main heat exchanger 4 from the path 18 is heated to an intermediate temperature, and is led out of the intermediate part of the main heat exchanger 4 to the path 20 and is insulated to about normal pressure by the expansion turbine 21. Expands, causing cold.

[0005] Oxygen-enriched air that has produced cold is supplied to a route 19.
And then joins with the oxygen-enriched air reduced to approximately normal pressure by the pressure reducing valve 22, is introduced into the main heat exchanger 4 through a path 23, and cools the raw material air to raise the temperature to normal temperature. Derived from path 24.

[0006]

However, in the above-described nitrogen production apparatus, the pressure of the product nitrogen gas depends on the pressure of the raw material air. Had to be compressed to the required pressure, and furthermore, the product yield was low and the basic unit was low due to rectification at high pressure in the rectification column.

[0007] Further, nitrogen gas obtained by operating the rectification column at a low pressure is also increased in pressure to a required pressure by a nitrogen compressor. Because of the possibility of contamination, application to an apparatus for producing ultra-high-purity nitrogen gas has been difficult.

Accordingly, an object of the present invention is to provide a method and an apparatus for producing nitrogen capable of collecting ultrahigh-purity nitrogen gas at a high pressure while improving the product yield and the unit consumption.

[0009]

In order to achieve the above object, a method for producing nitrogen according to the present invention comprises introducing a compressed, purified, and cooled raw material air into a rectification column to perform cryogenic liquefaction rectification separation. In the method of sampling nitrogen in the air as a product, a part of the raw material air is introduced into a low-pressure column at low pressure and rectified, and the nitrogen gas separated at the top of the column is liquefied by a condenser, and the obtained liquefaction Nitrogen is pressurized and introduced as a reflux liquid at the top of the high-pressure column, and high-pressure raw material air is introduced at the bottom of the high-pressure column, and nitrogen gas at the top obtained by rectification in the high-pressure column is used as a product. It is characterized by being collected as.

In the method of the present invention, the high-pressure raw material air is obtained by branching a part of the low-pressure raw material air to a predetermined high-pressure state, or
The raw air in the low pressure state is characterized in that a part of the raw air that has been raised to a high pressure state is branched and expanded and lowered to a predetermined low pressure state by an expansion turbine.

Further, the nitrogen producing apparatus of the present invention comprises
A low-pressure tower and a high-pressure tower into which purified and cooled raw material air are introduced. The low-pressure tower has a path for introducing low-pressure raw material air to the lower part of the tower, a nitrogen gas rectified and separated at the upper part of the tower, and a rectifying part at the bottom of the tower A condenser for liquefying nitrogen gas by heat exchange with the separated oxygen-enriched liquefied air, a path for returning part of the liquefied nitrogen liquefied by the condenser to the top of the low-pressure column as a reflux liquid, and a remaining part of the liquefied nitrogen. A path for increasing the pressure by a liquefied nitrogen pump and introducing it as a reflux liquid to the top of the high-pressure column, wherein the high-pressure tower is configured to introduce liquefied nitrogen from the condenser to the top of the tower as a reflux liquid; A path for introducing air to the bottom of the tower,
At the top of the tower, there is provided a path for discharging the rectified nitrogen gas as a product.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. First, FIG. 1 shows a first embodiment of a nitrogen production apparatus to which the present invention is applied. This nitrogen production apparatus has a low-pressure column 31 and a high-pressure column 32 as rectification columns.
1 and rectified and separated to collect ultra-high-purity liquefied nitrogen.
High-pressure column 3 into which the remaining raw material air is introduced
The high-pressure column 32 is used to obtain a high-pressure ultra-high-purity nitrogen gas by using it as a reflux liquid of No. 2.

First, the raw material air, which has been raised to a low pressure state in accordance with the operating pressure of the low pressure column 31 by the air compressor 41, is introduced into the adsorber 43 through the after cooler 42, and contains impurities such as water and carbon dioxide contained therein. Is removed and purified,
It is branched into a path 44 and introduced into a main heat exchanger 45, cooled to near a liquefaction point by heat exchange with product nitrogen or the like, and introduced into a lower portion of the low-pressure column 31 from a path 46 while maintaining a low pressure state.

The low-pressure raw material air introduced into the low-pressure column 31 is separated into nitrogen gas at the top of the column and oxygen-enriched liquefied air at the bottom of the column by a cryogenic liquefaction and separation operation. In the rectification separation in the low-pressure column 31, the operation is performed in a state where the relative volatility is improved by the lower pressure as compared with the conventional apparatus, the separation of oxygen and nitrogen is performed favorably, and the yield of nitrogen is reduced. improves.

The nitrogen gas separated at the upper part of the low pressure column 31 is
After being introduced into the condenser 48 from the path 47 to be condensed and liquefied and converted into liquefied nitrogen and led out to the path 49, the liquid is branched into a path 50 and a path 51, and the liquefied nitrogen in the path 50 returns to the top of the low-pressure column 31. Then, it becomes a reflux liquid of the low-pressure column 31. The liquefied nitrogen branched to the path 51 is boosted by the liquefied nitrogen pump 33 to a high pressure state corresponding to the operating pressure of the high-pressure tower 32, that is, the pressure at which the product nitrogen gas is taken out.
2 and becomes the reflux liquid of the high-pressure column 32.

The oxygen-enriched liquefied air at the bottom of the low-pressure column 31 is led out to a passage 53, reduced to an intermediate pressure by a pressure reducing valve 54, branched into a passage 55 and a passage 56, and branched into a passage 55. Oxygen-enriched liquefied air is introduced into the condenser 48 and serves as a cooling source for liquefying the nitrogen gas, which itself evaporates and becomes oxygen-enriched air. The oxygen-enriched air led out of the condenser 48 joins the path 56 and then passes through the path 57.
, And branches into a path 58 and a path 59. The oxygen-enriched air introduced into the main heat exchanger 45 from the path 58 rises to an intermediate temperature, and passes from the intermediate part of the main heat exchanger 45 to the path 60.
And adiabatically expanded to near normal pressure by the expansion turbine 61 to generate cold.

[0017] The oxygen-enriched air that has generated the cold passes through a path 59.
And then joins with the oxygen-enriched air reduced to approximately normal pressure by the pressure reducing valve 62, is introduced into the main heat exchanger 45 via the path 63, and cools the raw material air to raise the temperature to normal temperature. Derived from path 64.

On the other hand, the adsorber 43 is led out to
The low-pressure raw material air that has branched to the high-pressure state is pressurized by the secondary compressor 65 to a high-pressure state corresponding to the output pressure of the product nitrogen gas, and then cooled by the main heat exchanger 45 to pass from the path 66 to the lower part of the high-pressure column 32. Will be introduced. In the high-pressure column 32, rectification is performed by the high-pressure raw material air introduced into the lower part and the high-pressure liquefied nitrogen introduced through the passage 52,
Ultra-high purity nitrogen gas is separated at the top of the column, and oxygen-enriched liquefied air is separated at the bottom of the column.

The oxygen-enriched liquefied air discharged from the bottom of the tower to the path 67 is decompressed by the pressure reducing valve 68, and then joins with the oxygen-enriched liquefied air output from the low-pressure tower 31 to the path 53 to form a condenser 48. , The expansion turbine 61, the main heat exchanger 45, and the like.

The ultra-high-purity nitrogen gas led out from the upper part of the high-pressure column 32 to the path 69 is recovered from the path 70 after recovering the temperature in the main heat exchanger 45.

As described above, by liquefying the nitrogen gas separated in the low-pressure column 31 which is low in pressure and excellent in product yield to obtain a reflux liquid, the amount of the reflux liquid can be increased as compared with the conventional method. The amount of air can be reduced, and the product yield can be improved. Furthermore, since the entire amount of the raw air is not increased to a high pressure state higher than the pressure of the product nitrogen gas, the required power of the air compressor can be reduced, and especially when the pressure of the product nitrogen gas is high, the product yield is improved. With the synergistic effect of the above, the basic unit can be significantly reduced.

In the embodiment shown in FIG. 1, the feed air system is described as one system up to the adsorber 43. However, the feed air system is divided into two systems from the stage of the air compressor 41 or from the stage after discharge. An adsorber may be provided downstream of the secondary compressor 65 separately from the adsorber 43.

FIG. 2 shows a second embodiment of a nitrogen production apparatus to which the present invention is applied. The same components as those in the embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

First, the whole amount of the raw air is compressed to a high pressure state corresponding to the operating pressure of the high-pressure tower 32 by the air compressor 41, and then passed through the aftercooler 42 and the adsorber 43 to the main heat exchanger 45. be introduced. A part of the high-pressure raw material air branches off to the path 71 in the middle of the main heat exchanger 45, expands to a low-pressure state pressure corresponding to the operating pressure of the low-pressure tower 31 by the expansion turbine 72, and generates cold, It is derived to the route 73. A part of the high-pressure raw material air derived from the main heat exchanger 45 to the path 74 is branched to the path 75 and reduced in pressure to a low-pressure state by the pressure reducing valve 76, and then the low-pressure raw material air in the path 73 is reduced. And both are introduced into the lower part of the low-pressure column 31 via the path 77. On the other hand, the high-pressure raw material air that is led from the main heat exchanger 45 to the path 74 and branched to the path 78 is introduced into the lower part of the high-pressure column 32 while maintaining the high-pressure state.

In the same manner as described above, the nitrogen gas separated at the upper part of the low-pressure column 31 is liquefied in a condenser 48, a part of which is used as a reflux liquid of the low-pressure column 31, and the remaining part is a liquefied nitrogen pump 33.
The pressure is increased to a high pressure state, and rectification is performed using each as a reflux liquid of the high-pressure column 32, so that an ultra-high-purity nitrogen gas of a predetermined pressure is obtained from the upper part of the high-pressure column 32.

Also in the present embodiment, the nitrogen gas separated in the low-pressure column 31 is liquefied, and the obtained liquefied nitrogen is used as the reflux liquid of both columns. The unit consumption can be reduced by reducing the amount of air.

[0027]

Next, the same purity and the same amount were obtained by using the nitrogen production apparatus of each configuration of the first embodiment apparatus shown in FIG. 1, the second embodiment apparatus shown in FIG. 2, and the conventional apparatus shown in FIG. The results of comparison of the product yield and the basic unit when producing high-purity nitrogen gas are described. The sampling condition of product nitrogen gas is 1030N
m ³ / h, pressure 7.0 kg / cm ² G, oxygen content 1p
pm or less.

Table 1 shows the calculation results of the amount of raw air and the pressure, product yield, unit consumption, etc., when producing product nitrogen gas under the above conditions.

[0029]

[Table 1]

[0030]

As described above, according to the method and apparatus for producing nitrogen of the present invention, it is possible to improve the product yield and the unit consumption, and to produce ultra-high-purity nitrogen gas at high pressure. Cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an example of a nitrogen production apparatus to which the present invention is applied.

FIG. 2 is a system diagram showing another example of the nitrogen production apparatus.

FIG. 3 is a system diagram showing an example of a conventional nitrogen production apparatus.

[Explanation of symbols]

31 low pressure tower, 32 high pressure tower, 33 liquefied nitrogen pump,
41 ... air compressor, 42 ... after cooler, 43 ... adsorber, 45 ... main heat exchanger, 48 ... condenser, 54 ... pressure reducing valve, 61 ... expansion turbine, 62 ... pressure reducing valve, 65 ... secondary compressor, 68 ... pressure reducing valve, 72 ... expansion turbine, 76 ... pressure reducing valve

Claims (4)

[Claims] 1. A method of introducing a compressed, purified, and cooled raw material air into a rectification column to perform cryogenic liquefaction rectification and to collect nitrogen in the raw material air as a product, wherein a part of the raw material air is reduced in pressure. Introduced into the low-pressure column in the state and rectified, the nitrogen gas separated at the top of the column is liquefied by a condenser, and the resulting liquefied nitrogen is pressurized and introduced as a reflux liquid at the top of the high-pressure column,
A method for producing nitrogen, comprising introducing high-pressure raw material air into the bottom of the high-pressure column, and collecting, as a product, nitrogen gas at the top obtained by rectification in the high-pressure column. 2. The nitrogen production method according to claim 1, wherein the high-pressure raw material air is obtained by branching and raising a part of the low-pressure raw material air. 3. The nitrogen production method according to claim 1, wherein the raw air in the low pressure state is obtained by branching a part of the raw air which has been raised to a high pressure state and expanding and reducing the pressure by an expansion turbine. 4. A low-pressure column and a high-pressure column into which compressed, purified, and cooled raw material air is introduced, wherein the low-pressure column has a path for introducing low-pressure raw material air to a lower portion of the column, and nitrogen rectified and separated at the upper portion of the column. A condenser for liquefying nitrogen gas by heat exchange between the gas and oxygen-enriched liquefied air rectified and separated at the bottom of the column, and a path for returning a part of the liquefied nitrogen liquefied by the condenser to the top of the low-pressure column as a reflux liquid A path for increasing the pressure of the remainder of the liquefied nitrogen with a liquefied nitrogen pump and introducing the liquid nitrogen to the top of the high-pressure column as a reflux liquid, wherein the high-pressure column introduces liquefied nitrogen from the condenser as a reflux liquid to the top of the column. A nitrogen production apparatus, comprising: a path for introducing high-pressure raw material air into the lower part of the tower; and a path for leading out the rectified and separated nitrogen gas as a product at the top of the tower.