JP2980756B2 - Ultra high purity nitrogen production method and apparatus - Google Patents

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 ultra-high-purity nitrogen having a low content of low-boiling components such as hydrogen, helium and neon used in a semiconductor production process and the like. Feeding the raw air to the lower rectification column of the double rectification column, condensing and liquefying the gaseous nitrogen rectified and separated from the raw air in the lower rectification column with the condenser, and condensed and liquefied with the condenser The present invention relates to an ultrapure nitrogen production method and an apparatus for producing a product liquid nitrogen by introducing nitrogen as a reflux liquid to the top of the lower rectification column, and extracting a part of the reflux liquid from the lower rectification column.

[0002]

2. Description of the Related Art Conventionally, as a method and apparatus for producing high-purity nitrogen, gaseous nitrogen rectified and separated from raw material air is conventionally condensed in a condenser, and at the same time, a large amount of low-boiling components not condensed and liquefied are contained. After discharging the condensed gas and removing the low-boiling components contained in the gaseous nitrogen from the rectification column, the condensed and liquefied liquid nitrogen with low low-boiling components is introduced as a reflux liquid into the top of the rectification column. A part of the liquid nitrogen introduced as the reflux liquid is derived from a rectification plate several stages below the rectification plate at the top of the rectification column to rectify the low-boiling components contained in the liquid nitrogen. Techniques for producing high-purity product nitrogen by separation have been proposed (for example, Japanese Utility Model Laid-Open No. 64-45).
290 publication).

[0003]

The above prior art discloses a method of discharging uncondensed gas which has not been condensed and liquefied in a condenser, and a method of purifying a portion of liquid nitrogen introduced as a reflux liquid at the top of a rectification column. Low-boiling components are removed by extracting from the rectifying plate several stages below the rectifying plate to produce high-purity product nitrogen, but rectifying and separating the low-boiling components in the rectification column. On the other hand, as part of the liquid nitrogen introduced as the reflux liquid is led out from the rectification plate below the rectification plate at the top of the rectification column, product nitrogen with a low boiling point component can be obtained. There is a disadvantage that certain oxygen tends to remain in the product nitrogen as an impurity, and there is a limit to the extent of further purifying the product nitrogen. The present invention has been made in view of the above circumstances, and by devising a process for treating raw air and liquid nitrogen derived from a rectification plate several stages below the rectification plate at the top of the rectification column, the product It is an object of the present invention to further purify liquid nitrogen.

[0004]

A first feature of the present invention to achieve the above object is to supply raw air to a lower rectification column of a double rectification column, and to supply the raw air to the lower rectification column. The gaseous nitrogen rectified and separated from the liquid nitrogen is condensed and liquefied in a condenser, and the liquid nitrogen condensed and liquefied in the condenser is introduced as a reflux liquid into the top of the lower rectification column, and a part of the reflux liquid is partially purified by the lower rectification column. An ultrapure nitrogen production method for producing a product liquid nitrogen derived from a distillation tower, comprising: Step of oxidizing hydrogen and carbon monoxide in raw air B. B. a step of removing from the raw material air the water and carbon dioxide gas generated by the oxidation of hydrogen and carbon monoxide and the water and carbon dioxide gas originally contained in the raw material air; Step of supplying raw air from which water and carbon dioxide have been removed to the lower rectification column. E. a step of discharging uncondensed gas that has not been condensed and liquefied in the condenser to remove low-boiling components contained in the gaseous nitrogen; A part of the liquid nitrogen introduced as the reflux liquid is led out from a rectification plate several stages below the rectification plate at the top of the lower rectification column, and the low-boiling components contained in the liquid nitrogen are purified. Step of fractionation F. After supercooling and freely expanding liquid nitrogen derived from the rectification plate at the lower stage , ultra-high purity liquid is separated by gas-liquid separation by a gas-liquid separator.
To generate and body nitrogen and waste gas, process which is discharged the separated the waste gas removing low-boiling components contained in the liquid nitrogen G. A part of the ultra-high purity liquid nitrogen is transferred from the gas-liquid separator.
The gas-liquid separator and the storage tank provided at
Using the height difference between the storage tank and the inflow, the product liquid nitrogen
H. as a storage step The remaining part of the ultra-high purity liquid nitrogen is transferred to the top of the low pressure rectification column.
Into the rectification section of the low-pressure rectification column
Step of rectifying gas ascending in the pressure rectification tower The above steps A to H are included.

A second feature of the present invention to achieve the above object is that raw air is supplied to a lower rectification column of a double rectification column and rectified and separated from the raw air in the lower rectification column. Gaseous nitrogen is condensed and liquefied in a condenser, and liquid nitrogen condensed and liquefied in the condenser is introduced as a reflux liquid into the top of the lower rectification column, and a part of the reflux liquid is derived from the lower rectification column. to produce a product liquid nitrogen to a ultra high purity nitrogen production device, I. An oxidation means to oxidize hydrogen and carbon monoxide in the feed air, J. Removing means for removing, from the raw material air, the water and carbon dioxide gas generated by the oxidizing means and the water and carbon dioxide gas originally contained in the raw material air; K. And the feed air moisture and carbon dioxide are removed supply path for supplying to said lower rectification column, L. A discharge passage for discharging the uncondensed gas which has not condensed and liquefied by the condenser, M. A lead-out passage for deriving a portion of the liquid nitrogen introduced as the reflux liquid from the rectification plate under several stages than fine Tomeban of the lower rectification column top, N. After supercooling and freely expanding liquid nitrogen derived from the rectification plate at the lower stage , ultra-high purity liquid is separated by gas-liquid separation by a gas-liquid separator.
Generates body nitrogen and waste gas, and discharges the separated waste gas.
To remove low boiling components contained in the liquid nitrogen
Means for performing A part of the ultra-high purity liquid nitrogen is transferred from the gas-liquid separator.
The gas-liquid separator and the storage tank provided at
Using the height difference between the storage tank and the inflow, the product liquid nitrogen
Means for storing as P. The remaining part of the ultra-high purity liquid nitrogen is transferred to the top of the low pressure rectification column.
Into the rectification section of the low-pressure rectification column
Means for rectifying gas rising in the pressure rectification column
In the configuration.

[0006]

According to the constitutions A, B and C, hydrogen, which is one of the low-boiling components in the raw air, is oxidized to produce water, and the hydrogen in the raw air is removed as moisture, thus containing hydrogen. A very small amount of feed air is fed to the lower rectification column. Then, by the configuration of D, uncondensed gas containing a large amount of low-boiling components not condensed and liquefied in the condenser was discharged to remove low-boiling components contained in gaseous nitrogen from the lower rectification column. Thereafter, the condensed and liquefied liquid nitrogen having a low boiling point component is introduced into the top of the lower rectification column as a reflux liquid,
According to the configuration, a part of the liquid nitrogen introduced as the reflux liquid is derived from the rectification plate several stages below the rectification plate at the top of the lower rectification column, and the low boiling point component contained in the liquid nitrogen There are rectification separation, the configuration of the F, low-boiling components which can not be rectified separated by rectification plate to drain separated gas rich in gasified easily the lower boiling point components have been further removed, the structure of the G Yo
Of ultra-high-purity liquid nitrogen separated by a gas-liquid separator
Into a storage tank provided below the gas-liquid separator,
Utilizing the difference in height between the gas-liquid separator and the storage tank
Pump, etc. by flowing in and storing as product liquid nitrogen
The use of liquid nitrogen
The ultra-high purity is maintained, and the configuration of H allows the gas-liquid separator
Of the ultra-high-purity liquid nitrogen separated in
Into the rectification section of the low-pressure rectification column
Adopt a configuration to rectify gas rising in the pressure rectification tower
In, while avoiding the contamination of impurities into the low-pressure rectification,
An oxygen-rich liquid introduced into the upper and lower center of the low pressure rectification column,
And liquid nitrogen introduced into the upper part of the low pressure rectification column.
Therefore, rectification in the low-pressure rectification column can be promoted.
As a result, liquid nitrogen with higher purity than before is produced.

Further, the I, J, K, L, M, N, O, P
According to the above structure , hydrogen, which is one of the low-boiling components in the raw air, is oxidized to remove the hydrogen in the raw air as moisture, and the raw air having a very low hydrogen content is supplied to the lower rectification column. And removes the low-boiling components contained in the gaseous nitrogen from the lower rectification column by discharging uncondensed gas containing a large amount of low-boiling components that were not condensed and liquefied by the condenser. Liquid nitrogen having a low boiling point component is introduced as a reflux liquid into the top of the lower rectification column, and a part of the liquid nitrogen introduced as the reflux liquid is purified a few stages below the rectification plate at the top of the lower rectification column. low boiling point component contained in the liquid nitrogen is rectified separated derives from Tomeban further gas-liquid separation
Separation gas containing a large amount of low-boiling components that are easily vaporized is discharged by gas-liquid separation by a vessel to further remove low-boiling components that could not be rectified and separated by the rectification plate, and further separated by gas-liquid separation.
Part of the ultra-high purity liquid nitrogen below the gas-liquid separator
In the storage tank provided at the position, the gas-liquid separator and the storage tank
Using the difference in the height position of the product, as product liquid nitrogen
By storing, there is no need to use any pumps etc.
In short, the ultra-high purity of the product liquid nitrogen is maintained,
The remaining ultra-pure liquid nitrogen separated by the gas-liquid separator is
Introduced to the top of the pressure rectification column, and the reflux liquid in the rectification section of the low pressure rectification column
To rectify the gas that rises in the low-pressure rectification tower.
To avoid the entry of impurities into the low-pressure rectification.
While oxygen is being introduced into the upper and lower central portions of the low-pressure rectification column.
Liquid and liquid nitrogen introduced at the top of the low pressure rectification column.
Promotes rectification in low-pressure rectification towers
As a result , liquid nitrogen having a higher purity than before can be produced.

[0008]

According to the present invention, a part of liquid nitrogen after rectifying and separating low-boiling components is rectified several stages below the rectifying plate at the top of the lower rectifying column with little residual high-boiling components, oxygen. The low-boiling components that have been removed from the plate and have not been rectified and separated can be removed by discharging the gas separated by gas-liquid separation, and the product liquid nitrogen can be further purified. In particular, in the present invention, since the raw material air having a very low hydrogen content is used, the removal efficiency of hydrogen, which is one of the low-boiling components, is high, and thus the product liquid nitrogen is further purified. be able to.

[0009]

1 and 2 are flow diagrams showing an embodiment of an ultrapure nitrogen production method and apparatus according to the present invention, in which a raw air is fed to a medium pressure rectification column which is a lower rectification column of a double rectification column. 5, gaseous nitrogen rectified and separated from the raw material air in the medium pressure rectification tower 5 is condensed and liquefied in a condenser 15 provided at the bottom of the low pressure rectification tower 6 which is the upper rectification tower of the double rectification tower. The condensed and liquefied liquid nitrogen is introduced again as a reflux into the top of the medium-pressure rectification column 5, and a part of the reflux liquid is rectified several stages below the rectification plate at the top of the medium-pressure rectification column 5. , And further supercooled by a supercooler 9, free-expanded, then gas-liquid separated by a gas-liquid separator 10, and a part of ultrahigh-purity liquid nitrogen is derived as product liquid nitrogen.

The raw air passes through an air filter 1 to remove dust from the air. The raw air is led to an air compressor 2 through a pipe P1 and compressed to a pressure of about 5 kg / cm ² G. As an example of a device for oxidizing carbon monoxide and hydrogen, it is introduced into a converter 3a filled with an oxidation reaction catalyst such as platinum or palladium. Most of the carbon monoxide and hydrogen in the raw air is oxidized by the converter 3a to carbon dioxide and water, and the decarburized dry storage unit 3b is cooled by the pipe P2.
The cooling and removal of carbon dioxide gas and water in the raw material air are carried out, and the unreacted hydrogen remaining without being oxidized by the converter 3a is occluded. It is introduced into the heat exchanger 4 at P3. The cooling and decarburizing dry storage unit 3b includes a hydrogen storage alloy such as a titanium-iron system and a magnesium-nickel system in addition to an adsorbent such as carbon dioxide (carbon dioxide), synthetic zeolite for adsorbing water, and alumina. A packed adsorption tower is provided to constitute a device for removing moisture and carbon dioxide and a hydrogen storage device. In this adsorption tower, carbon dioxide, moisture and unreacted hydrogen in the raw material air are removed.

The raw material air introduced into the heat exchanger 4 is:
From the top of the low-pressure rectification tower 6, pipe P19, supercooler 9, pipe P
The high-purity nitrogen gas introduced into the heat exchanger 4 through 20 and the waste gas from the gas-liquid separator 10 are supplied to a waste gas pipe P12 for introducing the waste gas from the low-pressure rectification tower 6 to the supercooler 7. The exhaust gas pipes P31 and P32 to be connected are connected to each other, and the waste gas from the low-pressure rectification tower 6 and the gas-liquid separator 10 introduced into the heat exchanger 4 through the pipe P33 from the supercooler 7 and the low-pressure Stay tower 6
Oxygen gas introduced into the heat exchanger 4 from the intermediate pressure rectification tower 5 through the pipe P22 through the pipe P22.
The mixture is cooled to near the liquefaction point by exchanging heat with the nitrogen gas introduced into the column, and is introduced into the bottom of the medium-pressure rectification tower 5 through the pipe P4, and the rectification sections A, B, and It is rectified by C to produce nitrogen gas and liquid nitrogen at the top and oxygen-rich liquid at the bottom.

The oxygen-rich liquid accumulated at the bottom of the medium-pressure rectification column 5 is introduced into the liquid air filters 8a and 8b to be used by switching through a pipe P5, and the hydrocarbon content concentrated in the oxygen-rich liquid is reduced. After being removed, it is introduced into a supercooler 7 through a pipe P6, exchanges heat with the waste gas from the low-pressure rectification tower 6 and the gas-liquid separator 10, and is supercooled, and is freely cooled by an expansion valve V1 provided in the pipe P7. After being expanded and cooled, it is introduced into the upper and lower central portions of the low-pressure rectification column 6 via a pipe P8. Liquid nitrogen formed in the upper and lower central portions of the medium pressure rectification tower 5 is introduced into the supercooler 7 from the liquid reservoir R3 via the pipe P9, and exchanges heat with waste gas from the low pressure rectification tower 6 and the gas-liquid separator 10. It is supercooled, is guided to an expansion valve V2 by a pipe P10, expands freely, is further cooled, and is introduced into the upper part of the low-pressure rectification column 6 by a pipe P11.

[0013] The low boiling components (helium (H) in the feed air after removing most of the hydrogen by the converter 3a.
e), hydrogen (H ₂ ), neon (Ne)) are generally about 5,000 vol. PPB (VPPB) for helium, about 1 vol. PPB (VPPB) for hydrogen, and about 15,000 vol. PPB (VPPB) for neon. However, in the oxygen-rich liquid accumulated at the bottom of the medium pressure rectification column 5, helium contains about 20 VP.
PB and hydrogen are dissolved at 0 VPPB and neon is dissolved at about 400 VPPB, and the remainder is concentrated in nitrogen gas at the top of the medium pressure rectification column 5. Then, the nitrogen gas produced at the top of the medium-pressure rectification tower 5 is introduced into a condenser 15 provided at the bottom of the low-pressure rectification tower 6 via a pipe P35 in the rectification tower, and the liquid in the low-pressure rectification tower 6 It is condensed and liquefied by heat exchange with oxygen. At this time, most of the low-boiling components introduced into the condenser 15 together with the nitrogen gas are not liquefied but gaseous and pass from the lower part of the condenser 15 through a pipe P58 as a discharge path, and a total of about 1,000,000 The valve V8 is used as uncondensed nitrogen gas containing low boiling components of 2,000 VPPB to 20,000,000 VPPB (about 0.1 to 2.0% by volume).
Exhausted through.

The liquid nitrogen condensed and liquefied in the condenser 15 is introduced as a reflux liquid into the liquid reservoir R1 of the medium-pressure rectification column 5 through a pipe P36.
Since it contains a low boiling point component of 000 VPPB, it is rectified in a rectification section C consisting of several rectification plates provided at the top of the medium pressure rectification column 5 in order to further reduce the low boiling point component. Liquid nitrogen containing low-boiling components of about 330 VPPB in total is stored in a liquid reservoir R2 provided below the rectification section C. The liquid nitrogen led out of the liquid reservoir R2 by the pipe P13 as a lead-out path is a high-purity nitrogen gas (low boiling point component totaling about 1,000 VP
PB) is supercooled by heat exchange with PB, taken out through a pipe P14, freely expanded by an expansion valve V4 to further lower the temperature, and partially vaporized liquid-liquid mixed nitrogen is connected to a gas-liquid separator 10 through a pipe P15. To be introduced. The liquid nitrogen in a gas-liquid mixed state introduced into the gas-liquid separator 10 is subjected to gas-liquid separation, and the separated nitrogen gas contains a low boiling point component of about 3,000 VPPB in total. To the valve V5
To adjust the pressure, and discharge from the pipe P32. As a result,
The liquid nitrogen separated by the gas-liquid separator 10 has a total of about 10 V
PPB is purified to ultra-high purity containing only low-boiling components (when helium and hydrogen are helium and hydrogen, helium is about 0.05 VPPB and hydrogen is 0.00 VPPB, for a total of about 0.05 VPPB). It has become.

The liquid level controller LI of the gas-liquid separator 10 is controlled so that the amount of liquid nitrogen separated by the gas-liquid separator 10 becomes substantially constant.
C and the expansion valve V4 are linked to each other, and the separated ultrahigh-purity liquid nitrogen is stored as a product liquid nitrogen in storage tanks (not shown) in pipes P16 and P51 whose flow rate is controlled by a valve V6 with a flow controller. ). The product liquid nitrogen is led out from the gas-liquid separator 10 to the storage tank by a head difference, that is, a difference in the height position between the gas-liquid separator 10 and the storage tank. Ultra high purity of nitrogen is maintained. Further, of the ultra-high purity liquid nitrogen separated by the gas-liquid separator 10, the remaining ultra-high purity liquid nitrogen which has not been converted into the product liquid nitrogen is supplied to the pipes P17 and P18 whose flow rates are controlled by the flow controller valve V7. To control the flow rate to a constant level,
The gas which is introduced at the top and becomes the reflux liquid of the rectification section F of the low-pressure rectification column 6 and rectifies the gas which rises in the low-pressure rectification column 6 is rectified.

The high-purity nitrogen gas introduced into the supercooler 9 from the top of the low-pressure rectification column 6 through the pipe P19 passes through the pipe P20 and the heat exchanger 4 to become high-purity nitrogen gas at normal temperature and low pressure.
At 52, it is extracted as high-purity product nitrogen gas. Medium-pressure high-purity nitrogen gas, which is led out from the top of the medium-pressure rectification tower 5 through a pipe P22 and exchanged heat with the heat exchanger 4 to become a normal temperature, is partially converted into product nitrogen through a branch pipe P53 from a pipe P24. Extracted as gas. The low pressure rectification tower 6 transfers heat from the medium pressure rectification tower 5 at the bottom thereof and rectifies it in the rectification sections D, E and F.
Producing high purity nitrogen gas at the top and liquid oxygen at the bottom,
Product liquid oxygen is taken out through a pipe P54. The oxygen gas produced at the lower part of the low-pressure rectification column 6 can be taken out through the pipe P21, the heat exchanger 4, and the pipe P55.

In order to take out ultra-high-purity liquid nitrogen, liquid oxygen, and the like in large quantities as liquid products, it is necessary to supply cold. Therefore, the medium-pressure high-purity nitrogen gas, which has become normal temperature from the medium-pressure rectification tower 5 through the pipe P22 and the heat exchanger 4, is supplied to the pipe P
The high-purity nitrogen gas that has been introduced into the compressor 12 at 24 and has been compressed and has become high pressure is supplied to the heat exchanger 11 via a pipe P26 and cooled until it is partially liquefied, and is led out to an expansion valve V3 via a pipe P29. Free expansion is performed to medium pressure, a part is gas, and the remainder is liquid and introduced into the medium pressure rectification tower 5 through the pipe P30 to replenish the cold. Part of the high-purity high-purity nitrogen gas supplied from the compressor 12 to the heat exchanger 11 via the pipe P26 is branched and supplied to the expander 13 via the pipe P27, and after being adiabatically expanded and cooled by the expander 13, the pipe P28 is cooled. Before entering the heat exchanger 4 and merging with the medium-pressure high-purity nitrogen gas branched from the pipe P22 to the pipe P23.
1 and becomes a cold source of high-pressure and high-purity nitrogen gas from the pipe P26.
From the pipe 25, the pipe P24 joins the medium-pressure high-purity nitrogen gas and is introduced into the compressor 12.

The waste gas from the low-pressure rectification tower 6 and the gas-liquid separator 10 introduced from the subcooler 7 to the heat exchanger 4 through the pipe P33 is discharged from the pipe P56, and a part of the waste gas is discharged. After being supplied to the cooled decarburization drying storage unit 3b through the pipe P34 and used for its regeneration, it is discharged from the pipe P57.

[Another embodiment] In the embodiment, the pipe P35
Is cooled in a nitrogen condenser 15 and then introduced into a separately provided gas-liquid separator to separate the condensed and liquefied liquid nitrogen and non-condensed non-condensed nitrogen gas into gas and liquid. The pipe P36 may be introduced into the liquid reservoir R1 of the intermediate pressure rectification tower 5 and the uncondensed nitrogen gas may be discharged through the pipe P58.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a flow diagram showing an ultrapure nitrogen production method and its apparatus.

FIG. 2 is a flow diagram showing a method and an apparatus for producing ultra-high purity nitrogen.

[Explanation of symbols]

 3a Oxidizing means 3b Removing means 5 Lower rectification column 10 Gas-liquid separator 15 Condenser P3 supply path P4 supply path P13 outlet path P31 discharge path P58 discharge path

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F25J 1/00-5/00 C01B 21/04

Claims (2)

(57) [Claims] 1. A feed air is supplied to a lower rectification column (5) of a double rectification column, and gaseous nitrogen rectified and separated from the feed air in the lower rectification column (5) is supplied to a condenser (15). Liquid nitrogen condensed and liquefied and condensed and liquefied in the condenser (15) is introduced as a reflux liquid to the top of the lower rectification column (5), and a part of the reflux liquid is removed from the lower rectification column (5). An ultrapure nitrogen production method for producing and producing product liquid nitrogen, comprising the steps of oxidizing hydrogen and carbon monoxide in raw material air, and water and carbon dioxide generated by oxidation of hydrogen and carbon monoxide and Removing the moisture and carbon dioxide gas originally contained in the raw air from the raw air, supplying the raw air from which the moisture and carbon dioxide have been removed to the lower rectification column (5), The uncondensed gas that has not been condensed and liquefied in the condenser (15) is discharged and contained in the gaseous nitrogen. A step of removing the low-boiling components that have been contained, and extracting a part of the liquid nitrogen introduced as the reflux liquid from a rectification plate several stages below the rectification plate at the top of the lower rectification column (5). Rectifying and separating the low-boiling components contained in the liquid nitrogen by subjecting the liquid nitrogen derived from the rectification plate several stages below to supercooling and free expansion .
The gas and liquid are separated in (10) to separate ultra-high purity liquid nitrogen and waste gas.
Raises, removing the low-boiling component is discharged the separated the waste gas contained in the liquid nitrogen, the greater
Part of the high-purity liquid nitrogen is removed from the gas-liquid separator (10).
The gas-liquid separator (10) is also stored in a storage tank provided at a lower position.
Using the difference in height between the tank and the storage tank,
Storing it as body nitrogen; and
The remainder is introduced into the top of the low pressure rectification column (6),
Low-pressure rectification tower (6)
And a step of rectifying a gas that rises in temperature. 2. A feed air is supplied to a lower rectification column (5) of a double rectification column, and gaseous nitrogen rectified and separated from the feed air in the lower rectification column (5) is passed through a condenser (15). Liquid nitrogen condensed and liquefied and condensed and liquefied in the condenser (15) is introduced as a reflux liquid to the top of the lower rectification column (5), and a part of the reflux liquid is removed from the lower rectification column (5). An ultrapure nitrogen production apparatus for producing a product liquid nitrogen by licensing out hydrogen and carbon monoxide in raw material air.
a) removing means (3b) for removing, from the raw material air, water and carbon dioxide produced by the oxidizing means (3a), and moisture and carbon dioxide originally contained in the raw material air; Supply paths (P3) and (P4) for supplying raw air from which gas has been removed to the lower rectification column (5), and a discharge path for discharging uncondensed gas that has not been condensed and liquefied in the condenser (15). (P58), and a lead-out path (P13) for leading a part of the liquid nitrogen introduced as the reflux liquid from a rectification plate several stages below the rectification plate at the top of the lower rectification column (5); After supercooling and freely expanding the liquid nitrogen derived from the rectification plate several stages below, the liquid nitrogen is separated into gas and liquid by a gas-liquid separator (10) to produce an ultra-high purity liquid.
Generates body nitrogen and waste gas, and discharges the separated waste gas.
To remove low boiling components contained in the liquid nitrogen
And a part of the ultra-high purity liquid nitrogen,
The storage tank provided below the separator (10) is
Utilizing the difference in height between the gas-liquid separator (10) and the storage tank
Means for flowing and storing as product liquid nitrogen;
The remainder of the ultra-high purity liquid nitrogen is transferred to the top of the low pressure rectification column (6).
Into the rectification section of the low-pressure rectification column (6).
And a means for rectifying gas rising in the low-pressure rectification column (6) .