JPH11325720A - Manufacture of ultra-high-purity nitrogen gas and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing ultra-high-purity nitrogen gas that can be effectively utilized with inexpensive facilities. SOLUTION: In a method for filing compressing feed air, cooling it to a low temperature, and then introducing it to a rectifying column 7, performing its subcooling liquefaction separation for manufacturing an ultra-high-purity nitrogen gas, and for filling one portion of the amount of cold required for the subcooling liquefaction separation is supplied from the outside of the subcooling liquefaction separation system with the cold energy of the high-purity liquid nitrogen, one portion of a reflux liquid (ultra-high-purity liquid nitrogen) being generated by a condenser 9 at the upper portion of the rectifying tower 7 and is stored at an ultra-high-purity liquid nitrogen tank 25, and then ultra- high-purity liquid nitrogen being stored in the ultra-high-purity liquid nitrogen tank 25 is vaporized on backup.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying 99.999 purity.
The ultra-high purity product nitrogen gas can be stably used in semiconductor manufacturing processes and other chemical processes and analysis processes that require 999% or more (ultra-high purity) product nitrogen gas.
The present invention relates to an ultrahigh-purity nitrogen gas production method which can be produced and supplied at low cost, and an apparatus used therefor.

[0002]

2. Description of the Related Art Conventionally, as a means for supplying ultra-high-purity nitrogen gas having an impurity oxygen concentration of 10 ppb or less, an ultra-high-purity nitrogen gas producing apparatus has been installed at a gas consuming site (for example, a site of a semiconductor manufacturing plant). An ultrahigh-purity nitrogen gas produced by this apparatus is directly supplied to a semiconductor production process by piping. The apparatus shown in FIG. 4 is used as such an ultrahigh-purity nitrogen gas producing apparatus. In FIG. 4, reference numeral 1 denotes an air compressor which compresses raw air taken in from outside to produce compressed air. Reference numeral 2 denotes a catalyst tower that oxidizes CO, hydrogen, and hydrocarbons in compressed air to generate CO ₂ and moisture, and uses a platinum-based or palladium-based catalyst as a catalyst. 3 is a CFC cooler. No. 4 adsorbs and removes CO ₂ , moisture and the like in the compressed air.
This is a pair of adsorption towers, and activated alumina, zeolite and the like are used as an adsorbent. Reference numeral 5 denotes a main heat exchanger that cools the compressed air that has passed through the adsorption tower 4 to an extremely low temperature. Reference numeral 6 denotes a supply pipe, which serves to feed compressed air cooled to a very low temperature by the main heat exchanger 5 to a lower portion of the rectification column 7. 7
Is a rectification column, in which liquid air accumulates at the bottom and ultra-high-purity nitrogen gas stays at the top. 8 is a rectification column 7
And a condenser 9 is provided inside the reboiler. Liquid air collected at the bottom of the rectification column 7 is fed into the reboiler 8 through a supply pipe 13 with an expansion valve 13a. The condenser 9 has a rectification column 7
A part of the ultra-high-purity nitrogen gas taken out from the inside into a product nitrogen gas take-out pipe 12 is sent through the first reflux pipe 10 to be liquefied, and then liquefied through the second reflux pipe 11.
Returned to the top. On the other hand, the ultra-high purity nitrogen gas passing through the condenser 9 functions to heat and vaporize the liquid air stored in the reboiler 8. Reference numeral 12 denotes a product nitrogen gas extraction pipe with a flow control valve 12a, which takes out ultrapure nitrogen gas remaining at the top of the rectification column 7, sends it to the main heat exchanger 5, and compresses the gas through the main heat exchanger 5. In addition to cooling the air, it acts to raise itself to room temperature and send it out of the apparatus as product nitrogen gas. Reference numeral 14 denotes an exhaust gas pipe for extracting non-condensable gas such as hydrogen and He that is not condensed in the condenser 9 from the gas phase of the reflux liquid and discharging the gas to the outside of the apparatus. Numeral 15 takes out the impurity gas (air having a high nitrogen concentration) accumulated in the upper part of the reboiler 8, guides it into the main heat exchanger 5, cools the compressed air passing through the main heat exchanger 5, and discharges the compressed air to the outside. It is an exhaust gas pipe. Reference numeral 18 denotes a liquid nitrogen storage tank for storing high-purity liquid nitrogen (generally, impurity oxygen concentration of 10 ppm or less) supplied from outside the apparatus. High-purity liquid nitrogen from the liquid nitrogen storage tank 18 is introduced with a liquid nitrogen supply valve 19a. It is introduced into the upper part of the rectification column 7 via a pipe 19. Reference numeral 20 denotes a backup pipe, which includes an evaporator 21, a nitrogen purifier 22, and a pressure control valve 23.

[0003] Using such a device,
Nitrogen gas can be produced. That is, first, Hara
Charge air is introduced into the air compressor 1 where it reaches the required pressure.
After the pressure is increased, the catalyst tower 2, the CFC cooler 3, and the adsorption tower 4
CO and hydrocarbons, CO _Two， Removing water, main heat exchange
To the exchanger 5. Here, the air cooled to extremely low temperature
The gas is introduced into the rectification column 7, and the rising gas inside the rectification column 7 and the condenser
9 is a superfluous liquid flowing down the rectification column 7 as a reflux liquid.
By bringing pure liquid nitrogen into gas-liquid contact, the top of the rectification column 7
Part is concentrated with ultra-high purity nitrogen gas, and 30-
A liquid air rich in 40% oxygen is stored. To this oxygen
After reducing the rich liquid air through the expansion valve 13a,
The product is introduced into a boiler 8 where the product nitrogen
Feed through gas extraction pipe 12 and first reflux pipe 10
Heat exchange with part of the ultra-high purity nitrogen gas
By producing pure liquid nitrogen,
And After that, this exhaust gas is passed through the exhaust gas pipe 15
Through the main heat exchanger 5 and exchanges heat with the raw material air.
To room temperature. In addition, ultra-high purity nitrogen gas is
Take out from the top of the rectification column 7 by the raw gas extraction pipe 12
Into the main heat exchanger 5 and constantly exchange heat with the raw air.
After the temperature is raised to the temperature, it is used as product nitrogen gas. Meanwhile, the main heat exchange
To compensate for the heat exchange loss in the heat exchanger 5 and the cooling heat loss due to the heat entering outside.
For this purpose, the liquid nitrogen supply valve 19a is
To supply high-purity liquid nitrogen to the upper part of the rectification column 7.

[0004] When such an apparatus is stopped for some reason, or when the consumption of the product nitrogen gas exceeds the generating capacity of the apparatus, high-purity liquid nitrogen from the liquid nitrogen storage tank 18 is supplied to the evaporator 21 by air or air. After the temperature is raised to normal temperature by heat exchange with water or another fluid, the nitrogen is purified to ultra-high purity by the nitrogen purification device 22 and supplied as a backup as product nitrogen gas.

[0005]

However, in the case of the above-mentioned ultra-high purity nitrogen gas producing apparatus, in the event that the apparatus is stopped or the like, the high-purity liquid nitrogen stored in the liquid nitrogen storage tank 18 as a backup supply is provided. Therefore, the oxygen concentration of the product nitrogen gas becomes about 10 ppm, so that ultra-high purity liquid nitrogen gas cannot be taken out as product nitrogen gas. Therefore, in the event that the apparatus is shut down, it is necessary to provide a nitrogen purifying apparatus 22 for purifying the high-purity liquid nitrogen stored in the liquid nitrogen storage tank 18 to ultra-high purity, which requires a great deal of cost. And

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for producing ultra-high-purity nitrogen gas which can be effectively used with inexpensive equipment, and an apparatus used therefor.

[0007]

In order to achieve the above object, the present invention provides a method of compressing raw air, cooling the raw air to a low temperature, introducing the compressed air into a rectification means, where it is subjected to cryogenic liquefaction and separation to obtain ultra-high purity. A method of producing nitrogen gas and applying a part of the amount of refrigeration required for the cryogenic liquefaction separation with the cryogenic energy of high-purity liquid nitrogen supplied from outside the cryogenic liquefaction separation system, An ultra-high-purity nitrogen gas production method is described in which a part of the ultra-high-purity liquid nitrogen obtained in the separation is taken out from the rectification means and stored, and the stored ultra-high-purity liquid nitrogen is vaporized and used at the time of backup. According to a first aspect, air compression means for compressing raw air, a main heat exchanger for cooling the compressed air having passed through the air compression means to a low temperature, and compressed air cooled to a low temperature by the main heat exchanger are introduced. For cryogenic liquefaction and separation A nitrogen gas extraction pipe for extracting ultra-high-purity nitrogen as a gas from the rectification means, a storage means for receiving and storing high-purity liquid nitrogen from outside the apparatus, and cooling the high-purity liquid nitrogen in the storage means. An introduction path leading to the rectification means as energy,
An ultra-high-purity liquid nitrogen storage means for taking out and storing a part of the ultra-high-purity liquid nitrogen obtained during the cryogenic liquefaction separation from the rectification means, and an ultra-high-purity liquid nitrogen storage means for storing in the ultra-high purity liquid nitrogen storage means at the time of backup A second aspect of the present invention is to provide an ultra-high-purity nitrogen gas producing apparatus which is provided with a backup pipe for gasifying and extracting high-purity liquid nitrogen and introducing it to the nitrogen gas extraction pipe.

That is, in the ultrahigh-purity nitrogen gas producing method of the present invention, a part of the ultrahigh-purity liquid nitrogen obtained at the time of cryogenic liquefaction separation by the rectification means is taken out from the rectification means and stored. At the time of backup (for example, when the apparatus is stopped for some reason or when the consumption of the product nitrogen gas exceeds the generating capacity of the apparatus), the stored ultra-high-purity liquid nitrogen is vaporized and used. Therefore, ultra-high purity nitrogen gas can be taken out as product nitrogen gas at the time of backup. In addition, there is no need to provide a nitrogen purification device 22 requiring a great deal of cost as in the conventional example.
On the other hand, according to the apparatus of the present invention, the above method can be easily performed. In the present invention, “ultra-high-purity nitrogen gas” means a nitrogen gas having higher purity than high-purity liquid nitrogen supplied from outside the cryogenic liquefaction / separation system.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the ultrahigh-purity nitrogen gas producing apparatus according to the present invention. In the present embodiment, in the ultrahigh-purity nitrogen gas producing apparatus shown in FIG. 4, an ultrahigh-purity liquid nitrogen tank 25 is provided, and the ultrahigh-purity liquid nitrogen tank 25 and an intermediate portion of the second reflux pipe 11 are withdrawn. (Flow control valve) First extraction pipe 26a with 26b,
The extraction pump 27 is connected to the second extraction pipe 26c via the second extraction pipe 26c so that a part of the reflux liquid (ultra high purity liquid nitrogen) flowing down the second reflux pipe 11 is extracted and stored in the ultra high purity liquid nitrogen tank 25. I have to. Also, a backup pipe 2 from the bottom of the ultra-high purity liquid nitrogen tank 25
8 (the evaporator 21 and the pressure control valve 23 similar to the conventional example are attached to the backup pipe 28) are joined to the product nitrogen gas extraction pipe 12. Further, the gas or ultra-high-purity liquid nitrogen generated by heat entering the ultra-high-purity liquid nitrogen tank 25 is
The flash gas generated when the gas is supplied to the product is passed through the pressure release pipe 29 and merges with the product nitrogen gas extraction pipe 12. The pressure relief pipe 29 has a pressure relief valve 29
a is provided to prevent the pressure in the ultrahigh-purity liquid nitrogen tank 25 from rising.

Using such an apparatus, an ultrahigh-purity nitrogen gas can be produced as follows. That is,
First, raw material air is introduced into the air compressor 1, where the pressure is increased to a required pressure (3.0 to 9.0 kg / cm ² G), and then introduced into the catalyst tower 2 to remove CO and hydrogen. Next, after the temperature is lowered to a predetermined temperature in the CFC cooler 3, the CO ₂ and moisture are removed through the adsorption tower 4 and introduced into the main heat exchanger 5. Here, the air cooled to a very low temperature is fed to a rectification column 7 operated at a pressure of about 2.5 to 8.8 kg / cm ² G.
(This rectification tower 7 may be a stack of several tens of trays or a stack of ordered packings). The rectification tower 7 is refluxed by the rising gas inside the rectification tower 7 and the condenser 9. The ultrahigh-purity nitrogen gas is concentrated at the top of the rectification column 7 by bringing the ultrahigh-purity liquid nitrogen descending in the rectification column 7 into gas-liquid contact, and 30 to 40% of the nitrogen gas is concentrated at the bottom of the rectification column 7. Stores oxygen-rich liquid air. The oxygen-rich liquid air is supplied to the expansion valve 13.
After reducing the pressure to about 0.2 to 5.0 kg / cm ² G through a, the mixture is introduced into the reboiler 8, where it is sent from the top of the rectification column 7 through the product nitrogen gas removal pipe 12 and the first reflux pipe 10. By performing heat exchange with a part of the ultra-high-purity nitrogen gas to produce ultra-high-purity liquid nitrogen, it vaporizes itself and becomes exhaust gas. After that, the exhaust gas is introduced into the main heat exchanger 5 through the exhaust gas pipe 15, and the temperature is raised to room temperature by heat exchange with the raw material air. Then, the ultrahigh-purity nitrogen gas is taken out from the top of the rectification column 7 and introduced into the main heat exchanger 5, where the temperature is raised to room temperature by heat exchange with the raw material air, and then the product nitrogen gas is obtained.

On the other hand, a part of the reflux liquid produced by the condenser 9 is taken out of the second reflux pipe 11 continuously or intermittently by the pump 27 as necessary, and the pressure is increased. (The pressurization of ultra-high-purity liquid nitrogen by the pump 27 may be performed after the ultra-high-purity liquid nitrogen is once stored in the ultra-high-purity liquid nitrogen tank 25). This ultra-high purity liquid nitrogen tank 25
The internal pressure is kept constant (approximately 2.0
８8.5 kg / cm ² G).

A liquid nitrogen storage tank is provided to compensate for the heat exchange loss in the main heat exchanger 5, the cooling loss due to external intrusion heat, and the cooling loss caused by taking out ultra-high-purity liquid nitrogen into the ultra-high-purity liquid nitrogen tank 25. 18 to liquid nitrogen supply valve 19
a, high-purity liquid nitrogen having a pressure of about 4.0 to 9.0 kg / cm ² G is supplied to the top of the rectification column 7. At this time, the position where the high-purity liquid nitrogen is supplied in the rectification column 7 is determined by the purity of the liquid nitrogen. The lower the purity, the more the liquid nitrogen is supplied from the upper portion of the rectification column 7 to the vicinity of the middle.

When the apparatus is stopped for some reason or when the consumption of the product nitrogen gas exceeds the capacity of the apparatus, the ultra-high-purity liquid nitrogen from the ultra-high-purity liquid nitrogen tank 25 is supplied to the evaporator 21 by air. Alternatively, the temperature is raised to normal temperature by heat exchange with water or other fluid, and then supplied as a backup as product nitrogen gas. Further, a gas generated by heat entering the ultrahigh-purity liquid nitrogen tank 25 or a flash gas generated when ultrahigh-purity liquid nitrogen is supplied to the ultrahigh-purity liquid nitrogen tank 25 is supplied to the pressure relief valve 29a.
Through to the product nitrogen gas, and is effectively used as a part of the product nitrogen gas.

As described above, in the above embodiment, a part of the reflux liquid (ultra high purity liquid nitrogen) generated by the condenser 9 is taken out and stored in the ultra high purity liquid nitrogen tank 25. Sometimes, ultra-high purity liquid nitrogen tank 2
By vaporizing and using the ultrahigh-purity liquid nitrogen stored in 5, the ultrahigh-purity nitrogen gas can be taken out as product nitrogen gas. Moreover, the nitrogen purifier 22 required in the conventional example can be omitted, and the cost is reduced.

FIG. 2 shows another embodiment of the ultrahigh-purity nitrogen gas producing apparatus according to the present invention. In this embodiment,
In the ultrahigh-purity nitrogen gas producing apparatus shown in FIG. 1, the ultrahigh-purity liquid nitrogen tank 25 is located below the extraction pipe 26. In this case, a part of the reflux liquid can be supplied to the ultrahigh-purity liquid nitrogen tank 25 only by the liquid head pressure. Other parts are the same as those of the embodiment shown in FIG. 1, and the same parts are denoted by the same reference numerals. Also in this embodiment, the same operation and effect as those of the embodiment shown in FIG. 1 are obtained, and the temperature rise of the pump 27 and the like in the embodiment shown in FIG. 1 can be omitted, and the structure is simplified. There is an advantage that the equipment is inexpensive.

FIG. 3 shows still another embodiment of the ultrapure nitrogen gas producing apparatus of the present invention. In this embodiment, in the ultrahigh-purity nitrogen gas producing apparatus shown in FIG.
When a booster is required for the backup supply, instead of a rotating machine such as a pump 27, two series of pressurized tanks 31,
32 are provided.

More specifically, the two pressurized tanks 31 and 32 are set to be lower in pressure or lower than the ultrahigh-purity liquid nitrogen tank 25, respectively. Branch pipe 3 with switching valves 34a, 35a provided on connecting pipe 33 extending from the bottom
4, 35 are connected. In addition, both pressurized tanks 3
1, 32 have pressure relief valves 31a, 3
2a, and self-pressurizing pipes 36, 37 communicating the bottom and the top thereof are mounted.
39 and pressure control valves 36a, 37a. Both pressurized tanks 31, 32 are connected to the backup pipe 28 by pipes 40, 41 with switching valves 40a, 41a. When the apparatus is operating normally, the ultra-high-purity liquid nitrogen stored in the ultra-high-purity liquid nitrogen tank 25 is supplied to the two pressurizing tanks 31 and 32 by the two switching valves 34 a and 3.
5a and both the pressure relief valves 31a and 32a are opened, and filling is performed using a pressure difference. When this filling is completed, both the switching valves 34a and 35a and both the pressure release valves 31a and 32a are closed, and in this state, the charged ultra-high-purity liquid nitrogen is removed from the bottoms of the two pressurized tanks 31 and 32. It is taken out and passed through the pressurized evaporators 38 and 39, where it is exchanged with air or water and vaporized and introduced into the tops of both pressurized tanks 31 and 32.
The two pressurizing tanks 31 and 32 themselves are self-pressurized. Other parts are the same as those of the embodiment shown in FIG. 1, and the same parts are denoted by the same reference numerals.

When the need for backup supply arises, the ultrahigh-purity liquid nitrogen in one of the two pressurized tanks 31 and 32 is passed through the evaporator 21. After that, it is backed up and supplied as product nitrogen gas. For example, when the backup supply is performed from the first pressurized tank 31 and the ultrahigh-purity liquid nitrogen in the first pressurized tank 31 is completely consumed, the second pressurized tank 3
The supply from 2 is started. At the same time, the first pressurized tank 3
The first pressure control valve 36a is closed, and the first pressure relief valve 31a is opened. Thereby, when the internal pressure of the first pressurized tank 31 starts to decrease and becomes lower than the internal pressure of the ultrahigh-purity liquid nitrogen tank 25, the switching valve 34a is opened, and the ultrahigh-purity liquid nitrogen Start filling. Thereafter, the same cycle is repeated. Also in this embodiment, the same operation and effect as those of the embodiment shown in FIG. 1 are obtained, and since a plurality of pressurized tanks 31 and 32 are provided, it is possible to stably produce and supply ultra-high-purity nitrogen gas. Can be.

In the embodiment shown in FIG. 3, two series of pressurized tanks 31 and 32 are provided. However, the present invention is not limited to this, and three or more series of pressurized tanks may be provided. Good.

[0021]

As described above, according to the air separation apparatus of the present invention, a part of the ultrahigh-purity liquid nitrogen obtained at the time of cryogenic liquefaction and separation by the rectification means is taken out from the rectification means and stored. In addition, at the time of backup (when the apparatus is stopped for some reason or when the consumption of the product nitrogen gas exceeds the generating capacity of the apparatus, etc.), the stored ultra-high-purity liquid nitrogen is vaporized and used. . Therefore, ultra-high purity nitrogen gas can be taken out as product nitrogen gas at the time of backup. In addition, there is no need to provide a nitrogen purification device 22 requiring a great deal of cost as in the conventional example. On the other hand, according to the apparatus of the present invention, the above method can be easily performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a configuration diagram showing still another embodiment of the present invention.

FIG. 4 is a configuration diagram of an ultrahigh-purity nitrogen gas production apparatus showing a conventional example.

[Explanation of symbols]

 7 rectification tower 9 condenser 25 ultra-high purity liquid nitrogen tank

Claims (3)

[Claims] The raw material air is compressed, cooled to a low temperature and introduced into a rectification unit, where it is subjected to cryogenic liquefaction and separation to produce ultra-high purity nitrogen gas, and the amount of refrigeration required for the cryogenic liquefaction and separation is determined. A method in which a part of the ultra-high-purity liquid nitrogen obtained during the cryogenic liquefaction separation is fractionated by rectifying the cryogenic liquefaction separation system. A method for producing ultra-high-purity nitrogen gas, wherein the ultra-high-purity liquid nitrogen stored is vaporized and used at the time of backup during storage. 2. The rectification means according to claim 1, wherein the rectification means includes a rectification column, and a condenser for generating a reflux liquid in the rectification column, and a part of the reflux liquid generated by the condenser is stored. Item 7. The method for producing ultrahigh-purity nitrogen gas according to Item 1. 3. An air compressor for compressing raw air, a main heat exchanger for cooling the compressed air passing through the air compressor to a low temperature, and compressed air cooled to a low temperature by the main heat exchanger. Rectification means for cryogenic liquefaction and separation, a nitrogen gas extraction pipe for taking out ultra-high-purity nitrogen as a gas from the rectification means, storage means for receiving and storing high-purity liquid nitrogen from outside the apparatus, An introduction path for guiding the high-purity liquid nitrogen in the storage means to the rectification means as cold energy, wherein a part of the ultra-high-purity liquid nitrogen obtained in the cryogenic liquefaction separation is used as the rectification means. A super-high-purity liquid nitrogen storage means for taking out and storing the ultra-high-purity liquid nitrogen stored in the ultra-high-purity liquid nitrogen storage means at the time of backup, and gasifying and taking out the ultra-high-purity liquid nitrogen for introduction into the nitrogen gas extraction pipe An ultra-high-purity nitrogen gas producing apparatus characterized by comprising a pipe.