JPH02272288A - Argon recovery method - Google Patents

Abstract

PURPOSE:To enable argon having a high recovering efficiency and the low density of nitrogen to be separated and recovered by separating and removing nitrogen contained in argon-containing exhaust gas by two steps of an adsorption treatment step of a pressure fluctuation adsorption method and a crude argon separation step of an air low-temperature separation method. CONSTITUTION:Argon-containing exhaust gas generated from an equipment 1 is pressurized by a compressor 5 after dust has been eliminated from said exhaust gas, and is supplied to an adsorber 6 that treats the exhaust gas by a pressure fluctuation adsorption method i.e., a PSA method, and adsorption treatment is performed in the adsorber so that nitrogen becomes 2% or so. The argon gas thus concentrated is, if hydrogen is present therein, allowed to react with oxygen contained in the exhaust gas to form moisture in a dehydrogenenating device 12, and the resultant moisture is dehumidified and removed. The argon-concentrated gas is introduced into a crude argon column 18 that treats the same by an air low-temperature separation method, to remove nitrogen, thereby recovering argon in high yields.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for recovering argon gas from argon-containing exhaust gas in argon-using equipment, such as argon oxygen blowing furnaces and RH vacuum degassing equipment.

(b) Prior art Recently, argon gas has been widely used in the refining process of steel manufacturing. Because it enables decarburization without oxidizing chromium chromium and also provides good quality, it has attracted attention as a new method for molten high-chromium steel and has been adopted for refining.

Similarly, the molten steel degassing method, which is carried out for the purpose of degassing during the refining process during the steelmaking process, involves exposing t9m to a vacuum to reduce harmful hydrogen, nitrogen, and oxygen gases as impurities in the molten m+. An inert gas is passed through the molten steel as a reflux gas and a tuyere cooling gas, and argon is especially used as the inert gas when producing low nitrogen steel.

In addition, not only for the above-mentioned chromium-containing steel but also for ordinary refining, a method of oxygen refining while stirring molten steel with argon has been adopted for the purpose of improving decarburization efficiency. Moreover, the amount used is also on the rise.

Argon gas used for such purposes is industrially produced by further concentrating argon-containing gas obtained from an air cryogenic separation device using an argon recovery method. Since argon gas is contained in the air at only about 0.93%, it is expected that there will be a shortage of supply to meet the demand in the future. It is also very expensive.

Therefore, in order to reduce the amount of argon used, attempts have been made to separate and recover argon from the used exhaust gas and reuse it.

For example, Japanese Patent Publication No. 50-6999 discloses that the exhaust gas is isolated from the outside air and collected, - brought into contact with a carbon oxide selective absorption liquid (such as pure ammonia solution), - carbon oxide removed and argon recovered. discloses a method to do so. In addition, Japanese Patent Publication No. 52-28750 discloses that oxygen is added to the collected exhaust gas isolated from the outside air, carbon oxide is burned and converted to carbon dioxide, and then the carbon dioxide is liquefied at about -100°C. A method for condensing, removing, and recovering argon is disclosed.

However, these processes have not been put into practical use because they have complicated equipment configurations and involve regeneration of the absorption liquid, which requires high movement costs, making it difficult to recover argon economically.

Therefore, argon recovery methods using pressure fluctuation adsorption methods are currently the mainstream. In the recovery method using the pressure fluctuation adsorption method, if nitrogen is present in the exhaust gas, it is impossible to completely adsorb and remove this nitrogen.

When recovering argon is reused in an argon-oxygen blowing furnace, if the nitrogen concentration is high, the nitrogen concentration in the steel will rise and the specification will be exceeded, so the nitrogen concentration in the recovered argon should be 0.2x.
It is necessary to do the following.

On the other hand, when nitrogen is removed by pressure fluctuation adsorption, there is a relationship shown in Figure 2 between the nitrogen concentration in the argon-enriched gas and the argon yield expressed by the following formula. (%) has the disadvantage that it decreases as the nitrogen concentration in the recovered argon decreases.

(c) Problems to be Solved by the Invention The problem to be solved by the present invention is to obtain an argon recovery method with high yield and low nitrogen concentration when separating and recovering argon from argon-containing exhaust gas. .

(d) Means for Solving the Problems The argon recovery method of the present invention is a method for recovering argon from argon-containing exhaust gas discharged from equipment using argon, in which the exhaust gas is adsorbed by a pressure fluctuation adsorption method. The above-mentioned problem has been solved by a means that consists of converting the argon-containing gas into an argon-containing gas, and then introducing the argon-enriched gas into a crude argon column in an air cryogenic separation method to recover argon.

When the argon-containing exhaust gas contains hydrogen,
After removing hydrogen, the argon Fa1i! Preferably, the gas is introduced into a crude argon column in the air cryogenic separation process to recover argon.

It is preferable that the crude argon column top blow gas in the air cryogenic separation method is subjected to adsorption treatment by the pressure fluctuation adsorption method to recover argon again.

(E) Example Next, an example of the method of the present invention will be described below with reference to FIG. In the figure, (1) is equipment using argon, such as an argon-oxygen blowing furnace and RH vacuum degassing equipment. The argon-containing exhaust gas generated from the equipment (1) is sucked in by the induced blower (2), and then passed through the dust remover (3).
After the dust is removed, the exhaust gas holder (4
). After that, the exhaust gas is pressurized to about 5 to 10 atmospheres by the compressor (5), and the exhaust gas is pressurized by the pressure fluctuation adsorption method (
Hereinafter referred to as the PSA method. ) is supplied to the adsorption device (6).

The adsorption device (6) based on the PSA method uses a zeolite system (which selectively adsorbs carbon oxide, carbon dioxide and nitrogen).
It consists of adsorption towers (7a) to (7c) filled with adsorbents (mixtures of silica, silica, and alumina), a vacuum pump (8), and a series of automatic switching valves (9). Each adsorption tower (7a
) to (7c), by the operation of the automatic switching valve (9) group, an adsorption treatment cycle consisting of, for example, pressure equalization, pressurization, adsorption, desorption, and purge is repeated, whereby - carbon oxide, carbon dioxide, and Nitrogen is adsorbed and removed, and argon gas is taken out.

Here, it is better to adsorb and remove carbon monoxide, carbon dioxide, and nitrogen in the exhaust gas as much as possible to obtain a highly purified argon enriched gas, but as for nitrogen, the greater the degree of removal, the more The disadvantage is that the argon yield is reduced.

Figure 2 shows the nitrogen concentration (
%) and the argon yield (%). It can be seen that the argon yield (%) decreases (deteriorates) as more nitrogen is adsorbed and removed (as the nitrogen concentration in the argon concentrated gas decreases).

Therefore, in the present invention, the adsorption treatment is performed so that as much nitrogen as possible remains, and this residual nitrogen is introduced into the crude argon column in the air cryogenic separation method described later, thereby increasing the argon yield in the adsorption treatment step. It is something that improves.

If hydrogen is present in the exhaust gas, the argon gas thus concentrated is subjected to an oxidation reaction with oxygen in the exhaust gas in the hydrogen removal device 12 to form water, and is dehumidified and removed. A pb catalyst tower is generally used as a hydrogen removal device.

This argon enriched gas from which hydrogen has been removed is introduced into a crude argon column 18 in the air cryogenic separation method described later.

Next, an air separation apparatus using the air cryogenic separation method will be explained.

0@ indicates an air separation device using an air cryogenic separation method, and the production of pure argon in this air cryogenic separation method consists of the following steps (A) to (1).

(A) Inhale air and use a bag filter to remove dust, etc. from the air.

(B) The raw air is compressed to 5k by the raw air compressor 14.
Compress to g/cd. If necessary, the raw air is washed and cooled in a water washing tower (not shown).

(C) By exchanging heat between the raw air and impure nitrogen, pure nitrogen, and oxygen in the heat exchanger 15 to lower the temperature of the raw air, carbon oxide and the like are separated as solids.

(D) Part of the compressed raw air is sent to the expansion turbine 16.
It was expanded and used as a cold source.

(E) Feedstock air is introduced from the lower part of the air separation column 17, and by utilizing the difference in boiling point (liquefaction point), oxygen in the air,
Separate into nitrogen and argon. On the other hand, hydrocarbons contained in the feed air are adsorbed by a hydrocarbon adsorption device (not shown), and acetylene contained in liquid oxygen is adsorbed by an acetylene adsorption device (not shown).

(F) Product nitrogen is extracted from the upper part of the upper column of the air separation column 17, and product oxygen is extracted from the lower part of the upper column.

From the middle of the upper tower, a gas with an argon purity of about 12% and almost no nitrogen is extracted as a feed gas.

(G) The feed gas is separated in the crude argon column 18 using the same principle as the air separation column 17, and about 96% of the crude argon is separated.

As described above, crude argon can be continuously extracted from air through the steps (A) to (G). This crude argon is used as a refining gas in an argon-oxygen blowing furnace.

By the way, if the nitrogen concentration in the argon-concentrated gas obtained by adsorbing argon-containing exhaust gas by the above-mentioned pressure fluctuation adsorption method (PSA method) is removed to 0.2% or less, the yield decreases.

Therefore, in the present invention, the nitrogen removal in the psA method is limited to about 2%, and the remaining nitrogen is removed by introducing it into the crude argon column 18 in the air cryogenic separation method (G), thereby achieving a high yield. Collect argon. As shown in step (G) above, in the crude argon 18, nitrogen is removed to about 0.1x and o2 to about 4x by utilizing the difference in boiling point (liquefaction point), and the crude argon is separated.

Here, the appropriate amount of nitrogen in the argon enriched gas by the PSA method introduced into the crude argon column 18 is about 2χ, and if it exceeds this value, the nitrogen concentration in the crude argon will increase. Therefore, in the adsorption treatment by the PSA method, the flow rate of the argon condensed gas is adjusted, for example, by the control valve 23 so that the amount of nitrogen is about 2χ, and then the gas is introduced into the crude argon column 18. Thereby, the argon yield in the adsorption treatment process can be increased, and argon with a low nitrogen concentration can be collected.

Further, in the crude argon column 18, fa-condensed nitrogen is blown into the upper part of the column, and by recovering this top-blown gas 19 to the adsorption device 6, the argon yield is further improved.

Specific examples of the argon recovery method of the present invention will be described below.

Mountain slope gas treatment was carried out using the RH vacuum degassing equipment under the operating conditions shown in Table 1, and the argon-containing exhaust gas shown in Table 2 that was exhausted at that time was stored in an exhaust gas holder, and then argon was recovered using an adsorption device using the PSA method.

As a result, an argon-enriched gas having the composition shown in Table 3 was obtained with a yield of about 75%.

Table 1 Next, this argon concentrated gas 100Nrd/H was mixed with Pb
After removing hydrogen in the catalyst tower, it was dehumidified and introduced into a crude argon tower. As a result, N! Crude argon of 0.1χ, ox 4m was stably obtained, and the argon yield by the PSA method was ps
Compared to 67% when nitrogen was adsorbed and removed up to 0.1χ, the method of the present invention improved it to 75%.

An additional 1% yield improvement was achieved by PSA re-recovery of the top blow gas from the crude argon column with the composition shown in Table 4.

(f) Effects According to the method of the present invention, nitrogen in the argon-containing exhaust gas is separated and removed in two steps: an adsorption treatment step using a pressure fluctuation adsorption method and a crude argon separation step using an air cryogenic method. This makes it possible to separate and recover argon with high recovery efficiency and low nitrogen concentration.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing one embodiment of the method of the present invention, and FIG. 2 is a graph showing the relationship between the nitrogen concentration in the argon I condensed gas and the argon recovery rate in the pressure fluctuation adsorption method. 1...Argon toilet equipment. 3... Dust remover 5... Compressor. 7a to 7c --- adsorption tower. 9...Automatic switching valve. 12...Hydrogen removal device. 14... Raw air compressor 16-expansion turbine 18... Crude argon column. 19...-crude argon tower top blower gas 2--induced blower 4--exhaust gas holder. 6--Adsorption device 8-Vacuum pump 10-Air separation device 13...Filter 15...Heat exchanger. 17...Air separation tower patent applicant: Sumitomo Metal Industries, Ltd. Kyodo Oxygen Co., Ltd.

Claims (1)

[Claims] 1. In a method for recovering argon from argon-containing exhaust gas discharged from equipment using argon, the exhaust gas is subjected to adsorption treatment by a pressure fluctuation adsorption method to form an argon-concentrated gas, and then the argon concentration is performed. An argon recovery method characterized by introducing gas into a crude argon column in an air cryogenic separation method to recover argon. 2. A claim characterized in that when the argon-containing exhaust gas contains hydrogen, after removing hydrogen, the argon concentrated gas is introduced into a crude argon column in an air cryogenic separation method to recover argon. Item 1. Argon recovery method. 3. The argon recovery method according to claim 1, wherein the crude argon column top blow gas in the air cryogenic separation method is adsorbed by the pressure fluctuation adsorption method to recover argon again.