JPS60122709A - Method for recovering argon - Google Patents

Abstract

PURPOSE:To recover efficiently Ar from Ar-base exhaust gas by burning H, CO and hydrocarbon in the exhaust gas, adding CO to remove oxygen, and adsorbing the remaining components except Ar. CONSTITUTION:Gas exhausted from a silicon furnace is a composition contg. CO, CO2, hydrocarbon, hydrogen, oxygen, moisture, etc. besides Ar as the principal component. The exhausted gaseous composition is introduced into catalytic burners 9, 10 through a heater 8 and piping 12. In the burner 9, hydrogen, CO and hydrocarbon in the composition are selectively burned by the action of a catalyst (the 1st stage). In the burner 10, oxygen remaining in the composition passed through the 1st stage is removed by adding CO and causing a catalytic reaction (the 2nd stage). Exhaust gas produced by the catalytic burning is pressurized with a compressor 15 and introduced into an adsorption tower 21a, 21b or 21c through piping 17 to remove impurities by adsorption. The resulting concd. Ar is stored in a product gas tank 26 through piping 27.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a method for recovering argon, and is a method for separating and purifying only argon contained in an exhaust gas composition discharged from a furnace using argon, for example, a silicon furnace in particular. and how to recover it.

[Background of the invention]

A silicon furnace is a furnace used to produce single crystal silicon by pulling up single crystal silicon from melted crude silicon through seeds, and argon is used as an atmospheric gas during production.

The exhaust gas composition discharged from this silicon furnace contains argon at a high concentration of 96 to 98%. Moreover, since argon is expensive, there is a tendency to separate and recover it from the exhaust gas composition and reuse it. As such an argon recovery method, for example, as shown in JP-A-54-20295 and JP-A-54-31415, hydrocarbons, hydrogen, carbon oxides and oxygen contained in the exhaust gas composition of a silicon furnace are A method has been disclosed in which oxygen is added to transform the mixture into moisture and carbon dioxide, excess oxygen is removed by reaction in an oxygen removal column, and moisture, carbon dioxide, etc. are adsorbed and removed in an adsorption column. In such a method,
Since hydrogen gas is used for regeneration in the deoxygenation cylinder,
This has the problem that a small amount of hydrogen remains, increasing the hydrogen concentration in the recovered argon gas, and increasing the size of the equipment used for recovery. In addition,
50, there is a method of recovering argon by oxidizing carbon monoxide in the exhaust gas composition and solidifying and separating the generated carbon dioxide using a cryogenic method, and a method of recovering argon as shown in Japanese Patent Publication No. 50-8999. discloses a method for recovering argon by removing carbon monoxide and carbon dioxide from an exhaust gas composition using a copper-ammonia complex and using an alkali, respectively.

The former method requires deep cooling to about -1ooc, which makes the structure of the device complicated, while the latter method requires absorption and dissipation operations, making it difficult to put it to practical use. It had some problems.

[Purpose of the invention]

An object of the present invention is to remove oxygen, which has chemical properties similar to argon, in advance when recovering argon from exhaust gas compositions discharged from silicon furnaces, etc., thereby making it possible to recover argon efficiently and economically and industrially. The purpose of the present invention is to provide a method for recovering alkones that can be carried out in the following manner.

[Summary of the invention]

The gist of this invention is to convert carbon monoxide, hydrogen, and hydrocarbons contained in an exhaust gas composition into moisture and carbon dioxide, which are easily adsorbed in the presence of oxygen, and to further add carbon monoxide to the remaining oxygen. The idea is to convert the gas into carbon dioxide, separate impurities from the gas composition using an adsorption/desorption method that utilizes a pressure difference, and concentrate and recover argon.

That is, the present invention provides a method for recovering argon from an exhaust gas composition mainly composed of argon and containing carbon monoxide, hydrogen, hydrocarbons, hydrogen dioxide, oxygen, etc., which is discharged from a silicon furnace. A first step in which hydrogen, carbon oxide, and hydrocarbons are combusted by bringing the entire composition into contact with the catalyst, and carbon monoxide is added to the gas composition that has passed through the first step and brought into contact with the catalyst to combust oxygen. a second step of removing argon, and a third step of concentrating and collecting argon by adsorbing the components excluding argon from the gas composition that has passed through the second step onto an adsorbent under pressure. A method for recovering argon is provided. Furthermore, the space velocity of the exhaust gas composition in the first step is kept below 15,000 h-, the combustion temperature (catalyst layer temperature) is kept below 60 (I'), and in the catalytic combustion of the second step, the gas composition is space velocity 15000
h-″1 KL or less, and the combustion temperature (catalyst layer temperature) is 30
It is characterized in that it is carried out while maintaining the conditions of 0 to 400 tll'.

Hereinafter, the present invention will be explained in detail according to the drawings.

FIG. 1 is a process block diagram of recovering argon from the exhaust gas composition of a silicon furnace in the present invention.

1 is a silicon furnace, and argon is blown into it from a pipe 2 connected to the bottom of the silicon furnace 1. The exhaust gas composition 3 discharged from the silicon furnace 1 is guided to an oil fume separator 5 by a vacuum pump 4. Oil is removed from the exhaust gas composition by this oil fume separator 5 and stored in a cushion tank 6. Next, the exhaust gas composition that has passed through the cushion tank 6 is sent by a compressor 7 via a heater 8 to contact combustors 9, 10, and an adsorption tower 11, where only argon is purified and recovered. In the argon recovery method, purified argon from which components other than argon have been substantially removed is supplied to the silicon furnace 1 again through the pipe 2.

FIG. 2 is a structural diagram further showing an example of the argon recovery method. In the figure, 12 is a pipe connected to the heater 8, and the exhaust gas composition that has passed through the heater 8 shown in FIG. Guided by lO. In the contact MfS burner 9, hydrogen, carbon oxide, and hydrocarbons in the exhaust gas composition are selectively burned by the action of the catalyst. Oxygen necessary for this combustion reaction is supplied from the oxygen supply pipe 13 as needed in addition to the oxygen contained in the exhaust gas composition. That is, this step corresponds to the first step. next,
In the second step, the catalytic combustor IO, carbon monoxide is added to the residual oxygen in the exhaust gas composition that has passed through the first step, and
The catalyst is brought into contact, reacted, and removed. Carbon monoxide necessary for the reaction is supplied from the supply pipe 14.

The catalytically combusted exhaust gas composition is pressurized by the compressor 15, and the heat generated thereby is released by the cooler 6. In this way, the pressurized exhaust gas composition is transferred to the pipe 17
It is sent to the third process through solenoid valve 18, 19 or 20.
through each adsorption tower 21a, 21b still 21C
is press-fitted into the

These suckers? The concentrated argon from which impurities have been adsorbed and removed by the pressure-adsorption treatment in the first towers 21a to 21C is
The product gas is stored in a product gas tank 26 via a piping 25 from a solenoid valve 22, 23, or 24. Concentrated argon gas is taken out via piping 27 as needed.

As described above, the present invention consists of a first step, a second step, and a third step, and before the third step, residual oxygen in the exhaust gas composition is reacted with carbon monoxide via a catalyst. It is characterized in that it is removed and subjected to the next adsorption treatment.

In other words, since oxygen has similar chemical properties to argon, it is difficult to separate it from argon due to adsorption.

Next, the catalyst used in the first step and the second step will be explained.

In the first step, platinum/alumina, palladium, alumina, etc. may be used as a catalyst for the combustion of oxygen, hydrogen, carbon oxide, and hydrocarbon, but platinum is used as a catalyst in the coexistence of hydrogen and carbon oxide. It is not preferable because it is strongly damaged by carbon oxide, resulting in a significant decrease in activity.

On the other hand, palladium is suitable as a catalyst for a system in which hydrogen and carbon oxide coexist, since its activity is less reduced by carbon monoxide than platinum. In the present invention, a palladium-alumina catalyst is used as the catalyst for the catalytic combustor. Note that the catalyst carrier is not limited to alumina, and other known carriers may also be used.

As the catalyst used for the reaction between oxygen and carbon monoxide in the second step, palladium and alumina are suitable as mentioned above. On the other hand, the adsorption tower in the second step is filled with an adsorbent such as zeolite 5A, which is more likely to selectively adsorb -carbon oxide, carbon dioxide, and water than argon. The adsorption pressure during selective adsorption in this way is
Although it depends on the performance of the adsorbent, a cage pressure of several atmospheres is sufficient.

Next, an adsorption operation cycle using a pressure difference adsorption/desorption method in the third step will be explained.

The adsorption operation cycle is exemplified by a series of three adsorption towers as shown in FIG. 2, and consists of six operations shown in Table 1. Each adsorption tower 2
12 to 21C consist of five stages of adsorption operations: equalization, pressurization, adsorption, desorption, and purging, and each operation performs the following operations.

Table 1 Pressure equalization stage: Some argon concentrated in other towers in the adsorption stage is added to the adsorption tower under normal pressure, where the adsorbent has been regenerated by purge, and the pressure inside the adsorption tower is increased. averaged. This ensures that the gas composition entering the next pressurization and adsorption step is richer in argon than the original exhaust gas composition, thereby improving the concentration and yield of recovered argon.

Pressurization stage +\i: The combustion-treated exhaust gas composition is pressurized into the pressure-equalized column until the desired adsorption operating pressure is reached.

Desorption stage: The pressure inside the column is lowered to atmospheric pressure, and
Carbon monoxide, carbon dioxide, nitrogen and moisture adsorbed in the previous stage are released. It is effective to operate the column at a reduced pressure below atmospheric pressure.

Purge stage A part of concentrated argon from other towers in the adsorption stage is introduced from the top into the tower under atmospheric pressure, washes and regenerates the adsorbent, and then is purged from the bottom of the tower.

Next, the operating procedure of the adsorption tower shown in FIG. 2 will be described in detail according to Table 1.

In the first operation, adsorption columns 21a, 21b and 21C enter the stages of adsorption (21a), pressure (21b) and desorption (21C), respectively. After that, the solenoid valve 22°28.
29 and 30 are open, solenoid valves 18, 31° 19.32
, 23, 20, 24, 33.34 and 35 are closed. By this valve operation, carbon monoxide, carbon dioxide, nitrogen, and moisture are adsorbed by the adsorbent from the exhaust gas composition that falls in the adsorption tower 21a, and the remaining argon is
5 and enters the product gas tank 26.

On the other hand, the adsorption tower 21b is in the pressure equalization stage, and from the adsorption tower 21a through the solenoid valve 28, piping 36, and solenoid valve 29, the adsorption tower 21
b. The pressure inside the adsorption tower 2/:b is increased from atmospheric pressure by one concentrated argon, and the second operation begins. Furthermore, in the adsorption tower 21C in the desorption stage, impurity components in the exhaust gas composition adsorbed in the previous stage are discharged via the electromagnetic valve 30 and the gas discharge pipe 37, and the internal pressure of the tower is accordingly lowered.

In the second operation, the adsorption tower 21a continues to enter the adsorption stage, and the adsorption towers 21b and 21C enter the pressurization and purging stages, respectively. At that time, the solenoid valves 22, 28, 19, 30 and 33 are opened, while the solenoid valves 18, 31, 32, 23,
29, 20 and 24 are closed. By this valve operation, the exhaust gas composition is transferred to the adsorption tower 21b whose pressure was equalized in the previous operation by the compressor 15, the cooler 16, the gas feed pipe, and the solenoid valve 19.
It is supplied and pressurized through. Further, concentrated argon is introduced from the adsorption tower 21a into the adsorption tower 21C which has entered the purge stage through the electromagnetic valve 28, the piping 36 and the -TDI valve 33, and the adsorbent is regenerated.

The purge gas after the regeneration process is discharged to the outside of the system via the solenoid valve 30 and piping 37.

In the third operation, adsorption towers 21a, 21b and 21
C enters the desorption, adsorption and pressure equalization stages.

In this case, solenoid valves 31, 23, 29 and 33 are opened, while solenoid valves 18, 22, 28, 19, 32° 20 and 30 are closed. By this valve operation, the adsorption tower 21a
The impurity components in the exhaust gas composition adsorbed in the previous stage are discharged via the electromagnetic valve 31 and the gas discharge pipe 37, and the internal pressure of the column is accordingly lowered. The adsorption tower 21b enters the adsorption stage, where carbon dioxide, nitrogen, and water from the exhaust gas composition are adsorbed by the adsorbent, and the remaining argon is passed through the electromagnetic valve 23 and the piping 25 to the product gas tank 26. Man,
Oh. On the other hand, the adsorption tower 21C is in the pressure equalization stage;
b to the tower 2 via the solenoid valve 29, piping 36 and solenoid valve 33.
Introduced within 1C.

Similarly, in the fourth operation, the adsorption towers 21a, 21
b and 21C are purge and adsorption, respectively.

Operated as a pressurization stage. At that time, among the solenoid valves, 31.28, 23.29 and 20 are opened, and 18, 2
2.19, 32.30 and 24 are closed. In the fifth operation, the adsorption towers 21a and 21b are operated as pressure equalization and 48th floor desorption, respectively, and the adsorption tower 21C is operated as an adsorption stage. At that time, solenoid valves 2B, 32.24 and 33 are opened, and 18° 31.22, 19, 23, 29.20 and 30
is closed.

In addition, in the sixth operation, the adsorption tower 21a.

21b and 21C are operated as pressurization, purge and adsorption stages, respectively. At this time, 18.32 of the solenoid valves
, 29.24 and 33 were held, and 31.22, 28,
19, 23.20 and 30 are closed.

In the above description, the concentrated argon supplied to all the pressure equalization stages and the adsorption tower in the purge stage was supplied from the adsorption tower in the adsorption stage, but it can also be supplied from the product gas tank through the solenoid valve 35. You can also do it. In the figure, 38 and 39 are throttle valves.

Furthermore, in the present invention, as shown in FIG. 3, a vacuum pump 40 is disposed in the piping 37, and by reducing the pressure inside the column, it is possible to desorb the impurity gas component that has been adsorbed to a small extent. According to this method, since the adsorbent is efficiently regenerated, the above-mentioned purge step can be omitted and it is effective in improving the recovery rate of argon.

In the above explanation, the case where three adsorption towers are connected in series in the third step has been explained as an example, but the number of adsorption towers is not limited in any way in the present invention, and FIGS. 2 and 253 are the embodiments. This is just an example.

Now, the gases emitted from the silicon furnace are mainly composed of argon, carbon oxide, and carbon dioxide.

It is made of a hydrocarbon-based composition containing hydrogen, barium, water, etc.

[Embodiments of the invention]

Examples of the present invention will be described below.

Sialbon was recovered from the exhaust gas composition discharged from the silicon furnace using the apparatus shown in FIG. 2 used in the method of the present invention.

The gas components of the exhaust gas composition are as shown in Table 2. The fuel m4 in the first step 2 is filled with palladium and alumina catalyst, and the space velocity of the exhaust gas composition is adjusted to 1000~20.
The combustion temperature was varied from 20 to 600C at 000h-1.

Table 2 (% i) Figure 4 is a diagram showing the relationship between the space velocity of the exhaust gas composition and the combustion temperature in the first step.

As is clear from the figure, the space velocity of the exhaust gas composition is 15
000h-1 or more, it is necessary to raise the catalyst temperature to 6000h-1 or more in order to completely burn the hydrocarbons.

However, when the temperature in the layer of the catalytic combustor exceeds 600 C, hydrocarbons are thermally decomposed to produce carbon, and the carbon is deposited on the catalyst layer, resulting in a sharp drop in catalytic activity. Therefore, in order to efficiently burn hydrocarbons, it is preferable that the space velocity is kept at 15,000 h'' or less and the combustion (catalyst layer) temperature is kept at 600 C or less.

Further, FIG. 5 shows the relationship between the combustion process and the carbon removal rate in the second step of combustion, in which carbon monoxide is added excessively to the oxygen remaining in the exhaust gas composition. Here, co is the amount of hydrogen gas contained in the exhaust gas composition, and C is the amount of oxygen gas subjected to combustion treatment.

In this second step, the space velocity of the exhaust gas composition is reduced to 1
500 h-1, residual oxygen was removed by adding excessive carbon monoxide to the exhaust gas composition at a fuel temperature in the range of 300 to 400C. As a result, residual oxygen could be reduced to below IP.

Gas analysis of the exhaust gas composition treated in the first step and the second step as described above resulted in the results shown in Table 3.

Table 3 (Top) Next, the exhaust gas compositions that had passed through the first and second steps were sent to the third step, where they were subjected to pressure difference adsorption treatment.

The pressure difference adsorption process uses an adsorption tower with a volume of 20 t
2 to 6 edges/tri G, desorption was performed at atmospheric pressure, and cycle times were 135 to 270 seconds.

As a result, the final amount of argon recovered was 99.9 to 9
At a concentration of 9.999%, the recovery was 50-65%. Argon recovery Jt is SOO~16 per unit time
It became 00't.

Furthermore, as shown in Figure 3, detachment]! l! In the process, the adsorption tower was operated under a reduced pressure of 4 g to 50 to 150 cm, and the purge step was omitted. As a result, the recovered argon concentration was 99.9-99.999%, and the recovery rate was 50-75%, the same as above.

〔Effect of the invention〕

As explained above, according to the argon recovery method of the present invention, it is possible to recover high concentration argon from the exhaust gas composition discharged from a furnace using argon, particularly a silicon furnace, and at a high yield. It has the remarkable effect of being able to be recovered. Furthermore, since -carbon oxide is also concentrated, it has the advantage that it can be recovered and reused as fuel and chemical raw materials.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the process for recovering argon from the exhaust gas composition of a silicon furnace, etc. according to the present invention, Fig. 2 is a structural system diagram showing a series of methods for recovering argon according to the present invention, and Fig. 3 is a process block diagram of the present invention. FIG. 4 is a structural diagram showing another example of the argon recovery method according to the present invention, which shows the relationship between the wall velocity of the exhaust gas composition and the CH4 combustion preparation ('l'clI4) in the first step of the present invention.
5 is a diagram showing the relationship between fuel temperature and oxygen removal in the second step of the present invention. 1... Silicon furnace, 8... Heater, 9.10...
Catalytic combustor, 1=1=, 21 a to 21 b... absorption tower. Agent Patent Attorney Tatsuyuki Unuma! 4 i Prisoner Diagram 2

Claims (1)

[Claims] 1. A method for recovering argon from an exhaust gas composition containing argon as a main component and containing carbon monoxide, hydrogen, hydrocarbons, carbon dioxide, oxygen, etc., in which the exhaust gas composition is used as a catalyst. A first step in which hydrogen, carbon oxide and hydrocarbons are combusted by bringing them into contact, and a second step in which oxygen is removed by adding carbon monoxide to the gas composition that has passed through the first step and bringing it into contact with a catalyst. and a third step of concentrating and collecting argon by adsorbing components other than argon from the gas composition that has passed through the second step onto an adsorbent under pressure. Method. 2. A method for recovering argon, characterized in that in the first step described in claim 1, the space velocity of the exhaust gas composition is 1500 h-1 or less, and the temperature of the catalyst layer is 600 C or less.