JPS60155881A - Recovery device for argon from silicon furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an argon recovery device from a silicon furnace suitable for recovering argon from a reduced pressure silicon furnace.

[Background of the invention]

Traditionally, argon recovery from silicon furnaces uses oil rotary vacuum pumps in the case of depressurized silicon furnaces, but this furnace generates a lot of hydrocarbons including oil mist, which significantly pollutes the argon. Therefore, only exhaust gas from atmospheric silicon furnaces has been subject to recovery.

The prior art will be explained with reference to FIG. .

Exhaust gas from the normal pressure silicon furnace I is pressurized to 9/iG by the compressor 2, heated to a predetermined temperature level by the heater 3, and sent to the decarburization/deoxidation device H.

This exhaust gas contains light hydrocarbons such as CH4 in addition to inorganic gases mainly composed of N2,0□. As disclosed in Publication No. 49-4631 and automobile exhaust gas treatment technology, hydrocarbons and 02
Perform the removal of.

0□ is added to the pressurized exhaust gas, and a combustion reaction of hydrocarbons is carried out in the decarburization reaction tower 4. As a reaction example, the case of methane is shown below.

CHJ +202-CO2+2 [20+ 192 k
cal/mal-illll secondary decarburization reaction tower 4, usually 4
In order to carry out the reaction at a temperature of 00° C. or higher and to ensure a predetermined argon purity, it is necessary to remove these hydrocarbons to about 1 ppn or less at the outlet of the decarburization reaction tower 4. For this reason, an excess of about 1 inch of 02 is added in advance.

Since this reaction surplus 02 minutes is difficult to separate from argon in a cryogenic separator, H2 is added in the deoxidizing reaction tower 5.
The reaction surplus 0□ was removed by the following reaction.

H2+'02-H20+58kcal/mol -...
...(2) Also in this case, 02 is converted to 1 at the deoxidizing reaction tower 5 output []
Since it is necessary to remove it to below ppm, approximately 1% excess H2 is added in advance.

The 11□0 and C02 generated in the decarburization and deoxidation reactor 4.5 are processed, for example, in a cryogenic air separation device. That is, the exhaust gas discharged from the deoxidizing reaction tower is passed through the cooler 6 and the refrigerator 7.
After cooling, lI20 and CO2 are dehydrated and deCO2
The device is a temperature difference swing type adsorption tower (T8A, ) filled with adsorbents such as molecular sieves and alumina gel.
It is adsorbed and removed in step 8 and sent to a cryogenic separator. At this stage, the main components of the exhaust gas are Ar, H2, and N2.

Two adsorption towers 8 are normally installed, and they are generally switched over every 4 to 24 hours, and while one is adsorbing, the other is regenerated and reused alternately. This is carried out by heating to 200 to 300°C using a heater 9.

In the cryogenic separator, the required amount of refrigeration is adjusted by the liquid level controller 13 of the rectification column 11, and the Ar gas containing H2 and N2 is cooled to the cryogenic temperature by the heat exchanger 10 using the refrigeration of LN2. Then, in the rectification column 11, H2, N2, A, and r were separated by rectification and recovered as product argon.

In addition to 2, the cryogenic separation equipment includes a nitrogen gas compressor 1 that circulates nitrogen for the reboiler and condenser of the rectification column 11.
2nd prize is included.

However, this conventional argon recovery device has the following problems.

In the case of a reduced-pressure silicon furnace, an oil rotary vacuum pump is often used, and heavy oil waste I is discharged from the vacuum pump. In addition, compared to the exhaust gas from a normal-pressure silicon furnace that does not use a vacuum pump, the exhaust gas from a reduced-pressure silicon furnace contains inorganic gases mainly composed of N2,0□, as well as CH, This is due to the high concentration of light hydrocarbons. This is because the amount of alcon used as inert gas in the reduced pressure silicon furnace is less than half that of the normal pressure silicon furnace.

Therefore, at the outlet of the vacuum pump, in addition to light hydrocarbons, there is a high concentration of heavy hydrocarbons including oil mist.
An example of analysis of the exhaust gas from a vacuum silicon furnace shows that even when converted to methane concentration, the concentration has reached approximately 30,000 pI)m. Light hydrocarbons (
CH4 to C5) CH, converted to 1 0 0 0 0 p
pm Heavy hydrocarbons (C6 and above) CH, converted to 20000 ppm Argon gas Residue When this exhaust gas is directly passed through a conventional decarburization reaction tower and reacted and combusted, for example, in the following case. When taken, exhaust gas elbow: 1. If OONmVh, methane concentration = 3chi (methane conversion value of hydrocarbon) methane fi: 10
0x0.03 = 3N@7h (same as above) (more heat than the old modelffl: 3/224X192000=25700
0kcal/h Specific heat of argon: 0.222 kcal/Nm'(
:.

Catalyst temperature rise: 25700/100XO222= 1
If the temperature at the inlet of the reaction tower is 40'C, the temperature at the outlet of the reaction tower reaches about 1200°C, and there is a problem that the equipment configuration cannot be accommodated with ordinary materials.

Even if the decarburization reaction tower 4 is specially designed to withstand high temperatures, the following problems occur, including when using a conventional atmospheric pressure silicon furnace with a low impurity concentration.

Since the exhaust gas is discharged from dozens of silicon furnaces, the concentration of impurities such as hydrocarbons in the exhaust gas fluctuates depending on the operation status of the silicon furnace. The reaction temperature was unstable, and a large amount of expensive catalyst was required to carry out a sufficient reaction.

In addition, the reaction heat in the deoxidizing reaction tower 5 causes the temperature to further rise from the decarburizing reaction tower 4 by about 200 to 400°C, depending on the amount of excess 02. It was not possible to control the reaction by cooling in the reaction tower 411D, that is, by cooling the deoxidizing reaction tower 5 and without adjusting the temperature.

In addition, the problem of high hydrocarbon concentration is caused by dehydration and
Hydrocarbons in the exhaust gas are also generated in the CO2 removal equipment, and are all converted to CO2 and N20 in the above reaction process, so they are adsorbed and removed here. , the load on the adsorption tower is large, and the conventional adsorption tower is regenerated! In the J method, the old N2 gas used for regeneration is
As shown in the example below, the amount of recovered argon is about 6@, and the nitrogen gas cost is too high, so argon recovery is not economically viable.

Examples using conventional methods are shown below.

Example adsorption tower 2 units Processing argon gas amount: 6 N m'/h Adsorption tower dimensions: 216.3φ x 2000J x 2.8 Adsorbent filling amount:
41 to 97 units Switching time = 8 hours Regeneration heater 1 unit Regeneration gas fluid 2 N2 gas dry Regeneration gas amount: 36Nm”/11 Regeneration gas temperature: 300°C Heating time: 4 hours Therefore, in the conventional method, the hydrocarbon concentration This was only possible in the case of low-pressure silicon furnaces, and it was technically impossible to recover argon discharged from vacuum silicon furnaces.

[Purpose of the invention]

An object of the present invention is to provide an argon recovery device from a silicon furnace that can recover argon from a reduced pressure silicon furnace in which the concentration of impurities, particularly hydrocarbons, in the exhaust gas of the silicon furnace is high.

[Summary of the invention]

The present invention removes hydrocarbons and oxygen from exhaust gas from a silicon furnace mainly composed of argon containing hydrocarbons with a decarburization/acidification device consisting of a decarburization reaction tower and a deoxidation reaction tower, and removes hydrocarbons and oxygen with an adsorption tower.・In the argon recovery device from a silicon furnace, which removes moisture and carbon dioxide gas in a CO2 decarbonization device and then sends it to a cryogenic separation device and performs rectification separation to recover argon, By installing a heavy hydrocarbon removal device between the equipment and removing heavy hydrocarbons caused by the oil rotary vacuum pump, the load on the decarboxylation/acidification equipment and dehydration/CO2 removal equipment is reduced. This made it possible to recover argon from a vacuum silicon furnace.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

The waste from the oil rotary vacuum pump n that reduces the pressure in the depressurized silicon furnace 21 to about 10 Torr is several kg by the compressor n.
It is sealed to a pressure of 1/2 inch and sent to a heavy hydrocarbon removal system. This exhaust gas contains heavy hydrocarbons including oil mist in addition to light hydrocarbons, which are also included in the case of the normal pressure type.

In the heavy hydrocarbon removal equipment, the oil mist separator 5, which has a built-in filter material such as wire mesh or glass wool, mechanically removes oil mist using the principles of collision and diffusion, and then removes it using an adsorbent such as activated carbon or alumina gel. The heavy hydrocarbons are removed in the heavy hydrocarbon removal column filled with the following: The remaining exhaust gas containing light hydrocarbons is sent to the decarburization/deoxidation equipment i\n. Multiple heavy hydrocarbon removal towers are installed and used alternately as necessary.

In the decarburization/deoxidation equipment, the exhaust gas heated in the heater row is 0.
In the decarburization reaction tower 4 filled with a metal catalyst such as palladium or copper, reactions such as formula (1) are carried out in the same way as in the normal pressure type. The reaction temperature is adjusted by the heater path described above to obtain the reaction temperature necessary to reduce the hydrocarbon content to 1 ppm or less.

This exhaust gas is passed through a precooler 31 so that an appropriate reaction temperature can be obtained to keep the outlet oxygen concentration at 11) pm or less even in the deoxidizing reaction tower 30 packed with a metal catalyst.
It is precooled by adjusting the flow rate of the bypass pipe 32. I]2 is added to the precooled exhaust gas, and the reaction of formula (2) is carried out between the deoxidizing reaction towers in the same way as in the atmospheric pressure type.

The lI20 and CO2 generated in the decarburization and deoxidation reaction tower A, 30 are cooled in the cooler 33, and then dehydrated and deoxidized.
Two loads are adsorbed and removed in an adsorption tower 35 filled with molecular sorb or alumina gel, and sent to a cryogenic separation device.

As a dehydration/CO2 removal device, a commonly used temperature difference swing type (T
Even if SA) is applied, heavy hydrocarbons including oil mist are separated in the previous stage, so in the exhaust gas example above,
The exhaust gas contains only about 1 ton of CO2, and the amount of N2 gas required to regenerate the CO2 adsorption tower 35 is
(It is about 25 times that of Soargon IN, and (compared to the previous method, the N2 gas consumption can be halved, and the unit price of N2 gas is cheaper than argon gas, so even if the method is Argon recovery is possible.

More preferably, the adsorption device is a device that regenerates the adsorbent by utilizing the pressure difference between adsorption and desorption, as shown in FIG. Pressure difference swing type adsorption device (P
By using S A ), it is possible to further reduce the amount of regenerated nitrogen gas.

Two or more adsorption towers are installed, and usually 10 to 2 adsorption towers are installed.
It is switched to use at 0 minutes, and N2 gas at room temperature can be used for regeneration.

The cryogenic separator ♀ is composed of a heat exchanger 37, a rectification column A, a silicon gas compressor 39, etc., but the cryogenic separator i (, 3
In step 6, the required amount of refrigeration is adjusted by the liquid level controller 40, and the charged LN2 is recovered as a refrigeration and converted into room-temperature N,
It comes out as a gas, but this N2 gas is also used as CO2.
By providing the conduit 41 so that the adsorption tower can be used as regeneration gas, reuse becomes possible, further increasing economic efficiency.

Hereinafter, specific examples of the present invention will be described.

Example 1 Hydrocarbons in exhaust gas are 30,000 ppm in terms of methane
(in which heavy hydrocarbons are 20,000 ppm), and other conditions are as follows.

Exhaust gas it: 100 Nm'/h Methane concentration: ] 0000 ppm (methane equivalent value of light hydrocarbons) Methane amount: 100 x O,0] Nm"/b (
Same as above) From equation (1), calorific value: 1/22.4X'+92000=8570k
cal/h Specific heat of argon: 0.222 kcal/
Nm”C catalyst temperature rise: 8570/100xO, 22
2 = 386°C When the decarburization reaction tower 4 input temperature is 200°C, the decarburization reaction tower 9 outlet temperature: 200-1-386 = 586°C
However, when the load on the heater section mentioned above is automatically adjusted and the reaction temperature of decarburization reaction tower 4 is set to 500℃, the temperature of decarburization reaction tower 4 is adjusted to 500-386 = 114℃. will be done. This is approximately 200 at precooler 31.
Pre-cool to ℃. In the deoxidizing reaction tower (9), the amount of exhaust gas: 10
100N/h Surplus 02 concentration = 1% Surplus 02 amount: ] 0Ox0.01=INm'/h(
2) Calorific value from formula: 2.0/22.4X58000=51.80
kcal/h catalyst temperature”-Bamboo: 5180/100X0
．． 222=233℃ Therefore, deoxidizing reaction tower outlet temperature: 200-1-233=433
℃.

By installing a heavy hydrocarbon removal bag [24], the amount of hydrocarbons at the inlet of the decarburization/deoxidation equipment can be reduced to 10,000 by removing heavy hydrocarbons, including oil mist in the exhaust gas.
ppm, and the limits of the catalyst used in the device can be significantly reduced. Further, both the decarburization and deoxidation reaction tower pairs 30 can be kept at about 600° C. or lower, and there are no problems with the materials of the equipment.

Furthermore, by using a method of automatically adjusting the reaction temperature in the decarburization reactor, stable reaction conditions can be ensured even when the amount and composition of exhaust gas fluctuate.

In addition, by appropriately controlling the reaction temperature at the inlet of the deoxidizing reaction tower (capital), the exhaust gas can stably follow changes in composition.

Furthermore, by removing heavy hydrocarbons including oil mist in the previous stage, even when using a temperature swing type adsorption tower, the use of N2 gas is reduced compared to conventional methods.
In addition, if a pressure difference swing type adsorption tower is used for the dehydration/deCO2 removal equipment, the internal heater and refrigerator that are required with the temperature difference swing type adsorption tower can be omitted. and the N required for regeneration of the adsorbent
The amount of 2 gas required in the temperature difference swing type is about 25 times that of argon (2), but this can be further halved.

Example 2 (TSA method) % Formula % Processing argon gas: 6 N m'/l + adsorption tower dimensions: 216.3φX1700J? X2.8 to adsorbent filling amount: 35 to 9/group Switching time = 8 hours Regeneration heater 1 unit Regeneration gas fluid 2N2 gas dry Regeneration gas ffi: 15 N m'/h Regeneration gas temperature: 300℃ Heating time: 4-hour Example 3 ('PSA method) % Formula % Processing argon gas amount: 1 8 Nm"/h Adsorption tower dimensions: 216.3φX2601X2.8 Adsorbent filling amount:
53 to 9/unit switching time: 10 minutes Regeneration gas fluid: N2 gun dry Regeneration gas amount: 2ONm'/h By using N2 used as cold in the cryogenic separator directly as regeneration gas, it is economical again. was able to increase. In other words, it is more economical to increase or decrease the amount of N2 gas for regeneration according to fluctuations in the amount of exhaust gas, but in the case of a pressure difference swing type adsorption tower, the amount of N2 gas required for regeneration is Since T and N2 (il) may be less than 4, the amount of N2 gas required for regeneration can be indirectly increased or decreased by the amount of LN2, which can be easily adjusted according to the amount of exhaust gas.

〔Effect of the invention〕

As described above, the present invention utilizes a reduced pressure silicon furnace and a decarburization/decarburization process.
A heavy hydrocarbon removal device that removes heavy hydrocarbons such as oil mist is installed between the decarburization/acidation device and dehydration/dehydration device to remove heavy hydrocarbons from exhaust gas. Since the load on the C02 device is reduced, it is possible to economically recover argon from a vacuum silicon furnace, which was technically impossible with conventional devices.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an argon recovery device from a silicon furnace according to the prior art, Fig. 2 is a system diagram of an argon recovery device from a silicon furnace showing an embodiment of the present invention, and Fig. 3 is a humidity difference swing. FIG. 4 is a diagram showing the pressure difference swing type adsorption principle.

Claims (1)

[Scope of Claims] 1. Hydrocarbons and oxygen are removed and adsorbed in a decarburization/acidification device consisting of a decarburization reaction tower and a deoxidation reaction tower, which is exhaust gas from a silicon furnace mainly composed of argon containing hydrocarbons. In an argon recovery device from a silicon furnace, in which water and carbon dioxide are removed in a dehydration/deCO2 device consisting of a tower, the argon is sent to a cryogenic separation device, and rectified and separated to recover argon. An argon recovery device from a silicon furnace, characterized in that a heavy hydrocarbon removal device is installed between a decarburization/acidification device. 2. A patent claim in which the heavy hydrocarbon removal device is composed of an oil mist separator that mechanically removes oil mist, and a heavy hydrocarbon removal column that adsorbs and removes the remaining heavy hydrocarbons removed by the oil mist separator. An apparatus for recovering argon from a silicon furnace according to item 1. 3. Claim 1, wherein a heater for adjusting the reaction temperature is provided on the intake side of the decarburization reaction tower of the decarburization/acidification device, and a precooler for adjusting the reaction temperature is provided on the inlet side of the deacidification reaction tower. Or an argon recovery device from a silicon furnace according to item 2. 4. Claim 1 or 2, or $
An argon recovery device from a silicon furnace according to item 3.