JPH0529834B2 - - Google Patents

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. , is unsuitable for recovery, and for this reason only exhaust gas from atmospheric silicon furnaces is subject to recovery.

The prior art will be explained with reference to FIG.

The exhaust gas from the normal pressure silicon furnace 1 is passed through the compressor 2.
The pressure is increased to several kg/cm ² G in the heater 3, and after the temperature is raised to a predetermined temperature in the heater 3, it is sent to a decarburization/deoxidation device.

This exhaust gas contains inorganic gases mainly consisting of N ₂ and O ₂ as well as light hydrocarbons such as CH ₄ .
As disclosed in Publication No. 1330, Japanese Patent Publication No. 49-4631, and automobile exhaust gas treatment technology, etc.
Hydrocarbons and O ₂ are removed in a reaction column filled with metal catalysts such as palladium and copper.

O ₂ 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.

CH ₄ +2O ₂ →CO ₂ +2H ₂ O + 192kcal/mal... (1) In this decarburization reaction tower 4, the reaction is normally carried out at a temperature of 400°C or higher, and in order to ensure a predetermined argon purity of these hydrocarbons, At the 4th outlet of the decarburization reaction tower
It is necessary to remove it to about 1 ppm or less. For this reason, approximately 1% excess O ₂ is added in advance.

This reaction surplus _O2 is difficult to separate from argon in a cryogenic separator, so it is not used in the decarburization reaction tower 5.
H ₂ is added, and the reaction excess O ₂ is removed by the following reaction.

H ₂ + 1/2O ₂ → H ₂ O + 58 kcal/mol… (2) In this case as well, it is necessary to remove O ₂ to 1 ppm or less at the outlet of the deoxidizing reaction tower 5, so approximately 1% excess H ₂ must be removed in advance. Add extra.

H ₂ O generated in the decarburization/deoxidation reactors 4 and 5
and CO ₂ are treated, for example, in a cryogenic air separation unit. That is, after the exhaust gas discharged from the deoxidizing reaction tower is cooled by a cooler 6 and a refrigerator 7, it is converted into H ₂ O and CO _{2 .}
is adsorbed and removed by a temperature difference swing adsorption tower (TSA) 8, which is a dehydration/CO ₂ dehydration device filled with adsorbents such as molecular sieves and alumina gel, and sent to a cryogenic separation device. At this stage, the exhaust gas is Ar
The main components are H ₂ and N ₂ .

Two adsorption towers 8 are usually installed, and generally four to four adsorption towers 8 are installed.
They are switched and used every 24 hours, and while one is adsorbing, the other is regenerated and reused alternately. For this regeneration, N ₂ gas is heated to 200 to 300°C with a regeneration heater 9. It is done.

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 H ₂ and N ₂ is cryogenically cooled in the heat exchanger 10 using the refrigeration of LN ₂ . In the rectification column 11, H ₂ , N ₂ and Ar
It was then subjected to rectification separation and recovered as product argon.

In addition, the cryogenic separator is equipped with a nitrogen gas compressor 12 that circulates nitrogen for the reboiler and condenser of the rectification column 11.

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

In the case of low-pressure silicon furnaces, oil rotary vacuum pumps are often used, and heavy oil mist is discharged from the vacuum pumps. 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 consisting of N ₂ and O ₂ .
One example is the high concentration of light hydrocarbons, including CH ₄ . This is because the amount of argon 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, the concentration of heavy hydrocarbons including oil mist is high, and an example of analysis of vacuum silicon furnace exhaust gas shows that the concentration reaches approximately 30,000 ppm in terms of methane concentration. ing.

Example of exhaust gas composition analysis for a vacuum silicon furnace Inorganic gas (N ₂ , O _2, etc.) 2 mol% Light hydrocarbons (about CH ₄ to C ₅ ) 10000 ppm converted to CH ₄ Heavy hydrocarbons (more than C ₆ ) converted to CH ₄ 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 the exhaust gas amount is 100Nm ³ /h, the methane concentration is 3% (hydrocarbon (methane conversion value) Methane amount: 100 x 0.03 = 3Nm ³ /h (same as above) From equation (1) Calorific value: 3/22.4 x 192000 = 257000kcal/h Specific heat of argon: 0.222kcal/Nm ³ ℃ Catalyst temperature rise: 25700/100 x 0.222 = 1160°C, and 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, which poses a problem that cannot be handled with normal materials due to the equipment configuration.

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.

As exhaust gas is emitted from dozens of silicon furnaces, the concentration of impurities such as hydrocarbons in the exhaust gas tends to fluctuate depending on the operating conditions of the silicon furnaces.
The reaction temperature in the decarburization reaction tower 4 of the decarburization/deoxidation device was not stable, and a large amount of expensive catalyst was required to carry out a sufficient reaction.

In addition, due to the reaction heat in the deoxidizing reaction tower 5, excess
Although it depends on the amount of O ₂ , the temperature rises by about 200 to 400°C from the decarburization reaction tower 4, so in order to perform a stable reaction, cooling at the outlet of the decarburization reaction tower 4, that is, deoxidation It was impossible to control the reaction without adjusting the reaction temperature at the inlet of the reaction tower 5.

In addition, the problem of high hydrocarbon concentration also occurs in the downstream dehydration/CO ₂ equipment, and the hydrocarbons in the exhaust gas are all converted to CO ₂ and H ₂ O in the reaction process, so they are adsorbed and removed here. However, since the CO ₂ concentration is very high at about 3% in the above example, the load on the adsorption tower is large, and in the conventional adsorption tower regeneration method, the amount of N ₂ gas used for regeneration is as follows. As shown in the example, approximately 6 times the amount of recovered argon is required,
Since the cost of nitrogen gas is too high, argon recovery is not economically viable.

Examples using conventional methods are shown below.

Example Adsorption tower 2 units Processing argon gas amount: 6Nm ³ /h Adsorption tower dimensions: 216.3φ×200×2.8t Adsorbent filling amount: 41Kg/unit Switching time: 8 hours Regeneration heater 1 unit Regeneration gas fluid: N ₂ Gas drying Regeneration gas amount: 36Nm ³ /h Regeneration gas temperature: 300℃ Heating time: 4 hours For this reason, the conventional method is limited to the case of normal pressure silicon furnaces with low hydrocarbon concentration, and is applicable only to vacuum silicon furnaces. It was technically impossible to recover the argon discharged from the reactor.

[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 the exhaust gas from a silicon furnace, which mainly consists of argon containing hydrocarbons, using a decarburization/acidification device consisting of a decarburization reaction tower and a deoxidation reaction tower, and dehydrates it using an adsorption tower.・In an argon recovery device from a silicon furnace, which removes moisture and carbon dioxide gas in a CO ₂ decarbonization device and then sends it to a cryogenic separation device and performs rectification separation to recover argon, the decarburization and decarburization A heavy hydrocarbon removal device is installed between the acid equipment and the heavy hydrocarbons caused by the oil rotary vacuum pump, reducing the load on the decarboxylation/acidification equipment and dehydration/ _CO2 removal equipment. 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.

Exhaust gas from the oil rotary vacuum pump 22 that reduces the pressure in the depressurized silicon furnace 21 to about 10 Torr is boosted to several kg/cm ³ G by the compressor 23 and sent to the heavy hydrocarbon removal device 24 . 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.

The heavy hydrocarbon removal device 24 includes an oil mist separator 2 with a built-in filter material such as wire mesh or glass wool.
In step 5, after mechanically removing the oil mist using the collision and diffusion principle, the heavy hydrocarbons are removed in a heavy hydrocarbon removal column 26 filled with an adsorbent such as activated carbon or alumina gel, and the remaining light hydrocarbons are removed. The exhaust gas containing . A plurality of heavy hydrocarbon removal columns 26 are installed and used selectively as necessary.

In the decarburization/deoxidation device 27, O ₂ is added to the exhaust gas heated by the heater 28, and in the decarburization reaction tower 29 filled with a metal catalyst such as palladium or copper, the exhaust gas is processed by the formula (1) etc. as in the normal pressure type. Let the reaction take place. The reaction temperature is adjusted by the aforementioned heater 28 so as to obtain the reaction temperature necessary to reduce the hydrocarbon content to 1 ppm or less.

In the deoxidizing reaction tower 30 packed with a metal catalyst like the decarburizing reaction tower 29, the flow rate of this exhaust gas is controlled by the precooler 31 and the bypass pipe 32 so that an appropriate reaction temperature can be obtained to keep the outlet oxygen concentration to 1 ppm or less. Pre-cooled by conditioning. H ₂ is added to the precooled exhaust gas, and the reaction of formula (2) is carried out in the deoxidizing reaction tower 30 in the same way as in the normal pressure type.

This decarburization occurred in the deoxidizing reaction towers 29 and 30.
After H ₂ O and CO ₂ are cooled in the cooler 33,
It is removed by adsorption in an adsorption tower 35 filled with molecular sieves and alumina gel in a dehydration/deCO ₂ device 34,
It is sent to a cryogenic separator 36.

Even when the commonly used temperature difference swing type (TSA), whose adsorption operation principle is shown in Fig. 3, is applied to the dehydration/CO ₂ removal device 34, heavy hydrocarbons containing oil mist are removed at the front stage. Therefore, in the exhaust gas example mentioned above, the exhaust gas contains only about 1% of CO ₂ , and the CO ₂ adsorption tower 3
The amount of N ₂ gas required for the regeneration of 5 is about 2.5 times the amount of recovered argon, and even compared to _the conventional method
Since gas consumption can be halved and the unit price of N ₂ gas is lower than that of argon gas, argon recovery can be achieved economically even as it is.

More preferably, the adsorption device is one that regenerates the adsorbent by utilizing the pressure difference between adsorption and desorption, as shown in FIG.
By using a pressure differential swing adsorption device (PSA) as disclosed in Japanese Patent No. 78615, it is possible to further reduce the amount of regenerated nitrogen gas.

Two or three or more adsorption towers are installed, and usually
It can be switched and used in 10 to 20 minutes, and room temperature N ₂ gas can be used for regeneration.

The cryogenic separation device 36 includes a heat exchanger 37 and a rectification column 3.
8. It is composed of a nitrogen gas compressor 39, etc. In the cryogenic separator 36, the required amount of refrigeration is adjusted by a liquid level controller 40, and the charged LN ₂ is collected in a cold state and converted into room-temperature N ₂ It comes out as a gas,
By providing the conduit 41 so that this N ₂ gas can be used as it is as regeneration gas for the CO ₂ adsorption tower 35, reuse becomes possible and economical efficiency is further increased.

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

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

Exhaust gas amount: 100Nm ³ /h Methane concentration: 10000ppm (methane equivalent value of light hydrocarbons) Methane amount: 100 x 0.01Nm ³ /h (same as above) From equation (1) Calorific value: 1/22.4 x 192000 = 8570kcal/h Specific heat of argon: 0.222 kcal/Nm ³ ℃ Catalyst temperature rise: 8570/100 x 0.222 = 386 ℃ When the decarburization reaction tower 29 inlet temperature is 200 ℃ Decarburization reaction tower 29 outlet temperature: 200 + 386 = 586 ℃, The load on the heater 28 mentioned above is automatically adjusted, and when the reaction temperature of the decarburization reaction tower 29 is set to 500°C, the inlet temperature of the decarburization reaction tower 29 is adjusted to 500-386 = 114°C. Become. This is precooled to about 200°C in a precooler 31. In the deoxidizing reaction tower 30, Exhaust gas amount: 100Nm ³ /h Surplus O ₂ concentration: 1% Surplus O ₂ amount: 100 × 0.01 = 1Nm ³ /h By equation (2) Calorific value: 2.0 / 22.4 × 58000 = 5180kcal / h Catalyst temperature rise: 5180/100×0.222=233°C. Therefore, deoxidation reaction tower 30 outlet temperature: 200+233=433°C.

By installing the heavy hydrocarbon removal device 24, the amount of hydrocarbons at the inlet of the decarburization/deoxidation device 27 can be reduced to 10,000 ppm by removing heavy hydrocarbons including oil mist from the exhaust gas. , the amount of catalyst used in the device can be significantly reduced. In addition, both the decarburization and deoxidation reaction towers 29 and 30
The temperature can be kept at about 600°C or less, and there are no problems with the material of the device.

Furthermore, by using a method for automatically adjusting the reaction temperature at the inlet of the decarburization reaction tower 29, stable reaction conditions can be ensured even when the amount and composition of exhaust gas fluctuate.

Moreover, by installing a precooler 31 and a bypass pipe 32 at the inlet of the deoxidizing reaction tower 30, which can appropriately adjust the reaction temperature, it is possible to stably follow increases and decreases in the amount of exhaust gas and changes in the composition.

Furthermore, by removing heavy hydrocarbons including oil mist in the previous stage, the amount of _N2 gas used can be halved compared to conventional methods even when a temperature swing adsorption tower is used. but,
Furthermore, when a pressure difference swing type adsorption tower is used in the dehydration/deCO ₂ equipment 34, the regeneration heater and refrigerator that are required in the temperature difference swing type adsorption tower can be omitted, and the adsorbent Required _N2 for regeneration
The gas amount is approximately the same as the argon amount in the temperature difference swing type.
The required 2.5 times the amount required can be further halved.

Example 2 (TSA method) Adsorption tower 2 units Processing argon gas amount: 6Nm ³ /h Adsorption tower dimensions: 216.3φ×1700×2.8t Adsorbent filling amount: 35Kg/unit Switching time: 8 hours Regeneration heater 1 unit Regeneration Gas fluid: _N2 gas dry Regeneration gas amount: 15Nm ³ /h Regeneration gas temperature: 300℃ Heating time: 4 hours Example 3 (PSA method) Adsorption tower 2 units Processing argon gas amount: 18Nm ³ /h Adsorption tower dimensions: _216.3 ^φ _{_} By using it for regeneration gas, we were able to once again improve economic efficiency. In other words, it is more economical to increase or decrease the amount of N ₂ 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 N ₂ gas required for regeneration is Since the amount of LN ₂ required for cooling is less than that required for cooling, LN ₂ can be easily adjusted according to the amount of exhaust gas.
Depending on the amount, the amount of _N2 gas required for regeneration can be indirectly increased or decreased.

〔Effect of the invention〕

As described above, the present invention installs a heavy hydrocarbon removal device for removing heavy hydrocarbons such as oil mist between the reduced pressure silicon furnace and the decarburization/acidification device, and removes heavy hydrocarbons from exhaust gas. By removing hydrocarbons, the load on the decarburization/acidification equipment and dehydration/CO ₂ removal equipment is reduced, so it is possible to replace the reduced pressure silicon furnace, which was technically impossible with conventional equipment. argon recovery can be made economically possible.

[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 temperature difference swing type adsorption system. Diagram showing the principle. FIG. 4 is a diagram showing the principle of pressure difference swing type adsorption. 1... Ordinary pressure silicon furnace, 2, 23... Compressor,
3,28... Heater, 4,29... Decarburization reaction tower, 5,
30...Deacidification reaction tower, 6,33...Cooler, 7...Freezer, 8...Adsorption tower (TSA), 9...Regeneration heater, 1
0,37... Heat exchanger, 11,38... Rectification column, 1
2, 39...Nitrogen gas compressor, 13,40...Liquid level controller, 21...Reducing pressure type silicon furnace, 22...Oil rotary vacuum pump, 24...Heavy hydrocarbon removal device, 25
...Oil mist separator, 26...Heavy hydrocarbon removal column, 27...Decarburization/deoxidation device, 31...Precooler, 32
...Bypass pipe, 34...Dehydration/ _CO2 removal device, 35...
CO ₂ adsorption tower, 36... cryogenic separation device, 41... conduit.

Claims (1)

[Scope of Claims] 1. Hydrocarbons and oxygen are removed from the exhaust gas from a silicon furnace, which mainly contains argon and contains hydrocarbons, in a decarburization/acidification device consisting of a decarburization reaction tower and a deoxidation reaction tower, and an adsorption tower. In an argon recovery device from a silicon furnace, water and carbon dioxide are removed in a dehydration/deCO ₂ device, which is then 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 inlet 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. An argon recovery device from a silicon furnace according to claim 1, 2, or 3, which uses a pressure differential swing type adsorption tower as the dehydration/CO ₂ device.