JP2004331432A - Method and apparatus for recovering fluorine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of efficiently recovering fluorine from a decomposition product gas of a PFC gas used in a CVD apparatus or the like. <P>SOLUTION: Method of recovering fluorine from the decomposition product gas produced by the decomposition of the PFC gas is performed by removing a solid powdery component contained in the decomposition production gas by passing the decomposition product gas through a dry powder removing apparatus (4) to obtain a dust-free gas and supplying the dust-free gas to a dry fluorine recovering reaction apparatus (5) in which a fluorine absorbent composed of a salt, hydroxide or oxide of an alkaline earth metal alone or the mixture of them is filled to react hydrogen fluoride in the decomposition production gas with the alkaline earth metal to recover as alkaline earth metal fluoride. As the fluorine absorbent, calcium carbonate or calcium hydroxide is suitably used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for processing a decomposition product gas containing a harmful component such as HF (hydrogen fluoride) generated by decomposing a PFC (Perfluorocompounds) gas used in a semiconductor film formation process or the like.
[0002]
[Prior art]
The PFC gas is a general term for fluorine-containing gases such as CF4, C2F6, C3F8, NF3, SF6, and WF6, and is a gas used as an etching gas or a cleaning gas in a semiconductor manufacturing process. This PFC gas is a stable gas and is harmless except for NF3. However, the used PFC gas removes harmful components and also decomposes the PFC gas to be released into the atmosphere.
[0003]
This PFC gas treatment method is a treatment method of a decomposition product gas containing a harmful gas such as HF generated by decomposing the PFC gas, and various treatment methods have been proposed in recent years. In this typical treatment method, PFC gas is decomposed by hydrolysis, combustion decomposition, oxidative decomposition, thermal decomposition, etc., and the generated gas containing HF generated by this decomposition is washed with water or alkaline water to make it harmless. This is a wet method (for example, see Patent Documents 1 and 2). This conventional processing method will be described with reference to FIG.
[0004]
FIG. 3 is a process diagram showing a gas processing step when a PFC gas is used for cleaning the CVD apparatus. In a film forming step, a source gas such as silane gas (SiH4) is supplied to the CVD apparatus 1 from a pipe L1, It is decomposed in the CVD apparatus 1 to form a silicon film on the surface of the substrate, and the unreacted silane gas is sucked from the pipe L2 by the vacuum pump 2 and is supplied from the pipe L8 in the vacuum pump 2 It is diluted with the gas and supplied to the combustion type abatement apparatus 3 from the pipe L3. Here, the silane gas is burned together with the fuel gas supplied from the pipe L9 to form a solid silicon oxide (SiH4 + 2O2 → SiO2 + 2H2O), detoxified, and supplied to the wet detoxifier 20 via the pipe L4. The silicon oxide, which is fine dust, is washed away with water and released into the atmosphere from the pipe L6 as a harmless gas.
[0005]
On the other hand, a reactive silicon compound such as amorphous silicon by-produced in the film forming step and other by-products adhere to and deposit on the surface of the CVD apparatus 1 and the pipe L2, and the deposit is deposited on the substrate. If adhered to the film forming surface, the quality of the product may be degraded. Therefore, PFC gas is periodically supplied into the CVD apparatus 1 for cleaning. In this cleaning step, a PFC gas as a cleaning gas is supplied from the pipe L7 into the CVD apparatus 1, the reactive silicon compound deposited in the CVD apparatus 1 is decomposed, and the unreacted PFC gas and the unreacted PFC gas are supplied through the pipe L2. It is diluted with the nitrogen gas sent from the pipe L8 and sent to the combustion type abatement apparatus 3 from the pipe L3 via the vacuum pump 2. Here, the PFC gas generates HF by a reaction with water generated by combustion of the fuel gas supplied from the pipe L9 (for example, in the case of CF4, CF4 + 2H2O → 4HF + CO2). The decomposition product gas containing HF is supplied to the wet detoxification apparatus 20 through the pipe L4. This HF is a highly corrosive gas that is highly corrosive, but is soluble in water. Therefore, it is absorbed by water in the wet detoxification apparatus 20 and discharged as an acidic waste liquid from the pipe L22 to the outside of the system. . The acidic waste liquid is appropriately drained after being subjected to an alkali treatment. Alternatively, there is a method in which alkaline water is supplied to the wet-type abatement apparatus 20 to allow the HF absorption and the neutralization reaction to proceed simultaneously. The gas from which HF has been absorbed and removed is discharged out of the system from the pipe L6 as a detoxifying gas.
[0006]
However, when a gas absorption reaction is performed by gas-liquid contact in the wet detoxification apparatus 20, it is inevitable that the liquid component in the gas becomes a mist and accompanies the gas stream, and HF is dissolved in the mist. Since hydrofluoric acid is contained, this mist treatment is required. Therefore, as described in Patent Document 3, there has been proposed a method of removing the mist of the exhaust gas from the wet abatement apparatus 20 before discharging the exhaust gas to the atmosphere.
[0007]
[Patent Document 1]
JP-A-10-337439 (see FIG. 1 and abstract)
[Patent Document 2]
JP-A-11-70322 (see FIG. 1 and claims)
[Patent Document 3]
JP 2001-149749 A (see FIG. 1 and abstract)
[0008]
[Problems to be solved by the invention]
In the conventional method of treating a gas produced by decomposing PFC gas by a wet method as described above, there is a problem of mist treatment as shown in Patent Document 3. Therefore, a cyclone, a filter, or the like is used as a mist removal device. However, a step of cleaning the removed mist with alkaline water is also required, and an increase in not only equipment costs but also running costs is inevitable.
[0009]
Further, when the HF is neutralized with an aqueous solution of an alkali metal hydroxide or an aqueous solution of an alkaline earth metal hydroxide as alkaline water, an alkali metal fluoride or an alkaline earth metal fluoride is generated. Since there are too many impurities to collect and reuse the waste gas, it is discarded as industrial waste, and after all, it can be said that harmful exhaust gas is merely changed and discarded. This remains as a fundamental problem of the conventional wet abatement method.
[0010]
The present invention has been made in view of the above-described problems, and aims to provide a new treatment method that solves the problem of mist entrainment and the problem of disposing and changing fluorine in a wet type abatement device at once, and to provide an apparatus therefor. Is what you do.
[0011]
[Means for Solving the Problems]
The present invention has been made to achieve the above object at the same time, and the feature of the fluorine recovery method of the present invention is that the problem of mist entrainment is basically solved by using a dry type abatement device as the abatement device. By using various salts, oxides and hydroxides of alkaline earth metals alone or as a mixture thereof as a harmful gas absorbent for the dry abatement system, fluorine can be converted into alkali metal fluoride. To be collected. Specifically, it is a method for recovering fluorine from a decomposition product gas generated by decomposition of a PFC gas, wherein the decomposition product gas is passed through a dry powder removing device to obtain solid powder contained in the decomposition product gas. After removing the components to form a dust-free gas, the mixture is supplied to a dry fluorine recovery reactor filled with a fluorine absorbent consisting of various salts, oxides, and hydroxides of the alkaline earth metal alone or a mixture thereof. In this case, fluorine in the decomposition product gas is reacted with the alkaline earth metal and recovered as an alkaline earth metal fluoride.
[0012]
The fluorine absorbent is preferably a calcium compound consisting of calcium carbonate, nitrate, sulfate, oxalate, hydroxide or oxide alone or a mixture thereof. If a calcium compound is used, the recycling of raw materials for PFC gas production will be realized.
[0013]
Further, the fluorine recovery device according to the present invention is a dry powder removal device for removing solid fine particles in the decomposition product gas, and recovers fluorine from the dust-free gas from which the solid fine particles are removed by the powder removal device. And a dry fluorine recovery reactor filled with a fluorine absorbent for
The fluorine absorbent is formed into an appropriate shape from an alkaline earth metal carbonate or hydroxide or a mixture thereof,
The dry fluorine recovery reactor, the main reaction tower, the recovery reaction tower, the nitrogen purge tower and the absorbent replacement tower, is configured to be able to sequentially switch the process,
The dust-free gas is supplied in series to the recovery reaction tower via the main reaction tower, and in the switching step of the reaction tower, the recovery reaction tower is the main reaction tower, the main reaction tower is the nitrogen purge tower, and the nitrogen The purge tower is configured to be sequentially switched to an absorbent replacement tower, and the absorbent replacement tower is configured to be sequentially switched to a recovery reaction tower.
[0014]
Further, the dry-type fluorine recovery reactor is constituted by a plurality of reaction towers filled with the fluorine absorbent, and a method of supplying the dust-free gas while sequentially switching into the reaction tower is preferable, and more specifically, The reaction tower is composed of a main reaction tower, a recovery reaction tower, a nitrogen purge tower, and an absorbent replacement tower, and the dust-free gas is supplied in series to the recovery reaction tower via the main reaction tower, In the tower switching step, the recovery reaction tower is switched to the main reaction tower, the main reaction tower is switched to the nitrogen purge tower, the nitrogen purge tower is switched to the absorbent replacement tower, and the absorbent replacement tower is switched to the recovery reaction tower. Eggplant is preferred.
[0015]
Further, in the recovery reaction tower, a first recovery reaction tower and a second recovery reaction tower are arranged in series, and in the step of switching the reaction towers, the first recovery reaction tower is the main reaction tower and the second recovery reaction tower is It is a preferred embodiment that the first recovery reaction tower and the absorbent replacement tower can be sequentially switched to the second recovery reaction tower, respectively.
[0016]
Further, the exhaust gas from the nitrogen purge tower is combined with the outlet gas of the main reaction tower and supplied to the recovery reaction tower, and the exhaust gas from the nitrogen purge tower is combined with the dust-free gas and supplied to the main reaction tower. And both are preferred embodiments.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of the fluorine recovery method of the present invention. The same components as those in FIG. 3 are denoted by the same reference numerals, and redundant description is omitted. In the cleaning step of the CVD apparatus 1, the PFC gas supplied as a cleaning gas is supplied to the combustion type abatement apparatus 3 via a vacuum pump 2, and is hydrolyzed as described above to form a harmful HF gas and a solid gas. Fine particles of silicon dioxide (SiO2) as a substance are generated, and flow into the dry powder removing device 4 as one of the main devices of the present invention from the pipe L4 as a decomposition product gas. Here, the fine particles of SiO2 are removed to form a dust-free gas. Since the decomposition product gas has a high temperature, the dry powder removing device 4 uses a filter or an electric dust collector that can withstand the high temperature.
[0018]
The dust-free gas from which the fine particles have been removed is supplied via a pipe L5 to a dry fluorine recovery reactor 5 which is a characteristic device of the present invention. In the dry fluorine recovery reactor 5, a fluorine absorbent composed of one or more of various salts of alkaline earth metals, hydroxides or oxides, or one or more of mixtures thereof is charged in pellets, briquettes, granules, or the like. It is formed into a honeycomb shape and filled. For example, carbonates such as calcium carbonate [CaCO3], barium carbonate [BaCO3], magnesium carbonate [MgCO3], strontium carbonate [SrCO3], calcium sulfate [CaSO4], barium sulfate [BaSO4], magnesium sulfate [MgSO4], strontium sulfate Sulfates such as [SrSO4], nitrates such as calcium nitrate [Ca (NO3) 2], barium nitrate [Ba (NO3) 2], magnesium nitrate [Mg (NO3) 2], strontium nitrate [Sr (NO3) 2] Oxalates such as calcium oxalate [(COO) 2Ca], barium oxalate [(COO) 2 Ba], magnesium oxalate [(COO) 2Mg], strontium oxalate [(COO) 2 Sr], calcium hydroxide [Ca (OH ) 2], barium hydroxide [Ba (OH 2), magnesium hydroxide [Mg (OH) 2], hydroxide such as strontium hydroxide [Sr (OH) 2], or calcium oxide [CaO], barium oxide [BaO], magnesium oxide [MgO], Oxides such as strontium oxide [SrO] can be used, but the most preferred one is calcium carbonate or calcium hydroxide which is inexpensive and easily available. Will be described as an example. When such a fluorine absorbent comes into contact with HF, fluorine becomes stable and harmless CaF2 (calcium fluoride) by the reaction of CaCO3 + 2HF → CaF2 + H2O + CO2. The gas discharged from the dry fluorine recovery reactor 5 is a nitrogen gas introduced as a diluent gas from the pipe L8, and water vapor and carbon dioxide gas generated by the above reaction. Will be released.
[0019]
The calcium fluoride generated in the dry-type fluorine recovery reactor 5 is taken out of the device 5 when a predetermined reaction rate is reached, and is reused as a fluorine source which is a raw material of PFC gas or a raw material of a welding flux. Is possible. In particular, when a fluorine absorbent is formed from high-grade calcium carbonate as a raw material, the generated calcium fluoride also has a high purity, so that it can be reused as an extremely useful fluorine source. Become.
[0020]
As the structure of the dry fluorine recovery reactor 5, a fixed bed type reaction tower in which the fluorine absorbent is formed into pellets, briquettes, granules, or honeycombs, and filled in the reaction tower, or the fluorine absorbent has an appropriate particle size. There is a fluidized bed type reaction tower which fluidizes and reacts the pulverized material, and it goes without saying that the present invention can be carried out using any of the reaction towers. However, the fixed bed type reaction tower shown in FIG. explain.
[0021]
That is, FIG. 2 is a flowchart showing a configuration example of the fluorine recovery reactor 5 using a fixed-bed type reaction tower. The reaction tower is composed of five towers (R1 to R5) and operates while switching each tower. is there. This reaction tower is filled with a fluorine absorbent such as pellets formed from calcium carbonate to form a fixed bed type reaction layer. This reaction tower is composed of a main reaction tower R3, a first recovery reaction tower R4, a second recovery reaction tower R5, a nitrogen purge tower R2, and an absorbent replacement tower R1, and is filled with a new fluorine recovery agent. The absorbent replacement tower R1 is switched to the second recovery reaction tower R5, the second recovery reaction tower R5 to the first recovery reaction tower R4, the first recovery reaction tower R4 to the main reaction tower R3, and the main reaction The column R3 is configured to switch to a nitrogen purge column R2.
[0022]
In the reactor column having the above configuration, the dust-free gas from which the fine particles are removed by the powder removing device 4 is first supplied from the pipe L5 to the main reaction tower R3, and then to the first recovery via the pipes L14 and L15. The gas enters the reaction tower R4, then enters the second recovery reaction tower R5 via the pipe L16, and is discharged into the atmosphere from the pipe L6 as a detoxifying gas containing no HF gas. Here, the main reaction tower R3 and the first and second recovery reaction towers R4 and R5 are connected in series, and most of the HF in the dust-free gas is mainly absorbed in the main reaction tower R3. First, the residual HF is recovered in the second recovery reaction towers R4 and R5.
[0023]
The nitrogen purge tower R2 is a main reaction tower R3 in the previous step, and the fluorine absorption reaction by the internal fluorine recovery agent reaches a predetermined reaction rate, and most of the calcium carbonate is calcium fluoride. Since the gas containing HF supplied from the pipe L5 in the previous step remains in the tower, a nitrogen gas is supplied from the pipe L12 to replace the internal gas with nitrogen, and an outlet containing the residual HF gas is provided. The gas joins with the outlet gas of the main reaction tower R3 via the pipe L13 at the pipe L15, is supplied to the first recovery pipe L4, and the fluorine recovery reaction from the residual HF gas is performed. The residual HF gas can be recovered from the pipe L17 indicated by the dotted line in the figure and supplied to the inlet side of the main reaction tower R3.
[0024]
Next, the nitrogen purge tower R2 becomes an absorbent replacement tower R1 in the next step, and the fluorine absorbent filled therein is taken out as calcium fluoride and shipped for reuse for a predetermined use. . At the same time, the empty reaction tower is filled with a new fluorine absorbent, and in the next step, it becomes the second recovery reaction tower R5.
[0025]
In this way, the plurality of reaction towers R1 to R5 are sequentially switched to recover fluorine. As a method for determining the switching time, an HF monitor is installed at the outlet pipe L16 of the first recovery reaction tower R4. Then, the concentration of HF contained in the outlet gas is measured, and when the measured concentration reaches 3 ppm of the HF gas discharge standard, switching is performed. In this case, the fluorine is recovered from the exhaust gas of the first recovery reaction tower R4 containing 3 ppm of HF gas by the second recovery reaction tower R5, so that it is discharged from the outlet pipe L6 of the second recovery reaction tower R5. The HF concentration in the gas to be used can reliably be 3 ppm or less. In this case, when the HF concentration in the outlet gas of the first recovery reaction tower R4 reaches 3 ppm, the reaction rate of the fluorine absorbent in the main reaction tower R3 reaches a predetermined reaction rate level, for example, 90%. %, It is necessary to previously set the filling amount of the fluorine absorbent.
[0026]
By sequentially switching the respective reaction towers R1 to R5 in the above manner, fluorine in the gas generated by the decomposition of the PFC gas is almost recovered as calcium fluoride, and the purity of the recovered calcium fluoride is limestone. When used as a fluorine absorbent, 90% or more is calcium fluoride, and the balance is almost calcium carbonate, which is a high-grade fluorine source.
[0027]
In the above description, calcium carbonate was used as an example of the fluorine absorbent. However, PFC gas was produced using calcium fluoride as a raw material and calcium in the raw material was recovered as calcium sulfate. If calcium sulfate by-produced in the process is used as the fluorine absorbent, a complete recycling system of fluorine and calcium can be constructed. In addition, if flue gas desulfurization gypsum, which is a typical by-product calcium sulfate, is used as the fluorine absorbent, it will contribute to expanding the applications of the gypsum.
[0028]
Further, in the above description, two recovery reaction towers, the first recovery reaction tower R4 and the second recovery reaction tower R5, are used, but this may be one tower. In short, what is necessary is just to set the fluorine absorption capacity of the reaction tower so that the HF concentration in the exhaust gas discharged into the atmosphere from the pipe L6 becomes 3 ppm or less.
[0029]
In the nitrogen purge tower R2, nitrogen gas is supplied from the pipe L12, but dry air can be used as a purge gas. In this sense, the nitrogen purge in the present invention is used in the sense including the air purge.
[0030]
Further, in the above description, a combustion type abatement device is exemplified as the abatement device for the PFC gas. However, the abatement device to which the present invention is applied is not limited to this, and the thermal abatement device of the PFC gas may be used. Any form can be used as long as it is a decomposer that generates HF by a device, a hydrolysis device, or another PFC gas decomposer.
[0031]
Further, in FIG. 1, only one vacuum pump 2 for evacuating the CVD apparatus 1 is shown. However, this may be achieved by installing a plurality of vacuum pumps in series to increase the exhaust gas treatment capacity. It is possible.
[0032]
FIG. 1 shows an example in which the processing line for the source gas such as silane supplied to the CVD apparatus 1 and the processing line for the PFC gas are the same line. However, when NF3 is used as the PFC gas, Since there is a risk of explosion when SiH4 and NF3 are mixed, a path from the outlet pipe L2 of the CVD apparatus 1 to the combustion type abatement apparatus 3 in FIG. Can be used as a PFC gas processing line. However, since this causes an increase in equipment cost, nitrogen gas is injected into the outlet gas of the CVD apparatus 1 from the pipe L8 to dilute the concentration of SiH4 or PFC gas in the exhaust gas to suppress the explosion below the explosion limit, as shown in the figure. This is a practical measure.
[0033]
Further, FIG. 1 shows a CVD apparatus as an apparatus using a PFC gas. However, in the present invention, an apparatus using a PFC gas is not limited to a CVD apparatus, and an etching apparatus or other PFC gas is used. It goes without saying that the present invention can be applied as a technique for treating a PFC gas decomposition reaction gas in an apparatus.
[0034]
Next, examples of the present invention will be described.
[Example 1]
(1) Fluorine absorbent Purified calcium carbonate powder was added with a binder, and pellets having a particle size of 1 to 2 mm were produced by an extrusion molding method.
(2) Two reactors in which the above-mentioned fluorine absorbent pellets are packed in a cylindrical pipe having an inner diameter of 22 mm and filled at a height of a packed bed of 75 mm are arranged in series, one of which is a main reactor and the other is a recovery reactor. Three sets of rows were made.
(3) Fluorine recovery test With the temperature of the three sets of reaction tower rows maintained at 100 ° C., a sample gas of HF 2.0% (remaining nitrogen) was supplied at 5, 10, 20 liters / min (vacuum speed ( At a flow rate of about 5000, 10000, 20000 hr-1) in terms of SV), a fluorine recovery reaction was carried out by flowing DC from the main reaction tower to the recovery reaction tower, and the difference in the reaction rate due to the difference in SV value was evaluated. did. Note that the HF concentration in the outlet gas of the recovery reaction tower during the reaction test was analyzed, and the reaction test was terminated when the analysis value exceeded 3 ppm. After the completion of the reaction, each of the main reactions in the three sets of reaction tower rows and the pellets in each of the recovery reaction towers were taken out, and the conversion rate (reaction rate) of CaF2 was measured. The conversion was calculated according to a chemical analysis based on JIS-K1468-1978.
(4) Test results (a) First set of reaction tower rows (SV = 5000 hr-1)
・ CaF2 conversion of pellets in the main reaction tower: 95.7%
・ CaF2 conversion of pellets in the recovery tower: 63.8%
・ Total conversion: 79.7%
(B) Second set of reaction tower rows (SV = 10000 hr-1)
・ CaF2 conversion of pellets in the main reaction tower: 95.1%
・ CaF2 conversion of pellets in the recovery tower: 36.6%
・ Total conversion: 65.8%
(C) Third set of reaction tower rows (SV = 20,000 hr-1)
・ CaF2 conversion of pellets in the main reaction tower: 94.0%
・ CaF2 conversion of pellets in the recovery tower: 14.7%
・ Total conversion: 54.3%
[0035]
As is evident from the above test results, the conversion rate (reaction rate) of each reaction tower tended to decrease as the SV value increased. However, in all the main reaction towers, 90% or more of calcium carbonate was fluorinated. It can be seen that it has been converted to calcium iodide. In particular, under the condition that the SV value is 10,000 hr-1 or less, a high conversion of 95% or more is obtained, so that it can be understood that high-grade calcium fluoride can be easily produced by appropriately selecting the operating conditions. . The reaction rate of the recovery reaction tower is a level of slightly less than 15% to slightly more than 60%, which should be the next main reaction tower by switching the reaction tower as described above. Since the HF concentration in the outlet gas from the column is less than 3 ppm until the end of the reaction test, the HF concentration in the exhaust gas is not affected by the degree of the reaction rate of the recovery reactor. It is optional to increase the number of the recovery reactors to one or two according to the degree of the reaction rate of the recovery reactor when the HF concentration in the reactor reaches 3 ppm.
[0036]
【The invention's effect】
As described above in detail, according to the present invention, the harmful gas including the HF gas generated by the decomposition of the PFC gas is subjected to a dry absorption reaction using a fluorine absorbent represented by calcium carbonate. The problem of the treatment of acidic mist containing HF, which was a problem in the absorption method, the problem of the treatment of highly corrosive acidic wastewater that absorbed and dissolved HF, and the hydrofluoric acid obtained by neutralizing this acidic wastewater. The problem of wastewater containing the compound slurry will be completely eliminated.
[0037]
Furthermore, it should be noted that by-product fluoride, which was only an industrial waste in the conventional wet treatment method as described above, can be recovered as a useful fluorine source such as high-grade calcium fluoride. If a PFC gas is produced using calcium fluoride or the like, a fluorine recycling system can be constructed. In particular, the current situation of relying on China for the supply of calcium fluoride as a fluorine source is not favorable in terms of industrial policy, so the construction of the above-mentioned fluorine recycling system can be said to be an extremely useful measure for Japanese industry as well. .
[0038]
Also, if a method of operating while switching a plurality of reaction towers is adopted as a dry-type fluorine recovery reaction apparatus, it becomes possible to efficiently produce high-grade calcium fluoride with a reaction tower having a simple configuration, and inexpensive equipment. It will be possible to build a fluorine recycling system with investment.
[0039]
In particular, if calcium sulfate produced as a by-product in the PFC gas production process is used as a fluorine absorbent, both the fluorine and calcium components of the generated calcium fluoride will be the components of the original calcium fluoride. Can also be constructed.
[0040]
Further, in a factory where a PFC decomposition gas is treated using a wet-type abatement apparatus, if a dry-type powder removal apparatus and a dry-type abatement apparatus are installed instead of the wet-type abatement apparatus, the fluorine of the present invention can be obtained. Since the recovery method can be implemented, it is possible to construct a fluorine recycling system while effectively utilizing existing facilities.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for recovering fluorine from a PFC decomposition product gas according to the present invention.
FIG. 2 is a flow chart showing a switching operation procedure of the dry fluorine recovery reactor used in the present invention.
FIG. 3 is a flowchart showing a conventional method for treating PFC decomposition product gas.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 CVD apparatus 2 Vacuum pump 3 Combustion type abatement apparatus 4 Dry powder removal apparatus 5 Dry fluorine recovery reactor R1 Absorbent replacement tower R2 Nitrogen purge tower R3 Main reaction tower R4 First recovery reaction tower R5 Second recovery reaction tower L1 ~ 9, L12 ~ L16 Piping

Claims (12)

In a method of recovering fluorine from a decomposition product gas generated by decomposition of a PFC gas,
The decomposition product gas is passed through a dry-type powder removal device (4) to remove solid powder components contained in the decomposition product gas to form a dust-free gas. Hydrogen fluoride in the decomposition product gas is reacted with the alkaline earth metal by supplying to a dry fluorine recovery reactor (5) filled with a fluorine absorbent consisting of a substance or an oxide alone or a mixture thereof. For recovering fluorine as alkaline earth metal fluoride by heating The method for recovering fluorine according to claim 1, wherein the fluorine absorbent is a calcium compound composed of calcium carbonate, nitrate, sulfate, oxalate, hydroxide or oxide alone or a mixture thereof. The method for recovering fluorine according to claim 2, wherein the calcium compound uses a calcium compound by-produced in a PFC gas production plant. The dry fluorine recovery reactor (5) includes a plurality of reaction towers (R1 to R5) filled with the fluorine absorbent, and supplies the dust-free gas while sequentially switching the inside of the reaction tower. The method for recovering fluorine according to any one of claims 1 to 3, The reaction tower (R1 to R5) includes a main reaction tower (R3), a recovery reaction tower (R4, R5), a nitrogen purge tower (R2), and an absorbent replacement tower (R1). The gas is supplied in series to the recovery reactors (R4, R5) via the main reactor (R3). In the process of switching the reactors, the recovery reactor is the main reactor and the main reactor is the nitrogen. 5. The fluorine recovery method according to claim 4, wherein the purge tower, the nitrogen purge tower, and the absorbent replacement tower are sequentially switched to a recovery reaction tower, respectively. The recovery reaction tower has a first recovery reaction tower (R4) and a second recovery reaction tower (R5) arranged in series, and in the step of switching the reaction towers, the first recovery reaction tower is a main reaction tower. 6. The fluorine recovery method according to claim 5, wherein the first recovery reaction tower is switched to the first recovery reaction tower, and the absorbent replacement tower is switched to the second recovery reaction tower. 7. The fluorine recovery method according to claim 5, wherein an exhaust gas from the nitrogen purge tower (R2) is combined with an outlet gas of the main reaction tower (R3) and supplied to the recovery reaction tower (R4). The fluorine according to claim 5 or 6, wherein the exhaust gas from the nitrogen purge tower (R2) is combined with the dust-free gas supplied to the main reaction tower (R3) and supplied to the main reaction tower (R3). Collection method A fluorine recovery apparatus for recovering fluorine from a decomposition product gas generated by decomposition of a PFC gas,
A dry powder removing device (4) for removing solid fine particles in the decomposition product gas;
A dry fluorine recovery reactor (5) filled with a fluorine absorbent for recovering fluorine from the dust-free gas from which solid fine particles have been removed by the powder removal device (4);
Has,
The fluorine absorbent is formed into an appropriate shape from an alkaline earth metal salt, a hydroxide or an oxide alone or a mixture thereof,
The dry-type fluorine recovery reactor (5) includes a main reaction tower (R3), a recovery reaction tower (R4, R5), a nitrogen purge tower (R2), and an absorbent replacement tower (R1) in order. It is configured to be switchable,
The dust-free gas is supplied in series to the recovery reaction towers (R4, R5) via the main reaction tower (R3). In the step of switching the reaction towers, the recovery reaction tower is connected to the main reaction tower, A fluorine recovery apparatus characterized in that the tower is configured to be sequentially switched to a nitrogen purge tower, the nitrogen purge tower to an absorbent replacement tower, and the absorbent replacement tower to a recovery reaction tower. The recovery reaction tower has a first recovery reaction tower (R4) and a second recovery reaction tower (R5) arranged in series, and in the step of switching the reaction towers, the first recovery reaction tower is a main reaction tower. 10. The fluorine recovery apparatus according to claim 9, wherein the tower, the second recovery reaction tower is switched to the first recovery reaction tower, and the absorbent replacement tower is switched to the second recovery reaction tower, respectively. The fluorine recovery apparatus according to claim 10, wherein an exhaust gas from the nitrogen purge tower (R2) is combined with an outlet gas of the main reaction tower (R3) and supplied to the first recovery reaction tower (R4). The fluorine according to claim 9 or 10, wherein an exhaust gas from the nitrogen purge tower (R2) is combined with a dust-free gas supplied to the main reaction tower (R3) and supplied to the main reaction tower (R3). Collection device

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