JP4701825B2 - Exhaust gas treatment agent supply system and supply method - Google Patents

Description

  The present invention relates to an exhaust gas treatment system and a treatment method thereof, and more specifically, efficiently and harmless acidic gas components in exhaust gas generated when a PFC (perfluorocompound) discharged from a semiconductor or liquid crystal manufacturing factory is decomposed by a PFC decomposition apparatus. The present invention relates to an exhaust gas treatment system and a treatment method thereof.

A PFC having a high global warming potential is used in an etching process or a CVD cleaning process in a semiconductor or liquid crystal manufacturing factory. PFC is a general term for fluorine compounds such as CF ₄ , C ₂ F ₆ , C ₃ F ₈ , CHF ₃ , C ₄ F ₈ , SF ₆ , and NF ₃ . As a PFC treatment method, a combustion method, a plasma method, a catalyst method, and the like are known. Currently, the PFC decomposition method using the catalytic method is widespread in terms of simple maintenance, low running cost, and high PFC decomposition rate. However, in any of the treatment methods, hydrogen fluoride, which is a highly corrosive acidic gas, is generated after PFC decomposition.

  Currently, the mainstream method is to remove the generated hydrogen fluoride gas by a wet cleaning method. The advantage of the wet cleaning method is that a high hydrogen fluoride removal rate can be obtained. In addition, since a large amount of acid water is discharged, it is necessary to attach an acid gas treatment facility. Due to the growing social needs of zero wastewater, the acidic exhaust gas treatment method is being promoted from a wet cleaning method to a dry method using chemicals.

Waste incineration facilities have been using the bag filter method as an acid gas treatment method that has been replaced by a wet cleaning method. In the bag filter system, calcium hydroxide or sodium hydrogen carbonate is supplied to a duct or the like in an exhaust gas path, and the acidic components are removed by fixing halogens as CaCl ₂ and NaCl by a neutralization reaction. Japanese Patent Laid-Open No. 2002-361040 (Patent Document 1) installs a laser gas analyzer on either or both of the upstream side and downstream side of a dust collecting means (bag filter) for treating exhaust gas containing acidic components. It is described that the supply amount of the alkaline chemical supplied to treat the acidic gas is increased or decreased based on the measurement result of the laser gas analyzer.

JP 2002-361040 A

  In the invention described in Patent Document 1, gas to be processed such as HCl and SOx discharged from a waste incineration facility is the object of gas analysis. However, the hydrogen fluoride gas (HF) discharged by decomposing PFC is highly corrosive and has a high possibility of breaking the analyzer, so that it is difficult to directly analyze it. In addition, when an acidic gas amount is measured by a laser gas analyzer upstream of the dust collecting means and an alkaline agent corresponding to the measured amount is supplied, an alkaline agent appropriate for gas removal is supplied after analysis. It is difficult to supply an alkaline agent corresponding to the measured gas amount in real time.

  An object of the present invention is to measure the amount of a compound that generates a highly corrosive acidic gas such as hydrogen fluoride by decomposition and efficiently supply an acidic gas removing agent for removing the acidic gas to the acidic gas processing apparatus. The object is to provide a system and method for reducing running costs.

  A feature of the present invention that solves the above problems is that a gas analyzer is installed upstream of the catalytic PFC cracking device, and the amount of PFC flowing into the PFC cracking device is measured, thereby having high corrosiveness at the outlet of the PFC cracking device. This is an exhaust gas treatment system that calculates the amount of acid gas in the exhaust gas containing hydrogen fluoride gas, determines the amount of the removal agent to be supplied from the calculation result, and efficiently supplies the acid gas removal agent.

  The effect obtained by the present invention is to efficiently remove hydrogen fluoride by adjusting the amount of acid gas removing agent to be supplied by calculating the amount of hydrogen fluoride at the outlet of the catalytic PFC decomposition apparatus. As a result, the use of an excess acid gas removing agent and the amount of waste produced by removing hydrogen fluoride can be suppressed, and the running cost is expected to be reduced.

  In addition, it is possible to predict the generation amount even for acidic gas that is difficult to monitor, thereby adjusting the supply amount of the acidic gas removing agent necessary for removing the acidic gas as appropriate. In addition to reducing the cost of extra supply of the agent, the amount of solid waste discharged can be reduced, and the burden on the final disposal site can be reduced.

  In addition, by measuring the PFC upstream of the PFC decomposition unit, the amount of the acid gas removal agent to be supplied to the acid gas treatment device installed at the subsequent stage of the PFC decomposition unit is determined. There is a sufficient margin, it can respond to changes in the flow rate of acidic gas, and can be supplied efficiently.

  In addition, by installing a gas analyzer upstream of the catalytic PFC cracking unit and measuring the amount of PFC flowing into the unit, the deterioration of the catalyst can be clearly determined, and the catalyst replacement time can be determined early. it can.

  As typical methods for decomposing PFC, there are a catalytic method, a plasma method, and a combustion method. In any method, hydrogen fluoride gas is generated by the decomposition.

  For example, typical reaction examples when PFC is hydrolyzed by a catalytic method are shown in formulas (1) to (4).

CF ₄ + 2H ₂ O ⇒ 4HF + CO ₂ (1)
C ₂ F ₆ + 3H ₂ O ⇒ CO + CO ₂ + 6HF (2)
SF ₆ + 3H ₂ O ⇒ SO ₂ + 6HF (3)
2NF ₃ + 3H ₂ O ⇒ NO + NO ₂ + 6HF (4)
Therefore, if the PFC decomposition rate by the catalyst is known in advance, the amount of generated HF can be predicted by measuring the amount of PFC. The amount of PFC is measured before decomposition using a gas analyzer installed upstream of the PFC cracking unit, and the amount of acid gas in the exhaust gas containing highly corrosive hydrogen fluoride gas at the outlet of the PFC cracking unit is calculated directly. Accordingly, it is possible to reduce the material to be removed and to perform a process in response to the change in the flow rate without being affected by the change in the measurement value due to the corrosion of the analyzer.

  It is desirable to install a water spray tower for removing solids at the front stage of the catalytic PFC decomposition apparatus. By installing the water spray tower, it is possible to remove the solid matter in the exhaust gas containing PFC flowing into the catalytic PFC decomposition apparatus. Moreover, the acidic component in the exhaust gas contained before decomposition can be removed, and the load on the gas analyzer can be reduced. If the acidic component contained in the exhaust gas does not affect the gas analysis, a method of removing only solid matter in the exhaust gas by installing a dust filter or bag filter instead of the water spray tower may be used. .

  Examples of a gas analyzer that measures PFC include a laser gas analyzer, gas chromatography (GC), and a Fourier transform infrared spectrophotometer (FT-IR). The analyzer suitable for the present invention has a short measurement time and can perform continuous measurement.

  As an acid gas removing agent that removes acid gas such as hydrogen fluoride gas generated in the catalytic PFC decomposition apparatus by the above reaction, basic salts of alkali metals and alkaline earth metals such as calcium hydroxide, sodium hydroxide, Potassium hydroxide, magnesium hydroxide, sodium bicarbonate, sodium carbonate, calcium carbonate, calcium oxide can be used. In order to obtain a high hydrogen fluoride removal rate and removal agent utilization rate, it is desirable that the above compounds have a high alkali metal or alkaline earth metal content and a high specific surface area.

  An acid gas removing agent is supplied to the mixing chamber, which is an exhaust gas path, and mixed with the acid gas discharged from the catalytic PFC decomposition apparatus. It is desirable to heat the mixing chamber, so that the moisture in the gas is prevented from condensing by heating, and the apparatus is prevented from being corroded by hydrogen fluoride dissolved in the condensed water. Further, the acid gas removing agent may be supplied directly into the flue instead of being supplied to the mixing chamber.

  As the solid matter collecting device, a bag filter device composed of a filter cloth having acid resistance and a material of the device is desirable. It collects the chemicals that have reacted in the flue and deposits unreacted calcium hydroxide on the filter cloth surface to remove unreacted hydrogen fluoride. The acid gas removing agent deposited on the filter cloth surface is peeled off with compressed air or the like. This suppresses an increase in pressure loss in the apparatus system.

  The bag filter device material needs to be changed according to the operating temperature. For use at a high temperature of 200 ° C. or higher, nickel-based alloys such as Inconel and Hastelloy are good. If it is used at 200 ° C or lower, the water vapor contained in the exhaust gas will condense, and acidic gases such as hydrogen fluoride may dissolve in it, which may corrode metal materials such as Inconel. Resin is desirable, and vinyl chloride or the like can be used if the temperature can be lowered to 60 ° C. or lower. In any case, a corrosion-resistant material is desirable.

  It is desirable to change the material of the filter cloth material according to the hydrogen fluoride concentration and the temperature use conditions of the bag filter. If the reaction temperature is 150 ° C. or less, a filter cloth made of polyester, polypropylene, or acrylic is preferable, and if it is 150 ° C. or more, heat resistant nylon, polyimide, polyphenylene sulfide (PPS), or polytetrafluoroethylene (PTFE) filter cloth is desirable. If the corrosion resistance to acid is 150 ° C. or lower, polypropylene is excellent, and if it is 150 ° C. or higher, PPS and PTFE are excellent.

  It is desirable to install a drain tank downstream of the bag filter. By installing the drain tank, moisture in the exhaust gas that has passed through the bag filter can be collected. In addition, even if hydrogen fluoride gas that could not be collected by the bag filter flows out, hydrogen fluoride can be collected in the condensed water by passing it through the drain tank. The hydrogen concentration can be reduced to one-tenth or less. It is desirable to install a drain tank in the downstream part of the blower or the ejector if the exhaust gas is high temperature, or in the upstream part if the exhaust gas is low temperature.

  The reactivity of acidic gas such as hydrogen fluoride and acidic gas removing agent is considered to change depending on the exhaust gas temperature, moisture content, operating conditions such as flow rate, and exhaust gas composition. A large amount of the acid gas is removed when passing through the acid gas removing agent deposited on the surface of the filter cloth described above. Therefore, the exhaust gas filtration rate on the filter cloth surface is an important parameter for the reaction between the acid gas and the acid gas removing agent. Desirably, the filtration speed is designed to be 2.0 m / min or less.

  In addition, when the moisture content of the exhaust gas is high, moisture adheres to the acid gas removal agent deposited on the surface of the filter cloth, causing clogging of the filter cloth. In addition, the acidic gas is dissolved in the moisture, which affects the reaction between the acidic gas and the acidic gas removing agent. Therefore, it is desirable to heat the piping inside or to the bag filter.

  As a method of heating the pipe to the bag filter, it is desirable to heat the pipe with a heater. More preferably, a heater is installed in the mixing chamber for supplying the acid gas removing agent. Moreover, as a heating method of the bag filter, it is desirable to install a rod heater inside the filter cloth and heat from the inside of the filter cloth.

  From the amount of PFC measured by the gas analyzer, the amount of acidic gas such as hydrogen fluoride discharged after the catalytic PFC decomposition apparatus is calculated, and when supplying the acidic gas removing agent from the calculation result, the amount of acidic gas removing agent is It is desirable to supply more than is necessary to theoretically remove the acid gas. Since the reactivity of acid gas and acid gas removal agent is considered to change depending on the exhaust gas temperature, moisture content, and flow rate, the correlation of acid gas removal efficiency by acid gas removal agent in the above parameter change is experimentally or calculated. Obviously, when supplying the acid gas removal agent, it is desirable to supply these acid gas removal agents in such an amount that the acid gas can be completely removed in consideration of these factors.

  Therefore, an exhaust gas temperature measuring device or the like can be provided. In that case, it is necessary to install in the upstream of a decomposition | disassembly apparatus for the reason similar to said flow measuring device.

  Hereinafter, the present invention will be described in detail with reference to examples.

  The system flow of the present invention is shown in FIG. In a system in which a gas component that decomposes to generate an acid gas is decomposed in a gas decomposition step, and the generated acid gas is decomposed in an acid gas treatment step by an acid gas removal agent supplied from an acid gas removal agent supply step, The gas analyzer installed upstream of the decomposition process measures the amount of gas components that decompose to produce acid gas, and predicts the amount of acid gas produced by decomposition from the measured gas amount. It is a system which supplies an acid gas removal agent from a gas removal agent supply process.

  The processing flow of PFC discharged from a dry etching apparatus in a semiconductor manufacturing factory will be described below as an example, and will be described in more detail.

A processing flow of PFC in a semiconductor manufacturing factory is shown in FIG. The PFC discharged from the semiconductor manufacturing factory is sent to the solid matter removing scrubber to remove the solid content in the gas. The gas that has passed through the scrubber is sent to the PFC decomposition apparatus at the rear stage to decompose the PFC. The amount of PFC in the gas is measured by the PFC amount measuring device installed in the upstream part of the PFC decomposition device, and the amount of acidic gas such as hydrogen fluoride generated by the decomposition is calculated based on the PFC decomposition rate that is known in advance. The amount of the acid gas removing agent necessary for removing the acid gas is predicted, and the prediction result is output to the acid gas removing agent supply silo. The acidic gas such as hydrogen fluoride generated by the PFC decomposition in the PFC decomposition unit is mixed with the acidic gas removal agent supplied from the acidic gas removal agent supply silo in the acidic gas removal agent supply chamber provided on the flue. Sent to the bug filter. The bag filter collects the reacted chemicals and deposits an unreacted acid gas removal agent on the filter cloth surface. By passing the acid gas through the deposited acid gas removal agent, the unreacted acid gas is removed. , Discharge outside the system.

  An example of the apparatus configuration in the present invention is shown in FIG.

The exhaust gas from the semiconductor manufacturing process contains PFC-containing gas that has not been consumed in the dry etching process. The PFC-containing gas is freed of solids and acidic components by the water spray tower 100, introduced into the catalytic PFC decomposition apparatus 103, and decomposed by the catalyst 104. Since the PFC decomposition reaction by the catalyst is based on hydrolysis, the reaction water 11 is always allowed to flow into the decomposition apparatus.

  A gas analyzer 112 measures the amount of PFC flowing into the catalytic PFC decomposition apparatus at regular intervals in the upstream portion of the catalytic PFC decomposition apparatus. It is desirable to measure the moisture content in the exhaust gas, the exhaust gas flow rate, etc. at the same time as measuring the PFC amount. The value measured by the gas analyzer 112 is output to the control device 113, and the control device calculates the amount of acid gas generated when the measured amount of PFC is decomposed. In consideration of the calculation result and parameters such as the temperature of the mixing chamber 105, the amount of exhaust gas, and the moisture content in the exhaust gas, the amount of acid gas removing agent capable of completely removing the acid gas is calculated. The calculation result is sent to the acidic gas removing agent supply silo 114, and the input acidic gas removing agent amount is supplied to the mixing chamber 105.

  The acidic gas discharged from the catalytic PFC decomposition apparatus 103 and the acidic gas removing agent supplied from the acidic gas removing agent supply silo 114 are mixed in the mixing chamber 105.

  The exhaust gas in which the acid gas and the acid gas removing agent are mixed in the mixing chamber 105 is sent to the bag filter 107. The bag filter 107 removes acid content by passing the acid gas through the acid gas removing agent deposited on the surface of the filter cloth 108, and at the same time, removes solid components such as the acid gas removing agent. The reactivity of the acid gas remover and acid gas on the filter cloth surface is affected by the filtration rate. In order to prevent deterioration of the filter cloth material and maintain a high acid gas removal rate, it is desirable to design the filtration speed to be 2.0 m / min or less.

  Further, the acid gas removing agent containing moisture is deposited on the surface of the filter cloth and raises the pressure in the apparatus. It is necessary to periodically feed compressed air 12 to remove solid components such as acid gas remover deposited on the filter cloth surface.

Taking CF ₄ as an example in the PFC, when 1 mol of CF ₄ is completely decomposed by the catalytic PFC decomposition apparatus 103 of FIG. 2, 4 mol of hydrogen fluoride is generated from the reaction formula (5). To do. From the reaction formula (6), the amount of calcium hydroxide required to decompose 4 moles of hydrogen fluoride is 2 moles. The hydrogen fluoride gas produced here and the supplied calcium hydroxide do not react 1: 1, but the reactivity varies depending on parameters such as temperature, moisture content, gas flow rate and the like. Therefore, the value which considered those parameters is output to the acidic gas removal agent supply silo 114, and the supplied acidic gas removal agent amount is supplied.

CF ₄ + 2H ₂ O → 4HF + CO ₂ (5)
4HF + 2Ca (OH) ₂ → 2CaF ₂ + 4H ₂ O (6)
The amount of acid gas removing agent to be supplied is determined from the amount of acid gas generated by decomposing other PFCs (C ₂ F ₆ , SF ₆ , NF ₃ etc.) by the same method.

  In this embodiment, calcium hydroxide and hydrogen fluoride gas are reacted at 200 to 400 ° C.

Hydrogen fluoride was supplied by cracking CF ₄ with a catalyst.

The reactivity index of calcium hydroxide and hydrogen fluoride was evaluated by the value of theoretical reaction rate. The theoretical reaction rate is the time (A) that is completely consumed when the charged calcium hydroxide reacts one-to-one with hydrogen fluoride generated by decomposing CF ₄ and actually at the bottom of the Inconel tube. It was expressed as a ratio to the time (B) at which hydrogen fluoride was detected.

Theoretical reaction rate (%) = B / A * 100
The theoretical reaction rates at 200-400 ° C. of two different calcium hydroxides A and B used in the test are shown in FIG. Calcium hydroxide B showed a higher reaction rate in the same temperature range, and both calcium hydroxides A and B had a reaction rate of 99% or more at a reaction temperature of about 320 ° C. Also, the reaction rate decreased with increasing temperature. The theoretical reaction rate here is 100% when calcium hydroxide and hydrogen fluoride react one-to-one. Therefore, hydrogen fluoride that can be treated by increasing the amount of calcium hydroxide under the condition of 100% or less. The amount of is expected to increase. For example, it is desirable that the input amount of calcium hydroxide is 2 to 3 times when the reaction rate is 60 to 80%, and 4 to 5 times when the reaction rate is 60% or less.

  Table 1 shows the BET specific surface areas of calcium hydroxides A and B.

  Calcium hydroxide B, which has a high reaction rate in the same temperature range, has a larger specific surface area. It is considered that the reactivity is high because calcium hydroxide and hydrogen fluoride are in efficient contact. It is desirable that the drug used has a high specific surface area.

  Filtration speed is a factor that affects the removal of solids and acid gases in the bag filter system. The reaction on the filter cloth surface of the bag filter was simulated, and the theoretical reaction rate was measured by changing the linear velocity of the gas passing through the calcium hydroxide filled with the fixed bed. The temperature of the packed bed was about 300 ° C., and the linear velocity was 1.7 to 3.2 m / min.

  The test results are shown in FIG. As the linear velocity increases, the theoretical reaction rate shows a gradual downward trend. Although depending on the pressure resistance of the filter cloth material, if the linear velocity (filtration rate) is 2.0 m / min or less, a reaction rate of 80% or more can be expected when calcium hydroxide and hydrogen fluoride are reacted one-on-one. .

It is the figure which showed the processing system flow of this invention. It is the figure which showed the PFC processing flow of the semiconductor manufacturing factory in this invention. It is the figure which showed the apparatus structure of this invention. It is the figure which showed the temperature change of the HF removal ability by 2 types of calcium hydroxide. It is the figure which showed the relationship between linear velocity and HF removal ability.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Water spray tower, 102,106 ... Heater, 103 ... Catalytic PFC decomposition device, 105 ... Mixing chamber, 107 ... Bag filter, 108 ... Filter cloth, 109 ... Solid substance collection tank, 112 ... Gas analyzer, 113 ... control device, 114 ... acid gas removal agent supply silo.

Claims (6)

A gas decomposition step of decomposing PFC in exhaust gas by a catalytic PFC decomposition device to generate acid gas; an acid gas treatment step of removing acid gas discharged from the gas decomposition step; and an acid gas in the acid gas treatment step An exhaust gas treatment method comprising a removal agent supply step for supplying a removal agent,
Said removing agent supplying step, the PFC quantity flowing into the catalytic PFC decomposition device measured by the installed gas analyzer to the catalytic PFC decomposition apparatus upstream portion, the PFC decomposition rate known in advance, were measured PFC An exhaust gas treatment method characterized by predicting the amount of acidic gas produced by decomposition from the amount and supplying the acidic gas removing agent from the removing agent supply means based on the prediction result. A gas processing method according to claim 1, wherein the exhaust gas processing method characterized in that said removing agent is a powder of alkali metal, alkaline earth metal basic salts. A gas processing method according to claim 1, wherein, with any amount of operating conditions or gas composition of the removing agent, the exhaust gas processing method characterized in that predicted based on the PFC amount. 2. The exhaust gas treatment method according to claim 1, wherein a gas temperature is measured by a temperature analyzer installed upstream of the gas decomposition step, and a removal agent amount calculated from a prediction result of the acid gas amount is adjusted. An exhaust gas treatment method characterized by that. The PFC in the exhaust gas is decomposed by the catalyst, and the catalyst type PFC decomposition device that generates acid gases and acid gas treatment apparatus for removing acid gas discharged from the catalytic PFC decomposition apparatus, acidic the acid gas processing device An exhaust gas treatment device having a removal agent supply device for supplying a gas removal agent,
Installed in the catalytic PFC decomposition apparatus upstream portion, and a gas analyzer for measuring the PFC quantity flowing into the catalytic PFC decomposition apparatus, by PFC decomposition rate known in advance, PFC amount measured by the gas analyzer An exhaust gas treatment comprising: an acidic gas removal agent supply device that predicts the amount of acidic gas generated after passing through the catalytic PFC decomposition device based on the above and supplies an acidic gas removal agent based on the prediction result apparatus. 6. The exhaust gas treatment apparatus according to claim 5 , further comprising a gas temperature measuring device installed upstream of the catalytic PFC decomposition device , wherein the acidic gas removing agent supply device is configured to measure the acidic gas according to a measurement result of the gas temperature. An exhaust gas treatment apparatus characterized by adjusting an amount of a removing agent.

Images