JP3636617B2 - Perfluorocarbon gas removal method and removal apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for removing exhaust gases derived from cleaning and etching processes during the manufacture of electronic circuit elements such as semiconductors and liquid crystals, and is also suitable for removing gases generated during aluminum refining. Regarding what is possible.
[0002]
[Prior art]
Hereinafter, the field of the present invention will be described by limiting the removal of gas used in cleaning and etching processes in the manufacture of electronic circuit elements, but the present invention is also applicable to the removal of gas generated in aluminum refining.
[0003]
One group of gases used here is PFC. This is an abbreviation for perfluorocarbon, CF_Four, CHF_Three, C₂F₆Is a representative compound. When using Compound instead of Carbon, NF_Three, SF₆, SF_FourFluorine compounds not containing C such as are added as targets.
[0004]
Although the present invention has been established for the purpose of removing the former PFC that has not yet reached the technically usable range as a removal apparatus and removal method even today, it can of course be applied to all PFCs including the latter. It is a technology that can be done.
[0005]
CF_Four, C₂F₆PFCs represented by the above are nonflammable, and the toxicity of the gas itself to the human body is unknown, and at least acute and subacute toxicity is not known. However, since the compound itself is stable, when released into the atmosphere, it will remain unchanged over a long period of time. Life to consumption in the atmosphere is CF_Four50,000 years, C₂F₆It is said to be 10,000 years, and the global warming potential (CO₂Is the comparison value with 1 as CF)_FourAt 4,400, C₂F₆It is 6,200 (as of 20 years), and has a problem that cannot be left on the global environment. Therefore, CF_Four, C₂F₆Establishment of a means for removing PFC represented by
[0006]
However, the former PFC, ie CF_Four, CHF_Three, C₂F₆Since the C—F bond is stable (the bond energy is as high as 120 kcal / mol), the compound represented by is not easily decomposed, and it is extremely difficult to remove it by simple thermal oxidative decomposition.
[0007]
For example C₂F₆In this case, since the decomposition proceeds by cutting the C—C bond branch, the treatment air volume can be removed by restricting the treatment air volume to 250 liters / min or less at a treatment temperature of 1000 ° C._FourNeeds to cut C—F having the largest binding energy, requires 1400 ° C. even in the above-mentioned air volume, and it is still difficult to remove 80% or more.
[0008]
In addition, the achievement of a high temperature atmosphere of 1400 ° C. or higher is limited by the heating element material in the case of an electric heater, and it is almost impossible to use for a long time. In addition, it is difficult to keep the entire apparatus warm, and even in the combination of heat insulating materials, the entire volume becomes large and the apparatus is not compact. More importantly, the thermal energy cost is excessive.
[0009]
The following new proposals are shown in this field. International Publication Number WO94 / 05399 #Method of Decomposing Gaseous Halocarbon #_FourO in the removal of₂Although there is a report that the decomposition temperature is possible at 600 to 700 ° C. when coexisting, the details could not be removed under these conditions even if the description was re-examined in detail.
[0010]
Furthermore, H₂There is an attempt to introduce gas actively and to thermally decompose PFC, but it is necessary to increase the processing temperature.₂Since the gas is flammable and explosive, it can be used for safety reasons.
[0011]
[Problems to be solved by the invention]
Therefore, there is a need for a removal method and a removal apparatus that can decompose and remove PFC components at a low temperature (low heat energy consumption) as much as possible at a high removal rate.
[0012]
[Means for Solving the Problems]
  The removal method and removal apparatus of the present invention removes the PFC component at low temperature, the derived F component is separately washed or immobilized and the other components are basically CO 2.₂, H₂An apparatus and method for releasing as O into the atmosphere is proposed. Specifically, in the method for removing perfluorocarbon gas according to claim 1, the gas to be treated is washed with water,Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasIs mixed with the gas to be treated after washing with water to release free O₂It is characterized in that it is thermally decomposed in the absence of water, and then the fluorine compound generated by the thermal decomposition is removed by washing with water, and then combusted in the presence of external air to combust and remove combustible components.
[0013]
  The method for removing perfluorocarbon gas according to claim 2, wherein the gas to be treated is washed with water,Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasIs mixed with the gas to be treated after washing with water to release free O₂It is characterized in that it is thermally decomposed in the absence of air, and then the gas after heat decomposition is combusted in the presence of external air to burn and remove combustible components, and then the fluorine compound produced by the heat decomposition is removed by washing with water.
[0014]
  The method for removing perfluorocarbon gas according to claim 3, wherein the gas to be treated is washed with water,Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasIs mixed with the gas to be treated after washing with water to release free O₂The fluorine compound generated by thermal decomposition in the absence of oxygen and then the thermal decomposition is CaO or CaCO_ThreeIt is characterized in that it is chemically adsorbed on the granular material and removed, and then burned in the presence of external air to burn and remove combustible components.
[0015]
  The perfluorocarbon gas removal method according to claim 4 is the removal method according to claim 1, claim 2 or claim 3, wherein the gas mixed with the gas to be treated after water washing at the time of thermal decomposition is CH._Four, C₂H₆, C_ThreeH₈,Or C _Four H _Ten Any one of these or a mixture of two or more of these or NH _Three Mixed gasIt is characterized by being.
[0016]
  The apparatus for removing perfluorocarbon according to claim 5 includes a first water scrubber (1) for washing the gas to be treated and a gas decomposition tower (2) provided downstream of the first water scrubber (1). ), A second water scrubber (3) provided downstream of the gas decomposition tower (2), and a treated gas provided downstream of the second water scrubber (3) in the presence of external air Comprising a combustion tower (4) for burning in the gas decomposition tower (2),Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasThe treated gas mixed with the mixed gas of₂It is characterized in that it can be thermally decomposed in the absence of water.
[0017]
  The apparatus for removing perfluorocarbon according to claim 6 includes a first water scrubber for washing the gas to be treated, a gas decomposition tower provided downstream of the first water scrubber, and a downstream of the gas decomposition tower. A combustion tower for burning the treated gas in the presence of external air, and a second water scrubber provided on the downstream side of the combustion tower, the gas decomposition tower comprising:Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasThe treated gas mixed with the mixed gas of₂It is characterized in that it can be thermally decomposed in the absence of water.
[0018]
  The apparatus for removing perfluorocarbon according to claim 7 includes a first water scrubber for washing the gas to be treated, a gas decomposition tower provided downstream of the first water scrubber, and a downstream of the gas decomposition tower. CaO or CaCO provided on the side_ThreeAn adsorption tower filled with particulates, and a combustion tower provided on the downstream side of the adsorption tower in order to burn the treated gas in the presence of external air,Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasThe treated gas mixed with the mixed gas of₂It is characterized in that it can be thermally decomposed in the absence of water.
[0019]
The perfluorocarbon removing device according to claim 8 is the removing device according to claim 6, wherein the gas decomposition tower (12) and the combustion tower (14) are integrally formed through a heat-resistant partition wall (13). The gas decomposition combustion tower (11) is provided.
[0020]
  The perfluorocarbon removing apparatus according to claim 9 includes a first water scrubber (31) for washing the gas to be treated, and a gas decomposition combustion tower (1) provided downstream of the first water scrubber (31). 21) and a second water scrubber (32) provided downstream of the gas decomposition combustion tower (21). The gas decomposition combustion tower (21) includes a first water scrubber (31) and a second water scrubber (31). 2 is disposed above the water scrubber (32), and the gas decomposition combustion tower (21) is located on the downstream side of the gas decomposition tower (22) and the heat decomposition partition wall (22) ( 23) has a combustion tower (24) partitioned with the gas decomposition tower (22) in communication with the upper end thereof, and the gas decomposition combustion tower has a plurality of electric A heater (26) is installed, and a plurality of heat-resistant rods (29) having a heat shielding effect are horizontally installed below the electric heater (26), and the gas decomposition tower (22)Lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas only, or lower saturated hydrocarbon gas and NH _Three Gas, or lower unsaturated hydrocarbon gas and NH _Three Gas, or lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH _Three gasThe treated gas mixed with the mixed gas of₂The combustion tower (24) is capable of burning the gas subjected to the heat decomposition treatment in the gas decomposition tower (22) in the presence of external air.
[0021]
The main unit operations of the above invention are the following three stages.
(a) PFC pyrolysis
(b) Cleaning exhaust or immobilization removal of generated fluorine compounds
(c) Combustion removal of other combustible components
The most important configuration of the present invention is the PFC pyrolysis described in (a) above, with a removal rate of 90% or more in a temperature range significantly lower than the ambient temperature required for ordinary simple pyrolysis [{introduction of the removal device] PFC concentration in gas− (PFC concentration in released gas / PFC concentration in removal device introduction gas)} × 100].
[0022]
The thermal decomposition of the PFC forming the essence of the present invention is performed by using an electric heater or a liquid fuel such as LPG or LNG as a heat source, CH_Four, H₂Any means of flame combustion using a gaseous fuel such as CO as a heat source may be used, and the position of the heat source used for heating may be outside or inside the reaction tower.
[0023]
  PFC is the main component in the space of the gas decomposition tower, and N as the normal carrier gas₂To be treated is introduced. MorehereLower saturated or unsaturated hydrocarbons (where lower is C₁~ C₈Refers to the component, especially C₁~ C_FourComponent saturated hydrocarbons are preferred)Alone or with these _Three Mixed gasSupply at the same time.
[0024]
In that case, for example, O in CVD₂Or O_ThreeWhen used together, the residual gas used as exhaust gas flows into the gas decomposition tower.₂, O_ThreeAlternatively, one condition is that external air is not injected and at least the atmosphere in the gas decomposition tower is not brought into an oxidized state.
[0025]
Under such circumstances, the PFC is decomposed when the PFC concentration in the gas to be processed, the amount of the processing gas flow, and the space temperature in the gas decomposition tower are set to predetermined conditions. In this case, the atmospheric temperature is the processing temperature in the PFC alone or in the oxidizing atmosphere system. It was confirmed that PFC can be almost completely removed even at a temperature lower by several hundred degrees C.
[0026]
  This is because hydrocarbons and NH introduced as cracking agents for PFC_ThreeUndergoes thermal decomposition in a non-oxidizing atmosphere (for example, when propane is used, methane, ethane, ethylene,propylene, Hydrogen and various decomposition products are generated), and the active hydrogen in the radical state generated in the decomposition process contributes to the decomposition of PFC, and the F component of PFC is F₂Or it is thought that it is because it is isolated as HF.
[0027]
In the case of PFC alone or in an oxidizing atmosphere system, it is extremely difficult to achieve a result that the removal rate exceeds 80% even when using a high temperature range close to the limit of the material used. The decomposition mechanism of the compound in the gas decomposition tower is It is completely different from the present invention.
[0028]
The treated gas discharged from the gas decomposition tower according to the present invention is F₂Or it becomes carbon soot according to the hydrocarbon cracking gas and conditions of HF and cracking agent. And both F type exhaust gas and combustible gas of both components are processed harmlessly, respectively.
[0029]
That is, the former is absorbed and dissolved in water through a water scrubber, or CaO or CaCO._ThreeIt is separated by chemical adsorption with a solid absorbent, and exhausted outside the system. The latter burns in the presence of external air and releases the final process gas to the atmosphere.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to preferred embodiments.
[0031]
In the removal apparatus of the present invention, various apparatuses that perform three elements (a) thermal decomposition of PFC, (b) cleaning exhaust or fixed removal of generated fluorine compounds, and (c) combustion removal of other combustible components are cabinets. Is housed in one piece.
[0032]
FIG. 1 is a view showing an outline of the removing apparatus of the present invention. In the figure, (1) is a front water scrubber (first water scrubber) provided upstream (upstream) of the gas decomposition tower (2). The PFC-containing treated gas sent through the PFC-containing treated gas introduction pipe (5) is first guided to the front water scrubber (1) and washed with water.
[0033]
The gas to be treated discharged from the front water scrubber (1) is sent to the gas decomposition tower (2) through the water tank (10). The heating in the gas decomposition tower (2) may be an external heating method or an internal heating method. In any case, the inside of the gas decomposition tower (2) is corrosive F.₂And / or HF is generated and is attacked by metal materials. Therefore, a high Ni content alloy such as Inconel (trademark) or an inner surface is made of Al.₂O_ThreeIt is necessary to coat with the main ceramic. When an electric heater is installed inside, Al is used to protect the heater.₂O_ThreeInsert the heating element into the protective ceramic tube.
[0034]
N₂CF with an inert gas as a carrier_Four, C₂F₆The spent gas of PFC typified by is introduced into the gas decomposition tower (2).₂, O_ThreeSuch residual gas of the oxidant is simultaneously introduced into the removing device. However, dare O₂Alternatively, no additional oxidant such as air is introduced.
[0035]
  And as a reducing atmosphere positively, a lower (C₁~ C₈Component) saturated or unsaturated hydrocarbonsSingle or these and NH _Three Mixed gasIs introduced into the gas decomposition tower (2) through the reducing atmosphere forming agent introduction pipe (6).
[0036]
Lower saturated or unsaturated hydrocarbons include methane, ethane, propane, n- or iso- (hereinafter the same) butane, pentane, hexane, heptane, octane, ethylene, propylene, butylene, butadiene, as well as benzene, toluene and xylene. Aromatic hydrocarbons such as these can also be used. City gas can also be used.
[0037]
However, in the ratio of hydrocarbons C and H, the more C, the more the remaining C and the more likely to cause soot._Four, C₂H₆, C_ThreeH₈, C_FourH_TenEtc. are preferably used.
[0038]
NH_ThreeSince it also has a function as a hydrogen supplier in which a plurality of hydrogens are combined as in the case of hydrocarbons, it can also be used as a reducing atmosphere forming agent. Furthermore, NH_ThreeIs used, the HF produced in the gas decomposition tower is neutralized to give NH._FourBy forming the salt of F, it can be expected that the device material is effective in preventing corrosion.
[0039]
As the reducing atmosphere forming agent, any one of the above gases may be used alone, or two or more kinds may be mixed and used.
[0040]
The concentration of PFC that can be removed in the present invention is in a wide range, and in the range of 100 ppm to 5%, at least 90% or more can be removed. Although removal is possible even in a concentration range of 100 ppm or less or 5% or more, a removal rate of 90% or more may not be achieved.
[0041]
The processing gas flow rate in the present invention is preferably in the range of 5 to 700 liters / min. Processing is possible even at 5 liters / min or less, but the energy efficiency of the apparatus is low, resulting in useless operation. On the other hand, if it is 700 liters / min or more, the energy transfer to the processing gas becomes insufficient and the removal rate tends to decrease.
[0042]
The gas amount of the reducing atmosphere forming agent that coexists when decomposing PFC is 0.1 to 3 mol per mol of PFC. Use of 0.1 mol or less is insufficient in reducing the decomposition temperature and increasing the removal rate, which is the object of the present invention. When the amount is 3 mol or more, treatment with a PFC removal rate of 90% or more can be performed. The generation of such pyrolysis products is increased, and the waste of hydrocarbons and the subsequent process of the processed gas become complicated, which is not preferable.
[0043]
The temperature in the cracking tower can be processed even in a low temperature range of several hundreds of degrees Celsius compared to simple thermal cracking (including oxidative cracking) which is not the method of the present invention, regardless of whether the heat source is placed inside or outside the tower.
[0044]
In the case of simple pyrolysis, for example, C₂F₆As an example, in the temperature range of 1100 to 1200 ° C., the removal rate is only 80 to 85%, and CF in the treated gas is further increased._FourThe by-product appears. CF_FourIn this case, even in the temperature range of 1400 ° C., the removal rate is only 70%, which is far from the 90% targeted by the present invention. When an electric heater is used as a heat source, long-term use at around 1400 ° C. is technically difficult, and should preferably be stopped at 1100 ° C. or less.
[0045]
In contrast, according to the present invention, conventional PFC alone or O₂It can be removed at a lower temperature than the decomposition reaction in the presence of, for example, C₂F₆850 ℃ is enough for CF_FourThen, it can be processed at a removal rate of 90% or more at 1000 to 1200 ° C.
[0046]
Hydrocarbons introduced into the cracking tower can be used for the oxidation of PFC in the CVD cleaning process.₂Or O_ThreeIf the remaining amount is used, it disappears by reaction, and further thermally decomposes at a given temperature to decompose into various components.
[0047]
For example, in the case of propane, it is thermally decomposed at 780 ° C. and converted into substances such as methane, ethane, ethylene, propylene, hydrogen, and carbon. In the process, C₂F₆, CF_FourPFCs like₂Alternatively, the F component is eliminated in the form of HF.
[0048]
The fluorine component of PFC treated in the gas decomposition tower is F₂Or / and exhausted in the form of HF. This treated gas can be dissolved in water by passing the rear water scrubber (second water scrubber) (3), or it can be either CaO or CaCO._ThreeLed to an adsorption tower with a solid packing of CaF₂Is removed by adsorption.
[0049]
The gas body from which the F component has been eliminated by any of the above methods is sent to the treated gas combustion tower (4). Here, it is mixed with the external air sent through the air introduction pipe (9), the combustible component is burned, and finally CO.₂, H₂After returning to O, it is discharged into the atmosphere through the atmospheric discharge gas discharge pipe (8). In the figure, (7) is a suction fan.
[0050]
The treated gas combustion tower (4) and the rear water scrubber (3) are reversed in position so that the gas treated in the gas decomposition tower is burned in the treated gas combustion tower (4) and then the rear water scrubber ( It may be cooled through 3) and released into the atmosphere. That is, as long as the treated gas combustion tower (4) and the rear water scrubber (3) are arranged in series, either one may be first.
[0051]
[Example 1]
In this embodiment, the first water scrubber, the gas decomposition tower, the second water scrubber, and the combustion tower are processed in this order.
[0052]
CF_FourIs 1%, N₂A 99% mixed gas of 30 liters / min was passed through the front water scrubber (first water scrubber) and then passed through the gas decomposition tower. This gas decomposition tower has a structure in which the inner wall is covered with an alumina castable refractory material, and 15 rod-shaped electric heaters (enclosed in an alumina protective tube) are set up and held in a suspended state.
[0053]
A gas mixture of 90% propane and 10% n-butane as a reducing atmosphere forming agent was supplied to the gas decomposition tower at 0.3 liter / min. The heater surface temperature was maintained at 1100 ° C. F generated as a by-product after processing through the rear water scrubber (second water scrubber) while being suctioned by a fan provided outside the cabinet and maintaining the negative pressure inside the system.₂And HF were absorbed and dissolved in water. The amount of water used in this case was 10 liters / min.
[0054]
Next, the gas washed with the second water scrubber was led to a combustion tower whose internal temperature was maintained at 500 ° C., and was oxidized and burned in the presence of air introduced from the outside. CF in treated gas_FourWhen the concentration was measured, it was 50 ppm and CF_FourThe removal rate of was 99.5%.
[0055]
[Comparative Example 1]
Same CF as Example 1_FourA gas having the composition was supplied to the same removing apparatus as in Example 1 at an air flow rate of 30 liters / min. The heater surface temperature is kept at 1100 ° C., and no hydrocarbon gas or the like as a reducing atmosphere forming agent is supplied._FourThe concentration of was measured and found to be 9100 ppm. That is, the removal rate was only 9%.
[0056]
Furthermore, when the heater surface temperature was instantaneously raised to 1450 ° C. under the above conditions and the gas concentration after the treatment was measured, it was 3200 ppm and the removal rate was 68%.
[0057]
After processing by supplying additional air of 5 liters / min from the outside under this temperature condition, CF in the treated gas_FourWhen the concentration was measured, it was 3000 ppm, that is, the removal rate was 70%.
[0058]
From the above results, it can be seen that the present invention can remove PFC almost completely despite the fact that the temperature is lowered by 350 ° C. from the comparative example. Since the object can be achieved at a temperature as low as 300 to 400 ° C. in this way, the energy cost can be reduced, and the range of material selection is widened from the viewpoint of the heat resistance of the apparatus.
[0059]
[Example 2]
This example is also an example in the case of processing in the order of the first water scrubber, the gas decomposition tower, the second water scrubber, and the combustion tower. Example 1 is the PFC to be treated and the reducibility to be used. The atmosphere forming agent is different.
[0060]
C₂F₆Is 2%, N₂However, a mixed gas of 100 liters / min consisting of 97.9% and oxygen 0.1% was supplied to the gas decomposition tower after passing through the front scrubber.
[0061]
This gas decomposing tower is made of SUS316L, and its inner wall is covered with an alumina castable refractory material, and an electric heater wire is wound around the outer periphery of the tower and heated from the outside.
[0062]
The gas decomposition tower was supplied with 4 liters / min of city gas (13A) consisting of 88% methane, 6% ethane, 4% propane, and 2% butane as a reducing atmosphere forming agent. The internal space temperature of the gas decomposition tower was kept at 850 ° C. The treated gas was washed with a rear water scrubber (feed water 15 liters / min) and then exhausted through a combustion tower maintained at 600 ° C. supplied with external air.
[0063]
Under these conditions, soot (fine powdered carbon) floated in water in the rear water scrubber, and mist-like soot moved to the combustion tower and was removed.
[0064]
C in air emission₂F₆When the concentration was measured, it was 400 ppm, and the removal rate was 98%. In the processing gas, CF_FourThe presence of was not recognized.
[0065]
[Example 3]
Under the conditions of Example 2 above, an apparatus provided in an adsorption tower filled with soybean-sized and granular CaO was used instead of the rear water scrubber, and the gas treated in the gas decomposition tower was passed through this adsorption tower. Under the condition of suction with an external fan, no acidic component was found in the exhaust gas.
[0066]
[Comparative Example 2]
The PFC exhaust gas was treated under the same conditions as in Example 2 except that no city gas was supplied. C in air emission₂F₆As a result, 1.76% remained. That is, the removal rate was 12%. Also, CF in the processing gas_FourWas a new byproduct. Therefore, the PFC removal rate is worse than the 12% mentioned above.
[0067]
The same conditions except that the space temperature in the tower is kept at 1150 ° C under the above conditions.₂F₆As a result, C in the exhaust gas was removed.₂F₆The concentration was 4000 ppm and the removal rate was 80%. CF_FourIngredient by-products were also confirmed.
[0068]
[Example 4]
This embodiment is a modification of the apparatus, and FIG. 2 is a diagram showing an outline of the apparatus of this embodiment, in which (A) is a plan view and (B) is a front view.
[0069]
In the figure, (11) is a gas decomposition combustion tower, and a gas decomposition chamber (12) having a role as a gas decomposition tower and a combustion chamber (14) having a role as a combustion tower are heat-resistant partition walls. (13) are provided adjacently and integrally. That is, in the apparatus of the present embodiment, the gas decomposition combustion tower (11) can be considered as the gas decomposition tower and the combustion tower formed integrally with the partition walls. (This also applies to Example 5 described later.)
The partition wall (13) is made of a ceramic material, and for example, a blanket made of kao wool can be used.
[0070]
A ceramic lining thermal insulation layer (15) is arranged around the gas decomposition combustion tower (11). (16) is a heater, (17) is a hydrocarbon gas introduction pipe, and (18) is an air introduction pipe.
[0071]
The gas to be treated introduced into the gas decomposition chamber (12) via the front water scrubber (1) is decomposed in a reducing atmosphere in the gas decomposition chamber (12), and the partition wall (13 ) It flows into the adjacent combustion chamber (14) from the upper gap, burns in an oxidizing atmosphere, and then is cooled and washed with a water scrubber (3) provided downstream, and then released into the atmosphere.
[0072]
The gas decomposition chamber (12) and the combustion chamber (14) are adjacent to each other with a partition wall (13) between them, and there is no water scrubber between them, so it is never cooled, reducing energy consumption. can do.
[0073]
With such an apparatus configuration, the entire apparatus can be made more compact than the case where the gas decomposition section tower (2) and the combustion tower (4) are separately provided as in the standard apparatus shown in FIG. This can reduce the installation floor space.
[0074]
In addition, it is not necessary to install a water tank directly under the gas decomposition combustion tower (11), and it can be installed at a position shifted laterally from directly below. Can be saved.
[0075]
Further, the external air introduced into the combustion chamber (14) through the air introduction pipe (18) is moved from the gas decomposition chamber (12) through the partition wall (13) while moving downward in the combustion chamber (14). Since it is heated by receiving energy, the energy consumption can be further reduced.
[0076]
Next, the gas decomposition section tower (2) and the combustion tower (4) are separately provided as in this embodiment and the apparatus shown in FIG. 1, and the gas decomposition section tower (2) and the combustion tower (4) are provided. The removal rate and energy consumption of the independent type with a water scrubber in between were compared.
[0077]
First, in the independent type, CF_FourIs 1.5%, N₂Is passed through a cracking tower (2) with a mixture gas of 90% propane and 10% n-butane at a rate of 0.6 liter / min. Held at 0C.
[0078]
When the gas discharged from the combustion tower (4) was analyzed, it was 500 ppm, CF_FourThe removal rate of was 96.7%. The power consumption in the steady state was 7 kW / h.
[0079]
Since the internal volume of the decomposition tower (2) is 24 liters and the processing gas flow rate is 60.6 liters / mim = 3636 liters / hr,
SV (space velocity) = 3636/24 = 151.5hr^-1  It becomes.
[0080]
On the other hand, the same gas composition and heater temperature as above were maintained for the apparatus of this example, and CF_FourAfter removal of CF, CF in the treated gas_FourThe concentration was 400 ppm, and the removal rate was 97.3%.
[0081]
The power consumption in the steady state was 3.5 kW / h, which was about half that of the independent type.
[0082]
In addition, since the internal volume of the gas decomposition chamber (12) of this example is 21 liters and the processing gas flow rate is 60.6 liters / mim = 3636 liters / hr,
SV = 3636/21 = 173.1hr^-1  It becomes.
[0083]
That is, it can be seen that the apparatus of this example can obtain a removal rate almost equal to that of the independent type, although the SV is slightly large, and can reduce the energy consumption to ½.
[0084]
[Example 5]
The present embodiment relates to an apparatus in which the PFC gas removal rate is improved and the thermal energy efficiency is further improved at a temperature that can be used in an electric heater.
[0085]
In order to improve the PFC gas removal rate, it is necessary to transmit sufficient energy to the gas to be treated and to provide a facility structure that can secure a sufficient time for that purpose.
[0086]
Therefore, in this embodiment, the electric heater is arranged horizontally, heat dispersion and heat shielding are sufficiently performed, and a heat-resistant rod like a grate is provided below the electric heater in order to give a stirring effect to the gas flow. Are installed horizontally.
[0087]
FIG. 3 is a diagram showing an outline of the apparatus of this embodiment. (30) is a PFC-containing treated gas introduction pipe, (20) is a water tank, (31) is a first water scrubber, (21) is a gas decomposition combustion tower, (32) is a second water scrubber, (33) Is an atmospheric gas release pipe. The gas decomposition combustion tower (21) is disposed above the first water scrubber (31) and the second water scrubber (32).
[0088]
4 is a side sectional view of the gas decomposition combustion tower (21), and FIG. 5 is a plan view of the gas decomposition combustion tower (21). The gas decomposition combustion tower (21) is partitioned into a gas decomposition chamber (22) that functions as a gas decomposition tower and a combustion chamber (24) that functions as a combustion tower by a partition wall (23) having heat resistance. However, there is a gap at the upper end of the partition wall (23), and the gas decomposition chamber (22) and the combustion chamber (24) communicate with each other through this gap. Therefore, the gas decomposed in the reducing atmosphere in the gas decomposition chamber (22) can flow into the combustion chamber (24) from the gap above the partition wall (23).
[0089]
As in the fourth embodiment, the gas decomposition chamber (22) and the combustion chamber (24) are adjacent to each other with a partition wall (23) therebetween, and there is no water scrubber between the two, so that the gas decomposition chamber (22) and the combustion chamber (24) are not once cooled. Therefore, energy consumption can be reduced.
[0090]
The partition wall (23) is made of a ceramic material, and for example, a blanket made of kao wool can be used. In the gas decomposition combustion tower (21), a ceramic lining heat insulation layer (25) is formed in order to reduce loss of heat energy. (27) is a reducing atmosphere forming agent introduction pipe, and (28) is an air introduction pipe.
[0091]
(26) is a rod-shaped electric heater, which is installed in the horizontal direction so as to penetrate the gas decomposition combustion tower (21) and the partition wall (23) therein. The reason why the electric heater (26) is installed horizontally is that the heater temperature tends to be biased when it is placed upright (suspended).
[0092]
That is, even if the upper part of the heater has reached the set temperature, the atmosphere in the gas decomposition chamber (22) becomes hotter due to the influence of airflow, so the lower layer below the center part of the heater has a sufficient temperature required for decomposition. It is difficult to hold. On the other hand, if the lower layer is controlled to be equal to or higher than the set temperature, the upper part of the heater is likely to be overheated, resulting in poor energy efficiency and a problem such that the heater heating element is likely to melt.
[0093]
In this regard, when the electric heater (26) is installed horizontally, a uniform temperature distribution can be maintained in the length direction of the electric heater (26), and the temperature atmosphere necessary for PFC gas pyrolysis can be formed without difficulty. can do.
[0094]
In addition, when installing a removal device in a clean room, there is often no sufficient space between the ceiling of the clean room and the removal device, and the electric heater is installed in a suspended state when replacing the heater due to a failure. However, if the heater is installed horizontally as in the present embodiment, the electric heater (26) is taken out in the lateral direction, so that the operation is extremely easy.
[0095]
The number of electric heaters used is preferably about 6 to 12, and the heaters are arranged at equal intervals in 2 to 4 stages, but the horizontal installation positions in each stage are shifted so that the gas does not easily go straight. In this embodiment, considering the ease of practical use, a total of nine lines with three rows in three rows were used. The electric heater (26) used here is 99.5% α-Al with an outer diameter of 40φ.₂O_ThreeA protection tube (26b) with a SiC heating element (26a) inserted therein was used.
[0096]
(29) is a plurality of heat-resistant bars installed in the horizontal direction 100 mm below the lowermost electric heater (26), and is installed in the horizontal direction so as to penetrate the partition wall (23). In this embodiment, the electric heater (26) and the heat-resistant rod (29) are arranged so as to be parallel (the longitudinal directions are the same), but may be arranged so as to be orthogonal to each other.
[0097]
The heat-resistant rod (29) has a heat resistance of 1300 ° C or higher and F₂It is preferable to have corrosion resistance to HF gas, and ceramic rods can be used.₂O_ThreeA rod-shaped body having a circular cross-section mainly composed of is preferred. The heat-resistant rod (29) may be solid or hollow (pipe shape), and in this example, 99.5% α-Al with 10 mmφ₂O_ThreeAlthough a total of 48 pipes were used in a five-stage configuration using pipes made of pipes, the pipe diameter and the number of pipes used are not limited to this, and may be determined as appropriate. As in the case of the heater (26), the arrangement is such that the horizontal installation position in each stage is shifted so that the gas does not travel straight.
[0098]
The heat-resistant rod (29) has the same effect as the grate in the furnace structure, receives heat from the upper heater, prevents heat energy from being dissipated below the gas decomposition combustion tower (21), and PFC. The reducing atmosphere forming body introduced from the containing gas body and the reducing atmosphere forming body introduction pipe (27) is preheated.
[0099]
Further, while passing through the gap between the plurality of heat-resistant rods (29), the PFC-containing gas body and the reducing atmosphere forming body are mixed by turbulent flow generated by the heat-resistant rod (29).
[0100]
Furthermore, since the flow rate is reduced by the heat-resistant rod (29), a sufficient residence time in the gas decomposition combustion tower (21) can be secured, and the removal rate can be improved.
[0101]
The electric heater (26) is installed so as to penetrate the gas decomposition combustion tower (21) and the partition wall (23) therein, and the heat-resistant rod (29) is also installed so as to penetrate the partition wall (23). These sealing points are coated with a sealing agent mainly composed of ceramic fiber having heat resistance and corrosion resistance to prevent gas leakage.
[0102]
In the apparatus of this example, the temperature of each part is
Heater surface: 1200-1350 ° C
Gas decomposition chamber space and combustion chamber space: 1200-1300 ℃
Lower part of the gas decomposition chamber (below the heater and above the heat-resistant rod): 800 ° C
The lowest part of the gas decomposition chamber (gas to be treated under the heat-resistant rod): 200 to 300 ° C
Lower part of combustion chamber (below heater, above heat-resistant rod): 1200 ° C
Lower part of combustion chamber (process gas discharge part below heat-resistant rod): 800 ° C
Immediately after passing through the second water scrubber: 200 ° C
Met. From this result, it can be seen that the heat dissipation rod (29) effectively prevents the downward dissipation of the heat energy.
[0103]
Next, removal was actually performed using the apparatus of this example.
[0104]
CF_FourIs 1%, N₂Was introduced into a gas decomposition chamber (22) located above via a first water scrubber (31).
[0105]
In addition, propane was introduced into the gas decomposition chamber (22) as a reducing atmosphere forming agent from a reducing atmosphere forming agent introduction pipe (27) connected to the upper side of the first scrubber (31)._FourAnd subjected to thermal decomposition in the presence of.
[0106]
The gas pyrolyzed in the gas decomposition chamber (22) moves from the gap above the partition wall (23) to the combustion chamber (24), and in the combustion chamber (24) together with external air introduced from the air introduction pipe (28). The combustible components are burned and removed by combustion, cooled and washed in the second water scrubber (32) located below the combustion chamber (24), and then released into the atmosphere.
[0107]
CF in the gas exhausted from the second water scrubber (32)_FourThe concentration was measured and found to be 50 ppm. That is, CF_FourThe removal rate of was 99.5%. The power consumption used for the above removal was 9 kW / h.
[0108]
Next, NH is used as a reducing atmosphere forming agent instead of propane._ThreeCF under the same conditions except using 3.6 liters / mim of gas_FourWas removed. As a result, CF in the treated gas_FourThe concentration was 60 ppm and the removal rate was 99.4%.
[0109]
[Comparative Example 3]
For comparison, nine electric heaters were set up in a suspended state, and the same apparatus as in Example 5 was used except that no heat-resistant rod was used._FourWas removed.
[0110]
The amount of processing gas was reduced to 120 liters / mim and treated with 1.2 liters / mim of propane at the same temperature._FourThe concentration was 2.500 ppm and the removal rate was 75%.
[0111]
In addition, the power consumption at this time was 15 kW / h, which was 1.7 times that when the apparatus of Example 5 was used. This also shows that the removal apparatus of Example 5 has a high removal rate and low energy cost.
[0112]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a removal method and a removal apparatus that can decompose and remove PFC components at a low removal rate at a low temperature. Therefore, PFC gas that is difficult to remove can be removed at a low energy cost. Further, if the apparatus configuration is such that the heat loss is minimized, it can be removed at a lower energy cost.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a removal apparatus of the present invention.
FIG. 2 is a diagram showing an outline of a removal apparatus according to a fourth embodiment.
FIG. 3 is a diagram showing an outline of a removing apparatus according to a fifth embodiment.
4 is a side sectional view of a gas decomposition combustion tower of Example 5. FIG.
5 is a plan view of a gas decomposition combustion tower according to Embodiment 5. FIG.
[Explanation of symbols]
(1) Front water scrubber (first water scrubber)
(2) PFC removal and decomposition tower
(3) Rear water scrubber (second water scrubber)
(4) Treated gas combustion tower
(5) PFC-containing treated gas introduction pipe
(6) Reducing atmosphere forming agent introduction tube
(7) Suction fan
(8) Atmospheric gas release pipe
(9) Air introduction pipe
(10) Aquarium
(11) Gas decomposition combustion tower
  (12) Gas decomposition chamber
(13) Bulkhead
(14) Combustion chamber
(15) Ceramic lining insulation layer
(16) Heater
(17) Hydrocarbon gas introduction pipe
(18) Air inlet pipe
(21) Gas decomposition combustion tower
(22) Gas decomposition chamber
(23) Bulkhead
(24) Combustion chamber
(26) Electric heater
(29) Heat-resistant rod

Claims (9)

Wash the gas to be treated, and then lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas alone, or lower saturated hydrocarbon gas and NH ₃ gas, or lower unsaturated hydrocarbon gas and NH ₃ gas, or lower saturated hydrocarbon Mix the gas, lower unsaturated hydrocarbon gas and NH ₃ gas into the gas to be treated after washing with water and thermally decompose it in the absence of free O ₂ , and then wash away and remove the fluorine compound generated by the thermal decomposition with water. Then, the method for removing perfluorocarbon gas, which comprises burning in the presence of external air to burn off flammable components. Wash the gas to be treated, and then lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas alone, or lower saturated hydrocarbon gas and NH ₃ gas, or lower unsaturated hydrocarbon gas and NH ₃ gas, or lower saturated hydrocarbon A mixed gas of gas, lower unsaturated hydrocarbon gas and NH ₃ gas is mixed with the gas to be treated after washing with water and thermally decomposed in the absence of free O ₂ , and then the thermally decomposed gas is present in the presence of external air. A method for removing perfluorocarbon gas, comprising burning and removing flammable components by burning, and then washing and removing the fluorine compound produced by thermal decomposition. Wash the gas to be treated, and then lower saturated hydrocarbon gas or lower unsaturated hydrocarbon gas alone, or lower saturated hydrocarbon gas and NH ₃ gas, or lower unsaturated hydrocarbon gas and NH ₃ gas, or lower saturated hydrocarbon A mixed gas of gas, lower unsaturated hydrocarbon gas and NH ₃ gas is mixed with the gas to be treated after washing with water and thermally decomposed in the absence of free O ₂ , and then the fluorine compound generated by the thermal decomposition is CaO or CaCO _{3. A} method for removing perfluorocarbon gas, wherein the particulate material is chemically adsorbed and removed, and then burned in the presence of external air to burn and remove combustible components. The gas to be mixed with the gas to be treated after water washing at the time of thermal decomposition is either CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , a mixed gas of these two or more, or NH ₃ mixed with these The method for removing perfluorocarbon gas according to claim 1, wherein the gas is a perfluorocarbon gas. A first water scrubber for washing the gas to be treated; a gas decomposition tower provided downstream of the first water scrubber; a second water scrubber provided downstream of the gas decomposition tower; A combustion tower provided on the downstream side of the second water scrubber for burning the treated gas in the presence of external air, wherein the gas decomposition tower comprises a lower saturated hydrocarbon gas or a lower unsaturated hydrocarbon gas; Or a mixed gas of lower saturated hydrocarbon gas and NH ₃ gas, or lower unsaturated hydrocarbon gas and NH ₃ gas, or mixed gas of lower saturated hydrocarbon gas, lower unsaturated hydrocarbon gas and NH ₃ gas. An apparatus for removing perfluorocarbon, which is capable of thermally decomposing a processing gas in a state free of free O ₂ . A first water scrubber for washing the gas to be treated, a gas decomposition tower provided downstream of the first water scrubber, and a treated gas provided downstream of the gas decomposition tower in the presence of external air And a second water scrubber provided on the downstream side of the combustion tower, wherein the gas decomposition tower is a lower saturated hydrocarbon gas or a lower unsaturated hydrocarbon gas alone, or a lower water scrubber. Frees the gas to be treated mixed with saturated hydrocarbon gas and NH ₃ gas, or lower unsaturated hydrocarbon gas and NH ₃ gas, or mixed gas of lower saturated hydrocarbon gas, lower unsaturated hydrocarbon gas and NH ₃ gas An apparatus for removing perfluorocarbon, which can be thermally decomposed in the absence of O ₂ . Filled with a first water scrubber for washing the gas to be treated, a gas decomposition tower provided on the downstream side of the first water scrubber, and a CaO or CaCO ₃ granule provided on the downstream side of the gas decomposition tower And a combustion tower provided on the downstream side of the adsorption tower for burning the treated gas in the presence of external air, the gas decomposition tower comprising a lower saturated hydrocarbon gas or a lower inert gas. Only saturated hydrocarbon gas, or lower saturated hydrocarbon gas and NH ₃ gas, or lower unsaturated hydrocarbon gas and NH ₃ gas, or mixed gas of lower saturated hydrocarbon gas, lower unsaturated hydrocarbon gas and NH ₃ gas , and An apparatus for removing perfluorocarbon, wherein the mixed gas to be treated can be thermally decomposed in a state free of free O ₂ .   7. The perfluorocarbon removing apparatus according to claim 6, further comprising a gas decomposition combustion tower in which the gas decomposition tower and the combustion tower are integrally formed through heat-resistant partition walls. A first water scrubber for washing the gas to be treated, a gas decomposition combustion tower provided downstream of the first water scrubber, and a second water scrubber provided downstream of the gas decomposition combustion tower The gas decomposition combustion tower is disposed above the first water scrubber and the second water scrubber, and the gas decomposition combustion tower is located on the downstream side of the gas decomposition tower and the heat decomposition tower. The gas decomposition tower has a combustion tower that is partitioned in a state where the gas decomposition tower and the upper end portion thereof are in communication with each other, and a plurality of electric heaters are installed in the gas decomposition combustion tower in a horizontal direction so as to penetrate the partition wall. A plurality of heat-resistant rods having a heat shielding effect are installed in the horizontal direction below the electric heater, and the gas decomposition tower includes only a lower saturated hydrocarbon gas or a lower unsaturated hydrocarbon gas, or a lower saturated hydrocarbon gas and NH ₃ gas, or a lower It is heated decompose saturated hydrocarbon gas and NH ₃ gas, or the lower saturated hydrocarbon gas and lower unsaturated hydrocarbon gas and NH ₃ gas to be treated is mixed with the gas mixture of the gas in a state under no free O ₂ The apparatus for removing perfluorocarbon is characterized in that the combustion tower is capable of burning the gas thermally decomposed in the gas decomposition tower in the presence of external air.

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