CN1341478A

CN1341478A - Evil-removing method of perfluocarbon or perfluoride and evil-removing device

Info

Publication number: CN1341478A
Application number: CN 00126859
Authority: CN
Inventors: 今村启志
Original assignee: Koken Science & Technology Co Ltd
Current assignee: Koken Science & Technology Co Ltd
Priority date: 2000-09-07
Filing date: 2000-09-07
Publication date: 2002-03-27
Anticipated expiration: 2020-09-07
Also published as: CN1227054C

Abstract

The present invention provides a method capable of high-effectively decomposing and removing perfluoro-carbon (PFC) or perfluorinated component at the temp. as low as possible, and is characterized by that in the treated gas discharged from production equipment and containing perfluoro-carbon or perfluorinated component mixing one kind of hydrocarbon gas or ammonia gas or their mixture and then making the above-mentioned gas mixture undergo the process of thermal decomposition under the condition of non-oxidative atmosphere so as to implement said invention.

Description

Method and apparatus for detoxifying perfluorocarbon or perfluorocarbon

The present invention relates to a method and apparatus for removing harmful gas generated in the process of manufacturing electronic circuit elements such as semiconductors and liquid crystals, particularly in the cleaning and etching steps, and also relates to a method and apparatus for removing harmful gas generated in the process of refining aluminum.

Hereinafter, the present invention will be described with reference to the removal of harmful gases used in cleaning and etching processes, when the present invention is limited to the manufacture of electronic circuit elements.

In a semiconductor manufacturing apparatus such as CVD (chemical vapor deposition), a deposition gas (e.g., SiH) is used for forming various thin films₄、Si₂H₆、SiH₂Cl₂、TEOS、PH₃、B₂H₆、NH₃、N₂O, etc.), a cleaning gas (e.g., NF) is typically used after the deposition process is terminated₃、C₂F₆、CF₄、SF₆Etc.) cleaning theinside of the semiconductor manufacturing apparatus.

These gases themselves have various hazardous properties such as flammability, explosiveness, corrosiveness, toxicity, and the like. Therefore, before being discharged into the atmosphere, it is necessary to perform detoxification (detoxification treatment) by using a detoxification mechanism having a means such as oxidation heating.

In the case of a gas used in a CVD semiconductor manufacturing apparatus, a new decomposition product (for example, F) is generated due to a complicated decomposition reaction₂、HF、SiO_xEtc.) which are exhausted together with the undecomposed deposition gas and cleaning gas。

As an example of the above, the operation of a semiconductor manufacturing apparatus such as CVD in semiconductor manufacturing is generally performed as follows:

using SiH₄Deposition of a deposition gas (toxic and explosive to the human body) → → purging residual SiH in the CVD chamber with nitrogen gas₄Gas → → with C₂F₆Cleaning gas (having a greenhouse effect but not harmful) cleaning the inside of the CVD chamber → → cleaning using nitrogen as the CVD chamber cleaning gas → → repeating the following.

The gases used for the CVD cleaning include PFCs. It is an abbreviation of Perfluorocarbon (Perfluorocarbon), and representative compounds thereof are tetrafluoromethane, trifluoromethane, hexafluoroethane and the like. If the above carbon (carbon) is changed to a compound (compound), the PFC also means NF₃、SF₆、SF₄And the like carbon-free perfluoro compounds.

The present invention is established as a detoxifying device and a detoxifying method for the purpose of removing the former PFC (perfluorocarbon), which hasnot been technically achieved so far, but it is needless to say that the present invention can be applied to detoxification of all PFCs (perfluorocompounds) including the latter.

With CF₄、C₂F₆The PFC as a representative is a non-flammable substance, 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, it can be retained for a long period of time after being discharged into the atmosphere. The life consumed in the atmosphere is fifty thousand years for tetrafluoromethane and one thousand years for hexafluoroethane, while the global greenhouse effect coefficient (1 for carbon dioxide) is 4400 for tetrafluoromethane and 6200 for hexafluoroethane (after 20 years), and there is a problem that it cannot be placed in the global environment. Therefore, it is desired to establish a means for eliminating the hazards of PFCs represented by tetrafluoromethane and hexafluoroethane.

However, the former PFC, i.e., a compound represented by tetrafluoromethane, trifluoromethane and hexafluoroethane, is not easily decomposed because of its stable C — F bond (bond energy is as large as 130 kcal/mol), and is extremely difficult to decompose by simple thermal oxidation.

For example, although it is possible to limit the amount of air to be treated to 250 liters/min or less at a treatment temperature of 1000 ℃ for hexafluoroethane to decompose C-C chains, it is necessary to cut C-F bonds having the largest bond energy for tetrafluoromethane, and 1400 ℃ is required even at the above air flow, and thus it is difficult to achieve 80% or more of the effect.

In addition, the use of an electric heater is limited by the material of the heating element in order to achieve a high temperature of 1400 ℃ or higher, and thus, the use for a long time is almost impossible. Further, it is difficult to keep the temperature of the entire apparatus, and even if a heat insulating material is used in combination, the entire volume is too large to make a small apparatus. More importantly, the heat energy consumption is too high.

Further, a novel proposal has been made in the art of "method for decomposing gaseous halocarbons" disclosed in International publication No. WO94/05399, in which, for example, when tetrafluoromethane is detoxified, if oxygen is present in the gas, the gas is allowed to exist at 600 to 700 ℃.

Although it has been tried to decompose PFC by actively introducing hydrogen gas, it is not decided from the viewpoint of safety because the treatment temperature must be high and hydrogen gas is a flammable and explosive gas.

In view of the above, it is desired to provide a method and an apparatus for removing harmful substances capable of decomposing and removing harmful substances at as low a temperature as possible (low heat energy consumption) with a high rate of removing harmful substances from PFC.

The harm eliminating method and device can eliminate PFC harm at low temperature, the derived fluorine component is eliminated by single washing or fixing mode, and other components are basically converted into carbon dioxide and water to be discharged into the atmosphere. The specific method comprises the following steps:

a process for producing a gas to be treated containing perfluorocarbon or perfluorocompound, which is discharged from a production facility, is characterized by mixing a hydrocarbon gas or ammonia gas with one or more gases and then thermally decomposing the mixed gas at a temperature lower than that in the conventional process (600 to 1300 ℃) in a non-oxidizing atmosphere.

The "non-oxidizing atmosphere" is described in detail later, but it means that oxygen does not exist around the mixed gas when the mixed gas is thermally decomposed.

The gas to be treated is washed with water in advance, and not only soluble components and dust contained in the gas to be treated discharged from the production facility are removed before the gas decomposition treatment, but also perfluorocarbons or perfluorocompounds are thermally hydrolyzed when the gas to be treated contains water.

When the excessive amount of hydrocarbon gas is added, since unreacted hydrocarbon gas is present in the thermal decomposition gas and carbon is produced in the thermal decomposition reaction, it should be removed by burning in the following step. The "combustible component" means "residual hydrocarbon gas" and "carbon".

If the above description is in CF₄、C₂F₆Under non-oxidizing atmosphere, and is C₃H₈The thermal decomposition reaction of (2) can be represented as follows:

(free radical)

… … (decomposition in gas decomposition tower or gas decomposition chamber)

… … (burning in a burning tower or a burning chamber)

6HF … is removed by a second scrubber or absorber

And removing the fluorine-containing compound produced by the thermal decomposition by washing with water or chemical adsorption. The order of the water washing or chemisorption step and the combustible component combustion removal step may be either first or second.

The specific device comprises the following equipment:

(a) a gas decomposition tower (2) for mixing one or more of hydrocarbon gas and ammonia gas in a gas to be treated containing perfluorocarbon or perfluorocompound discharged from a production facility and thermally decomposing the mixed gas in a non-oxidizing atmosphere;

(b) a combustion tower (4) for burning combustible components in the gas decomposed in the gas decomposition tower (2);

(c) a heater (16) disposed in the gas decomposition tower (2) and the combustion tower (4);

(d) a reducing atmosphere forming agent introduction pipe (6) for supplying a reducing atmosphere forming agent to the gas decomposition tower (2);

(e) an air inlet pipe (9) for supplying air to the combustion tower (4); and

(f) a second water scrubber (3) connected in series with the combustion tower (4) or an adsorption tower (3a) filled with granular calcium oxide or calcium carbonate.

A first water scrubber (1) for washing the gas to be treated containing perfluorocarbon or perfluorocompound discharged from the production facility with water before the gas is decomposed may be provided upstream of the gas decomposition column (2).

A first water scrubber (1), a gas decomposition tower (2), a second water scrubber (3) or a gas decomposition combustion tower (11) (21) may be provided on the water tank (10), and these apparatuses may be separately provided.

The combustion tower (4) and the second water scrubber (3) or the adsorption tower (3a) may be located upstream, as shown in fig. 1(a) and (B). Although the adsorption column (3a) is upstream of the combustion column (4) in FIG. 1C, the combustion column (4) may be upstream of the adsorption column (3 a).

As shown in FIGS. 2A, B and C and FIGS. 3 to 5, the

gas decomposition chambers

12 and 22 and the

combustion chambers

14 and 24 may be partitioned by

partition walls

13 and 23 to integrate the gas combustion/

decomposition towers

11 and 21. Details about the gas combustion decomposition towers (11) (21) will be described later.

The main unit operation of the above invention is divided into the following three stages:

(a) thermal decomposition of PFCs

(b) Cleaning exhaust or fixation removal of generated fluorine-containing compound

(c) Combustion removal of other combustible components (residual hydrocarbon gas and carbon)

The most important constituent step of the present invention is the thermal decomposition of the PFC in the above-mentioned (a), which is a treatment method for achieving a destruction rate "[ concentration of PFC contained in gas introduced into the destruction apparatus- (concentration of PFC contained in exhaust gas/concentration of PFC introduced into gas in the destruction apparatus). times.100]" of 90% or more under the condition that the atmospheric temperature required for the usual simple thermal decomposition is greatly lowered.

The thermal decomposition of PFC, which is the core of the present invention, may be performed by using an electric heater as a heat source, or by using a liquid fuel such as Liquefied Petroleum Gas (LPG) or Liquefied Natural Gas (LNG) or a gas fuel such as methane, hydrogen, or carbon monoxide as a flame combustion means, and the position of the heat source for heating may be outside or inside the gas decomposition tower (2) (or the gas decomposition chambers (12) (22) in the following, where the gas "decomposition tower" is mentioned, including the gas decomposition chambers (12) (22) except for fig. 2 to 5.

The space of the gas decomposition tower (2) is filled with a gas to be treated, which is generally mixed with nitrogen as a carrier gas and contains PFC as a main component. And a lower saturated or unsaturated hydrocarbon gas (wherein "lower" means a saturated hydrocarbon having a C1-C8 component, particularly preferably a C1-C4 component) or ammonia gas, or a mixed gas of these gases, is supplied at the same time.

In this case, one of the conditions is, for example, the use of O in combination in CVD₂Or O₃In the case of (1), although the used sweep gas flows into the decomposition tower in the form of exhaust gas, no other O is artificially injected₂And O₃Or outside air, at least the inside of the gas decomposition tower is not changed into an oxidation state. This state is a state in which free oxygen is not present in the gas decomposition tower (2) or the gas decomposition chambers (12) (22) in a non-oxidizing atmosphere.

In this state, although the decomposition of the PFC is carried out under predetermined conditions such as the PFC concentration in the gas to be treated, the flow rate of the treatment gas, and the temperature of the space in the gas decomposition column, it was confirmed that the temperature of the atmosphere gas at this time can be almost completely removed even if it is several hundred degrees lower than the treatment temperature in the gas system under the oxidizing atmosphere.

This is considered to be because the hydrocarbon gas or ammonia gas introduced as thePFC decomposition treatment agent is thermally decomposed in a non-oxidizing atmosphere (for example, when propane is used, various decomposition products such as methane, ethane, ethylene, propylene, and hydrogen are produced), active hydrogen in a radical state is produced in the decomposition process to decompose the PFC, and the F component in the PFC is F₂Or the separation of the HF form.

In addition, the results that the destruction rate reached more than 80% were difficult to obtain even at high temperatures near the temperature limit of the materials used, either alone or in an oxidizing atmosphere, indicating that the decomposition mechanism of the compounds in the gas decomposition tower is completely different from that of the present invention.

According to the present invention, the process gas discharged from the gas decomposition tower is changed into F₂Or HF, and the decomposition treating agent becomes carbon black depending on the remaining hydrocarbon decomposition gas and conditions. Therefore, both the fluorine-containing exhaust gas and the combustible gas are treated to be harmless.

That is, the former is absorbed and dissolved in water by a water scrubber, or is separated by adsorption with a calcium oxide or calcium carbonate solid adsorbent and discharged to the outside of the system. Which burns it in the presence of outside air, becoming the final treatment gas, which is discharged into the atmosphere.

The invention is illustrated by the following preferred examples.

In the detoxifying device of the present invention, various devices for carrying out the three elements of (a) thermal decomposition of PFC, (b) generation of cleaning exhaust gas containing fluorine compounds or fixation detoxification, (c) combustion detoxification of other combustible components, and the like are integrally combined and housed.

FIG. 1 is a schematic view of the harmful removal apparatus of the present invention. In fig. 1, (1) is a front water scrubber (first water scrubber) provided at the front end (upstream side) of the gas decomposition tower (2). The gas to be treated containing PFC, which is sent through the gas inlet pipe (5) for treatment containing PFC, is first passed through the front water scrubber for washing.

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 gas decomposition column (2) is heated by an electric heater (16), and external heating or internal heating can be adopted. In this embodiment, a vertical electric heater (16) is vertically installed in the gas decomposition tower (2) from the ceiling. In either case, the corrosive gas F is present in the gas decomposition column (2)₂And HF occur, and the metal material is corroded by these substances, it is necessary to manufacture the gas decomposition tower (2) using a high nickel content alloy such as ィンコネル (Inconel) (trademark) alloy, or to coat the inner surface of the gas decomposition tower (2) with a ceramic material mainly composed of alumina. When the electric heater (16) is installed inside the gas decomposition tower (2), a heating element should be inserted into the alumina ceramic protection tube for the purpose of protecting the heater.

After cleaning the inside of a chamber of a semiconductor manufacturing apparatus such as CVD with a PFC gas, nitrogen gas is fed into the chamber, and the PFC gas used in the chamber is purged with the nitrogen gas. Since the flushing nitrogen becomes the carrier gas, although CF will be used₄And C₂F₆The gas used for PFC as a representative is introduced into the gas decomposition column (2),but in this case, O is used for CVD₂And O₃Such that the oxidant sweep gas is also simultaneously introduced into the abatement device. However, it is not necessary to forcibly divide the gasThe decomposing tower (2) is supplemented with oxidant such as oxygen or air.

A PFC gas is decomposed in a reducing atmosphere by actively introducing a lower saturated or unsaturated hydrocarbon (C1-C8 component), ammonia gas or a mixed gas thereof as a reducing atmosphere forming agent into a gas decomposition column (2) through a reducing atmosphere forming agent introduction pipe (6).

As the lower saturated or unsaturated hydrocarbon, there can be used methane, ethane, propane, n-or iso-butane (hereinafter, the same applies), pentane, hexane, heptane, octane, ethylene, propylene, butene, butadiene, or aromatic hydrocarbons such as benzene, toluene, xylene. In addition, urban carbon gas may also be used.

However, the hydrocarbon is preferably methane, ethane, propane, butane, or the like because carbon residue increases as the ratio of C to H increases, and carbon tends to be generated.

Further, ammonia is bonded to a plurality of hydrogen atoms similarly to hydrocarbons, and has a function as a hydrogen atom donor, and therefore, ammonia can be used similarly as a reducing atmosphere forming agent. In the case of using ammonia, HF produced in the gas decomposition column is neutralized to produce NH₄F salt, and thus the effect of preventing corrosion of the device material is expected.

The reducing atmosphere forming agent may be any one of the above gases alone, or two or more of the above gases may be mixed and used.

At least 90% of harmful substances in the range of 100ppm to 5% can be removed in a wide range of PFC concentration where the invention can remove harmful substances. On the other hand, harmful substances of 100ppm or less and 5% or more are also removed, but the removal rate may not reach 90% or more.

The air volume of the treatment gas in the invention is preferably in the range of 5-700L/min. When the air volume is treated below 5L/min, the energy efficiency of the device is reduced and the device does not work. On the other hand, if the amount is more than 700 liters/minute, the effect of the process gas on energy transfer is insufficient, and the destruction rate tends to decrease.

The amount of the gas of the reducing atmosphere forming agent coexisting during decomposition of the PFC is 0.1 to 3 moles per 1 mole of the PFC. When the amount of the catalyst is 0.1 mol or less, the effect of lowering the decomposition temperature and improving the destruction rate, which are the objects of the present invention, is insufficient, and when the amount is 3 mol or more, the destruction rate can be 90% or more, but the amount of thermal decomposition products such as carbon in the exhaust gas is increased, the hydrocarbons are wasted, and the subsequent steps of the treated gas become complicated, which is not preferable.

The temperature in the gas decomposition column (2) can be treated in a temperature region several hundred degrees lower than that in the case where the heat source is not simply thermally decomposed (including oxidative decomposition) regardless of whether the heat source is placed inside or outside the gas decomposition column (2).

In the case of simple thermal decomposition, e.g. C₂F₆In the processing example, the processing temperature is 1100 to 12The harm removal rate in a temperature range of 00 ℃ is only 80-85%, and by-products CF are generated in the treated gas₄. In addition, for CF₄In particular, the highest damage-removing rate is only 70% even in the 1400 ℃ temperature region, which is far lower than 90% of the target of the invention. When the electric heater (16) is used as a heat source, it is technically difficult to use the heater for a long time at about 1400 ℃, and the heater should be used only at 1100 ℃.

In contrast, the use of the existing PFCs alone or in the presence of oxygen according to the invention makes it possible to eliminate damage at low temperatures, for example C₂F₆850 ℃ is sufficient for the treatment, and for CF₄The treatment can be carried out at a detoxification rate of 90% or more at 1000 to 1100 ℃.

When oxygen or ozone is used as the oxidizing gas for PFC in the CVD cleaning step, the hydrocarbon gas introduced into the decomposition tower reacts with the residual components of oxygen or ozone to be consumed, and is further thermally decomposed at the treatment temperature to be changed into various components.

For example, in the case of propane, thermal decomposition at 780 ℃ results in methane, ethane, ethylene, propylene, hydrogen, and carbon. In the process, C₂F₆And CF₄Such substances also participate in the decomposition of PFCs by F₂Or the F component is separated from the HF component.

F component of PFC treated in gas decomposition tower as F₂And/or the HF form is vented. The treated gas is passed through a rear water scrubber (second scrubber) (3) to dissolve the F component in water, or introduced into an adsorption tower having a solid packing of calcium oxide or calcium carbonate to thereby obtain CaF₂The form is removed by adsorption.

The gas from which the F component has been removed in any of the above methods is fed to a treated gas combustor (4). The combustible components are mixed with outside air sent through an air inlet pipe, and the mixture is combusted to form carbon dioxide and water, and then the carbon dioxide and water are discharged into the atmosphere through an air outlet pipe (8). In the drawing, (7) shows a suction fan.

The treated gas can be discharged into the atmosphere by cooling the gas treated in the gas decomposition tower through the rear water scrubber (3) after being burned in the combustion tower (4) by reversing the positions of the treated gas combustion tower (4) and the rear water scrubber (3). That is, the treated gas combustor (4) and the rear water scrubber (3) may be arranged in series.

[ example 1]

This example is an example of treatment with the first water scrubber (1), the gas decomposition column (2), the second scrubber (3) and the combustion column (4) in this order.

Will contain 1% CF₄And 99% N₂30 liters of the mixed gas (2) was subjected to water washing in the front water scrubber (1) (first scrubber) and then introduced into the gas decomposition column (2). The inner wall of the gas decomposition tower (2) is covered with a castable refractory made of alumina, and 15 rod-like electric heaters (16) (enclosed in an alumina protective tube) are provided inside the tower and held in a suspended state therein.

A mixed gas of 90% propane and 10% n-butane was supplied as a reducing atmosphere forming agent into the gas decomposition tower (2) at a rate of 0.3 liter/min. The heater surface temperature was maintained at 1100 ℃. F by-produced during gas decomposition treatment is maintained in a negative pressure state in the system by suction of a fan (7) provided outside the apparatus, and is decomposed by a rear water scrubber (3) (second water scrubber)₂And HF absorption dissolved in water. The amount of water used in this case was 10 liters/min.

Then, the gas washed by the second water scrubber (3) is introduced into a combustion tower (4) maintained at 500 ℃ and is subjected to oxidation combustion in the coexistence of air introduced from the outside. CF in the treated gas₄Concentration, determined as 50ppm, CF₄The pest eliminating rate is 99.5%.

[ COMPARATIVE EXAMPLE 1]

CF was supplied to the same apparatus as in example 1 at an air volume of 30 liters/minute in the same apparatus as in example 1₄A constituent gas. Then, the surface temperature of the heater was maintained at 1100 ℃ and CF in the treated gas was removed from the hydrocarbon gas used as the reducing atmosphere forming agent₄The concentration of (B) was determined to be 9100ppm, i.e., the pesticidal rate was only 9%.

Under the above temperature condition, the flow rate is further increased from the outside by 5L/minFilling air, and treating CF in the gas₄The concentration was determined to be 3000ppm, CF₄The pest control rate is 70%.

The above results show that, in comparison with the comparative example, the temperature of the present invention is 350 ℃ lower, but the harm can be almost completely eliminated. Therefore, the purpose of eliminating harmful substances can be achieved at a temperature as low as 300 to 400 ℃, so that the energy consumption can be reduced, and the selection range of materials is widened from the viewpoint of the heat resistance of the device.

[ example 2]

This example is also an example of treatment in the order of the first water scrubber (1), the gas decomposition column (2), the second scrubber (3), and the combustion column (4), but the PFC as the treatment object and the reducing atmosphere forming agent used are different from those in example 1.

Will consist of 2% C₂F₆、97.5％N₂And 0.1% oxygen, and 100 liters/min, and then fed into the gas decomposition column through the front scrubber.

This gas decomposition tower (2) was made of SUS316L, the inner wall of which was covered with alumina castable refractory, and the outer periphery of which was wound with heating wires (not shown), which was a structure for heating from the outside. Inside this decomposition column (2), a city carbon gas (13A) composed of 88% methane, 6% ethane, 4% propane and 2% butane was supplied as a reducing atmosphere forming agent at a rate of 4 liters/minute. The temperature of the inner space of the decomposition column (2) was maintained at 850 ℃. The treated gas was washed in a rear water scrubber (3) (supplied with water at a rate of 15 liters/minute), passed through a combustion tower (4) supplied with air from the outside and maintained at 600 ℃ and then discharged.

Under these conditions, carbon powder (powdery carbon) is suspended in the rear water scrubber (3), and the carbon in the form of mist is sent to the combustion tower (4) and removed.

Discharge into atmospheric gas C₂F₆The measured value was 400ppm, the destruction rate was 98%, and the presence of CF in the treatment gas was not observed₄。

[ example 3]

Under the conditions of the above example 2, the gas treated by the gas decomposition tower (2) was passed through the adsorption tower (3a) using an apparatus having an adsorption tower (3a) filled with granular calcium oxide of soybean grain size in place of the rear water scrubber (3). Under the condition of suction by the external fan (7), no pickling solution component is found in the discharged gas.

[ COMPARATIVE EXAMPLE 2]

PFC exhaust gas was treated under the same conditions as in example 2, except that city carbon gas was not supplied. C remaining after gas detection in atmosphere₂F₆The concentration was 1.76%. That is, the pesticidal rate was 12%. In addition, CF is newly by-produced in the process gas₄. Therefore, the PFC clearance is inferior to the above-mentioned 12%.

The same as above except that the temperature of the space in the column was kept at 1150 ℃ for C₂F₆Exhaust gas C after detoxification₂F₆The concentration is 4000ppm, and the pest-removing rate is 80%. In addition, CF is found as a by-product₄And (3) components.

[ example 4]

This embodiment is a modification of the apparatus of the present invention, and fig. 2 is an outline of the apparatus of the present invention, in which (a) is a top sectional view and (B) is a front sectional view.

In FIG. 2, (11) is a gas decomposition/combustion tower, and a decomposition chamber (12) functioning as a gas decomposition tower and a combustion chamber (14) functioning as a combustion tower are adjacently connected to each other by a heat-resistant partition wall (13) to form a single unit. That is, in the apparatus of the embodiment of the present invention, the gas decomposition/combustion tower (11) can be regarded as a device in which the decomposition tower and the combustion tower are integrally connected by a partition wall. (this is the same as in example 5 hereinafter.)

The partition wall (13) is made of a ceramic material, and for example, a partition wall made of カォゥ - ル can be used.

A ceramic lining heat insulation layer (15) is arranged around the gas decomposition combustion tower (11).

(16) The heater is a heater which is suspended from a top plate (11a) of the gas decomposition/combustion tower (11) and is disposed in the gas decomposition chamber (12) and the combustion chamber (14). (17) A reducing atmosphere forming agent introducing pipe is connected to a pipe 5a connecting the front water scrubber 1 and the gas decomposition chamber 12, and the reducing atmosphere forming agent is mixed into the gas to be treated which has been washed with water by the front water scrubber 1, and the mixed gas is sent to the gas decomposition combustion tower 11.

(18) Is an air introduction pipe connected to the combustion chamber (14) and configured to introduce outside air into the combustion chamber (14).

The gas to be treated introduced into the gas decomposition chamber (12) through the front water scrubber (1) is decomposed in a reducing atmosphere in the gas decomposition chamber (12), flows into the adjacent combustion chamber (14) through the upper gap of the partition wall (13) with heat energy preserved, is burned in an oxidizing atmosphere, is cooled and washed by the water scrubber (3) disposed downstream thereof, and is discharged into the atmosphere.

The gas decomposition chamber (12) and the combustion chamber (14) are separated by a partition wall (13), and are communicated with each other through a communication port (11b) at the upper end of the partition wall (13), and the gas to be treated which is decomposed while rising in the gas decomposition chamber (12) enters the combustion chamber (14) through the communication port (11b), and flows in the direction of the water tank (10) while being combusted. Therefore, since there is no cooling problem between the two due to the absence of the rear water scrubber (3) shown in fig. 1, energy consumption can be reduced.

With the apparatus having such a structure, the entire apparatus can be made more compact and the floor space for installation of the apparatus can be reduced as compared with the standard apparatus shown in FIG. 1, that is, as compared with the case where the gas decomposition tower (2) and the combustion tower (4) are separately installed.

In addition, since the water tank (10) is not required to be provided directly below the gas decomposition tower (11), and the water tank (10) can be provided in a horizontal position after the gas decomposition/combustion tower (11), heat loss due to water in the water tank (10) heated by radiant heat from the upper high-temperature portion (i.e., the decomposition/combustion tower (11)) can be also saved.

Furthermore, the outside air introduced into the combustion chamber (14) through the air introduction pipe (18) is heated by the heat energy in the gas decomposition chamber (12) through the partition wall (13) in the process of moving downward in the combustion chamber (14), and therefore the energy used can be further reduced.

The present example is compared with the independent type of apparatus shown in FIG. 1, in which the gas decomposition tower (2) and the combustion tower (4) are separately provided and a water scrubber is provided between the gas decomposition tower (2) and the combustion tower (4), in terms of the destruction rate and the energy consumption.

First, a separate type of apparatus was explained, and 1.5% CF was introduced into the decomposition column (2) at a rate of 60 liters/min₄And 98.5% N₂To which a mixed gas of 90% propane and 10% n-butane as a reducing atmosphere forming agent was supplied at a rate of 0.6 liter/min, and a heater was maintained at 1300 ℃.

After analysis of the gas discharged from the combustion tower (4), it contains CF₄500ppm, the pest eliminating rate is 96.7 percent. In addition, the power consumption in the normal state is 7 kilowatt/hour.

Since the internal volume of the decomposition column (2) was 24 liters and the flow rate of the treatment gas was 3636 liters/hr, the reaction time was set to 60.6 liters/min

SV (space flow rate) 3636/24 151.5/hr.

On the other hand, for the apparatus of this example, CF was heated at the same gas composition and heater temperature as described above₄After decontamination, CF in the treated gas₄The concentration is 400ppm, and the pest-removing rate is 97.3%.

Normally the power consumption is 3.5 kw/h and the energy consumption is only about 1/2 for the stand-alone device.

Since the internal volume of the gas decomposition chamber is 21 liters and the flow rate of the process gas is 60.6 liters/min 3636 liters/hr in this example, the process gas flow rate is controlled so that

SV 3636/21 173.1/hr.

That is, the apparatus of this embodiment not only has much higher SV but also can achieve almost the same pesticidal rate as the stand-alone type apparatus and further can reduce the energy consumption to 1/2.

[ example 5]

The present embodiment relates to a device for improving the PFC destruction rate and further improving the thermal efficiency at a temperature at which an electric heater (26) can be used.

In order to increase the destruction rate of the PFC gas, it is necessary to provide a device structure capable of sufficiently transmitting energy to the gas to be processed and ensuring the processing time thereof.

Therefore, in the present embodiment, in order to provide the electric heater (26) horizontally and to ensure heat transmission and shielding and to provide sufficient stirring effect to the air flow, a plurality of heat-resistant bars (29) are horizontally provided in a grate pattern below the electric heater.

Fig. 3 shows an outline of the apparatus of the present embodiment. (30) The reactor is a gas introduction pipe to be treated containing PFC, (20) a water tank, (31) a first water scrubber, (21) a gas decomposition combustion tower, (32) a second water scrubber, and (33) a gas exhaust pipe to the atmosphere. A gas to be treated containing PFC discharged from a production facility is sent to a first water scrubber 31 through a space above a water tank 20 via a gas inlet pipe 30 containing PFC. Of course, it may be introduced directly from the lower end of the first water scrubber (31).

FIG. 4 is a side sectional view of the gas decomposition burner (21), and FIG. 5 is a horizontal sectional view of the gas decomposition burner (21). The gas decomposition/combustion tower (21) is divided into a gas decomposition chamber (22) functioning as a gas decomposition tower and a combustion chamber (24) functioning as a combustion tower by a heat-resistant partition wall (23), and a communication port (21b) for communicating the decomposition chamber (22) with the combustion chamber (24) is provided at the upper end of the partition wall (23). Therefore, the gas decomposed in the gas decomposition chamber (22) in a reducing atmosphere can flow into the combustion chamber (23) from the communication port (21b) at the upper part of the partition wall (23).

Similarly to example 4, the decomposition chamber 22 and the combustion chamber 24 are partitioned and adjacent by the partition wall 23, and the second water scrubber 3 is not present between them, so that there is no problem that the gas is cooled by the second water scrubber 3 after the gas decomposition treatmentas shown in fig. 1, and therefore, the energy consumption can be reduced.

The partition wall (23) is made of a ceramic material, and for example, a partition wall made of カォゥ - ル can be used. In order to reduce the heat energy loss of the gas decomposition burner (21), the insulating lining layer (25) is formed of a ceramic material. (27) The reducing atmosphere forming agent inlet pipe (28) is an air inlet pipe.

(26) Is an electric heating rod, and is arranged to penetrate through the gas decomposition combustion tower (21) and the internal partition wall (23) thereof in the horizontal direction. The reason why the electric heating rod (26) is installed in the horizontal direction is that temperature unevenness is likely to occur when the electric heating rod is installed vertically.

That is, even if the upper portion of the heater reaches a set temperature, the atmosphere in the gas decomposition chamber (22) is heated by the airflow, and therefore, when the electric heater (26) is vertically installed, it is difficult to ensure a sufficient temperature for decomposition in the lower layer below the center of the heater. On the other hand, if the lower layer temperature is controlled to be higher than the set temperature, the upper part of the heater is easily in an overheated state, which not only reduces the energy efficiency, but also easily causes problems such as the fusing of the heating element (26a) in the electric heater (26).

In this case, if the electric heater (26) is horizontally disposed, the temperature can be uniformly distributed along the longitudinal direction of the electric heater (26), and an atmosphere gas having a temperature required for thermal decomposition of the PFC gas can be formed reasonably.

In addition, when the damage eliminating device is arranged in the clean room, enough space is not ensured between the top plate of the clean room and the damage eliminating device, and the electric heater (26) is arranged in a vertical state in the vertical state when the heater with a fault is replaced, which is not suitable for operation, but the electric heater (26) can be taken out along the horizontal direction when the electric heater (26) is arranged horizontally like the embodiment, so the damage eliminating device has the advantage of extremely easy operation.

The number of the electric heaters (26) used is preferably 6 to 12, and the electric heaters are arranged in 2 to 4 rows at equal intervals, and the horizontal arrangement positions of the rows are staggered when the electric heaters are arranged, so that gas is difficult to directly enter.

(29) A plurality of heat-resistant rods are horizontally arranged at a position 100 mm below the electric heaters (26) at the lowest row and penetrate through the partition wall (23) along the horizontal direction. In the present embodiment, the electric heater (26) and the heat-resistant rod (29) are disposed in parallel (disposed in the same longitudinal direction), but may be disposed in a direction orthogonal to each other.

The heat-resistant bar (29) preferably has a heat resistance of 1300 ℃ or higher and has a heat resistance to F₂And HF, and ceramic rods and the like can be used, but Al is used₂O₃Rods with a circular cross-section as the main component are particularly suitable. The heat-resistant rod (29) can be solid (bar) or hollow (tube)Although 99.5% α -Al of 10 mm in diameter is used in this example₂O₃The pipe produced was composed of 5 sections and a total of 48, but the pipe diameter and the number of the sections used were not limited thereto and can be determined by appropriate selection. The arrangement of the heater (26) makes it difficult for the gas to travel straight, and the horizontal positions of the segments are offset from each other.

The heat-resistant bar (29) has the same effect as the grate in the boiler structure, namely, the heat-resistant bar can prevent the heat energy from being transferred to the lower part of the gas decomposition combustion tower (21) due to the heating of the upper heater, and can preheat the gas containing PFC and the reducing atmosphere forming agent fed by the reducing atmosphere forming agent inlet pipe.

In addition, the PFC-containing gas and the reducing atmosphere forming agent flowing through the gaps between the plurality of heat-resistant bars (29) can be mixed by the turbulence generated by the heat-resistant bars (29).

Since the flow velocity is reduced by the heat-resistant bar (29), the residence time of the gas in the gas decomposition tower (21) can be sufficiently ensured, and the destruction rate can be increased.

Since the electric heater 26 is provided to penetrate the gas decomposition/combustion tower 21 and the inner partition wall 23 thereof and the heat-resistant rod 29 is also provided to penetrate the partition wall 23, a heat-resistant and corrosion-resistant sealing agent containing ceramic fibers as a main component should be applied to the penetration portion to prevent gas leakage.

The temperature of each part in the device of the embodiment is as follows:

heater surface: 1200 to 1350 DEG C

Gas decomposition chamber space and combustion chamber space: 1200 to 1300 DEG C

Lower part of gas decomposition chamber (below heater, above heat-resistant bar): 800 deg.C

Lowest part of the gas decomposition chamber (part of the gas to be treated below the heat-resistant bar):

200～300℃

lower part of combustion chamber (below heater, above heat-resistant bar): 1200 deg.C

Lowermost part of combustion chamber (treatment gas exhaust part below heat-resistant bar): 800 deg.C

Second water scrubber outlet rear: at 200 ℃. These results show that the heat-resistant bar (29) effectively prevents the downward propagation of thermal energy.

Further, the device of this example was used to actually remove the harmful substances.

At a flow rate of 140 liters/min, 1% CF₄、99％N₂Through the first scrubber(31) Is introduced into the decomposition chamber (22) in the upper position.

Propane used as a reducing atmosphere forming agent is introduced into the gas decomposition chamber (22) through a reducing atmosphere forming agent introduction pipe (27) connected to the upper part of the first scrubber (31) at a flow rate of 1.4 l/min for use in the reaction with CF₄Thermal decomposition in the presence of co-solvent.

The gas (23) thermally decomposed in the gas decomposition chamber (22) is moved into the combustion chamber (24) from the gap at the upper part of the partition wall (23), and is burned in the combustion chamber (24) together with the outside air fed from the air inlet pipe (28) to remove combustible components, and is cooled and washed by a second water scrubber (32) located below the combustion chamber (24), and is discharged into the atmosphere.

After analysis of the gas discharged from the second water scrubber (32), CF₄Was 50 ppm. That is to say CF₄The pest control rate was 99.5%. In addition, the electricity consumption for the above-mentioned pest control was 9 kw/h.

Except that ammonia gas was used as the reducing atmosphere forming agent at a flow rate of 3.6 liters/min, the harm was removed under the same conditions as described above. As a result of CF in the treated gas₄60ppm, CF₄The pest control rate was 99.4%.

[ COMPARATIVE EXAMPLE 3]

The same procedure as in example 5 was conducted except that 9 electric heaters were installed in a relatively vertical direction and no heat-resistant rod was used at allDevice pair CF₄And (4) removing the harm.

The amount of the treatment gas was reduced to 120 liters/min, and CF in the treated gas was found after the treatment with 1.2 liters/min propane at the same temperature₄2500ppm, 75% of the harmful components are removed.

The amount of electric power consumed at this time was 15 kw/hr, which was 1.7 times that of the apparatus of example 5. This also shows that the detoxification apparatus of example 5 has a high detoxification rate and low energy consumption.

FIG. 6 shows an example in which an electric heater 26 is provided in parallel with a partition wall 23, in addition to the embodiment shown in FIG. 3. In the case of FIG. 4, the electric heater 26 is fixed to the partition wall 23 so that the through-holes 23a of the partition wall 23 penetrated by the electric heater 26 are completely closed to prevent the exhaust gas from flowing from the decomposition chamber 22 into the combustion chamber 24 through the through-holes 23a of the partition wall 23. In this case, when the electric heater (26) is energized to heat, Al of the electric heater (26)₂O₃The protective tube (26b) is broken by the restraint of the partition wall (23) when thermally expanded, but when the electric heater (26) is arranged in parallel with the partition wall (23), the electric heater (26) isfree from the partition wall (23), and when electricity is applied theretoIt is not damaged when heated.

[ Effect of the invention]

As described above, the present invention can provide a method and an apparatus for removing harmful substances, which have a high efficiency of removing harmful substances from PFC components that are difficult to remove at low temperatures and can remove harmful substances with low power consumption.

[ brief description of the drawings]

Fig. 1(a) shows a schematic structural diagram of a pest control device in embodiment 1 of the present invention. (B) A schematic structural view showing a modification of the harmful-removal device according to embodiment 1 of the present invention. (C) A schematic structural view of a pest control device in embodiment 3 of the present invention is shown.

Fig. 2(a) and (B) are top and front sectional views of the harmful removing apparatus in embodiment 4 of the present invention. (C) An elevation cross-sectional view of another structure of the device of example 4 above.

Fig. 3 is a schematic front sectional view showing the structure of a harmful removing device in embodiment 5 of the present invention.

Fig. 4 is a side sectional view of an exploded burner tower of the apparatus of fig. 3.

Fig. 5 is a top cross-sectional view of an exploded burner tower of the apparatus of fig. 3.

Fig. 6 is a front sectional view showing another structure of the harmful means of the present invention shown in fig. 3.

[ description of the figures using symbols]

(1) Front water scrubber (first scrubber)

(2) PFC harm-removing decomposition tower

(3) Rear water scrubber (second scrubber)

(4) Treated gas combustion tower

(5) Introducing pipe containing PFC treated gas

(6) Reducing atmosphere forming agent introducing pipe

(7) Suction fan

(8) An exhaust pipe (9) leading-in pipe (10) leading to atmosphere and a water tank (11) gas decomposition combustion tower (12) gas decomposition chamber

(13) Partition wall

(14) Combustion chamber

(15) A heater (17) with a ceramic-lined heat-insulating layer (16), a hydrocarbon gas inlet pipe (18), an air inlet pipe (21) and a gas decomposition combustion tower

(22) Gas decomposition chamber

(23) Partition wall

(24) Heat-resistant bar of electric heater (29) in combustion chamber (26)

Claims

1. A method for detoxifying perfluorocarbons or perfluorocarbons, characterized by mixing one or more of a hydrocarbon gas and an ammonia gas with a gas to be treated containing perfluorocarbons or perfluorocarbons discharged from a production facility, and then thermally decomposing the mixed gas in a non-oxidizing atmosphere.

2. The method for detoxifying perfluorocarbons or perfluorocarbons as claimed in claim 1, wherein the mixed gas is thermally decomposed at 600 to 1300 ℃ in a non-oxidizing atmosphere.

3. The method for detoxifying perfluorocarbons or perfluorocarbons as claimed in claim 1 or 2, wherein water is added to said mixed gas.

4. A method for detoxifying perfluorocarbons or perfluorocompounds, comprising the steps of:

(a) a step of mixing a hydrocarbon gas or an ammonia gas with a gas to be treated containing perfluorocarbon or perfluorocompound discharged from a production apparatus, and thermally decomposing the mixed gas in a non-oxidizing atmosphere;

(b) burning the thermally decomposed gas, removing a combustible component from the thermally decomposed gas, and

(c) and (3) washing with water or removing fluoride generated by thermal decomposition by chemical adsorption.

5. A method for detoxifying perfluorocarbons or perfluorocompounds, comprising the steps of:

(a) a step of mixing a hydrocarbon gas or an ammonia gas with a gas to be treated containing a perfluorocarbon or a perfluorocompound discharged from a production facility, and thermally decomposing the mixed gas in a non-oxidizing atmosphere;

(b) a step of removing fluoride produced by thermal decomposition by water washing or chemical adsorption, and

(c) burning the thermal decomposition gas to remove combustible components in the thermal decomposition gas.

6. The method for detoxifying perfluorocarbons or perfluorocarbons as claimed in claim 4 or 5, wherein the gas to be treated containing perfluorocarbons or perfluorocarbons discharged from the production apparatus is first washed with water and then thermally decomposed ina non-oxidizing atmosphere.

7. A method for detoxifying perfluorocarbons or perfluorocompounds, comprising the steps of:

(a) a step of washing the gas to be treated containing perfluorocarbon or perfluorocompound discharged from the production apparatus with water;

(b) a step of mixing a hydrocarbon gas or an ammonia gas, or a mixture of two or more gases, and thermally decomposing the mixed gas in a non-oxidizing atmosphere;

(c) burning the thermally decomposed gas, removing a combustible component from the thermally decomposed gas, and

(d) and (3) washing with water or removing fluoride generated by thermal decomposition by chemical adsorption.

8. The method for detoxifying a perfluorocarbon gas as claimed in any one of claims 1, 2, 3, 4, 5 or 7, wherein the gas mixed with the gas to be treated at the time of the heat treatment is a mixed gas of one or more of methane, ethane, propane, butane or ammonia gas.

9. A harm-removing device for perfluorocarbons or perfluorocarbons is characterized by comprising the following devices:

(a) a gas decomposition tower for mixing one or more of hydrocarbon gas and ammonia gas with a gas to be treated containing perfluorocarbon or perfluorocompound discharged from a production facility and thermally decomposing the mixed gas in a non-oxidizing atmosphere;

(b) a combustion tower connected to the gas decomposition tower and configured to combust a combustible component in the treated gas decomposed in the decomposition tower;

(c) a heater disposed in the gas decomposition chamber and the combustion chamber;

(d) a reducing atmosphere forming agent introduction pipe for supplying a reducing atmosphere forming agent to the gas decomposition chamber;

(e) an air inlet pipe for supplying air to the combustion chamber; and

(f) a second water scrubber disposed downstream of the combustion tower.

10. A harm-removing device for perfluorocarbons or perfluorocarbons is characterized by comprising the following devices:

(b) a reducing atmosphere forming agent introduction pipe for supplying a reducing atmosphere forming agent to the gas decomposition chamber;

(c) a second water scrubber disposed on a downstream side of the gas decomposition tower;

(d) a combustion tower connected to the downstream side of the second water scrubber for burning combustible components in the scrubbing gas scrubbed by the second water scrubber;

(e) a heater disposed in the gas decomposition chamber and the combustion chamber; and

(f) an air inlet pipe for supplying air to the combustion chamber.

11. A harm-removing device for perfluorocarbons or perfluorocarbons is characterized by comprising the following devices:

(b) a combustion tower connected to the downstream side of the gas decomposition tower for burning combustible components in the gas after decomposition treatment in the gas decomposition tower;

(e) an air inlet pipe for supplying air to the combustion chamber; and

(f) an adsorption tower filled with granular calcium oxide or calcium carbonate and arranged at the downstream of the combustion tower.

12. A harm-removing device for perfluorocarbons or perfluorocarbons is characterized by comprising the following devices:

(c) an adsorption tower which is arranged at the downstream of the combustion tower and is filled with granular calcium oxide or calcium carbonate;

(d) a combustion tower connected to the downstream side of the adsorption tower for burning the combustible component in the adsorption treatment gas discharged from the adsorption tower;

(f) an air inlet pipe for supplying air to the combustion chamber.

13. A harm-removing device for perfluorocarbons or perfluorocarbons is characterized by comprising the following devices:

(a) a decomposition combustion tower is composed of

A gas decomposition chamber for mixing one or more of a hydrocarbon gas and an ammonia gas in a gas to be treated containing perfluorocarbon or perfluorocompound discharged from a production apparatus, and thermally decomposing the above mixed gas in a non-oxidizing atmosphere, and

a combustion chamber for burning combustible components in the decomposition processing gas in the decomposition chamber,

the decomposition chamber and the combustion chamber are integrated by a heat-resistant partition wall, and are communicated with each other at the upper end part of the partition wall;

(b) a heater arranged in the gas decomposition chamber and the combustion chamber;

(c) a reducing atmosphere forming agent introduction pipe for supplying a reducing atmosphere forming agent to the gas decomposition chamber;

(d) an air inlet pipe for supplying air to the combustion chamber; and

(e) a second water scrubber disposed downstream of the gas decomposition combustor.

14. A harm-removing device for perfluorocarbons or perfluorocarbons is characterized by comprising the following devices:

(a) the decomposition combustion tower comprises:

a combustion chamber for burning combustible components in the gas decomposed in the decomposition chamber,

the decomposition chamber and the combustion chamber are integrated by a heat-resistant partition wall and are communicated with each other at the upper ends thereof;

(d) an air inlet pipe for supplying air into the combustion chamber; and

(e) an adsorption tower installed downstream of the gas decomposition/combustion tower and filled with granular calcium oxide or calcium carbonate.

15. The detoxifying device for perfluorocarbons or perfluorocompounds according to any one of claims 9 to 14, wherein the first water scrubber is provided upstream of the gas decomposition burner, and the gas to be treated containing perfluorocarbons or perfluorocompounds discharged from the production device is washed with water and then subjected to gas decomposition.

16. The perfluorocarbon or perfluorocompound detoxifying device as claimed in any one of claims 9 to 14 wherein said heater is disposed horizontally in said gas decomposition chamber and said combustion chamber.

17. The apparatus for detoxifying perfluorocarbons or perfluorocompounds as claimed in any one of claims 9 to 14, wherein said grate is disposed horizontally below said heaters in said gas decomposition chamber and said combustion chamber.

18. The harmful removing device for the perfluorocarbons is characterized by comprising the following equipment:

(a) a first water scrubber for washing a gas to be treated containing perfluorocarbon or perfluorocompound discharged from a production apparatus with water;

(b) the gas decomposition combustion tower is composed of:

a gas decomposition chamber connected to the upper end of the first water scrubber and mixing either one or more of a hydrocarbon gas and an ammonia gas with the gas to be treated washed with water in the first water scrubber, thermally decomposing the mixed gas in a non-oxidizing atmosphere, and

a combustion chamber for burning combustible components in the gas decomposed by the decomposition chamber,

the gas decomposition chamber and the combustion chamber are integrated by a heat-resistant partition wall, and are communicated with each other at the upper ends thereof;

(c) a heater horizontally disposed in the gas decomposition chamber and the combustion chamber;

(d) a grate horizontally arranged below the heater in the gas decomposition chamber and the combustion chamber;

(e) a reducing atmosphere forming agent introduction pipe for supplying a reducing atmosphere forming agent to the gas decomposition chamber;

(f) an air inlet pipe for supplying air to the combustion chamber;

(g) a second water scrubber connected to the lower end of the combustion chamber; and

(h) a water tank is provided with a first water scrubber and a second water scrubber.