JP3856598B2 - Pyrolysis device for harmful component-containing gas - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal decomposition apparatus for gases containing harmful components such as chlorofluorocarbons, and in particular, combustion suitable for high-efficiency decomposition of flue gas containing chlorofluorocarbons such as PFC and CFC by improving the thermal efficiency and uniformly heating gaseous non-heated substances The present invention provides a system, and particularly relates to an apparatus for decomposing harmful component-containing gas heat suitable for reducing NOx, CO, and HC (hydrocarbons), which are typical harmful substances in exhaust gas.
[0002]
[Prior art]
In recent years, the issue of global warming has been highlighted, and the emission of gases such as CO ₂ produced by mass consumption of fossil fuels has been regulated. General chlorofluorocarbon (CFC), which has been developed as a refrigerant for air conditioners and refrigerators, has been regulated and replaced by chlorofluorocarbon, and is not currently manufactured. On the other hand, fluorocarbons (PFC) discharged from the semiconductor manufacturing process are used in small quantities, but their global warming potential is said to be 1000 to 10,000 times that of CO _2. In view of the increase, it cannot be ignored, the standards for these regulations have been formulated, and PFC crackers have already been developed.
[0003]
There are various types of PFC crackers that have already been developed. The PFC cracking apparatus using combustion according to the present invention will be described. Hydrocarbon gas fuel, specifically propane or methane, is used for PFC decomposition by this method. However, the combustion method is a diffusion combustion method or a premixed combustion method using normal room temperature air, and no special new technology is adopted. That is, a high-temperature environment is created by hydrocarbon combustion, and chlorofluorocarbon and the like are burned and decomposed in this atmosphere. However, the heat used in the decomposition of the exhaust gas is released into the atmosphere as it is or cooled by a water cooling device installed in the downstream part of the device, that is, water is sprayed into the combustion gas to sensible heat and evaporation of water. It was cooled using latent heat and discharged at a gas temperature of 100 ° C. or lower, and no heat recovery was performed. The reason is that since the exhaust gas apparatus is used in a clean room, it must be compact, and there is an environment where a heat exchanger using a heat transfer tube cannot be used.
[0004]
In industrial heating devices, high-temperature air combustion systems (heat storage combustion, also known as regenerative systems) are often seen in recent years. In many cases, a plurality of burners are provided with heat accumulators, and the burners are alternately switched (alternate combustion) to bring the air passing through the heat accumulators to a high temperature exceeding 1000 ° C.
[0005]
The advantage of this method is that the heat that is taken out of the system by combustion exhaust gas can be used effectively for heating the combustion furnace, so it is excellent in energy efficiency and the multiple burners are switched at specific time intervals, so the inside of the furnace burns Since it is disturbed by the gas and a sufficient mixing and diffusion effect is obtained, the temperature in the furnace is made uniform, and the material to be heated (solid or gas) installed in the furnace is heated uniformly. Furthermore, since the maximum temperature is suppressed as compared with the conventional combustion method, NOx can also be suppressed low. That is, in the case of gas combustion, there is no nitrogen content in the fuel, and only combustion air exists, so the generated NOx is mainly Thermal NOx, and this NOx increases rapidly when the ambient temperature exceeds 1400 ° C. For this reason, a uniform method is effective for low NOx so that the temperature in the furnace does not become 1400 ° C. or higher.
[0006]
[Problems to be solved by the invention]
In high-temperature air combustion, since the combustion air is at a high temperature of 1000 ° C. or higher, self-ignition occurs at the same time as the fuel and air are encountered, so it is low for flame stabilization like conventional diffusion combustion and premixed combustion. Although it has the characteristics that the flow velocity region is secured, specifically, the combustion air flow velocity is not reduced and the formation of flame holders and swirling jets is not required, premixing is a backfire due to the characteristics of self-ignition. It is impossible to suppress, and in diffusion combustion, it becomes difficult to suppress the generation of thermal NOx because it becomes locally hot at the downstream part of the combustion input position, and even in high temperature air combustion, low NOx combustion The limit of was visible.
The subject of this invention is solving the said problem at the time of carrying out high temperature air combustion of harmful component containing gas, such as Freon, with gas fuel.
[0007]
[Means for Solving the Problems]
The invention claimed in the present application in order to solve the above-mentioned problems is as follows.
(1) A device that burns a gas containing fuel containing harmful components such as chlorofluorocarbon with combustion air preheated to 200 ° C or higher and having an oxygen partial pressure of 21% or lower, and decomposes the harmful components as the gas fuel burns. A venturi portion comprising an enlarged portion and a reduced portion of the gas flow path, four or more gas fuel injection nozzles provided at intervals on a peripheral wall of the reduced portion of the venturi portion , and a upstream flow of the venturi portion A heat accumulator provided in the gas vent, a gas fuel injection nozzle provided toward the gas flow path of the venturi section, a recess provided in parallel with a flow path length direction on the enlarged partial peripheral wall of the venturi section, A means for supplying a harmful component-containing gas to the upstream of the regenerator, the venturi portion or the downstream of the venturi portion together with the combustion air is provided.
( 2) The thermal decomposition apparatus according to ( 1 ), wherein the gas fuel injection nozzle is arranged in a direction in which a swirl is performed with respect to a main flow of combustion air.
( 3) The thermal decomposition apparatus according to ( 1) or (2), wherein the venturi section has a structure in which a twist is applied in a circumferential direction so that the combustion air flow is swirled.
( 4) The thermal decomposition apparatus according to any one of (1) to ( 3) , wherein an outer peripheral portion of the venturi portion has a water cooling structure.
( 5) The thermal decomposition apparatus according to any one of (1) to ( 4) , wherein a check valve is provided in the gas fuel injection nozzle.
(6) A device that burns a gas containing toxic components such as chlorofluorocarbon together with gas fuel in combustion air preheated to 200 ° C or higher and having an oxygen partial pressure of 21% or less, and decomposes the toxic components as the gas fuel burns. A venturi portion having an enlarged portion and a reduced portion of the gas flow path, a heat accumulator provided in the upstream of the venturi section, and a gas fuel injection nozzle provided toward the gas flow path of the venturi section And a hollow provided in the enlarged partial peripheral wall of the venturi section in parallel with the flow path length direction, and supplying the harmful component-containing gas together with the combustion air to the upstream side of the heat accumulator, the venturi section, or the downstream section of the venturi section And the venturi section has a structure in which a twist is applied in the circumferential direction so that the combustion air flow is swirled.
[0008]
[Action]
According to the present invention, since the gas temperature can be made uniform not only in the furnace but also in the vicinity of the burner, the amount of NOx generated in the furnace can be suppressed as much as possible.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory view of the overall structure of a combustion decomposition apparatus for exhaust gas discharged from a semiconductor manufacturing facility containing silane and chlorofluorocarbon. This apparatus includes a combustion furnace 1 having a U-shaped structure, a pair of burners 3 connected to both ends of the U-shaped structure of the combustion furnace 1, a heat accumulator 5 and a scrubber 6, and an exhaust gas containing harmful components such as silane. Is pretreated by the pretreatment device 2 together with the combustion gas, and then the absorption tower 10 is alternately supplied via the flow path switching unit 7 to the system that supplies the scrubber 6 through the flow path switching unit 7 and the gas that has passed through the scrubber 6. And a blower 9 for discharging the exhaust gas purified by the absorption tower 10 to the outside of the system.
[0010]
When the concentration of silane in the gas to be treated is high, there is a possibility of causing the problem of blockage of the entire apparatus, so silane or the like contained in the exhaust gas is removed in advance. That is, removal of the decomposition and silane freon contained in the exhaust gas is more efficient was conducted by another device, the silane is oxidized (burned) to SiO ₂ in the combustion air in the pretreatment device, the SiO ₂ powder To remove. At this time, part of the chlorofluorocarbon is also decomposed, but most of it remains in the exhaust gas as it is. Therefore, it is desirable to perform combustion decomposition with the apparatus of the present invention having a heat accumulator.
[0011]
The harmful component-containing exhaust gas is treated by the pretreatment device 2 together with the combustion air if necessary, and then passes through the flow path switching device 7 to be scrubber 6, heat accumulator 5, burner 3, combustion furnace 1, burner 3, heat accumulator. It is processed through the vessel 5, the flow switching device 7, and the absorption tower 10, and is discharged to the outside through the blower 9. Then, the flow path is switched at regular intervals, and the gas flow and the burner used are reversed. CFCs and the like in the exhaust gas are decomposed and removed inside the combustion furnace, and removed as HF by the scrubber 6 and the absorption tower 10.
[0012]
2 is a cross-sectional view of a burner device according to an embodiment of the present invention, FIG. 3 is an arrow view along the line III-III in FIG. 2, and FIG. 4 is a diagram showing the fuel injection nozzle 13 as the main flow of combustion air. It is a schematic sectional drawing of the burner apparatus arrange | positioned with respect to the direction which turns with respect to it. This burner device has a venturi portion 12 composed of an enlarged portion 14 and a reduced portion 15 of a gas flow path, a heat accumulator 5 provided in the upstream of the venturi section 12, and a gas flow path of the venturi section 12. A gas fuel injection nozzle 13 provided, a recess 19 provided in an enlarged partial peripheral wall of the venturi section in parallel to the flow path length direction, and a harmful component-containing gas to the venturi section 12 together with the combustion air 17 The flow path to be provided is provided. The combustion air 17 passes through the heat accumulator 5 together with the harmful component-containing gas, and is heated from room temperature to 1000 ° C., and then the flow velocity is accelerated through the reduction unit 15 and comes into contact with the gas fuel injected from the fuel injection nozzle 13. Mix and ignite. Thereafter, the combustion gas that has been heated and expanded by combustion is jetted into the combustion furnace 1 along the enlarged portion 14. The feature of this device is that it has a venturi structure that can secure a sufficient air flow velocity, so that high-temperature air and fuel are rapidly mixed, and the backfire is prevented by avoiding the diffusion of fuel to the upstream portion.
[0013]
As shown in FIG. 3, the venturi rear enlarged portion has a recess 19. Although the size of the depression cannot be specified, the spread angle is preferably within 30 degrees with respect to the burner axis direction. When this angle exceeds 30 degrees, separation of the air flow at the enlarged portion 14 becomes insufficient, and the flame holding function is deteriorated. Since the expansion angle of the venturi expansion portion 14 is 6 to 7 degrees, the expansion angle of the hollow portion is preferably 10 to 30 degrees. In FIGS. 3 and 4, the lattice that can be seen at the center of the burner is a ceramic honeycomb that is the heat accumulator 5. The number of fuel nozzles 13 should be large (four in the case of this figure), but there are problems in manufacturing, and if solid particles are present in the combustion air, the fuel nozzles will be clogged. Therefore, it is preferable to increase the mixing performance of the combustion air and the fuel gas by providing a speed difference.
[0014]
In the present invention, as shown in FIG. 4, the gas fuel injection nozzle 20 may be arranged so that the injection direction is tangential to the circular cross-section flow path, that is, swirl with respect to the main flow of combustion air. preferable. With such a configuration, sufficient mixing of fuel and high-temperature combustion air can be achieved, the radial flow velocity distribution at the burner outlet portion can be made uniform, and an increase in gas residence time in the furnace can be suppressed.
In a normal diffusion burner, the fuel injection speed is faster than the combustion air speed. However, since the fuel mass flow rate is lower than that of the combustion air, the combustion injection speed is quickly attenuated. In many cases, the mixing effect cannot be obtained.
[0015]
Next, the basic concept of high-temperature air combustion and the interaction between each component will be described. FIG. 5 is a diagram showing the conventional combustion method and the region of the high-temperature air combustion when arranged by the combustion air temperature and the oxygen concentration in the air. When high temperature air is used, combustion is possible even in an oxygen concentration region where combustion is not possible in a normal gas phase. The vertical axis represents the dilution air temperature, and the horizontal axis represents the oxygen concentration in the combustion air. In the figure, the white area is an area where combustion is impossible. A relatively low temperature region (up to 500 ° C.) is a conventional temperature region, but in this method, when the combustion oxygen concentration is reduced to about 15%, self-combustion is no longer possible. However, when the combustion air temperature is increased to 1000 ° C., combustion can be performed in the gas phase even when the oxygen concentration in the combustion air is 3%. The fact that stable combustion is possible even when the oxygen concentration in the combustion air is low indicates that it is suitable for treating waste gas containing harmful substances.
[0016]
FIG. 6 is a system diagram of a waste gas treatment system of the present invention using a high-temperature air combustion system based on such a principle. Since this figure is a system diagram, the detailed configuration of each device is not shown, but the basic configuration is the same as that of FIG. Hereinafter, in order to explain the function of the system, a series of operations from the start of the apparatus to the normal operation will be described.
[0017]
The phenomenon that the flame peculiar to high temperature air combustion becomes invisible and the brightness in the furnace becomes uniform requires that the temperature of combustion air exceeds 800 ° C. Therefore, in the cold start, the temperature in the furnace is raised by igniting the startup burner 24 separately installed in any one of the burners 3-1 and 3-2. Then, when the furnace temperature reaches about 800 ° C., the alternating combustion of the two burners 3-1 and 3-2 in the figure is started. At this time, the gas to be treated is mixed with the combustion air for the first time and supplied to the apparatus. The mixed gas first passes through the flow path switching device 22 and flows into the heat accumulator 5-1. Thereafter, the gas passes through the burner 3-1, is mixed with fuel, burns, and enters the combustion furnace 1. And after passing the burner 3-2 and the heat accumulator 5-2, it cools with the wet scrubber 23 through the flow-path switching apparatus 22, and is discharged | emitted out of the system. Normally, depending on the heat capacity of the heat accumulators 5-1 and 5-2, for example, after about 1 minute, the flow path switching device 22 is operated to reverse the gas flow, and this time the heat accumulator 5-2 and the burner 3- 2 so that the mixed gas flows first. At this time, since the heat accumulator 5-2 is heated, when the mixed gas passes through this apparatus, it is heated from room temperature to 1000 ° C.
[0018]
Next, the flame condition and flame holding of the burner part will be described. Although the combustible region is divided based on the relationship between the diluted air temperature shown in FIG. 5 and the oxygen concentration in the diluted air, the combustion air temperature is time-sequentially when alternating combustion is performed as in the device. Change. That is, the fluctuation repeats like a rectangular wave, influenced by the heat capacity and combustion temperature of the regenerator, the air flow rate, the processing gas flow rate, and the like. The fluctuation interval is generally preferably about 1 minute, but it is expected that the air temperature will decrease with the deterioration of the apparatus and with the transient change in the amount of treated exhaust gas. As a countermeasure, it is necessary for the burner to cope with the expansion of the stable combustion range. Specifically, a flame 19 is provided by providing a recess 19 in the venturi expansion portion 14 in FIG. If high-temperature air of 800 ° C. or higher is supplied, the fuel is stably ignited only by encountering the air, but when the temperature is lowered, the flame position gradually flows to the rear and finally misfires. The depression 19 prevents this. FIG. 10 shows a flame holding situation by the recess 19. The flow separates in the recess structure behind the fuel and stagnates in this region 33 . Since the residence time here increases, the flame is held. In the figure, 34 indicates an ignition position. The flame-holding mechanism is that the heat generated in the depression becomes an ignition source and the flame propagates to the mainstream. Now, when this burner is burning, some SiO ₂ particles are also entrained in the combustion air, so that some SiO ₂ adheres to this recess. However, as shown in FIG. 11, when the burner is stopped and the other burners are combusted, the gas flow is reversed, and the gas reversing along the recess 19 has an effect of peeling off and cleaning the deposits. It is done.
[0019]
12 and 13 are sectional views of a burner apparatus showing another embodiment of the present invention. In the embodiment of FIG. 12, the cooling pipe 40 is incorporated in the flow reducing portion 15 and the subsequent flow expanding portion 14 after the mixed gas has passed through the regenerator 5. The combustion air temperature is about 1000 ° C. at the outlet portion of the regenerator 5 and 1400 ° C. at the enlarged portion. In order to protect the burner structure in such an ultra-high temperature region from oxidation and melting phenomenon. It is desirable to install a cooling pipe as shown in FIG.
[0020]
In FIG. 13, in addition to the cooling pipe, the combustion injection nozzle has a check valve structure. That is, a check valve structure is provided in order to prevent particles from adhering to or entering the fuel injection nozzle 13 when the burner is stopped. The check valve 41 is provided on the fuel injection nozzle inlet side of the fuel manifold, and includes a spring 41 and a needle that is urged by the spring 41 and fitted into the fuel injection nozzle inlet. The gas fuel 43 is supplied from the side surface of the fuel manifold where the needle is located. During combustion, the needle of the check valve 41 is lifted by the fuel pressure, and the combustion passes through the fuel injection nozzle 13 and is supplied to the burner to form a flame. However, when the burner is in a resting state, the fuel pressure decreases and is urged by the spring 42, and the valve 41 closes the fuel nozzle 13. That is, when the burner is stopped, even if the combustion gas flows backward to the burner, the combustion gas does not flow into the fuel nozzle 13, and even if particles are included in the combustion gas, there is a possibility of flowing into the nozzle. Lower.
[0021]
Next, FIG. 7 shows a method for directly introducing an exhaust gas containing silane and chlorofluorocarbon into a combustion furnace. When the concentration of silane is low (<1%), the influence of SiO ₂ deposition on the pipes and inside of the apparatus is not so important, so a method of sending exhaust gas directly to the combustion furnace is desirable from the viewpoint of safety. Figure 8 is a system diagram of a case of supplying through a pretreatment apparatus 28 including silane, Freon flue gas as shown in FIG.
[0022]
FIG. 9 is an explanatory view showing an example in which exhaust gas is directly introduced into the combustion furnace as shown in FIG. That is, in this case, the injection nozzle 32 is disposed from the corner portion of the combustion furnace 1 toward the center portion of the combustion furnace 1 so that the particles do not accumulate at the stagnation position in the furnace, and the silane-containing and chlorofluorocarbon-containing exhaust gas is placed in the center of the furnace. It is preferable to arrange so as to inject toward.
[0023]
【The invention's effect】
According to the present invention, it becomes possible to decompose harmful component-containing gas in an ultra-high temperature region, which is impossible with the conventional combustion method, and highly efficient exhaust gas treatment can be performed. In particular, in the exhaust gas treatment, a gas having a low oxygen concentration can be combusted safely, so that it is possible to decompose harmful components that were impossible with the conventional combustion method. And since the said apparatus employ | adopts a regeneration system, it has the advantage which can use combustion exhaust gas temperature effectively, can obtain high thermal efficiency, and can suppress running cost.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing the overall configuration of a thermal decomposition apparatus for harmful component-containing gas according to the present invention.
2 is a cross-sectional view of a burner device used in the apparatus of FIG.
FIG. 3 is an arrow view along III-III of the apparatus of FIG. 1;
4 is a front explanatory view of a burner apparatus in which the gas fuel injection nozzle of the apparatus of FIG. 1 is arranged so that the gas fuel is blown in the swirling direction from the periphery of the high-temperature air.
FIG. 5 is a conceptual diagram comparing the size of an ignition region of high-temperature air combustion with conventional combustion.
FIG. 6 is a system diagram of an apparatus according to the present invention using a high-temperature air combustion system as a processing apparatus for waste gas containing harmful gas.
FIG. 7 is a system diagram of the thermal decomposition apparatus of the present invention when exhaust gas is directly introduced into a high-temperature air combustion furnace for processing.
FIG. 8 is a system diagram of a thermal decomposition apparatus according to the present invention in which exhaust gas is treated in advance by a pretreatment apparatus and silane and the like are decomposed and then treated.
9 is a cross-sectional view of a burner device when the exhaust gas shown in FIG. 7 is directly introduced into a combustion furnace.
FIG. 10 is an explanatory diagram showing a situation where an ignition or flame holding effect can be obtained by the effect of gas stagnation in a recess in the burner device used in the present invention.
FIG. 11 is an explanatory diagram of a burner device used in the present invention, showing a gas flow when combustion gas containing SiO ₂ particles and the like from a combustion furnace passes through the venturi part and the depression part.
FIG. 12 is a cross-sectional view of the burner device showing a structure for cooling the structure of the combustion gas diffusion portion in the ignition region of the burner device used in the present invention.
FIG. 13 is a cross-sectional view of the burner device of the present invention in which a check valve is applied to the manifold portion of the fuel nozzle.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Combustion furnace, 2 ... Pretreatment apparatus, 3 ... Burner, 4 ... Exhaust gas, 5 ... Heat storage device, 6 ... Scrubber, 7 ... Channel switching machine, 8 ... Circulating water pump, 9 ... Blower, 10 ... Absorption tower, DESCRIPTION OF SYMBOLS 11 ... Fuel manifold, 12 ... Benchery part, 13 ... Gas fuel injection nozzle, 14 ... Expansion part, 15 ... Reduction part, 17 ... High temperature air, 18 ... Gas fuel supply pipe, 19 ... Recess, 20 ... Swirling gas fuel injection nozzle .

Claims (6)

A device that burns a gas containing a harmful component such as chlorofluorocarbon together with gas fuel in combustion air having a partial pressure of oxygen of 21% or less, preheated to 200 ° C. or more, and decomposes the harmful component together with the combustion of the gas fuel, A venturi portion composed of an enlarged portion and a reduced portion of the gas flow path; four or more gas fuel injection nozzles provided at intervals on a peripheral wall of the reduced portion of the venturi portion ; and a pre-stream of the venturi portion. A heat accumulator, a gas fuel injection nozzle provided toward the gas flow path of the venturi part, a recess provided parallel to the flow path length direction on the enlarged partial peripheral wall of the venturi part, and the front of the heat accumulator And a means for supplying a harmful component-containing gas together with the combustion air to a flow, a venturi portion or a downstream portion of the venturi portion. The gas fuel injection nozzle pyrolysis apparatus according to claim 1, wherein the swivel is disposed in such a direction to the main flow of the combustion air. The thermal decomposition apparatus according to claim 1, wherein the venturi portion has a structure in which a twist is applied in a circumferential direction so that the combustion air flow is swirled. The thermal decomposition apparatus according to any one of claims 1 to 3 , wherein an outer peripheral portion of the venturi portion has a water cooling structure. Pyrolysis apparatus according to any one of claims 1 to 4, characterized in that a check valve to the gas fuel injection nozzle. A device that burns a gas containing a harmful component such as chlorofluorocarbon together with gas fuel in combustion air having a partial pressure of oxygen of 21% or less, preheated to 200 ° C. or more, and decomposes the harmful component together with the combustion of the gas fuel A venturi portion composed of an enlarged portion and a reduced portion of the gas flow path; a heat accumulator provided in the upstream of the venturi section; a gas fuel injection nozzle provided toward the gas flow path of the venturi section; A recess provided in an enlarged partial peripheral wall of the venturi portion in parallel with the flow path length direction, and means for supplying the harmful component-containing gas together with the combustion air to the upstream side of the heat accumulator, the venturi portion, or the downstream side of the venturi portion. And the venturi section has a structure in which a twist is applied in the circumferential direction so that the combustion air flow is swirled.

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