JP4306889B2 - Gas permeate carrying catalyst - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention allows a gas exhaust made of ceramic fiber carrying a catalyst to permeate combustion exhaust gas containing harmful gases such as nitrogen oxides and organochlorine compounds, and decomposes and detoxifies the harmful gases by the action of the catalyst. As regards gas permeators that can be used, nitrogen oxide and organochlorine compound decomposing devices equipped with the gas permeators include waste incinerators, combustion facilities that use fossil fuels such as coal, various industrial furnaces for iron and metallurgy, cement The present invention is useful for facilities for decomposing and detoxifying nitrogen oxides and organochlorine compounds in gases discharged from firing furnaces, refractory firing furnaces, petroleum refining facilities, chemical plants, and the like.
[Prior art]
A honeycomb is well known as a catalyst shape for decomposing nitrogen oxides and organic chlorine compounds such as PCDD (polychlorinated dibenzodioxin) and PCDF (polychlorinated dibenzofuran) contained in combustion exhaust gas. For nitrogen oxides in particular, titanium oxide is used as a carrier, and a honeycomb composed of vanadium pentoxide and tungsten trioxide catalyst components is housed in a container, and the combustion exhaust gas containing pre-injected ammonia is passed through the honeycomb cells. Many plants have already been installed that decompose nitrogen oxides into nitrogen gas and water to make them harmless.
[0003]
Regarding the catalytic element for decomposing a cyclic organic chlorine compound such as dioxin in the combustion exhaust gas discharged from the incineration plant, an application relating to its shape has been filed, for example, in Japanese Patent Laid-Open No. 6-386. These catalyst honeycombs have been manufactured by extruding a slurry-like material made of powder of titanium oxide, vanadium pentoxide, tungsten oxide or the like with a mold or the like, followed by drying and firing processes.
[0004]
An application example of a denitration apparatus having a three-stage catalyst honeycomb formed in this way will be described with reference to FIG. The exhaust gas containing nitrogen oxides and organochlorine compounds discharged from an incinerator or the like is injected with ammonia (NH ₄ ) as a reducing agent by an ammonia injection device 109 provided in the exhaust gas duct 101 and flows into the denitration device inlet 102. Then, it passes through the gas passage of the denitration honeycomb 103 and flows in the direction of the arrow 104. At this time, a part of the nitrogen oxide (NOX) in the exhaust gas is reduced by the reaction with the catalyst on the channel wall surface of the honeycomb, and becomes water (H ₂ O) and nitrogen (N ₂ ) to form the catalyst honeycomb 103. Spill from.
[0005]
In addition to the original exhaust gas components, the combustion exhaust gas flowing out from the catalyst honeycomb 103 includes water and nitrogen gas in which a part of the nitrogen oxide is reduced by ammonia in addition to unreacted nitrogen oxide and ammonia. The gas pressure is recovered in the second stage catalyst honeycomb inlet space 105, passes through the gas passage of the next stage catalyst honeycomb 106, and flows in the direction of arrow 107. Thereafter, nitrogen oxides are sequentially reduced in the order of the second and third stages by the same function, the nitrogen oxide concentration is reduced, and the flue gas 111 exiting the denitration device outlet 110 is oxidized to the environmental regulation value or less. The concentration of objects is reduced and discharged.
[0006]
Note that the catalyst honeycomb 103 shown in FIG. 6 is composed of an assembly of smaller honeycomb elements. A typical example of this honeycomb element is shown in FIG. For example, the honeycomb elements that are usually used generally have dimensions of about 200 mm, 200 mm, and 500 mm in length, width, and height at a cell pitch of 5 mm. FIG. Above, it is typically 4 cells × 4 cells.
[0007]
The honeycomb element 112 guides combustion exhaust gas containing ammonia gas from one opening 113 in the direction of an arrow 114, and is exposed to the wall surface of the gas passage in the cell or in contact with the catalyst at a depth of approximately 20 microns from the wall surface. The nitrogen oxides in the combustion exhaust gas thus reduced are reduced to water and nitrogen gas by the action of the catalyst, and are discharged in the direction of arrow 116 from the other opening 115 of the honeycomb element.
[0008]
However, among the nitrogen oxides in the combustion exhaust gas that passes through the gas passages in the honeycomb element 112, a large amount of nitrogen oxides are discharged from the opening 115 without contacting the catalyst. The ratio of reducing oxide (denitration rate) remains at about 15 to 30%. Therefore, as shown in FIG. 6, the honeycomb group is generally configured to be multi-stage to increase the denitration rate.
[0009]
[Problems to be solved by the invention]
However, the honeycomb containing the catalyst component of vanadium pentoxide and tungsten trioxide using titanium oxide as a carrier as described above is composed of vanadium pentoxide and tungsten trioxide which play a role of decomposing nitrogen oxides and organochlorine compounds. Since it is dispersedly supported in titanium oxide, the vanadium pentoxide and tungsten trioxide that are exposed on the flow path wall of the gas in the honeycomb or at a depth of approximately 20 microns from the flow path wall are excluded. However, most of the catalysts are buried in the honeycomb structure and have a drawback of not functioning as a catalyst.
[0010]
Furthermore, in such a honeycomb-shaped catalyst, even when a clean gas that does not contain dust that has been previously removed by a bag filter or the like is passed, dust gradually accumulates on the wall of the honeycomb gas flow path over a long period of time. In consideration of the reduction in the cross-sectional area of the flow path caused by this, it is necessary to secure a gas flow-path cross-sectional area of at least about 3 mm × 3 mm. In addition, the accumulation of dust on the gas flow path wall of the honeycomb covers the chemically active catalyst surface with dust, impeding contact between the gas and the catalyst, resulting in a decrease in catalyst performance. There is also a drawback that it is necessary to periodically regenerate the catalyst honeycomb or replace it with a new catalyst honeycomb.
[0011]
Furthermore, in plants that do not have dust removal means such as bag filters on the upstream side of the gas, a honeycomb having a gas flow path area of about 10 mm × 10 mm is usually used in consideration of a reduction in the cross-sectional area of the gas flow path due to dust adhesion. However, the specific surface area is smaller than that of the honeycomb through which the clean gas is passed, and there is a disadvantage that the apparatus is enlarged. In addition, in order to flow a gas containing a large amount of dust through the flow path, a soot blow device is required to remove dust adhering to the flow path surface, and dust that cannot be removed by soot blow is applied to the wall of the gas flow path of the honeycomb. As in the case of a honeycomb that gradually accumulates and passes a clean gas, it has the disadvantage of requiring periodic honeycomb regeneration or replacement with a new honeycomb.
[0012]
[Means for Solving the Problems]
Hereinafter, means for solving the problems according to the present invention will be described in detail with reference to the drawings. The fiber 1 and the powdered catalyst 3 shown in FIG. 1 are aggregates obtained by mixing and laminating a large amount of minute substances having a fiber diameter and particle size of 100 microns or less, and each single element is a minute that cannot be illustrated. Although it is a substance, it is expressed in a large shape as an illustration in consideration of convenience in explaining the present invention.
[0013]
As shown in FIG. 1, the ceramic fiber gas permeator 4 carrying the catalyst according to the invention of claim 1 is entirely composed of ceramic fibers having a fiber diameter in the range of 1 to 10 microns and a fiber length of at least 10 mm. Of ceramic fiber 1 occupying 50% or more of the ceramic fiber, and a porosity of 75% or more and 95% or less, and a ceramic fiber molded body having a thickness of at least 10 mm or more, vanadium pentoxide or tungsten trioxide. Or a powdery catalyst 3 having an average particle size of 20 microns or more and 80 microns or less composed of the both compounds is dispersed and supported substantially uniformly to form a gas permeation body 4, and from one wall surface 5 of the gas permeation body, nitrogen Existence of oxides or organic chlorine compounds such as PCDD (polychlorinated dibenzodioxin, PCDF (polychlorinated dibenzofuran)) or both Permeate the flue gas containing harmful gas from the direction of arrow 6 and let the flue gas contained in the gas decompose and detoxify with a catalyst to flow out from the other wall surface 7 in the direction of arrow 8. Features.
[0014]
The powdery catalyst 3 contained in the ceramic fiber-made gas permeator 4 supporting the catalyst is preferably contained in an amount of 15 wt% ± 10 wt% with respect to the total weight of the gas permeator 4. The reason is that when the proportion of the powdered catalyst 3 in the gas permeator 4 is 5% by weight or less, nitrogen oxides and organochlorine compounds in the combustion exhaust gas flowing through the ceramic fiber gas permeator 4 are sufficient. It is because it is discharged without being decomposed. Further, if the ratio of the powdered catalyst 3 in the gas permeable body 4 is 25% by weight or more, the ratio of the powdered material in the ceramic fiber molded body is increased, and the strength of the gas permeable body 4 is decreased. Absent.
[0015]
The thus formed gas permeable body, a combustion exhaust gas containing nitrogen oxides and organic chlorine compounds, the other wall surface from one wall, to flow through the interior molding of the ceramic fibers, the inner molded body All of the catalysts that are dispersed and supported substantially uniformly function effectively, and only the catalyst exposed to the wall surface and the catalyst up to a depth of 20 microns from the wall surface function as in the prior art honeycomb, and the flow of the honeycomb Compared to the fact that most of the nitrogen oxides and organochlorine compounds in the flue gas passing through the road are discharged without contact with the catalyst, the nitrogen oxides and organochlorine compounds contained in the exhaust gas are in contact with the catalyst. The chances of being broken down greatly increase. In other words, it is possible to decompose the nitrogen oxides and organochlorine compounds equivalent to those of the honeycomb with a catalyst amount of about 1/3 to 1/10 of the catalyst amount required for the honeycomb.
[0016]
If the gas permeator formed in this way is used, dust contained in the gas is trapped on the gas inlet side wall surface of the gas permeator and does not enter the gas permeator. In addition, the catalyst is covered with the dust by the dust accumulated on the wall surface and is cut off from the gas, and the phenomenon that the function of the catalyst is deteriorated does not occur.
[0017]
As the fiber constituting the gas permeable material, any ceramic fiber can be used as long as it has a heat resistance of at least 500 ° C. or more, has corrosion resistance against combustion exhaust gas, and can form a molded body . A fiber composed of a single component of alumina, silica, magnesia, glass, silicon carbide, or silicon nitride, a fiber composed of these compounds, or a ceramic fiber composed of a composite composition of these fibers has high heat resistance, corrosion resistance, and marketability. Particularly preferred in terms.
[0018]
As the catalyst dispersedly supported on the gas permeable material, it is possible to use a catalyst formed in advance in the form of a powdered catalyst using titanium oxide having excellent affinity with vanadium pentoxide or tungsten trioxide.
[0019]
In addition, as a method for producing a gas permeable material made of ceramic fibers in which a catalyst is dispersed and supported, for example, a single component or a composite component of a metal sol such as alumina sol, silica sol, titanium sol and a surfactant such as starch. The catalyst powder is added to the aqueous solution and stirred, and the ceramic fibers are sequentially added to make a slurry-like mixture of the catalyst and ceramic fibers. Then, only the solid content can be captured and the liquid components can permeate. It can be cast into a mold, molded, removed from the mold after drying, and fired to obtain a molded body.
[0020]
Alternatively, a larger amount of ceramic fiber is put into a mixed solution composed of the metal sol, surfactant, and catalyst to form a plastic gel material composed of the catalyst and the ceramic fiber, and then extrusion molding or press molding, drying treatment, and You may obtain a molded object by baking processing.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the ceramic fiber gas permeator carrying the catalyst according to the first aspect of the invention has many advantages over the conventional honeycomb carrying the catalyst, and the embodiment thereof will be described below. Will be described in detail with reference to the drawings.
[0022]
FIG. 2 shows an embodiment of a nitrogen oxide and organochlorine compound decomposition apparatus using the ceramic fiber gas permeate carrying the catalyst according to the present invention having the square block shape shown in FIG.
[0023]
Combustion exhaust gas containing nitrogen oxides and organic chlorine compounds passes through the gas duct 9, mixes with ammonia injected from the ammonia injection device 17, and is led into the device from the inlet 10 of the harmful gas decomposition device. A permeate group 13 in which a plurality of permeators 12 are gathered flows in the direction of the arrow 11, and nitrogen oxides and organochlorine compounds are decomposed and made harmless by the catalyst dispersedly supported inside the permeate. Out of group 13. The detoxified gas that has flowed out of the gas permeator group 13 is discharged from the harmful gas decomposition apparatus outlet 15 in the direction of the arrow 16 through the collecting portion 14. In addition, when using this harmful gas decomposing apparatus only for the purpose of decomposing organochlorine compounds, it is not necessary to inject ammonia.
[0024]
The thickness of the gas permeation body according to the present invention in the gas flow direction ensures a residence time in which the nitrogen oxides and organochlorine compounds contained in the combustion exhaust gas can sufficiently come into contact with the catalyst dispersedly supported in the gas permeation body. Therefore, it is desirable that the thickness is at least 10 mm.
[0025]
It is desirable to control the temperature of gas at the inlet of the nitrogen oxide and organochlorine compound decomposition apparatus of the combustion exhaust gas within the range of 300 ° C. ± 100 ° C., which is the temperature range in which the catalyst functions most efficiently. The sulfurous acid gas inside is oxidized to become sulfuric acid, and the temperature range in which ammonium sulfate produced by reaction of this sulfuric acid with the injected ammonia can eliminate the possibility of poisoning the catalyst is set to 300 ° C. ± 50 ° C. preferable.
[0026]
The ceramic fiber gas permeate carrying the catalyst according to the present invention has a higher ability to decompose nitrogen oxides and organochlorine compounds than the conventional catalyst honeycomb, and the conventional catalyst zone having a plurality of stages has one stage. Can fully function.
[0027]
FIG. 3 shows another example of the ceramic fiber gas permeable material carrying the catalyst according to the present invention. Unlike the block shape shown in FIG. 1, it is formed into a cylindrical shape with both ends open.
[0028]
Combustion exhaust gas containing nitrogen oxides and organochlorine compounds flows from the combustion gas inlet 18 toward the arrow 19, flows from the entire surface 20 of the inner surface of the cylinder toward the entire surface 21 of the outer wall of the cylinder, in the direction of the arrow 22, The nitrogen oxides and organochlorine compounds in the combustion exhaust gas are decomposed and rendered harmless by the catalyst dispersedly supported in the ceramic fibers constituting the cylinder, and flow out from the outer wall surface 21. In this case as well, it is desirable that the cylindrical shape has a thickness of at least 10 mm or more in order to ensure a residence time that allows sufficient contact with the catalyst dispersedly supported in the gas permeable material.
[0029]
FIG. 4 shows an embodiment of an apparatus for decomposing nitrogen oxides and organochlorine compounds using a ceramic fiber gas permeator carrying a catalyst formed in a cylindrical shape with both ends opened in this way. In FIG. 4, the same reference numerals as those in FIG. 2 are assigned to the same parts and functions as those in FIG.
[0030]
Combustion exhaust gas containing nitrogen oxides and organochlorine compounds flowing from the apparatus inlet 10 flows through the gas inlets of the respective cylinders in the direction of the arrow 23 and from the inner wall surface of the cylinder to the outer wall surface in the direction of the arrow 24. The gas flows through the gas collecting portion 14, passes through the gas outlet 15 of the apparatus, and is discharged in the direction of the arrow 16. In the case of the present embodiment, the cylindrical gas permeable body 25 whose both ends are open has a structure in which both ends thereof are supported by tube plates 26 and 27 provided in the container. As described above, nitrogen oxides and organochlorine compounds in the combustion exhaust gas are decomposed and detoxified by the action of the catalyst dispersedly supported inside the material constituting the cylinder. Furthermore, it is desirable to maintain the apparatus inlet gas temperature at 300 ° C. ± 100 ° C., more preferably 300 ° C. ± 50 ° C. as described above. Also, the description of the same parts as those in FIG. 2 is omitted.
[0031]
FIG. 5 shows another embodiment of a nitrogen oxide and organochlorine compound decomposition apparatus using a ceramic fiber gas permeate carrying a catalyst formed in a cylindrical shape. 5 that indicate the same parts and functions as those in FIG. 2 are denoted by the same symbols as those in FIG.
[0032]
In the case of the present embodiment, the cylindrical gas permeable body is a so-called candle type in which one end is open and the other end is closed, the open upper end is supported by the tube plate 30, and the cylindrical gas permeable body 31 is suspended. It has a structure to do.
[0033]
Combustion exhaust gas containing nitrogen oxides and organochlorine compounds flowing from the apparatus inlet 10 shown in FIG. 5 flows in the direction of arrow 28 from the outer wall surface of each cylinder toward the inner wall surface, and from the cylindrical gas permeator outlet. It flows in the direction of the arrow 29, passes through the gas collecting portion 14, passes through the gas outlet 15 of the apparatus, and is discharged in the direction of the arrow 16. As described above, the gas temperature at the inlet of the apparatus is more preferably 300 ° C. ± 50 ° C. Further, as described above, it is desirable to have a cylindrical shape having a thickness of at least 10 mm.
[0034]
Further, when the gas permeable material according to the present invention is formed into a block shape shown in FIG. 1, for example, the same vertical, horizontal, and high as the honeycomb element 112 of FIG. 7 which is a structural unit of the prior art honeycomb 103 shown in FIG. By adjusting the size, the honeycomb of the existing denitration device can be removed and replaced with the ceramic fiber gas permeator according to the present invention. The gas permeator thus replaced has a higher function of decomposing nitrogen oxides and organochlorine compounds than in the case of a honeycomb. Therefore, the three-stage honeycomb group shown in FIG. Even with a single-stage configuration, the same or higher resolution of nitrogen oxides and organochlorine compounds as in the case of a three-stage honeycomb group can be obtained.
[0035]
【The invention's effect】
As described above, according to the present invention, the combustion exhaust gas containing nitrogen oxides and organochlorine compounds penetrates the inside of the ceramic fiber gas permeator carrying the catalyst in the ceramic fiber molded body. As a result, all the catalysts dispersed and supported inside the material function effectively without being interrupted by gas, and even with a small amount of catalyst, nitrogen oxides and organochlorine compounds in the combustion exhaust gas are practically used. It can be reduced to a sufficient level.
[0036]
Furthermore, compared to the conventional catalyst honeycomb, the combustion exhaust gas can be passed through a relatively small volume, and the nitrogen oxides and organochlorine compounds can be decomposed more efficiently than before. In combination with a reduction in the amount of catalyst used, this greatly contributes to a reduction in the manufacturing cost of the apparatus.
[0037]
Also, the dust contained in the combustion exhaust gas is captured by the wall of the gas permeable body according to the present invention, and the dust does not permeate inside the gas permeable body. A phenomenon that the catalyst function is impaired by being covered with dust in the combustion exhaust gas does not occur, and the high catalyst function can be maintained for a long period of time.
[Brief description of the drawings]
FIG. 1 is a perspective view of a gas permeable body made of a block-like ceramic fiber according to an embodiment of the present invention.
2 is an assembly cross-sectional view and system diagram of a harmful gas decomposition apparatus incorporating the block ceramic fiber gas permeator of FIG. 1; FIG.
FIG. 3 is a perspective view of a cylindrical ceramic fiber gas permeator with both ends open according to an embodiment of the present invention.
4 is an assembly cross-sectional view and system diagram of a harmful gas decomposition apparatus incorporating the cylindrical ceramic fiber gas permeation body of FIG. 4;
5 is an assembly cross-sectional view and system diagram of the harmful gas decomposition apparatus incorporating the cylindrical ceramic fiber gas permeable body of FIG. 4 and having a cylindrical shape with one end closed.
FIG. 6 is an assembly sectional view and system diagram of a harmful gas decomposition apparatus having a conventional catalyst honeycomb group having a three-stage configuration.
FIG. 7 is a perspective view of a conventional catalyst honeycomb.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ceramic fiber 2 Gas permeation | transmission thickness 3 Catalyst powder 4 Gas permeation | transmission 5 Gas inlet surface 6 Gas inflow direction 7 Gas outlet surface 8 Gas outflow direction 9 Combustion exhaust gas duct 10 Gas decomposition apparatus inlet 11 Block-shaped gas permeator gas inlet Surface 12 Block-shaped gas permeator 13 Block-shaped gas permeator group 14 Gas collecting portion 15 Noxious gas decomposition device outlet 16 Gas outflow direction 17 Ammonia injection device 18 Cylindrical gas permeator gas inlet 19 Cylindrical gas permeator gas inflow direction 20 Cylindrical gas permeator gas inflow surface 21 Cylindrical gas permeator gas outflow surface 22 Cylindrical gas permeator gas outflow direction 23 Cylindrical gas permeator inlet 24 Cylindrical gas permeator gas permeation direction 25 Cylindrical gas permeator 26 Cylinder Upper gas plate 27 for cylindrical gas permeator Lower tube plate 28 for cylindrical gas permeator Candle type gas permeator Gas permeation direction 29 Cand Type gas permeate gas outlet direction 30 candle gas permeation-body tube plate

Claims (5)

In a ceramic fiber molded body , a powdered catalyst having an average particle diameter of 20 microns or more and 80 microns or less composed of vanadium pentoxide, tungsten trioxide or a mixture of both is in the range of 15% by weight to 10% by weight with respect to the total weight. A gas permeation body made of ceramic fiber carrying a catalyst, characterized in that a gas permeation body is formed by being dispersed and supported by the above. The ceramic fiber molded body is composed of ceramic fibers having an average fiber diameter in the range of 1 to 10 microns and a fiber length of at least 10 mm or more, accounting for 50% or more of the total, and the porosity is 75% or more. 2. The ceramic fiber gas permeator carrying a catalyst according to claim 1 , wherein the content is in the range of 95% or less. 2. The powder catalyst according to claim 1, wherein the powder catalyst is a powder catalyst having an average particle diameter of 20 μm or more and 80 μm or less made of vanadium pentoxide, tungsten trioxide or a mixture of both with titanium oxide as a carrier. A ceramic fiber gas permeator carrying a catalyst. The ceramic fiber gas-permeating material carrying the catalyst is made by adhering ceramic fibers and ceramic fibers to the catalyst using a single component or a plurality of components selected from a metal sol selected from alumina sol, silica sol, and titanium sol. The ceramic fiber-supported gas permeator according to claim 1, wherein the ceramic fibers and the ceramic fibers and the catalyst are firmly bonded by drying or drying and firing treatment thereafter. The ceramic fiber is a fiber composed of a single component of alumina, silica, magnesia, glass, silicon carbide, or silicon nitride, a fiber composed of these compounds, or a ceramic fiber composed of a composite composition of these fibers. The gas permeator made of ceramic fiber supporting a catalyst according to claim 1.

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