JPH05306808A - Catalyic combustion device - Google Patents

Abstract

PURPOSE:To keep activity of catalytic assemblies for a long period of time and prolong their lives by using a first catalytic assembly carrying a catalytic composed mainly of an oxide of noble metal and a second catalytic assembly carrying a catalytic composed mainly of an oxide of transition metal. CONSTITUTION:A cylindrical flow passage 1 has, in part thereof, a catalytic assembly 31 having a honeycomb structure and carrying a catalyst composed mainly of an oxide of noble such as palladium, which is disposed on the upstream side of the interior of said flow passage, and a catalytic assembly 32 having a honeycomb structure and carrying a catalyst composed mainly of an oxide of transition metal such as manganese, which is disposed on the downstream side of the interior of the flow passage, each catalytic assembly being provided at two places separately along a direction 5 in which inflammable gas flows. Further, a gap 8 is provided between these catalytic assemblies, and a porous solid layer 71 made of a heat-resistant material is provided in the gap 8. Accordingly, the catalytic assembles 31, 32 can be usually used at temperatures suitable to their respective capabilities, and a mixed gas can be burned even when it is preheated at a relatively low temperature. Since the catalytic assembly 31 composed mainly of an oxide of noble metal is disposed om the upstream side and permits the mixed gas having a relatively low temperature to pass there through, its life can be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a first catalyst body carrying a catalyst mainly composed of a noble metal oxide such as palladium, and a transition metal oxide such as manganese. The present invention relates to a catalytic combustion apparatus that uses a second catalyst body carrying a catalyst mainly composed of, and can reduce the unburned content even if the preheating temperature of the combustible gas is low.

 (Prior Art) Conventionally, there are the following first to fourth examples of this type of oxidation catalyst combustion apparatus. In this first example, as shown in FIG. 4, the catalyst body is integrally formed. That is, the heat insulating material 2 is provided on a part of the inner wall surface of the flow path 1 having a cylindrical cross section, and the catalyst body 3 having a honeycomb structure of the heat resistant material is provided inside the flow path 1. Combustible gas that has been preheated to a temperature at which catalytic combustion is possible flows into the catalyst inlet 4 in the direction of arrow 5.

 While this combustible gas passes through the gaps of the lattice, it contacts the catalytic body to carry out catalytic combustion, rises to the catalytic combustion temperature and flows out from the outlet end 6, and this outflowing gas is used for heating and other purposes. Used.

 The second conventional example (Japanese Patent Laid-Open No. 58-200916) uses a manganese-based catalyst body and a palladium-based catalyst body for the purpose of solving the problem of the first example. The manganese-based catalyst is placed upstream of the fuel gas and the palladium-based catalyst is placed downstream of the manganese-based catalyst.

 Furthermore, the third conventional example (Japanese Patent Laid-Open No. 59-176509) is intended to enable stable combustion even at a high air-fuel ratio, and is only a certain distance from the catalyst body outlet end. It is provided with a honeycomb type shield plate.

 The fourth example of the related art (Japanese Patent Laid-Open No. 61-186704) is intended to have excellent low-temperature ignitability and enable high-temperature, high-load combustion, and it is possible to use the upstream side catalyst and the downstream side. The flow velocity passing between the side catalysts is changed.

 (Problems to be Solved by the Invention) Each of the conventional examples described above has the following problems. That is, in the first example, since the catalyst body is integrally configured, it is difficult to burn in a wide range from low calorie to high calorie. In the second example, the first problem can be solved, but the problem is that the catalyst body containing manganese as a main component does not burn unless a combustible gas whose preheating temperature is high, for example, 550 ° C to 650 ° C is added. In this case, the unburned content of the fuel gas is large, and the palladium-based catalyst is capable of catalytic combustion when the preheating temperature of the combustible gas at the catalyst inlet end is about 400 ° C to 450 ° C. This catalyst alone has a large amount of unburned methane, and the palladium-based catalyst cannot maintain its activity for a long time.

 In the third example, since the honeycomb type shield does not have a function of heat storage or solid heat transfer, the unburned content of the fuel gas increases.

 Also, in the fourth example, the upstream catalyst is designed so that the temperature does not rise during normal combustion, and the area where it blows off is narrowed to increase the flow velocity, so the pressure of the fluid passing through the catalyst layer is increased. The loss becomes large and combustible gas must be sent with high pressure.

 Compared with the conventional method, the present invention is capable of burning a mixed gas of air and combustible gas even if it is preheated to a relatively low temperature, and has a very low unburned content for each catalytic combustion. It is an object of the present invention to provide a catalytic combustion device that can effectively use the above, and can maintain the activity of the catalyst body mainly composed of a noble metal oxide for a long period of time and extend its life.

 [Structure of the Invention] In order to achieve the above-mentioned object, the first invention is such that the outer side is covered with a cylindrical wall, and the multi-layered lattice-shaped honeycomb structure is made of a heat-resistant material inside the wall. A first catalyst body carrying a catalyst mainly composed of a noble metal oxide in a device for catalytic combustion by supplying both fuel for oxidative combustion and combustion air to a catalyst body carrying an oxidation catalyst on the surface of the structure. And a second catalyst body carrying a catalyst mainly composed of a transition metal oxide, the first catalyst body is provided on the upstream side of the flow of the fuel and air, and the second catalyst body is provided downstream of the first catalyst body. A porous solid layer made of a heat-resistant material is provided on the side, and the second catalyst body is provided on the downstream side of the porous solid layer. The second invention is characterized in that a porous solid layer made of a heat-resistant material is provided at the final stage of the downstream outlet of the second catalyst body of the first invention.

 (Operation) According to the present invention, compared to the conventional method, the mixed gas of air and combustible gas can be burned even when preheated to a relatively low temperature, and each of them can be burned in a state where the unburned content is very small. The catalytic combustion can be effectively used, and it becomes possible to maintain the activity of the catalytic body mainly composed of a noble metal oxide for a long period of time and extend the life thereof.

 Regarding the above operation, the present applicant conducted experiments on various oxidation catalysts under various experimental conditions, and as a result, the following facts were found, and the above-mentioned operation was clarified from this. The palladium-based catalyst body is capable of catalytic combustion when the preheating temperature of the combustible gas at the catalyst inlet end is about 400 ° C to 450 ° C, but this catalyst alone has a large amount of unburned methane.

 When the palladium-based oxidation catalyst is installed next to the manganese-based oxidation catalyst, the heat from the manganese-based catalyst, which is at a high temperature, is transferred to the palladium-based catalyst by radiation and heat transfer, and the palladium-based catalyst reaches a high temperature, which shortens its active life. This can be prevented by placing a porous solid between both catalysts.

 For manganese-based catalysts, if the preheating temperature of the flammable gas at the catalyst inlet end is raised to about 550 to 650 ° C, catalytic combustion proceeds and the combustion rate is high and the unburned content can be lowered below the environmental regulation value. it can.

 By providing a porous solid layer made of heat-resistant ceramic at the outlet end of the catalyst body, it is possible to perform catalytic combustion with a higher burning rate and less unburned material.

 Then, as a means for solving the high ignition temperature of the high temperature heat resistant combustion catalyst, which has been a problem in the past, two systems of oxidation catalysts of noble metal oxides such as palladium and transition metal oxides such as manganese are simultaneously assembled. It was found that by using them together, it is possible to obtain a catalytic combustor with a high preheating temperature even with a low preheating temperature. That is, the object is achieved by placing a low temperature ignitable catalyst body mainly containing a noble metal oxide on the upstream side of the fuel gas flow and a high temperature heat resistant catalyst body mainly containing a transition metal oxide downstream thereof. ..

 Further, by providing a porous solid at the outlet end of the catalyst body, the burning rate can be increased and the unburned content can be reduced.

 (Example) Hereinafter, the Example of this invention is described with reference to drawings. FIG. 1 is a sectional view showing an embodiment thereof. A heat insulating material 2 is provided on an inner surface of a part of the flow path 1 having a cylindrical cross section, and an upstream catalyst body 31 and a downstream catalyst medium 32 having a honeycomb structure are provided inside the heat insulation material 2 and a flow of a combustible gas. In addition to being provided at two locations along the direction 5, a gap (catalyst boundary) 8 is provided between the upstream side catalyst body 31 and the downstream side catalyst body 32, and the intermediate porous solid 71 is provided in the gap 8. Further, a porous solid 72 is provided on the downstream side (outlet side) of the catalyst body 32.

 As the porous solids 71 and 72, a heat-resistant ceramic material such as aluminum is used, and the porosity is large, and the solid and the space of the porous solid are configured to be substantially uniform at a porosity of about 80% to 95%. When converted to the equivalent mesh, the mesh size is about 13 to 20 mesh.

 The structure of the catalyst bodies 31 and 32 is, as shown in the perspective view of FIG. 2, a cylindrical shape around the outer periphery of a honeycomb structure having a honeycomb structure unit 9 having a large number of lattice spaces 91 in a multi-stage stack structure. The material surrounded by the outer wall 11 is made of a heat resistant material such as ceramics made of alumina.

 In the honeycomb structure unit 9, the length l in the flow direction of this one step is a value that is sufficiently smaller than the outer diameter D and is about one-tenth, and the catalyst body 31 and the catalyst body 31 32 are configured.

 The catalyst body 31 having such a structure carries a catalyst mainly composed of a noble metal oxide such as palladium. The side catalyst body 32 carries a catalyst mainly composed of a transition metal oxide such as manganese.

 The catalyst bodies 31 and 32 are formed by stacking a plurality of honeycomb structure units 9 each having a length l so that the length in the fuel gas flowing direction becomes the length L as shown in FIG.

 In the above-described embodiment, the combustible gas can be burned at a low preheating temperature, the upstream catalyst body 31 determines the catalyst amount so that the combustion temperature is not so high, and the catalyst body 31 and the catalyst body 31 Since the porous solid 71 is provided between 32 to prevent the influence of the radiation on the downstream side, the active life of the catalyst body 31 is extended.

 The temperature distribution curve 12 of each layer in FIG. 1 is as shown in FIG. As is clear from this figure, the combustible gas temperature is preheated to 420 ° C. and flows in, and combustion is performed at about 500 ° C. at the inlet end 4 of the upstream side catalytic body 31 and inside the catalytic body 31 at the outlet of the catalytic body 31. The temperature rises up to 700 ℃ as much as it is done, and it goes out.

 Radiation from the large downstream side between the inlet and the outlet of the next porous solid 71 reaches the inlet 700 ° C. and the outlet 820 ° C. due to the temperature difference across the porous solid 71. The unburned component is catalytically burned inside the downstream catalyst body 32, and rises to 820 ° C. at the inlet of the catalyst body 32, to 1020 ° C. at the outlet end 6, and further rises to 1060 ° C. in the outlet porous solid 72 and flows out. ..

 This temperature distribution curve 12 is an example of the case where the mixing ratio of the combustible gas and air is a certain amount, but the temperature distribution from the inlet end 4 to the outlet end 6 is the same regardless of the amount. Is.

 When the catalyst body 31 and the catalyst body 32 are connected and installed without providing the porous solid 71 between the catalyst bodies 31 and 32 as in the embodiment, the temperature distribution as shown in FIG. This is not possible, and the temperature rise at the inlet of the catalyst body 3 is much larger than that in FIG. 3, and the temperature rises to about 1000 ° C. at the outlet of the catalyst body 3. Compared with this conventional method, in the present invention, the upstream catalyst body 31 can maintain a relatively low temperature, and thus the palladium catalyst can maintain the activity for a long period of time. Further, since the downstream side catalyst body 32 can maintain a predetermined combustion temperature, the combustion rate is close to complete combustion and almost no unburned part remains.

 Further, the combustion of the catalyst body 32 is promoted by the porous solid 72 provided on the downstream side of the catalyst body 32, and the unburned content is further reduced.

 [Effects of the Invention] According to the present invention described above, the following effects can be obtained. (1) Since the catalyst medium mainly composed of noble metal oxide and the catalyst body mainly composed of transition metal oxide can be usually used at temperatures suitable for their respective performances, the conventional method can be used. Compared with a mixture gas of air and combustible gas, it can be burned even if it is preheated to a relatively low temperature, and each catalytic combustion can be effectively used with a very small amount of unburned gas. ..

(2) The catalyst body composed mainly of a noble metal oxide, which is arranged on the upstream side in the fuel gas flow direction, can be adjusted so as to maintain a comparatively low temperature, so that the catalyst activity can be maintained for a long period of time. It is possible to extend the service life by holding it for a long time.

[Brief description of drawings]

 1 is a sectional view showing an embodiment of the catalytic combustion apparatus of the present invention, FIG. 2 is a perspective view showing an example of the constitution of the catalyst body of FIG. 1, and FIG. 3 is a flow chart of the embodiment of FIG. FIG. 4 is a diagram showing an example of a temperature distribution in the direction, and FIG. 4 is a sectional view showing an example of a conventional catalyst combustion device. DESCRIPTION OF SYMBOLS 1 ... Flow path, 2 ... Heat insulating material, 31 ... Palladium type catalyst body, 32 ... Manganese type catalyst body, 5 ... Combustible gas flow, 71 ... Intermediate porous solid, 72 ... Exit porous solid, 9 ... Honeycomb structure Unit, 91 ... Keiko space.

Claims (2)

[Claims] 1. An outer surface is covered with a cylindrical wall, and a multilayer lattice honeycomb structure is made of a heat-resistant material inside the wall, and the catalyst body having an oxidation catalyst supported on the surface of the structure is oxidized and burned. In an apparatus for supplying both fuel and combustion air for catalytic combustion, a first catalytic body carrying a catalyst mainly composed of a noble metal oxide and a second catalytic body carrying a catalyst mainly composed of a transition metal oxide. A medium is used, the first catalyst body is provided on the upstream side of the flow of fuel and air, and a porous solid layer made of a heat-resistant material is provided on the downstream side of the first catalyst body. A catalytic combustion device, wherein the second catalyst body is provided on the downstream side of the layer. 2. An outer surface is covered with a cylindrical wall, and a multilayer lattice honeycomb structure is made of a heat-resistant material inside the wall, and a catalyst body having an oxidation catalyst supported on the surface of the structure is oxidatively burned. In an apparatus for supplying both fuel and combustion air for catalytic combustion, a first catalytic body carrying a catalyst mainly composed of a noble metal oxide and a second catalytic body carrying a catalyst mainly composed of a transition metal oxide. A medium is used, the first catalyst body is provided on the upstream side of the flow of fuel and air, and a porous solid layer made of a heat-resistant material is provided on the downstream side of the first catalyst body. A catalytic combustion apparatus, wherein the second catalyst body is provided on the downstream side of the layer, and a porous solid layer made of a heat-resistant material is provided at the final stage of the downstream side outlet of the second catalyst body.