JPH0156328B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field> The present invention relates to a combustion catalyst system for lower hydrocarbon fuel and a combustion method using the same. Specifically, lower hydrocarbon fuels having 1 to 4 carbon atoms such as methane, ethane, propane, and butane, especially flame-retardant methane or natural gas containing methane as a main component, are catalytically burned, and nitrogen oxides (hereinafter referred to as , NOx), carbon monoxide (hereinafter referred to as CO), unburned hydrocarbons (hereinafter referred to as UHC),
The present invention relates to a catalyst system for obtaining a combustion gas that does not substantially contain harmful components such as catalytic converters, etc., and for using its calorific value as various energy sources, and a combustion method using the same. <Prior Art> A catalytic combustion system is known in which a dilute gas mixture of fuel mixed with air at a low concentration that does not fall within the combustible range is introduced into a catalyst layer and catalytically combusted on the catalyst to obtain high-temperature combustion gas. Furthermore, when using such a catalytic combustion system to obtain combustion gas at a temperature of, for example, 600°C to 1500°C,
For example, even if air is used as an oxygen source, little or no NOx is generated, and CO,
It is also well known that it can be obtained without substantially containing UHC. Various systems have been proposed that utilize this clean, high-temperature combustion gas to generate heat or power, and general industrial exhaust gas treatment and thermal power recovery systems have already been put into practical use. In addition, in recent years, in response to increasing NOx regulations, research has begun to be conducted on the use of this high-temperature combustion gas as a primary power source such as gas turbines for power generation. When used for these purposes, the combustion gases are 6
It is normal to reach a high temperature of 1000 to 1300 degrees Celsius under ~15 atmospheres, and there is a trend towards higher temperatures and pressures to improve the efficiency of gas turbines. When a catalyst is used under such conditions, the catalytic performance of a normal catalyst rapidly deteriorates due to the high temperature, and in the worst case scenario, the catalyst carrier melts down and scatters, damaging turbine blades, etc. there is a possibility. As a combustion method that avoids catalyst deterioration and damage as described above and achieves the same purpose, fuel is catalytically burned in the catalyst layer, the gas temperature is raised to a temperature that induces secondary gas phase combustion, and then the catalyst layer is heated to a temperature that induces secondary gas phase combustion. The remaining unburned fuel is burned in a secondary gas phase at the rear, or if necessary, secondary fuel is introduced and the remaining unburned fuel and newly added secondary fuel are burned in a secondary gas phase. A combustion method has been discovered that produces clean combustion gas at or above the desired temperature. In this case, the purpose of combustion in the catalyst layer is to raise the gas temperature to a temperature that induces secondary gas phase combustion, and it is not necessarily necessary to completely burn the gas in the catalyst layer, but to induce secondary gas phase combustion. If the gas temperature reaches a temperature higher than Rather, it is preferable that there is a large amount of remaining unburned fuel. The entire amount of fuel that can achieve the desired temperature may be introduced into the catalyst layer, a portion of which is combusted in the catalyst layer to raise the temperature, and then the remaining unburned fuel may be burned in the secondary gas phase. A portion may be left behind and introduced from the rear of the catalyst layer as a secondary fuel to be combined with the remaining unburned fuel and subjected to secondary gas phase combustion. In this case, it is possible to avoid setting the temperature of the catalyst layer higher than necessary, and it is possible to avoid deterioration and damage to the catalyst, which is more preferable. The temperature required to induce secondary gas-phase combustion here is determined by the type of fuel, residual fuel concentration (theoretical adiabatic combustion gas temperature), linear velocity, etc., but it varies widely depending on the type of fuel. . In other words, in the case of easily flammable fuels such as propane and diesel oil, a temperature of about 700°C is sufficient under normal usage conditions, but when using flame-retardant methane or natural gas whose main component is methane, In this case, a high temperature of 750 to 1000°C is required, although it varies depending on the usage conditions. <Object of the Invention> Therefore, an object of the present invention is to provide a novel catalyst system for combustion of lower hydrocarbon fuel. Another object of the present invention is to catalytically burn a lower hydrocarbon fuel, particularly flame-retardant methane or natural gas containing methane as a main component, to obtain a combustion gas that does not substantially contain harmful components, and to reduce its calorific value. The object of the present invention is to provide a catalyst system for use as a variety of energy sources and a combustion method using the same. Still another object of the present invention is to catalyze methane, which is said to be relatively flame-retardant among hydrocarbons, or a natural gas fuel mainly composed of methane, from normal pressure to high pressure and at high linear velocity. Ignition at low temperature,
The temperature is raised to a temperature sufficient to induce secondary gas-phase combustion, and then secondary fuel is introduced as necessary to combust the remaining unburned fuel and secondary fuel in the gas phase to achieve the desired purpose. It is an object of the present invention to provide a catalyst system suitable for use in a combustion system that raises the temperature to a high temperature or higher, and a combustion method using the same. Another object of the present invention is to ignite flame-retardant fuel, mainly methane, at a high linear velocity and under pressure at as low a temperature as possible, and to raise the combustion gas temperature to a temperature of 750 to 1000 degrees Celsius. It is an object of the present invention to provide a catalyst system having low pressure loss and durability, and a combustion method using the same. <Means of the Invention> These objects aim to provide a flow of a flammable gas mixture containing lower hydrocarbons and molecular oxygen.
A pre-catalyst layer filled with a catalyst containing an active ingredient made of palladium, platinum and nickel oxide on the gas inlet side, and an active ingredient made of platinum and an active ingredient made of platinum and palladium on the outlet side. A catalyst comprising a rear catalyst layer filled with a catalyst containing one selected from the group, and an active component comprising palladium and nickel oxide between the front and rear catalyst layers. The combustible mixed gas is supplied to the catalyst system, and at least a part of the lower hydrocarbons in the mixed gas is transferred to the catalyst. This is achieved by providing a method of combustion of lower hydrocarbon fuels which comprises heating the combustion gases to a temperature at which they are subjected to catalytic combustion in a system to induce secondary gas phase combustion. The catalyst system according to the present invention essentially divides the catalyst into three layers: a catalyst that can be ignited at a relatively low temperature is used in the front layer and the middle layer, and a catalyst is used in the rear layer.
It is made up of optimally designed high-temperature combustion catalysts that can raise the combustion gas temperature to 750 to 1000℃, and the catalyst used in the front layer consists of palladium, platinum, and nickel oxide as active ingredients. The catalyst used in the middle stage is a catalyst system consisting of palladium and nickel oxide as active components, and the catalyst used in the latter stage is a catalyst system consisting of platinum or platinum and palladium as active components, and the combustion method is a catalyst system consisting of palladium and nickel oxide. This is done so that the combustion temperature does not exceed 1000℃. Catalysts containing palladium as the main active component are known to have particularly excellent low-temperature ignition of methane, as well as excellent heat resistance at high temperatures of around 1000°C. However, when a conventional catalyst containing palladium as an active ingredient is used for the purpose of the present invention, the palladium is oxidized and loses its methane ignition performance because it is exposed to high concentrations of oxygen at temperatures below 500°C near the entrance of the catalyst layer. On the other hand, in the high temperature region near the outlet of the catalyst layer, the combustion reaction by the catalyst is suppressed, probably due to a change in the oxidation state of palladium, and the combustion gas temperature is effectively 750℃.
The drawback is that it cannot rise to higher temperatures. In contrast, according to the present invention, by coexisting a small amount of platinum in the front stage catalyst near the catalyst system inlet, the decline in methane ignition performance due to palladium oxidation is prevented, and low-temperature ignition performance is maintained for a long period of time. Furthermore, we have discovered that by effectively using the middle layer catalyst, we can stably raise the combustion gas temperature to 600 to 750℃ at high linear velocity and under pressure. It was discovered that the presence of platinum further promotes combustion, allowing the combustion gases to reach temperatures of 750-1000°C. As a result, the catalyst layer as a whole is capable of igniting methane or natural gas fuel containing methane as its main component at high linear velocity, under pressure, and at low temperatures, and raising the combustion gas to a temperature of 750 to 1000 degrees Celsius. Moreover, it has become possible to maintain this performance for a long time. In the present invention, it is preferable to coexist nickel oxide in the catalyst of the front catalyst layer. In this case, the presence of nickel improves the low-temperature ignition performance of methane, which is a flame-retardant fuel, and the oxidation of nickel Since oxygen is stably supplied to palladium as a substance, the combustion gas temperature can be raised to 650 to 900°C even at high linear velocity and under pressure. Further, it is also preferable that palladium be present as an active component in the catalyst of the latter catalyst layer. In this case, it was discovered that the presence of palladium prevents platinum from being oxidized to PtO ₂ and sublimating even at high temperatures of 1000°C. In the present invention, a three-stage system is provided in which a middle catalyst layer made of a catalyst containing palladium and nickel oxide as active components is provided between the above-mentioned front catalyst layer and rear catalyst layer. It was found that this is an excellent combustion catalyst system. In particular, the first half of the catalyst system has a two-stage structure, where the first half is a catalyst layer containing the aforementioned palladium-platinum-nickel oxide as an active component, and the second half is a catalyst layer containing palladium-nickel oxide as an active component. layer, the combustion activity of the first half catalyst system is improved even under high linear velocity and pressurized conditions, and the combustion function of the second stage catalyst, which has platinum or platinum-palladium as the active ingredient, is smoothly exerted. It became possible to force him to do so. In this case, in the first half of the first half catalyst system,
The temperature is raised to a temperature in the range of 500 to 800℃, and the temperature in the second half of the first half catalyst system (middle catalyst layer) is 650 to 800℃.
In the temperature range of 900℃ and in the downstream catalyst layer
Combustion activity is maintained at a high level by respectively increasing the temperature in the range of 750-1000°C. This catalyst system is characterized by a three-stage structure that takes advantage of the characteristics of each precious metal or combines them. In other words, this catalyst system ignites at a low temperature of 300 to 400℃, and
It has a combustion activity to achieve a combustion gas temperature of ℃,
It is also necessary to have heat resistance at 1000°C or higher. However, as described above, palladium alone does not lose its ignition performance as the combustion progresses, and due to its characteristics, the combustion gas temperature does not substantially rise to a high temperature of 750° C. or higher. Even a palladium-nickel oxide catalyst loses its ignition performance in the same way as palladium alone. In addition, when platinum alone is used to burn methane or LNG, it is impossible to ignite at 300 to 400℃, and an ignition temperature of 500℃ or higher is essentially required, but the combustion activity is excellent, especially at high linear speeds. , has sufficient combustion activity under pressurized combustion conditions.
In addition, palladium-platinum-nickel oxide or palladium-platinum catalysts have sufficient ignition performance; I can't. As described above, the single-stage structure in which the entire catalyst layer has the same composition has its own drawbacks, and cannot be used as a practical catalyst, especially under pressurized combustion conditions, and is not preferred. In the present invention, the catalysts for the front layer, middle layer, and rear layer may be prepared separately, and both catalysts may be directly connected or installed with a space between them, or they may be installed in the inlet portion of an integrated catalyst. A complete catalyst may be obtained by supporting the front stage catalyst in the intermediate part, the middle stage catalyst in the outlet part, and the latter stage catalyst in the outlet part. Although a pellet type catalyst can be used, a monolith type catalyst is preferred for the purpose of reducing pressure loss. Any monolith carrier commonly used in the field can be used, especially cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate,
Heat-resistant ceramic materials such as aluminum titanate, petalite, spodium, aluminosilicate, magnesium silicate, zirconia spinel, zircon-mullite, silicon carbide, and silicon nitride, and metal materials such as Kanthal and Feclaroy are used. The cell size of the monolithic carrier is preferably large as long as the combustion efficiency is not reduced, and each catalyst layer may have the same cell size or a combination of different cell sizes. ~400 cells are used. The total catalyst layer length varies depending on the inlet linear velocity used, but is usually 50 to 50 mm due to the need to reduce pressure loss.
500 mm is adopted, and the length of each layer of the front layer, middle layer, and rear layer is also optimally selected depending on the usage conditions such as inlet linear velocity and inlet temperature, but usually 20 to 250 mm is adopted for each layer. The catalyst used in the first layer is usually a monolithic carrier coated with an active refractory metal oxide such as alumina, silica-alumina, magnesia, titania, zirconia, or silica-magnesia, preferably alumina, titania, or zirconia. do. The amount of oxide coated is 5 to 50% by weight, preferably 10 to 30% by weight, based on the finished catalyst. Alumina is particularly preferred, and is further stabilized by adding an alkaline earth metal oxide such as barium or strontium, a rare earth metal oxide such as lanthanum, cerium, neodymium or praseodymium, or silicon, preferably a rare earth metal oxide. preferable.
The amount added is 2 to 20% by weight, preferably 5 to 15% by weight, based on the oxide. Thereafter, the active principal components of palladium, platinum and nickel are impregnated and catalyzed in the form of water-soluble or alcohol-soluble compounds. Alternatively, the active main component can be supported on an active, refractory metal oxide in advance and then catalyzed by coating it on a monolithic carrier. The active ingredient, platinum, can also be supported together with the active refractory metal oxide in the form of platinum black having an average particle size of 0.01 to 5 microns. Examples of water-soluble salts include nitrates, sulfates, phosphates, halides, and dinitrodiamino salts. Examples include palladium nitrate, palladium chloride, dinitrodiaminoplatinum, chloroplatinic acid, nickel nitrate, nickel chloride, etc. A carrier is impregnated with an aqueous solution of these and heated at 400 to 1000°C.
It is preferably obtained by firing at a temperature of 600 to 900°C for 1 to 24 hours, preferably 2 to 6 hours. The amount of active components supported in the catalyst used in the first layer is 0.5 to 15% by weight as palladium, preferably 2 to 10% by weight as palladium, and 0.1 to 10% as platinum per finished catalyst.
10% by weight, preferably 0.2-5% by weight, and 0.1-20% by weight as NiO for nickel, preferably 1% by weight.
A range of ~10% by weight is suitable, and the weight ratio of platinum to palladium is 0.01 to 1, preferably
It ranges from 0.1 to 0.6. The catalyst forming the middle layer is also prepared in the same manner as above. The palladium/nickel ratio in the catalyst layer containing palladium-nickel oxide as an active ingredient, which forms the front and middle layers, is set at a Pd/NiO weight ratio of 0.001 to 20, preferably 0.1 to 5. Used together. Similarly, the catalyst used in the latter layer can be catalyzed by supporting platinum or platinum and palladium. The amount of active component supported is from 0.1 to 15% by weight as platinum per finished catalyst, preferably from 0.2 to 10% by weight, and if palladium is added, from 0.1 to 15% by weight as palladium, preferably 0.2%.
A range of 10% by weight is preferred, and in the case of catalysts containing palladium and platinum as active components, the weight ratio of platinum to palladium is in the range 0.01 to 20, preferably 0.2 to 10. If platinum is the only active ingredient, the catalyst will be too active and the temperature in the catalyst layer will rise to over 1000°C, potentially causing deactivation due to platinum sublimation. Avoid this and reduce the catalyst layer temperature.
In order to maintain the temperature below 1000℃, it is particularly preferable to use coarsened platinum particles such as platinum black, other methods that reduce the amount of platinum supported, and calcination of the finished catalyst at a high temperature exceeding 1000℃ before use. Preferable methods include a method in which the catalyst cell size and layer length are optimally selected. Further, by coexisting palladium with platinum, it is possible to prevent sublimation of platinum, and it is also possible to control the combustion activity of platinum. These can be optimally selected depending on the usage conditions, that is, the type of fuel, temperature (theoretical adiabatic combustion gas temperature), linear velocity, pressurization conditions, etc. Pressurization conditions can range from normal pressure to 25 atm, but preferably 6 to 15 atm. Regarding fuel concentration, if the lower hydrocarbon fuel is methane,
1.51 to 4.75% by volume, preferably 2.37 to 4.31% by volume of primary fuel, depending on the temperature of the mixed gas introduced into the catalyst system, up to a temperature at which secondary gas phase combustion is induced by the primary fuel. 0 to 3.24 when further supplying secondary fuel to heated combustion gas
% by volume, preferably 0.44-2.38 % by volume. Furthermore, the linear speed is 7 to 40 m/s, preferably
The speed is 10 to 30 m/sec. That is, if the speed is less than 7 m/sec, a flashback phenomenon may occur, while if the speed exceeds 40 m/sec, excessive blow-by of the fuel will occur, resulting in insufficient combustion. The fuel used in the combustion system using the catalyst of the present invention is methane or a fuel containing methane as a main component. A typical example is natural gas. Natural gas contains approximately 80% or more methane, although the composition ratio varies slightly depending on the region of production. Further, fermented methane from activated sludge treatment and low-calorie methane gas from coal gasification are also fuels used in the present invention. Also more flammable ethane,
Propane and butane can also be used, and of course light oil and the like can also be used. The catalyst system of the present invention or the combustion method using the catalyst system can be optimally incorporated into a gas turbine system for power generation as described above, but it can also be incorporated into a power generation boiler, a heat recovery boiler, a gas engine, etc. It is used to efficiently recover heat and power through post-processing of city gas, city gas heating, etc. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these Examples. Example 1 Diameter with 200 cells/in2 aperture
A cordierite honeycomb carrier measuring 25.4 mm and 50 mm in length was coated with a mixed slurry of alumina powder and nickel oxide containing 5% by weight of lanthanum oxide, dried, and then fired at 700°C in air. 19 as lanthanum oxide-containing alumina per finished catalyst
6% by weight of nickel oxide was coated and supported. Next, this was immersed in an aqueous solution containing palladium nitrate and dinitrodiaminoplatinum, dried, and calcined in air at 900°C for 5 hours to obtain a finished catalyst.
A completed catalyst was obtained by supporting 4.0% by weight of palladium and 0.8% by weight of platinum. Example 2 As in Example 1, 6% by weight of nickel oxide and palladium were added per finished catalyst.
A completed catalyst was obtained by supporting 1.2% by weight of platinum and 0.3% by weight of platinum. Example 3 A slurry of alumina powder containing 7% by weight of lanthanum oxide and 3% by weight of neodymium oxide was coated on the same carrier as in Example 1, and calcined in air at 800°C to achieve oxidation per finished catalyst. A 30% by weight alumina containing lanthanum and neodymium oxide was supported and coated. Next, this carrier is immersed in an aqueous solution containing palladium nitrate and nickel nitrate, dried, and then calcined in air at 700°C for 5 hours to obtain palladium per finished catalyst.
4.7% by weight and 13.3% by weight as nickel oxide
A completed catalyst was obtained by supporting the . Example 4 Diameter with 100 cells/in2 aperture
25.4 mm, length 50 mm mullite honeycomb carrier, 2
A mixed slurry of alumina powder and nickel oxide containing lanthanum oxide and 5 weight % cerium oxide was coated and calcined in air at 900°C to produce 15 weight lanthanum oxide and cerium oxide containing alumina per finished catalyst. %, nickel oxide 3.7
% by weight was supported. Next, this was immersed in an aqueous solution containing palladium nitrate, dried, and calcined in air at 800° C. for 4 hours, so that 2.5% by weight of palladium was supported on the finished catalyst to obtain a finished catalyst. Example 5 As in Example 3, per finished catalyst,
A finished catalyst was obtained in which 2.7% by weight of palladium and 13.3% by weight of nickel oxide were supported. Example 6 21% by weight of lanthanum oxide-containing alumina was prepared in the same manner as in Example 1 except that nickel oxide was not included.
was coated and supported. Next, this was immersed in an aqueous solution containing chloroplatinic acid in the same manner as in Example 1, so that 2.0% by weight of platinum was supported on the finished catalyst to obtain a finished catalyst. Example 7 Diameter with 200 cells/in2 aperture
A 25.4 mm aluminum titanate honeycomb carrier was coated with a slurry of alumina powder containing 8% by weight lanthanum oxide and 2% by weight silica and platinum black powder having an average particle size of 1 micron, and then dried. Afterwards, it is calcined in air at 900℃ for 2 hours to produce alumina powder containing lanthanum oxide and silicon dioxide per finished catalyst.
A finished catalyst was obtained with a loading of 18% by weight and 2.2% by weight as platinum. Example 8 A finished catalyst was obtained in the same manner as in Example 6 except that the amount of platinum black supported was 0.6% by weight. Example 9 In the same manner as in Example 3 except that it did not contain nickel oxide, the catalyst was immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid to obtain palladium per finished catalyst.
A completed catalyst was obtained by supporting 3.6% by weight of platinum and 1.8% by weight of platinum. Comparative Example 1 A finished catalyst was obtained in the same manner as in Example 3 except that it did not contain nickel. Example 10 Using a sufficiently warmed cylindrical combustor, from the upstream side, the catalyst obtained in Example 1 was placed in the first layer, the catalyst obtained in Example 3 was placed in the middle layer, and the catalyst obtained in Example 6 was placed in the second layer. The catalyst was charged at 350°C at the inlet temperature.
A methane-air mixture gas containing methane by volume % was introduced at 167 Nm ³ per hour under a pressure of 10 atmospheres, and the combustion efficiency and catalyst bed outlet temperature were measured. In this case, the catalyst inlet linear velocity was about 30 m/sec. As a result, the combustion efficiency was approximately 74%, and the catalyst layer outlet temperature was approximately
It was 850℃. Next, when the methane concentration was increased to 4.1% by volume, the combustion efficiency became 100%, resulting in clean combustion gas containing virtually no UHC, CO, or NOx.
In this case, the temperature at a point 100mm behind the catalyst layer is approximately 1300.
℃, but the catalyst layer outlet temperature was approximately 900℃. Subsequently, a similar combustion experiment was conducted by introducing methane equivalent to 3% by volume from upstream of the catalyst bed and the remaining methane equivalent to 1.1% by volume from 30 mm behind the outlet of the catalyst bed. As a result, the catalyst bed outlet temperature was approximately 895℃,
Clean combustion gas of approximately 1300℃ was obtained. This performance was maintained for 1000 hours. Example 11 Using the catalyst shown in Table 1 in the same manner as in Example 10, methane equivalent to 3% by volume was introduced from upstream of the catalyst layer, and methane equivalent to the remaining 1.1% by volume was introduced from 30 mm behind the outlet of the catalyst layer. and conducted combustion experiments. The results are shown in Table 1. Using the catalyst system according to the present invention, clean combustion gas of approximately 1300°C can be obtained even though the catalyst bed temperature is maintained below 1000°C, which does not cause a decrease in activity. On the other hand, the catalyst system using the catalyst of Comparative Example 1 in the first stage rapidly became unable to ignite. In addition, in a catalyst system using the catalysts of Example 6 in the front stage, Example 3 in the middle stage, and Example 9 in the rear stage, ignition did not occur in the front stage catalyst, but some ignition occurred in the middle stage catalyst and the rear stage catalyst.
The outlet temperature is 670℃, and Comparative Example 1 is added later.
In the catalyst system using the above catalyst, combustion did not occur in the latter stage, and the outlet temperature was 680°C, and in both cases, secondary combustion was not induced behind the catalyst layer.

[Table] Example 12 In the same manner as in Example 10, the catalyst obtained in Example 2 was filled in the first stage, the catalyst obtained in Example 5 in the middle stage, and the catalyst obtained in Example 8 in the second stage. temperature 300
A combustion experiment was conducted by introducing propane equivalent to 1.3% at ℃ from upstream of the catalyst layer and the remaining 0.5 equivalent from 30 mm behind the outlet of the catalyst layer. As a result, the catalyst layer outlet temperature was 960℃,
A clean combustion gas of approximately 1300°C containing virtually no UHC, CO, and NOx was obtained. This performance was maintained for 1000 hours.

Claims (1)

[Claims] 1. Contains an active component consisting of palladium, platinum, and nickel oxide on the gas inlet side with respect to a flow of a flammable mixed gas containing a lower hydrocarbon having 1 to 4 carbon atoms and molecular oxygen. and a catalyst containing one selected from the group consisting of an active ingredient made of platinum and an active ingredient made of platinum and palladium on the outlet side. and a middle catalyst layer filled with a catalyst containing an active component of palladium and nickel oxide between the front and rear catalyst layers. Catalyst system for combustion of lower hydrocarbon fuels. 2 Each active ingredient is dispersed and supported on a monolithic carrier coated with at least one refractory oxide selected from the group consisting of alumina, silica-alumina, magnesia, titania, zirconia, and silica-magnesia. The catalyst system according to claim 1, characterized in that: 3 A catalyst containing an active component consisting of palladium, platinum, and nickel oxide is packed on the gas inlet side for a flow of a combustible mixed gas containing a lower hydrocarbon having 1 to 4 carbon atoms and molecular oxygen. and a latter catalyst layer filled with a catalyst containing one selected from the group consisting of an active component made of platinum and an active component made of platinum and palladium on the outlet side. The combustible mixed gas is fed into a combustion catalyst system comprising a middle catalyst layer filled with a catalyst containing an active component of palladium and nickel oxide between the front and rear catalyst layers. and catalytically combusting at least a portion of the lower hydrocarbons in the mixed gas in the catalyst system to raise the temperature of the combustion gas to a temperature at which secondary gas phase combustion is induced. How to burn fuel.