JPS6352283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst system for catalytically burning methane-based fuel and a combustion method using the same. Specifically, the present invention catalytically burns flame-retardant methane or natural gas fuel mainly composed of methane on a catalyst to produce nitrogen oxides (hereinafter referred to as NOx), carbon monoxide (hereinafter referred to as CO), and nitrogen oxides. The present invention provides a catalyst system and a combustion method using the same for obtaining combustion gas that does not substantially contain harmful components such as combustion hydrocarbons (hereinafter referred to as UHC) and using the heat value as various energy sources. . More specifically, the present invention uses a catalyst to ignite and burn methane, which is said to be relatively difficult among hydrocarbons, or a natural gas fuel containing methane as a main component at a low temperature under high linear velocity. The temperature is raised to a temperature sufficient to induce gas-phase combustion, and then secondary fuel is introduced as necessary to cause gas-phase combustion of the remaining unburned fuel and secondary fuel to reach the desired temperature. The present invention provides a catalyst system that is suitably used in combustion systems that raise temperatures to higher temperatures, and a combustion method using the catalyst system. A catalytic combustion system is known in which a dilute gas mixture in which fuel is 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, little or no NOx is generated even if air is used as the oxygen source, and CO, UHC, etc.
It is also well known that it can be obtained without substantially containing it. 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. It has only been put into practical use in the temperature range. 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
It is normal to reach a high temperature of 1000 to 1300 degrees Celsius, and there is a tendency to raise the temperature even higher 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, the catalyst carrier melts down and scatters.
There is a possibility of damaging the turbine blades. As a combustion method that avoids catalyst deterioration and damage as described above and achieves the same purpose, a part of the fuel is combusted in the catalyst layer, the gas temperature is raised to a temperature that induces secondary gas phase combustion, and then Perform secondary gas-phase combustion of the remaining unburned fuel behind the catalyst layer, or introduce secondary fuel if necessary to perform secondary combustion of the remaining unburned fuel and newly added secondary gas-phase combustion. A combustion method has been discovered that can produce clean combustion gas at or above the desired temperature. By using this method, it is possible to minimize NOx, which is generated in large amounts in the usual flame combustion method, because the flame combustion area can be made as small as possible. 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 residual unburned fuel because gas phase combustion is more likely to occur. 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. This method is more preferable since it is possible to avoid raising the temperature of the catalyst layer to an unnecessarily high temperature, thereby avoiding deterioration and damage to the catalyst. The temperature required to induce secondary gas phase combustion is
It is determined by the type of fuel, residual fuel concentration (theoretical adiabatic combustion gas temperature), linear velocity, etc., and 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 some cases, high temperatures of 750 to 1000°C are required, although this varies depending on the conditions of use. Due to recent fuel circumstances, the fuel used for this purpose is mainly methane or natural gas containing methane as its main component, and the present invention ignites this flame-retardant fuel at a high linear velocity and at as low a temperature as possible. The purpose of the present invention is to provide a catalyst that can raise the temperature of combustion gas to a temperature of 750 to 1000°C. As a catalyst suitably used for this purpose, a noble metal catalyst is suitable, and a catalyst containing palladium as an active component is particularly desirable. Catalysts containing palladium as an active component are particularly excellent in low-temperature ignition of methane, and also have excellent heat resistance of about 1000°C. However, when a catalyst containing palladium as an active ingredient is used for the purpose of the present invention, the palladium is oxidized and loses methane ignition performance because it is exposed to high concentrations of oxygen at temperatures below 500°C near the inlet of the catalyst layer. On the other hand, the temperature near the exit of the catalyst layer is high, and the combustion reaction by the catalyst is suppressed, probably due to a change in the oxidation state of palladium, and the temperature of the combustion gas does not rise above 750℃, which is a drawback. I discovered that. The present inventors have focused on the excellent characteristics of a catalyst containing palladium as an active ingredient, and have completed the present invention as a result of intensive research aimed at overcoming the drawbacks of conventional catalysts. That is, the catalyst system according to the present invention includes a first layer catalyst having excellent low-temperature ignitability which is made of palladium and platinum as active ingredients, a second layer catalyst which is made of platinum as an active ingredient, and then a second layer catalyst which is made of platinum as an active ingredient. Alternatively, it is formed by optimally combining a third layer catalyst made of palladium and platinum. According to the invention, the first
The presence of a small amount of platinum in the layered catalyst prevents the deterioration of methane ignition performance due to palladium oxidation, and maintains low-temperature ignition performance for a long time.
The temperature of the combustion gas can be raised to 700-800℃, and then the temperature of the combustion gas can be raised to 750-900℃ by the second layer catalyst containing platinum as an active ingredient, which changes the oxidation state of palladium. It is carried to the third layer avoiding the temperature range where combustion is suppressed, which is thought to be caused by. Furthermore, combustion is promoted by the third layer catalyst with excellent heat resistance, and the combustion gas is reduced to 800 to 1000
They discovered that it is now possible to reach temperatures of 10°F. As a result, the catalyst layer as a whole can ignite methane or natural gas fuel with methane as its main component at low temperatures, raise the combustion gas to a temperature of 800 to 1000 degrees Celsius, and maintain its performance for a long time. This made it possible to maintain it for a long period of time. Each layer of catalyst may be prepared separately, and each catalyst may be directly connected or installed with a space between them, or a complete catalyst may be obtained by supporting each layer of catalyst in an integrated catalyst. The shape of the catalyst is preferably a monolith type for the purpose of reducing pressure loss. Any monolith support commonly used in the field can be used, in particular cordierite, mullite, alpha-alumina, zirconia, titania, titanium phosphate, aluminum, titanate, betalite, spodiumen, aluminosilicate, silica. Heat-resistant ceramic materials such as magnesium oxide, 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.
500mm is adopted, and the length of each catalyst layer also depends on the inlet linear velocity.
It is optimally selected depending on usage conditions such as inlet temperature, but usually each layer has a thickness of 25 to 250 mm. The catalyst used in the first layer is usually prepared by coating the monolithic support with an active refractory metal oxide such as alumina, silica-alumina, magnesia, titania, zirconia, or silica-magnesia. Alumina or zirconia is particularly preferred;
Furthermore, alkaline earth metal oxides such as barium and strontium, lanthanum, cerium, neodymium,
Adding rare earth metal oxides such as praseodymium,
It is more preferable to use it after stabilizing it. Thereafter, the active components palladium and platinum are impregnated and catalyzed in the form of water-soluble salts. 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. Palladium is 2 to 100 g per finished catalyst,
Preferably, 5 to 50 g of platinum is supported, and the weight ratio of platinum to palladium is 0.2 to 50%, preferably
It is used by adding 0.5 to 30%. The catalyst used in the second layer can be catalyzed by supporting platinum in the same way, but in this case, the catalyst is too active and the temperature in the catalyst layer rises to over 1000℃, causing sublimation of platinum. It may cause deactivation phenomenon. In order to avoid this and keep the catalyst layer temperature below 950℃, there are two ways to reduce the amount of platinum supported.
Several methods have been discovered, including a method in which the finished catalyst is calcined at a high temperature of over 1000℃ prior to use, a method in which coarsened platinum particles such as platinum black are used, and a method in which the cell size and layer length of the catalyst are optimally selected. However, these can be optimally selected depending on the conditions of use, ie, the type of fuel, concentration (theoretical adiabatic combustion gas temperature), linear velocity, etc. In addition, the catalyst used in the third layer can be catalyzed by supporting palladium or palladium and platinum in the same manner as the catalyst used in the first layer. 200 g, preferably 5 to 100 g, and the supported amount of platinum is 0 to 20 g, preferably 0 to 10 g. Alternatively, the catalyst may be directly supported on a monolithic carrier without using the catalyst-coactive refractory metal oxide in each layer. 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. Naturally, more flammable propane, light oil, etc. can also be used. The catalyst of the present invention or the combustion system using the catalyst 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, or a combustion system that uses gas from a gas engine. It is used to efficiently recover heat and power through post-processing, 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 an alumina powder slurry containing 5% by weight of lanthanum oxide, and fired at 900°C in air to coat and support 100 g per carrier. . This was then immersed in an aqueous solution containing palladium nitrate and chloroplatinic acid, dried and heated in air at 700 °C.
Calculated at °C, per 1 carrier, as palladium
A completed catalyst was obtained by supporting 10 g of platinum and 2 g of platinum. Example 2 In the same manner as in Example 1, 100 g of alumina powder containing 5% by weight of lanthanum oxide was coated and supported on each carrier. Next, this was immersed in an aqueous solution containing chloroplatinic acid, dried, and calcined in air at 900°C to support 2 g of platinum per carrier to obtain a completed catalyst. Example 3 In the same manner as in Example 1, 150 g of alumina powder containing 7% by weight neodymium oxide was added per carrier.
It was coated. Next, in the same manner as in Example 1, 20 g of palladium and 5 g of platinum were supported per carrier to obtain a completed catalyst. Example 4 Using alumina powder containing 7% by weight lanthanum oxide and 3% by weight neodymium oxide, 120 g of the alumina powder was coated and supported on each carrier in the same manner as in Example 1. This was then immersed in an aqueous solution containing a nitric acid solution of dinitro-diaminoplatinum, dried, and left in the air.
By burning at 1150°C, 15g of platinum was supported on each carrier to obtain a completed catalyst. Example 5 25.4 diameter with 40 cells/in2 aperture
mm, 10% by weight on a mullite honeycomb carrier with a length of 15 mm
Coated with a slurry of alumina powder containing lanthanum oxide and 20% by weight cerium oxide, and exposed to air.
It was fired at 1000°C to coat and support 80 g per carrier. Next, in the same manner as in Example 4, 15 g of platinum was supported on each carrier to obtain a completed catalyst. Example 6 A honeycomb carrier similar to Example 1 was coated with a slurry of alumina powder containing 5% by weight of cerium oxide and platinum powder having an average particle size of 5 μm, dried, and heated to 900°C. By calcining the catalyst, 100 g of alumina containing 5% by weight of cerium oxide and 10 g of platinum were supported on each carrier to obtain a completed catalyst. Example 7 A complete catalyst was obtained in exactly the same manner as in Example 1 except that it did not contain platinum. Example 8 A finished catalyst was obtained in exactly the same manner as in Example 3 except that platinum was not contained. Example 9 Using a sufficiently warmed cylindrical combustor, the catalyst obtained in Example 1 was placed in the first layer on the upstream side, the catalyst obtained in Example 2 was placed in the second layer, and the example was placed in the third layer. The catalyst obtained in step 1 was filled, and a methane-air mixture gas containing 3% by volume of methane was introduced at an inlet temperature of 350° C. at 17.3 Nm ³ per hour, and the combustion efficiency and catalyst bed outlet temperature were measured. In this case, the linear velocity at the entrance of the catalyst layer was about 30 m/sec. As a result, the combustion efficiency was approximately 81%, and the catalyst layer outlet temperature was approximately 920°C. Next, when the methane concentration was increased to 4.1% by volume, the combustion efficiency was 100%, and a clean combustion gas containing virtually no unburned hydrocarbons, carbon monoxide, or nitrogen oxides was obtained. In this case, the rear of the catalyst layer
The temperature at the 100 mm point reached approximately 1300°C, but the catalyst layer outlet temperature was approximately 925°C. 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 920℃,
Clean combustion gas of approximately 1300℃ was obtained. This performance was maintained for 500 hours. Example 10 Using the catalyst shown in Table 1 in the same manner as in Example 9, 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 systems not according to the present invention, that is, the catalyst system using the catalyst of Example 3 in the second layer and the catalyst system using the catalyst of Example 8 in the first layer, both achieved the objective. Combustion temperature cannot be determined. 【table】

Claims (1)

[Claims] 1. From the inlet side for the flow of a methane-based fuel-air mixture gas, the first layer is a catalyst layer containing palladium and platinum as active components, and the second layer is a catalyst layer containing platinum as an active component. A combustion catalyst system, characterized in that the third layer is a catalyst layer containing palladium or palladium and platinum as active components. 2. The catalyst system according to claim 1, wherein each active component is dispersed and supported on a monolithic carrier coated with alumina. 3 The alumina coating layer is lanthanum, yttrium,
3. The catalyst system according to claim 2, wherein the catalyst system is stabilized by at least one oxide selected from the group consisting of cerium, samarium, neodymium and prasedym. 4 For the flow of methane-based fuel-air mixed gas, from the inlet side, the first layer is a catalyst layer containing palladium and platinum as active ingredients, the second layer is a catalyst layer containing platinum as an active ingredient, and the third layer is palladium. Alternatively, a combustion catalyst system comprising a catalyst layer containing palladium and platinum as active components is used, and only a portion of the fuel is combusted in the system to a temperature that induces secondary gas phase combustion. A combustion method characterized by raising the temperature of combustion gas to a maximum temperature. 5. The combustion method according to claim 4, wherein each active ingredient is dispersed and supported on a monolithic carrier coated with alumina. 6 The alumina coating layer is lanthanum, yttrium,
The combustion method according to claim 5, wherein the combustion method is stabilized by at least one oxide selected from the group consisting of cerium, samarium, neodymium and praseodymium. 7 Set the combustion gas temperature to 700 to 800 in the first catalyst layer.
7. The combustion method according to claim 4, 5 or 6, characterized in that the temperature is raised to 750-900°C in the second catalyst layer and 800-1000°C in the third catalyst layer. 8 With respect to the flow of methane-based fuel-air mixture gas, from the inlet side, the first layer is a catalyst layer containing palladium and platinum as active ingredients, the second layer is a catalyst layer containing platinum as an active ingredient, and the third layer is palladium. Alternatively, a combustion catalyst system comprising a catalyst layer containing palladium and platinum as active components is used, and all or part of the fuel is combusted in the system to a temperature that induces secondary gas phase combustion. A combustion method characterized by further supplying a secondary fuel to the heated gas to cause secondary gas phase combustion.