JPS6257887B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of combustion of methane or methane-based fuels such as natural gas containing methane as a main component and coal gasified low-calorie gas. To be more specific, the present invention enables complete oxidative combustion of flame-retardant methane-based fuel in catalytic combustion at a low preheating temperature and at a high linear velocity without producing nearly any nitrogen oxides (hereinafter referred to as NOx). The present invention provides a method for burning fuel in a combustion catalyst system for using the generated heat as a primary energy source for a gas turbine or the like for power generation.

BACKGROUND ART Catalytic combustion systems have been known that use lower hydrocarbons such as methane, ethane, and propane as fuel and perform a combustion reaction in a diluted state that does not fall within the combustible range to produce high-temperature gas. and using such catalysts at relatively high temperatures, e.g.
It is well known that in systems that produce combustion gas between 1000℃ and 1500℃, little or no NOx is generated even if air is used as the oxygen source. It is also widely used in collection systems. For example, Special Publication No. 52-36294, Special Publication No. 53-37485, Special Publication No. 56-501233, and
In the specification of Publication No. 501234, a high temperature gas of 800 to 1650°C is obtained using propane, butane, diesel oil, etc. as fuel and a high temperature heat resistant catalyst.
Systems have been proposed that can be used as power sources for gas turbines, etc., while systems that can be used to treat various industrial exhaust gases and
Catalytic combustion systems have also been put into practical use as power recovery systems, and have been proposed, for example, in publications such as JP-A-50-4876 and JP-A-53-34669.

However, the latter combustion catalyst system has a low linear velocity and low combustion temperature, making it insufficient for use as a primary power source, while the former system uses hydrocarbon fuel with a high carbon number, which is easy to burn. This article merely examines its practicality, and does not disclose anything about burning a flame-retardant fuel such as methane at high linear velocity and low ignition temperature. In other words, when using a fuel whose main component is flame-retardant methane, the ignition temperature requires a high ignition temperature of 500°C or higher, and a considerable proportion of the fuel is required to bring the fuel-air mixture above this ignition temperature. must be combusted using a pre-burner, resulting in increased NOx generation.

In order to solve these problems, the present inventors developed flame-retardant methane at low preheating temperature and high linear velocity.
The present invention was completed by conducting research on a method for complete oxidative combustion without producing much NOx.

That is, the present invention provides (1) a first catalyst layer containing palladium as an active component on the inlet side, followed by a second catalyst layer containing platinum as an active component, and a fuel mainly containing methane is provided thereon; A mixture of gas and molecular oxygen is introduced, and by combustion of the first catalyst layer,
The temperature is raised to 400-800℃, and then the second
A method for completely burning fuel containing mainly methane, which is characterized by raising the temperature to 700 to 1500°C by combustion in a catalyst bed.

(2) The method according to (1) above, wherein the palladium and/or platinum catalyst is supported on a monolithic carrier coated with alumina and/or zirconia.

(3) The alumina and/or zirconia coating layer is stabilized by at least one rare earth element oxide selected from the group consisting of lanthanum, cerium, yttrium, samarium, neodymium and praseodymium.
(2) The method described.

(4) A first catalyst layer containing palladium as an active ingredient is provided on the inlet side, followed by a second catalyst layer containing platinum as an active ingredient, and chromium, cobalt, terbium, lanthanum, cerium, A third catalyst layer containing as an active ingredient an oxide or composite oxide of at least one element selected from the group consisting of neodymium, praseodymium, and ythtrium is provided, and this layer contains a fuel mainly containing methane and molecular oxygen. 400 to 800 by combustion in the first catalyst layer.
The temperature is raised to 700-1000°C by combustion in the second catalyst layer, and finally the temperature is raised to 900-1000°C by combustion in the third catalyst layer.
A method for completely burning fuel containing mainly methane, which is characterized by raising the temperature to 1500℃.

The present invention will be explained in more detail below.

As is well known, catalysts containing palladium as a main active component have a low methane ignition temperature and are excellent catalysts for methane combustion. However, as a result of experiments conducted by the present inventors, when a highly concentrated methane-air mixture exceeding 1.5% by volume was introduced into the catalyst layer at a high linear velocity, it ignited at a low temperature of about 300°C;
% complete combustion was not achieved.

Furthermore, even if the amount of supported palladium was increased or the length of the catalyst layer was increased, the same results were obtained, and it was confirmed that the catalyst was not satisfactory for the purpose of the present invention.

On the other hand, a catalyst containing platinum as the main active component can completely burn methane 100% at the same time as ignition, but its ignition temperature is as high as 500°C or higher, and when used for the purpose of the present invention, pre-combustion is not possible. This results in the production of NOx.

The present inventors investigated the possibility of using a mixed catalyst of platinum and palladium in anticipation of the synergistic effect of the methane combustion characteristics of platinum and palladium as described above. It only shows the same combustion characteristics as the catalyst as a component, and in systems with a high proportion of platinum, a synergistic effect between the two is recognized, but 100%
It became clear that complete combustion could not be achieved.
Also, oxides of chromium, cobalt, terbium, lanthanum, cerium, neodymium, praseodymium, yttrium, etc., and composite oxides of these base metals, such as lanthanum-cobalt, lanthanum-cobalt-strontium, and other oxides, i.e., perovskite-type composite oxides. Although the ignition temperature of methane is as high as around 1000°C for catalysts whose active ingredients are methane, they also found that they have excellent heat resistance and can maintain their high activity even when exposed to high temperatures exceeding 1500°C. It is.

The combustion conditions for the methane-containing gas employed in the present invention are that the gas inlet linear velocity is 1 to 100 m/s, preferably 1 to 50 m/s, and the pressure is normal pressure to 30 atm, preferably normal pressure to 15 m/s. Atmospheric pressure and fuel concentration are calorific values,
Depending on the preliminary temperature and the acquisition temperature, any concentration is possible and can be varied accordingly. For example, when used in gas turbines for power generation, the preheating temperature is 300
℃, and the combustion temperature is 1200℃, the concentration of methane as a mixed gas with air will be around 3.8% by volume. Therefore, when targeting high purity methane, a range of 1.5 to 5% by volume can be adopted. In order to satisfy such combustion conditions and based on the above findings, the present inventors optimized the arrangement of each catalyst layer and the length of the catalyst layer.

The optimal length of each catalyst layer varies depending on the fuel type, concentration, preheating temperature, catalyst activity, linear velocity, etc., and cannot be specified, but in general, it is necessary to activate the palladium in the first stage. The length of the catalyst layer, which is the main component, is
400-800 depending on the heat generated by combustion in this layer.
It is preferable to keep the length as short as possible so that an outlet temperature of .degree. C. can be obtained.

This is because it is possible to reduce pressure loss by preventing activity deterioration due to excessive combustion and by shortening the total catalyst layer length.

The length of the second-stage catalyst layer, whose main active component is platinum, is preferably as long as possible from the viewpoint of combustion efficiency, but for the purpose of reducing pressure loss, it is necessary to determine the optimal layer length that can achieve 100% combustion efficiency. It should be adopted.

Furthermore, when the combustion gas temperature reaches a high temperature of 1,200 to 1,500°C, the high-temperature stability of the catalyst system can be improved by replacing part of the second-stage catalyst with a base metal oxide catalyst that is stable at high temperatures.

Each catalyst layer may be connected or a space may be provided between the catalyst layers.

The shape of the catalyst is preferably a monolith type for the purpose of reducing pressure loss. In addition, the cell size is preferably large as long as the combustion efficiency does not decrease.
Each catalyst layer may have the same cell size or may have different cell sizes.

The monolith carrier used in the present invention can be any carrier commonly used in the field, especially cordierite, mullite, α-
Heat-resistant ceramics such as alumina, zirconia, titania, titanium phosphate, aluminum titanate, petalite, spodumene, aluminosilicate, magnesium silicate, zirconia-spinel, zircon-mullite, silicon carbide, silicon nitride, kanthal, feclaroy, etc. metal ones are used.

Usually, the above monolithic support is made of alumina or silica.
Alumina, magnesia, titania, zirconia,
Used by coating with active refractory metal oxide such as silica-magnesia. Alumina or zirconia is particularly preferred, and alkaline earth metal oxides,
It is more preferable to add a rare earth metal oxide to stabilize it before use.

After that, it is impregnated with active main components such as platinum and palladium to become a catalyst. Alternatively, the active main component can be supported on an active, refractory metal oxide in advance, and then coated on a monolithic carrier to be catalyzed.

In addition to the above manufacturing method, for catalysts whose active main component is a base metal oxide, which is used as necessary,
It may be supported directly on a monolithic carrier, or it may be catalyzed by mixing it with a powder of an oxide or the like forming a ceramic monolith in advance, and then molding it into a monolith and firing it.

The fuel used in the combustion method of the present invention is methane or a fuel containing methane as a main component. A typical example is natural gas. Although the composition ratio of natural gas varies slightly depending on the production area, it is approximately 80%
Contains more than methane. Fermented methane from activated sludge treatment and low-calorie gas from coal gasification are also fuels that can be used in the present invention.

The catalytic combustion system using the combustion method of the present invention is optimally incorporated into a gas turbine system for power generation as described above, but is also suitable for use in boilers for power generation, gas turbines and boilers for heat recovery, and gas engines. It is used to efficiently recover heat and power from gas 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 having a length of 25.4 mm and a length of 50 mm was coated with a slurry of alumina powder containing 5% by weight of ceria, and the slurry was fired in air at 700°C so that 100 g of the carrier was coated. This was then immersed in an aqueous solution containing chloroplatinic acid, dried, and calcined in air at 700°C to form platinum as carrier 1.
It carried 10g per serving.

A catalyst was prepared in the same manner using an aqueous solution of palladium nitrate, in which 10 g of palladium was supported on each carrier.

1 palladium catalyst is placed in the cylindrical combustor from the inlet side.
(50 mm), then 2 platinum catalysts (100 mm), and a methane-air mixture containing 3% by volume of methane was introduced at 20.74 ^Nm3 per hour, and the preheating temperature was gradually increased to combust the methane. The rate was measured.
In this case, the linear velocity at the inlet of the catalyst bed is 30 m/sec at 500°C.

Figure 1 shows the combustion state of this catalyst system, with the methane combustion rate on the vertical axis and the inlet temperature (preheating temperature) on the horizontal axis. Ignition occurs at inlet temperature of 300℃, 360℃
reached 100% combustion. In addition, Figure 4 shows the results of examining the outlet temperature of each catalyst layer when the preheating temperature of this catalyst system, which reached 100% combustion at 360°C, was increased to 400°C.

As shown at 1 in Fig. 4, this catalyst system
Approximately at catalyst bed outlet temperature (catalyst axial length 50mm position)
The temperature reached 740°C, and the temperature at the outlet of the second catalyst layer (at a position of 150 mm in length in the axial direction of the catalyst) reached approximately 1090°C. When this outlet gas was analyzed, unburned methane, carbon monoxide, and nitrogen oxides were hardly detected.

Example 2 A catalyst was prepared in the same manner as in Example 1 except that alumina powder containing 5% by weight of lanthana (La ₂ O ₃ ) was used instead of ceria-stabilized alumina. Next, the combustor was installed so that the palladium catalyst was packed in a length of 30 mm and the platinum catalyst was packed in a length of 120 mm, and the combustion rate was measured in the same manner as in Example 1. The results are shown in Figure 1, 2.

Example 3 Zirconia powder containing 2% by weight of yttria (Y ₂ O ₃ ) was used instead of ceria-stabilized alumina, a honeycomb carrier made of mullite was used instead of cordierite, and palladium was used as carrier 1. A catalyst was prepared in the same manner as in Example 1, except that 5 g of platinum was supported per carrier. Next, the combustion rate was measured in the same manner as in Example 1 by installing the combustor so that the palladium catalyst filling length was 30 mm and the platinum catalyst filling length was 120 mm. The results are shown in 3 in Figure 1. Further, the outlet temperature of each catalyst layer at a preheating temperature of 400° C. is shown in 3 in FIG. 4, and unburned methane, carbon monoxide, and nitrogen oxides were hardly detected in the outlet gas.

Example 4 In Example 1, the combustion rate was measured by setting the packing length of the palladium catalyst to 20 mm and the packing length of the platinum catalyst to 130 mm. The results are shown in 4 in Figure 1.

Example 5 300 cells/as cordierite honeycomb carrier
A palladium catalyst and a platinum catalyst were prepared in the same manner as in Example 2 using a square inch catalyst. Next, the combustor was installed so that the palladium catalyst was filled with a length of 20 mm and the platinum catalyst was filled with a length of 100 mm, and the combustion rate was measured in the same manner as in Example 1. The results are shown in 5 in FIG.

Example 6 In Example 1, the combustion rate was measured with the palladium catalyst packed in a length of 100 mm and the platinum catalyst packed in a length of 50 mm. Even if it is increased, the methane combustion rate is 70
It remained at %. Therefore, the filling length of the platinum catalyst is
When the combustion rate was similarly measured at 100 mm, a combustion rate of 100% was obtained at a preheating temperature of 315°C. This is shown at 6b in FIG.

Example 7 Using the catalyst system of Example 4, the inlet gas linear velocity was
The combustion rate was similarly measured at 500°C at a rate of 20 m/sec. The results are shown in 7 in Figure 2.

Example 8 A palladium catalyst and a platinum catalyst were prepared in the same manner as in Example 1 except that zirconia powder containing 2% by weight of yttria (Y ₂ O ₃ ) was used instead of ceria-stabilized alumina. .

Furthermore, an aluminum titanate honeycomb carrier having a diameter of 25.4 mm and a length of 50 mm with pores of 200 cells/square inch was immersed in an aqueous chromium nitrate solution.
Pulled, dried and fired, chromium oxide per carrier
A 20g supported catalyst was prepared.

Using a catalyst system with a palladium catalyst packing length of 20 mm, a platinum catalyst packing length of 80 mm, and a chromium catalyst packing length of 50 mm, a methane-air mixture containing 3.8% by volume of methane was fed at a rate of 20 m/s at 500 °C. When the combustion rate was measured by introducing the gas at a linear velocity, the results shown in 8 in FIG. 2 were obtained. Further, the temperature at the outlet of each catalyst layer at a preheating temperature of 400° C. is shown in 8 in FIG. Note that almost no carbon monoxide or nitrogen oxides were detected in the combustion gas.

Example 9 The same catalyst system as in Example 8 was used, except that a mullite carrier was used instead of the aluminum titanate carrier, an aqueous cobalt nitrate solution was used instead of chromium nitrate, and a catalyst carrying 30 g of cobalt oxide per carrier was used. As a result of conducting a similar combustion test, almost the same results as in Example 8 were obtained.

Example 10 Diameter with 200 cells/in2 aperture
A catalyst prepared by mixing powders of neodymium oxide and terbium oxide on a mullite carrier of 25.4 mm and 50 mm in length, adding water to form a slurry, coating it, and calcining it in the same manner as in Example 1, so that 20 g of each was supported on each carrier. adjusted.

Using a catalyst system combining the above catalysts after the catalyst system of Example 2, a methane-air mixture containing 3.8% by volume of methane was heated at 500°C with an inlet gas linear velocity of 30 m/s. When the combustion rate was measured, the results shown in 10 in Figure 2 were obtained.

Note that almost no carbon monoxide or nitrogen oxides were detected in the combustion gas.

Comparative Examples 1 to 2 Using each catalyst prepared in the same manner as in Example 1, the methane combustion rate was measured in the same manner except for the palladium catalyst only and the platinum catalyst only, each with a packing length of 150 mm. However, the results shown in 1 and 2 in FIG. 3 were obtained. No. 1 shows the methane combustion rate using only the palladium catalyst, and although combustion started at a temperature of 300°C or lower, even if the preheating temperature was increased to 600°C, only 60% or less was burned. No. 2 shows the combustion rate of only the platinum catalyst, and although the combustion rate reached 100%, combustion did not start unless the temperature was raised to 500°C or higher.

Comparative Example 3 In the catalyst preparation method in Example 1, carrier 1
A catalyst system was set up so that 5 g of palladium and 15 g of platinum were supported per catalyst, and the catalyst was packed with a length of 150 mm.The methane combustion rate was measured in the same manner as in Example 1. We obtained the results shown below. As can be seen, this comparative catalyst system exhibited poor combustion rates approximately similar to the palladium catalyst.

Example 11 Using the catalyst system of Example 2, a preheating temperature of 400
℃, and the inlet gas linear velocity was set to 30 m/sec.
When a combustion test was conducted by introducing a methane-air mixture containing 3.8% by volume of methane, the platinum catalyst outlet temperature reached approximately 1300°C. Furthermore, almost no unburned methane, carbon monoxide, or nitrogen oxides were detected in the combustion gas.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between methane combustion rate and inlet gas temperature (preheating temperature) by the catalyst systems of Examples 1, 2, 3, 4, and 5, and FIG. and 10 catalyst systems, and FIG. 3 is that of the catalyst systems of Comparative Examples 1, 2 and 3. Figure 4 shows Examples 1 and 3.
8 is a graph showing the temperature reached by the gas at the outlet of each catalyst layer in the catalyst system No. 8.

Claims (1)

[Claims] 1. A first catalyst layer containing palladium as an active component is provided on the inlet side, followed by a second catalyst layer containing platinum as an active component, and a fuel containing mainly methane and a fuel containing mainly methane are provided. By introducing a mixed gas with molecular oxygen and burning it in the first catalyst layer, 400 to 800
A method for completely burning a fuel mainly containing methane, characterized by raising the temperature to a temperature of 700 to 1500 °C by combustion in a second catalyst layer. 2. The method according to claim 1, wherein the palladium and/or platinum catalyst is supported on a monolithic carrier coated with alumina and/or zirconia. 3. Claim 2, characterized in that the alumina and/or zirconia coating layer is stabilized with at least one rare earth element oxide selected from the group consisting of lanthanum, cerium, yttrium, samarium, neodymium, and praseodymium. Method described. 4 A first catalyst layer containing palladium as an active ingredient is provided on the inlet side, followed by a second catalyst layer containing platinum as an active ingredient, and chromium, cobalt, terbium, lanthanum, cerium, neodymium, A third catalyst layer containing as an active ingredient an oxide or composite oxide of at least one element selected from the group consisting of praseodymium and ythtrium is provided, and a fuel mainly containing methane is mixed with molecular oxygen. Introduce the gas and
The temperature is raised to 400-800℃ by combustion in the catalyst layer, and then the temperature is raised to 700℃ by combustion in the second catalyst layer.
A method for completely burning a fuel mainly containing methane, characterized by raising the temperature to a temperature of ~1000°C and finally raising the temperature to a temperature of 900~1500°C by combustion in a third catalyst layer.