JPH0247262B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a combustion catalyst, and particularly to a catalytic combustion catalyst suitable for high-load combustion, and a combustion apparatus using the catalyst. In recent years, many attempts have been made to downsize boilers and various combustors by using a so-called catalytic combustion method in which a combustion reaction is promoted using a catalyst. In the catalytic combustion method, the volumetric combustion rate (kcal/m ³ h), which is the amount of heat generated per unit volume and time, is several tens of times larger than that of the conventional flame combustion method. It is possible to set it to 1. In addition, the catalytic combustion method (1) Nitrogen oxide (NOx)
(2) complete combustion is possible at low oxygen concentrations, and the practical application of this method is eagerly awaited. However, in the above catalytic combustion method, when the catalyst is used under high load conditions, the catalyst deteriorates due to the heat of combustion, which is a major obstacle to practical application. For this reason, (1) recirculation of combustion gases;
(2) Measures to avoid thermal deterioration of the catalyst using methods such as fuel dispensing are being considered. That is, FIG. 1 shows an improved example of combustion gas recirculation, in which the air introduced from the air introduction pipe 3 is preheated by the heat exchanger 8, and then fuel is injected from the pipe 2. After being uniformly mixed in the mixer 5, the mixture is introduced into the catalyst device 1A loaded with the catalyst body 1, and subjected to catalytic combustion. The combustion exhaust gas of the catalyst device 1A is taken out through a heat recovery device 4, and a part of it is passed through a pipe 6 and sent to a fuel injection pipe 2 by an air blower 7.
The remaining exhaust gas is sent to the heat exchanger 8 described above, where the heat is recovered, and then discharged to the outside from the piping 9. FIG. 2 shows an example of improvement by dispensing fuel. Air introduced from air introduction pipe 3 is preheated via preheater 10, then fuel is injected from pipe 2, and then air is introduced into mixer 5. After being mixed in the combustion exhaust gas, it is introduced into the catalytic combustion device 1A, where it is catalytically combusted, and then heat is recovered in the heat recovery device 4. After the heat recovery, fuel is injected from the pipe into the combustion exhaust gas, and the fuel is injected into the combustion exhaust gas again. Mixer 5, catalytic combustion device 1
After the above-described operations are repeated in A and the heat recovery device 4, the combustion exhaust gas is discharged to the outside from the pipe 9. However, method (1) (Fig. 1) has the disadvantage that the amount of gas handled for recirculation increases several times, which not only diminishes the advantages of catalytic combustion, but also complicates the device structure. Furthermore, in the method (2) (FIG. 2), since the fuel is dispensed, the structure becomes complicated, and the ignition temperature becomes high because the fuel is operated under conditions of low fuel concentration. In order to eliminate the above disadvantages, it is possible to divide the catalyst layer and perform partial combustion, but in this case,
Thermal runaway may cause partial sintering of the catalyst, or only a portion of the catalyst may be heated, making it impossible to continue uniform combustion, and producing carbon monoxide and unburned carbon, which are partial combustion products. There is a problem with generating it. An object of the present invention is to improve the drawbacks of the above-mentioned prior art, to provide a combustion catalyst body that can easily cope with high-load combustion conditions and that is less likely to undergo thermal deterioration. The present invention provides a catalyst body having a catalyst for catalytic combustion on the wall surface of a channel through which a fuel-containing gas passes, the channel wall surface having catalytic activity and the channel wall surface having no catalytic activity;
Alternatively, two types of flow paths, including a flow path having a lower catalytic activity than the flow path, are arranged so as to be in contact with each other through a wall surface. The catalyst body of the present invention has an opening shape such as a rectangular, circular, or hexagonal shape and has a flow path parallel to the gas flow.
It is preferably applied to so-called monolith catalyst bodies. Hereinafter, the present invention will be explained in more detail with reference to the drawings. 3 to 7 are diagrams schematically explaining the principle of the present invention. First of all, Fig. 4 schematically shows the combustion situation in a conventional monolithic catalyst. The mixed gas of air and fuel flows into the catalyst from the direction of the arrow and comes into contact with the surface of catalyst 1. Burns and generates heat. At that time, part of the combustion heat passes through the inside of the catalyst, becomes a heat flow 12, and is transmitted in the opposite direction to the gas flow, thereby preheating the air-fuel mixture. Due to the temperature increase caused by this, the combustion reaction proceeds more rapidly, but as a result, the preheating of the gas mixture by the aforementioned reverse heat flow is enhanced, further promoting the combustion reaction. Ru. As a result, a narrow and extremely high temperature combustion zone 13 is formed inside the catalyst body, and combustion is almost completed in this zone. FIG. 4 shows the temperature distribution of the catalyst in this case, and the enthalpy of the mixed gas increases due to the heat flow 12 in the opposite direction, as described above.
The temperature of the combustion zone due to catalytic combustion (solid line A) is not only higher than that of non-catalytic flame combustion shown by dotted line B, but also reaches a high temperature that far exceeds the adiabatic flame temperature C, making it easy for thermal deterioration of the catalyst to progress. Become. As shown above, the width of the combustion zone formed in current catalysts is extremely narrow, and most combustion reactions proceed rapidly in that area, so partial combustion can be stably achieved by shortening the catalyst length. It is difficult in principle to implement. Therefore, in the present invention, the gas flow path of the catalyst is made inhomogeneous, the heat flow is dispersed in the cross-sectional direction, the heat flow in the opposite direction is reduced, and stable partial combustion is made possible. That is, schematically the fifth
As shown in the figure, a flow path 15 having a catalyst layer 11 on its surface and a flow path 16 having no catalyst layer are placed adjacent to each other in the monolithic catalyst. In this way, the flow path 15
The combustion heat generated on the catalyst layer 11 inside flows as a heat flow 12 in the six directions of the flow path, and is used only for preheating the mixed gas, and the catalyst layer 11 is cooled.
Heat deterioration is prevented. Also, due to the heat flow 12,
The heat flow in the opposite direction to the gas inflow direction is reduced, and as shown in D in FIG. 6, an extreme temperature rise in the heating zone no longer occurs, and thermal deterioration of the catalyst is significantly reduced. Furthermore, in the case of the present invention, partial combustion is realized structurally by providing a flow path 16 without a catalyst layer 11, so that unstable combustion phenomena that occur in the case of a method of separating narrow reaction zones can be avoided. Local heating no longer occurs. In addition, the mixed gas flowing into the flow path 15 has no effect on the catalyst layer 11 before reaching the outlet of the flow path.
This allows for complete combustion, and the production of unused carbon and carbon monoxide is also suppressed. Furthermore, unlike in the case of fuel dispensing, the air ratio of the inflowing gas can be selected to be close to 1, so there is an advantage that ignition can be started easily. Note that the flow path 1 having the catalyst layer 11 shown in FIG.
5 and 16 may be reversed as shown in FIG. 5A. As shown in FIG. 7, the catalyst body of the present invention has a channel 15 having a catalyst component on the inner surface and a channel 16 not having the same layered and arranged alternately,
As shown in FIG. 8, an example is a channel arranged in a staggered manner in the cross section of the channel, but in short, the channel 15 and 16 are arranged in a staggered manner.
It is sufficient that the two types of flow paths are arranged so that some or all of the outer surfaces thereof are in contact with each other, and various other modifications may be considered. For example, the flow paths 15 and 16 do not necessarily have to have the same cross-sectional area, and the principle of this patent is that the inner surface of the flow path 16 may be covered with a catalyst layer having a lower activity than the catalyst on the inner surface of the flow path 15. It is within the range that can be easily inferred from. Further, the material of the catalyst layer 11 or the carrier 14 may be any combustion catalyst, such as a metal or a metal oxide. Next, FIG. 9 shows an example of a combustion device using the combustion catalyst of the present invention. This device includes a preheater 10 for introducing air from a pipe 3, a fuel injection pipe 2 for supplying fuel to the preheated air, a mixer 5 for mixing the fuel and air, and a preheater 10 for introducing air from the mixer 5. It consists of a combustion device 1A that burns fuel-air mixed gas,
This combustion device 1A consists of relatively short monolithic catalyst bodies 20 and heat recovery units 4 arranged alternately. This monolithic catalyst 20 consists of the one shown in FIGS. 7 and 8 described above. By dividing the catalyst layers in this way and arranging them alternately with heat transfer tubes that serve as heat recovery devices, and removing combustion heat while partially combusting the fuel in each catalyst layer, the maximum temperature of the catalyst is limited, and In each catalyst body 20, as shown in Fig. 5, combustion heat is dispersed in the cross-sectional direction of the flow path, so extremely stable split combustion is achieved, and it is fully applicable to high-load combustion with an air ratio close to 1. A heat recovery device can be configured to obtain Note that the catalyst body of the present invention is applicable not only to the combustion device shown in FIG. 9 but also to the combustion devices shown in FIGS. 1 and 2. Hereinafter, the present invention will be explained in more detail with reference to specific examples. Example: The channel shape is a square with a side of 2 mm, and the partition wall thickness is 0.5 mm.
A certain mullite carrier is cut into pieces of 30 mm square and 30 mm long, and a water slurry of 350 mesh powder containing 0.5 wt% platinum supported on alumina (γ-Al ₂ O ₃ ) has a structure as shown in Figure 7. It was poured into the flow channel. After drying this at 140°C for 2 hours, it was calcined at 500°C for 2 hours to deposit catalyst powder to a thickness of about 0.1 mm on the mullite support. Comparative Example The same carrier as in the example was cut into a shape of 30 mm square and 15 mm long, and a catalyst was deposited on the inner walls of all the channels in the same manner. Experimental Example A mixed gas of 8 vol% methane (the remainder air) was preheated to 400°C for the example catalyst and comparative catalyst.
A catalytic combustion test was conducted by contacting at a flow rate of 35 N/min. Table 1 shows the performance of both catalysts immediately after the experiment and after 10 hours.

[Table] From the results in Table 1, the catalyst according to the present invention has no change in long-term catalytic performance and generates little CO, whereas the catalyst according to the comparative example had high initial activity, but A significant amount of CO was produced, and the fire misfired several hours later due to decreased activity. As described above, according to the present invention, stable partial catalytic combustion is possible under conditions of an air ratio close to 1, and, for example, a high-load combustion-heat recovery system can be configured in combination with a heat recovery device. Therefore, the catalyst body of the present invention is particularly suitable for catalytic combustion boilers and the like.

[Brief explanation of the drawing]

Figures 1 and 2 are equipment system diagrams showing a conventional catalytic combustion system, Figure 3 is a model diagram showing the combustion situation inside a conventional catalyst body, Figure 4 is a diagram showing its temperature distribution, and Figure 5 , FIG. 5A is a model diagram of a catalyst body showing the principle of the present invention, FIG. 6 is a diagram showing its temperature distribution, and FIGS. 7 and 8 are configuration diagrams of a catalyst body showing examples of the present invention, respectively. , FIG. 9 is an equipment system diagram of a high-load combustion-heat recovery system incorporating the catalyst body of the present invention. 1, 20... Catalyst body, 2... Combustion injection pipe, 3
... Air introduction pipe, 4 ... Heat recovery device (heat transfer tube), 9
...Exhaust piping.

Claims (1)

[Claims] 1 In a catalyst body having a catalyst for catalytic combustion on the wall of a channel through which a fuel-containing gas passes, there is a channel whose wall surface has catalytic activity, and a channel which has no catalytic activity or has less catalytic activity than the channel. A combustion catalyst body characterized in that two types of flow paths are arranged so as to be in contact with each other through a wall surface.