JPH04324011A - Catalytic combustion apparatus - Google Patents

Abstract

PURPOSE:To restrain the stress concentration due to thermal strain, etc., by a method wherein combustion catalyst layers are formed into a shape having partly cut-off segment cross section horizontal to the flow path direction, and the combustion catalyst layers are piled up in such a manner that the adjacent combustion catalyst layers in the flow path direction compensate the cut-off sections each other. CONSTITUTION:A preheating combustion chamber 1, a lean fuel gas mixing chamber 2, a cylindrical catalytic combustion chamber 3 and a combustion gas exhaust part 4 are arranged in sequence along the combustion gas flow path, and combustion catalyst layers 5 consisting of honeycomb catalysts each having a large number of through- holes are arranged along two or more flow paths. The catalyst layers 5 are formed in a shape having partly cut-off segment section horizontal to the flow path direction, and arranged in staggered rows in the flow path direction so that the adjacent catalyst layers compensate the cut-off segmental parts each other and those edges overlap so as to cover the whole section. Those two or more catalyst layers 5 are piled and held from the front and back and clearances are provided between the catalyst layers 5, preventing an increase in draft resistance and generation of local thermal strain.

Description

[Detailed description of the invention]

0001

[Industrial application field] NO in exhaust gas from combustion equipment
Due to the progress of environmental pollution caused by x, it is desired to develop means for significantly suppressing NOx in the combustion process. That NOx
The premixed catalytic combustion method uses a honeycomb-shaped combustion catalyst having a large number of through passages in the flow direction as one of the suppressing means.
It is known that high-load combustion is possible at temperatures of 1,100 to 1,300 degrees Celsius, and that the generation of NOx can be extremely suppressed. This feature is due to the ultra-low NO of gas turbines.
Consideration is being given to using the present invention as a means to achieve x, as a means to re-combust the exhaust fuel and air mixture of fuel cells, or to apply it to boilers, industrial burners, etc. The present invention relates to a catalytic combustion device in which a plurality of combustion catalyst layers having a large number of through holes in the thickness direction are arranged side by side in a flow path direction, and for example, relates to a catalytic combustion device for low NOx as described above.

0002

[Prior Art] Development of a combustion catalyst layer for the premixed catalytic combustion method has been considered in the past, with a structure in which precious metals such as palladium and platinum are supported on a cordierite honeycomb substrate via a coating material such as alumina. It's coming. However, although the cordierite honeycomb substrate can have a fairly low coefficient of thermal expansion of approximately 1 x 10-6/°C and has good thermal shock resistance, its strength decreases at temperatures above 1300°C.
There are problems with high temperature use. In addition, in a catalyst with this configuration,
When the temperature exceeds 1000°C, precious metals evaporate and transpire.
There have been problems such as activity deterioration due to a decrease in specific surface area due to progress of sintering of the coating material.

[0003] Therefore, the inventors of the present invention proposed a new high-temperature combustion catalyst layer capable of exhibiting a long active life by using a combustion catalyst layer mainly composed of palladium on a cordierite honeycomb base in the first stage, and a combustion catalyst layer mainly composed of palladium on a cordierite honeycomb base in the middle and rear stages. 120 each
We are proposing a catalytic combustion device in which a combustion catalyst layer obtained by directly honeycomb-forming a manganese-substituted layered aluminate catalyst sintered at 0°C and 1300°C is arranged. As described above, in practical combustion catalyst devices, catalysts suitable for each operating temperature are arranged from low to high temperatures. The combustion catalyst layer used in the middle to rear stages is a manganese-substituted layered aluminate catalyst directly formed into a honeycomb shape.The thickness of each layer is limited, and multiple layers are arranged side by side with gaps between the layers. The reason for reducing the thickness of this layer is that the coefficient of thermal expansion of this catalyst layer is 6 to 8 x 10-6.
/°C, which is considerably larger than that of cordierite honeycomb, so this is to prevent destruction due to thermal stress caused by temperature differences in the thickness direction. The combustion catalyst layer is
Each layer was integrally formed in a shape that covered the entire cross section perpendicular to the flow path direction, and was arranged side by side in the flow path direction with the gap. The gap was secured, for example, by disposing a ring-shaped metallic spacer 7 between adjacent combustion catalyst layers 5, 5 in the combustion chamber 3, as shown in FIG. These gaps 6 also serve to prevent an increase in ventilation resistance due to misalignment of the through holes between the catalyst layers.

0004

Problems to be Solved by the Invention In order to make the above-mentioned high-temperature combustion catalyst layer a more practical combustion catalyst layer, it is necessary to increase the combustion capacity. Therefore, in order to increase the gas throughput of the combustion catalyst layer without compromising its low NOx performance, it is necessary to increase the area of the catalyst layer, but while maintaining the dimensional accuracy and strength of the honeycomb, There are naturally limits to how big it can be. For example, for a combustion catalyst layer that requires not only strength but also high activity and 200 or more cells per square inch, the size limit is about 200 mm in diameter or 200 mm square.

[0005] So far, for example, there have been methods of manufacturing small catalytic combustion devices and connecting them in parallel in a multi-type.
Alternatively, attempts have been made to increase the capacity by bonding or joining a plurality of segments of a honeycomb catalyst having a size within a size equivalent to a diameter of 200 mm to increase the cross-sectional area.

However, the former multi-type catalytic combustion device connected in parallel is not practical because the entire device is large and complicated, resulting in high cost and difficult to maintain. The latter bonding method uses a different material from the combustion catalyst layer for adhesion, but the combustion catalyst layer
Since it is used at a temperature exceeding 00°C, it has the disadvantage that the bonded portion is likely to deteriorate due to a solid phase reaction between the two. In addition, bonding methods using the same amount of materials have the advantage of suppressing solid phase reactions between materials and making the coefficient of thermal expansion of the materials the same, but the thickness of the bonded area is different from the cell wall thickness. It is difficult to make them equal, and the longer the length of the bonding surface, the more uneven the mechanical strength and temperature distribution will be due to the non-uniformity of the thickness.
There was a problem that cracks were likely to occur. This problem is particularly problematic because the thermal stress is several times higher in the combustion catalyst layer of manganese-substituted layered aluminate, which has a coefficient of thermal expansion of 6 to 8 x 10-6/°C, which is larger than that of cordierite honeycomb. is important.

[0007] Furthermore, there is a risk that the honeycomb catalyst may be damaged due to concentration of stress due to differences in thermal expansion coefficient and thermal conductivity between the metal spacers and the honeycomb catalyst, or due to differences in mechanical strength.

[0008] An object of the present invention is to reduce the concentration of stress caused by the thermal strain, etc., and to prevent deformation and cracking even in a combustion catalyst layer with low mechanical strength, such as the above-mentioned honeycomb catalyst. However, it is an object of the present invention to provide a catalytic combustion device that can process a large amount of gas by increasing the diameter of the catalytic combustion chamber without impairing catalyst performance such as low NOx.

[0009]

[Means for Solving the Problem] In order to achieve this object, the characteristic configuration of the catalytic combustion device according to the present invention is that the combustion catalyst layer is formed in a shape in which a part of the cross section perpendicular to the flow path direction is missing, and The combustion catalyst layers that are adjacent to each other in the flow path direction have their ends overlapped to cover the entire cross section so as to compensate for each other's missing cross sections.

0010

[Function] Each of the combustion catalyst layers has a shape in which a part of the cross section perpendicular to the flow path direction of the catalytic combustion chamber is missing. Since the combustion catalyst layers adjacent to each other are overlapped at their ends, by pressing from both sides in the direction of the flow path, the plurality of combustion catalyst layers can be separated without using an adhesive or the like.
The catalyst can be easily held in the combustion chamber, and
The gaps are formed between every other combustion catalyst layer facing each other in the flow path direction, and the adjacent combustion catalyst layers overlap their ends to compensate for the missing cross sections. Since the entire cross section is covered, in order for gas to pass from one gap to the next, it must pass through the combustion catalyst layer between them.

[0011]

Effects of the Invention: The gap between the combustion catalyst layers, which was conventionally provided using a metal spacer, is secured by allowing the combustion catalyst layer itself to act as a spacer between the previous and next combustion catalyst layers. , it is possible to prevent an increase in ventilation resistance due to misalignment of the through holes between each catalyst layer, and it is possible to simply connect multiple segments with a relatively small adhesive surface or joint surface, or to butt them together without using adhesive, etc. Even if each catalyst layer is formed, the combustion catalyst layers that are adjacent to each other in the direction of the flow path can be easily supported by simply overlapping their ends and pressing them from both sides in the direction of the flow path. be able to. In other words, even in a large-capacity combustion device, the combustion catalyst layer can be divided into relatively small segments, so compared to a single, large combustion catalyst layer, each segment expands even if the expansion rate is the same. The amount is smaller and therefore thermal shock failure is less likely to occur. The thickness of each combustion catalyst layer is determined by
However, in the case of the present invention, since no spacer is particularly required, it is easy to use a thickness of about 10 mm, which is close to the manufacturing limit, and the thickness of the combustion catalyst layer can be reduced. Since the thickness can be made extremely thin, thermal stress fractures due to uneven temperature distribution in the thickness direction are less likely to occur. Also, if a missing part is formed in the combustion catalyst layer, 1
Since the length of the abutting surfaces of the segments that form the combustion catalyst layer of the layer can be shortened, even if they are bonded together, non-uniformity in mechanical strength and temperature distribution due to non-uniform thickness is unlikely to occur. Therefore, the problem of easy cracking near the bonded area is alleviated. Therefore, destruction of the combustion catalyst layer due to thermal distortion caused by metallic spacers, adhesives, etc. can also be prevented.

As a result, even if the combustion catalyst layer has low mechanical strength, such as the above-mentioned honeycomb catalyst, stress concentration due to thermal strain etc. can be reduced, deformation and cracking can be prevented, and low N0x can be achieved. It was possible to provide a catalytic combustion device that can process a large amount of gas by increasing the diameter of the catalytic combustion chamber without impairing performance such as combustion.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the catalytic combustion apparatus according to the present invention will be described below with reference to the drawings. As shown in the axial cross section of the catalytic combustion device in FIG. A combustion catalyst layer 5 made of a honeycomb catalyst and having a large number of through holes in the thickness direction.
A plurality of are arranged in the catalytic combustion chamber along the flow path,
The combustion catalyst layer 5 is formed in a shape in which a part of the cross section perpendicular to the flow path direction of the catalytic combustion chamber 3 is missing, and is arranged in a staggered manner in the flow path direction of the combustion chamber 3, so that the flow path The catalytic combustion device is configured such that the ends of the combustion catalyst layers adjacent to each other in the direction are overlapped to cover the entire cross section so as to compensate for the missing cross section. With this configuration, the large-diameter combustion chamber 3
A plurality of the combustion catalyst layers 5 arranged inside can be easily held from the front and rear, that is, from the left and right in the figure. In addition, since there is no need to use a metal spacer or adhesive to form the gap shown by 6 in the figure between the combustion catalyst layers 5, the ventilation resistance and local heat generated when using these Distortion can also be prevented. The combustion chamber 3 is configured as a catalyst cassette in which the combustion catalyst layer 5 is held between metal frames from the outside via a semi-cylindrical hardened heat insulating material 7 formed by compression molding of high temperature heat-resistant ceramic fibers. is designed so that the entire catalyst cassette can be easily replaced. 9 in the diagram
is a high-strength holder to prevent the segment from being blown off at the catalyst outlet. Figure 2 (a), (
B), (C), and (D) show various examples of the holder 9,
Depending on the shape of the combustion catalyst layer 5, holders having various shapes other than these can be considered. FIG. 3(a) shows the state in which the combustion catalyst layers 5 are stacked and installed in the catalytic combustion chamber 3 in a vertical position. Each combustion catalyst layer 5
The segments have a size that allows easy extrusion molding, and are formed into fan shapes of the same shape, which are quadrants of a circular cross section perpendicular to the flow path of the catalytic combustion chamber 3, plus an overlap margin. These two segments are abutted at their essential parts, and the combustion catalyst layers 5 formed in a bow tie shape are stacked one on top of the other as shown in (a) with a 90° shift. (B) shows how the two overlapping combustion catalyst layers 5 are viewed in the flow path direction. The length of the abutting surface of the segments is 20 mm in order to suppress dead space caused by overlapping before and after the segments.
The following is desirable.

[Another embodiment] The shape of the combustion catalyst layer 5 is as follows:
For example, as shown in FIGS. 4A and 4B, a trefoil shape may be formed by abutting segments in the shape of a sextant of a circular cross section perpendicular to the flow path of the catalytic combustion chamber 3 plus an overlap margin. Alternatively, as shown in FIGS. 5A and 5B, or FIG. Various shapes can be considered, such as a checkerboard pattern in which segments of different shapes are butted together at the corners. These segments forming the same plane can be fixed in relative position by mutual pressing force when they abut against each other at the corners, but they may also be bonded together with an adhesive or the like. Even with such adhesion, there are fewer harmful effects than when the peripheries of these segments are all bonded to fill the same plane, since each segment has a free end that releases stress due to thermal strain. The catalytic combustion chamber 3
The cross section of may be a shape other than a circle, such as a polygon. By making the combustion catalyst layer 5 polygonal in shape and matching the shape thereof, positioning in the circumferential direction during installation is easy, and even after installation, it will not shift in the circumferential direction due to vibrations or the like. In order to form the catalytic combustion chamber 3 into a cassette, methods other than those described in the above embodiments may be used, such as wrapping the stack of combustion catalyst layers with wet felt made of high-temperature heat-resistant ceramic fibers and making them adhere to and integrate with the stack by heat curing. It may depend on the method.

[Experiment example] Number of cells 200/in2, thickness 1
One layer of combustion catalyst layer 5 made of palladium-cordierite with a thickness of 0 mm, four layers of combustion catalyst layer 5 made of low-temperature activated manganese-substituted hexaaluminate with a cell count of 300/in2 and a thickness of 10 mm, and a cell count of 300. /in2, thickness 10
Two layers of combustion catalyst layers 5 made of high-temperature heat-resistant manganese-substituted hexaaluminate with a thickness of 2 mm were arranged in the above order and cured by heating using wet felt, thereby forming a cassette as shown in the combustion chamber 3 of FIG. As shown in FIG. 3, each combustion catalyst is formed by combining fan-shaped segments in a bow tie shape,
They are overlapped in the same way as in the example. The effective diameter of the combustion catalyst layer is 220 mm. The butt parts of the segments were glued together. This cassette was installed in a catalytic combustion device for a 150 kW gas turbine, shifted to catalytic combustion mode, operated at rated load for 4 hours, and then stopped. The temperature of the combustion catalyst layer at startup was 1000°C, the maximum temperature of the combustion catalyst layer in catalytic combustion mode was 1200°C, and the startup time was about 20 seconds. The catalytic combustion efficiency at rated load was over 99%. As a result, there was no abnormality in the appearance of the catalyst cassette, and no cracks were detected during observation of each catalyst layer 5, indicating that a catalytic combustion device capable of holding such a catalyst is not subject to rapid temperature rise, cooling, or , it has been demonstrated that it can sufficiently withstand thermal stress in steady-state combustion.

[Comparative Experimental Example] For the combination of catalysts in the above experimental example, the combustion catalyst layer 5 of each stage was divided into four parts made of the same material and glued together, each having a diameter of 220 mm and a thickness of 20 mm, with no missing parts, and , was formed into a circular shape that covered the entire cross section of the channel. Each combustion catalyst layer 5 was disposed via a spacer and formed into a cassette in the same manner as in the above experimental example, and the cassette was installed in a catalytic combustion apparatus similar to that in the above experimental example, and a turbine installation test was conducted. As a result, combustion performance similar to the above experimental example was obtained, but
Except for the combustion catalyst layer 5 made of palladium cordierite in the first stage, all of the combustion catalyst layers 5 made of manganese-substituted hexaaluminate in the second and subsequent stages were found to have cracks locally at or near the adhesion site. It was done. Therefore, it has been found that it is difficult to ensure long-term durability in a catalytic combustion device using this catalyst holding method. Incidentally, although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings by the reference numerals.

[Brief explanation of drawings]

FIG. 1 is an axial sectional view showing an embodiment of a catalytic combustion device according to the present invention.

[Fig. 2] A perspective view showing the holder of the embodiment.

[Fig. 3] A perspective view and a plan view showing a state in which the combustion catalyst layers of the example are stacked.

[Fig. 4] A perspective view and a plan view of a combustion catalyst layer in another example.

[Fig. 5] A perspective view and a plan view of a combustion catalyst layer in another example.

[Fig. 6] A perspective view of a combustion catalyst layer in another example.

[Figure 7]
Axial cross-sectional view of a catalytic combustion chamber of a conventional catalytic combustion device

[Explanation of symbols]

5 Combustion catalyst layer

Claims (3)

[Claims] 1. A catalytic combustion device in which a plurality of combustion catalyst layers (5) having a large number of through holes in the thickness direction are arranged side by side in the direction of the flow path, the combustion catalyst layers (5) being arranged perpendicularly to the direction of the flow path. The combustion catalyst layers (5) adjacent to each other in the direction of the flow path are formed so that a part of the cross section is missing, and the end portions of the combustion catalyst layers (5) are overlapped to compensate for the missing cross section. A catalytic combustion device that covers the entire cross section. 2. The catalytic combustion device according to claim 1, wherein the combustion catalyst layer (5) has a honeycomb shape having a large number of through holes in the direction of the flow path. 3. The catalytic combustion device according to claim 1, wherein the combustion catalyst layer (5) of each layer is divided into a plurality of layers in a direction perpendicular to the flow path.