JPS63283758A - Production of laminar catalyst for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To prevent deterioration of strength by applying a catalytic component on a substrate wherein aluminum oxide is melt-stuck on a lath board and also covering it with a film material and compressing it. CONSTITUTION:A base plate is formed by melt-sticking aluminum oxide on a lath board. Paste in which silica-alumina base fiber is blended with catalytic paste is applied on this substrate. A laminar material 9 applied with this catalyst is passed through the interval 24 between an upper roll 11 and a lower roll 12. In this case, both surfaces of the laminar material 9 are covered with a film 15 such as a polyethylene film. Then the obtained laminar catalyst is dried at 10-180 deg.C and thereafter calcined at 300-700 deg.C. Thereby the catalyst can be mass-produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a catalyst for removing nitrogen oxides from exhaust gas, and particularly relates to a method for manufacturing a plate-shaped catalyst for removing nitrogen oxides with low flow resistance of exhaust gas. be.

[Conventional technology]

Recently, from the viewpoint of pollution prevention, it has been desired to float exhaust gas from various combustion equipment. In particular, various measures have been taken to remove nitrogen oxides (hereinafter referred to as NOx) in exhaust gas. One method is to mix a reducing agent such as NH3 (ammonia) into the exhaust gas, and then introduce the exhaust gas to a denitrification device that has a built-in catalyst and bring it into contact with the catalyst to selectively reduce NOx in the exhaust gas. It is being done.

[Problem that the invention seeks to solve]

Some of the conventional denitrification devices described above have a layer of granular catalyst with a predetermined thickness so that the exhaust gas passes through the catalyst layer, but when the exhaust gas contains soot and dust, the dust flows into the catalyst layer. There have been problems in that the flow resistance increases and the function deteriorates due to the accumulation of particles on the surface. Therefore, honeycomb shaped catalysts with catalyst surfaces parallel to the flow of exhaust gas,
Plate catalysts are being used or are being considered. However, when producing large honeycomb catalysts, there are problems in terms of manufacturing technology or mechanical strength of the catalyst itself.

In addition, plate-shaped catalysts are manufactured by coating a catalyst on a substrate in order to provide strength, but there is a problem that the catalyst easily peels off or falls off due to the weak adhesion between the catalyst and the substrate. This is not only due to adhesion, but also because the coated catalyst layer and substrate repeatedly expand and contract due to temperature changes in the exhaust gas, causing cracks in the catalyst layer and promoting peeling.

Additionally, in order to provide the role of a spacer when the plate catalysts are arranged at predetermined intervals in the exhaust gas flow path, uneven portions are formed on the catalysts to maintain the spacing between adjacent plate catalysts. For example, Utility Model Application No. 50-122658, Utility Model Application No. 5
0-122659 etc.). However, when forming irregularities on a plate-shaped catalyst, using a normal fully curved flat plate as a substrate, cracks and cracks occur in the irregularities or their surrounding areas, resulting in a decrease in strength and the separation of the catalyst layer from the metal substrate. There was a problem that it was easy to fall off.

[Means for solving the problems] The present invention has been made to solve the above problems,
In a method for producing a nitrogen oxide removal catalyst in which a catalyst component is coated on a thin metal plate, a substrate is formed by welding aluminum oxide onto a lath plate made of a thin stainless steel plate, and a catalyst is applied to this substrate. After coating the surface of the plate-shaped body formed by applying the ingredients with a smooth film-like object, the plate-shaped body is compressed by being sandwiched between two mold bodies each having a plurality of irregularities. This is a method for producing a plate-shaped catalyst for removing nitrogen oxides, which is characterized by forming a plate-shaped catalyst for removing nitrogen oxides.

The metal plate used as the substrate of the plate-shaped catalyst must have good adhesive properties and must also have sufficient strength and corrosion resistance during use.

The inventor of the present invention has considered them, and as a result, a lath-processed stainless steel substrate is selected.

The reaction temperature of the reactor is usually set at 250 to 450°C, taking into account the characteristics of the catalyst and the gas flow rate. Therefore, is it necessary for the metal substrate for the plate-shaped catalyst to have sufficient strength for use in such high-temperature gases? According to the inventors' experiments, it was revealed that aluminum substrates do not have sufficient high temperature strength, and that mild steel or stainless steel (18% Crwi or 18% CrCr-8Ni substrates) are used. The metal substrate is subjected to lath processing and chevron processing during catalyst production, and the workability of these processes is comparable for both mild steel and stainless steel.

Next, we investigated the corrosion resistance of the metal substrate. The metal substrate needs to withstand sulfur oxides contained in combustion exhaust gas, especially sulfuric acid produced by SO3 adsorption. According to the experimental results, mild steel naturally corrodes violently, but stainless steel exhibits sufficiently excellent corrosion resistance even against 5% sulfuric acid, and was found to be suitable as a metal substrate for plate-shaped catalysts.

Next, we investigated the method of supporting the catalyst on the substrate. In order to provide a plate-shaped catalyst with high activity and durability, it is necessary to consider (a) the amount of catalyst supported, and (b) the adhesion between the metal substrate and the catalyst component due to its structure and properties. In order to satisfy the requirements, machining and thermal spraying of the substrate surface were investigated.

First, the machining of the substrate surface will be described. If the catalyst component is applied directly to a smooth metal plate, the adhesion and amount of support will be insufficient, so some kind of surface treatment is required. Therefore, after applying various machining processes to a metal plate, a catalyst is coated, dried, and fired to form a plate-shaped catalyst.
The amount of catalyst supported and the removability of the coated catalyst were investigated.

As a result, it was found that a substrate in which a thin stainless steel plate lath-processed and coated with a catalyst by the process shown in FIG. 6 is suitable in terms of the amount of catalyst supported. The lath plate manufactured by the process shown in FIG. 6 has a porosity of about 79%, and a large amount of catalyst is supported.

As mentioned above, in terms of the amount of catalyst supported, it is best to use a substrate with through-holes and high porosity, such as metal lath processed plates, but it is also effective to provide fine irregularities on the surface to improve peeling resistance. It is. Therefore, we investigated a method of spraying metal onto a metal lath plate to form fine irregularities on its surface.

Points to be considered when carrying out thermal spraying are (a) thermal spraying method and thermal spraying material, and (b) thermal spraying conditions.

Thermal spraying methods include the arc method using flames such as acetylene and electricity, but the major difference between the flame method and the arc method is that the spraying material, which has been melted into droplets, is heated in a space gas atmosphere until it reaches the object to be sprayed. It depends on the degree of progress of oxidation.

That is, whether or not the material is oxidized before reaching the substrate, which is the object to be thermally sprayed, affects the corrosion resistance of the thermally sprayed layer.

Next, the results of selecting thermal spray materials will be described. As with the case of substrates, sulfuric acid resistance is an issue with thermal spray materials for forming fine protrusions on substrates.

According to JIS, stainless steel, mild steel, aluminum,
Zinc etc. are specified as thermal spray materials, but sulfuric acid resistance is 5US316>5US304>5U3430>5S4
The order is 1>aluminum>zinc. So 5US30
4 or 5US31 as thermal spraying material on SUS430 substrate
6. SUS 430° aluminum was arc sprayed under the spraying conditions shown in Table 1, and its corrosion resistance was compared in an accelerated test using 5% sulfuric acid. The results showed that thermal spraying with aluminum had the best corrosion resistance, which was completely different from what was expected. It was found that the unique corrosion resistance of the aluminum sprayed layer was largely dependent on the spraying method. In other words, corrosion resistance is determined by the oxidation of the sprayed metal by oxygen in the atmosphere during the time the sprayed material is melted in an arc or flame (acetylene-oxygen-air), atomized by the gas flow, and reaches the object to be sprayed. It is related to the degree.

Table 1 Electric arc spraying creates an atmosphere with an oxygen partial pressure of 20%, while flame spraying creates a combustion exhaust gas atmosphere with a low oxygen partial pressure. Therefore, it is thought that corrosion resistance is improved because electric arc spraying with a high oxygen partial pressure produces oxides on the surface, and aluminum spraying produces alumina (A1203). In thermal spraying of SUS materials, oxidation due to high temperatures acts in the opposite direction, resulting in a decrease in corrosion resistance. The amount of aluminum welded is 0.05 to 0.25
kg/d, a catalyst was applied to the substrate, and the peeling characteristics of the catalyst were investigated. As a result, it was found that the peeling rate was significantly improved compared to the peeling rate of 20% without thermal spraying, and that the larger the amount of welding, the smaller the peeling rate. However, when the amount of welding is 0.1 kg/cd or more, the peeling rate is about 4% and no significant change is observed, so when implementing the present invention, it is preferable that the amount of welding is about 0.1 kg/cd or less.

Next, we considered whether a lath-processed metal substrate coated with aluminum spraying would be suitable as a substrate.

did. From the viewpoint of catalytic activity, the thickness of the substrate was approximately 111 mm.

The process of applying lath processing to a metal plate is shown in FIG. 6 as described above, and the lath process increases the thickness of the metal plate by about 3 times and the length by 1.6 times, for example.

Therefore, for example, in order to obtain a substrate with a thickness of about 1 mm, it is necessary to use a stainless steel plate with a thickness of 0.3 fi as the substrate material. Lath machining involves the process of making alternating staggered cuts (a) and the process of pulling in a direction perpendicular to the direction of the cuts (a).
b) After processing, it has a three-dimensional structure as shown in FIGS. 7A and 7B.

In the present invention, in addition to corrosion resistance and peeling resistance, inorganic fibers are added to the catalyst component applied to the substrate in order to further improve these properties and to improve wear resistance. It was confirmed that the addition of inorganic fibers is effective not only in improving mechanical properties but also in improving denitrification performance.

Various types of inorganic fibers are known, but the properties required of the inorganic fibers added to the catalyst are high acid resistance and strength, and from this point of view, ceramic fibers are particularly preferred in the present invention. used. Whiskers have high strength, but are significantly more expensive (and metal fibers have problems with corrosion resistance.

Next, silica-alumina fibers were added to the catalyst paste applied to the substrate, and the peeling resistance was investigated.

The fiber has a diameter of 3 in consideration of kneadability with the catalyst paste.
Silica/alumina short fibers with a diameter of 0μ and a length of about 50 m were used, but the catalyst paste was coated on the substrate with the added amount of fibers varied in the range of 1 to 15 wt%. As a result of measuring the peeling rate in a drop test, the addition of inorganic fibers in small amounts (for example, about 1 wt%) has a significant effect, but when 5 wt% or more of fiber is added, the catalyst peeling rate becomes almost saturated. I understand.

In the present invention, a plurality of protrusions are formed on one side or both sides of a plate-shaped body coated with a catalyst mixed with inorganic fibers on the surface of a stainless steel lath plate manufactured as described above. .

The situation is shown in Figure 1. The plate-shaped body 9 coated with the catalyst is passed through a small gap 24 formed between the upper roll 11 and the lower roll 12. The roll 11.12 is provided with a plurality of projections 22 and depressions 23. Furthermore, when both rolls rotate and come into contact, the depth, size, and shape of the convex portion 22 of the roll 11 are matched with the concave portion 23 of the roll 12, and the concave portion 23 is exactly overlapped with the convex portion 22 so that the depth, size, and shape match. It is formed.

The plate-shaped body 9 that has passed between the rolls 11 and 12 becomes a plate-shaped catalyst lO having a plurality of convex portions 2 and concave portions 3. When the plate-like body 9 is passed between the rolls 11 and 12, both sides of the plate-like body 9 are covered with a smooth and thin film 15 such as a polyethylene film. This is to prevent part of the catalyst applied to the plate from peeling off and adhering to the roll. Note that when the plate-shaped body passes between the rolls 11 and 12, the catalyst is reliably pressed onto the substrate by both rolls on the flat portions other than the convex portions and concave portions.

The plate-like catalyst produced by the method of the present invention has a 100 to 18
After drying at 0°C, it is fired at 300 to 700°C or used as it is.

Figure 2 shows a situation in which the manufactured plate-shaped catalysts are stacked and used. The plate-shaped catalysts that are vertically adjacent to each other have a convex part 2 and a concave part 3.
A predetermined gap is maintained between the two.

FIG. 3 is a perspective view taken along the line QQ in FIG. 2.

FIG. 4 shows one embodiment of forming the protrusions 22 and recesses 23 on the roll shown in FIG.
This is an example in which a roll is implanted in the roll 11 and can be replaced. FIG. 5 shows an example in which a protruding mold 22 and a recessed mold 23 can be screwed into the rolls 11 and 12 with screws 2o, respectively. Of course, the outer peripheral surfaces 25 of molds 22 and 23 are cylindrical.

〔Effect of the invention〕

The catalyst produced by the method of the present invention has high mechanical rigidity and strength, high resistance to corrosive components in exhaust gas, no falling off of the catalyst from the substrate, and high production capacity (speed) during continuous production. Therefore, mass production of catalysts is underway.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the process of forming irregularities on a plate-shaped catalyst in the present invention, Fig. 2 is an explanatory diagram of the usage situation of the formed plate-shaped catalyst, and Fig. 3 is a Q-Q cut of Fig. 2. A side view, FIGS. 4 and 5 are explanatory diagrams for forming a mold that gives unevenness to a plate-shaped catalyst, FIG. 6 is an explanatory diagram of lath processing, and FIG. 7A is a cross-section of a lath-processed metal plate. FIG. 7B is a plan view of the lath-processed metal plate. 2... Convex portion of plate-shaped catalyst, 3... Concave portion of plate-shaped catalyst, 9
... Plate-like body whose surface is coated with a catalyst component, 10 ... Plate-like catalyst after molding, 11 ... Upper roll, 12 ... Lower roll, 15 ... Polyethylene film, 22 ...
- Convex portion provided on the roll, 23... Concave portion provided on the roll, 24... Gap between the upper roll 11 and the lower roll 12.

Claims (1)

[Claims] (1) In a method for producing a nitrogen oxide removal catalyst in which a catalyst component is coated on a thin metal plate, a substrate is formed by welding aluminum oxide onto a lath plate made from a thin stainless steel plate. By coating the surface of a plate-like body made by applying a catalyst component on a substrate with a smooth film-like material, and compressing it by sandwiching it between a pair of mold bodies each having a plurality of convex portions and corresponding concave portions. A method for producing a plate-shaped catalyst for removing nitrogen oxides, comprising forming a plurality of convex portions and/or concave portions on the plate-shaped body.