PLATE-SHAPED CATALYST AND METHOD OF PRODUCING SAME

Abstract: A plate-shaped catalyst for denitration of exhaust gas and a method of producing the same, having a large surface area and being saved in usage of the base metal thereof, which catalyst comprises an expanded metal strip the both surfaces of which are roughened, a catalytic layer coated on the entire surface area of said expanded metal strip, and conical convex and concave portions, adjoining to one another at a predetermined distance on said expanded metal strip having the catalytic layer thereon, the surfaces of said catalytic layer being formed with wave-shapes at a pre­ determined pitch without deforming substantially the expanded metal strip. The plate-shaped catalysts are piled in a flame box so that said convex and concave portion may not meet with one another by means of the convex and concave portions as spacers thereof to form a catalyst unit.

Description: The present invention relates to a plate-shaped catalyst and a method of producing the same, and more particularly to a plate-shaped catalyst for denitration using an expanded metal strip as a base plate. In the past, in United States Patent No. 4,567,630, there was described a plate-shaped catalyst for denitration using an expanded metal strip as a base plate. A method for producing this plate-shaped catalyst mainly includes: a step of forming an expanded metal strip; a step of spray-coating molten metal onto the expanded metal strip to form roughened surfaces thereon; a step of coating a catalytic substance onto the thus surface-roughened expanded metal strip; a step of holding the catalyst strip thus obtained by the catalyst coating step between an upper and a lower sheets to protect the surfaces thereof; a step of applying pressure to the catalyst strip to closely attach the catalytic substance onto the roughened surfaces for flattening the surfaces out; a step of applying press-work to thus obtained catalyst strip to form it into a predetermined shape; and a step of cutting the catalyst strip to the specified length to obtain a plate-shaped catalyst. During the above-described steps, the plate-shaped catalyst strip which is prepared by coating the catalytic substance onto the expanded metal Strip is press-worked to form V-shaped ridges on the both surfaces thereof, plate-shaped catalysts obtained by cutting the catalyst strips are piled up on each other by use of the ridges as spacers, and are put in practical use as a catalyst unit. When the catalyst unit is used as an exhaust gas denitrating catalyst unit, exhaust gases mixed with a reducing agent such as ammonia are passed through a multiplicity of channels formed by the piled-up upper and lower plate-shaped catalysts and the ridges thereof, whereby nitrogen oxides (NOx) contained in the exhaust gases catalytically are reacted with ammonia in the exhaust gases, so that the exhaust gases can be purified. In the aforesaid plate-shaped catalyst unit, since the expanded metal strip is press-worked to form the ridges being V-shaped in cross section as the spacers after coating the catalyst substance onto the expanded metal strip, the expanded metal strip is bent into a form being V-shaped in cross section at a predetermined distance, whereby the expanded metal strip is reduced in size in a direction of bending. For this reason, in order to obtain the plate-shaped catalyst unit having the predetermined length, it is necessary to use the expanded metal strip having the size allowing for the reduction in size due to the aforesaid press working. For example, in order to finish the expanded metal strip to the width of 500mm, it is necessary to use the expanded metal strip having a width of about 525mm. According to the present invention there is provided a plate-shaped catalyst (1) comprising: an expanded metal strip (12) having roughened surfaces; said surface-roughened expanded metal strip (12) having a layer of a catalytic substance coated on each entire surface thereof, characterised in that said catalytic layer is formed with a wave-shaped profile (14) independent of the expanded metal strip, having a predetermined pitch, characterised in that and said expanded metal strip (12) having the catalytic layer (14) formed thereon is formed with a plurality of convex and concave portions (2, 2A) adjoining one another and separated by a predetermined distance. According to a further aspect of the present invention there is provided a method of coating a catalytic substance (11) on a surface-roughened expanded metal strip (12); characterised by a step of passing said expanded metal strip having the catalytic substance coated thereon through a pair of rolls (7, 7A) having formed thereon a wave-shaped profile arranged at a pitch of from 1 to 3mm and having a plurality of adjoining convex and concave pressing portions (16, 16A) and arranged such that said wave-shaped profiles and said convex and concave pressing portions on respective rolls mesh with each other, , to form convex and concave portions (2, 2A) in the expanded metal strip (12) and to form wave-shaped profile in the surfaces of the catalytic substance layer, with the rolling pressure arranged such that said expanded metal strip (12) is not substantially deformed except for the formation of said convex and concave portions (2, 2A). Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a perspective view showing an example of the plate-shaped catalyst according to the present invention; Fig. 2 is an enlarged view showing a portion II in Fig. 1; Fig. 3 is an explanatory view showing an example of the processes of producing the plate-shaped catalyst according to the present invention; Fig. 4 is a perspective view showing the expanded metal strip as being the base strip of the plate-shaped catalyst according to the present invention; Fig. 5 is an enlarged view showing a portion V in Fig. 4; Fig. 6 is a sectional view in the direction indicated by the arrows from the line VI-VI in Fig. 5; Fig. 7 is a sectional view showing a state in which a wave-shaped catalytic layer is formed in the direction of expanding of the expanded metal strip (an arrow-indicated direction E in Fig. 6); Fig. 8 is a sectional view in the direction indicated by the arrows from the line VIII -VIII in Fig. 5, showing a state in which the wave-shaped catalytic layer is formed in a direction perpendicular to the direction of expanding of the expanded metal strip; Fig. 9 is an explanatory view showing the step of passing the expanded metal strip coated thereon with the catalytic substance through the wave-shape rolls having the specified convex and concave portions for press-working; Fig. 10 is a perspective view showing a state in which the plate-shaped catalysts obtained by cutting the catalyst strip press-worked in Fig. 9 are piled up on each other; Fig. 11 is a sectional view in the direction indicated by the arrows from the line XI-XI in Fig. 10; Fig. 12 is an explanatory view of the process showing the case where a cutting machine is provided between the coating rolls for coating the catalytic substance onto the expanded metal strip and the pressing rolls for press-working the wave-shapes and the convex and concave portions on the catalyst strip; Fig. 12A is a plan view corresponding to Fig. 12; and Figs. 13 and 14 are charts showing the results of the denitrating tests and the peel strength tests by use of the plate-shaped catalysts according to the present invention, respectively. The present invention will hereunder be described in detail with reference to the accompanying drawings. Referring to Fig. 1, a plate-shaped catalyst 1 according to the present invention includes: a catalytic layer attached on the entire area of the both surfaces of the surface-roughened expanded metal strip so as to block openings formed in the expanded metal strip; convex and concave portions 2 and 2A adjoining to one another which are provided at a predetermined distance on the expanded metal strip having thereon the catalytic layer; and a wave-shaped profile 14 arranged at a predetermined pitch on the surfaces of the catalytic layer. Figs. 4 and 5 show the expanded metal strip 12 used in the present invention. Examples of dimensions shown in Fig. 5 are: 4.5mm for an interval A; 2.05mm for an interval B; 0.75mm for an interval C; and 0.2mm for an interval D. The expanded metal strip can be available in the market. However, when slits are formed in a planar metal plate at a predetermined distance and the plate is expanded in a direction perpendicular to the slits (herein, referred to as the "direction E of expanding") to form openings 15 having a predetermined size, the expanded metal strip can be easily produced. This expanded metal plate thus obtained is spray-coated thereon with a metal such as aluminum in order to allow the catalytic substance to easily attach thereonto, so that the surfaces thereof can be roughened. The catalytic substances is coated on the entire areas of the both surfaces of the expanded metal strip thus surface-roughened in such a manner to block the openings 15 formed in the expanded metal strip as the catalytic substance. This catalytic substance includes denitrating catalytic components such as Ti, V, Mo, W, etc., and besides, may further includes a reinforcing component such as inorganic fibers when necessary. The catalytic substance is normally supplied in a plasticized state having 70-90 wt % of water, being easily formable. The coating amount of the catalytic substance on the expanded metal strip is 60-90 wt %, preferably 70-85 wt %. This plate-shaped catalyst is passed between rolls 7 and 7A (Refer to Figs. 3 and 9) having the wave-shapes arranged at the predetermined pitch and the convex and concave portions so as to form the wave-shapes on the surfaces of the catalytic layer, and simultaneously the convex and concave portions adjoining to one another are formed on the expanded metal strip. By combining a direction of the wave-shapes of the wave-shape rolls with a direction of feeding the expanded metal strip, the wave-shapes shown in Figs. 7 and 8 are formed. More specifically, Fig. 7 shows a case where the direction of the wave-shapes of the wave-shape rolls is aligned with the direction of expanding direction E of the expanded metal strip, whereby the catalytic layer 14 having the generally uniform thickness is formed on the surfaces of the expanded metal strip. On the other hand, when the direction of the wave-shapes of the wave-shape rolls perpendicularly intersects the direction of expanding of the expanded metal strip as shown in Fig. 8, the wave-shapes are formed only by the catalytic layer on the both surfaces of the expanded metal strip. The pitch P (a distance from a crest to the following crest) of the wave-shapes of the catalyst itself according to the present invention is preferably 1.5-2.5mm. Furthermore, the height of the wave-shape is preferably about 1-3mm. The convex portion 2 and the concave portion 2A are formed of conical shapes similar to each other, and formed by the pair of pressing rolls 7 and 7A having the wave-shapes and the conical convex and concave portions 16 and 16A equal in depth at the same time as the formation of the wave-shapes, said wave-shapes and convex and concave portions being in mesh with each other. The convex portions 2 and the concave portions 2A, which are formed on the plate-shaped catalyst, are preferable to adjoin to one another, since the convex portions and the concave portions advantageously do not meet with one another at the time the plate-shaped catalysts are piled up each other by use of the convex and concave portions as the spacers as shown in Fig. 10. These convex portions 2 and concave portions 2A may be arranged in a zigzag manner in addition to the checkerboard manner as shown in Fig. 1. An example of the method of producing the plate-shaped catalyst according to the present invention will hereunder be described with reference to Fig. 3. In this system, rolls 3 and 3A for coating a catalytic slurry, the wave-shape pressing rolls 7 and 7A and a cutting machine 8 are serially arranged, whereby a process of coating a catalytic substance 11, a pressing process and a cutting process are continuously applied to the expanded metal strip. Between the coating rolls 3 and 3A, papers or plastic sheets 4 are provided on and under the expanded metal strip, so that the catalytic substance is prevented from adhering to the coating rolls 3 and 3A, and the surfaces of the catalyst is finished flat. Also, between the wave-shape pressing rolls 7 and 7A, plastic sheets or papers (kraft paper, for example) 5 are provided on and under the catalytic strip, and the catalyst strip is pressed to be dense at the same time with the formation, so that the catalyst can be prevented from falling off and the catalytic substance can be prevented from adhering to the wave-shape pressing rolls. The catalytic substance 11 is supplied onto the expanded metal strip which is fed between the coating rolls 3 and 3A, pressed between the coating rolls, and spread onto the undersurface of the expanded metal strip through the openings thereof, whereby the catalytic layer coating the both surfaces of the expanded metal strip is formed. The catalyst strip having been threaded through the coating rolls 3 and 3A is passed through the pressing rolls 7 and 7A having the wave-shapes and the convex and concave portions, where the catalytic strip is formed into aforesaid predetermined shape. A plate-shaped catalyst 6 having threaded through the wave-shape pressing rolls is cut with blades 10 in a cutting machine 8 to a predetermined length, whereby a plate-shaped catalyst 6A can be obtained. As the plastic sheet 4 or 5, it is preferable to use a sheet of polyethylene, polypropylene, polyester or the like. Fig. 9 is the explanatory view showing the pressing rolls 7, 7A and thereabout. Formed on the pressing rolls 7 and 7A are the wave-shapes being V-shaped in cross section at a pitch of 1.5-2.5mm in a direction normal to the circumferential direction, and the conical convex portions 2 and concave portions 2A adjoining to one another are provided at a predetermined distance. In this case, in the expanded metal strip integrally attached thereonto with the catalytic layer, the base strip is also deformed to a predetermined shape at the convex portions 2 and the concave portions 2A as shown in Fig. 2. However, in the other wave-shaped portion of the catalytic strip, only the catalytic layer on the surfaces is formed to provide the wave-shaped portions, but the expanded metal strip itself is not deformed into the wave-shapes. Pressure of the pressing rolls is suitably set in consideration of the above. The expanded metal strip as being the base strip is partially deformed at the convex and concave portions and the wave-shapes are formed only on the catalytic layer as described above, so that the catalyst strip can be produced without changing the dimensions of the expanded metal strip. In order to form the wave-shapes on the surfaces of the catalytic layer of the catalyst strip without substantially deforming the expanded metal strip as the base strip, it is preferable to form the wave-shapes having about a pitch one half the pitch of the openings of the expanded metal strip. This is because, as shown in Figs. 7 and 8, the wave-shapes on the surfaces of the expanded metal strip itself meet with the wave-shapes formed on the catalytic layer, so that the adherability (peel strength and resistance to abrasion) is improved. Fig. 7 shows a case where the wave-shapes of the catalytic layer 14 are formed in the same direction as the expanding direction E of the expanded metal strip 12, and Fig. 8 shows a case where the wave-shapes of the catalytic layer 14 are formed in a direction perpendicular to the expanding direction E. In the case of Fig. 7, the catalytic layer is attached more strictly (in the more uniform thickness) to the surfaces of the expanded metal strip than the case of Fig. 8. In the case of Fig. 8, the catalytic layer is attached to the expanded metal strip in an ununiform thickness, and, from the viewpoint of resistance to abrasion, the case of Fig. 7 is superior to the case of Fig. 8. The wave-shapes of the pressing rolls shown in Fig. 9 are formed in the direction normal to the circumferential direction. However, so-called star-shaped rolls, in which the wave-shapes are formed in the circumferential direction, may be used. A multiplicity of plate-shaped catalysts 6A obtained by the process shown in Fig. 3 are piled up one another by use of the convex portions 2 and the concave portions 2A of the plate-shaped catalysts as the spacers as shown in Fig. 10 and housed in a suitable frame member, to thereby form a catalytic unit. In Fig. 10, a flowing direction of the exhaust gases is indicated by an arrow G. When the exhaust gases are passed through parallel to the wave-shapes as described above, the higher denitrating performance can be obtained. However, the passing direction of the exhaust gases is not limited to this, and such an arrangement of the plate-shaped catalysts may be adopted that the exhaust gases may be passed in a direction oblique to the wave-shapes or passed in a direction perpendicular to the direction G in Fig. 10. Next, Figs. 12 and 12A show a case where the cutting machine 8 is provided between the coating rolls 3 and 3A and the pressing rolls 7 and 7A. according to the present invention, no substantial change in size in the widthwise direction occurs due to threading through the pressing rolls 7 and 7A, so that, even if the cutting machine is provided in front of the pressing rolls, the plate-shaped catalyst 6A constantly having the predetermined shape can be produced. EXAMPLE As the base strip, there was used the expanded metal strip having the dimensions shown in Fig. 5 and being surface-roughened by spray-coating molten aluminum thereonto at a rate of 30g/m². The expanded metal strip thus surface-roughened was coated thereon with a denitrating catalytic slurry (concentration of catalyst: 70 wt %) containing therein titanium oxide, vanadium oxide or molybdenum oxide as the catalyst, by use of the coating rolls (coating amount to the expanded metal strip: 77 wt %). Subsequently, the expanded metal strip was subjected to the pressing rolls shown in Fig. 9 (diameter of rolls: 157mm; pitch of wave-shapes: 2mm; depth of wave-shapes: 2mm; height of conical convex and concave portions: 3mm; outside diameter: 16mm; R of vertex of cone: 3-4mm; 20 pieces/roll; and zigzag arrangement), to thereby produce the plate-shaped catalysts having wave-shapes and the convex and concave portions according to the present invention. The plate-shaped catalysts thus obtained were piled up on each other to provide a catalytic unit as shown in Fig. 10, passed therethrough with the exhaust gases in parallel to the wave-shapes (in a direction indicated by the arrow G), and subjected to a denitrating test (AV (air velocity): 51m/m, temperature: 350°C, NH₃/NO₂ = 1.2), using ammonia as the reducing agent. Furthermore, to evaluate the peel strength of the catalyst, a release amount of the catalyst was measured such that the plate-shaped catalyst having the predetermined dimensions was dropped ten times from a height of one meter. For comparison, a flat plate-shaped catalyst (the amount of coating onto the flat plate-shaped was 77 wt %) having the ridges being V-shape in cross section was prepared, and subjected to the denitration test and the dropping test performed in the same manner as described above. Figs. 13 and 14 show the results thus obtained. From the results shown above, it was shown that the plate-shaped catalyst according to the present invention was improved in denitration rate by about 2.5% (from 78.3% to 80.8%) and improved considerably in peel strength in the dropping test (averaged 0.78g/T.P. (Total Pieces) was reduced to 0.45g/T.P.) as compared with the conventional flat plate-shaped catalyst. In addition to the improvements in the denitration rate and peel strength as described above, in the plate-shaped catalyst according to the present invention, the expanded metal strip can adopt the same width as the width of the plate-shaped catalyst as being the final product, whereby there is no need for cutting the expanded metal strip considering the reduction in width thereof due to the working, whereby the cutting loss and handling of the expanded metal strip are improved, so that the usage of the base strip can be decreased as compared with the conventional one. Furthermore, when the base strips of the same dimensions are used, the present invention can produce a plate-shaped catalyst having a larger surface area being in contact with the exhaust gases than the conventional one. The conical convex and concave portions provided on the plate-shaped catalyst do not form the channels for the exhaust gas flow as compared with the conventional plate-shaped catalyst, in which the ridges of V-shape in cross section are formed, so that the dispersion properties of the exhaust gases can be improved. According to the present invention, the specified wave-shapes and convex and concave portions are formed on the plate-shaped catalyst, so that the usage of the expanded metal strip as the base strip can be reduced to save the raw material, and further, the surface area of the catalysts can be increased to improve the rate of reaction. The preferred embodiments of the present invention can provide plate-shaped catalyst and a method of producing the same, wherein the size of the base strip, as it is, becomes equal to the size of the plate-shaped catalyst and a catalytic surface area equal to or more than one of the conventional plate-shaped catalyst, without the expanded metal strip as the base strip being reduced in size during the formation of the plate-shaped catalyst.

Claims: A plate-shaped catalyst (1) comprising: an expanded metal strip (12) having roughened surfaces; said surface-roughened expanded metal strip (12) having a layer of a catalytic substance coated on each entire surface thereof; characterised in that said catalytic layer is formed with a wave-shaped profile (14) independent of the expanded metal strip, having a predetermined pitch, and said expanded metal strip having the catalytic layer (14) formed thereon is formed with a plurality of convex and concave portions (2,2A) adjoining one another and separated by a predetermined distance. A plate-shaped catalyst according to claim 1, wherein said catalyst is an exhaust gas denitrating catalyst. A plate-shaped catalyst according to claim 1, wherein said expanded metal strip (12) has openings therein of pitch in a direction of expanding of about 2mm, the pitch of openings arranged in a direction perpendicular to the direction of expanding is about 4.5mm and a pitch of said wave-shaped profile is about 2mm. A plate-shaped catalyst according to claim 1, wherein said surface-roughened expanded metal strip (12) is formed of an expanded metal strip on which molten metal is spray-coated. A plate-shaped catalyst according to claim 1, wherein said wave-shaped profile formed on the surfaces of the catalytic layer is formed in a direction perpendicular to the direction of expanding of said expanded metal strip (12). A plate-shaped catalyst according to claim 1, wherein said wave-shaped profile is formed in a direction in parallel to the direction of expanding of said expanded metal strip (12). A method of coating a catalytic substance (11) on a surface-roughened expanded metal strip (12); characterised by a step of passing said expanded metal strip having the catalytic substance (11) coated thereon through a pair of rolls (7,7A) having formed thereon a wave-shaped profile arranged at a pitch of from 1 to 3mm and having a plurality of adjoining convex and concave pressing portions (16,16A) and arranged such that said wave-shaped profiles and said convex and concave pressing portions on respective rolls mesh with each other, to form convex and concave portions (2,2A) in the expanded metal strip (12) and to form the wave-shaped profile in the surfaces of the catalytic substance layer, with the rolling pressure arranged such that said expanded metal strip (12) is not substantially deformed except for the formation of said convex and concave portions (2,2A). The method of producing a plate-shaped catalyst according to claim 7, wherein said catalytic substance is an aqueous slurry containing therein 70-90 wt % of an exhaust gas denitrating catalyst. The method of producing a plate-shaped catalyst according to claim 7, wherein said expanded metal strip (12) has openings therein of pitch in a direction of expanding (E) of about 2mm, a pitch of the openings in a direction perpendicular to the direction of expanding is about 4.5mm and a pitch of the wave-shaped profile of the rolls (7,7A) is about 2mm. The method of producing a plate-shaped catalyst according to claim 7, wherein said expanded metal strip (12) is one in which molten metal is spray-coated onto said expanded metal strip (12). The method of producing a plate-shaped catalyst according to claim 7, wherein said wave-shaped profile on the rolls (7,7A) is arranged in a direction perpendicular to axes of rolls and said expanded metal strip is fed to the rolls (7,7A) in a direction perpendicular to a direction of expanding (E) of said expanded metal strip (12). The method of producing a plate-shaped catalyst according to claim 7, wherein said wave-shaped profile on the rolls (7,7A) is arranged in a direction perpendicular to the axes of the rolls and said expanded metal strip (12) is fed to the rolls (7,7A) in a direction in parallel to a direction of expanding (E) of said expanded metal strip. The method of producing a plate-shaped catalyst according to claim 7, wherein a step of cutting the plate-shaped catalyst is provided between said step of coating a catalytic substance on said expanded metal strip (12) and said step of forming the surfaces of a catalytic layer on said expanded metal strip (12) into the wave-shaped profile.

Inventors: ISHIDA, NOBUYOSHI KURE WORKS, KUWADA, KAZUHIKO AKITSU BRANCH, MICHIMOTO, TAKASHI KURE WORKS, NAKAMOTO, YUKINARI AKITSU BRANCH
Applicants: BABCOCK-HITACHI KABUSHIKI KAISHA
Application year: 1988
Main classification: B01J35
IPC codes: B01J35, B01D53, B01J37