HONEYCOMB CATALYTIC APPARATUS

Abstract: A catalytic combustion apparatus for gas turbine or an exhaust gas purifier apparatus comprises a honeycomb structure (20) disposed in a flow tube (10). A ring-­ shaped fringe region of the lower-course end face of the honeycomb structure (20) abuts against a ring-shaped second supporting member (40). The second supporting member (40) has a plurality of passages (42) which allow a fluid to flow out downstream from the fringe region. In this arrangement, the fluid from the fringe region is caused to flow downstream through these passages (42). Accordingly, tensile thermal stress is reduced, so that the honeycomb structure (20) is prevented from being damaged thereby. Since the honeycomb structure (20) is supported by the second supporting member in planar contact therewith, moreover, stress is prevented from being concentrated on part of the structure (20). Thus, the honeycomb structure (20) can be securely supported without being damaged by any stress.

Description: The present invention relates to a honeycomb catalytic apparatus for a gas turbine or an exhaust gas purifier apparatus and having a honeycomb structure impregnated with a catalyst. A high-speed high-temperature fluid flows through the honeycomb structure. In a catalytic combustion apparatus for gas turbine, a honeycomb structure impregnated with a catlyst is mounted in a tube through which a high-speed high-temperature fluid, e.g., a combustion gas, flows downstream. In this arrangement, the combustion gas is subjected to a catalytic reaction, and its temperature is kept below a predetermined level (1,300°C), so that production of NO x is restrained. For the same purpose, an exhaust gas purifier apparatus is also provided with a honeycomb structure. The honeycomb structure has upper- and lower-course end faces extending at right angles to the axial direction in which the combustion gas flows. The structure also includes a number of cells which allow the combustion gas to flow from the upper-course end face to the lower-course end face, and cause the gas to come into satisfactory contact with the catalyst. The honeycomb structure is formed of a ceramic material, e.g., cordierite, in order to be able to be fully impregnated with the catalyst. This ceramic material, however, is very brittle. The honeycomb structure is surrounded and radially supported by a cylindrical supporting member which has a shock absorbing effect. Thus, even though the honeycomb structure and the tube are expanded to different degrees by the combustion gas, due to the difference in coefficient of linear expansion between them, the shock absorbing supporting member absorbs the force from the tube to press the structure. In this manner, the brittle honeycomb structure is prevented from being damaged. The honeycomb structure is also supported in the axial direction of the tube. Thus, it is prevented from being dislocated in the axial direction by means of the high pressure of the combustion gas. More specifically, a ring-shaped fringe region of the lower-course end face of the honeycomb structure abuts against the ring-shaped supporting member. In this arrangement, the honeycomb structure is supported in the axial direction, and the combustion gas is allowed to flow out downstream from a central region of the lower-course end face of the structure. The ring-shaped fringe region, however, is covered by the ring-shaped supporting member. Accordingly, the combustion gas cannot flow out downstream from the fringe region, and catalytic reaction can hardly take place in the fringe region. As a result, the temperature of the fringe region is lower than that of the central region. In other words, a temperature gradient is created in the radial direction of the honeycomb structure. Thus, tensile thermal stress may possibly be produced between the fringe region and the central region, and damage the structure. US-A-4115071 discloses a honeycomb catalytic apparatus comprising a tube having an axial direction in which a fluid flows and a radial direction perpendicular to the axial direction. A honeycomb structure is disposed in the tube and is impregnated with a catalyst. A first supporting member is fixed in the tube and surrounds the honeycomb structure to support the honeycomb structure in the radial direction. A ring-shaped second support member is fixed in the tube in contact with a ring-shaped fringe region of a lower-course end face of the honeycomb structure, thereby supporting the honeycomb structure in the axial direction. The ring-shaped supporting member is formed with passages but these do not permit fluid to flow through the ring-shaped fringe region. DE-A-2432285 discloses a honeycomb catalytic apparatus having a tube which has an axial direction in which the fluid flows and a radial direction perpendicular to the axial direction. A honeycomb structure is disposed in the tube and is impregnated with a catalyst. A supporting member is fixed in the tube and surrounds the honeycomb structure thereby supporting the honeycomb structure in the radial direction. DE-A-2248442 discloses a honeycomb catalytic apparatus with the same general features. In the exhaust gas purifier apparatus, a flow tube for an exhaust gas has a taper portion whose diameter becomes smaller with distance from its upper-course end. The lower-course edge of the honeycomb structure abuts against the taper portion, thereby axially supporting the structure. In other words, the lower-course edge of the honeycomb structure is supported by the taper portion in linear contact therewith. Therefore, catalytic reaction can take place even in the fringe region, and no thermal stress can be produced. The pressure of the exhaust gas in the purifier apparatus is lower than that of the combustion gas in the catalytic combustion apparatus. Thus, in the exhaust gas purifier apparatus, the honeycomb structure cannot be dislocated downstream even though it is supported by the taper portion only in linear contact therewith. If the supporting method using the taper portion is applied to the catalytic combustion apparatus, however, stress may possibly be concentrated on the lower-course edge of the honeycomb structure, thereby damaging the structure, since the pressure of the combustion gas is relatively high. An object of the present invention is to provide a honeycomb catalytic apparatus in which a honeycomb structure is securely mounted and which prevents production of thermal stress in the structure and concentration of stress on part of the structure, thereby preventing the honeycomb structure from being damaged by stress. According to the present invention, there is provided a honeycomb catalytic apparatus comprising: a tube through which a fluid flows downstream, said tube having an axial direction in which the fluid flows and a radial direction perpendicular to the axial direction; a honeycomb structure disposed in the tube and impregnated with a catalyst, said honeycomb structure having upper- and lower-course end faces extending at right angles to the axial direction and a plurality of cells which allow the fluid to flow from the upper-course end face to the lower-course end face, said lower-course end face having a ring-shaped fringe region defined thereon; a first supporting member fixed in the tube and surrounding the honeycomb structure, thereby supporting the honeycomb structure in the radial direction; and a ring-shaped second supporting member fixed in the tube and contacting with the ring-shaped fringe region of the lower-course end face of the honeycomb structure, thereby supporting the honeycomb structure in the axial direction, said second supporting member having a plurality of passage, characterized in that the passages are so situated that the passages allow the fluid to flow out downstream from the fringe region. According to the invention, the honeycomb structure is supported in the axial direction by the ring-shaped second supporting member, and in the radial direction by the first supporting member. Thus, the honeycomb structure is securely supported by the two supporting members. The fluid from the gas is caused to flow out downstream from the ring-shaped fringe region can be caused to flow downstream through the passages of the ring-shaped second supporting member. Also in this fringe region, therefore, catalytic reaction can take place without restraint. Accordingly, a temperature difference can hardly be produced between the fringe region and a central region of the honeycomb structure. Namely, the honeycomb structure can hardly be subjected to any temperature gradient in the radial direction. In consequence, tensile thermal stress in the radial direction is reduced, so that the honeycomb structure is prevented from being damaged thereby. Further, the honeycomb structure is axially supported by the ring-shaped second supporting member in planar contact therewith. Thus, stress is prevented from being concentrated on part of the honeycomb structure, so that the structure cannot be damaged by stress concentration. Thus, according to the present invention, the honeycomb structure can be securely supported without being damaged by any stress. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view of a flow tube of a catalytic combustion apparatus for gas turbine or an exhaust gas purifier apparatus according to a first embodiment of the present invention, as taken along the axis thereof; Fig. 2 is a schematic view of a honeycomb structure in the flow tube, as taken from the upper-course side; Fig. 3 is a schematic view of a ring-shaped second supporting member in the flow tube, as taken from the upper-course side; Fig. 4A is a schematic view of a second supporting member according to a modification of the first embodiment, as taken from the upper-course side; Fig. 4B is a sectional view of the second supporting member of Fig. 4A, as taken along the axis thereof; Fig. 5A is a schematic view of a second supporting member according to another modification of the first embodiment, as taken from the upper-course side; Fig. 5B is a sectional view of the second supporting member of Fig. 5A, as taken along the axis thereof; and Fig. 6 is a sectional view of a flow tube of a catalytic combustion apparatus for gas turbine or an exhaust gas purifier apparatus according to a second embodiment of the present invention, as taken along the axis thereof. Referring now to Fig. 1, there is shown flow tube 10 of a catalytic combustion apparatus for generating gas turbine or an exhaust gas purifier apparatus according to a first embodiment of the present invention. A high-speed high-temperature fluid is caused to flow downstream (from left to right in Fig. 1) in tube 10. In the catalytic combustion apparatus, a combustion gas is caused to flow downstream in tube 10, and is then supplied through the outlet of the tube to a generating gas turbine (not shown) which is connected to the tube outlet. In the exhaust gas purifier apparatus, an exhaust gas is caused to flow downstream in tube 10. Tube 10 has an axial direction, in which the fluid flows, and a radial direction perpendicular to the axial direction. Honeycomb structure 20 shown in Fig. 2 is disposed in tube 10. Structure 20 has upper- and lower-course end faces which extend at right angles to the axial direction. It also includes a number of cells 21 which allow the combustion gas to flow from the upper-course end face to the lower-course end face, and cause the gas to come into satisfactory contact with a catalyst. The honeycomb structure is formed of a ceramic material, e.g., cordierite, in order to be able to be fully impregnated with the catalyst. Cells 21 are arranged at a density of 16 to 32 per centimetre square (100 to 200 to one inch square). The pitch of cells 21 ranges from 1.5 to 1.8 mm. Honeycomb structure 20 is surrounded by cylindrical first supporting member 30 fixed to the inner wall of tube 10, so that it is supported in the radial direction. Supporting member 30 is formed of a material which has a shock absorbing effect. Thus, even though structure 20 and tube 10 are expanded to different degrees by the combustion gas, due to the difference in coefficient of linear expansion between them, supporting member 30 absorbs the force from tube 10 to press structure 20. In this manner, the honeycomb structure is prevented from being damaged. Further, honeycomb structure 20 is supported in the axial direction by ring-shaped second supporting member 40 fixed to the inner wall of tube 10. Thus, a ring-shaped fringe region of the lower-course end face of structure 20 abuts against the ring-shaped upper-course end face of supporting member 40. The inside diameter of second supporting member 40 is shorter than the outside diameter of honeycomb structure 20 by a predetermined margin. Thus, structure 20 is prevented from being dislocated downstream, and the combustion gas is allowed to flow out downstream from a central region of the lower-course end face of structure 20. In the present invention, moreover, second supporting member 40 has a number of comb teeth 41 formed on the inside thereof with respect to the radial direction, so as to face the ring-shaped fringe region of the lower-course end face of honeycomb structure 20, as shown in Fig. 3. Each tooth 41 extends in the axial direction of the second supporting member so as to cover the overall length thereof. Defined between teeth 41 are passages 42 which allow the combustion gas to flow out downstream from the ring-shaped fringe region. The pitch of passages 42 is 1.0 mm, which is shorter than the pitch of cells 21. Passages 42 and cells 21 may be arranged at substantially equal pitches. The following is a description of the operation of the apparatus. When the combustion gas or exhaust gas enters the cells of honeycomb structure 20, it undergoes a catalytic reaction. Thereafter, most of the gas is caused to flow downstream through the central region of the lower-course end face of structure 20. As a result, the temperature of the gas is kept below a predetermined level, so that production of NO X is restrained. In the conventional case, the gas is not allowed to flow out downstream from the ring-shaped fringe region of the lower-course end face of honeycomb structure 20. According to the present invention, however, ring-shaped second supporting member 40 has a number of passages 42 which face the fringe region. In this arrangement, the gas is caused to flow out downstream from the ring-shaped fringe region through passages 42, as indicated by arrow A in Fig. 1. Also in this fringe region, therefore, catalytic reaction can take place without restraint. Accordingly, a temperature difference can hardly be produced between the fringe region and the central region of the honeycomb structure. Namely, the honeycomb structure can hardly be subjected to any temperature gradient in the radial direction. In consequence, tensile thermal stress in the radial direction is reduced, so that the honeycomb structure is prevented from being damaged thereby. Thus, according to the present invention, honeycomb structure 20 is supported in the axial direction by ring-shaped second supporting member 40, and in the radial direction by first supporting member 30. In other words, the honeycomb structure is securely supported by the two supporting members. As mentioned before, moreover, the tensile thermal stress in the radial direction is reduced, so that honeycomb structure 20 is prevented from being damaged by the tensile stress. Further, honeycomb structure 20 is axially supported by ring-shaped second supporting member 40 in planar contact therewith. Thus, stress is prevented from being concentrated on part of structure 20, so that structure 20 cannot be damaged by stress concentration. Thus, according to the present invention, the honeycomb structure can be securely supported without being damaged by any stress. Figs. 4A and 4B show a modification of the second supporting member. In this case, each passage 42 extends in the axial direction of second supporting member 40 so as to cover half the length thereof, and hole 43 is formed on the lower-course side of passages 42. In this arrangement, the gas from the ring-shaped fringe region is caused to flow downstream through passages 42 and hole 43. Figs. 5A and 5B show another modification of the second supporting member. In this case, second supporting member 40 includes outer ring member 45 fixed to the inner wall of tube 10 and inner ring member 46 fixed to the inner wall of member 45. Inner member 46 is formed of a porous Structure having a number pores which define passages 42. In this arrangement, the gas from the ring-shaped fringe region is caused to flow downstream through the pores of the porous structure. Fig. 6 shows a second embodiment of the present invention. In this case, third supporting member 50 is disposed on the upper-course side of honeycomb structure 20. Thus, a second ring-shaped fringe region of the lower-course end face of structure 20 abuts against the lower-course end face of supporting member 50. Second and third supporting members 40 and 50, like the modification shown in Fig. 5, is composed of outer ring member 45 and porous inner ring member 46. In this arrangement, honeycomb structure 20 can be more securely supported by second and third members 40 and 50 without entailing production of any thermal stress therein.

Claims: A honeycomb catalytic apparatus comprising: a tube (10) through which a fluid flows downstream, said tube (10) having an axial direction in which the fluid flows and a radial direction perpendicular to the axial direction; a honeycomb structure (20) disposed in the tube (10) and impregnated with a catalyst, said honeycomb structure (20) having upper- and lower-course end faces extending at right angles to the axial direction and a plurality of cells (21) which allow the fluid to flow from the upper-course end face to the lower-course end face, said lower-course end face having a ring-shaped fringe region defined thereon; a first supporting member (30) fixed in the tube (10) and surrounding the honeycomb structure (20), thereby supporting the honeycomb structure (20) in the radial direction; and a ring-shaped second supporting member (40) fixed in the tube (10) and contacting with the ring-shaped fringe region of the lower-course end face of the honeycomb structure (20), thereby supporting the honeycomb structure (20) in the axial direction, said second supporting member (40) having a plurality of passage (42), characterized in that the passages (42) are so situated that the passages (42) allow the fluid to flow out downstream from the fringe region. A honeycomb catalytic apparatus according to claim 1, characterized in that said second supporting member (40) has a plurality of comb teeth (41) between adjacent ones of which the passages (42) are defined, the comb teeth (41) having a width sufficient to support the honeycomb structure (20) in the axial direction, the passages (42) having a width such that the fluid of the fringe region of the honeycomb structure can flow out downstream, and the pitch of the passages (42) being substantially equal to the pitch of the honeycomb structure (20). A honeycomb catalytic apparatus according to claim 1, characterized in that said second supporting member (40) includes a plurality of comb teeth (41) formed on the inside thereof with respect to the radial direction so as to face the ring-shaped fringe region, said passages (42) being defined between the teeth (41). A honeycomb catalytic apparatus according to claim 1, characterized in that each said passage (42) open out into a hole (43) and extends in the axial direction of the second supporting member (40) so as to cover a middle length thereof. A honeycomb catalytic apparatus according to claim 1, characterized in that each said passage (42) extends in the axial direction of the second supporting member (40) so as to cover the overall length thereof. A honeycomb catalytic apparatus according to claim 1, characterized in that the pitch of said passages (42) is shorter than that of the cells (21) of the honeycomb structure (20). A honeycomb catalytic apparatus according to claim 1, characterized in that the pitch of said passages (42) is substantially equal to that of the cells (21) of the honeycomb structure. A honeycomb catalytic apparatus according to claim 1, characterized in that said second supporting member (40) is formed of a porous structure having a number of pores defining the passages (42). A honeycomb catalytic apparatus according to claim 1, characterized in that said upper-course end face has a second ring-shaped fringe region defined thereon, and which further comprises a ring-shaped third supporting member (50) fixed in the tube (10) and contacting with the second fringe region of the honeycomb structure (20), thereby supporting the honeycomb structure (20) in the axial direction, said third supporting member (50) having a plurality of passages which allow the fluid to flow from the upper-course side into the second fringe region. A honeycomb catalytic apparatus according to claim 1, characterized in that said tube (10) has a lower-course outlet adapted to be connected to a gas turbine.

Inventors: HANDA, SUSUMU, KAWAKAMI, TAKASHI INTELLECTUAL PROPERTY DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA, THE TOKYO ELECTRIC POWER CO., INC.
Application year: 1990
Main classification: F01N3
IPC codes: B01J35, F01N3, B01D53