Figure 1. Physical representation of the integral heat exchange structure in which the catalytic reactor employs an arrangement of catalyzed and non-catalyzed substrate passages for providing passive cooling of the catalytic reactor.
The catalyst generally has one or more metal containing components which are catalytically active towards promoting the desired oxidation reactions. Furthermore, the catalyst coating is applied on selected ones of the wall surface regions exposed to certain ones of the passages, whereas selected others of the wall surfaces exposed to certain others of the passages are free of the catalyst coating. In such manner, the substrate is provided with the arrangement of catalyzed passages in which the mixture is catalytically reacted and non-catalyzed passages in which the mixture is substantially not reacted but instead provides passive cooling of the substrate. Also, the selected ones of the surface regions have catalyst coating thereon and the selected others of the surface regions being free of catalyst coating are on common wall sections such that a catalytic reaction can occur in those passages bordered by the catalyzed surface regions concurrently as cooling occurs in those passages being adjacent thereto and bordered by the non-catalyzed surface regions. Any arrangement of catalyzed and non-catalyzed passages is possible. In one arrangement, the catalyzed to non-catalyzed passages are in a ratio of one-to-one. In another arrangement, they are in a ratio of three-to-one.
The integral heat exchange within the catalytic reactor is illustrated schematically in Figure 2 in which at least a portion of the thermal combustion of the fuel takes place in the expansion zone of the catalytic reactor to counteract the cooling effect of the expansion of the gases. The catalyst structure desirably comprises a support and a combustion catalyst. The support is preferably metal. It may be corrugated and rolled or otherwise assembled in such a way that the combusting gas flows from end to end through the length of the corrugations. The catalyst is placed only on a portion of the corrugations in such a way that the catalyst is in heat exchange relationship to a surface having no catalyst. The heat produced on the catalyst flows thorough the structure wall to the flowing gas at the opposite non-catalytic wall. The heat also flows to the adjacent combusted gas. The catalyst and its structure provide an exceptionally stable and temperature moderated structure having long life. The catalyst structure is particularly useful in fuel combustion processes and the fuel combustion processes. The structure is preferably a platinum-group, metal-based catalyst on a metal monolith. The metal monolith is assembled from or fabricated from metallic materials having a catalytic surface and an adjunct non-catalytic surface. One side of the catalyst structure component has catalyst upon it and the other side of the catalyst structure component is essentially catalyst-free. The preferred supports for this catalytic zone are metallic. Metallic supports in the form of honeycombs, spiral rolls of corrugated sheet, columnar, or other configurations having longitudinal channels or passageways permitting high space velocities with a minimal pressure drop are desirable in this service. They are malleable, may be mounted and attached to surrounding structures more readily, and offer lower flow resistance due to walls which are thinner than can be readily manufactured in ceramic supports. Another practical benefit attributable to metallic supports is the ability to survive thermal shock. Such thermal shocks occur in gas turbine operations when the turbine is started and stopped and, in particular, when the turbine must be rapidly shut down. In any event, the catalyst is deposited, or otherwise placed, on at least a portion of the walls within the metal supports’ channels or passageways in the amounts specified. By the phrase ”at least a portion” is meant that each channel need not be coated along its entire length. In some instances, catalyst placement along a portion of the length of the channel will be sufficient. Several types of support materials are satisfactory in this service: aluminum, aluminum-containing or aluminum-treated steels, ferrous alloys, certain stainless steels, or any high temperature metal alloy, including nickel or cobalt alloys where a catalyst layer can be deposited on the metal surface.