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.