Unitized catalyst panel

There is provided a relatively large unitized monolithic catalyst panel especially adapted for use in the exhaust lines or conduits of stationary power plants to remove pollutants from the exhaust, especially those using hydrocarbon fuels as a source of power. The panels are characterized by top, bottom and side frame plates in rectangular relation, front and rear stiffener bars extending between the top and bottom plates, separator plates at intervals and in parallel relation extending between the side frame plates to define a grid, and corrugated thin metal foil layers disposed within and filling the spaces within the frame, which foil has a catalytically active surface formed thereon. These devices are useful in removing such pollutants as NO.sub.X from exhaust gas streams.

This invention relates to relatively large unitized catalyst panels 
especially adapted for use in the exhaust lines or conduits of stationary 
power plants. More particularly, this invention relates to a construction 
for such large unitized panels, which panels are useful for the removal of 
pollutants from the exhaust of power plants, especially those utilizing 
hydrocarbon fuels as a source of power. 
BACKGROUND OF THE INVENTION AND PRIOR ART 
Power plants, co-generation plants and other large industrial power 
generators typically have one or more "curtainwall" type catalytic 
converters mounted in the exhaust stream conduit. Usually, these 
converters promote the conversion of carbon monoxide, unburned 
hydrocarbons, and nitrogen oxides (NO.sub.x) into environmentally 
acceptable substances. 
Typically, the converters are made of ceramic or metallic honeycomb 
material in which the surfaces exposed to the exhaust gas has been treated 
with a catalytic material to promote the desired conversion. The 
honeycombs are generally encased in a metal frame approximately two feet 
on a side and called "modules". A plurality of these modules are then seal 
welded together to form large panels (generally about 10 feet on a side), 
which panels are in turn fastened and sealed into a suitable frame for 
mounting in the exhaust conduit. A typical exhaust conduit might contain 
one to ten panels each of which contains 20 to 30 modules. 
Because the large panels must match up and seal against their corresponding 
frames in the exhaust conduit, they must be dimensionally correct. 
Although module dimensions are irrelevant to the function of the finished 
product, this necessitates that the modules each have unusually tight 
dimensional specifications to avoid dimensional stack-up problems. 
Also, the modules must be seal welded together to form the final panel, 
which is an expensive and labor intensive process. 
This invention provides a manner of constructing a unitized panel to 
replace the built-up module type panels are up to 10 or more feet on side. 
The cost of manufacturing many modules each with tight tolerances, and 
seal-welding them together, is avoided. Less structural material is 
required in the panel allowing more catalyst to be exposed to the exhaust 
gas and reducing pressure drop through the unit. Project lead time is 
greatly reduced and labor costs are less. There is provided a panel 
construction characterized by a corrugated metal foil catalyst support 
along with metallic framing and support structures, said metal desirably 
being stainless steel. 
BRIEF STATEMENT OF THE INVENTION 
Briefly stated, the present invention is in a rectangular unitized 
monolithic honeycomb catalyst panel comprising parallel top and bottom 
frame plates, and parallel side frame plates orthogonally related thereto. 
A plurality of stiffener bars is provided at spaced intervals, preferably 
uniformly spaced intervals, extending between the top and bottom frame 
plates from both the front and rear marginal edges of said top and bottom 
frame plates. Parallel stop bars are provided against the inside surfaces 
of each of said side plates and extending between said top and bottom 
frame plates. A plurality of separator plates in parallel spaced relation 
and extending between the side plates is also provided. These are 
preferably notched to accept the front and rear stop bars and the front 
and rear stiffener bars. This assembly defines a grid of rectangles, 
desirably uniformly sized, and preferably, albeit not essentially, square 
rectangles. The spaces between successive separator plates, and the spaces 
between the uppermost and lowermost separator plates and the adjacent top 
and bottom frame plates, respectively, are filled with nonnesting 
corrugated catalyst supporting metal foil laminations. These laminations 
may be created by layering one course of corrugated foil upon the 
preceeding course, as in accordion folding, or by placing percut strips 
equal in length to the distance between the side plates one on top of the 
preceeding with the same surfaces of the strip in contact.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now, more particularly, to FIG. 1, there is shown a catalyst 
panel, generally indicated by the number 10, in accordance with the 
present invention. The panel 10 is a rectangle, preferably a square, 
having a top plate 12 and a bottom plate 14, and side plates 16 and 18, 
respectively, defining the perimeter of the panel. Stiffening ribs 20 and 
22 are provided and welded, or otherwise secured, to the top plate 12. In 
like manner, the bottom plate 14 is provided with stiffening ribs 24 and 
26. Although two longitudinally extending and parallel stiffening ribs 20 
and 22, for example are shown, any suitable stiffening means may be 
employed such as a thicker top plate 12, or a single stiffening rib may be 
used. 
The side plates in FIG. 1 are each provided with vertically extending stop 
bars, such as stop bars 28 and 28a as shown in FIG. 2 secured thereto by 
an suitable means, e.g., welding. In FIG. 1, stop bar 30 is shown against 
side plate 18. Although dual stops, e.g., 28, 28a, and 30 and the hidden 
mate thereto (not shown) are preferred, single stop bars may be used 
extending along the median line of the side plates 16 and 18 (FIG. 1). 
Extending in vertical parallel arrays, front and back, between the top 
plate 12 and the bottom plate 14 is a series of stiffener boars 40, 40a 
(not shown in FIG. 1) 42, 42a (not shown in FIG. 1) 44, 44a (not shown in 
FIG. 1) and 46, 46a (not shown in FIG. 1). FIG. 2 shown the front and rear 
stiffener bars 40 and 40a. 
Extending in horizontal parallel array between the side plates 16 and 18 is 
a eries of separator plates 32, 34, 36, and 38. The details of the 
separator plates which are in a preferred embodiment of this invention are 
best shown in FIG. 5. FIG. 5 shows the details of separator plate 32 
having rear stiffener bar notches 48 and front stiffener bar notches 50 
adapted and dimensioned to accommodate the rear stiffener bars 40a (FIG. 
2), 42a, 44a, and 46a, and front stiffner bars 40, 42, 44, 46 (FIG. 1). 
The separator plate 32 also has corner notches 52 and 54, front and back, 
adapted and dimensioned to accommodate the stop bars, for example, stop 
bars 28 and 28a, (FIG. 2.). 
The combination of the top and bottom plates 12 and 14, the side plates 16 
and 18, the separator plates 32, 34, 36 and 38, the front and rear 
stiffener bars 40, 40a, 42, 42a, 44, 44a, 46, and 46a define 25 squares in 
the form of a square grid. The horizontal rectangles, such as those 
defined by the top plate 12 and the separator plate 32, are then filled 
with substantially nonnesting corrugated thin metal foil layers, such as 
foil layers 56, 58, and 60 partially shown in FIG. 1, extending from side 
plate 16 and side plate 18. Each of the horizontal rectangles 62, 64, 66, 
68, and 70 (FIG. 1) are so filled with the corrugated thin metal foil 
layers. These layers may be formed by accordion folding a single strip of 
corrugated thin metal foil, or by layering strips of corrugated thin metal 
foil one on top of the other in a manner such that contiguous layers do 
not nest together substantially, and thus cut down on open area. In 
accordion folding, the top surface of one layer contacts the same top 
surface of the next layer, the "top surface" being the surface on top as 
the thin metal strip passed through the corrugating gears. The same 
arrangement of contacting surfaces is provided in the case of layering 
individual strips in which case successive layers are flipped over before 
assembly into the panel. Reference may be had to U.S. Pat. No. 4,711,009 
for the details of apparatus and the method of forming a strip of 
corrugated thin metal e.g., 0.001 to 0.003 inch thick aluminum coated 
stainless steel foil. The disclosure of the foregoing U.S. Patent is 
incorporated herein by reference thereto. 
According to that patent, a chevron pattern corrugation is formed, although 
a pattern wherein the apices of the chevrons are rounded off (to provide a 
modified chevron pattern, such as better shown in FIG. 6) is preferred to 
stress relieve the foil at these points. After passing the foil through 
the corrugating gears, it is stress relieved with heat, and then given one 
or more wash coats of aluminum oxide, or zirconium oxide and baked. This 
provides a porous surface in which a catalyst may be deposited as provided 
in said patent. The catalyst is desirably palladium, or palladium/rhodium, 
or vanadium pentoxide or any other catalyst or combination thereof useful 
in removing pollutants from exhaust gas streams. Such chevron or modified 
chevron patterns will not nest if accordion folded or layered by reversing 
successive layers as above described. Moreover, the modified chevron 
pattern (FIG. 6) affords good mixing of the gases, or mixing of the 
exhaust gas with a reacting gas, e.g., ammonia, as in a selective 
catalytic reduction unit, or SCR, within the panel. 
In fabricating the panels of this invention, the frame plates 12, 14, 16 
and 18 with stiffening ribs 20, 22, 24, and 26 and stop bars 28, 28a, 30 
and 30a (not shown) attached are welded together to form the perimeter of 
the panel 10. The frame plates in conjunction with the stiffening ribs and 
stop bars are designed with such a cross-section as to make the completed 
panel stiff enough to maintain its shape during fabrication and handling, 
and when in the exhaust stream. 
Rear stop bars 28a and 30a (not shown) are attached to the frame plates 
before the catalytic foil is installed in the panel 10. 
Rear stiffener bars 40a, 42a, 44a and 46a, oriented vertically on about 2 
foot centers horizontally, are welded to the top and bottom frame plates 
12 and 14 before the catalytic foil is installed in the panel 10. 
Horizontal spacing of the stiffner bars is designed so that there will not 
be a structural failure of the catalyst foil under operating conditions 
when the panel 10 is the exhaust stream. Front stiffener bars 40, 42, 44, 
and 46 are installed after the foil is installed in the panel 10. The 
various stop bars are designed with such a cross-section as to maintain 
frame stiffness in handling and in use, as well as to accommodate the 
difference in thermal expansion between the frame and the catalyst foil. 
This precaution ensures that the foil ends are retained under all 
conditions of thermal expansion. 
Catalytic metal foil material, cut into lengths of approximately 10 feet, 
and laid up horizontally so as to fill the opening formed by the top and 
bottom frame plates 12 and 14, or the rectangular sections 62, 64, 66, 68, 
and 70, respectively. This can be layers of foil strips with chevron or 
modified chevron as shown in FIG. 6, with every other layer reversed so 
that adjacent layers do not nest one within the next. Alternatively, the 
catalyst foil pack may be alternate layers of flat and corrugated foil 
material. Also, the catalyst pack can be a continuous strip of catalytic 
foil with chevron corrugations or modified chevron corrugations, in 
accordion or zig-zag folded form, each layer being about 10 feet long from 
fold line to fold line. 
Instead of a chevron or modified chevron pattern, a pattern of straight 
corrugations across the foil, but at an angle oblique (e.g. 80.degree. to 
the edge) to the marginal edges of the foil may be used. The latter is 
layered in the same manner as described above for the chevron or the 
modified chevron patterns. Alternatively, corrugations may be in a 
straight line across the foil normal to the longitudinal marginal edges of 
the foil and wherein successive corrugations peaks have a variable pitch. 
Reference may be had to Ser. No. 198,042, filled May 24, 1988, now U.S. 
Pat. No. 4,810,588 filed concurrently herewith entitled "Nonnesting, 
Straight Corrugation Metal Foil and Method for Making Same" on which the 
inventors are Wesley A. Bullock and William W. Whittenberger, for the 
details of variable pitch corrugations. 
Separator plates (FIG. 5) are layered horizontally into the frame opening 
with the catalytic foil at intervals of about 2 feet vertically. As 
previously indicated, the separator plates 32, 34, 36, and 38 have notches 
48 and 52, and corner notches 52 and 54 (FIG. 5) that match up with the 
locations of the front and rear stop bars and the front and rear stiffener 
bars. Separator plates 32, 34, 36, and 38 are simply laid in the frame at 
the appropriate time when the catalytic foil is being laid in. After all 
the foil is in place, and all the front stiffener bar are installed, the 
separator plates are fastened to the front and rear stop bars and the 
front and rear stiffener bars using a pinning or welding technique. The 
separator plates 32, 34, 36, and 38 have a designed cross-section so as to 
resist the tendency of the panel 10 to bend under the pressure of the gas 
stream. Spacing of the separator plates 32, 34, 36, and 38 is designed 
such that sagging of tall stacks of catalyst foil due to high temperatures 
can be avoided. 
The foregoing construction technique is applicable to panels, rectangular 
or square, of sizes in the range of 3 feet on a side up to about 15 feet 
on a side.