Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Reexamination Certificate
1999-03-22
2001-09-04
Knode, Marian C. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
C422S173000, C422S177000, C422S211000, C165S058000, C165S138000
Reexamination Certificate
active
06284206
ABSTRACT:
TECHNICAL FIELD
This invention relates to a selective oxidizer assemblage which is formed from a plurality of repeating subassemblies. More particularly, this invention relates to a fuel gas selective oxidizer assemblage which is more compact and lighter in weight than conventional selective oxidizer assemblages which are used in fuel cell power plants.
BACKGROUND ART
Some fuel cell power plants include fuel gas selective oxidizers which are operable to reduce carbon monoxide to low levels in a reformed fuel gas, such as natural gas, before the gas is used as a fuel for fuel cell power plants. The procedure involves passing a mixture of the reformed fuel gas and gaseous oxygen through a catalytic bed which is capable of oxidizing carbon monoxide in an exothermic reaction. The reaction proceeds at controlled temperatures which are within a given range of about 360° F. to about 170° F. The temperature of the catalyst bed must be maintained above a particular threshold temperature which is between about 220° F. to about 360° F. at the entry stage of the catalyst bed, where the gases being treated are relatively rich in carbon monoxide, and will be reduced to lower temperatures of about 170° F. to about 220° F. at latter stages of the catalyst bed where the carbon monoxide content of the gas is lower. However, with good temperature control and heat transfer, the temperature can be as high as 240° F. in the low temperature bed.
The catalysts typically used are platinum catalysts which are deposited on alumina granules. U.S. Pat. No. 5,330,727, granted Jul. 19, 1994 to J. C. Trocciola et al discloses a selective oxidizer assemblage which is proposed for use in a fuel cell power plant and describes the temperature regimes required to properly oxidize the carbon monoxide. The type of oxidizer shown in the aforesaid patent is conventionally referred to as a “shell and tube” heat exchanger.
The shell and tube fuel cell power plant selective oxidizers require a large amount of heat transfer surface area between the catalyst bed and the coolant in order to maintain the controlled temperatures needed to produce the degree of carbon monoxide oxidization required to operate the fuel cells properly. This need for large heat transfer surface area, when met by using catalyst-coated granules requires that the catalyst coated granules be diluted, which results in undesirably large and heavy oxidizer assemblies. For example, a 20 KW acid fuel cell power plant that includes a shell and tube oxidizer component requires a volume of about 4 cubic feet for the oxidizer. Higher power fuel cell power plants, such as 200 KW plants or larger, will require proportionately larger fuel gas oxidizers.
U.S. Pat. No. 5,853,674, granted Dec. 29, 1998 discloses a selective oxidizer assemblage which does not utilize catalyzed pellets, but rather uses a corrugated catalyst bed core which has catalyzed walls. The corrugated catalyst bed core forms parallel passages for the fuel being selectively oxidized, and also forms adjacent parallel coolant passages which are disposed in direct heat exchange relationship with the catalyst bed gas passages. This assemblage is lighter in weight and more compact than a selective oxidizer which uses catalyzed pellets and, because of the very high surface area of the corrugated core, provides very efficient heat transfer between the catalyzed bed passages and the coolant passages. The assemblage is formed from a sequence of essentially flat plates which are sandwiched around the corrugated passages, and the assemblage has a repeating pattern of catalyzed bed passages and non-catalyzed coolant passages. Gas flow reversal manifolds connect the catalyzed bed passages with the coolant passages. While the aforesaid flat plate assemblage makes a significant improvement in the reduction of weight and size, it does not fully meet the requirements and it does not sufficiently mix the flow pattern of the gases passing through it because of the inclusion of the corrugated gas flow passages. Thus the corrugated design provides a more desirable size and weight selective oxidizer assemblage, but the catalyzed pellet design provides a more extensive gas mixing flow pattern.
It would be desirable to provide a selective oxidizer which provides greater heat exchange capabilities in a smaller package. It would be highly desirable to provide a selective oxidizer assemblage for a process gas which is suitable for use in a fuel cell power plant, which selective oxidizer assemblage provides a gas mixing flow pattern of the catalyzed pellets and is compact and light in weight like the catalyzed wall selective oxidizer described above. It would be highly desirable to provide a process fuel gas selective oxidizer which is suitable for use in a fuel cell power plant, which selective oxidizer provides the necessary catalyzed and non-catalyzed coolant surface areas, but is compact, strong, and light in weight.
DISCLOSURE OF THE INVENTION
This invention relates to a selective oxidizer assemblage which provides the necessary catalyzed and heat transfer surface area, is compact and light weight, and provides an internal extensive gas mixing flow pattern. The selective oxidizer assemblage of this invention is similar to the above-referenced corrugated passage selective oxidizer assemblage, in that it includes a series of essentially flat plate assemblage components. Each of the selective oxidizer components includes a catalyzed oxidizer component which is positioned adjacent to a heat exchanger component. At an entry end of the assemblage, a high temperature selective oxidizer component is connected to a fuel manifold. In this case, not shown is an initial O
2
or air injection tube which results in a fuel-oxygen mixture being fed into the high temperature oxidizer component. The opposite end of each component is provided with a flow reversal manifold that directs the fuel gas-steam mixture emanating from the catalyzed flow passage component back into an adjacent non-catalyzed heat exchanger flow passage component A selective oxidizer exit manifold is also disposed at the first end of each component to direct the emerging gas stream to the next station in the power plant. Adjacent selective oxidizer components are separated from each other by heat exchanger gas passage components through which the process gas flows. Thus, each of the catalyzed flow units is disposed directly adjacent to a heat exchanger unit, and the adjacent catalyzed flow passage units and heat exchanger units share a common wall.
As with the above-referenced selective oxidizer assemblage, the flat plate components of the selective oxidizer assemblage may be formed from planar metal sheets which are separated from each other by monolithic open cell foam gas flow passage components. However, in this configuration the flat plates are replaced with heat exchanger elements. This addition means improved temperature control in each of the sections of the selective oxidizer which results in a further reduction in size and weight. The monolithic selective oxidizing gas flow components are provided with a network of interconnected open cells, the surfaces of which are wash coated with a high surface area catalyst support, such as alumina or silica-alumina and catalyzed with noble metal catalysts such as platinum, palladium, rhodium, or the like, or with a noble metal catalyst which is promoted with metal oxides, such as iron oxide, cerium oxide, manganese dioxide, or the like. The open cell foam network provides the high surface area support needed to provide sufficient catalyst surface area to properly reduce the CO content of the fuel gas. In fact, the catalyzed surface area of the open cell foam is up to twice that of the catalyzed surface area of the corrugated panels described in the above-mentioned patent. The open cell foam network also provides an effective gas mixing flow pattern for gases passing through the monolith, since the gases will flow both laterally and longitudinally through the monolith. The metal heat exchanger elements which make up
Corrigan Thomas J.
Hildreth Derek W.
Lesieur Roger R.
Doroshenk Alexa A.
International Fuel Cells LLC
Jones William W.
Knode Marian C.
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