Gas: heating and illuminating – Generators
Reexamination Certificate
1999-01-19
2001-03-20
Beck, Shrive (Department: 1764)
Gas: heating and illuminating
Generators
C048S094000, C048S127700, C048S198800, C422S198000, C422S203000
Reexamination Certificate
active
06203587
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to a fuel gas steam reformer assemblage which is formed from a plurality of repeating sub-assemblies. More particularly, this invention relates to a fuel gas steam reformer assemblage which is compact and lighter in weight than conventional steam reformer assemblages used in fuel cell power plants.
2. Background Art
Fuel cell power plants include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas, into hydrogen and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature of about 1,250° F. to about 1,600° F. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. A typical reformer will consist of a plurality of reaction tubes which are contained in a housing that is insulated for heat retention. The reaction tubes are heated by burning excess fuel gas in the housing and passing the burner gasses over the reaction tubes. The individual reaction tubes will typically include a central exhaust passage surrounded by an annular entry passage. The entry passage is filled with the catalyzed alumina pellets, and a fuel gas-steam manifold is operable to deliver the fuel gas-steam mixture to the bottom of each of the entry passages whereupon the fuel gas stream mixture flows through the catalyst beds. The resultant heated hydrogen and carbon dioxide gas mixture then flows through the central exhaust passages in each tube so as to assist in heating the inner portions of each of the annular catalyst beds; and thence from the reformer for further processing and utilization.
Steam reformers require a large amount of surface area in the catalyst bed in order to provide a high degree of catalyst-fuel mixture interaction and a large heat transfer surface area to produce the amount of hydrogen required to operate the fuel cells at peak efficiency. This need for large catalyst bed and heat transfer surface area, when met by using catalyst-coated (hereinafter “catalyzed”) pellets in tubular reformers, results in undesirably large and heavy reformer assemblies. For example, a commercially available 200 KW acid fuel cell power plant includes a steam reformer component which has a volume of about 150 to 175 cubic feet; and weighs about 3,500 lbs.
U.S. Pat. No. 5,733,347, granted Mar. 31, 1998 discloses a steam reformer assembly which does not utilize catalyzed pellets, but rather uses a corrugated reformer core which has catalyzed walls. The corrugated reformer core forms parallel passages for the fuel being reformed, and also forms adjacent parallel burner gas passages which are disposed in direct heat exchange relationship with the reformer passages. Likewise, the reformer passages are in direct heat exchange relationship with the regenerator passages. This assembly is lighter in weight and more compact than a steam reformer which uses catalyzed pellets and, because of the very high surface area of the corrugated core, provides very efficient heat transfer between the catalyzed reformer passages and the burner gas and regenerator passages. The assembly is formed from a sequence of essentially flat plates sandwiched around corrugated passages, and the assembly has a repeating pattern of burner passage, reformer passage, regenerator passage, reformer passage, burner passage, etc.. Gas flow reversal manifolds connect the reformer passages with the regenerator passages. While the aforesaid flat plate assembly accomplishes the desired reduction in weight and size, it does not diffuse the gas flow patterns 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 reformer assembly, but the catalyzed pellet design provides a more desirable diffuse gas flow pattern. It would be highly desirable to provide a steam reformer which is suitable for use in a fuel cell power plant, which reformer supplies the diffuse gas flow pattern of the catalyzed pellets and is compact and light in weight like the catalyzed wall reformer described above.
DISCLOSURE OF THE INVENTION
This invention relates to a steam reformer structure which provides the necessary catalyzed and heat transfer surface area, is compact and light weight, and provides an internal diffuse gas flow pattern. The steam reformer structure of this invention is similar to the above-referenced patented reformer assembly in that it is formed from a series of essentially flat plate reformer components. Each of the reformer components includes outer reformer passages sandwiched around a plurality of central regenerator/heat exchanger passages. At a first end of the component, the reformer passages are connected to a fuel-steam manifold which feeds the fuel-steam mixture into the reformer passages. The opposite end of each component is provided with a flow reversal manifold that directs the fuel gas-steam mixture emanating from the outer reformer passages back into the central regenerator/heat exchanger passages. A reformer exit manifold is also disposed at the first end of each component to direct the reformed gas stream to the next fuel processing station in the power plant. Adjacent reformer components are separated from each other by burner gas passage plates through which the reformer burner gases flow. Thus, each of the reformer passage plate units is disposed directly adjacent to a burner passage plate unit, and the adjacent reformer and burner passages share a common wall.
The flat plate components of the steam reformer assembly may be formed from planar metal sheets which are separated from each other by monolithic gas flow passage components. The monolithic gas flow components are provided with a network of interconnected open cells, the surfaces of which are catalyzed with a nickel catalyst, or with noble metal catalysts such as platinum, palladium, rhodium, nobium, or the like. The open cell foam network also provides the high surface area needed to provide sufficient catalyst to properly reform 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. The open cell foam network also provides a diffuse gas flow pattern for gases passing through the monolith, since the gases will flow both laterally and longitudinally through the monolith. The metal sheets which make up the flat plate reformer and burner components of the assemblage have both surfaces covered with a catalyzed alumina coating. The walls of the regenerator sections of the assemblage are not catalyzed.
The surfaces to be catalyzed will be primed by means of a conventional wash coating process such as that provided by W. R. Grace and Co. or Englehard Corp.. The wash coating process produces a porous alumina layer which forms the base for the catalyst coating. Such wash coatings are presently used to produce automobile catalytic converters, wood stove catalytic emission units, and the like. The metal plates used to form the flat plate components are steel alloy plates containing aluminum which can be brazed or spot welded together with the foam; surface treated; wash coated; and then selectively coated with the catalyst. By catalyzing the reformer and burner passage heat transfer walls in the assemblage, operating temperatures of the reformer assemblage can be kept at a minimum. The use of the flat plate and open cell monolith construction, with its maximized surface area, allows minimization of the reformer size and weight. The walls of the regenerator heat exchanger passages are not catalyzed, although they may be provided with the wash coat primer layer. The core of the open cell monolith may be formed from nickel, stainless steel, an aluminum-stainless steel alloy, or a ceramic material. It will be understood that the interstices as well as the outside surfaces of the open cell monolith is wash coated and, where desirable, is also catalyzed.
It is therefore an object
Corrigan Thomas J.
Lesieur Roger R.
Beck Shrive
International Fuel Cells LLC
Jones William W.
Varcoe Frederick
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