Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1999-02-16
2001-03-13
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C422S211000, C422S241000
Reexamination Certificate
active
06200696
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to fuel cell assemblies and, in particular, to fuel cell assemblies using internal reforming.
So-called direct carbonate fuel cell assemblies are known in which the assemblies convert a hydrocarbon fuel directly to direct current electricity. In these fuel cell assemblies, the fuel is internally reformed to produce hydrogen for fuel cell use. Fuel cell produced water and heat are used by the reforming reactions. The reforming and fuel cell reactions are carried out in thermal and mass transfer communication such that the heat and water produced by the fuel cell are made available in-situ for the reforming reactions.
Two different types of direct fuel cell assemblies have emerged. In the direct internal reforming assembly described in U.S. Pat. No. 3,488,226, reforming catalyst is placed in the anode compartment of each fuel cell directly in communication with the cell environment. In the alternate indirect internal reforming assembly described in U.S. Pat. No. 4,877,693, the bulk of the reforming is carried out internally in reforming units placed in between fuel cell groups in a stack. A group of cells typically might be comprised of five to fifteen fuel cells. The reforming units are in thermal communication with the fuel cells so that the reforming reaction is able to draw the necessary heat from the nearby cells.
A hybrid assembly incorporating both the direct and indirect internal reforming derives the benefits of the direct arrangement (that is high fuel conversion) and the indirect arrangement (longer catalyst life, higher fuel cell performance, and more uniform temperature distribution). In the hybrid assembly, reforming catalysts are placed in the anode compartment of each fuel cell and a reforming plate is placed in between fuel cell groups.
U.S. Pat. No. 5,175,062 describes a reforming unit used for indirect internal reforming and its integration with a direct fuel cell assembly which incorporates a combination of direct and indirect internal reforming. The assembly of the '062 patent has certain disadvantages in reliability and costs which are associated with the fuel supply line connections to the reforming unit.
More particularly, fuel and steam need to be distributed to each of the reforming units. A full-size fuel cell assembly requires 30 to 40 connections for this distribution. In the '062 patent, these connections are made by welding a feed tube to each reforming unit at one end and to a fuel delivery header at the other end. Since the reforming units are electrically live, they must be electrically isolated from the metallic fuel supply header. The '062 patent utilizes dielectric breaks in the feed lines for this purpose.
As can be appreciated, the fuel feed lines of the '062 patent are at the highest pressure with respect to other gas streams. Because of their location external to the fuel cell stack, the entire lines, including their connections at the reforming units and at the dielectric breaks, need to be fully protected against gas leaks for the entire life of the fuel cell assembly. This is made more difficult by the fact that the each feed line connection is subjected to thermo-mechanical stresses during transportation and operation. Therefore, the design of the gas leak protection for the feed lines needs to be very robust to enhance reliability.
The currently available dielectric breaks for voltage isolation of the feed lines comprise ceramic tubes joined with metallic transition pieces, by a brazing process, for ease of connection with the metallic tubes of the feed lines. These types of fittings are expensive and, furthermore, are not rated for the desired >500° C. temperature operation of a carbonate fuel cell assembly, as the brazing compound available for joining the metal feed tube and the ceramic fitting is not stable at these temperatures. Thus, complete gas tightness of these joints throughout the life of the fuel cell assembly is not fully assured.
It is, therefore, an object of the present invention to provide a fuel cell assembly with internal reforming and with improved gas leak protection for the fuel feed lines.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, the above and other objectives are realized in a fuel cell assembly in which fuel cells capable of internally reforming fuel and at least one fuel reformer are arranged in a fuel cell stack having a plurality of faces. One face of the fuel cell stack includes the fuel inlet port and reformed fuel outlet port of the fuel gas reformer and the fuel inlet ports of the fuel cells. A manifold is provided to sealingly enclose this one face of the fuel cell stack, and a reformer fuel delivery system for the fuel reformer is arranged entirely within this manifold.
By situating the reformer fuel delivery system within the manifold, if a gas leak occurs, the fuel is contained within the manifold and can still be reformed and utilized in the fuel cells of the assembly. The gas leak protection constraints on the reformer fuel delivery system are thus significantly lessened.
In the fuel cell assembly described hereinbelow, the reformer fuel delivery system includes a fuel supply header and feed lines connecting the header to the individual fuel reformers of the assembly. Each feed line includes first and second spaced feed line sections, one of which connects to the header and the other of which connects to a respective reformer. A ceramic tube connects and bridges the first and second feed line sections and provides electrical isolation for the feed line.
The feed lines are further provided with a fan-like rotatable end or transition duct for coupling the line to the respective fuel reformer. The first and second feed line sections are each provided with a bellows for stress relief.
REFERENCES:
patent: 3488226 (1970-01-01), Baker et al.
patent: 4647516 (1987-03-01), Matsumura et al.
patent: 4788110 (1988-11-01), Bernard
patent: 4873155 (1989-10-01), Hirota et al.
patent: 4877693 (1989-10-01), Baker
patent: 4983470 (1991-01-01), Kimura et al.
patent: 5175062 (1992-12-01), Farooque et al.
patent: 5426002 (1995-06-01), Matsumura et al.
patent: 5470670 (1995-11-01), Yasumoto et al.
patent: 5660941 (1997-08-01), Farooque et al.
Allen Jeffrey P.
Farooque Mohammad
Novacco Lawrence J.
Energy Research Corporation
Kalafut Stephen
Robin Blecker & Daley
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