Manifold and sealing assembly for fuel cell stack

Details Manifold and sealing assembly for fuel cell stack Manifold and sealing assembly for fuel cell stack

2001-03-01

2003-03-11

Ryan, Patrick (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000

Reexamination Certificate

active

06531237

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to fuel cell systems and, in particular, to manifold assemblies for use with the fuel cell stacks of such systems.
In present day fuel cell systems, manifolds are used to supply and extract fuel and oxidant gasses to and from the fuel cell stack of the system. In some cases, the stack is situated in an enclosure and the enclosure serves as a manifold for one of the gasses. In such an arrangement, a minimum of three additional manifolds is required to provide inlet and exit passages for the other gases of the system. In other cases, where an enclosure does not serve as a manifold, a minimum of four manifolds is required In systems of this type, it is also customary to compress the manifolds against the stack. An example of a stack compression system is described for example in copending U.S. patent application Ser. No. 09/651,921, filed Aug. 31, 2000, assigned to the same assignee hereof. In systems of this type it is also conventional to provide a manifold seal assembly for the external manifolds of the system. A typical seal assembly is disclosed, for example, in U.S. Pat No. 4,467,018.
FIG. 1
shows a typical fuel cell stack
1
in which four manifolds are employed. As shown, the stack
1
includes a number of fuel cell assemblies
11
A and electrolyte matrices
11
B which are stacked on one another. The arrangement of these components is such that the reactant gases flow in the stack
1
in cross-flow configuration. More particularly, the fuel and oxidant gases flow into respective anode and cathode inlet manifolds
2
A and
3
A, respectively, and then through the stacked cell assemblies. Exhausted fuel and oxidant gases are then extracted from the cell assemblies via anode and cathode outlet manifolds
2
B and
3
B. Manifold seal assemblies
4
are also provided and act as seals between the manifolds
2
A,
3
A,
2
B and
3
B and the stack
1
.
More particularly, as shown in
FIG. 2
, each of the fuel cell assemblies
11
is comprised of a cathode electrode
12
, cathode corrugated current collector
13
, bipolar plate
14
, anode corrugated current collector
15
, and anode electrode
16
. The bipolar plates
14
include end flaps
14
A at each end which provide flat sealing surfaces as discussed in U.S. Pat. Nos. 5,773,161, 5,399,438 and 4,514,475.
These flat surfaces together result in flat vertical peripheral areas
1
A for the stack
1
, while the end plates
6
provide flat horizontal peripheral areas
1
B for the stack. It is against these flat peripheral areas that the anode and cathode manifolds
2
A,
2
B,
3
A and
3
B are sealed. Each manifold seal assembly
4
includes a stack side compressible gasket
4
A, a dielectric frame assembly
4
B and a manifold side compressible gasket
4
C, all of which interface with a respective one of the manifolds. These components permit each seal assembly not only topside sealing but also to limit the electrolyte movement from the top to the bottom of the stack, to limit the electrolyte movement from the stack across the dielectric frame assembly to the manifold, and to allow differential movement between the stack and manifold.
More particularly, each gasket
4
A provides a seal between the bipolar plates
14
of the fuel cell assemblies
11
and the dielectric frame assembly
4
B. The gaskets
4
A are further adapted to limit undesirable transport of electrolyte from the positive to negative lend of the stack. If unchecked this electrolyte migration causes the cells at the negative end of the stack to flood and depletes cells of electrolyte from the positive end. Methods of adapting the gaskets
4
A in this way are disclosed, for example, in U.S. Pat. Nos. 4,591,538, 4,643,954, 4,761,348 and 5,110,692. These methods, while they reduce electrolyte migration, do not eliminate all the transport and also add cost to the fuel cell stack
1
.
The dielectric frame assemblies
4
B provide electrical isolation between the stack
1
and the associated metallic manifolds. As shown in
FIG. 1
, a typical frame assembly includes horizontal and vertical members
5
A,
5
B which are joined at joints
5
C via aligned slots
5
D,
5
E and a key
5
F. This configuration allows for the differential movement between the stack and the frame assembly (see, e.g., U.S. Pat. No. 4,414,294). To withstand stresses caused by the differential movement, the frame assemblies
4
B require high-density ceramics. These ceramics must also be highly polished for assuring required voltage isolation, as described in U.S. patent application No. 09/736,549, filed on Dec. 13, 2000, also assigned to the same assignee hereof. As can be appreciated, the need for high-density, highly polished ceramics also increases the overall cost of the fuel cell stack
1
.
While the frame assembly of
FIG. 1
includes opposing horizontal and opposing vertical members, the term “frame assembly” as used herein is intended to mean an assembly that includes at least two opposing frame members and, hence, includes within its meaning assemblies that have opposing horizontal members only, and assemblies that have both opposing horizontal members and opposing vertical members. As also used herein the term “supporting frame assembly” is intended to mean a frame assembly that supports one or more members of another frame assembly, and the term. “supported frame assembly” is intended to mean a frame assembly having one or more of its members supported by another frame assembly.
It is therefore an object of the present invention to provide a manifold and manifold sealing assembly which overcomes the above-discussed disadvantages of prior assemblies.
It is also an object of the present invention to provide a manifold and manifold sealing assembly having a reduced number of parts.
It is a further object of the present invention to provide a manifold and manifold sealing assembly which permit a reduction in the number of parts of the dielectric frame assemblies and in the number of gaskets.
It is also an object of the present invention to provide a manifold and manifold sealing assembly which permit the use of simplified bipolar plates.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, the above and other objectives are realized in a manifold and manifold sealing assembly including a plurality of frame assemblies and a plurality of manifolds. One or more of the frame assemblies is a supporting frame assembly and one or more of the frame assemblies is a supported frame assembly. Each supporting frame provides structural support for a part of one of the supported frame assemblies facing a face of the fuel cell stack adjacent to the face faced by the supporting frame assembly. In further accordance with the invention, the manifold abutting a supporting frame assembly is adapted to sealing engage with areas of the manifold abutting the associated supported frame assembly.
In the embodiment of the invention to be disclosed hereinafter, each supporting frame assembly includes a vertical member adjacent to a vertical side of the associated fuel cell stack face which supports at its upper and lower ends upper and lower horizontal members of the associated supported frame assembly. These horizontal members are, in turn, situated adjacent to upper and lower ends of the associated fuel cell stack face.
Also, in this embodiment, each manifold situated adjacent to a supporting frame assembly has a peripheral flange having a vertical side with an extension which extends beyond the vertical end of the associated fuel cell stack face. This extension serves as a sealing member for a vertical side of the peripheral flange of the manifold situated adjacent to the supported frame. The latter manifold has a central region which extends beyond the vertical edge of the associated fuel cell stack face so as to permit the sealing engagement.
Additionally, in the disclosed embodiment, a supported frame assembly abutting a given face of the fuel cell stack is supported by two supporting frame assemblies abutting the faces of the stack wh

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