Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-04-28
2002-06-25
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S084000
Reexamination Certificate
active
06410177
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 9-295519, filed Oct. 28, 1997, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, and more particularly to a fuel cell having improved gas manifolds in order to reduce the weight and cost thereof.
A fuel cell has a structure that hydrogen obtained by reforming hydrocarbon fuel, such as natural gas or methane gas, and air which is an oxidizer are supplied to the body of the fuel cell. As a result, electro-chemical reactions are caused to occur through an electrolyte, such as phosphate solution, so that electric energy is generated. A plurality of the single cells each having the power generating function are stacked so that a cell stack structure is formed.
FIG. 1
is an exploded perspective view showing a conventional cell stack structure of a fuel cell. That is, a single cell
1
of a fuel cell body is structured such that a fuel electrode
3
, to which hydrogen is supplied in a direction indicated by an arrow A shown in
FIG. 1
, is disposed on either side of a matrix layer
2
having an electrolyte. Moreover, an air electrode
4
is disposed on the other side of the matrix layer
2
, the air electrode
4
being supplied with air in a direction indicated by an arrow B shown in the drawing. Moreover, grooved electrode substrates
5
and
6
are stacked to interpose the fuel electrode
3
and air electrode
4
. Moreover, a separator
7
is stacked adjacent to either of the grooved electrode substrate
5
or
6
. A cooling plate
8
is stacked whenever a plurality of the single cells
1
are stacked so that one sub-stack
9
is formed. A multiplicity of the sub-stacks
9
are stacked so that a cell stack
10
is formed.
A clamping plate
11
is joined to each of the uppermost portion and the lowermost portion of the cell stack
10
. The cell stack
10
and the upper and lower clamping plates
11
are clamed by tie rods
12
so that an integrated cell stack
13
is formed.
As shown in
FIG. 2
, a pair of fuel-gas manifolds
15
a
and
15
b
opposing to each other and a pair of air-gas manifolds
16
a
and
16
b
opposing to each other are joined to four side surfaces of the cell stack
13
structured as described above. Thus, fuel gas and air flow perpendicular to each other. A gasket
18
is disposed between the cell stack
13
and each of the gas manifolds
15
a
and
15
b
and air-gas manifolds
16
a
and
16
b
to prevent rise in a problem, such as deterioration in the power generating efficiently caused from leakage of air or the fuel gas.
The overall body of the conventional gas manifold is made of a metal material. Since the fuel cell is operated at high temperatures of about 200° C., great heat radiation takes place from the metal gas manifold. As a result, excessively great energy loss takes place. Therefore, a heat insulating material (not shown) is applied to the outer surface of each of the metal gas manifolds.
When fuel and air are supplied to the gas manifolds
15
a
and
16
b
respectively, a portion of the phosphoric acid, with which the matrix layer
2
of the single cell
1
and the grooved electrode substrates
5
and
6
forming the cell stack
10
are impregnated, is diffused in the flows of the fuel gas and air. As a result, the portion of the phosphoric acid is, in the form of steam of phosphoric acid, discharged to the outside of the cell stack (that is, to the inside portion of the gas manifolds).
Since the temperatures of the gas manifolds are somewhat lower than those of the cell stack, a portion of steam of the phosphoric acid discharged to the inside portions of the gas manifolds is, however, condensed and allowed to adhere to the inner walls of the gas manifolds. If the fuel gas and air containing phosphoric acid are brought into direct contact with the inner surfaces of the metal gas manifolds, the metal gas manifolds are vigorously eroded. As a result, holes are undesirably quickly formed.
To overcome the above-mentioned problem, a method of protecting the gas manifolds from phosphoric acid has been disclosed in Jpn. Pat. Appln. 4,950,563, in which the inner surfaces of the gas manifolds are coated with fluororesin.
However, the method of coating the inner surfaces of the gas manifolds with the fluororesin having the following problems cannot completely prevent erosion of the gas manifolds by dint of the phosphoric acid.
That is, the method of coating the inner surfaces of the gas manifolds with the fluororesin suffers from a problem in that phosphoric acid is undesirably introduced through a pin hole. The coefficient of linear expansion of resin coating is about ten times that of the gas manifold. Therefore, the coating method encounters defective adhesion of the resin coating owning to repetition of change in the temperature caused from start and interruption of the operation and change in the load. Therefore, there arises a problem in that the coating is separated.
Since the coating has a relatively small thickness, the phosphoric acid can easily penetrate the coating. Therefore, there arises a problem in that the matrix is eroded and realized reliability is unsatisfactory. To improve the reliability of the coating, the thickness of the coating film must be enlarged. Therefore, heating, coating and cooling processes must be repeated many times. As a result, a long time and great labor are required to complete the above-mentioned processes. Since the coating process and the process for manufacturing the gas manifolds are performed in series, the manufacturing process cannot be shortened.
In addition to the above-mentioned problems, the conventional gas manifold made of a metal material and thus having a great weight must have strong joining and holding structures. Moreover, great clamping force is required. As a result, there arises a problem in that the cost cannot be reduced.
When the gas manifolds are inspected, the heat insulating materials must be separated. Then, the heavy gas manifolds disposed on the four side surfaces of the cell stack cell must be removed. Therefore, the inspection cannot easily be performed and a long time is required.
A first object of the present invention is to provide a fuel cell incorporating gas manifolds each having light weight and small cost.
A second object of the present invention is to provide a fuel cell having gas manifolds each having a simple structure and permitting inspection to easily be performed.
A third object of the present invention is to provide a fuel cell which is capable of preventing leakage of gas from a corner of a cell stack.
A fourth object of the present invention is to provide a fuel cell having gas manifolds with which areas for joining the gas manifolds to the cell stack can be reduced.
BRIEF SUMMARY OF THE INVENTION
To achieve the foregoing objects, according to concept
1
of the present invention, there is provided a gas manifold which is disposed on each of side surfaces of a cell stack, wherein each of the gas manifolds comprises: plate-like heat insulating structures disposed on the side surfaces of the cell stack to oppose each other; and corner members disposed in corners of the cell stack.
According to concept
1
of the invention having the above-mentioned structure is able to significantly reduce the weight as compared with the conventional structure in which the overall body of the gas manifold is made of a metal material. Since the weight can be reduced, assembly and decomposition can easily be performed. Since the channel-shape corner member is disposed at each corner, a stable shape of the gas manifold can be maintained. Moreover, uniform distribution of gas to the cell stack can be performed.
A gas manifold according to concept
2
of the present invention has a structure according to concept
1
, wherein the heat insulating structure comprises an internal sheet member and an external heat insulating member which oppose the ce
Gocho Yoshitsugu
Iyasu Kotaro
Kano Akio
Moriyama Yoshihiro
Tanaka Kazuhisa
Kabushiki Kaisha Toshiba
Kalafut Stephen
Mercado Julian A.
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