One piece sleeve gas manifold for cell stack assemblies such...

Details One piece sleeve gas manifold for cell stack assemblies such... One piece sleeve gas manifold for cell stack assemblies such...

2002-09-10

2004-07-20

Bell, Bruce F. (Department: 1746)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000, C429S006000, C204S257000, C204S269000, C204S278500, C096S007000, C165S166000

Reexamination Certificate

active

06764787

ABSTRACT:

TECHNICAL FIELD
This invention relates to a single-piece sleeve manifold which will supply, contain and remove fluids, including fuel reactant gases, oxidant reactant gases, and cooling fluids, in fuel cell stack assemblies, electrochemical cell stack assemblies, and including exchange gases in enthalpy exchange devices.
BACKGROUND ART
In cell stack assemblies, it is known to use internal reactant and coolant manifolds as well as external coolant and reactant manifolds. Internal manifolds generally comprise passageways made within the various plates that constitute the cells of the cell stack assemblies. This renders the plates themselves much more expensive than plates which are fabricated for use with external manifolds. Internal manifolds have potential leakage paths between the plates of every cell, the leakage thereby being to the external environment. While external manifolds may also leak gases to the external environment, the avoidance of such leaks is more easily accomplished. Internal manifolds are generally smaller in cross-section than external manifolds and are better suited for pure reactants (like pure hydrogen) and high reactant operating pressures.
External manifolds consist of manifold shells, manifold seal gaskets, and a mechanical loading or restraint system to hold the manifolds in compression, tightly against the edges of the cell stack.
A fuel cell module
10
of U.S. Pat. No. 4,345,009, shown in FIG.
1
and in cross section in
FIG. 2
, is one example of the manifold and containment systems known in the art. The lower right corner of
FIG. 2
is the corner of the module
10
pointing toward the viewer in FIG.
1
. The module
10
includes a stack
12
of fuel cells
14
. As shown in
FIG. 3
, each fuel cell
14
comprises a gas porous anode electrode
16
and a gas-porous cathode electrode
18
spaced apart with a layer
20
, such as a liquid electrolyte retaining matrix or a proton exchange membrane, disposed therebetween. Each electrode
16
,
18
includes a very thin catalyst layer
19
,
21
, respectively, on the surface thereof adjacent the layer
20
. An electrically conductive, gas impervious plate
22
may separate adjacent fuel cells in the stack
12
. Each fuel cell in the stack may include one separator plate
22
such that the phrase “fuel cell” will encompass a repeating unit of the stack which includes one separator plate. The fuel cells of this exemplary embodiment may be the same as shown in U.S. Pat. No. 4,115,627 in which the electrolyte is phosphoric acid. However, fuel cell stacks with proton exchange membrane electrolytes, as in U.S. Pat. No. 6,024,848, have similar manifold and restraint problems.
In this embodiment every third fuel cell
14
′ (
FIG. 3
) includes a coolant carrying layer
24
disposed between the electrode
16
and the separator plate
22
. Passing in-plane through this layer
24
are coolant carrying passages
26
. The coolant flowing through these passages carries away the heat generated by the fuel cells. The number of coolant layers
24
and passages
26
required by a stack is dictated by a variety of factors which are not relevant here. Although the coolant passages
26
are shown as extending to the surface
32
for clarity, in an actual fuel cell stack they would not do so. The stack
14
is completed by top and bottom flat graphite current collector blocks
27
,
28
, respectively, bonded to the separator plates
22
at each end of the stack, and pressure plates
66
,
68
.
As shown in the drawing, the outer edges
29
of the stack components
16
,
18
,
20
,
22
,
24
,
27
and
28
form four outwardly facing planar surfaces which are the external surfaces of the stack
12
. Portions of two of these surfaces
30
,
32
are shown in FIG.
3
. Each of the four surfaces is substantially completely covered by a reactant gas manifold. An air or oxygen gas inlet manifold
34
covers the surface
30
while a fuel or hydrogen gas inlet manifold
36
covers the surface
32
. The opposing surfaces are covered by an air outlet manifold
38
and a fuel outlet manifold
40
(FIG.
2
).
The manifolding arrangement just described incorporates an outlet manifold on each side of the stack opposite an inlet manifold. However, as shown in U.S. Pat. No. 3,994,748 a fuel manifold covering one surface of the stack may be divided into two compartments to serve as both the inlet and outlet manifold, while the manifold on the opposite surface of the stack serves as a mixing manifold; the same configuration may be used for the air.
The anode electrode
16
and the cathode electrode
18
both comprise relatively thick substrates with ribs formed on one side thereof defining reactant gas channels
42
,
44
, respectively. The fuel gas channels
42
carry hydrogen or a hydrogen-rich gas across the cells from the fuel inlet manifold
36
to the fuel outlet manifold
40
. The air channels
44
carry air across the cells from the air inlet manifold
34
to the air outlet manifold
38
. The flat surface of each substrate, which is opposite to the surface having the ribs (and thus the gas channels), has a layer
19
,
21
of catalyst disposed thereon.
The graphite blocks
27
,
28
have the same outer dimensions as the other stack components, and their outwardly facing surfaces (two of which,
50
and
52
, can be seen in
FIG. 3
) provide smooth sealing surface for the top and bottom sealing flanges
54
,
56
of each manifold. A thick block at one end of the stack is required to accommodate the possible differences in stack height which could result from the buildup of the very small tolerances in the thickness of the many hundreds of components in the stack
12
. For example, a stack of 400 cells each having a thickness of about 0.64 cm (0.25 inch) with a tolerance of 0.01 cm (±0.004 inch) could have an overall height of anywhere from 250 to 258 cm (98.4 to 101.6 inches). The manifolds, on the other hand, have a fixed height. A large block thickness is thus required to ensure that both the top and bottom flanges
54
,
56
are located somewhere on the smooth sealing surfaces of the blocks
27
,
28
after the desired compressive force has been applied to the stack as hereinafter explained.
As best shown in
FIG. 2
, side flanges
58
, seal against the vertically extending external surfaces of the stack
12
near the corners of the stack which do not have reactant gas channels. A sealing material, such as a porous polytetrafluoroethylene, is disposed between the manifold flanges
54
,
58
and the surfaces of the stack. Steel bands
60
(
FIGS. 1 and 2
) surround the stack manifolds and hold them in sealing relationship with the stack and graphite blocks. Fasteners
62
connecting the ends of each band permit tightening the bands to the extent necessary to ensure adequate sealing.
To obtain good electrical, thermal, and sealing contact between the various components of the cells and the stack
12
, the module
10
includes a constraint system
64
. In this exemplary embodiment, the constraint system
64
comprises inflexible top and bottom steel end or pressure plates
66
,
68
, respectively, and tie rods
70
connecting the plates. The plates
66
,
68
rest flat against the graphite blocks
27
,
28
, respectively. In assembling a module
10
, the pressure plates
66
,
68
, the blocks
48
,
49
, and the various stack components are arranged one atop the other in proper sequence. This assembly is hydraulically loaded whereupon a preselected axial (i.e., perpendicular to the plane of the cells) load is applied to the plates
66
,
68
to compress the stack
12
. The tie bolts
70
are then tightened down to an extent that, when the assembly is removed from the press, the compressive force on the stack
12
is of approximately the desired magnitude. The manifolds
34
,
36
,
38
and
40
are then positioned against the sides of the stack and secured by the bands
60
.
Since the constraint system
64
and the manifolds
34
,
36
,
38
and
40
are made from similar materials (carbon steel) they have the same or appro

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