Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED SOLID OXIDE FUEL CELLS
Contractual Origin of the Invention
The United States Government has rights in this invention pursuant to an
employer-
employee relationship between the U.S. Department of Energy and the inventors.
Technical Field
The present invention is related to solid oxide fuel cells and particularly to
improvements
thereto.
Background of the Invention
Fuel cells are electrochemical systems that generate electrical current by
chemically
reacting a fuel gas and an oxidant gas on the surface of electrodes.
Conventionally, the
components of a single fuel cell include the anode, the cathode, the
electrolyte, and the
interconnect material. In a solid state fuel cell, such as solid oxide fuel
cells (SOFCs), the
electrolyte is in a solid form and insulates the cathode and anode one from
the other with respect
to electron flow, while permitting oxygen ions to flow from the cathode to the
anode, and the
interconnect material electronically connects the anode of one cell with the
cathode of an
adjacent cell, in series, to generate a useful voltage from an assembled fuel
cell stack. The
SOFC process gases, which include natural or synthetic fuel gas (i.e., those
contaiiung
hydrogen, carbon monoxide or methane) and an oxidant (i.e., oxygen or air),
react on the active
electrode surfaces of the cell to produce electrical energy, water vapor and
heat.
Several configurations for solid state fuel cells have been developed,
including the
tubular, flat plate, and monolithic designs. In a tubular design, each single
fuel cell includes
electrode and electrolyte layers applied to the periphery of a porous support
tube. While the
inner cathode layer completely surrounds the interior of the support tube, the
solid electrolyte
and outer anode layers are discontinuous to provide a space for the electrical
interconnection of
the single fuel cell to the exterior surface of adjacent, parallel cells. Fuel
gas is directed over the
exterior of the tubular cells, and oxidant gas is directed through the
interior of the tubular cells.
The flat plate design incorporates the use of electrolyte sheets, which are
coated on
opposite sides with layers of anode and cathode material. Ribbed distributors
may also be
provided on the opposite sides of the coated electrolyte sheet to form flow
channels for the
reactant gases. A conventional cross flow pattern is constructed when the flow
channels on the
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as opposed to co-flow patterns where the flow channels for the fuel gas and
oxidant gas are
parallel, allow for simpler, more conventional manifolds to be incorporated
into the fuel cell
structure. A manifold system delivers the reactant gases to the assembled fuel
cell. The coated
electrolyte sheets and distributors of the flat plate design are tightly
stacked between current
conducting bipolar plates. In an alternate flat plate design, uncoated
electrolyte sheets are
stacked between porous plates of anode, cathode, and interconnecting material,
with gas
delivery tubes extending through the structure.
The monolithic solid oxide fuel cell (MSOFC) design is characterized by a
honeycomb
construction that is fused together into a continuous structure. The MSOFC is
constructed by
tape casting or calendar rolling the sheet components of the cell, which
include thin composites
of anode-electrolyte-cathode (A/E/C) material and anode-interconnect-cathode
(A/I/C) material.
The sheet components are corrugated to form co-flow channels, wherein the
fluid gas flows
through channels formed by the anode layers, and the oxidant gas flows through
parallel
channels formed by the cathode layers. The monolithic structure, comprising
many single cell
layers, is assembled in a green or unfired state and co-sintered to fuse the
materials into a rigid,
dimensionally stable SOFC core.
These conventional designs have been improved upon in the prior art to achieve
higher
power densities. Power density is increased by incorporating smaller single
unit cell heights and
shorter cell-to-cell electronic conduction paths. SOFC designs have thus
incorporated thin
components which are fused together to form a continuous, bonded structure.
However, the
large number of small components, layers, and interconnections, in addition to
complex
fabrication steps, decreases the reliability of operational fuel cells. In
addition, any given fuel
cell design must be commercially viable as an alternative power generating
device, and,
therefore, factors affecting the economics of power generation by
electrochemical activity, such
as overall capital and operational costs to the user, must be comparable to
those of conventional
power generating systems.
Packaging for the fuel cells is known but it usually is a simple box around
the stack of
solid oxide fuel cells. Fox example, US Patent Nos. 4,824,724; 4,827,606; and
4,943,494
disclose a box arrangement for a tubular fuel cell design. US Patent Nos.
5,238,754; 5,268,241;
and 5,527,634 disclose packages which use end plates, tie bars and spring
loaded fasteners to
hold the fuel cell plates together.
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The present invention is to improved solid oxide fuel cells structures
including a housing
or cover for the solid oxide fuel cell structures, which can be a stack of
planar sheets that when
joined will resemble a monolithic honeycomb structure. The present invention
also includes
further improvements are beneficial in optimizing the overall system. In
addition, various
improvements in cell designs for planar fuel cells are disclosed, as well as
processes for making
them.
The present invention is a solid state electrochemical device that
incorporates planar
sheets of cathode flow passages, in various configurations and geometries,
with thin coatings of
electrolyte, anode and interconnect materials, which when the sheets are
assembled and bonded
together form a monolithic honeycomb structure defining tubular passages for
the air and gas to
pass through. Air will flow through cathode flow passages inside the cell
plates, wlule fuel will
flow through passages formed by spaces between adjacent cells. Electrically
insulating
manifolds, that are designed to keep the fuel and air separate, are bonded at
each end of the solid
oxide fuel cell structure to feed air and fuel to the appropriate passages in
the structure. Finally,
the fuel cell stack and manifolds are encased in a metal housing or cover to
provide the outer
walls of the manifold, complete the package, and define a discrete fuel cell
module that can be
used singly or in groups in fuel cell power generation systems.
Therefore, an object of the present invention is to provide a solid state fuel
cell design
incorporating an array of parallel cathode material tubes that improves fuel
distribution and
substantially eliminates the formation of hot spots within the fuel cell
assembly.
Another object of the present invention is to provide a solid state fuel cell
design
incorporating a unique array of parallel cathode material tubes that increase
the active surface
area per unit fuel cell, such that the overall power density of the assembled
fuel cell stack is
critically improved.
Yet another object of the present invention is to form the manifolds as an
integral part of
the cell plates and eliminate secondary operations to form the fuel laterals.
The primary advantage of the present invention is to provide all the
advantages of the
hollow extruded plate concept, while eliminating secondary operations and
integrating
components.
Additional obj ects, advantages and novel features of the invention will be
set forth in
part in the description which follows, and in part will become apparent to
those skilled in the art
upon examination of the following or may be learned by practice of the
invention. The objects
and advantages of the invention may be realized and attained by means of
instrumentation and
combinations particularly pointed out in the appended claims.
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Brief Description of the Drawings
The appended claims set forth those novel features which characterize the
invention.
However, the invention itself, as well as further objects and advantages
thereof, will best be
understood by reference to the following detailed description of a preferred
embodiment taken
in conjunction with the accompanying drawings, where like reference characters
identify like
elements throughout the various figures, in which:
Fig. 1 is an illustration of an assembled fuel cell stack constructed by
stacking planar
sheets of integrally connected tubular fuel cells, attaching manifold, and
encasing the assembly
in a housing;
Fig. 2 is an exploded view of the assembled fuel cell in Fig. 1;
Fig. 3 is a cross-sectional view of the planar sheet illustrated in Fig. 1;
Fig. 4 is an illustration of a single planar sheet of integrally connected
tubes;
Fig. 5 is a cross-sectional view of the tube sheet illustrated in Fig. 4;
Fig. 6 illustrates a stack of tube sheets shown in Figures 4 and 5 that are
coated and
sintered together to form the monolith;
Figs. 7 and 8 are an exploded and an assembled external manifold with passages
and
holes to provide fuel and air to each monolith passage;
Fig. 9 is a cross-sectional view of the assembled and attached manifold
illustrated in Fib
8;
Fig. 10 shows a different tube configuration combined with an internal
manifold
configuration;
Fig. 11 illustrates an asymmetric tube sheet;
Fig. 12 shows a series of the tube sheets of Fig. 11 assembled to form a
monolith stack
assembly;
Fig. 13 illustrates a tube shape incorporating ridges or sine-like ripples to
increase activ
surface area;
Fig. 14 illustrates a tube shape incorporating ridges or sine-like ripples in
a monolith
assembly;
Fig. 15 illustrates, in an exploded view, another tube shape as an extruded
sheet which
incorporates internal and external manifolds in a monolith assembly;
Figs. 16 and 17 illustrate a tube sheet made by a co-extrusion process having
a molded
manifold attached;.
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Fig. 19 is an exploded view and Fig. 20 is an assembled view of a fuel cell
incorporating
the tube sheet illustrated in Figs. 16 and 17;
Fig. 21 is an illustration of the mold assembly for making tube sheets using a
fugitive
molding process;
Fig. 22 is an illustration of a stack of tube sheets made using the fugitive
molding
process;
Fig. 23 is an enlarged illustration of the stack illustrated in Fig. 22; and
Fig. 24 is an exploded view and Fig. 25 is an assembled view of a fuel cell
incorporating
the tube sheet illustrated in Figs. 16 and 17 or the tube sheet illustrated in
Figs. 22 and 23.
Detailed Description of the Invention
The present invention relates to a solid state electrochemical device that
provides
increased active surface area and improves even distribution of a process gas.
The present
invention is described with respect to a detailed description of its
application in the operation of
a solid state fuel cell having a solid oxide electrolyte: a solid oxide fuel
cell (SOFC). However,
it will be obvious to those skilled in the art from the following detailed
description that the
invention is likewise applicable to any electrochemical system, including
electrolysis cells, heat
exchangers, chemical exchange apparatuses, and oxygen generators, among other
applications.
The present invention is directed to improving the process gas distribution
and available
active surface area in a solid state fuel cell having a unique solid oxide
fuel cell structure design.
In the fuel cell structure concept fuel and air enter the stack at one surface
and flow through
closely spaced parallel passages to a second surface where they exhaust
together. The stack is
made of cathode material cell plates with thin coatings of electrolyte, anode
and interconnect
materials. The cell plates will be bonded together to form a structure that
resembles, but is not
limited to, a monolithic honeycomb structure. The air flows through passages
inside the cell
plates. The fuel flows through passages formed by spaces between adjacent cell
plates. Nail
current collector members can be positioned within each cell plate to
significantly increase the
active surface area of the fuel cell stack.
This arrangement sequesters the air witlun the hollow cell plates, and
surrounds the cell
plates with fuel. By providing electrically insulating manifolds, that are
bonded to the ends of
the honeycomb monolith, the appropriate flow of the air and fuel is
facilitated, without the need
for cross-flow of the reactants. The manifolds are designed to keep the fuel
and air separate, and
feed them to the appropriate holes in the honeycomb-like structure. Further,
the designs allow
for internal manifolds in the form of fuel or air laterals. These are opening
through the plates
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for the circulation of the air and fuel. These design improvements can reduce
hot spots in the
fuel cell, but can also provide for electrical continuity since the surfaces
can be continuous.
An asymmetric tube monolith embodiment allows for air flow through an array of
parallel cathode material tubes, and fuel flows in parallel in the passages
between the tubes. The
tubes are coated with electrolyte and anode material layers except in the
interconnect area. The
interconnect area is coated with a conductive ceramic film. The cathode tubes
are the main
structural elements, and the anode Layer bonds them together to form unified
cell plates that can
be easily handled and stacked. The cell plates bond together during burn-in to
form a
monolithic honeycomb-like structure.
Current flows from the anode through the electrolyte layer to the cathode, and
then
through the interconnect to the anode of the next cell Layer. The fact that
the anode Layer
surrounds the cathode except in the interconnect area provides the electrical
continuity to make
both the top and bottom surfaces of the plates active.
Manifolds axe added to the extrusions to form complete cell plates. The inlet
maufold
forms a vertical air inlet passage with a seal around its perimeter when the
cell plates are
staclced. Air feed holes lead from the air inlet passage to each air tube in
the extrusion. The
stack is in a plenum and is surrounded by fuel that flows in between the
plates from each side
through the fuel inlet passages. Fuel flows into each fuel passage through
fuel metering notches.
The mixed exhaust manifold forms a vertical exhaust passage with a seal around
its outside
perimeter when the cell plates are stacked. Air exhaust flows into the mixed
exhaust manifold
through air exhaust holes and fuel exhaust flows into the mixed exhaust
manifold through fuel
exhaust notches.
This arrangement sequesters the air within the inlet manifold, cathode air
tubes, and
mixed exhaust manifold. These components are ceramics and not subject to
oxidation. The
stack is surrounded by fuel, creating a reducing environment in which metal
components such as
power takeoffs, pressure plates and tie bars may be used.
The cell plates include cathode, anode and electrolyte layers, and are made
using an
extrusion process. The manifolds are molded of cathode material and bonded to
each end of the
extrusions in the green state. The green cell plate assembly is then fired to
remove the binder
and fugitive materials, and consolidate the cathode and electrolyte layers.
The manifolds
become a unified part of the plate. Ceramic interconnect material is then
applied to the specified
areas using a plasma spray process, which will form a fully dense layer
without subsequent
firing. The plates axe then stacked. Tnitial burn-in reduces the anode nickel
oxide to metal and
sinters together the plates to form a monolith. The complete assembly includes
non-repeat
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features can be appreciated by considering the illustrations i.n the drawings.
Fig. 1 shows an assembled fuel cell 1, including a housing or cover 2 for
enclosing and
supporting the elements of the fuel cell. The fuel cell package will have a
fuel inlet 3, a fuel
outlet 4, an air outlet 6, and terminals 8 at the top and bottom of the fuel
cell.
Fig. 2 is an exploded view of the fuel cell package, which further illustrates
the
assemblage. The cover 2 comprises a top section 9 and a bottom section 10,
which are brought
together to enclose the fuel cell stack 11. When assembled, the fuel cell
stack 11 is placed
between a layer of nickel felt and a current collector plate, which is best
seen in a cross-section
of the fuel cell assembly shown in Fig. 3. The felt is indicated at 13.
Finally, a ceramic
insulator layer 14 is placed over the current collector plate. When the two
halves 9 and 10 are
assembled, they can be held in place by, for example, welding the two pieces
of the metal shell
so as to hold the assembly together in tension. This is facilitated by the use
of a spacer 14 in the
bottom half of the shell cover. The air and fuel passages in the fuel cell
stack are fed and
exhausted by manifold assemblies attached at each end of the fuel stack. As
seen in Fig. 2, the
inlet manifold 15 is attached to the fuel cell stack and defines inlet gallery
16. Manifold 17
defines a fuel exit gallery 22 and has an air outlet 6. Both manifolds 15 and
17 will have
packing grooves 18 around the periphery of the manifold for purposes of
sealing the manifold in
place when the inlet cover 19 and exit cover 20 are assembled with the cover
halves. As shown
in Fig. 3, air enters the fuel cell via inlet 21 while fuel enters via inlet
3. The fuel is distributed
via the fuel inlet gallery I6 and flows through the fuel cell stack I1,
exiting the stack via the fuel
exit gallery 22 to fuel exit plenum 23, and finally exit through the outlet 4.
The air flows
through the air tubes in the fuel cell stack and exits via fuel flow passages
in the staclc.
The fuel cell stack comprises an assembly of extruded tube sheets such as tube
sheet 30
illustrated in Figs. 4 and 5. Fig. 4 shows an individual planar tube sheet 30
of integrally
connected tubes 31. The sheet 30 may be constructed from any appropriate fuel
cell component
material and will include cathode, anode, electrolyte and interconnect
material, or any
combination thereof. As shown in Fig. 5, the cathode material 32 defines air
passages 33 and
have an electrolyte and anode coating 34 over the or co-extruded with the
extruded cathode
material. In addition, the bottom layer defining the air passages 33 will be
an interconnect and
anode coating 35.
As can be seen in Fig. 6, a plurality of planar sheets 30 are stacked so as to
define fuel
passages 36. Preferably, the sheets 30 are made from cathode materials in a
single extrusion
step, or by co-extruding the cathode materials as well as the electrolyte and
anode compositions.
Although, they can be made by extruding the cathode material and subsequently
coating the
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planar and composed of parallel rows of longitudinally aligned tubes that
extend the length of
the sheet. Although the tubes are illustrated as triangular in shape, the
tubes may have any
cross-section and may be symmetrical or asymmetrical. For example, the cross-
sections may be
triangular, rectangular, trapezoidal, circular, or polygonal in shape, among
other geometries.
As shown in Figs. 7 and 8, the assembled stack, which describes a honeycomb
stack, are
assembled with external manifolds or plate-like structures that bond to the
faces of the
honeycomb monolith. For example, as shown in Fig. 7, air passages 33 and fuel
passages 36 are
bonded to manifold structures 37 and 38. Manifold structure 37 is a
distributor for air via
passages 39 and fuel via passages 40 which connect to air passages 33 and fuel
passages 36,
respectively, in the fuel cell monolith. Header 38 is joined to distributor 37
and possesses air
holes 41 aligned with air passages 39 and 33 so that air passes through
openings 4I and 39 to
the air passages in the fuel cell stack. Header 38 and distributor 37 together
define a fuel gallery
47 with air passages 39 being sealed by the header 38. V~hen the covers or
housings 2 and 3 are
in place, a seal is formed with header 38 by placing appropriate seal material
in seal groove 18.
The seal may be refractory fiber rope. The seal provides enough compliance to
avoid stresses
caused by the differential thermal expansion created between the ceramic stack
and the metallic
stack containment structure.
The external manifold arrangement shown in Fig. 9 has connected air passages
41, 39
and 36 by joining the distributor 37 to the stack at 44 and the header 38 to
the distributor at 45.
The fuel gallery 43 distributes fuel through openings 40 into passages 36. The
air passages pass
straight through to the stack from the flat outside surfaces of the header
plate. Fuel surrounds
the sides of the stack and feeds into the stack fuel passages through the fuel
gallery. As noted
earlier, the shape of the air passages and the sheets is not critical.
As illustrated in Fig. 10, a tube sheet 50 may be made from octagonal-shaped
passageways in which the octagonal shape is cathodic material defnung an air
passageway 51
and the spaces between the tubes combined with the stack of tube sheet define
a fuel
passageway 52 with the cathode material being appropriately coated or co-
extruded with
electrolyte, anode, and/or interconnect material. An additional feature that
can be incorporated
is the use of internal manifolds where the connecting material between the
tubes defining the air
passages has been removed to create fuel laterals 53. Fuel laterals facilitate
the equalization of
the fuel between the levels of the fuel cell and prevent the occurrence of hot
spots in the
operation of the fuel cell.
Fig. 11 illustrates a tube sheet using an asymmetric tube structure. As shown,
the tube
sheet 54 can be a single extrusion of a cathode material in an asymmetric
shape with the
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be made by extruding individual tubes and subsequently connecting the tubes
prior to firing to
form a monolith.
As shown in Fig. 12, the cathode material defines the air passages 55, but
when the tube
sheets are stacked, the assemblage defines the fuel passages 56, with layer 57
being anode
material, layer 58 being electrolyte material, and layer 59 being interconnect
material so that
there is a continuous path for the electrons in the tube stack.
Another feature shown in Fig. 13, is the use of irregular shaped tube
configurations
where the extruded cathode material 60 defines the air passage 61 and has
coated thereon
electrolyte and anode material 62, and intercomzect material 63. When the
tubes are assembled,
as shown in Fig. 14, the tubes 60 also define fuel passages 64. As shown in
Figs. 13 and 14, the
small sine-like ripples allow an increase of up to 1.5 times the active area
for the anode at,
essentially, no increase in material costs.
Fig. 15 illustrates yet another tube shape, which can be made by extrusion and
in which
the air passages are at 68, and the fuel passages are at 69. This design will
increase the surface
area of the cathode. The tube stack can have fuel laterals 70 to facilitate
passage of fuel between
the fuel cell stacks. In addition, header 71 will be joined to the fuel stack
to facilitate the
distribution of air through air passages 68 and fuel through fuel passage
grooves 72.
Another approach to assembling the fuel cells is to co-extrude the stack as
shown in
Figs. 16, 17 and 18, in which the air passages are extruded tubes 75 and the
fuel passages are
notches or grooves 76. The sheets 77, when assembled, as shown in Figs. 19 and
20, will result
in the grooves 76 and the bottom surface of the next layer of the tube sheet
definng the fuel cell
passages. The headers can be molded separately and attached by "welding" or
the like to the
tube sheets. The "welding" is only suggestive in that with ceramic materials,
a bonding
composition is employed to hold or bond the parts together until they can be
fired to produce a
more permanent bond. For example, an inlet header 77, which defines an air
inlet space 78, and
a fuel inlet passage 79, can be attached on the inlet end of the plate 77, and
an outlet manifold
80 attached to the outlet end of the plate 77. The outlet has matching passage
holes 75 and
grooves for fuel passages 76. The exhausted air and fuel will exit together
via opening 81 in
exhaust manifold 80. When the cell plates 77 are stacked, for example 56 cell
plates with
manifolds could be stacked to provide a 42 vDC at 0.75 v/cell. A talc or
powdered mica could
be used on the manifold sealing areas to reduce leakage. The stack is then
assembled as shown
in Fig. 20 between end plates 84 and 85, having terminals 86 and 87, and
ceramic electrical
insulating plates 88 and 89 to separate the power take-off plates from the end
plate and the base
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92 and end plate 93.
Clamping load is provided by an endplate and a baseplate loaded by a pair of
tiebars and
springs. Ceramic electrical insulating plates separate the power takeoff
plates from the endplate
and baseplate. The plates can be, for example, Hastelloy X castings or any
alumina-coating
alloy which can provide long term endurance. Tiebars and springs can be, e.g.,
Inconel 716.
The tiebars can be extended so that the springs can be positioned outside the
hot zone. Inconel
spxings have a practical limit of about 600°C. Reactant gas inlet and
exhaust flows are through
poxts in the endplate. The endplate is electrically grounded, and comzections
may be made by
bolting or welding to the power takeoff plate lugs.
An alternative to extruding tube sheets and assembling molded headers would be
to
mold the tube sheets using a fugitive core material. As illustrated in Figs.
21, 22 and 23, a tube
sheet having an integral header could be manufactured by a mold assembly (as
illustrated in
Fig. 21), which included a lower cathode preform 100, an upper cathode preform
101, and a
fugitive core material 102 which is placed between the lower cathode preform
100 and the upper
cathode preform 101 to result in air passages when the cathode material is
fused to produce a
cathode monolith. When the fugitive core is bu~.ned off, the space that
remains will define air
passages 103, the manifold is defined by the molded material 104, and the fuel
inlet passage by
space 105, the fuel passages by space 106, and the fuel laterals by space 107.
Spaces will also
result for air laterals at 108.
The upper and lower cathode preforms can be made by compression molding or a
similar
suitable process. The fugitive coxes are made by compression or injection
molding from
polymer wax, a carbon powder composition, or other material that evaporates,
vaporizes,
decomposes, or is removed by heat with no residue left belund. A green upper
and green lower
cathode preforms are assembled with the fugitive core and the assembly is
pressed togethex with
the fugitive core in a die to join the preforms into a single green cathode
cell plate surrounding
the core. The assembly is then dried and fired to consolidate the cathode into
a porous ceramic.
The core supports the cathode material during the initial part of the firing
cycle, and is then
removed by vaporization or thermal decomposition. The result is a complete
hollow cathode,
including inlet and exhaust manifolds, and is ready for subsequent processing
to add electrolyte,
interconnect and anode layers. The sheets can then be assembled in a similar
manner to those
illustrated in Figs. 19 and 20 to provide a completed fuel cell.
Figs. 24 and 25 illustrate an alternative packaging design to that shown in
Figs. 19 and
20. Fig. 24 shows an exploded view and Fig. 25 shows an assembled view of a
packaging
similar to that shown in Figs. 1-3. As shown in Figs. 24 and 25, the upper
cover 111 and lower
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plenums. The pieces can be brought together and clamped, welded, or fixed by
any appropriate
means to maintain the fuel stack 115 in tension and in assembled relationship.
This can be
facilitated by the use of a mesh spring pack 116 placed in the lower cover or
fuel plenum 112.
When the assembly is completed, including ceramic insulators 117 and 118,
current collector
plates 119 and 120, which would produce electrical flow through terminals 121.
Air is fed into
the housing at 122 and a mixed exhaust is taken out at 123. Fuel is fed into
the plenum via fuel
inlet 124.
It may be desirable to take the fuel cell stack such as illustrated in Fig. 3
and combine
them end-to-end using a coupling header so as to provide an assembly having a
lower section
for low temperature and a second section for high temperature processing.
Also, several
monoliths can be combined into a single package module by connecting the
modules in series
with metal felt pads and/or electrical connections to create a larger package.
The fuel cells will operate by flowing the air and gas through the parallel
spaced
passages. Fuel flows in from each side through fuel inlet passages between the
cell plates. It
then flows through fuel metering slots, and on between the cell plates to the
exhaust end of the
cell stack. The fuel reacts with the air flowing through the internal air
passages to generate
electric power. The fuel laterals provide extended reactive surface area, as
well as electrical
continuity between upper and lower sides of the cell plates. The air laterals
improve the access
of air to the reactive layers compared to simple straight air passages. They
also facilitate the
handling of the fugitive core. The fuel and air passages empty into the
exhaust manifold (i.e., an
internal manifold similar to the air inlet manifold) and mix.
The foregoing embodiments of the present invention have been presented for the
purposes of illustration and description. These descriptions and embodiments
are not intended
to be exhaustive or to limit the invention to the precise form disclosed, and
obviously many
modifications and variations are possible in light of the above disclosure.
The embodiments
were chosen and described in order to best explain the principle of the
invention and its practical
applications to thereby enable others skilled in the art to best utilize the
invention in its various
embodiments and with various modifications as are suited to the particular use
contemplated. It
is intended that the invention be defined by the following claims.
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