Fuel cell generator containing a gas sealing means

A high temperature solid electrolyte electrochemical generator is made, operating with flowing fuel gas and oxidant gas, the generator having a thermal insulation layer, and a sealing means contacting or contained within the insulation, where the sealing means is effective to control the contact of the various gases utilized in the generator.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to solid electrolyte electrochemical cells, and more 
particularly provides a gas confinement scheme for a generator system 
comprised of such cells. 
2. Description of the Prior Art 
High temperature solid electrolyte fuel cells convert chemical energy into 
direct current electrical energy, typically at temperatures of from about 
700.degree. C. to 1200.degree. C. This temperature range is required to 
render the solid electrolyte sufficiently conductive for low power losses 
due to ohmic heating. With such cells, expensive electrode catalysts and 
refined fuels are not required. For example, carbon monoxide-hydrogen fuel 
mixtures can be used directly, without conversion. 
High temperature fuel cell generators employing interconnected, tubular 
fuel cells, with solid electrolytes, are disclosed by A. O. Isenberg, in 
U.S. Pat. No. 4,395,468, and by E. V. Somers et al., in U.S. Pat. No. 
4,374,184. Support tube, fuel electrode, air electrode, solid electrolyte, 
and interconnection configurations for individual fuel cells, are 
disclosed by A. O. Isenberg, in U.S. Pat. No. 4,490,444. In the Isenberg 
fuel cell generator, an exterior metal housing having a contacting, 
internal thermal insulation layer, usually low density alumina, surrounds 
a generating chamber containing a fuel inlet, a combustion product or 
preheating chamber containing a combustion product outlet, and an oxidant 
inlet chamber. The array of individual fuel cells are contained in the 
generator chamber. 
Yttrium stabilized zirconia is a prime electrolyte candidate for the fuel 
cells, and is used in a thin layer disposed between an air electrode and a 
fuel electrode, all supported on porous ceramic tubular support 
structures. The support tubes for thin film high temperature solid oxide 
electrolyte cells can be made of calcium stabilized zirconia, and serve as 
ducts for one of the reactants, fuel or oxidant. Many such fuel cells must 
be connected electrically in series for high voltages, since each cell has 
a terminal voltage of approximately 0.6 volt. 
Sealing and supporting of such fuel cells has been a concern because fuel 
and oxidant reactants must be separated to a large extent, to avoid 
interaction other than electrochemical combustion. Additionally, it has 
been found that water vapor formed in the generating chamber, and also 
carried into the preheating chamber, can carry water through the thermal 
insulation layer and condense it on any surfaces whose temperatures are 
below the dew point of the gas mixture in either chamber. Such a "heat 
pipe" type effect can reduce the insulating effectiveness of the 
insulation surrounding all of the chambers. Additionally, any hydrogen gas 
component of the inlet fuel, if permitted to permeate the thermal 
insulation in the generating chamber, will reduce the insulation value by 
displacing air, since hydrogen has a very high thermal conductivity 
compared with air. 
What is needed is a gas confinement scheme for the generator system; to 
separate the insulation layer from the fuel mixture, and/or to separate 
the gases found in the generating and preheating chambers. Such a scheme 
should not involve sealing arrangements. 
SUMMARY OF THE INVENTION 
The disclosed generators eliminate complex seals and allow the oxidant gas, 
fuel gas, fuel product gas, and an optional insulation gas to communicate 
in a controlled manner. In one concept the oxidant gas, and the fuel gas, 
which can contain hydrogen, will be separated by a seal passing through 
the porous, gas permeable thermal insulation, extending inwardly from the 
exterior housing and positioned at a point between the fuel gas inlet 
chamber and the combustion product chamber. In another concept the 
electrochemical generator will have a thermal insulation volume, 
containing thermal insulating gas, disposed between an exterior and 
interior housing, where the interior housing is disposed between and can 
act as a continuous seal between the thermal insulation and all internal 
gases and defines an interior volume containing electrochemical cells. In 
a third concept an expansion seal is preferably utilized in the interior 
housing at a point between the fuel gas inlet chamber and the combustion 
product chamber. The generator has associated therewith, means to 
introduce fuel gas and oxidant gas into the interior volume, and in the 
second and third concepts, insulating gas into the thermal insulation, 
where the insulating gas is maintained at a pressure higher than the other 
gases contained within the interior volume. 
In preferred form, a gas tight exterior housing having contacting internal 
thermal insulation surrounds an interior volume having three chambers 
which communicate among one another through controlled gas seepage. A fuel 
gas inlet, or generating chamber, is separated from a combustion product 
or preheating chamber by a gas porous partition. The combustion product 
chamber is separated from an oxidant gas or an air inlet chamber by a 
metal sheet. 
Tubular solid oxide electrolyte fuel cells are disposed within the interior 
housings and preferably extend from the combustion product chamber to the 
generating chamber. The tubular cells are closed-ended within the 
generating chamber, and open-ended within the combustion product chamber. 
The cells thus pass through and can be partially supported by the porous 
barrier. 
Oxidant carrying conduits are loosely supported at one end by the tube 
sheet, and extend through the combustion product chamber and into the open 
ends of the fuel cells. Each conduit corresponds to a single fuel cell and 
extends through the cell to a point near its closed end. The conduit 
includes an open end, or discharge holes, near the closed end of the fuel 
cell, so as to discharge air into the fuel cell. 
In the concepts utilizing an interior housing, a gas permeable, porous, 
internal thermal insulating layer will contain a thermal insulating gas, 
such as air, nitrogen, or argon, at a pressure P' allowing flow through 
the insulation, and the pressure P' will be greater than the fuel gas, 
fuel product gas, or oxidant gas pressure P. This air, or inert insulating 
gas will preferably be contained within the pore matrix of a gas permeable 
insulating material, such as a refractory, for example, alumina fibers. 
The internal thermal insulation will be disposed between the exterior 
housing and the interior housing also surrounding all three chambers. In 
the third concept, utilizing an expansion seal, there will generally be a 
controlled gas leakage; so that the pressurized, thermal insulating gas 
will slowly seep into at least the combustion product chamber at a 
pressure greater than the fuel gas or reacted fuel product gas, helping to 
prevent contamination of the insulation. In the concepts where the 
interior housing is used, the flowing thermal insulating gas can sweep 
away any hydrogen which may have been present in the fuel gas and which 
may have diffused through the metal interior housing. 
In the third concept, utilizing an expansion seal, the interior housing is 
made up of two adjoining sections which join in the area of the gas porous 
partition between the fuel gas inlet chamber and the combustion product 
chamber. The seal joint separating the two housing sections can be an 
expansion seal joint having a simple trough seal design, which compresses 
a porous, refractory material. This design allows for interior housing 
expansion and contraction upon thermal cycling or during operation of the 
fuel cell generator, and allows leakage flow of insulating gas from the 
thermal insulation pores into the interior volume of the generating 
chamber. Such controlled leakage of insulating gas prevents the fuel or 
reacted fuel product gas from entering and contacting the thermal 
insulation layer in the thermal insulation volume. The third concept can 
be used when a single piece interior housing, or the use of a metal seal 
through the insulation are not feasible or desired.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in U.S. Pat. No. 4,395,468, herein incorporated by reference, a 
fuel cell arrangement or stack can comprise a plurality of elongated 
annular fuel cells. Each fuel cell is preferably tubular and is 
electrically connected at least in series to an adjacent cell. The 
electrical connection is made along a selected axial length of the cells, 
preferably the entire electrochemically active length. Each cell generates 
an open circuit voltage of approximately 0.6 volt, and multiple cells can 
be connected in series in order to provide a desired system voltage. 
Referring now to FIGS. 1 through 4, there is shown one embodiment of a fuel 
cell generator 10 including an exterior housing 12. While the generator is 
shown in a square configuration in FIGS. 1 through 3, the generator and 
all associated housings can quite advantageously be of a circular or oval 
cross section. The exterior housing 12 surrounds at least one chamber, a 
fuel gas inlet or electrical energy generating chamber 14, containing a 
fuel gas, generally containing hydrogen, at a pressure P1. An oxidant gas 
inlet chamber 18, containing an oxidant gas at a pressure P2 can be 
utilized, as shown in FIGS. 1 through 4. A combustion product or 
preheating chamber 16 can also be contained within the housing 12. Other 
means for manifolding an oxidant into conduits 20 and then into the 
generating chamber can also be utilized. 
The exterior housing 12 is preferably comprised of 1/32 inch to about 1/16 
inch thick steel, and lined throughout with an internal thermal insulation 
22, initially containing air as an insulating gas. This thermal insulation 
is disposed as shown between opposite ends of the generator. In the 
concept shown in FIG. 1, where no internal housing is used between the 
porous thermal insulation 22 and the fuel, combustion, and oxidant gases, 
said gases, including water vapor will permeate the insulation. To prevent 
fuel gas or reacted fuel gas from inlet chamber 14 from contacting air or 
other oxidant, or passing to the other chambers 16 and 18, except through 
gas permeable partition 32, a seal 1, which can be a metal sheet inward 
extension of exterior metal housing 12, disposed through the thermal 
insulation 22 can be used at a point between fuel gas inlet chamber 14 and 
the other chambers 16 and 18, preferably contacting the porous partition 
32 and extending to the exterior housing, as shown. 
The concept shown in FIG. 1 could be used in large generators where heat 
loss through the exterior housing is not as important as simplicity of 
design. However, in many instances such heat losses are important and the 
thermal insulation must be protected from hydrogen gas permeation so that 
the insulation will retain its insulating gas within its pores. One method 
to accomplish this is to provide a continuous interior housing susceptible 
to only minor hydrogen permeation at generator operating temperatures, to 
insure the integrity of the thermal insulation. 
The continuous internal housing, shown as 13 in FIG. 2, is preferably 
comprised of materials resistant to hot contacting gases. Electrical 
insulation, to prevent possible shorting of fuel cells to the interior 
housing within the generator chamber, is shown as 15 in FIGS. 2 through 4. 
Penetrating the housings, and insulation, is a fuel inlet means or port 
24, shown in FIG. 4, an air inlet means or post 26, and a combustion 
product outlet means or port 28, as well as ports 57 for electrical leads 
58, shown in FIG. 4. Shown in FIG. 2 are insulating gas entry means or 
port 5 and insulating gas exit means or port 6. In the concept of FIG. 2, 
preferably utilizing a continuous interior housing acting as a continuous 
seal, any hydrogen that permeates the interior housing can be transported 
or flushed out by the stream of insulating gas that enters port 5 and 
exits port 6. The insulating gas will be fed into entry port 5 at a 
pressure effective to pass it through the porous thermal insulation, and 
preferably out the exit port 6. In its progress during generator operation 
it can sweep out hydrogen along the way, where the insulating gas is an 
inert gas, and/or consume i.e., combust, hydrogen where the insulating gas 
is air. Useful insulation gases include air, nitrogen or an inert gas such 
as argon, or mixtures thereof and are described in further detail later in 
the specification. Ports 5 and 6 pass through the exterior housing but not 
the interior housing. 
The generating chamber 14, shown in FIGS. 2 through 4, extends between an 
end wall 30 of the housing 12 and a gas porous partition 32. The 
preheating chamber 16 extends between the gas porous partition 32 and a 
support structure such as a metal sheet 34. The oxidant inlet chamber 18 
extends between the sheet 34 and another end wall 36 of the housing 12. 
The dividing barriers can include other structural types, and additional 
support and flow baffles can be incorporated. The shown barriers, the 
porous partition 32 and the sheet 34, need not be sealed structures. The 
porous partition 32, in particular, is designed to allow flow between the 
generating chamber 14, operating at an approximate pressure slightly above 
atmospheric, and the preheating chamber 16, operating at a slightly lower 
pressure than the generating chamber, as indicated by arrow 38. While the 
generator 10 is shown in a horizontal orientation in FIGS. 1 through 4, it 
can be operating in a vertical or other position, and, as mentioned 
previously, can be of a circular or other design. 
High temperature electrochemical cells, such as elongated, solid oxide 
electrolyte annular fuel cells 40 are disposed within the generator 
interior volume and extend between the preheating chamber 16 and the 
generating chamber end wall. The cells have open ends 42 in the preheating 
chamber 16, and closed ends 44 in the generating chamber 14. The fuel 
cells are preferably tubular, including a solid oxide electrolyte 
sandwiched between two electrodes, preferably supported on a tubular 
porous support. Each cell includes an electrochemically active length 46 
and an inactive length 48. The active length is contained within the 
generating chamber 14. The closed end 44 of the cell is electrochemically 
inactive, and can serve for final preheating of reactant fuel. 
Each individual cell generates approximately 0.6 volt, and a plurality are 
electrically interconnected, preferably in a series-parallel rectangular 
array. For descriptive purposes, the arrangement can be described as 
including rows 50 and columns 52. Each cell in a row 50 is electrically 
connected along its active length 46 to the next adjacent cell, preferably 
through direct contact of their outer peripheries. For the preferred 
configuration shown in FIG. 1, where fuel flows about each cell and an 
oxidant, such as air, flows within each cell, the anode is the outer 
periphery of each cell and the cathode is on the inside. Thus, 
cell-to-cell contact within a row is in parallel, among adjacent anodes. 
Each cell in a column 52 is electrically interconnected in series to the 
next adjacent cell 40. In the preferred configuration, this 
interconnection is made from the inner cathode of one cell to the outer 
anode of the next consecutive cell, through an interconnect 54. 
With the configuration described and shown in FIGS. 1 through 4, hundreds 
of cells can be so connected to achieve the desired voltage and current 
output. The direct current electrical energy thus generated is collected 
by a single current collector, preferably a conductive metal plate 56 or 
felt pad, positioned in electrical contact with each cell 40 in the first 
row 50', and a similar second collector (not shown), positioned in contact 
with the last row. Electrical leads 58, shown in FIG. 4, are accordingly 
provided to the current collectors. 
The oxidant conduits 20 are preferably loosely supported at one end in the 
sheet 34 as shown best in FIG. 4. The sheet 34 is preferably stainless 
steel, with bores 60 that fit loosely about the conduits 20 to allow free 
thermal expansion. The conduits 20 are preferably comprised of alumina, 
and the sheet 34 is covered with an insulation 62 such as low density 
alumina. A small leakage of oxidant, as indicated by arrow 63, is 
acceptable. 
The conduits 20 extend from the sheet 34 into the open end 42 of the fuel 
cells 40, a single conduit 20 corresponding to a single fuel cell. Each 
conduit 20 extends to the active length 46 of the fuel cell, and 
preferably close to the closed end 44 of the cell, as shown in FIG. 2, the 
conduit 20 being inserted close to, but spaced from, the closed end 44. 
Radial supports 64 can be utilized to support each conduit 20 within the 
corresponding fuel cell 40. Each conduit can be provided with a means for 
discharging a reactant medium into the fuel cell 40, such as openings 66. 
The conduits can also be open ended and spaced from the end 44 of the fuel 
cell, or can extend into direct contact with the end 44 of the cell, so 
long as thermal expansion is accommodated. 
The gas porous partition 32, which allows a throughput of depleted fuel, is 
preferably a porous ceramic baffle, such as one comprised of fibrous 
alumina felt, or ceramic plate segments with porous inserts such as 
ceramic wool plugs, surrounding each fuel cell 40. Small holes 9, shown in 
FIG. 5, can also be drilled through this partition 32. 
According to the third concept of this invention, the interior housing can 
consist of two sections and contain a separate seal 70, best shown in FIG. 
5. Preferably, this seal will allow for expansion of the interior housing, 
yet prevent hydrogen or water vapor entry. However, a separate, complete 
hydrogen seal would be very complicated. As an alternative, the seal 70 
could perform expansion and hydrogen exclusion functions, by allowing 
thermal insulating gas maintained at a pressure P' higher than any other 
gas within the generator, to seep or leak at a controlled rate into the 
interior volume 71 of the generator. The arrows shown in FIG. 5 indicate 
probable gas flow. The preferred sealing means 70 can be, for example, an 
expansion joint having the simple trough seal design shown most clearly in 
FIG. 5, where the interior housing 13 comprises two sections, 72 and 73. 
The seal 70 allows for longitudinal and radial expansion and contracting of 
sections 72 and 73 upon thermal cycling or during operation of the fuel 
cell generator. Preferably, section 73, will be made of a material 
resistant to hot oxidant gas, such as nickel based alloys with chromium 
and iron, for example Inconel 600, containing 76% Ni, 15% Cr and 8% Fe. 
Preferably, section 72, will be made of a material resistant to hot fuel 
gas, such as a very high chromium nickel alloy, for example Inconel 601, 
containing 60.5% Ni, 23% Cr, 14% Fe and 1.35% Al. Both sections will be 
from about 1/32 inch to about 1/16 inch thick. 
The preferred seal 70 could have, for example, inner lands 74 which could 
compress a flexible winding of alumina fiber sheet 75 into porous 
partition 32, as sections 72 and 73 move together due to longitudinal and 
radial thermal expansion. Additionally the bottom lip 76 of section 73 
would be forced down into the trough 77 of section 72, which trough could 
be filled with fine ceramic powder 78, such as alumina powder, or a 
packaging of flexible winding of alumina fiber sheet. As shown in FIG. 5, 
minimal insulating or other gas would flow through winding 75. The 
insulating gas would preferentially pass through to the inner land 74 
contained in preheating chamber 16. Any insulating gas passing through 
winding 75 would be immediately swept through the porous partition 32 or 
the opening 9. Any hyrodgen permeating the metal interior housing at 
operating temperature of the generator could be consumed, i.e., combusted, 
if the insulating gas is air, or if an inert gas is used, hydrogen could 
be swept through the valve 70 into the interior of the preheating chamber 
16 or swept through the insulation and possibly out a top vent, such as at 
81, maintaining the insulating efficiency of the thermal insulation 22. 
The gas permeable thermal insulation layer 22, will be from about 2 inches 
to about 8 inches thick, and made of any suitable thermal insulation 
having a low thermal conductivity. The thermal insulation will contain 
small interconnected voids or pores within the insulation matrix body 
capable of containing a gas. The preferred thermal insulation is a 
refractory material, such as compacted alumina fibers, preferably from 
about 1/4 inch to about 3 inches long. The preferred insulation density is 
from about 8 lb./cubic foot to about 15 lb./cubic foot, providing a 
porosity of from about 60% to about 85%. Naturally the more porous the 
insulation the more insulating gas it can contain. The minute voids or 
pores are designated as 79 in FIG. 5. 
The internal, gas permeable thermal insulation 22 is disposed between the 
interior housing and the gas tight exterior housing, and will contain a 
high molecular weight thermal insulating gas having a low thermal 
conductivity, i.e. a gas that has a molecular weight of at least about 12, 
preferably a molecular weight between 14 and 85, and that has an 
insulating effect substantially greater than hydrogen, for example, 
preferably, air, nitrogen, or an inert gas such as argon, or mixtures 
thereof. This gas has over 100 times the insulating effect of the 
refractory matrix, and it is essential to keep its composition intact. 
Argon is the most preferred insulating gas, since it would reduce the 
oxidation rate of outside surfaces of the interior housings. 
In the third concept of this invention, utilizing an expansion seal, and 
illustrated in FIGS. 4 and 5, the thermal insulating gas will be 
maintained at a pressure higher than the other gases contained within the 
interior volume near the seal, be they fuel gas, fuel product gas, or 
oxidant gas, so that thermal insulating gas flows into the interior volume 
of the generator, generally into the combustion preheating chamber 16, 
through the seal channel gas leakage means. Preferably, the thermal 
insulating gas will be at a pressure of at least about 0.05 psi. higher 
than the pressure of any gases near the seal. A preferred pressure 
differential to insure controlled leakage of thermal insulating gas would 
be from about 0.05 psi to about 0.2 psi higher than the pressure of any 
gases near the gas leakage means. Pressure differentials over about 0.2 
psi may cause structural deformation of the exterior and interior 
housings. This third concept allows insulating gas leakage as a means of 
controlling hydrogen and water vapor contamination of the thermal 
insulation and could be used if the use of a continuous interior housing 
presents fabrication or expansion problems justifying a more complicated 
sealing arrangement. The same pressue range is also applicable to the 
second concept, where a continuous interior housing is used, i.e., from at 
least about 0.05 psi to about 0.2 psi higher than the gases in the 
interior volume of the fuel cell generator. 
Usually, fuel enters inlet port 24 at a pressure P1 of about 14.9 psi, and 
oxidant enters inlet port 26 at about 15.1 psi, but due to pressure losses 
generally contacts reacted fuel gas at about 14.9 psi. Combustion product 
gases in combustion pre-heat chamber 16 exit outlet 28 at about 14.7 psi. 
In the concept utilizing an expansion seal, the insulating gas, given such 
other gas pressures, will be pumped through insulating gas inlet 80 and 
optional insulating gas inlet 81, and maintained at a pressure P'4 of 
about 15.15 psi to about 15.3 psi. 
The insulating gas inlet 80, and optional insulating gas inlet or top vent 
outlet 81, shown in FIGS. 3 and 4, provide means for passing the 
pressurized thermal insulating gas into the pores of the thermal 
insulating layer. The ports 80 and 81 pass through the gas tight exterior 
housing 12, but not through interior housing 13. Inlet 80 will discharge 
pressurized insulating gas into the pore volume of the insulation layer 
22. The pressurized insulating gas, which can be fed into the insulation 
layer at about 25.degree. C. in all instances where an interior housing is 
used, passes through the insulation layer via interconnected pores and 
channels and leaks out into the interior volume of the generator through 
seal 70, shown in FIGS. 3 through 5, preventing any other gases, including 
water vapor, near the gas leakage valve from contacting or permeating the 
thermal insulation layer. Thermal expansion of the interior housing will 
help reduce excess leakage of the insulating gas into the interior 
chambers of the generator. When port 81 is used as a vent, inert 
insulating gas such as Argon can be allowed to bleed off with any hydrogen 
it may be sweeping out. 
In FIG. 4, dense zirconia or alumina standoff means 82, shown which attach 
interior housing section 73 to the exterior housing 12. These standoffs 
resist any movement of housing section 73 and help control thermal 
expansion and contraction. Nickel alloy compression springs 83, which 
attach interior housing section 72 to the exterior housing 12 are also 
shown. These springs also help control thermal expansion of interior 
housing section 72, and prevent lip 76 from contacting the bottom of 
trough 77. Both of these expansion control means are optional. The 
electrical insulation 15 prevents shorting contact and need not contain 
insulating gas. These standoffs, springs and electrical insulation can be 
used when an interior housing is used. 
During operation, an oxidant such as air enters the inlet chamber 18 
through inlet port 26. The chamber 18 functions as an inlet manifold for 
the individual conduits 20. Air enters the conduits at a temperature of 
approximately 500.degree. C. to 700.degree. C., and a pressure above 
atmospheric, being initially heated prior to entering the housing by 
conventional means such as a heat exchanger coupled with a blower, not 
shown. The air flows within the conduits, through the preheating chamber 
16, where it is further heated to a temperature of approximately 
900.degree. C. The air then flows through the length of the conduit, being 
further heated to approximately 1000.degree. C., and is discharged through 
the openings 66, shown in FIG. 2, into the fuel cell 40. The air within 
the fuel cell electrochemically reacts at the fuel cell cathode along the 
active length 46, depleting somewhat in oxygen content as it approaches 
the open end 42 of the cell. The depleted air is discharged into the 
combustion product or preheating chamber 16. 
A fuel, such as hydrogen or a mixture of carbon monoxide with hydrogen, 
flows from pumping and preheating apparatus, not shown, into the 
generating chamber 14 through fuel inlet port 24, shown in FIG. 2. The 
fuel flows over and about the exterior of the fuel cells, 
electrochemically reacting at the anode. The fuel inlet port 24 is 
preferably located near the closed end 44 of the cells 40. The fuel 
accordingly depletes as it approaches the porous barrier 32. The depleted 
fuel, containing approximately five percent to fifteen percent of its 
initial fuel content, diffuses through the barrier 32 and into the 
combustion preheating chamber 16. 
The combustion product gas, including oxygen depleted air and depleted 
fuel, along with any air leaking into the preheating chamber 16 through 
the sheet 34, directly react exothermically. The heat of this reaction, 
which completely combusts the fuel, along with the sensible heat of the 
depleted fuel and air, is utilized to preheat the incoming air. The 
combustion products are discharged through combustion product outlet port 
28 at a temperature of approximateley 700.degree. C. The remaining energy 
in the combustion products can be utilized to preheat the incoming air or 
fuel through, for example, an external heat exchanger or to generate steam 
in conventional generating apparatus, not shown. 
It may also be desirable to preheat the fuel further prior to its 
contacting the active length 46 of the fuel cells 40. To acomplish this, 
the fuel cells 40 can include an enlarged inactive section 76 at the fuel 
entry end of the housing. The pressure in the preheating chamber 16 is 
lower than that of the generating chamber 14 or oxidant inlet chamber 18 
in order to assure controlled directional leakage. 
A generator in accordance with the arrangement described in self-starting, 
since fuel is essentially combusted to provide hot, oxidant-rich gases for 
the cathode. Additionally, preheated fuel provides the gas for the anode. 
Also, lean fuel is directly combusted with oxidant in the combustion 
product chamber to further preheat the oxidant until a load is applied to 
the cells, at for example, an active cell temperature of 700.degree. C., 
Ohmic heating (I.sup.2 R) in addition to the heat of the electrochemical 
reaction, including polarization and entropic heat, will bring the 
generator up to its median operating temperature of approximately 
1000.degree. C. at the active area. 
Electrical contacts to series-parallel connected cells is made preferably 
on the fuel side via metal plates, metal rods and felt metal pads. The 
contacts can be cooled in the feed through point of the external housing 
below the level where metal oxidation is detrimental.