Title of Invention

A SOLID OXIDE FUEL CELL SYSTEM AND METHOD OF OPERATING SAME

Abstract A solid oxide fuel cell system is disclosed. The fuel cell system comprises: a combustor (15); a plurality of solid oxide fuel cell stacks (3); a cathode exhaust conduit of the stacks; a reformer (9) adapted to reform a hydrocarbon fuel to a hydrogen containing reaction product and to provide the reaction product to the stacks; and a hot box (108), in which the stacks, the reformer and the combustor are located, wherein: the reformer is sandwiched between the combustor and the stacks; the combustor is thermally integrated with the reformer; the stack cathode exhaust conduit (203) is thermally integrated with the reformer, wherein the cathode exhaust conduit is adapted to heat the reformer using the cathode exhaust of the stacks, the reformer is adapted to be heated by the combustor, and the reformer is adapted to be heated by convective, radiative and/or conductive heat transfer from the stack.
Full Text [0001] This application claims benefit of priority of U.S. provisional
applications 60/537,899 filed on January 22, 2004 and 60/552,202 filed
on March 12, 2004, both of which are incorporated herein by reference in
their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention is generally directed to fuel cells and
more specifically to high temperature fuel cell systems and their
operation.
[0003] Fuel cells are electrochemical devices which can convert
energy stored in fuels to electrical energy with high efficiencies. High
temperature fuel cells include solid oxide and molten carbonate fuel cells.
These fuel cells may operate using hydrogen and/or hydrocarbon fuels.
There are classes of fuel cells, such as the solid oxide regenerative fuel
cells, that also allow teversed operation, such that oxidized fuel can be
teduced back to unoxidized fuel using electiical enerqy as an input.
BRIEF SUMMARY OF THE INVENTION
[0004] The preferred aspects of present invention provide a high
temporature fuel system, such as a solid oxide fuel cell system, with an
improved balance of plant efficiency. The system includes a thermally
integrated unit including a reformer, combustor and the fuel cell stack.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0005] Figures 1, 2 and 7 are schematics of fuel cell systems
according to preferred embodiments of the present invention.

[0006] Figures 3 and 6 are schematics of PSA gas separation
devices according to the preferred embodiments of the present invention.
[0007] Figure 4 is a schematic of a fuel cell system according to the
fifth preferred embodiment of the present invention.
[0008] Figure 5 shows the details of the system of Figure 4.
[0009] Figures 8A and 8B are schematics of integrated cylindrical
reformer, combustor and stack unit for a system with two stacks.
[0010] Figures 9A and 9B are schematics of integrated plate type
reformer, combustor and stack unit for a system with two stacks.
[0011] Figures 10A and 10B are schematics of integrated plate type
reformer, combustor and stack unit for a single stack system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] Figure 1 illustrates a fuel cell system 1 according to the
preferred embodiments of the present invention. Preferably, the system 1
is a high temperature fuel cell stack system, such as a solid oxide fuel cell
(SOFC) system or a molten carbonate fuel cell system. The system 1
may be a regenerative system, such as a solid oxide regenerative fuel cell
(SORFC) system which operates in both fuel cell (i.e., discharge) and
electrolysis (i.e., charge) modes or it may be a non-regenerative system
which only operates in the fuel cell mode.
[0013] The system 1 contains a high temperature fuel cell stack 3.
The stack may contain a plurality of SOFCs, SORFCs or molten carbonate
fuel cells. Each fuel cell contains an electrolyte, an anode electrode on
one side of the electrolyte in an anode chamber, a cathode electrode on
the other side of the electrolyte in a cathode chamber, as well as other


components, such as separator plates / electrical contacts, fuel cell
housing and insulation. In a SOFC operating in the fuel cell mode, the
oxidizer, such as air or oxygen gas, enters the cathode chamber, while
the fuel, such as hydrogen or hydrocarbon fuel, enters the anode
chamber. Any suitable fuel cell designs and component materials may be
used.
[0014] The system 1 contains any one or more of the following
elements, either alone or in any suitable combination. In a first
embodiment, the system 1 contains a desulfurizer 5 and a water-gas shift
reactor 7 that are thermally integrated with each other. The waste heat
from the reactor 7 is used to heat the desulfurizer 5 to its operating
temperature, thus reducing or eliminating the need for a separate
desulfurizer heater.
[0015] In a second embodiment, the system 1 contains a hydrocarbon
fuel reformer 9 and a hydrocarbon fuel by-pass line 11 fluidly connected
to the fuel inlet 13 of the high temperature fuel cell stack 3. The by-pass
line 11 by-passes the reformer 9 to provide unreformed hydrocarbon fuel
into the fuel inlet 13 of the high temperature fuel cell stack 3 to control
the temperature of the stack 3.
[0016] In a third embodiment, the hydrocarbon fuel reformer 9 is
located separately from but thermally integrated with the high
temperature fuel cell stack 3. A start-up burner 15 is thermally integrated
with the reformer 9. Preferably but not necessarily, a start-up burner 15
effluent outlet conduit 1 7 is fluidly connected to an oxidizer inlet 1 9 of
the high temperature fuel cell stack 3. This configuration allows the
system 1 to be started up using only the hydrocarbon fuel and oxidizer
without oxidizing SOFC anode electrodes. This configuration eliminates a


separately stored reducing or inert purge gas that is flushed through the
system to prevent the anode electrodes of the SOFCs from oxidizing.
[0017] In a fourth embodiment, a carbon monoxide separation
device 21, such as pressure swing adsorption (PSA) device is fluidly
connected to a fuel exhaust (i.e., the fuel outlet) 23 of the stack 3. A
carbon monoxide recycle conduit 25 has an inlet that is connected to the
outlet of the carbon monoxide separation device 21 and an outlet that is
fluidly connected to a fuel inlet 13 of the high temperature fuel cell stack
3. For example, the device 21 allows carbon monoxide to be separately
recirculated into a hydrocarbon fuel inlet conduit 27 of the stack 3 to
enhance the electrochemical reaction in the fuel cells of the stack 3.
Furthermore, since carbon monoxide is recirculated, less carbon monoxide
is provided into the atmosphere than if the carbon monoxide from the
system was simply flared or vented into the atmosphere.
[0018] In a fifth preferred embodiment, a PSA hydrogen separation
device 29 is fluidly connected to the fuel exhaust 23 of the stack 3. A
thermal output of the high temperature fuel stack 3 in addition to the fuel
exhaust is thermally integrated with at least a first column of the PSA
device 29 to heat the first column. This use of the stack 3 waste heat to
heat a PSA column under purge allows a reduction in the compression
requirements of the PSA device and/or an increase in the amount of gas
purification for the same level of compression.
[0019] In a sixth preferred embodiment, a solid oxide fuel cell system
with an improved balance of plant efficiency comprises a thermally
integrated reformer, combustor and stack, where the reformer is heated
by the stack cathode exhaust, by radiative and convective heat from the
stack and by the combustor heat during steady state operation. In a
seventh preferred embodiment, the system starts up with hydrogen


generated using a CPOX (catalytic partial oxidation) reactor. In an eighth
preferred embodiment, the system contains an energy efficient and self
sufficient water management subsystem. The system contains at least
one evaporator which uses stack anode exhaust to heat water being
provided into the inlet fuel stream.
[0020] I. FIRST EMBODIMENT
[0021] The elements of the system 1 of the first embodiment will now
be described. In prior art systems, organo-sulfur compounds (e.g.,
mercaptans, thiophenes) contained in natural gas fuel are hydrogenated
by adding hydrogen to the fuel inlet stream and reacting the mixture in a
desulfurizer over a suitable catalyst, such as cobalt-molybdenum. The
reaction produces CH4 and H2S gases. The H2S gas is subsequently
removed by reaction with a fixed sorbent bed, containing for example
ZnO or other suitable materials for removing this gas. Usually these
reactions are carried out at about 300 °C, and the catalyst and sorbent
can be contained in the same vessel.
[0022] Figure 1 illustrates an embodiment of a desulfurizer subsystem
of the first embodiment, which comprises the desulfurizer 5 and the
water-gas shift reactor 7 that are thermally integrated with each other.
[0023] The desulfurizer 5 preferably comprises the catalyst, such as
Co-Mo or other suitable catalysts, which produces CH4 and H2S gases
from hydrogenated, sulfur containing natural gas fuel, and a sorbent bed,
such as ZnO or other suitable materials, for removing the H2S gas from
the fuel inlet stream. Thus, a sulfur free or reduced sulfur hydrocarbon
fuel, such as methane or natural gas leaves the desulfurizer 5.
[0024] The water-gas shift reactor 7 may be any suitable device which
converts at least a portion of the water exiting the fuel cell stack 3 fuel


exhaust 23 into free hydrogen. For example, the reactor 7 may comprise
a tube or conduit containing a catalyst which converts some or all of the
carbon monoxide and water vapor in the tail gas exiting exhaust 23
through a fuel exhaust conduit 31 into carbon dioxide and hydrogen. The
catalyst may be any suitable catalyst, such as an iron oxide or a
chromium promoted iron oxide catalyst. The reactor 7 is preferably
located along conduit 31 between the fuel exhaust 23 and the PSA
hydrogen separation device 29. The reactor 7 works in tandem with the
PSA hydrogen separation device 29 by increasing the amount of free
hydrogen in the fuel side exhaust (i.e., anode exhaust or tail gas) by
converting some water present in the fuel side exhaust gas into
hydrogen. The reactor 7 then provides hydrogen and carbon dioxide to
the PSA hydrogen separation device 29, which separates the hydrogen
from the carbon dioxide. Thus, some of the water present in the fuel may
be converted to hydrogen in the reactor 7.
[0025] The desulfurizer 5 and the water-gas shift reactor 7 are
thermally integrated with each other. This means that waste heat from
the reactor 7 is transferred directly or indirectly to the desulfurizer 5. For
example, the desulfurizer 5 and the water-gas shift reactor 7 may be
located in the same hot box such that they are thermally integrated with
each other. Alternatively, the desulfurizer 5 and the water-gas shift
reactor 7 may be located in thermal contact with each other (i.e., in direct
physical contact or by contacting the same thermal mass). Alternatively,
the desulfurizer 5 and the water-gas shift reactor 7 may be connected by
a thermal conduit, such as a pipe containing a thermal transfer fluid, such
as water / steam or another fluid.
[0026] The desulfurizer 5 is fluidly connected to the fuel inlet 13 of
the fuel cell stack 3. The water-gas shift reactor 7 is fluidly connected to
the fuel exhaust 23 of the fuel cell stack. The term fluidly connected


means that the connection may be direct or indirect, as long as a gas or
liquid fluid may be provided through the connection. Preferably, the
desulfurizer 5 is connected to the fuel inlet 13 of the fuel cell stack 3 by
the fuel inlet conduit 27. A valve 28 controls the flow of fuel through
conduit 27. The water-gas shift reactor 7 is connected to the fuel
exhaust 23 of the fuel cell stack 3 by the fuel exhaust conduit 31. It
should be noted that the conduits 27 and 31 shown in Figure 1 contain
several portions or sections that are separated by various processing
devices, such as the desulfurizer 5 and the water-gas shift reactor 7.
[0027] A method of operating the fuel cell system 1 according to the
first embodiment includes providing a hydrocarbon fuel, such as natural
gas, into a desulfurizer 5 from a hydrocarbon fuel source 33, such as a
natural gas supply pipe or a hydrocarbon fuel storage tank or vessel. The
fuel is desulfurized in the desulfurizer 5 and is then provided directly or
indirectly into the fuel cell stack 3 through conduit 27 and inlet 13, as will
be described in more details with respect to the other embodiments of the
present invention.
[0028] The warm fuel exhaust is provided from the fuel cell stack 3
through exhaust 23 and conduit 31 into the water-gas shift reactor 7.
Preferably, the exhaust has given up some of the heat in heat exchangers
and other devices prior to entering the reactor. For example, an optional
fuel heat exchanger and water vaporizer 35 may be provided between the
conduits 27 and 31. The vaporizer 35 humidifies the fuel inlet stream in
conduit 27. The vaporizer 35 can be a device which supplies water vapor
based on cyclic desiccant beds or a rotating desiccant wheel (i.e.,
"enthalpy wheel") and which provides water vapor from an exhaust
stream in conduit 31 into the fuel inlet stream in conduit 27 or the
vaporizer 35 can be a steam generator which provides water vapor into
the fuel inlet stream from another water source.


[0029] The warm exhaust gases react with each other according to the
forward water gas shift reaction, CO + H2O -> CO2 + H2, in the reactor
7 and give up or provide heat to the desulfurizer 5 side and the incoming
fuel gases passing through it. Preferably, the reactor 7 supplies all of the
heat that is needed to operate the desulfurizer 5 at its standard operating
temperature, such as at least about 300 °C, and no other heating means
or heaters are used to heat the desulfurizer 5.
[0030] The hydrogen, carbon monoxide, carbon dioxide and water
vapor containing exhaust continues in conduit 31 to an optional
condenser 37, optional water knockout or separation device 39 and a
compressor 41, such as a reciprocating compressor, to the PSA hydrogen
29 and/or carbon monoxide 21 separation devices. The water knock out
system 39 separates the water from the fuel exhaust stream and
discharges it out of the water discharge conduit 43 controlled by valve
45, or recirculates it into the fuel heat exchanger and water vaporizer 35
using a positive displacement pump 47. The water is preferably provided
into the stack 3 when the stack 3 is operated to generate hydrogen while
generating little or no electricity in the fuel cell mode (i.e., no net
electricity is produced in the fuel cell mode), as will be described in more
detail below. The additional water is used to support fuel reforming as
needed. An optional water inlet conduit 49 may also be connected to the
water knockout device 39. Additional water may be provided for
bootstrapping, as the electrochemical process will ordinarily generate net
water. A flow control valve 51 position is controlled mechanically or by a
computer dependent on the water level in the water knockout device.
The valve 51 controls the amount of water provided into device 39
through conduit 49 based on the water level in the device 39.
[0031] II. SECOND EMBODIMENT


[0032] Figure 1 illustrates a system 1 of the second embodiment
containing the hydrocarbon fuel by-pass line 11 which allows feeding the
fuel cell stack 3 with an accurately controlled fuel input mixture for
improved control of broad range of operating conditions, such as stack 3
operating temperature.
[0033] In the prior art, SOFCs are commonly operated wjth
hydrocarbon fuels, such as methane. The methane may be partially or
fully steam reformed to form hydrogen and carbon oxides before it enters

the SOFC stack. Steam reformation is an endothermic process. If methane
is only partially steam reformed, the remaining methane will be reformed
within the SOFC. The endothermic reaction within the SOFC stack affects
the thermal balance of the SOFC stack.
[0034] Oxidation of hydrocarbons in the high temperature fuel cells
includes an endothermic reaction in which the hydrocarbon fuel, such as
methane or natural gas, is converted to hydrogen and carbon oxides. This
endothermic reaction may not be obvious in the net reaction occurring in
the fuel cell system. One example is a solid oxide fuel cell fed with
methane. In the net reaction, the methane is oxidized to carbon dioxide
and water. However, it is electrochemically highly unlikely for the
methane to be directly oxidized to the products. It is commonly assumed
that some methane first reacts with steam, which is almost always
present, to form hydrogen and carbon oxides. Then the hydrogen and
lower carbon oxides are oxidized. The water formed by the oxidation of
hydrogen can enable steam reformation of yet unconverted methane. The
result of this intermediate chemical reaction is heat consumption at the
location of the steam reformation.
[0035] Heat consumed by reformation inside the fuel cell thereby
creates a cooling effect. This cooling effect can be localized and create


temperature gradients and in turn thermal stresses which can damage part
of the fuel cell. Thus, the reformation is partly or completely performed
outside the fuel cell stack.
[0036] In the system 1 of the second embodiment, the hydrocarbon
fuel reformer 9 is located separately from the high temperature fuel cell
stack 3. The reformer is adapted to at least partially reform a hydrocarbon
fuel into a hydrogen fuel. The hydrocarbon fuel is provided into the
reformer 9 through the hydrocarbon fuel inlet conduit 27, connected to an
inlet of the reformer 9. A connecting conduit 53 connects the fuel inlet
13 of the high temperature fuel cell stack 3 with an outlet of the reformer
9.
[0037] The hydrocarbon fuel reformer 9 may be any suitable device
which is capable of partially or wholly reforming a hydrocarbon fuel to
form a carbon containing and free hydrogen containing fuel. For example,
the fuel reformer 9 may be any suitable device which can reform a
hydrocarbon gas into a gas mixture of free hydrogen and a carbon
containing gas. For example, the fuel reformer 9 may reform a humidified
biogas, such as natural gas, to form free hydrogen, carbon monoxide,
carbon dioxide, water vapor and optionally a residual amount of
unreformed biogas. The free hydrogen and carbon monoxide are then
provided into the fuel inlet 13 of the fuel cell stack 3 through conduit 53.
[0038] In a preferred aspect of the second embodiment, the fuel
reformer 9 is thermally integrated with the fuel cell stack 3 to support the
endothermic reaction in the reformer 9 and to cool the stack 3. The term
"thermally integrated" in this context means that the heat from the
reaction in the fuel cell stack 3 drives the net endothermic fuel
reformation in the fuel reformer 9. The fuel reformer 9 may be thermally
integrated with the fuel cell stack 3 by placing the reformer 9 and stack 3


in the same hot box and/or in thermal contact with each other, or by
providing a thermal conduit or thermally conductive material which
connects the stack 3 to the reformer 9. While less preferred, a separate
heater may also be used to heat the reformer 9 instead of or in addition to
the heat provided from the stack 3.
[0039] The hydrocarbon fuel by-pass line 11 is fluidly connected to the
fuel inlet 13 of the high temperature fuel cell stack 3. In other words, the
by-pass line may be connected directly to the inlet 13 or it may be
indirectly connected to the inlet 13 via the connecting conduit 53. The
terms "line" and "conduit" are used interchangeably, and include gas flow
pipes and other fluid flow ducts. The by-pass line 11 is adapted to provide
unreformed hydrocarbon fuel into the fuel inlet 1 3 of the high temperature
fuel cell stack 3.
[0040] Preferably, the by-pass line 11 branches off from the
hydrocarbon fuel inlet conduit 27 upstream of the reformer 9 and
connects to the connecting conduit 53 downstream of the reformer 9.
Preferably, the desulfurizer 5 is located upstream of a location where the
by-pass line 11 branches off from the hydrocarbon fuel inlet conduit 27,
such that sulfur is removed from the unreformed hydrocarbon fuel
provided through the by-pass line 11.
[0041] Alternatively, the by-pass line 11 does not have to branch off
from the fuel inlet conduit 27. In this case, the by-pass line 11 is
connected to a separate source of hydrocarbon fuel, such as a natural gas
pipe or a storage vessel. In this case, a separate desulfurizer is provided
in the by-pass line 11.
[0042] The system 1 further comprises a hydrocarbon fuel flow control
valve 55 in the by-pass line 11. The control valve 55 is adapted to
control a flow of the unreformed hydrocarbon fuel into the fuel cell stack


to control a temperature and/or other operating parameters of the fuel cell
stack. The valve 55 may be manually or remotely controlled by an
operator. Alternatively, the valve 55 may be automatically controlled by a
computer or other processing device. The valve 55 may be controlled
automatically or by an operator in response to detected or predetermined
parameters. For example, the temperature or other parameters of the fuel
cell stack 3 may be detected by a temperature detector or other
detectors, and the results provided to an operator or a computer. The
operator or computer then adjust the valve 55 to control the flow of the
unreformed hydrocarbon fuel through the by-pass line 11 into the fuel cell
stack 3 to control the fuel cell stack temperature or other parameters.
Alternatively, the by-pass valve 55 may be adjusted based on
predetermined parameters, such as based on time of stack 3 operation
that is stored in the computer memory.
[0043] A method of operating a high temperature fuel cell system 1 of
the second embodiment includes providing a hydrocarbon fuel into a
reformer 9 through the fuel inlet conduit 27 and at least partially
reforming the hydrocarbon fuel into hydrogen fuel in the reformer 9. The
hydrogen fuel from the reformer 9 is provided into a fuel inlet of a high
temperature fuel cell stack 3 through conduit 53. The unreformed
hydrocarbon fuel that does not pass through the reformer 9 is provided
into the fuel inlet of the high temperature fuel cell stack 3 through the by-
pass line 11 and optionally through conduit 53. The flow of the
unreformed hydrocarbon fuel through the by-pass line 11 that does not
pass through the reformer 9 is controlled by the valve 55 to control a
temperature and/or other operating parameters of the high temperature
fuel cell stack 3.
[0044] The oxidation of hydrogen or low carbon oxides inside a fuel cell
is an exothermic reaction. Heat generated by the exothermic oxidation


should be removed to attain stable operation. Unreformed methane can
aid in the removal of heat via the above described steam reformation in
the reformer 9.
[0045] Accurately controlling the amount of unreformed hydrocarbons
entering the stack allows control of the temperature of the fuel cells in
the stack. In an external reformer, the degree of reformation depends on a
variety of factors some of which may vary during operation. Thus, a
simple way of controlling the amount of unreformed hydrocarbons
entering the stack is the by-pass line 11 which by-passes the external
reformer 9 as shown in Figure 1. The bypass valve 55 controls the
amount of unreformed hydrocarbons entering the stack 3. More
specifically, the least amount of hydrocarbons entering the stack 3 is
limited by the finite conversion inside the external reformer. An upper limit
for the amount of unreformed hydrocarbons entering the stack 3 is posed
by reformation occurring outside the external reformer along by-pass line
11.
[0046] This method of the second embodiment is applicable not only to
solid oxide fuel cells, but any high temperature fuel cell fed by a fuel
which undergoes reformation reactions prior to oxidation. In the example
provided above, the reformation is an endothermic reaction, but there are
also reformation reactions that are exothermic. Examples of exothermic
reformation include but are not limited to partial oxidation of methane.
Methane, which is the major constituent of natural gas, is a very common
example of a hydrocarbon fuel that undergoes reformation, but other
hydrocarbon fuels, such as natural gas, propane and butane are possible.
Therefore the reformer by-pass 11 is applicable to various reformation
reactions and a variety of hydrocarbon fuels.


[0047] Figure 2 illustrates a system 101 of the first and second
embodiments having an alternative configuration from the system 1
shown in Figure 1. In the system 101 shown in Figure 2, the fuel heat
exchanger and water vaporizer 35 is located upstream of the desulfurizer
5. Thus, the fuel enters the heat exchanger and water vaporizer 35 prior
to entering the desulfurizer. The desulfurizer 5 and the water-gas shift
reactor 7 are located in the same hot box 103 (i.e., a warm box or fuel
conditioner). The fuel conditioner 103 also contains the catalytic start-up
burner 15, the fuel heat exchanger and water vaporizer 35 and an
optional fuel pre-reformer 105 which is thermally integrated with a fuel
exhaust heat exchanger 107. Thus, the catalytic start-up burner 15 in
the system 101 is located in the fuel conditioner 103 rather than
thermally integrated with the fuel cell stack 3. The start-up burner 15 is
fed by the stack fuel exhaust conduit 31 rather than by the hydrocarbon
fuel inlet conduit 27.
[0048] The fuel cell stack 3 is thermally integrated with the reformer 9
in the same hot box 108. The hot box 108 also contains an optional
radiative air heater 109 and an optional catalytic tail gas burner 110. The
tail gas burner 110 is provided with hydrocarbon fuel from a branch 111
of the hydrocarbon fuel inlet conduit 27, which is regulated by valve 112.
A valve 113 directs the fuel exhaust flow between the PSA hydrogen
separation device 29 and the tail gas burner 110. The oxidizer side
components are the same as in system 1 and will be described in more
detail below.
[0049] III. THIRD EMBODIMENT
[0050] Figure 1 illustrates a system 1 of the third embodiment, where
the system is brought up from room temperature to operating conditions
(i.e., at start-up) with only hydrocarbon fuel and air. No stored nitrogen or


hydrogen are required to protect the anodes from oxidation. The stack 3,
reformer 9 and start-up burner 1 5 comprise separate devices which are
thermally integrated with each other, such as being located in the same
hot box and/or being in thermal contact with each other and/or being
connected by a thermal fluid transfer conduit.
[0051] The anodes of SOFC systems are commonly made from
materials including metal oxides which have to be reduced to attain
electron conductivity and thereby enable the electrochemical reaction in
the anode chamber. Metallic oxides used include, but are not limited to
nickel oxide. One common difficulty with these metallic oxides is the
necessity to keep them reduced once they have been reduced. Re-
oxidation causes significant if not catastrophic performance degradation.
The prevention of re-oxidation is a technical challenge for the start-up of a
SOFC system.
[0052] Commonly, the fuel cell anode chamber is flushed with inert or
reducing gases, such as nitrogen or hydrogen, at start-up to prevent
anode electrode re-oxidation. For systems operated on hydrocarbon fuels,
nitrogen or hydrogen are not readily available. Instead one or both gases
are stored separately within or near the system for consumption during
start-up.
[0053] The inventor has realized that a SOFC system can be built and
operated such that the anode can be maintained in its reduced state while
the system is operating only on hydrocarbon fuel and air during start-up.
Figure 1 illustrates one configuration of a SOFC system 1 according to the
third embodiment.
[0054] As shown in Figure 1, the start-up burner 15 is thermally
integrated with the reformer 9 and the reformer 9 is thermally integrated
with the stack 3. As discussed above, the term "thermally integrated"


includes location in the same hot box, located in thermal contact with
each other and/or connection by a thermal transfer fluid conduit. The
hydrocarbon fuel inlet conduit 27 is fluidly connected to an inlet of the
reformer 9 and to a first inlet of the start-up burner 1 5 (such as via the
burner fuel delivery conduit 73). A burner oxidizer inlet conduit 57 is
connected to a second inlet of the start-up burner 15. The start-up
burner 15 effluent outlet conduit 17 is fluidly connected to an oxidizer
inlet 19 of the high temperature fuel cell stack 3. For example, the
effluent outlet conduit 17 may be connected directly into the oxidizer inlet
19 of the stack or it may be connected to an oxidizer inlet conduit 59
which is connected to the oxidizer inlet 19 of the stack 3. The system
also contains an oxidizer blower 61, such as an air blower, which
provides the oxidizer into the burner and stack through the conduits 57
and 59, and an oxidizer exhaust conduit 63 which removes oxidizer
exhaust from the stack 3. The system also contains an optional air filter
65 and an optional heat exchanger 67 which heats the oxidizer being
provided into the stack 3 through the oxidizer inlet conduit 59 using the
heat of the oxidizer exhaust being provided through the oxidizer exhaust
conduit 63. The system also contains valves 69 and 71 in conduits 57
and 59, respectively. The system also contains a burner fuel delivery
conduit 73 which is regulated by valve 75. The conduit 73 branches off
from conduit 27 or it may comprise a separate fuel delivery conduit.
[0055] The method of operating the system 1 according to the third
embodiment is as follows. Initially all components of the system are at
room temperature. The anodes of the SOFC stack are reduced from
previous operation. Valves 69 and 75 in conduits 57 and 73,
respectively, are open, while valve 71 in conduit 59 is closed.
[0056] Hydrocarbon fuel, which can be natural gas, and an oxidizer,
such as air or oxygen, are injected into the start-up burner 1 5 through


conduits 73 and 57, respectfully. The fuel and oxidizer are ignited in the
burner 15 by an ignitor. The heat stream from the combustion in the
burner 15 is directed at the thermally integrated reformer 9. The effluent
of the burner 15 is directed through conduits 17 and 59 into the oxidizer
inlet 19 (i.e., cathode chamber(s)) of the stack 3. The effluent is
exhausted from the stack 3 through conduit 63 and from there into the air
heat exchanger 67. It may be advantageous to operate the burner lean on
fuel to ensure that the cathode chamber(s) of the fuel cells in the stack
are always exposed to an oxidizing environment. The combustion raises
primarily the temperature of the reformer 9, secondarily the stack 3
temperature, and finally the air heat exchanger 67 temperature.
[0057] Fuel is directed through the desulfurizer 5, vaporizer 35 and the
reformer 9, into the stack 3 fuel inlet 13 (i.e., into the anode chamber(s)
of the fuel cells in the stack). The fuel may be directed into inlet 13
simultaneously with injecting fuel and oxidizer into the burner 15.
Alternatively, the fuel may be directed into the inlet 13 after it is directed
into the burner 15 but before the stack 3 reaches the anode oxidation
temperature. The fuel exhaust exits the stack 3 through conduit 31 and
water-gas shift reactor 7. The fuel picks up heat in the reformer 9 and in
the stack 3 and transports the heat to the water gas shift reactor 7 which
is thermally coupled to the desulfurizer 5. Thereby the desulfurizer 5 is
heated to operating conditions by the stack 3 exhaust, as provided in the
first embodiment. Some heat is also delivered to the water vaporizer 7.
[0058] The heat balance in the system is designed such that the
reformer 9 reaches its operating temperature (i.e., the temperature at
which it reforms the hydrocarbon fuel) before the stack 3 anode
chamber(s) reaches a temperature were re-oxidation of the anode
electrodes could occur. Also, enough heat is carried to the water
vaporizer 35 such that the inflowing fuel is sufficiently humidified to avoid


carbon formation in the hot components downstream of the water
vaporizer 35.
[0059] If these method parameters are satisfied, the SOFC anode
electrodes will be exposed to a hydrogen rich feed stream created by
steam reformation in the reformer 9 when a temperature at the anode is
reached at which re-oxidation can occur. At the same time, the
desulfurizer 5 is brought to operating temperature early enough to avoid
detrimental effects of excessive sulfur content in the fuel feed stream.
One preferred hydrocarbon fuel for this system is natural gas. However
other fuels, including but not limited to methane, propane, butane, or
even vaporized liquid hydrocarbons can be utilized.
[0060] After the start-up of the system 1 is completed (i.e., once
the stack reaches desired steady state operating conditions), hydrocarbon
fuel and oxidizer supply into the start-up burner is terminated either by an
operator or automatically by a computer and the start-up burner is turned
off. Valves 69 and 75 are closed and valve 71 is opened to provide an
oxidizer into the oxidizer inlet 19 of the solid oxide fuel cell stack 3. The
stack 3 then operates in the fuel cell mode to generate electricity from an
electrochemical reaction of the fuel provided through conduit 27 and
reformer 9 (and optionally through by-pass line 11) and oxidizer provided
through conduit 59. Thus, it should be noted that the oxidizer is
preferably not provided into oxidizer inlet 19 of the solid oxide fuel cell
stack 3 while the start-up burner 15 operates. Furthermore, no separately
stored reducing or inert gases are used to flush the anode chambers of
the solid oxide fuel ceils of the stack 3 during the start-up.
[0061] IV. FOURTH EMBODIMENT
[0062] Figure 1 illustrates a system 1 of the fourth embodiment, where
the carbon monoxide and hydrogen are separately extracted from the fuel


exhaust stream and recirculated into the fuel inlet stream and/or removed
from the system for other use.
[0063] The system 1 contains a hydrogen separation or purification
device 29 fluidly connected to a fuel exhaust 23 of the stack 3.
Preferably, the device 29 comprises a PSA device that is connected to the
exhaust 23 of the stack 3 by the fuel exhaust conduit 31. The PSA
device 29 is adapted to separate at least a portion of hydrogen from the
fuel exhaust while the fuel cell stack 3 generates electricity in a fuel cell
mode. A reciprocating pump 41 provides the fuel exhaust into the PSA
device 29. The hydrogen separation or purification device 29 preferably
contains the carbon monoxide separation device or unit 21 and a carbon
dioxide/water separation device or unit 30. Preferably, the devices 21
and 30 comprise PSA devices which respectively separate carbon
monoxide and carbon dioxide/water from the fuel exhaust and allow
hydrogen to pass through. Preferably, but not necessarily, the PSA
device 21 is located in series with and downstream from PSA device 30.
However, if desired, the PSA device 21 may be located upstream of PSA
device 30. Preferably, PSA devices 21 and 30 comprise different units of
a single PSA system 29, where each unit 21 and 30 contains at least two
PSA columns.
[0064] A carbon monoxide recycle conduit 25 recirculates the carbon
monoxide from the PSA device 21 into the fuel inlet conduit 27. A
carbon dioxide/water removal conduit 26 removes carbon dioxide and
water from device 30. The inlet of conduit 25 is connected to the outlet
of the carbon monoxide separation device 21 and the outlet of conduit 25
is fluidly connected to the fuel inlet of the high temperature fuel cell stack
3, such as via the fuel inlet conduit 27. Alternatively, the outlet of the
carbon monoxide recycle conduit 25 may be connected directly into the
reformer 9 and/or into the fuel inlet 1 3 of the stack 3.


[0065] The system further comprises an optional hydrogen recycle
conduit 77 which is controlled by a recirculated hydrogen flow control
valve 79. The inlet of the conduit 77 is connected to the outlet of the
hydrogen separation device 29. The outlet of the conduit 77 is fiuidly
connected to the fuel inlet 13 of the high temperature fuel cell stack 3,
such as directly connected to the inlet 13 or indirectly connected via the
fuel inlet conduit 27. If desired, the conduit 77 may be omitted and
hydrogen and carbon monoxide may be carried together through conduit
25, which may result in a higher purity product or lower compression
requirements. If desired, the flow of hydrogen passed through conduit 25
may be metered.
[0066] Preferably, the outlet of conduits 25 and 77 are merged
together into a recycle conduit 81, which provides the recirculated
hydrogen and carbon monoxide into the fuel inlet conduit 27, as shown in
Figure 1, or directly into the reformer 9 and/or the stack 3 fuel inlet 13.
However, the recycle conduit 81 may be omitted, and the conduits 25
and 77 may separately provide carbon monoxide and hydrogen,
respectively, into conduit 27, reformer 9 and/or stack 3 fuel inlet 13. The
system 1 also optionally contains a hydrogen removal conduit 83, which
removes hydrogen from the system 1 for storage or for use in a hydrogen
using device, as will be described in more detail below.
[0067] Figure 3 illustrates an exemplary two column PSA hydrogen
separation device 29, such as, for example, the carbon dioxide/water
separation unit 30 of a larger device or system 29 which also contains the
carbon monoxide separation unit 21 shown in Figure 1. Preferably, the
PSA device 29 operates on a Skarstrom-like PSA cycle. The classic
Skarstrom cycle consists of four basic steps: pressurization, feed,
blowdown, and purge. The device 29 contains two columns 83 and 85.
When one column is undergoing pressurization and feed, the other column


is undergoing blowdown and purge. In one exemplary configuration, the
device 29 may be operated using three three-way valves 87, 89 and 91
and one or more flow restrictors 93. Of course other configurations may
also be used. When the three-way valves are in the positions shown in
Figure 3, the pressurization and feed steps are essentially combined, and
the blowdown and purge steps are similarly combined.
[0068] The PSA device 29 operates as follows. A pressurized feed gas
(F), such as the fuel exhaust gas, containing CO2, FH2O, CO and H2 is
provided through the fuel exhaust conduit 31. Two-position, three-way
valves 87, 89 and 91 are simultaneously switched to the state shown in
Figure 3A. The feed is introduced to column 83 via valve 87 pressurizing
column 83. The adsorbent contained in column 83 selectively adsorbs the
CO2 and H2O. As the feed continues to flow, most of the H2 exits as
extract (E) via valve 91. The extract may be provided into conduits 77
and/or 83 shown in Figure 1, or into the carbon monoxide PSA device 21
to remove carbon monoxide from the extract. The device 21 operates in
the same way as the portion of the device 29 shown in Figure 3, except
the bed materials in the columns are selected to separate hydrogen from
carbon monoxide.
[0069] The switching of valve 89 exposes column 85 to a low pressure
line, resulting in the blowdown of column 85. The low pressure line 95 is
the output of column 83 that passes through one or more flow restrictors
93. Gases that were previously adsorbed during the previous cycle
desorb and flow out through valve 89, producing a desorbate stream (D).
The desorbate stream may be provided into the carbon monoxide PSA
device 21 to remove carbon monoxide from the desorbate stream.
Meanwhile, a relatively small quantity of high pressure extract gas flows
through the flow restrictor(s) 93 and through column 85 in the direction


opposite to the feed flow, forming a purge flow that helps remove
desorbate from column 85.
[0070] At a subsequent time, as column 83 approaches saturation, the
positions of all valves are switched. Thus, column 85 becomes the
column fed via valve 87 and is pressurized, and column 83 vents via
valve 89 and blows down. In this way the purity of the extract gas E is
maintained.
[0071] A method of operating the system 1 of the fourth embodiment
will now be described. A fuel and an oxidizer are provided into the fuel
cell stack 3 through conduits 27/53 and 59, respectively. A fuel side
exhaust stream is generated from the fuel cell stack 3 through conduit 31
while the fuel and the oxidizer are provided into the fuel cell stack 3
operating in a fuel cell mode (i.e., while the stack is generating
electricity). At least a portion of the hydrogen is separated from the fuel
side exhaust stream by the PSA hydrogen separation device 29 during the
fuel cell mode operation. For example, the hydrogen and carbon
monoxide are separated from carbon dioxide and water in the PSA carbon
dioxide/water separation device or unit 30. Then, at least a portion of
carbon monoxide is separated from the fuel side exhaust stream (i.e.,
from the hydrogen) in the PSA carbon monoxide separation device or unit
21. At least a portion of the separated carbon monoxide is recirculated
from PSA device 21 through conduits 25 and 81 into the fuel inlet gas
stream in the fuel inlet conduit 27 and/or in conduit 53. The separated
hydrogen from the PSA device 29 may also be recirculated into the fuel
inlet gas stream through conduits 77 and 31, or provided to a hydrogen
storage vessel or to a hydrogen using device 11 5 outside the system 1
through conduit 83, or both. The valve 79 may be used to determine the
portion of the separated hydrogen being provided through conduits 77
and 83.


[0072] V. FIFTH EMBODIMENT
[0073] Figures 1 and 4 illustrate a system 1 of the fifth embodiment,
which utilizes hydrogen separation from the fuel exhaust stream using
temperature-assisted pressure swing adsorption. In this system, the fuel
cell stack 3 thermal output and the PSA hydrogen separation device 29
are thermally integrated. In Figure 4, the carbon dioxide/water separation
unit 30 of the device 29 is illustrated for clarity.
[0074] A high temperature fuel cell system 1, such as a SOFC system,
produces hydrogen by way of hydrocarbon reforming reactions that occur
within the stack 3 and/or within the reformer 9. The hydrogen appears in
the system's tailgas (i.e., the stack exhaust), and can be effectively
separated and purified in a pressure-swing adsorption (PSA) device 29.
The gas compression costs associated with the PSA process can be
considerable. The process of the fifth embodiment takes advantage of
heat available from the other parts of the system 1 to reduce those
compression costs.
[0075] The PSA device 29 operates with a pressure differential
between its pressurization/loading and blow-down/purge steps. The
pressure differential, and the associated change in loading of the adsorbed
gases, produces the gas separation. Generally, the higher the pressure
differential, the more effective the separation and the less amount of
purge gas required. As shown in the example of Figure 3, the product gas
is typically used as the purge gas, and so its use often needs to be
minimized. Typically, the pressure ratio of the pressurization to purge
steps is approximately 10:1, and approximately 10 to 20% of the product
gas is lost as purge.
[0076] The SOFC stack 3 often operates at pressures near ambient,
and thus the fuel exhaust or tailgas containing hydrogen is also near


ambient. In a typical non-thermally integrated design, in order to reach
pressures effective for PSA, the tailgas should be compressed by about a
factor of 10. This pressurization is usually not an issue for hydrogen
production plants that use steam methane reforming, because they often
operate at about 10 atmospheres pressure or above.
[0077] If heat is provided during purging steps and removed during
loading steps, the separation process can be made more effective. This
would allow a lower level of compression to be used to achieve a similar
separation objective. Alternatively, a higher degree of purification may be
achieved for the same level of compression. This can occur because the
loading of a adsorbed gas is a strong function of temperature as well as
pressure.
[0078] In many separation systems it is not cost-effective to produce
and remove this heat. In a high temperature fuel cell system, such as a
SOFC system, however, heat of an adequate quality is readily available.
[0079] In one example shown in Figure 4, warm exhaust air from the
stack 3 flowing through oxidizer exhaust conduit 63 is used to heat a
PSA column under purge 85, and cool inlet air flowing through the
oxidizer inlet conduit 59 is used to cool a column 83 under load.
[0080] In another example, a coolant fluid may circulate between the
stack 3 operating at an elevated temperature and the PSA separation
system 29 through a circulation conduit. The fluid removes excess heat
from the stack 3 and carries it to the separation system 29, where it is
used to heat the gas used to purge the columns. There are a wide variety
of ways to achieve these effects using the various heat sources available
in a high temperature fuel cell system, such as a SOFC system.


[0081] Thus, in the system of the fifth embodiment, the compression
requirements for a pressure-swing adsorption separation system for
hydrogen are reduced by using waste heat from a SOFC stack to effect a
more efficient separation. Alternatively, a higher degree of purification
may be achieved for the same level of compression. In other words, the
extract purity is improved if the column being purged could be heated
with heat originating from a high temperature fuel cell stack, and the
column being fed could be cooled. Alternatively, the pressure of the feed
gas might be reduced, or the amount of purge gas might be reduced,
while the extract purity was maintained. The benefits of this method are
reduced capital equipment costs associated with compression and/or
higher product value associated with higher purity.
[0082] While the method of fifth embodiment was described with
respect to the carbon dioxide/water separation unit 30 of the PSA
hydrogen separation device 29, it may also be used with the PSA carbon
dioxide separation device or unit 21 in addition to or instead of the
carbon dioxide/water separation unit 30. In this case, the waste heat
from the high temperature fuel cell system is used to heat the column
under purge in the carbon monoxide separation device 21 in addition to or
instead of the column under purge in the carbon dioxide/water separation
unit 30. This may be accomplished by providing heat from the oxidizer
exhaust conduit 63 to the column under purge in device 21 and/or by
providing heat from the coolant fluid in the circulation conduit. If desired,
the column under load in the device 21 may be cooled by the cool inlet air
flowing through the oxidizer inlet conduit 59.
[0083] Since each column of the PSA devices 21 and 29 is alternated
between being the column under load and column under purge, the
oxidizer inlet conduit 59 and the oxidizer exhaust conduit 63 are thermally
integrated with ail columns of each applicable PSA device 21 and/or 29,


as shown in Figure 5. For example, each conduit 59, 63 may be split into
as many parallel branches as there are columns in the respective PSA
device. Each branch 59A, 59B, 63A, 63B of the respective conduit 59,
63 is thermally integrated with a respective column 83, 85, of the PSA
29 device. The flow of cool or hot air through each branch is controlled
by a valve 88. In other words, each PSA device column 83 and 85 is
thermally integrated with a branch 59A, 63A and 59B, 63B of both
conduits 59 and 63. However, only cool or warm air is provided to a
particular column depending on if the column is undergoing loading or
purging.
[0084] Likewise, if the coolant fluid is circulated between the stack 3
operating at an elevated temperature and the PSA separation system 29
through a circulation conduit, then the circulation conduit is split into
parallel branches, and each branch is thermally integrated with a
respective PSA column. The flow of the coolant fluid is controlled to
each branch by a valve, such that the warm coolant fluid flows only to
those columns that are undergoing purging.
[0085] It should be noted that the term "thermally integrated" in the
context of the fifth embodiment means that the conduit either thermally
contacts the respective PSA column or that it is located adjacent to and
preferably in the same thermal enclosure, such as a hot box or thermal
insulation, as the respective PSA column, to be able to transfer heat to
the column.
[0086] Figure 6 illustrates an alternative example of a PSA unit 21 or
30 of the PSA device 29, where all gas flows are decoupled. In the PSA
system shown in Figure 6, if valves V1, V2 and V3 (numbered 87, 89
and 91 in Figure 3) are replaced by pairs of two-way valves V1A - V3B
(i.e., a two-way valve would be placed on each horizontal branch


stemming from valves V1-V3, and locations V1, V2 and V3
corresponding to the valves 87, 89 and 91 become "T" shaped conduit
junctions), flow restrictors 93 are replaced by actuating valves V4A and
V4B, and the extract line is valved (V5), then all flows can be decoupled.
In particular, the blowdown / purge steps can be decoupled and the
pressurization / feed steps can be decoupled. This may have advantages
in terms of improvement of purity and reduction of purge losses, although
at the cost of additional equipment. Furthermore, the lengths of the feed
and purge steps can be decoupled. Either can be of arbitrary length.
Clearly this can interrupt the flow of purified extract, and so occasionally
additional beds are provided that increase the system's flexibility and do
not interrupt the flow.
[0087] VI. SIXTH EMBODIMENT
[0088] The elements of a system 201 of the sixth embodiment will
now be described with respect to Figure 7. Elements in Figure 7 with the
same numbers as in Figures 1 and 2 should be presumed to be the same
unless noted otherwise. If desired, the system 201 may be used with any
one or more suitable elements of the first, second, third, fourth and/or
fifth embodiments, even if these elements are not explicitly shown in
Figure 7.
[0089] In the sixth embodiment, steam methane reformation (SMR) is
used to preprocess natural gas before it is fed into the stack 3 for co-
generation of hydrogen and electricity from natural gas or other
hydrocarbon fuel using a solid oxide fuel cell system (i.e., a regenerative
or a non-regenerative system). SMR transforms methane to reaction
products comprising primarily carbon monoxide and hydrogen, as
described above. These reaction products are then oxidized in the SOFC
stack 3 at high temperature producing electricity. Excess hydrogen is


retrieved as a side product. Steam methane reformation reactions are
endothermic reactions which require heat, while oxidation reactions in
SOFC stack 3 are exothermic reactions which generate heat. This
provides a synergy for tight heat integration to improve overall Balance of
Plant (BOP) energy efficiency. By integration of reformer 9 and stack 3 in
the hot box 108, heat from the stack 3 can be transferred to the reformer
9 using convective, radiative and/or conductive heat transfer.
[0090] In system 1 illustrated in Figure 1, the reformer 9 is thermally
integrated with the stack 3 for heat transfer from the stack 3 to the
reformer 9. The stack 3 generates enough heat to conduct the SMR
reaction in the reformer 9 during steady-state operation of the system 1.
However, under some different operating conditions ranging from low to
high stack efficiency and fuel utilization, the exothermic heat generated
by the stack 3 and provided to the reformer 9 may be in greater than, the
same as or less than the heat required to support the steam methane
reforming reaction in the reformer 9. The heat generated and/or provided
by the stack 3 may be less than required to support steam reformation in
the reformer 9 due to low fuel utilization, high stack efficiency, heat loss
and/or stack failure/turndown. In this case, supplemental heat is supplied
to the reformer 9.
[0091] In a preferred aspect of the sixth embodiment, the system 201
provides the supplemental heat to the reformer 9 to carry out the SMR
reaction during steady state operation. The supplemental heat may be
provided from a burner 1 5 (more generally referred to in this embodiment
as a combustor) which is thermally integrated with the reformer 9 and/or
from a cathode (i.e., air) exhaust conduit which is thermally integrated
with the reformer 9. While less preferred, the supplemental heat may
also be provided from the anode (i.e., fuel) exhaust conduit which is
thermally integrated with the reformer. Preferably, the supplemental heat


is provided from both the combustor 15 which is operating during steady
state operation of the reformer (and not just during start-up) and from the
cathode (i.e., air) exhaust of the stack 3. Most preferably, the combustor
15 is in direct contact with the reformer 9, and the stack cathode exhaust
conduit 203 is configured such that the cathode exhaust contacts the
reformer 9 and/or wraps around the reformer 9 to facilitate additional heat
transfer. This lowers the combustion heat requirement for SMR.
[0092] Preferably, the reformer 9 is sandwiched between the
combustor 15 and one or more stacks 3 to assist heat transfer, as
illustrated in Figures 8-10 and as described in more detail below. The
combustor 15, when attached to the reformer 9, closes the heat balance
and provides additional heat required by the reformer. When no heat is
required by the reformer, the combustor unit acts as a heat exchanger.
Thus, the same combustor (i.e., burner) 15 may be used in both start-up
and steady-state operation of the system 201. When using combustion
catalysts coated on the conduit walls, natural gas is preferably
introduced at several places in the combustion zone to avoid auto ignition
and local heating.
[0093] Preferably, one or more sensors are located in the system 201
which are used to determine if the reformer requires additional heat and/or
how much additional heat is required. These sensors may be reformer
temperature sensor(s) which measure the reformer temperature and/or
process parameter sensor(s), which measure one or more of fuel
utilization, stack efficiency, heat loss and stack failure/turndown. The
output of the sensor(s) is provided to a computer or other processor
and/or is displayed to an operator to determine if and/or how much
additional heat is required by the reformer. The processor or operator
then controls the combustor heat output based on the step of determining
to provide an desired amount heat from the combustor to the reformer.


The combustor heat output may be controlled by controlling the amount
of fuel and air being provided into the combustor or by shutting off the
fuel and/or air being provided into the combustor. The combustor may be
controlled automatically by the processor or manually by operator actions.
[0094] Preferably, the combustor 15 exhaust is provided into the inlet
of the air heat exchanger 67 through conduit 205 to heat the air being
provided into the stack 3 through the exchanger 67. Thus, the stack
cathode exhaust is provided to the exchanger 67 indirectly through the
combustor 15. The configuration of system 201 differs from that of
system 1 illustrated in Figure 1 where the stack cathode exhaust is
provided directly into the exchanger 67 through conduit 63.
[0095] The reformer 9 is located in close proximity to the stack 3 to
provide radiative and convective heat transfer from the stack 3 to the
reformer. Preferably, the cathode exhaust conduit 203 of the stack 3 is
in direct contact with the reformer 9 and one or more walls of the
reformer 9 may comprise a wall of the stack cathode exhaust conduit
203. Thus, the cathode exhaust provides convective heat transfer from
the stack 3 to the reformer 9.
[0096] Furthermore, if desired, the cathode exhaust from the stack may
be wrapped around the reformer 9 by proper ducting and fed to the
combustion zone of the combustor 1 5 adjacent to the reformer 9 before
exchanging heat with the incoming air in the external air heat exchanger
67, as shown in Figures 8-10 and as described in more detail below.
Natural gas or other hydrocarbon fuel can be injected and mixed with
cathode exhaust air in the combustion zone of the combustor 15 to
produce heat as needed.
[0097] Figures 8-10 illustrate three exemplary configurations of the
stack, reformer and combustor unit in the hot box 108. However, other


suitable configurations are possible. The reformer 9 and combustor 15
preferably comprise vessels, such as fluid conduits, that contain suitable
catalysts for SMR reaction and combustion, respectively. The reformer 9
and combustor 1 5 may have gas conduits packed with catalysts and/or
the catalysts may be coated on the walls of the reformer 9 and/or the
combustor 1 5.
[0098] The reformer 9 and combustor 1 5 unit can be of cylindrical
type, as shown in Figure 8A or plate type as shown in Figures 9A and
10A. The plate type unit provides more surface area for heat transfer
while the cylindrical type unit is cheaper to manufacture.
[0099] Preferably, the reformer 9 and combustor 15 are integrated into
the same enclosure and more preferably share at least one wall, as shown
in Figures 8-10. Preferably, but not necessarily, the reformer 9 and
combustor 15 are thermally integrated with the.stack(s) 3, and may be
located in the same enclosure, but comprise separate vessels from the
stack(s) 3 (i.e., external reformer configuration).
[0100] In a preferred configuration of the system 201, fins 209 are
provided in the stack cathode exhaust conduit 203 and in the burner 15
combustion zone 207 to assist with convective heat transfer to the
reformer 9. In case where the reformer 9 shares one or more walls with
the cathode exhaust conduit 203 and/or with the combustion zone 207 of
the burner 15, then the fins are provided on the external surfaces of the
wall(s) of the reformer. In other words, in this case, the reformer 9 is
provided with exterior fins 209 to assist convective heat transfer to the
interior of the reformer 9.
[0101] Figures 8A and 8B show the cross-sectional top and front
views, respectively, of an assembly containing two stacks 3 and a
cylindrical reformer 9 combustor 15 unit 210. The combustion zone 207


of the combustor 15 is located in the core of the cylindrical reformer 9.
In other words, the combustor 15 comprises a catalyst containing channel
bounded by the inner wall 211 of the reformer 9. In this configuration, the
combustion zone 207 is also the channel for the cathode exhaust gas.
The space 215 between the stacks 3 and the outer wall 213 of the
reformer 9 comprises the upper portion of the stack cathode exhaust
conduit 203. Thus, the reformer inner wall 211 is the outer wall of the
combustor 15 and the reformer outer wall 213 is the inner wall of the
upper portion of stack cathode exhaust conduit 203. If desired, a
cathode exhaust opening 217 can be located in the enclosure 219 to
connect the upper portion 215 of conduit 203 with the lower portions of
the conduit 203. The enclosure 219 may comprise any suitable container
and preferably comprises a thermally insulating material.
[0102] In operation, a natural gas (and/or other hydrocarbon fuel) and
steam mixture is fed to the lower end of the reformer 9 through conduit
27. The reformed product is provided from the reformer 9 into the stack
anode (fuel) inlet 13 through conduit 53. The spent fuel is exhausted
from the stack through the anode exhaust 23 and conduit 31.
[0103] The air enters the stack through the cathode (air) inlet 19 and
exits through exhaust opening 217. The system 201 is preferably
configured such that the cathode exhaust (i.e., hot air) exists on the same
side of the system as the inlet of the reformer 9. For example, as shown
in Figure 8B, since the mass flow of hot cathode exhaust is the maximum
at the lower end of the device, it supplies the maximum heat where it is
needed, at feed point of the reformer 9 (i.e., the lower portion of the
reformer shown in Figure 8B). In other words, the mass flow of the hot
air exiting the stack is maximum adjacent to the lower portion of the
reformer 9 where the most heat is needed. However, the cathode
exhaust and reformer inlet may be provided in other locations in the


system 201. The hot air containing cathode exhaust is preferably but not
necessarily, provided into the combustion zone 207 of the combustor 1 5
through conduit 203.
[0104] Natural gas is also injected into the central combustion zone
207 of the combustor 15 where it mixes with the hot cathode exhaust.
The circular or spiral fins are preferably attached to the inner 211 and
outer 213 reformer walls to assist heat transfer. Heat is transferred to
the outer wall 213 of the reformer 9 from the stack 3 by convection and
radiation. Heat is transferred to the inner wall 211 of the reformer by
convection and/or conduction from the combustion zone 207. As noted
above, the reformer and combustion catalysts can either be coated on the
walls or packed in respective flow channels.
[0105] Figures 9A and 9B show the cross-sectional top and front
views, respectively, of an assembly containing two stacks 3 and a plate
type reformer 9 coupled with a plate type combustor 15. The
configuration of the plate type reformer-combustor unit 220 is the same
as the cylindrical reformer-combustor unit 210 shown in Figures 8A and
8B, except that the reformer-combustor unit 220 is sandwich shaped
between the stacks. In other words, the combustion zone 207 is a
channel having a rectangular cross sectional shape which is located
between two reformer 9 portions. The reformer 9 portions comprise
channels having a rectangular cross sectional shape. The fins 209 are
preferably located on inner 211 and outer 213 walls of the reformer 9
portions. The plate type reformer and combustion unit 220 provides more
surface area for heat transfer compared to the cylindrical unit 210 and
also provides a larger cross-sectional area for the exhaust gas to pass
through.


[0106] Figures 10A and 10B show the cross-sectional top and front
views, respectively, of an assembly containing one stack 3 and a plate
type reformer 9 coupled with a plate type combustor 15. Exhaust gas is
wrapped around the reformer 9 from one side. One side of the
combustion zone 207 channel faces insulation 219 while the other side
faces the reformer 9 inner wall 213.
[0107] VII. SEVENTH EMBODIMENT
[0108] Hot box 108 components, such as the stack 3 and reformer 9
are heated to a high temperature before starting (i.e., during the start-up
mode) to draw current from the stack as well as produce hydrogen.
Furthermore, the stack is preferably run in a reducing environment or
ambient using hydrogen until the stack heats up to a reasonably high
temperature below the steady state operating temperature to avoid
reoxidation of the anode electrodes. Stored hydrogen can be used for this
process. However, in the seventh preferred embodiment, a small CPOX
(catalytic partial oxidation) unit is used in the start-up mode of the
system, to make the system independent of external source of hydrogen.
[0109] Figure 7 illustrates the system 201 containing the CPOX unit
223. Any suitable CPOX device may be used. However, it should be
noted that the CPOX unit may be used during start-up of other suitable
SOFC systems, such as systems 1 and 101 shown in Figures 1 and 2,
respectively.
[0110] The system 201 preferably also includes a start-up heater 225
for heating the CPOX unit 223 during start-up and a mixer 227 for mixing
air and a hydrocarbon fuel, such as methane or methane containing
natural gas. The air and fuel are provided into the mixer through conduits
229 and 231, respectively. The mixed air and fuel are provided into the
CPOX unit 223 after being mixed in the mixer 227.


[0111] The CPOX unit 223 produces hydrogen from the air and fuel
mix. The produced hydrogen is sent with excess oxygen and nitrogen
through conduit 233 to the reformer 9. The hydrogen passes through the
reformer 9, the stack 3, the fuel heat exchanger 35, the shift reactor 7
and the condenser unit 37 and is provided to the combustor 1 5 through
conduit 235. The hydrogen is burned in the combustor 1 5 to heat up the
reformer 9 and stack 15. This process is continued until the system
heats up to a certain temperature, such as a temperature at which
oxidation of the anode electrodes is avoided. Then the CPOX unit 223 is
stopped or turned off, and a hydrocarbon fuel, such as natural gas, is
injected directly into the combustor 15 through conduit 73 to continue
the heating process. The combustor 15 is thermally integrated with the
reformer 9 and can be used during the start-up and during steady state
operation modes.
[01 12] VIII. EIGHTH EMBODIMENT
[0113] Figure 7 illustrates the system 201 with components configured
for efficient water management. However, it should be noted that the
below described components may also be configured for efficient water
management for other suitable SOFC systems, such as systems 1 and
101 shown in Figures 1 and 2, respectively.
[0114] A SOFC system in general can be self sufficient in water. Heat
is required to make steam required for the methane reformation. Water
from anode exhaust may be condensed and recycled back to the system.
Furthermore, water and natural gas may be fed to a heat exchanger for
transferring heat from the anode exhaust. However, under some
operating conditions, the heat recovered from anode exhaust gas may not
be sufficient to evaporate all the water needed in the reformation reaction
as well as to heat the fuel inlet steam mixture to a desired temperature


before feeding this mixture to the reformer. Thus, additional water
heating and management components may be added to the system 201
to evaporate all the water needed in the reformation reaction as well as to
heat the fuel inlet steam mixture to a desired temperature before feeding
this mixture to the reformer.
[0115] The system 201 shown in Figure 7 contains an additional
evaporator 237, an optional supplemental heater / evaporator 239 and a
steam / fuel mixer 241. The system operates as follows. The process of
steam generation, mixing steam with fuel, such as natural gas, and
preheating mixture may be done in four steps.
[0116] First, metered water is provided from the condenser 37 through
condensate pump 243, water knockout / tank 39, metering pump 47 and
optional water treatment device 245 into the evaporator 237. The
metered water is heated and at least partially evaporated in the
evaporator 237 by the heat from the anode exhaust provided into
evaporator from the shift reactor 7 through conduit 31.
[0117] Second, the partially evaporated water is provided from
evaporator 237 into the supplemental heater / evaporator 239.
Supplemental heat is supplied in the heater / evaporator 239 to complete
the evaporation process and superheat the steam.
[0118] Third, the steam is provided from the heater / evaporator 239
into the steam / fuel mixer 241. The steam is mixed with the fuel in the
mixer.
[0119] Fourth, the fuel and steam mix is provided from the mixer 241
into the fuel heat exchanger 35, where the mix is preheated using heat
from the hot anode exhaust. The fuel and steam mix is then provided
into the reformer through conduit 27.


[0120] Water vapor transfer devices such as enthalpy wheels can be
added to the system to reduce the heat required for the total evaporation
process. These devices can transfer water vapor from the anode exhaust
to incoming fuel stream.
[0121] As described above, the anode exhaust provided into the
condenser 37 is separated into water and hydrogen. The hydrogen is
provided from the condenser 37 via conduit 247 into the conduit 31
leading to the hydrogen purification subsystem 29 and into conduit 235
leading into the combustor 15. The flow of hydrogen from condenser 37
through conduits 31 and 235 may be controlled by one three way valve
or by separate valves 249 and 251 located in conduits 31 and 235,
respectively. The hydrogen from the hydrogen purification system 29
may be provided to the use/storage subsystem 115 via conduit 83, while
the carbon monoxide from subsystem 29 is provided to the burner or
combustor 15 and carbon monoxide and water from subsystem 29 are
exhausted.
[0122] IX. ELECTRICITY AND HYDROGEN GENERATION
[0123] The electrochemical (i.e., high temperature fuel cell) system of
the preferred embodiments of the present invention such as the solid
oxide electrochemical system, such as a SOFC or a SORFC system, or the
molten carbonate fuel cell system, can be used to co-produce hydrogen
and electricity in the fuel cell mode. Thus, while the prior art SORFC
system can generate either electricity in the fuel cell mode or hydrogen in
an electrolysis mode, the system of the preferred embodiments of the
present invention can co-produce both hydrogen and electricity (i.e.,
produce hydrogen and electricity together). The system of the preferred
embodiments generates a hydrogen rich exhaust stream using reforming
reactions that occur within the fuel cell stack and/or in a reformer in


thermal integration with the fuel cell stack. The amount of hydrogen
produced can be controlled by the operator. The hydrogen rich stream is
further conditioned if necessary and stored or used directly by the
operator. Thus, the high temperature electrochemical systems produce
purified hydrogen as a by-product of fuel reformation in the fuel cell
mode. The electrochemical system may operate in the fuel cell mode,
when no external electricity input is required, to generate diffusion of ions
across an electrolyte of the system. In contrast, a reversible or
regenerative electrochemical system operates in the electrolysis mode
when external electricity is required to generate diffusion of ions across
the electrolyte of the system.
[0124] It should be noted that the electrochemical system of the
preferred embodiments does not necessarily co-produce or co-generate
power or electricity for use outside the system. The system may be
operated to primarily internally reform a carbon and hydrogen containing
fuel into hydrogen with minimal power generation or without delivering or
outputting power from the system at all. If desired, a small amount of
power may be generated and used internally within the system, such as
to keep the system at operating temperature and to power system
components in addition to other parasitic loads in the system.
[0125] Thus, in one aspect of the preferred embodiments of the
present invention, the high temperature electrochemical system is a SOFC
or a SORFC system which co-produces electricity and hydrogen in the
fuel cell mode. A SOFC or SORFC system operates in the fuel cell mode
when oxygen ions diffuse through an electrolyte of the fuel cells from the
oxidizer side to the fuel side of the fuel cell containing the carbon and
hydrogen containing gas stream. Thus, when the high temperature
electrochemical system, such as a SOFC or SORFC system operates in
the fuel cell mode to generate hydrogen, a separate electrolyzer unit


operating in electrolysis mode and which is operatively connected to the
fuel cell stack is not required for generation of hydrogen. Instead, the
hydrogen is separated directly from the fuel cell stack fuel side exhaust
gas stream without using additional electricity to operate a separate
electrolyzer unit.
[0126] When an SORFC system is used rather than an SOFC
system, the SORFC system can be connected to a primary source of
electricity (e.g., grid power) and can accept electricity from the primary
source when desirable or can deliver electricity to the primary source
when desirable. Thus, when operating the SORFC system of the
preferred embodiments, the system operator does not have to sacrifice
electricity production to produce hydrogen and vice versa. The SORFC
system does not require a hot thermal mass which absorbs heat in the
fuel cell mode and which releases heat in the electrolysis mode for
operation or energy storage. However, a hot thermal mass may be used
if desired. Furthermore, the system may use, but does not require a fuel
reformer.
[0127] Furthermore, a relative amount of hydrogen and electricity
produced can be freely controlled. All or a portion of the hydrogen in the
fuel side exhaust stream may be recirculated into the fuel inlet stream to
provide control of the amount of electricity and hydrogen being co-
produced in the system, as will be described in more detail below. The
hydrogen product can be further conditioned, if necessary, and stored or
used directly in a variety of applications, such as transportation, power
generation, cooling, hydrogenation reactions, or semiconductor
manufacture, either in a pressurized or a near ambient state.
[0128] The system 1 or 101 shown in Figures 1 and 2 derives power
from the oxidation of a carbon and hydrogen containing fuel, such as a


hydrocarbon fuel, such as methane, natural gas which contains methane
with hydrogen and other gases, propane or other biogas, or a mixture of a
carbon fuel, such as carbon monoxide, oxygenated carbon containing gas,
such as methanol, or other carbon containing gas with a hydrogen
containing gas, such as water vapor, H2 gas or their mixtures. For
example, the mixture may comprise syngas derived from coal or natural
gas reformation. Free hydrogen is carried in several of the system
process flow streams. The carbon containing fuel is provided into the
system from a fuel source, which may comprise a fuel inlet into the fuel
cell stack, a fuel supply conduit and/or a fuel storage vessel.
[0129] The fuel cell stack 3 preferably contains the fuel cells, separator
plates, seals, gas conduits, heaters, thermal insulation, control electronics
and various other suitable elements used in fuel cell stacks.
[0130] The system 1, 101 and 201 also contains at least one hydrogen
separator, such as the PSA hydrogen separation device 29. The system
1, 101 and 201 also contains an optional hydrogen conditioner 114, as
shown in Figures 1 and 2. The hydrogen conditioner 114 may be any
suitable device which can purify, dry, compress (i.e., a compressor), or
otherwise change the state point of the hydrogen-rich gas stream
provided from the hydrogen separator 29. If desired, the hydrogen
conditioner 114 may be omitted.
[0131] The system 1, 101 and 201 also contains a hydrogen
storage/use subsystem 115, as shown in Figure 2. This subsystem 115
may comprise a hydrogen storage vessel, such as a hydrogen storage
tank, a hydrogen dispenser, such as a conduit which provides hydrogen or
a hydrogen-rich stream to a device which uses hydrogen, or a hydrogen
using device. For example, the subsystem 115 may comprise a conduit
leading to a hydrogen using device or the hydrogen using device itself,


used in transportation, power generation, cooling, hydrogenation
reactions, or semiconductor manufacture.
[0132] For example, the system 1, 101 and 201 may be located in a
chemical or a semiconductor plant to provide primary or secondary (i.e.,
backup) power for the plant as well as hydrogen for use in hydrogenation
(i.e., passivation of semiconductor device) or other chemical reactions
which require hydrogen that are carried out in the plant.
[0133] Alternatively, the subsystem 115 may also comprise another
fuel cell, such as an SOFC or SORFC or any other fuel cell, which uses
hydrogen as a fuel. Thus, the hydrogen from the system 1, 101 and 201
is provided as fuel to one or more additional fuel cells 115. For example,
the system 1, 101 and 201 may be located in a stationary location, such
as a building or an area outside or below a building and is used to provide
power to the building. The additional fuel cells 115 may be located in
vehicles located in a garage or a parking area adjacent to the stationary
location. In this case, the carbon and hydrogen containing fuel is
provided to the system 1, 101 and 201 to generate electricity for the
building and to generate hydrogen which is provided as fuel to the fuel
cell 115 powered vehicles. The generated hydrogen may be stored
temporarily in a storage vessel and then provided from the storage vessel
to the vehicle fuel cells 115 on demand (analogous to a gas station) or
the generated hydrogen may be provided directly from the system 1, 101
and 201 to the vehicle fuel cells 11 5.
[0134] In one preferred aspect of the present invention, the
hydrogen separator 29 is used to separate and route hydrogen from the
fuel side exhaust stream only into the subsystem 115. In another
preferred aspect of the present invention, the hydrogen separator 29 is
used to separate hydrogen from the fuel side exhaust stream and to route


all or a part of the hydrogen back into the fuel inlet 13 of the fuel cell
stack 3 through conduit 81, to route all or part of the hydrogen to the
subsystem 11 5 and/or to route the hydrogen out with the tail gas.
[0135] A preferred method of operating the systems 1, 101 and 201
will now be described. The systems are preferably operated so that
excess fuel is provided to the fuel cell stack 3. Any suitable carbon
containing and hydrogen containing fuel is provided into the fuel cell
stack. The fuel may comprise a fuel such as a hydrocarbon fuel, such as
methane, natural gas which contains methane with hydrogen and other
gases, propane or other biogas. Preferably, an unreformed hydrocarbon
fuel from the by-pass valve 11 and a hydrogen fuel from the reformer 9
are provided into the stack 3.
[0136] Alternatively, the fuel may comprise a mixture of a non-
hydrocarbon carbon containing gas, such as carbon monoxide, carbon
dioxide, oxygenated carbon containing gas such as methanol or other
carbon containing gas with a hydrogen containing gas, such a water
vapor or hydrogen gas, for example the mixture may comprise syngas
derived from coal or natural gas reformation. The hydrogen and water
vapor may be recycled from the fuel side exhaust gas stream or provided
from hydrogen and water vapor conduits or storage vessels.
[01 37] The reformation reactions occur within the fuel cell stack 3
and/or in the reformer 9 and result in the formation of free hydrogen in
the fuel side exhaust gas stream. For example, if a hydrocarbon gas
such as methane is used as a fuel, then the methane is reformed to form
a mixture containing non-utilized hydrogen, carbon dioxide and water
vapor in the fuel cell stack 3. If natural gas is used as a fuel, then the
natural gas may be converted to methane in a preprocessing subsystem


or it may be reformed directly to a non-hydrocarbon carbon containing gas
such as carbon monoxide in the reformer 9.
[0138] Preferably, the fraction of hydrogen separated by the
hydrogen separator 29 and the amount of total fuel provided to the fuel
cell stack 3 for electricity and hydrogen production are variable and under
the control of an operator operating a control unit of the system. An
operator may be a human operator who controls the hydrogen separation
and electricity production or a computer which automatically adjusts the
amount of hydrogen separation and electricity production based on
predetermined criteria, such as time, and/or based on received outside
data or request, such as a demand for electricity by the power grid and/or
a demand for hydrogen by the subsystem 115. Controlling these two
parameters allows the operator to specify largely independently the
amount of hydrogen produced and the amount of electricity generated.
The outside data or request may comprise one or more of electricity
demand, hydrogen demand, electricity price and hydrogen price, which
may be transmitted electronically to a computer system operator or
visually or audibly to a human system operator.
[0139] In one extreme, when the user of the system needs
electricity, but does not need additional hydrogen, then the operator can
choose to have the hydrogen containing streams recirculated back into
the fuel cell stack 3 by the separator 29 through conduit 81 by opening
valve 79, while providing no hydrogen or a minimum amount of hydrogen
to the subsystem 115, through conduit 83, where hydrogen flow may
also be controlled by a valve.
[0140] In another extreme, when the user of the system needs
hydrogen, but does not need any electricity generated, the operator can
choose to have the fuel cell stack 3 act primarily to internally reform the


carbon containing fuel into hydrogen with minimal power generation
and/or minimal or no external power output/delivery from the system. A
small amount of power may be generated to keep the system at operating
temperature and to power the hydrogen separator 29 and conditioner
114, if necessary, in addition to other parasitic loads in the system. All or
most of the hydrogen from the separator 29 is provided to the subsystem
11 5 rather than to the conduit 81. In this case, additional water from the
water supply 39 is preferably added to the fuel.
[0141] In the continuum between the two extremes, varying
amounts of hydrogen and electricity may be needed simultaneously. In
this case, the operator can choose to divert varying amounts of the
hydrogen from the separator 29 to conduits 81 and 83, while
simultaneously generating the desired amount of electricity. For example,
if more hydrogen is recirculated back into the fuel cell stack 3 through
conduit 81 by controlling valve 79, then more electricity is generated but
less hydrogen is available for use or storage in the subsystem 115. The
trade off between the amount of electricity and hydrogen produced can
vary based on the demand and the price of each.
[0142] The trade off between the amount of electricity and
hydrogen generated may also be achieved using several other methods.
In one method, the amount of fuel provided to the fuel cell stack 3 is kept
constant, but the amount of current drawn from the stack 3 is varied. If
the amount of current drawn is decreased, then the amount of hydrogen
provided to the hydrogen separator 29 is increased, and vice versa.
When less current is drawn, less oxygen diffuses through the electrolyte
of the fuel cell. Since the reactions which produce free hydrogen (i.e.,
the steam-methane reforming reaction (if methane is used as a fuel) and
the water-gas shift reaction) are substantially independent of the
electrochemical reaction, the decreased amount of diffused oxygen


generally does not substantially decrease the amount of free hydrogen
provided in the fuel side exhaust gas stream.
[0143] In an alternative method, the amount of current drawn from
the stack is kept constant, but the amount of fuel provided to the stack 3
is varied. If the amount of fuel provided to the stack 3 is increased, then
the amount of hydrogen provided to the hydrogen separator 29 is
increased, and vice versa. The amount of fuel may be varied by
controlling the flow of fuel through the fuel inlet conduit 27 by a
computer or operator controlled valve 28 and/or by controlling the flow of
fuel through the by-pass line 11 by valve 55.
[0144] In another alternative method, both the amount of current
drawn and the amount of fuel provided into the fuel cell stack 3 are
varied. The amount of hydrogen generated generally increases with
decreasing amounts of drawn current and with increasing amounts of fuel
provided into the fuel cell stack. The amount of hydrogen generated
generally decreases with increasing amounts of drawn current and with
decreasing amounts of fuel provided into the fuel cell stack.
[0145] Preferably, the systems of the preferred embodiments may
be operated at any suitable fuel utilization rate. Thus, 0 to 100 percent
of the fuel may be utilized for electricity production. Preferably, 50 to 80
percent of the fuel is utilized for electricity production and at least 10
percent, such as 20 to 50 percent, of the fuel is utilized for hydrogen
production. For example, a 100 kWe SOFC system may be used to
generate from about 70 to about 11 0 kWe of electricity and from about
45 to about 110 kg/day of high pressure hydrogen when 50 to 80
percent of the fuel is utilized for electricity production. The systems of
the preferred embodiments may be used to produce hydrogen cost


effectively. Thus, the method of the preferred embodiments provides a
reduction in the cost of hydrogen production.
[0146] If the fuel cell stack 3 is a solid oxide regenerative fuel cell
(SORFC) stack which is connected to a primary source of power (such as
a power grid) and a source of oxidized fuel (such as water, with or
without carbon dioxide), then the device can operate transiently in an
electrolysis mode as an electrolyzer to generate hydrogen streams,
methane streams, or mixtures when economically advantageous (e.g.,
when the cost of electricity is inexpensive compared to the cost of the
fuel containing bound hydrogen), or during times when the demand for
hydrogen significantly exceeds the demand for electricity. At other times,
the system 1, 101 and 201 can be used in the fuel cell mode to generate
electricity from the stored hydrogen or carbon containing fuel. Thus, the
system 1, 101 and 201 can be used for peak shaving.
[0147] The fuel cell systems described herein may have other
embodiments and configurations, as desired. Other components, such as
fuel side exhaust stream condensers, heat exchangers, heat-driven heat
pumps, turbines, additional gas separation devices, hydrogen separators
which separate hydrogen from the fuel exhaust and provide hydrogen for
external use, fuel preprocessing subsystems, fuel reformers and/or water-
gas shift reactors, may be added if desired, as described, for example, in
U.S. Application Serial Number 10/300,021, filed on November 20, 2002,
in U.S. Provisional Application Serial Number 60/461,190, filed on April 9
2003, and in U.S. Application Serial Number 10/446,704, filed on May
29, 2003 all incorporated herein by reference in their entirety.
Furthermore, it should be understood that any system element or method
step described in any embodiment and/or illustrated in any figure herein
may also be used in systems and/or methods of other suitable


embodiments described above, even if such use is not expressly
described.
[0148] The foregoing description of the invention has been
presented for purposes of illustration and description. It is not intended to
be exhaustive or to limit the invention to the precise form disclosed, and
modifications and variations are possible in light of the above teachings or
may be acquired from practice of the invention. The description was
chosen in order to explain the principles of the invention and its practical
application. It is intended that the scope of the invention be defined by
the claims appended hereto, and their equivalents.

WE CLAIM:
1. A solid oxide fuel cell system, comprising:
a combustor;
a plurality of solid oxide fuel cell stacks;
a cathode exhaust conduit of the stacks;
a reformer adapted to reform a hydrocarbon fuel to a hydrogen containing reaction
product and to provide the reaction product to the stacks; and
a hot box, in which the stacks, the reformer and the combustor are located,
wherein:
the reformer is sandwiched between the combustor and the stacks;
the combustor is thermally integrated with the reformer;
the stack cathode exhaust conduit is thermally integrated with the reformer, wherein the
cathode exhaust conduit is adapted to heat the reformer using the cathode exhaust
of the stacks,
the reformer is adapted to be heated by the combustor, and
the reformer is adapted to be heated by convective, radiative and/or conductive heat
transfer from the stack.
2. The system as claimed in claim 1, wherein the reformer is adapted to be heated by at least
one of radiative and convective heat transfer from the stack across a gap between the stack and
the reformer.
3. The system as claimed in claim 1, wherein the cathode exhaust conduit comprises a
lower portion and an upper portion and the upper portion of the cathode exhaust conduit
comprises a space located between the stacks and the reformer into which space the cathode
exhaust is provided from the stacks.

4. The system as claimed in claim 1, wherein the combustor comprises the combustor
conduit and a combustion zone containing a combustor catalyst such as described herein.
5. The system as claimed in claim 4, wherein the cathode exhaust conduit is connected to
an inlet of the combustor.
6. The system as claimed in claim 4, wherein the combustor shares at least one wall with the
reformer.
7. The system as claimed in claim 6, wherein the reformer comprises a catalyst containing
cylinder and the combustion zone comprises a catalyst containing tube located in the cylinder
core and the combustor tube wall comprises an inner wall of the reformer cylinder.
8. The system as claimed in claim 6, wherein the reformer comprises a catalyst containing
plate shaped reformer which shares one wall with a catalyst containing plate shaped combustor
combustion zone.
9. The system as claimed in claim 2, wherein the gap between the reformer and the stacks
comprises the cathode exhaust conduit of the stacks.
10. The system as claimed in claim 9, wherein an outer reformer wall contains fins which
extend into the cathode exhaust conduit and an inner reformer wall contains fins which extend
into the combustor.
11. The system as claimed in claim 1 comprising:
a condenser adapted to separate water from a stack anode exhaust;
an evaporator adapted to evaporate water to be provided into a stack inlet fuel stream;
a fuel - steam mixer adapted to mix the evaporated water and the stack inlet fuel stream;

a catalytic partial oxidation reactor adapted to provide hydrogen into the combustor
during system start up;
an air heat exchanger, wherein an outlet of the combustor is connected to a first inlet of
the air heat exchanger, an air inlet conduit is connected to a second inlet of the air heat
exchanger, and a first outlet of the air heat exchanger is connected to a cathode inlet of
the stacks;
a desulfurizer fluidly connected to fuel inlets of the stacks; and
a water-gas shift reactor fluidly connected to fuel outlets of the stacks, wherein the
desulfurizer and the water-gas shift reactor are thermally integrated with each other;
a connecting conduit connecting fuel inlets of the stacks with an outlet of the reformer;
a hydrocarbon fuel inlet conduit connected to an inlet of the reformer;
a hydrocarbon fuel by-pass line fluidly connected to the fuel inlets of the stacks,
wherein the by-pass line is adapted to provide unreformed hydrocarbon fuel into the fuel inlets of
the stacks;
a hydrogen separation device fluidly connected to the fuel outlets of the stacks;
a carbon monoxide separation device fluidly connected to the fuel outlets of the stacks;
a hydrocarbon fuel inlet conduit fluidly connected to fuel inlets of the stacks;
a carbon monoxide recycle conduit, whose inlet is fluidly connected to an outlet of the
carbon monoxide separation device and whose outlet is fluidly connected to the
fuel inlets of the stacks;
a PSA separation device fluidly connected to fuel outlets of the stacks; and
a thermal output of the stacks in addition to the fuel outlets is thermally integrated with at
least a first column of the PSA device.
12. A method of operating the solid oxide fuel cell system of one of the preceding claims, the
method comprising:
providing a hydrocarbon fuel and water vapor into the reformer;
reforming the hydrocarbon fuel in the reformer to form a hydrogen containing reaction
product;

providing the reaction product into the solid oxide fuel cell stack during steady state
operation of the stack; and
heating the reformer during steady state operation of the stack using the stack cathode
exhaust, the combustor and by transferring heat generated by the stack from the stack to
the reformer by convective, radiative and/or conducting heat transfer.
13. The method as claimed in claim 12, wherein the step of heating comprises heating the
reformer by passing the stack cathode exhaust adjacent to the reformer.
14. The method as claimed in claim 13 comprising providing the cathode exhaust into the
combustor after passing the stack cathode exhaust adjacent to the reformer.
15. The method as claimed in claim 12, wherein the step of heating comprises heating the
reformer by a combustion of a hydrocarbon fuel and air in the combustor.
16. The method as claimed in claim 15 comprising:
determining, in the manner such as described herein, if the reformer requires additional
heat for the reforming reaction; and
controlling the combustor heat output based on the step of determining to provide an
desired amount heat from the combustor to the reformer.
17. The method as claimed in claim 15 comprising providing the combustor exhaust into an
air heat exchanger to heat air being provided through the air heat exchanger into the stack.
18. The method as claimed in claim 17, wherein a space between the reformer and the fuel
cell stack comprises a cathode exhaust conduit of the fuel cell stack.
19. The method as claimed in claim 12, wherein the combustor heats the reformer by sharing
at least one wall with the reformer.

20. The method as claimed in claim 19, wherein the reformer comprises a catalyst containing
cylinder and the combustor comprises a catalyst containing tube located in the cylinder core and
the combustor tube wall comprises an inner wall of the reformer cylinder.
21. The method as claimed in claim 19, wherein the reformer-comprises a catalyst containing
plate shaped reformer which shares one wall with a catalyst containing plate shaped combustor.
22. The method as claimed in claim 19, wherein the reformer is located between the fuel cell
stack and the combustor.
23. The method as claimed in claim 12 comprising:
providing a hydrocarbon fuel and air into a catalytic partial oxidation reactor;
generating hydrogen in the catalytic partial oxidation reactor;
providing the generated hydrogen into the combustor at system start-up;
heating up the combustor, the reformer and the solid oxide fuel cell stack during system
start-up;
stopping the provision of hydrocarbon fuel and air into the catalytic partial oxidation
reactor once the stack reaches a predetermined operating temperature;
providing an anode exhaust from the fuel cell stack into a condenser;
separating water from the anode exhaust in the condenser;
providing water into an evaporator;
converting water to steam in the evaporator;
mixing the steam with a fuel being provided to the fuel cell stack; providing a
hydrocarbon fuel into a desulfurizer;
providing desulfurized hydrocarbon fuel from the desulfurizer into the fuel cell stack;
providing an anode exhaust from the fuel cell stack into a water-gas shift reactor;
providing heat from the water-gas shift reactor to the desulfurizer; and

providing unreformed hydrocarbon fuel that does not pass through the reformer into the
fuel inlet of the fuel cell stack.
24. The method as claimed in claim 12 comprising starting up the fuel cell system, wherein
starting up the fuel cell system comprises:
providing the solid oxide fuel cell stack at room temperature, wherein anode electrodes of
the solid oxide fuel cells in the stack are reduced from previous operation;
providing a hydrocarbon fuel and an oxidizer into the combustor; and
raising a temperature of the solid oxide fuel cell stack to an operating temperature using
heat from the combustor, such that no separately stored reducing or inert gases are used to flush
the anode chamber of the solid oxide fuel cells of the stack during the start-up.
25. The method as claimed in claim 12 comprising:
providing a fuel and an oxidizer such as described herein into the fuel cell stack;
generating an anode exhaust stream from the fuel cell stack while the fuel and the
oxidizer are provided into the fuel cell stack operating in a fuel cell mode;
separating at least a portion of hydrogen from the anode exhaust stream during the fuel
cell mode operation in a hydrogen separation device;
separating at least a portion of carbon monoxide from the anode exhaust stream during
the fuel cell mode operation in a carbon monoxide separation device; and
recirculating at least a portion of the separated carbon monoxide into a fuel inlet gas
stream.


A solid oxide fuel cell system is disclosed. The fuel cell system comprises: a
combustor (15); a plurality of solid oxide fuel cell stacks (3); a cathode exhaust conduit
of the stacks; a reformer (9) adapted to reform a hydrocarbon fuel to a hydrogen
containing reaction product and to provide the reaction product to the stacks; and a hot
box (108), in which the stacks, the reformer and the combustor are located, wherein: the
reformer is sandwiched between the combustor and the stacks; the combustor is thermally
integrated with the reformer; the stack cathode exhaust conduit (203) is thermally
integrated with the reformer, wherein the cathode exhaust conduit is adapted to heat the
reformer using the cathode exhaust of the stacks, the reformer is adapted to be heated by
the combustor, and the reformer is adapted to be heated by convective, radiative and/or
conductive heat transfer from the stack.

Documents:

02082-kolnp-2006 abstract .pdf

02082-kolnp-2006 claims.pdf

02082-kolnp-2006 correspondence others.pdf

02082-kolnp-2006 description(complete).pdf

02082-kolnp-2006 drawings.pdf

02082-kolnp-2006 form-1.pdf

02082-kolnp-2006 form-3 .pdf

02082-kolnp-2006 form-5.pdf

02082-kolnp-2006 international publication.pdf

02082-kolnp-2006 pct form.pdf

02082-kolnp-2006 priority document.pdf

02082-kolnp-2006-correspondence others-1.1.pdf

02082-kolnp-2006-form-3-1.1.pdf

02082-kolnp-2006-g.p.a.pdf

02082-kolnp-2006-priority document-1.1.pdf

2082-KOLNP-2006-ABSTRACT 1.1.pdf

2082-KOLNP-2006-ABSTRACT 1.2.pdf

2082-KOLNP-2006-ABSTRACT.pdf

2082-KOLNP-2006-AMANDED CLAIMS.pdf

2082-KOLNP-2006-ASSIGNMENT.pdf

2082-kolnp-2006-assignment1.1.pdf

2082-KOLNP-2006-CANCELLED PAGES.pdf

2082-KOLNP-2006-CLAIMS 1.1.pdf

2082-KOLNP-2006-CLAIMS 1.2.pdf

2082-KOLNP-2006-CORRESPONDENCE 1.2.PDF

2082-KOLNP-2006-CORRESPONDENCE.pdf

2082-kolnp-2006-correspondence1.1.pdf

2082-KOLNP-2006-DESCRIPTION (COMPLETE) 1.1.pdf

2082-KOLNP-2006-DESCRIPTION (COMPLETE) 1.2.pdf

2082-KOLNP-2006-DESCRIPTION (COMPLETE).pdf

2082-KOLNP-2006-DRAWINGS 1.1.pdf

2082-KOLNP-2006-DRAWINGS 1.2.pdf

2082-KOLNP-2006-DRAWINGS.pdf

2082-KOLNP-2006-EXAMINATION REPORT REPLY RECIEVED 1.1.pdf

2082-kolnp-2006-examination report.pdf

2082-KOLNP-2006-FORM 1 1.2.pdf

2082-KOLNP-2006-FORM 1 1.3.pdf

2082-KOLNP-2006-FORM 1-1.2.pdf

2082-KOLNP-2006-FORM 1.1.1.pdf

2082-kolnp-2006-form 13.1.pdf

2082-KOLNP-2006-FORM 13.pdf

2082-kolnp-2006-form 18.pdf

2082-KOLNP-2006-FORM 2 1.1.pdf

2082-KOLNP-2006-FORM 2 1.2.pdf

2082-KOLNP-2006-FORM 2.pdf

2082-KOLNP-2006-FORM 3-1.2.pdf

2082-KOLNP-2006-FORM 3.1.1.pdf

2082-kolnp-2006-form 3.pdf

2082-KOLNP-2006-FORM 5.1.1.pdf

2082-kolnp-2006-form 5.pdf

2082-KOLNP-2006-FORM-27.pdf

2082-kolnp-2006-gpa.pdf

2082-kolnp-2006-granted-abstract.pdf

2082-kolnp-2006-granted-claims.pdf

2082-kolnp-2006-granted-description (complete).pdf

2082-kolnp-2006-granted-drawings.pdf

2082-kolnp-2006-granted-form 1.pdf

2082-kolnp-2006-granted-form 2.pdf

2082-kolnp-2006-granted-specification.pdf

2082-KOLNP-2006-OTHERS 1.1.pdf

2082-KOLNP-2006-OTHERS.pdf

2082-KOLNP-2006-PA.pdf

2082-KOLNP-2006-PETITION UNDER RULE 137.pdf

2082-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf

2082-kolnp-2006-reply to examination report1.1.pdf

abstract-02082-kolnp-2006.jpg


Patent Number 247538
Indian Patent Application Number 2082/KOLNP/2006
PG Journal Number 16/2011
Publication Date 22-Apr-2011
Grant Date 18-Apr-2011
Date of Filing 24-Jul-2006
Name of Patentee BLOOM ENERGY CORPORATION
Applicant Address 1252 ORLEANS DRIVE, SUNNYVALE, CALIFORNIA
Inventors:
# Inventor's Name Inventor's Address
1 VENKATARAMAN, SWAMINATHAN 1144 ROLLINGDELL COURT, CUPERTINO 95014
2 FINN, JOHN, E 13155 FRANKLIN AVENUE, MOUNTAIN VIEW CA 94040
3 GOTTMANN, MATTHIAS 684 TORREYA AVENUE, SUNNYVALE, CA 94086
PCT International Classification Number H01M8/04,H01M8/00
PCT International Application Number PCT/US2004/041082
PCT International Filing date 2004-12-09
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/537,899 2004-01-22 U.S.A.
2 60/552,202 2004-03-12 U.S.A.