U.S. patent application number 16/750659 was filed with the patent office on 2020-05-21 for fuel cell system containing humidity sensor and method of operating thereof.
The applicant listed for this patent is BLOOM ENERGY CORPORATION. Invention is credited to Arne Ballantine, Andrew James Hall, Jayakumar Krishnadass, Venkat V. Ramani, David Weingaertner.
Application Number | 20200161671 16/750659 |
Document ID | / |
Family ID | 66328906 |
Filed Date | 2020-05-21 |
United States Patent
Application |
20200161671 |
Kind Code |
A1 |
Ballantine; Arne ; et
al. |
May 21, 2020 |
FUEL CELL SYSTEM CONTAINING HUMIDITY SENSOR AND METHOD OF OPERATING
THEREOF
Abstract
Various systems and methods disclosed herein may include a fuel
cell system that may dynamically respond to changes in steam
concentration in the fuel cell system. The fuel cell system may
include a fuel cell stack that produces an anode exhaust stream, an
anode recycle blower that receives the anode exhaust stream and
outputs an anode recycle stream, and a humidity sensor configured
to measure the steam concentration of the anode recycle stream. The
fuel cell system may also include a master controller configured to
receive steam concentration measurement from the humidity sensor
and control the operation of the anode recycle blower and/or other
components based on the steam concentration measurement.
Inventors: |
Ballantine; Arne; (Palo
Alto, CA) ; Krishnadass; Jayakumar; (Sunnyvale,
CA) ; Weingaertner; David; (Sunnyvale, CA) ;
Hall; Andrew James; (San Francisco, CA) ; Ramani;
Venkat V.; (Milpitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BLOOM ENERGY CORPORATION |
San Jose |
CA |
US |
|
|
Family ID: |
66328906 |
Appl. No.: |
16/750659 |
Filed: |
January 23, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15803461 |
Nov 3, 2017 |
10581090 |
|
|
16750659 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/04097 20130101;
H01M 8/04432 20130101; H01M 8/04746 20130101; H01M 8/04492
20130101; H01M 8/0668 20130101; H01M 8/04514 20130101; H01M 8/0432
20130101; H01M 8/2425 20130101; H01M 8/04402 20130101; H01M 8/2483
20160201; H01M 8/0267 20130101; H01M 2008/1293 20130101 |
International
Class: |
H01M 8/0267 20060101
H01M008/0267; H01M 8/2483 20060101 H01M008/2483; H01M 8/04089
20060101 H01M008/04089; H01M 8/2425 20060101 H01M008/2425; H01M
8/04746 20060101 H01M008/04746; H01M 8/0432 20060101 H01M008/0432;
H01M 8/04492 20060101 H01M008/04492; H01M 8/0438 20060101
H01M008/0438; H01M 8/0668 20060101 H01M008/0668 |
Claims
1. A fuel cell system, comprising: a fuel cell stack that produces
an anode exhaust stream; an anode recycle blower that receives the
anode exhaust stream and outputs an anode recycle stream; a
humidity sensor configured to measure a steam concentration of the
anode recycle stream; and a master controller configured to receive
steam concentration measurement from the humidity sensor and
control the operation of the anode recycle blower based on the
steam concentration measurement.
2. The system of claim 1, further comprising a pressure sensor
configured to measure an absolute pressure of the anode recycle
stream,
3. The system of claim 2, wherein the master controller is further
configured to receive an absolute pressure measurement from the
pressure sensor, and control the operation of the anode recycle
blower based on the steam concentration measurement and on the
absolute pressure measurement.
4. The system of claim 1, further comprising a flow meter, wherein
the master controller is further configured to receive a pressure
measurement from the flow meter and control the operation of the
anode recycle blower based on the steam concentration measurement
and the pressure measurement.
5. The system of claim 1, further comprising a flow meter
configured to measure differential pressure of the anode recycle
stream, wherein the master controller is further configured to
receive the differential pressure measurement from the flow meter
and control the operation of the anode recycle blower based on the
steam concentration measurement and the differential pressure
measurement.
6. The system of claim 1, wherein controlling the operation of the
anode recycle blower based on the steam concentration measurement
controls a steam to carbon ratio of the anode recycle stream.
7. The system of claim 1, wherein the master controller receives
the steam concentration measurement in real time or near real
time.
8. The system of claim 1, wherein the master controller is located
remotely from the humidity sensor.
9. The system of claim 1, wherein the humidity sensor is capable of
operating in temperatures between 85.degree. C. and 180.degree. C.
and wherein the humidity sensor is capable of operating in a
humidity range of 0% to 100%.
10. The system of claim 1, wherein the master controller is
configured to: compare the steam concentration to a threshold; and
control the operation of the anode recycle blower when the steam
concentration crosses the threshold.
11. A method of operating a fuel cell system, comprising: providing
a fuel inlet stream into a fuel cell stack; producing an anode
exhaust stream from operation of the fuel cell stack; providing the
anode exhaust stream to an anode recycle blower to output an anode
recycle stream; measuring a steam concentration of the anode
recycle stream; and controlling an operation of at least one
component of the fuel cell system to control a steam to carbon
ratio of the anode recycle stream.
12. The method of claim 11, wherein controlling the operation of at
least one component of the fuel cell system comprises changing a
speed of the anode recycle blower based on the measured steam
concentration of the anode recycle stream.
13. The method of claim 12, further comprising: measuring a
pressure of the anode recycle stream; and changing a speed the
anode recycle blower based on the measured steam concentration and
the measured pressure of the anode recycle stream.
14. The method of claim 13, wherein the pressure comprises a
differential pressure.
15. The method of claim 13, wherein the pressure comprises an
absolute pressure.
16. The method of claim 12, wherein: changing the speed of the
anode recycle blower controls the steam to carbon ratio of the
anode recycle stream; and the step of measuring the steam
concentration comprises measuring the steam concentration using a
humidity sensor which is located remotely from the fuel cell
stack.
17. The method of claim 12, wherein changing the speed of the anode
recycle blower comprises: comparing the steam concentration of the
anode recycle stream to a threshold; and changing the speed of the
anode recycle blower when the steam concentration crosses the
threshold.
Description
FIELD
[0001] The present disclosure relates to fuel cell systems and
methods of operating thereof, such as fuel cell systems containing
a humidity sensor.
BACKGROUND
[0002] Electrochemical devices, such as fuel cells, can convert
energy stored in fuels to electrical energy with high efficiencies.
In a fuel cell system, such as a solid oxide fuel cell (SOFC)
system, an oxidizing flow is passed through the cathode side of the
fuel cell while a fuel inlet flow is passed through the anode side
of the fuel cell. The oxidizing flow is typically air, while the
fuel flow can be a hydrocarbon fuel, such as methane, natural gas,
pentane, ethanol, or methanol. The fuel cell enables the transport
of negatively charged oxygen ions from the cathode flow stream to
the anode flow stream, where the ion combines with either free
hydrogen or hydrogen in a hydrocarbon molecule to form water vapor
and/or with carbon monoxide to form carbon dioxide. The excess
electrons from the negatively charged ion are routed back to the
cathode side of the fuel cell through an electrical circuit
completed between anode and cathode, resulting in an electrical
current flow through the circuit. A fuel cell system may include
multiple hot boxes, each of which may generate electricity. A hot
box may include a fuel inlet stream that provides oxidizing fuel to
one or more fuel stacks, where the fuel is oxidized during
electricity generation. The oxidized fuel (i.e., the anode or fuel
exhaust stream) travels through the fuel stacks and is exhausted
from the fuel stacks. A portion of the anode exhaust stream may be
recycled back into the fuel inlet stream.
SUMMARY OF THE INVENTION
[0003] Various systems disclosed herein may include a fuel cell
system that may dynamically respond to changes in steam
concentration in the fuel cell system. The fuel cell system may
include a fuel cell stack that produces an anode exhaust stream, an
anode recycle blower that receives the anode exhaust stream and
outputs an anode recycle stream, and a humidity sensor configured
to measure the steam concentration of the anode recycle stream. The
fuel cell system may also include a master controller configured to
receive steam concentration measurement from the humidity sensor
and control the operation of the anode recycle blower and/or other
components based on the steam concentration measurement.
[0004] Various methods disclosed herein for operating a fuel cell
system may include providing a fuel inlet stream into a fuel cell
stack, producing an anode exhaust stream from operation of the fuel
cell stack, providing the anode exhaust stream to an anode recycle
blower to output an anode recycle stream, and measuring, by a
humidity sensor, a steam concentration of the anode recycle stream.
The various methods may further include controlling, by a master
controller, the operation of one or more components in the fuel
cell module, including the anode recycle blower, based on the
measured steam concentration of the anode recycle stream.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic of a fuel cell system according to
various embodiments.
[0006] FIG. 2 is a schematic process flow diagram illustrating a
hot box in a fuel cell system according to various embodiments.
[0007] FIG. 3 is a schematic process flow diagram illustrating the
fuel cell system of FIG. 2 with an additional carbon dioxide
separator.
[0008] FIG. 4 is a schematic of a fuel cell module according to
various embodiments.
[0009] FIG. 5 is another schematic of a fuel cell module according
to various embodiments.
[0010] FIG. 6 is a process flow diagram of a method of operating a
fuel cell system according to various embodiments.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0011] Various examples will be described in detail with reference
to the accompanying drawings. References made to particular
examples and implementations are for illustrative purposes, and are
not intended to limit the scope of the written description or the
claims.
[0012] In a fuel cell system, the anode recycle stream that is fed
back into the fuel inlet stream may be a mixture of carbon monoxide
(CO), carbon dioxide (CO.sub.2), hydrogen (H.sub.2) and water
(e.g., water vapor, H.sub.2O), and the steady state temperature of
the anode recycle stream may range between 90.degree. C. to
180.degree. C. The composition of the anode recycle stream may be
determined from one time gas chromatography measurement. The anode
recycle stream composition and concentrations, along with other
measurements such as differential pressure and temperature, may be
used in flow calculations to determine anode recycle flow
characteristics.
[0013] If it is desired to change the fuel cell system process
conditions during operation or to introduce new capabilities to the
fuel cell system, then real time monitoring or near real time
monitoring of the composition and concentration of the various
components of the anode recycle stream may be useful. For example,
if carbon dioxide is removed from the anode recycle stream, then
some water (e.g., water vapor) may be removed along with the carbon
dioxide. However, removal of water from the anode recycle stream
may cause an imbalance in the steam to carbon ratio in the fuel
inlet stream provided to the fuel cell stacks, and cause undesired
coking of the anode electrodes of the fuel cells due to the lower
than desired steam to carbon ratio of the fuel inlet stream.
Physically opening the hot box of the fuel cell system and taking
apart the fuel cell stacks to analyze the amount of coking of the
anode electrodes is a destructive method of determining the coking
of the anode electrodes.
[0014] In order to avoid coking of the anode electrodes or other
undesirable fuel cell system operating states, it would be
beneficial if the steam concentration, or steam to carbon ratio, of
the anode recycle stream is monitored and adjusted in real time or
near real time (e.g., in 10 minutes or less, such as 30 seconds to
5 minutes for example). The steam to carbon ratio the anode recycle
stream may then be dynamically adjusted based on the real time
measurements. Therefore, real time monitoring of the anode recycle
stream composition may provide flexibility in changing the
operation of the fuel cell system to prevent damage to the fuel
cells and to improve fuel cell system performance.
[0015] The various embodiments described herein may allow for
continuous or real time monitoring of the humidity (e.g., steam
concentration) of the anode recycle stream in a fuel cell system by
using a humidity sensor (e.g., a steam sensor, referred to as a
"humidity/steam sensor" herein). Any change in the anode exhaust
stream humidity beyond an acceptable limit may be detected by the
sensor and communicated to a master controller. The master
controller may select actions in response to the measurements to
adjust the operation of the fuel cell system to improve performance
and/or avoid damage.
[0016] FIG. 1 illustrates a fuel cell system 100 according to one
embodiment of the present invention. Preferably, the system 100 is
a high temperature fuel cell stack system, such as a solid oxide
fuel cell (SOFC) system. The system 100 may be a regenerative
system such as a solid oxide regenerative fuel cell (SORFC) system
which operates in both fuel cell (i.e., discharge or power
generation) and electrolysis (i.e., charge) modes or it may be a
non-regenerative system which only operates in the fuel cell
mode.
[0017] The system 100 contains a high temperature fuel cell stack
106. The stack may contain a plurality of SOFCs or SORFCs. The high
temperature fuel cell stack 106 is illustrated schematically to
show one solid oxide fuel cell of the stack containing a ceramic
electrolyte, such as yttria or scandia stabilized zirconia, an
anode electrode, such as a nickel-stabilized zirconia cermet, and a
cathode electrode, such as lanthanum strontium manganite. Each fuel
cell contains an electrolyte, an anode electrode on one side of the
electrolyte 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 an 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 hydro-carbon fuel, enters the
anode chamber. Any suitable fuel cell designs and component
materials may be used. The system 100 further contains an anode
tail gas oxidizer (ATO) reactor 116, an anode recycle blower 122,
and an optional carbon dioxide separator 126. The carbon dioxide
separator 126 may be omitted in some embodiments.
[0018] The system 100 operates as follows. The fuel inlet stream is
provided into the fuel cell stack 106 through fuel inlet conduit
102. The fuel may comprise any suitable fuel, such as a hydrogen
fuel or a hydrocarbon fuel, including but not limited to 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, hydrogen gas or other mixtures. For
example, the mixture may comprise syngas derived from coal or
natural gas reformation. The fuel inlet conduit 102 provides the
fuel inlet stream to the anode side of the fuel cell stack 106.
[0019] Air or another oxygen containing gas is provided into the
stack 106 through an air inlet conduit 104. The air inlet conduit
104 provides air to the cathode side of the fuel cell stack
106.
[0020] Once the fuel and oxidant are provided into the fuel cell
stack 106, the stack 106 is operated to generate electricity and a
fuel exhaust stream. The fuel exhaust stream may contain hydrogen,
water vapor, carbon monoxide, carbon dioxide, some un-reacted
hydrocarbon gas, such as methane, and other reaction by-products
and impurities.
[0021] The fuel exhaust stream (i.e., the stack anode exhaust
stream) is provided from the stack 106 via fuel exhaust conduit
110. The air exhaust stream (i.e., the stack cathode exhaust
stream) is provided from the stack air exhaust outlet via air
exhaust conduit 112. The fuel exhaust conduit 110 is configured to
provide a portion of the fuel exhaust stream to the ATO reactor 116
via ATO input conduit 114 and recycle a portion of the fuel exhaust
stream via recycling conduit 120. The portion of fuel exhaust
provided to the ATO reactor 116 and recycled via recycling conduit
120 may vary. For example 10% of the fuel exhaust may be provided
to the ATO reactor 116 and 90% recycled. Alternatively, 50% of the
fuel exhaust may be provided to the ATO reactor 116, while 50% is
recycled. Additionally, 90% of the fuel exhaust or more may be
provided to the ATO reactor, while 10% or less is recycled. The
amount of recycled fuel provided into conduit 120 is controlled by
anode recycle blower 122 power (e.g., by its blowing speed). The
fuel exhaust stream provided into conduits 114 and 120 contains the
same composition or content of hydrogen, carbon monoxide, water,
and carbon dioxide. Air exhaust conduit 112 is configured to
provide the air exhaust stream to the ATO reactor 116.
[0022] The ATO reactor 116 receives the fuel exhaust stream and air
exhaust stream via ATO input conduit 114 and conduit 112,
respectively. The ATO reactor uses the combined fuel exhaust stream
and air exhaust stream to oxidize anode tail gas and output heated
oxidized fuel (i.e., reactor exhaust) to ATO exhaust conduit
118.
[0023] The anode recycle blower 122 is coupled to recycling conduit
120 to provide the recycled fuel exhaust stream from recycling
conduit 120 to a carbon dioxide separator 126 via recycling conduit
124. The anode recycle blower 122 may be computer or operator
controlled and may vary the amount and/or rate of the recycled fuel
exhaust stream being provided to the optional carbon dioxide
separator 126 and also the amount and/or rate of the carbon dioxide
free or carbon dioxide depleted recycled fuel exhaust stream being
provided back to the stack 106. As such, the anode recycle blower
122 may be used to increase or decrease the overall recycling rate
in system 100.
[0024] The carbon dioxide separator 126 may be a membrane type of
carbon dioxide separator which continuously removes carbon dioxide
by diffusion through the membrane. The carbon dioxide separator 126
may also include a separated carbon dioxide exhaust conduit 129
through which the separated carbon dioxide is removed from the
separator 126.
[0025] As illustrated in both FIG. 1, the purified recycled fuel
exhaust stream, with a reduced amount of carbon dioxide, is
provided back to the fuel inlet stream for the fuel stack 106 via
recycling conduit 128. The recycling of carbon dioxide depleted
fuel exhaust into the fuel inlet increases the performance of the
fuel cell stack 106.
[0026] FIG. 2 is a schematic representation of a fuel cell system
12 containing a hot box 13 and associated components, as described
in U.S. Pat. No. 8,563,180 issued on Oct. 22, 2013 and incorporated
herein by reference in its entirety.
[0027] The hot box 13 contains the plurality of the fuel cell
stacks 209, such as a solid oxide fuel cell stacks (where one solid
oxide fuel cell of the stack contains a ceramic electrolyte, such
as yttria stabilized zirconia (YSZ) or scandia stabilized zirconia
(SSZ), an anode electrode, such as a nickel-YSZ or Ni-SSZ cermet,
and a cathode electrode, such as lanthanum strontium manganite
(LSM)). The stacks 209 (corresponding to the fuel cell stack 106 of
FIG. 1A) may be arranged over each other in a plurality of columns
or segments.
[0028] The hot box 13 also contains a steam generator 203. The
steam generator 203 is provided with water through conduit 230A
from a water source 204, such as a water tank or a water pipe
(i.e., a continuous water supply), and converts the water to steam.
The steam is provided from generator 203 to mixer 205 through
conduit 230B and is mixed with the stack anode (fuel) recycle
stream in the mixer 205. The mixer 205 may be located inside or
outside the hot box of the hot box 13. Preferably, the humidified
anode exhaust stream is combined with the fuel inlet stream in the
fuel inlet line or conduit 229 downstream of the mixer 205, as
schematically shown in FIG. 2. Alternatively, if desired, the fuel
inlet stream may also be provided directly into the mixer 205, or
the steam may be provided directly into the fuel inlet stream
and/or the anode exhaust stream may be provided directly into the
fuel inlet stream followed by humidification of the combined fuel
streams. The steam generator 203 is heated by the hot anode tailgas
oxidizer ("ATO") 210 (corresponding to the ATO reactor 116 in FIG.
1) exhaust stream which is passed in heat exchange relationship in
conduit 219 with the steam generator 203.
[0029] The system operates as follows. The fuel inlet stream, such
as a hydrocarbon stream, for example natural gas, is provided into
the fuel inlet conduit 229 and through a catalytic partial pressure
oxidation (CPOx) reactor 211 located outside the hot box. During
system start up, air is also provided into the CPOx reactor 211
through CPOx air inlet conduit 213 to catalytically partially
oxidize the fuel inlet stream. The air may be blown through the air
inlet conduit 213 to the CPOx reactor 211 by a CPOx air blower. The
CPOx air blower may only operate during startup. During steady
state system operation, the air flow is turned off (e.g., by
powering off the CPOx air blower and closing a valve on the inlet
air stream) and the CPOx reactor acts as a fuel passage way in
which the fuel is not partially oxidized. Thus, the hot box 13 may
comprise only one fuel inlet conduit which provides fuel in both
start-up and steady state modes through the CPOx reactor 211.
Therefore a separate fuel inlet conduit which bypasses the CPOx
reactor during steady state operation is not required.
[0030] The fuel inlet stream is provided into the fuel heat
exchanger (anode recuperator)/pre-reformer 237 where its
temperature is raised by heat exchange with the stack 209 anode
(fuel) exhaust streams. The fuel inlet stream is pre-reformed in
the pre-reformer section of the heat exchanger 237 via the SMR
reaction and the reformed fuel inlet stream (which includes
hydrogen, carbon monoxide, water vapor and unreformed methane) is
provided into the stacks 209 through the fuel inlet conduit(s) 221.
The fuel inlet stream travels upwards through the stacks through
fuel inlet risers in the stacks 209 and is oxidized in the stacks
209 during electricity generation. The oxidized fuel (i.e., the
anode or fuel exhaust stream) travels down the stacks 209 through
the fuel exhaust risers and is then exhausted from the stacks
through the fuel exhaust conduits 223A (corresponding to the fuel
exhaust conduit 110 of FIG. 1) into the fuel heat exchanger
237.
[0031] In the fuel heat exchanger 237, the anode exhaust stream
heats the fuel inlet stream via heat exchange. The anode exhaust
stream is then provided via the fuel exhaust conduit 223B into a
splitter 207. A first portion of the anode exhaust stream is
provided from the splitter 207 the ATO 210 via conduit (e.g.,
slits) 243 (corresponding to the ATO input conduit 114 of FIG.
1).
[0032] A second portion of the anode exhaust stream is recycled
from the splitter 207 into the anode cooler 200 and then into the
fuel inlet stream. For example, the second portion of the anode
exhaust stream is recycled through conduit 231 (corresponding to
the recycling conduit 120 in FIG. 1) into the anode cooler (i.e.,
air pre-heater heat exchanger) where the anode exhaust stream
pre-heats the air inlet stream from conduit 233 (corresponding to
the air inlet conduit 104 of FIG. 1). The anode exhaust stream is
then provided by the anode recycle blower 223 (corresponding to the
anode recycle blower 122 in FIG. 1) into the mixer 205. The anode
exhaust stream is humidified in the mixer 205 by mixing with the
steam provided from the steam generator 203. The humidified anode
exhaust stream is then provided from the mixer 205 via humidified
anode exhaust stream conduit 241 (corresponding to the recycling
conduit 128 in FIG. 1) into the fuel inlet conduit 229 where it
mixes with the fuel inlet stream.
[0033] The air inlet stream is provided by a main air blower 225
from the air inlet conduit 233 into the anode cooler heat exchanger
200. The blower 225 may comprise the single air flow controller for
the entire system. In the anode cooler heat exchanger 200, the air
inlet stream is heated by the anode exhaust stream via heat
exchange. The heated air inlet stream is then provided into the air
heat exchanger (cathode recuperator 200) via conduit 214. The
heated air inlet stream is provided from heat exchanger 200 into
the stack(s) 209 via the air inlet conduit and/or manifold 225.
[0034] The air passes through the stacks 209 into the cathode
exhaust conduit 224 (corresponding to the air exhaust conduit 112
of FIG. 1) and through conduit 224 and mixer 240 into the ATO 210.
In the ATO 210, the air exhaust stream oxidizes the split first
portion of the anode exhaust stream from conduit 243 to generate an
ATO exhaust stream. The ATO exhaust stream is exhausted through the
ATO exhaust conduit 227 (corresponding to the ATO exhaust conduit
118 in FIG. 1) into the air heat exchanger 200. The ATO exhaust
stream heats air inlet stream in the air heat exchanger 200 via
heat exchange. The ATO exhaust stream (which is still above room
temperature) is then provided from the air heat exchanger 200 to
the steam generator 203 via conduit 219. The heat from the ATO
exhaust stream is used to convert the water into steam via heat
exchange in the steam generator 203. The ATO exhaust stream is then
removed from the system via the exhaust conduit 235. Thus, by
controlling the air inlet blower output (i.e., power or speed), the
magnitude (i.e., volume, pressure, speed, etc.) of air introduced
into the system may be controlled. The cathode (air) and anode
(fuel) exhaust streams are used as the respective ATO air and fuel
inlet streams, thus eliminating the need for a separate ATO air and
fuel inlet controllers/blowers. Furthermore, since the ATO exhaust
stream is used to heat the air inlet stream, the control of the
rate of single air inlet stream in conduit 233 by blower 225 can be
used to control the temperature of the stacks 209 and the ATO
210.
[0035] Thus, as described above, by varying the main air flow in
conduit 233 using a variable speed blower 225 and/or a control
valve is used to maintain the stack 209 temperature and/or ATO 210
temperature. In this case, the main air flow rate control via
blower 225 or valve acts as a main system temperature controller.
Furthermore, the ATO 210 temperature may be controlled by varying
the fuel utilization (e.g., ratio of current generated by the
stack(s) 209 to fuel inlet flow provided to the stack(s) 209).
Finally the anode recycle flow in conduits 231 and 217 may be
controlled by a variable speed anode recycle blower 223 and/or a
control valve to control the split between the anode exhaust to the
ATO 210 and anode exhaust for anode recycle into the mixer 205 and
the fuel inlet conduit 229 (corresponding to the fuel inlet conduit
102 of FIG. 1).
[0036] In the configuration illustrated in FIG. 2, there may be no
fuel and air inputs to the ATO 210. External natural gas or another
external fuel may not be fed to the ATO 210. Instead, the hot fuel
(anode) exhaust stream from the fuel cell stack(s) 209 is partially
recycled into the ATO as the ATO fuel inlet stream. Likewise, there
is no outside air input into the ATO. Instead, the hot air
(cathode) exhaust stream from the fuel cell stack(s) 209 is
provided into the ATO as the ATO air inlet stream.
[0037] Furthermore, the fuel exhaust stream is split in a splitter
207 located in the hot box 13. The splitter 207 is located between
the fuel exhaust outlet of the anode recuperator (e.g., fuel heat
exchanger) 237 and the fuel exhaust inlet of the anode cooler 200
(e.g., the air pre-heater heat exchanger). Thus, the fuel exhaust
stream is split between the mixer 205 and the ATO 210 prior to
entering the anode cooler 200. This allows higher temperature fuel
exhaust stream to be provided into the ATO because the fuel exhaust
stream has not yet exchanged heat with the air inlet stream in the
anode cooler 200. For example, the fuel exhaust stream provided
into the ATO 210 from the splitter 207 may have a temperature of
above 350 C, such as 350-500 C, for example 375 to 425 C, such as
390-410 C. Furthermore, since a smaller amount of fuel exhaust is
provided into the anode cooler 200 (e.g., not 100% of the anode
exhaust is provided into the anode cooler due to the splitting of
the anode exhaust in splitter 207), the heat exchange area of the
anode cooler 200 may be reduced.
[0038] FIG. 3 is a more detailed schematic of the fuel cell system
illustrated in FIG. 1 which includes the elements shown in FIG. 2.
Specifically, as shown in FIG. 3, any suitable carbon dioxide
separator, such as the membrane separator 126 described above, may
be located between the anode recycle blower 223 and the mixer 205
of FIG. 2.
[0039] Preferably, the carbon dioxide separator 126 is located
outside the hot box 13. The respective conduits 124 and 128 are
shown in FIG. 3.
[0040] The various embodiments described herein may allow for
continuous or real time monitoring of the humidity (e.g., steam
concentration) of the anode recycle stream in a fuel cell system. A
humidity or steam sensor may be added to measure the humidity of
the anode recycle stream. This sensor measures the total amount
and/or relative percent humidity (e.g., in the form on steam and/or
water vapor) and is referred to herein as "humidity/steam sensor".
If the steam sensor measures relative humidity, then it may also
optionally incorporate an absolute pressure measurement device into
the humidity sensor or as a separate sensor to measure the absolute
pressure of the stream which enters the steam sensor. The
information obtained from the humidity/steam sensor, as well as
from a flow meter attached to the anode recycle stream, may be
provided to a master controller. The master controller may control
various devices in the fuel cell system, such as an anode recycle
blower and one or more valves, to control the anode recycle stream
in order to improve performance and/or avoid damage to the fuel
cells.
[0041] FIG. 4 illustrates an example fuel cell module 400 in a fuel
cell system for use in the various embodiments. The fuel cell
module 400 may be similar to the system 12 and associated
components illustrated in FIG. 3. The fuel cell module 400 may
include a fuel inlet stream provided from a fuel inlet 402 (e.g.,
the fuel inlet conduit 102 in FIG. 1, such as the fuel inlet
conduit 29 in FIG. 2 or 3). The fuel inlet stream may be, for
example, a natural gas inlet flow. The fuel inlet stream may be fed
to a mixer 404 (e.g., mixer 205 in FIG. 2 or 3), which mixes the
fuel inlet stream with the recycled fuel that is part of the anode
exhaust stream from the anode recycle stream. The mixer 404
provides the mixed fuel to the fuel cell stack 406 (e.g., the fuel
cell stack (106, 209) of FIG. 1, 2 or 3), where it is consumed to
produce electricity.
[0042] The oxidized fuel spent by the fuel cell stack 406 may be
output as an anode exhaust stream into the anode exhaust heat
exchanger 408 (e.g., the fuel heat exchanger 237 in FIG. 2 or 3),
where anode exhaust stream may heat the fuel inlet stream via heat
exchange. The anode exhaust stream may then be provided via a fuel
exhaust conduit to a splitter (e.g., the splitter 207). A portion
of the anode exhaust stream may be diverted from the splitter to a
hot anode tailgas oxidizer, or ATO (e.g., ATO (116, 210) of FIG. 1,
2 or 3). Another portion of the anode exhaust stream may be
diverted from the splitter to an anode cooler (i.e., an air
pre-heater heat exchanger) and then to an anode recycle blower 410
(e.g., blower (122, 223) of FIG. 1, 2 or 3).
[0043] A humidity/steam sensor 412 may be placed at the output of
the anode recycle blower 410. The humidity/steam sensor 412 may be
used to measure the concentration of gaseous water present in the
anode recycle stream from the anode recycle blower 410. In some
embodiments, the humidity/steam sensor 412 may be capable of
operating in temperatures ranging from -50.degree. C. to
180.degree. C. In some embodiments, the humidity/steam sensor 412
may be capable of operating in humidity or steam concentration
ranges between 0% and 100%. In some embodiments, the humidity/steam
sensor 412 may not be affected by cross-interference due to the
presence of other cases in the anode recycle stream, such as carbon
monoxide, carbon dioxide, and hydrogen.
[0044] The humidity/steam sensor 412 may include a network adapter
and/or a communication interface (shown as dashed lines in FIG. 4)
for wired or wireless communication with a master controller 416
that may be located remotely from the humidity/steam sensor 412.
The humidity/steam sensor 412 may provide humidity/steam
concentration concentrations to the master controller 416 on a
continuous or real-time basis. In some embodiments, the response
time for the humidity/steam sensor 412 to transmit measurements to
the master controller 416 may be on the order of seconds. In some
embodiments, the master controller 416 may also control the
operation of the humidity/steam sensor 412, for example by setting
the rate at which the humidity/steam sensor 412 takes measurements.
The humidity/steam sensor 412 may include other components, such as
additional sensors (e.g., thermometers), memory, and I/O
components.
[0045] The anode recycle stream output from the anode recycle
blower 410 may be provided to a flow meter 414. The flow meter 414
may be, for example, a Venturi flow meter. The flow meter 414 may
measure the differential pressure of the anode recycle stream
output from the anode recycle blower 410. The flow meter 414 may
include a network adapter and/or a communication interface for
wired or wireless communication with the master controller 416. The
flow meter 414 may provide the differential pressure measurements
of the anode recycle stream to the master controller 416. The anode
recycle stream may then be fed back into the mixer 404 to be mixed
with fuel inlet stream. The fuel cell module 400 may include
additional components not illustrated in FIG. 4.
[0046] The master controller 416 may be a combination of hardware
and/or software, for example an ASIC, a FPGA, or a computing device
such as a server, desktop computer, or portable device. The master
controller 416 may take as input the humidity/steam concentration
measurements from the humidity/steam sensor 412 and the
differential pressure measurements from the flow meter 414. The
master controller 416 may also take input from other components in
the fuel cell module 400, such as thermocouples or other sensors,
and operational components of the fuel cell module 400 such as the
anode recycle blower 410, mixer 404, and fuel cell stack 406.
[0047] The master controller 416 may be configured to change the
operating conditions of the fuel cell module 400 based on the
humidity/steam measurements of the humidity/steam sensor 412 and/or
other inputs. The operating conditions that the master controller
416 may manipulate may include operating set points of fuel
utilization, water injection, and the amount of anode exhaust
stream recirculation (e.g., recycling) into the fuel inlet stream.
To implement these changes, the master controller may be configured
to control the operation of various components in the fuel cell
module 400, such as changing the speed of the anode recycle blower
410 and/or opening/closing various valves in the fuel cell module
400. For example, the master controller 416 may compare the
humidity/steam measurements, or change in the humidity/steam
measurements, to upper and/or lower thresholds. If the
humidity/steam concentration crosses an upper threshold, the master
controller 416 may reduce the speed of the anode recycle blower 410
to reduce the ratio of steam to carbon in the anode recycle stream.
If the relative change of the humidity/steam concentration crosses
a lower threshold, the master controller 416 may increase the speed
anode recycle blower 410 to increase the ratio of steam to carbon
in the anode recycle stream. This may prevent damage to the fuel
cell module 400 by preventing coking of the anode electrodes of the
fuel cells and/or other undesirable operating conditions. In this
manner, the humidity/steam sensor 412 and the master controller 416
may be used to monitor steam concentration in the anode recycle
stream of a fuel cell system in real time and respond to changes in
the steam concentration to improve performance and/or avoid damage
to the fuel cells.
[0048] In some embodiments, the master controller 416 may also be
configured to control carbon dioxide removal in the anode recycle
stream. This is shown in FIG. 5, which illustrates an example fuel
cell module 500 in a fuel cell system for use in the various
embodiments. The fuel cell module 500 may be similar to the fuel
cell module 400 illustrated in FIG. 4. For example, the fuel cell
module 500 may include fuel inlet 402, mixer 404, fuel cell stack
406, anode exhaust heat exchanger 408, anode recycle blower 410,
humidity/steam sensor 412, flow meter 414, and master controller
416 as described with reference to FIG. 4.
[0049] The fuel cell module 500 may also include a carbon dioxide
(CO.sub.2) removal system 502 and a bypass conduit 503 which
bypasses the CO.sub.2 removal system 502. The carbon dioxide
(CO.sub.2) removal system 502 may be a membrane type carbon dioxide
remover or it can be any other suitable carbon dioxide remover,
such as a canister trap (e.g., adsorption type carbon dioxide
remover) or an electrochemical carbon dioxide remover. The CO.sub.2
removal system 502 may remove carbon dioxide from the anode recycle
stream output of the anode recycle blower 410. In addition, one or
more valves, may be used to control the input and output of the
anode recycle stream to the CO.sub.2 removal system 502 and/or to
the bypass conduit 503.
[0050] The one or more valves may be any suitable valves, such as
continuous valves (e.g., butterfly or gate valves) which can
control the amount of flow through the valve in addition to being
completely closed or completely open. For example, there may be
three valves 504a-504c. However, two or more valves may be replaced
by a single multi-way (e.g., three-way or four-way) valve. For
example, valves 504a and 504c may be replaced by a single three-way
valve located at the location of valve 504a. Valves 504b and 504c
may be replaced by a single three-way valve located at the location
of valve 504b.
[0051] For example, the anode recycle stream input to the optional
CO.sub.2 removal system 502 may be reduced or stopped by partially
or fully closing the valve 504a. The anode recycle stream output of
the CO.sub.2 removal system 502 may be reduced or stopped by
partially or fully closing the valve 504b. The CO.sub.2 removal
system 502 may be completely bypassed if valves 504a and 504b are
closed and valve 504c in the bypass conduit 503 is opened. In some
embodiments, a portion of the anode recycle stream may be fed
through the CO.sub.2 removal system 502 and the remaining portion
may bypass the CO.sub.2 removal system 502 by passing it through
the bypass conduit 503 when all three valves 504a, 504b, 504c.
[0052] The master controller 416 may be configured to control the
operation of the valves 504a-504c. The master controller 416 may
open or close the valves 504a-504c to control the steam to carbon
ratio of the anode recycle stream based on measurements from the
humidity/steam sensor 412 and/or the flow meter 414. Thus the
master controller 416 may affect the operating conditions of both
the anode recycle blower 410 and the CO.sub.2 removal system 502 to
control the steam to carbon ratio of the anode recycle stream.
[0053] Thus, the anode recycle stream is provided through at least
one of a carbon dioxide removal system 502 and a bypass conduit 503
which bypasses the carbon dioxide removal system 502. The master
controller 416 controls a relative amount of the anode recycle
stream provided through the bypass conduit 503 and through the
carbon dioxide removal system 502 based on the measured steam
concentration of the anode recycle stream.
[0054] For example, if the master controller 416 detects that the
steam concentration of anode recycle stream crosses an upper
threshold the master controller 416 may control (e.g., change) the
speed of the anode recycle blower 410 to also change the steam to
carbon ratio of the anode recycle stream. In order to determine how
much water is removed in the CO.sub.2 removal system, it may also
be helpful to have a humidity sensor and flow meter for the gas
entering the CO.sub.2 removal system. Alternatively, the master
controller 416 may change the operating characteristics of valves
of 504a, 504b and/or 504c to change the percentage of fuel going
through the CO.sub.2 removal system. This has the primary effect of
changing the amount of water and CO.sub.2 removed by the CO.sub.2
removal system. The desired direction of the change depends on the
specific characteristics of the CO.sub.2 removal system.
[0055] In one embodiment the master controller 416 may conduct an
automated calibration and/or functional check of the humidity/steam
sensor 412 by changing fuel cell operating parameters (e.g., by
briefly turning on water flow, etc). The output of the
humidity/steam sensor 412 is then compared to the output prior to
turning on the water flow. If the sensor 412 detects the increased
humidity/steam after the water flow is turned on, then the sensor
passed the calibration/check. Otherwise, the master controller 416
may issue a service call to have the sensor 412 repaired and/or
recalibrated.
[0056] In another embodiment, a redundant humidity/steam sensor 412
is provided in case of natural and/or temperature based drift of
the sensor. A reading to trigger replacement or recalibration of
the main and/or redundant sensor 412 to protect the system may also
be performed.
[0057] FIG. 6 illustrates a method 600 for operating a fuel cell
system according to various embodiments. The fuel cell system may
include one or more fuel cell modules such as illustrated in FIGS.
4-5. In particular, each fuel cell module may include a
humidity/steam sensor and a master controller for measuring the
steam concentration of the anode recycle stream and controlling the
operation of the fuel cell module based on the measurements.
[0058] In block 602, the fuel cell module may provide a fuel inlet
stream to a fuel cell stack. The fuel inlet stream may include a
fresh fuel inlet (e.g., natural gas) as well as an anode recycle
stream from prior operation of the fuel cell stack. The fresh fuel
of the fuel inlet stream and the anode recycle stream may be mixed
together using a mixer (e.g., the mixer 404).
[0059] In block 604, the fuel cell module may generate an anode
exhaust stream while operating the fuel cell stack. The anode
exhaust stream may include oxidized fuel created while the fuel
cell stack is generating electricity. The composition of the anode
exhaust may include carbon monoxide, carbon dioxide, hydrogen,
steam and optionally unused, unreformed hydrocarbon fuel (e.g.,
methane).
[0060] In block 606, the fuel cell module may provide the anode
exhaust stream to an anode recycle blower 410 that outputs the
anode recycle stream. For example, the anode exhaust produced from
the fuel cell stack may be passed to a splitter. A portion of the
anode exhaust may be diverted from the splitter to an anode tailgas
oxidizer. Another portion of the anode exhaust may be diverted from
the splitter to an anode cooler heat exchanger and then to the
anode recycle blower. The speed of the anode recycle blower may
affect the steam to carbon ratio of the anode recycle stream.
[0061] In block 608, the fuel cell system may provide the anode
recycle stream to a carbon dioxide removal system 502, which may
remove a portion of carbon dioxide from the anode recycle stream.
There may be a number of valves (e.g., the valves 504a-504c) that
control the flow of the anode recycle stream into and out of the
carbon dioxide removal system and/or to bypass the carbon dioxide
removal system. For example, the valves may be located at the input
and output of the carbon dioxide removal system, as well as in a
bypass conduit 503 so that the entire or part of the anode recycle
stream may bypass the carbon dioxide removal system through the
bypass conduit 503.
[0062] In block 610, a humidity/steam sensor 412 located at the
output of the anode recycle blower 410 may measure the humidity
(e.g., steam) concentration of the anode recycle stream. The
humidity sensor may be capable of operating in temperatures ranging
from 85.degree. C. to 180.degree. C., and may be capable of
operating in humidity or steam concentration ranges between 0% and
100%. The humidity sensor may not be affected by cross-interference
due to the presence of other cases in the anode recycle stream,
such as carbon monoxide, carbon dioxide, and hydrogen.
[0063] In optional block 612, an optional flow meter (e.g., a
Venturi flow meter) 414 may measure the differential pressure of
the anode recycle stream. In block 614, the humidity sensor and
optionally the flow meter may transmit the humidity (e.g., steam)
concentration measurements and optionally the differential pressure
measurements to a master controller 416. For example, the humidity
sensor and the flow meter may be connected to the master controller
through a wired or wireless electronic connection. The measurements
may be transmitted in real time.
[0064] In block 616, the master controller 416 may control one or
more components in the fuel cell module, including the anode
recycle blower 410 and/or the valves 504a-504c surrounding the
carbon dioxide removal system 502 based on the humidity and
optionally based on the differential pressure measurements. For
example, the master controller may use the humidity and/or
differential pressure measurements to determine the steam
concentration and/or the steam to carbon ratio of the anode recycle
stream. The master controller may compare the steam concentration,
or change in steam concentration, to upper and/or lower thresholds.
The upper and lower thresholds may represent limits for safe
operation of the fuel cell module. Exceeding the limits may result
in damage to the fuel cell module or suboptimal performance.
[0065] If the steam concentration, or change in steam
concentration, crosses a threshold, the master controller may
control the operation of the anode recycle blower, the valves,
and/or other components to change the steam concentration. For
example, the master controller may increase the speed of the anode
recycle blower to increase the steam concentration in the anode
recycle stream. In another example, the master controller may
partially or fully close the valves leading to the carbon dioxide
removal system and partially or fully open the valve in the bypass
conduit 503 so that at least a portion of the anode recycle stream
bypasses the carbon dioxide removal system 502. This may result in
an increase in the concentration of carbon in the anode recycle
stream.
[0066] In this manner, the method 600 allows for real time
measurement of the steam concentration and steam to carbon ratio of
the anode recycle stream in a fuel cell module. The measurements
may then be used to dynamically control the operation of components
in the fuel cell module to change the steam concentration and steam
to carbon ratio of the anode recycle stream. This may allow the
fuel cell module to improve performance and avoid damage if the
steam concentration exceeds operational thresholds (e.g., avoiding
coking of the anode electrodes).
[0067] 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 pumps, turbines, additional gas separation devices,
hydrogen separators which separate hydrogen from the fuel exhaust
and provide hydrogen for external use, fuel processing subsystems,
fuel reformers and or water gas shift reactors, may be added if
desired. Furthermore, it should be understood that any system
element or method steps described in any embodiment and/or
illustrated in any figure may also be used in systems and/or
methods of other suitable embodiments described above even if such
use is not expressly described.
[0068] 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 maybe acquired a 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 as defined by the claims
appended hereto, and their equivalents.
* * * * *