U.S. patent application number 14/886991 was filed with the patent office on 2016-02-11 for sofc system with selective co2 removal.
The applicant listed for this patent is BLOOM ENERGY CORPORATION. Invention is credited to Arne Ballantine, John Finn, Matthias Gottmann, Chockkalingam Karuppaiah, James McElroy, Swaminathan Venkataraman.
Application Number | 20160043413 14/886991 |
Document ID | / |
Family ID | 48172766 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160043413 |
Kind Code |
A1 |
McElroy; James ; et
al. |
February 11, 2016 |
SOFC SYSTEM WITH SELECTIVE CO2 REMOVAL
Abstract
A system and method in which a high temperature fuel cell stack
exhaust stream is recycled back into the fuel inlet stream of the
high temperature fuel cell stack. The recycled stream may be sent
to a carbon dioxide separation device which separates carbon
dioxide from the fuel exhaust stream. The carbon dioxide separation
device may be a carbon dioxide trap, an electrochemical carbon
dioxide separator, or a membrane separator. A water separator may
be used in conjunction with the carbon dioxide separation device or
used separately to continuously remove water from the recycled
stream.
Inventors: |
McElroy; James; (Suffield,
CT) ; Gottmann; Matthias; (Sunnyvale, CA) ;
Karuppaiah; Chockkalingam; (Cupertino, CA) ;
Ballantine; Arne; (Palo Alto, CA) ; Venkataraman;
Swaminathan; (Cupertino, CA) ; Finn; John;
(Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BLOOM ENERGY CORPORATION |
SUNNYVALE |
CA |
US |
|
|
Family ID: |
48172766 |
Appl. No.: |
14/886991 |
Filed: |
October 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13282899 |
Oct 27, 2011 |
9190685 |
|
|
14886991 |
|
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Current U.S.
Class: |
429/412 |
Current CPC
Class: |
H01M 8/04291 20130101;
H01M 8/04097 20130101; H01M 8/04156 20130101; Y02E 60/50 20130101;
H01M 2008/1293 20130101; H01M 8/0668 20130101 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Claims
1. A fuel cell system, comprising: a fuel cell stack; a first
recycling conduit operatively connecting the fuel cell stack to a
carbon dioxide separation device, the first recycling conduit
adapted to recycle a portion of a fuel exhaust stream from the fuel
cell stack to the carbon dioxide separation device, the carbon
separation device adapted to remove carbon dioxide from the
recycled fuel exhaust stream creating a purified recycled fuel
exhaust stream; a second recycling conduit operatively connecting
the carbon dioxide separation device to the fuel inlet conduit, the
second recycling conduit adapted to provide the purified recycled
fuel exhaust stream to the fuel inlet conduit; and an exhaust
conduit operatively connecting the fuel cell stack to a collection
side of the carbon dioxide separation device, the exhaust conduit
adapted to provide a second portion of the fuel exhaust stream from
the fuel cell stack to sweep carbon dioxide from the collection
side of the carbon dioxide separation device.
2. The system of claim 1, further comprising: an air conduit
operatively connected to the exhaust conduit, the air conduit
adapted to provide air into the second portion of the fuel exhaust
stream provided to the collection side of the carbon dioxide
separation device.
3. The system of claim 1, further comprising: a membrane humidifier
operatively connected to the exhaust conduit, the membrane
humidifier adapted to provide water into the second portion of the
fuel exhaust stream provided to the collection side of the carbon
dioxide separation device.
4. The system of claim 1, further comprising: a water separator
operatively connected to the second recycling conduit, the water
separator adapted to remove water from the purified recycled fuel
exhaust stream; a membrane humidifier operatively connected to the
exhaust conduit, the membrane humidifier adapted to provide water
into the second portion of the fuel exhaust stream provided to the
collection side of the carbon dioxide separation device; and a
water conduit operatively connected to the water separator and
membrane humidifier, the water conduit adapted to provide water
from the water separator to the membrane humidifier.
5. The system of claim 1, wherein the carbon dioxide separation
device is a combination carbon dioxide and water separation device
further adapted to remove water from the recycled fuel exhaust
stream, and the fuel cell system further comprising: a membrane
humidifier operatively connected to the exhaust conduit, the
membrane humidifier adapted to provide water into the second
portion of the fuel exhaust stream provided to the collection side
of the carbon dioxide separation device; and a water conduit
operatively connected to the carbon dioxide separation device, the
water conduit adapted to provide water from the carbon dioxide
separation device to the membrane humidifier.
6. The system of claim 1, wherein the fuel cell stack is a solid
oxide fuel cell (SOFC) stack, the fuel cell system further
comprising: an anode tail gas oxidizer operatively connected to the
exhaust conduit, the anode tail gas oxidizer adapted to oxidize
SOFC anode and cathode exhaust prior to providing the second
portion of the fuel exhaust stream from the fuel cell stack to the
collection side of the carbon dioxide separation device.
7. A fuel cell system, comprising: a fuel cell stack; a first
recycling conduit operatively connecting the fuel cell stack to a
carbon dioxide separation device, the first recycling conduit
adapted to recycle a portion of a fuel exhaust stream from the fuel
cell stack to the carbon dioxide separation device, the carbon
separation device adapted to remove carbon dioxide from the
recycled fuel exhaust stream creating a purified recycled fuel
exhaust stream; a second recycling conduit operatively connecting
the carbon dioxide separation device to the fuel inlet conduit, the
second recycling conduit adapted to provide the purified recycled
fuel exhaust stream to the fuel inlet conduit; a humidifier,
adapted to humidify air; and an air conduit operatively coupled to
the humidifier and the carbon dioxide separation device, the air
conduit adapted to provide humid air to a collection side of the
carbon dioxide separation device.
8. The system of claim 7, further comprising: a water separator
operatively connected to the second recycling conduit, the water
separator adapted to remove water from the purified recycled fuel
exhaust stream; and a water conduit operatively connected to the
water separator and the humidifier, the water conduit adapted to
provide water from the water separator to the humidifier.
9. The system of claim 7, wherein the carbon dioxide separation
device is a combination carbon dioxide and water separation device
further adapted to remove water from the recycled fuel exhaust
stream, and the fuel cell system further comprising: a water
conduit operatively connected to the carbon dioxide separation
device, the water conduit adapted to provide water from the carbon
dioxide separation device to the humidifier.
10. The system of claim 7, wherein the humidifier is a spray
humidifier.
11. The system of claim 7, wherein the first recycling conduit is
operatively connected to a product side of the carbon separation
device and adapted to provide the fuel exhaust stream to the
product side of the carbon separation device, wherein the second
recycling conduit is operatively connected to the product side of
the carbon separation and adapted to receive purified recycled fuel
exhaust from the product side of the carbon separation device,
wherein the carbon dioxide separation device is adapted to enable
carbon dioxide to diffuse through a separator from the product side
to the collection side of the carbon dioxide separation device, and
wherein the fuel cell stack is a solid oxide fuel cell (SOFC)
stack, the system further comprising: a reactor operatively
connected to the fuel cell stack, the reactor adapted to oxidize a
SOFC fuel exhaust stream using a SOFC air exhaust stream to
generate a reactor exhaust stream; and an exhaust conduit
operatively connected to the reactor and the humidifier, the
exhaust conduit adapted to provide the reactor exhaust stream to
the humidifier.
12. The system of claim 10, wherein the carbon dioxide separation
device is an electrochemical separator or a membrane separator.
13. A fuel cell system, comprising: a fuel cell stack; a first
recycling conduit operatively connecting the fuel cell stack to a
carbon dioxide membrane separator, the first recycling conduit
adapted to recycle a portion of a fuel exhaust stream from the fuel
cell stack to the carbon dioxide membrane separator, the carbon
dioxide membrane comprising a carbon separating membrane containing
a tailored membrane adapted to selectively transport more carbon
dioxide than water from the recycled fuel exhaust, the carbon
dioxide membrane separator thereby adapted to remove carbon dioxide
from the recycled fuel exhaust stream creating a purified recycled
fuel exhaust stream; and a second recycling conduit operatively
connecting the carbon dioxide membrane separator to the fuel inlet
conduit, the second recycling conduit adapted to provide the
purified recycled fuel exhaust stream to the fuel inlet
conduit.
14. The system of claim 13, wherein the tailored membrane comprises
a polytetrafluoroethylene membrane.
15. The system of claim 13, further comprising a water separator
operatively connected to the second recycling conduit, the water
separator adapted to remove water from the purified recycled fuel
exhaust stream.
16. The system of claim 13, further comprising an air conduit
operatively connected to a collection side of the carbon dioxide
membrane separator, the air conduit adapted to provide purge air to
the collection side of the carbon dioxide membrane separator.
17. The system of claim 13, further comprising: an output conduit
operatively connected to a collection side of the carbon dioxide
membrane separator; and a vacuum pump operatively connected to the
output conduit, the vacuum pump adapted to pull carbon dioxide from
the collection side of the carbon dioxide membrane separator via
the output conduit.
18. A fuel cell system, comprising: a fuel cell stack; a first
recycling conduit operatively connecting the fuel cell stack to a
water separator, the first recycling conduit adapted to recycle a
portion of a fuel exhaust stream from the fuel cell stack to the
water separator, the water separator adapted to remove water from
the recycled fuel exhaust stream creating a drier recycled fuel
exhaust stream before any portion of the fuel exhaust stream is
recycled into the fuel inlet stream; a second recycling conduit
operatively connecting the water separator to the fuel inlet
conduit, the second recycling conduit adapted to provide the drier
recycled fuel exhaust stream to the fuel inlet conduit; and a
discharge conduit operatively connected to the water separator and
adapted to discharge the removed water out of the water separator
and away from the fuel inlet conduit.
19. The system of claim 18, wherein the water separator is a
vertically positioned water membrane separator, wherein the first
recycling conduit is operatively connected to a product side of the
water membrane separator and adapted to provide the fuel exhaust
stream to the product side of the water membrane separator, wherein
the second recycling conduit is operatively connected to the
product side of the water membrane separator and adapted to receive
the drier recycled fuel exhaust from the product side of the water
membrane separator, and wherein the water membrane separator is
adapted to enable water to diffuse through a membrane from the
product side to a collection side of the water membrane separator,
the system further comprising: an air conduit operatively connected
to the collection side of the water membrane separator, the air
conduit adapted to provide air into the collection side of the
water membrane separator; and wherein the discharge conduit is
operatively connected to the collection side of the water separator
and adapted to discharge the removed water and air out of the water
membrane separator and away from the fuel inlet conduit.
Description
BACKGROUND
[0001] The present invention relates generally to the field of fuel
cell systems and more particularly to fuel cell systems integrated
with carbon dioxide removal components.
[0002] Fuel cells are electrochemical devices which can convert
energy stored in fuels to electrical energy 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 reversed
operation, such that oxidized fuel can be reduced back to
unoxidized fuel using electrical energy as an input.
SUMMARY OF THE INVENTION
[0003] The embodiments of the invention provide a system and method
in which a high temperature fuel cell stack exhaust stream is
recycled back into the fuel inlet stream of the high temperature
fuel cell stack. The recycled stream may be sent to a carbon
dioxide separation device which separates carbon dioxide from the
fuel exhaust stream. The carbon dioxide separation device may be a
carbon dioxide trap, an electrochemical carbon dioxide separator,
or a membrane separator. The removal of carbon dioxide from the
recycled anode exhaust increases the efficiency of the high
temperature fuel cell stack. In one aspect of the invention, a
water separator is used in conjunction with the carbon dioxide
separation device to continuously remove water from the recycled
stream. The removal of water from the recycled anode exhaust stream
increases cell performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1A is a schematic of a fuel cell system according to an
embodiment of the present invention.
[0005] FIG. 1B is a schematic of a carbon dioxide separator of FIG.
1A.
[0006] FIG. 2 is a schematic of a carbon dioxide separator capable
of use with the embodiments of the present invention.
[0007] FIGS. 3-15 are schematics of fuel cell systems according to
embodiments of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0008] The embodiments of the invention illustrate how carbon
dioxide separation devices may be used together with a fuel cell
system, such as a solid oxide fuel cell system. Additional
embodiments illustrate how water separation devices may be used
together with a fuel cell system, such as a solid oxide fuel cell
system. Additional embodiments illustrate how carbon dioxide
separation devices and water separation devices may be used
together with a fuel cell system, such as a solid oxide fuel cell
system. It should be noted that other fuel cell systems, such as
molten carbonate systems, may also be used.
[0009] 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.
[0010] 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, a recirculation blower 122,
and a canister carbon dioxide trap 126.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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
blower 122 power or blowing speed. The fuel exhaust stream provided
into conduits 114 and 120 may contain 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.
[0015] 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.
[0016] A recirculation blower 122 is coupled to recycling conduit
120 to provide the recycled fuel exhaust stream from recycling
conduit 120 to a carbon dioxide canister trap 126 via recycling
conduit 124. The recirculation 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 carbon dioxide
canister trap 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
recirculation blower 122 may be used to increase or decrease the
overall recycling rate in system 100.
[0017] The carbon dioxide canister trap 126 may be any type carbon
dioxide trap, such as a consumable carbon dioxide trap. The carbon
dioxide canister trap 126 has no carbon dioxide conduit. Instead,
the carbon dioxide canister trap 126 is physically removed from the
SOFC system by an operator when it fills up with carbon dioxide and
is replaced with a clean trap. The carbon dioxide canister trap 126
may be placed downstream of the recirculation blower 122 and may be
used to extend hotbox life so long as the carbon dioxide canister
trap 126 may be routinely replaced. The carbon dioxide canister
trap 126 removes carbon dioxide from the recycled fuel exhaust
stream. Preferably, the carbon dioxide canister trap 126 removes
substantially all the carbon dioxide from the recycled fuel exhaust
stream. The carbon dioxide canister trap 126 may remove less than
50%, or more than 50%, such as 50% to 60%, 60% to 70%, 70% to 80%,
80% to 90%, or 90% to 100%, such at about 98%, about 99%, or about
99.5% of the carbon dioxide from the recycled fuel exhaust stream.
The carbon dioxide canister trap 126 may require daily change out
of its carbon dioxide gathering components, or other suitable
change out periodicity may be required. Bypass valve and conduit
(not shown) may be provided to allow carbon dioxide canister trap
126 replacement of without power generation interruption.
Preferably the carbon dioxide canister trap 126 is located outside
of the hot box containing the fuel stack 106 for easy access for
service personnel. Carbon dioxide canister trap 126 may be located
in system housing containing the hot box.
[0018] FIG. 1B illustrates a schematic of a carbon dioxide canister
trap 126 of FIG. 1A. The carbon dioxide canister trap 126 is shown
in greater detail in FIG. 1B. The carbon dioxide canister trap 126
may be comprised of two carbon dioxide canister traps 126A and
126B. A valve 125 may be provided to allow the diversion of the
recycled fuel exhaust stream from recycling conduit 124 to one or
both of carbon dioxide canister traps 126A or 126B. Additionally
the valve 125 may prevent the recycled fuel exhaust stream from
flowing to one or both of carbon dioxide canister traps 126A and
126B. Carbon dioxide canister traps 126A and 126B remove carbon
dioxide from the recycled fuel exhaust stream. A valve 127 may be
provided to allow the isolation of carbon dioxide canister traps
126A and 126B from recycling conduit 128. The operation of valve
125 and valve 127 may allow a system operator to pass recycled fuel
exhaust to one, both, or neither of the carbon dioxide canister
traps 126A and 126B at the same time. Valve 125 and valve 127 may
be configured to isolate either carbon dioxide canister trap 126A
and 126B from system 100. In other words, carbon dioxide canister
trap 126B may be isolated and replace while carbon dioxide trap
126A continues to function, and vice versa. This isolation may
facilitate trap change out or other maintenance or regulate the
rate of carbon dioxide removal without power generation
interruption.
[0019] As illustrated in both FIGS. 1A and 1B 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.
[0020] FIG. 2 illustrates an electrochemical carbon dioxide
separator 226 according to another embodiment of the present
invention. The electrochemical carbon dioxide separator 226 is one
type of carbon dioxide separator which may be used with embodiments
of the present invention. The electrochemical carbon dioxide
separator 226 may be a molten carbonate fuel cell operated in
electrolysis mode (i.e., with applied potential).
[0021] The electrochemical carbon dioxide separator 226 may receive
a recycled fuel exhaust stream input via recycling conduit 224. The
recycled fuel exhaust stream may consist of hydrogen, carbon
dioxide, water, and carbon dioxide. The recycling conduit 224 may
be coupled to the anode 206 chamber of the electrochemical carbon
dioxide separator 226. Air is provided to the electrochemical
carbon dioxide separator 226 via air input conduit 202 and used to
purge the electrochemical carbon dioxide separator 226. Electricity
is applied to the electrochemical carbon dioxide separator 226 from
a power supply 204 to operate electrochemical carbon dioxide
separator in electrolyzer mode. In an embodiment, the power supply
204 may comprise the fuel cell stack 106. The current applied
transfers carbonate ions (CO.sub.3.sup.-2) from the anode 206,
through the electrolyte 208, to the cathode 210 according to the
following reaction:
Anode: 2H.sub.2O.fwdarw.2H.sub.2+O.sub.2
O.sub.2+2CO.sub.2+2e.sup.-.fwdarw.CO.sub.3.sup.-2
Cathode: CO.sub.3.sup.%31 2.fwdarw.O.sub.2+2CO.sub.2+2e.sup.-
[0022] The cathode 210 chamber is coupled to a carbon dioxide
conduit 214 and carbon dioxide extracted from the recycled fuel
exhaust stream exits the electrochemical carbon dioxide separator
226 via the carbon dioxide conduit 214.
[0023] The anode 206 chamber is further coupled to a purified
recycled fuel exhaust stream conduit 212. Purified recycled fuel
exhaust stream exiting the carbon dioxide separator anode 206
chamber via the purified anode exhaust conduit 212 contains less
carbon dioxide than the recycled fuel exhaust stream that entered
the carbon dioxide separator 226 via the recycling conduit 224. As
a percentage of overall composition, the purified recycled fuel
exhaust stream in the purified recycled fuel exhaust stream conduit
212 contains a greater percentage of hydrogen than the recycled
fuel exhaust stream entering the carbon dioxide separator 206 via
recycling conduit 224. Preferably, the electrochemical carbon
dioxide separator 226 removes substantially all the carbon dioxide
from the recycled fuel exhaust stream. The electrochemical carbon
dioxide separator 226 may remove less than 50%, or more than 50%,
such as 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, or 90% to
100%, such at about 98%, about 99%, or about 99.5% of the carbon
dioxide from the recycled fuel exhaust stream.
[0024] FIG. 3 illustrates a system 300 according to an embodiment
of the invention. The system 300 is similar to system 100
illustrated in FIG. 1 and contains a number of components in
common. Those components which are common to both systems 100 and
300 are numbered with the same numbers in FIGS. 1 and 3 and will
not be described further.
[0025] One difference between systems 100 and 300 is that system
300 may utilize a carbon dioxide separator 326 as opposed to a
carbon dioxide canister trap 126. The carbon dioxide separator 326
may be any type carbon dioxide separator, such as a carbon dioxide
membrane separator or an electrochemical carbon dioxide separator
as discussed in relation to FIG. 2 above. Another difference
between systems 100 and 300 is that system 300 may utilize ATO
exhaust or SOFC cathode exhaust to sweep the collection side of the
carbon dioxide separator 326 to remove carbon dioxide. An
additional difference between systems 100 and 300 is that system
300 may bias the carbon dioxide separator 326 collection side gas
with water.
[0026] Recycling conduit 124 may be coupled to the carbon dioxide
separator 326. The recycled fuel exhaust stream is input to the
carbon dioxide separator 326 via the recycling conduit 124, and
carbon dioxide is removed from the recycled fuel exhaust stream to
produce a purified (e.g., carbon dioxide depleted) recycled fuel
exhaust stream. The purified recycled fuel exhaust stream exiting
the carbon dioxide separator 326 contains less carbon dioxide than
the recycled fuel exhaust stream that entered the carbon dioxide
separator 326 via the recycling conduit 124. As a percentage of
overall composition the purified recycled fuel exhaust stream
contains a greater percentage of hydrogen than the recycled fuel
exhaust stream entering the carbon dioxide separator 326 via
recycling conduit 124. Preferably, the carbon dioxide separator 326
removes substantially all the carbon dioxide from the recycled fuel
exhaust stream. The carbon dioxide separator 326 may remove less
than 50%, or more than 50%, such as 50% to 60%, 60% to 70%, 70% to
80%, 80% to 90%, or 90% to 100%, such at about 98%, about 99%, or
about 99.5% of the carbon dioxide from the recycled fuel exhaust
stream.
[0027] The carbon dioxide separator 326 is coupled to recycling
conduit 334. The purified recycled fuel exhaust stream, with a
reduced amount of carbon dioxide, is provided back to the fuel
inlet stream by the recycling conduit 334. The recycling of reduced
carbon dioxide fuel exhaust into the fuel inlet increases the
performance of the fuel cell stack 106.
[0028] The efficiency of the carbon dioxide separator 326 at
selecting for carbon dioxide is increased by the biasing of the
collection side of the carbon dioxide separator 326 by adding water
to the collection side of the carbon separator 326.
[0029] In one embodiment, the hot exhaust from the ATO reactor 116
is passed via hot exhaust conduit 118 to a cathode recuperator heat
exchanger 336 where the ATO exhaust exchanges heat with the air
inlet stream provided through air inlet conduit 104. The heat
exchanger helps to raise the temperature of the air in air inlet
conduit 104 and reduces the temperature of the ATO exhaust in
conduit 118 such that it does not damage the membrane humidifier
328.
[0030] In an alternative embodiment, all or a portion of the SOFC
cathode exhaust may be passed directly to the cathode recuperator
heat exchanger 336. A valve 349 may direct cathode exhaust from
conduit 112 to conduit 350. Valve 349 may alternatively be a
splitter (not shown) configured to direct a portion of the cathode
exhaust to conduit 350 and a portion of the cathode exhaust to the
ATO reactor. Valve 351 may be configured to direct the cathode
exhaust received from conduit 350 toward the cathode recuperator
heat exchanger 336 and prevent cathode exhaust from flowing to the
ATO reactor 116. Additionally, valve 351 may be coupled to a
conduit 352 to direct ATO exhaust and/or SOFC cathode exhaust out
of the system 300 as exhaust. The utilization of valves 349 and 351
and conduit 350 may allow either SOFC cathode exhaust or ATO
exhaust, a mixture of both ATO exhaust and SOFC cathode exhaust, or
neither ATO exhaust nor SOFC cathode exhaust to pass to the cathode
recuperator heat exchanger 336.
[0031] From the heat exchanger 336, the ATO exhaust conduit 118 may
be coupled to a membrane humidifier 328. Air is input to the
membrane humidifier 328 via conduit 118. Optionally, air may also
be input to the membrane humidifier as via air conduit 340 coupled
to the membrane humidifier 328. Air conduit 340 may input air
supplied by a blower, fan, or compressor (not shown).
[0032] In operation, the membrane humidifier 328 humidifies an air
or oxidized fuel stream for input into the carbon dioxide separator
326. The membrane humidifier 328 may comprise a polymeric membrane
humidifier.
[0033] Water may be input to the membrane humidifier 328 via a
water conduit 342 as necessary. Water is also may be collected by
the membrane humidifier 328 from the carbon dioxide conduit 332,
which is coupled between the carbon dioxide separator 326 and the
membrane humidifier 332. The water permeates across the membrane
from product side 328B to collection side 328A of membrane
humidifier 328. The water from the conduit 342 is mixed in the
membrane humidifier 328 with the ATO exhaust from conduit 118 and
the now humid air passes to humid air conduit 330.
[0034] Humid air conduit 330 is coupled to the carbon dioxide
separator 326 and the humid air or ATO exhaust is used to bias the
separation of carbon dioxide by the carbon dioxide separator 326.
Where a traditional carbon dioxide separator naturally selects for
water in a reaction, the presence of water on the collection side
of the carbon dioxide separator reduces the selection of water and
increases the efficiency of the carbon dioxide separator to select
for carbon dioxide. In this manner the increased amount of water in
the air entering the collection side of the carbon dioxide
separator 326 biases the carbon dioxide separator 326 to select for
carbon dioxide from the recycled fuel exhaust stream. Preferably,
the humid air or ATO exhaust contains a substantially equal amount
of water as the recycled fuel exhaust stream. The humid air or ATO
exhaust may contain about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%,
or 10% of the water contained in the recycled fuel exhaust stream.
The term "about" provides a variation based on given processes
variables, such as a variation of 10% or less, preferably 5% or
less. The humid air or ATO exhaust may also contain more than 100%
of the water contained in the recycled fuel exhaust stream, such as
about 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, or
200%.
[0035] Thus conduit 330 inputs a humid mix into the collection side
326A and conduit 332 outputs a carbon dioxide and humid mix from
the collection side 326A of carbon dioxide separator 326. Conduit
124 inputs the recycled fuel exhaust into the product side 326B and
conduit 334 outputs carbon dioxide depleted exhaust from the
product side 326B of carbon dioxide separator 326.
[0036] Thus, conduits 340 and/or 118 provide an oxidizer to the
collection side 328A and conduit 330 outputs a humidified oxidizer
from the collections side 328A of membrane humidifier 328. Conduit
332 inputs carbon dioxide and humid mix into product side 328B and
conduit 338 outputs carbon dioxide and from the product side
328B.
[0037] The humid air or ATO exhaust and carbon dioxide mixture
travels from the collection side of the carbon dioxide separator
via carbon dioxide conduit 332 to the membrane humidifier 328. The
membrane humidifier 328 removes a portion of the water from the
humid air mixture, and outputs carbon dioxide and air via output
conduit 338. As discussed above, the water removed from the carbon
dioxide conduit 332 by the membrane humidifier 328 may be used to
humidify air or ATO exhaust entering the membrane humidifier 328.
Thus, system 300 uses ATO exhaust or SOFC cathode exhaust to sweep
the carbon dioxide separator collection side and/or to bias the
collection gas with water.
[0038] FIG. 4 illustrates a system 400 according to an embodiment
of the invention. The system 400 is similar to system 100
illustrated in FIG. 1 and contains a number of components in
common. Those components which are common to both systems 100 and
400 are numbered with the same numbers in FIGS. 1 and 4 and will
not be described further.
[0039] One difference between systems 100 and 400 is that system
400 may utilize a carbon dioxide membrane separator 426 as opposed
to a carbon dioxide canister trap 126.
[0040] A carbon dioxide membrane separator 426 may be a carbon
dioxide membrane separator constructed with tailored membrane
structure 429 to block water transport from the product side 426B
(input side) to the collection side 426A of the carbon dioxide
membrane separator. The tailored membrane structure, (the product
side water block) 429 may be constructed of a material which allows
carbon dioxide to pass, but will not allow water to pass. One such
material which has been found to be effective for product side
water block construction is polytetrafluoroethylene (Teflon.RTM.).
The product side water block impedes water transport via
accumulation or blockage into the purging air of the carbon dioxide
membrane separator. The carbon dioxide membrane separator 426 may
be constructed in a manner similar to an electrochemical carbon
dioxide separator, but does not require the input of electrical
current to operate.
[0041] Recycling conduit 124 may be coupled to the carbon dioxide
membrane separator 426. The recycled fuel exhaust stream enters the
product side 426B of the carbon dioxide membrane separator 426 via
recycling conduit 124. The carbon dioxide membrane separator
removes carbon dioxide from the recycled fuel exhaust stream. As
previously discussed, the product side water block 429 of the
carbon dioxide membrane separator impedes the transport of water,
so only carbon dioxide is collected by the carbon dioxide membrane
separator 426 on the collection side 426A. Preferably, the carbon
dioxide membrane separator 426 removes substantially all the carbon
dioxide from the recycled fuel exhaust stream. The carbon dioxide
membrane separator 426 may remove less than 50% or greater than
50%, such as 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, or 90%
to 100%, such as about 98%, about 99%, or about 99.5% of the carbon
dioxide from the recycled fuel exhaust stream.
[0042] The purified recycled fuel exhaust stream exiting the
collection side 426A of the carbon dioxide membrane separator 426
contains less carbon dioxide than the recycled fuel exhaust stream
that entered the product side 426B of the carbon dioxide separator
426 via the recycling conduit 124. As a percentage of overall
composition the purified recycled fuel exhaust stream contains a
greater percentage of hydrogen than the recycled fuel exhaust
stream entering the carbon dioxide separator 426 via recycling
conduit 124.
[0043] The product side 426B of the carbon dioxide membrane
separator 426 is coupled to recycling conduit 434. The purified
recycled fuel exhaust stream, with a reduced amount of carbon
dioxide, is provided back to the fuel inlet stream by the recycling
conduit 434. The recycling of reduced carbon dioxide fuel exhaust
into the fuel inlet increases the performance of the fuel cell
stack 106.
[0044] Purge air is provided to the collection side 426A of the
carbon dioxide membrane separator 426 via air conduit 430 which is
operatively coupled to the collection side 426A of the carbon
dioxide membrane separator 426. Purge air removes carbon dioxide
from the collection side 426A of the carbon dioxide membrane
separator 426. The carbon dioxide membrane separator 426 is
operatively coupled to output conduit 432 and the air and carbon
dioxide mixture flows from the collection side 426A of the carbon
dioxide membrane separator 426 to the output conduit 432.
[0045] FIG. 5 illustrates a system 500 according to an embodiment
of the invention. The system 500 is similar to system 100
illustrated in FIG. 1 and contains a number of components in
common. Those components which are common to both systems 100 and
500 are numbered with the same numbers in FIGS. 1 and 5 and will
not be described further.
[0046] One difference between systems 500 and 100 is that system
500 utilizes a water separator 531 in series with the carbon
dioxide canister trap 126. The utilization of the water separator
531 allows water to be removed from the portion of the recycled
fuel exhaust stream recycled to the fuel cell stack 106. The
removal of water from the recycled fuel exhaust stream optimizes
the steam to carbon ratio and increases cell performance.
[0047] A purified recycled fuel exhaust stream, containing less
carbon dioxide, exits the carbon dioxide canister trap 126 via
recycling conduit 528 and passes to a water separator 531. The
water separator 531 may be any type water separator, such as a
water condenser separator where steam is cooled to liquid water,
which settles to the bottom of the separator while remaining gases
(e.g., carbon monoxide, hydrogen, etc) exit via recycling conduit
534. The water separator 531 continuously removes water from the
purified recycled fuel exhaust stream entering via recycling
conduit 528. A drain in the water separator 531 may provide the
collected water to water conduit 533. Preferably the water
separator 531 removes substantially 50% of the water from the
purified recycled fuel exhaust stream. The water separator 530 may
remove less than 50%, such as about 50%-40%, 40%-30%, 30%-20%,
20%-10%, 10%-1%, 5%, 0.99%, 0.01%, or 0.001% of the water from the
purified recycled fuel exhaust stream.
[0048] The purified recycled fuel exhaust stream exiting the water
separator 531 contains less water than the purified recycled fuel
exhaust stream that entered the water separator 531 via recycling
conduit 528. Compared to the fuel exhaust stream originally exiting
the fuel cell stack 106 via fuel exhaust conduit 110, the purified
recycled fuel exhaust stream exiting the water separator 531 via
recycling conduit 534 contains less water and less carbon dioxide
overall. The removal of carbon dioxide and water results in the
purified recycled fuel exhaust stream in recycling conduit 534
having an increased proportion of both hydrogen and carbon monoxide
as a percentage of volume when compared to the fuel exhaust stream
originally exiting the fuel cell stack 106 via the fuel exhaust
conduit 110.
[0049] The recycled fuel exhaust stream exits the water separator
531 via recycling conduit 534 and the purified recycled fuel
exhaust stream is provided back to the fuel inlet stream by the
recycling conduit 534. The recycling of reduced carbon dioxide fuel
exhaust into the fuel inlet increases the performance of the fuel
cell stack 106 and the reduction of water increases cell
performance.
[0050] FIG. 6 illustrates a system 600 according to an embodiment
of the invention. The system 600 is similar to system 500
illustrated in FIG. 5 and contains a number of components in
common. Those components which are common to both systems 500 and
600 are numbered with the same numbers in FIGS. 5 and 6 and will
not be described further.
[0051] One difference between systems 600 and 500 is that system
600 utilizes a combination carbon dioxide canister trap and water
separator device 626 rather than only a carbon dioxide canister
trap 126 and independent water separator 531. The combination
carbon dioxide canister trap and water separator device 626 may be
an integrated carbon dioxide trap and water separator. The
combination carbon dioxide canister trap and water separator device
626 functions in a similar manner to produce a purified recycled
fuel exhaust stream containing less carbon dioxide and less water
to recycle to the fuel cell stack 106, the difference being the
carbon dioxide and water are removed at the same time. The
combination carbon dioxide canister trap and water separator device
626 continuously removes carbon dioxide and water from the recycled
fuel exhaust stream. A drain on the combination carbon dioxide
canister trap and water separator device 626 may provide the
collected water to water conduit 633. The carbon dioxide canister
trap and water separator device 626 may remove carbon dioxide and
water in the same volumes and ratios as discussed above in relation
to system 500.
[0052] The combination carbon dioxide canister trap and water
separator device 626 receives the recycled fuel exhaust stream via
recycling conduit 124. The combination carbon dioxide canister trap
and water separator device 626 removes carbon dioxide and water
from the recycled fuel exhaust stream to produce a purified
recycled fuel exhaust stream. The purified recycled fuel exhaust
stream is passed from the combination carbon dioxide canister trap
and water separator device 626 to recycling conduit 634.
[0053] The purified recycled fuel exhaust stream exiting the
combination carbon dioxide canister trap and water separator device
626 contains less water than the recycled fuel exhaust stream that
entered combination carbon dioxide canister trap and water
separator device 626 via recycling conduit 124. Compared to the
fuel exhaust stream originally exiting the fuel cell stack 106 via
fuel exhaust conduit 110, the purified recycled fuel exhaust stream
exiting the combination carbon dioxide canister trap and water
separator device 626 via recycling conduit 634 contains less water
and less carbon dioxide overall. The removal of carbon dioxide and
water results in the purified recycled fuel exhaust stream in
recycling conduit 634 having an increased proportion of both
hydrogen and carbon monoxide as a percentage of volume when
compared to the fuel exhaust stream originally exiting the fuel
cell stack 106 via the fuel exhaust conduit 110.
[0054] The purified recycled fuel exhaust stream exits the
combination carbon dioxide canister trap and water separator device
626 via recycling conduit 634 and the purified recycled fuel
exhaust stream is provided back to the fuel inlet stream by the
recycling conduit 634. The recycling of reduced carbon dioxide fuel
exhaust into the fuel inlet increases the performance of the fuel
cell stack 106 and the reduction of water increases cell
performance.
[0055] FIG. 7 illustrates a system 700 according to an embodiment
of the invention. The system 700 is similar to system 300
illustrated in FIG. 3 and contains a number of components in
common. Those components which are common to both systems 300 and
700 are numbered with the same numbers in FIGS. 3 and 7 and will
not be described further.
[0056] One difference between systems 300 and 700 is that system
700 utilizes a water separator 731 in series with the carbon
dioxide separator 326. The utilization of the water separator 731
allows water to be removed from the recycled fuel exhaust stream
recycled to the fuel cell stack 106. The removal of water from the
recycled fuel exhaust stream increases cell performance.
[0057] A purified recycled fuel exhaust stream, containing less
carbon dioxide, exits the carbon dioxide separator 326 via
recycling conduit 728 and passes to a water separator 730. The
water separator 731 may be any type water separator, such as a
water condenser separator. The water separator 731 continuously
removes water from the purified recycled fuel exhaust stream
entering via recycling conduit 728.
[0058] A drain on the water separator 731 may provide the collected
water to water conduit 733. Water conduit 733 is operatively
coupled to the product side 328B of the membrane humidifier 328,
and provides water to the membrane humidifier 328. The presence of
water received from the water separator 731 via the water conduit
733 may eliminate the need for water conduit 342 present in system
300.
[0059] The purified recycled fuel exhaust stream exiting the water
separator 731 contains less water than the purified recycled fuel
exhaust stream that entered the water separator 731 via recycling
conduit 728. Compared to the fuel exhaust stream originally exiting
the fuel cell stack 106 via fuel exhaust conduit 110, the purified
recycled fuel exhaust stream exiting the water separator 731 via
recycling conduit 734 contains less water and less carbon dioxide
overall. The removal of carbon dioxide and water results in the
purified recycled fuel exhaust stream in recycling conduit 734
having an increased proportion of both hydrogen and carbon monoxide
as a percentage of volume when compared to the fuel exhaust stream
originally exiting the fuel cell stack 106 via the fuel exhaust
conduit 110.
[0060] The purified recycled fuel exhaust stream exits the water
separator 731 via recycling conduit 734 and the purified recycled
fuel exhaust stream is provided back to the fuel inlet stream by
the recycling conduit 734. The recycling of reduced carbon dioxide
fuel exhaust into the fuel inlet increases the performance of the
fuel cell stack 106 and the reduction of water optimizes the steam
to carbon ratio and increases cell performance.
[0061] FIG. 8 illustrates a system 800 according to an embodiment
of the invention. The system 800 is similar to system 700
illustrated in FIG. 7 and contains a number of components in
common. Those components which are common to both systems 700 and
800 are numbered with the same numbers in FIGS. 7 and 8 and will
not be described further.
[0062] One difference between systems 800 and 700 is that system
800 utilizes a combination carbon dioxide and water separator 826
rather than only a carbon dioxide separator 326 and independent
water separator 731. The combination carbon dioxide and water
separator 826 functions in a similar manner to produce a purified
recycled fuel exhaust stream containing less carbon dioxide and
less water to recycle to the fuel cell stack 106, the difference
being the carbon dioxide and water are removed at the same time.
The combination carbon dioxide and water separator 826 continuously
removes carbon dioxide and water from the recycled fuel exhaust
stream.
[0063] The combination carbon dioxide and water separator 826
receives the recycled fuel exhaust stream via recycling conduit
124. The combination carbon dioxide and water separator 826 removes
carbon dioxide and water from the recycled fuel exhaust stream to
produce a purified recycled fuel exhaust stream. The purified
recycled fuel exhaust stream is passed from combination carbon
dioxide and water separator 826 to recycling conduit 834.
[0064] The purified recycled fuel exhaust stream exiting the
combination carbon dioxide and water separator 826 contains less
water than the recycled fuel exhaust stream that entered the
combination carbon dioxide and water separator 826 via recycling
conduit 124. Compared to the fuel exhaust stream originally exiting
the fuel cell stack 106 via fuel exhaust conduit 110, the purified
recycled fuel exhaust stream exiting the combination carbon dioxide
and water separator 826 via recycling conduit 834 contains less
water and less carbon dioxide overall. The removal of carbon
dioxide and water results in the purified recycled fuel exhaust
stream in recycling conduit 828 having an increased proportion of
both hydrogen and carbon monoxide as a percentage of volume when
compared to the fuel exhaust stream originally exiting the fuel
cell stack 106 via the fuel exhaust conduit 110.
[0065] The purified recycled fuel exhaust stream exits the
combination carbon dioxide and water separator 826 via recycling
conduit 834 and the purified recycled fuel exhaust stream is
provided back to the fuel inlet stream by the recycling conduit
828. The recycling of reduced carbon dioxide fuel exhaust into the
fuel inlet increases the performance of the fuel cell stack 106 and
the reduction of water optimizes the steam to carbon ratio and
increases cell performance.
[0066] The water and carbon dioxide removed from the combination
carbon dioxide and water separator 826 mixes with purge air
received from humid air conduit 330 and exits the combination
carbon dioxide and water separator 826 via carbon dioxide conduit
832. The membrane humidifier 328 removes water from the carbon
dioxide, water, and air mixture received via carbon dioxide conduit
832. The water removed by the membrane humidifier 328 may be used
to humidify the input air to the membrane humidifier 328. In this
manner, the need for water conduit 342 present in system 300 may be
eliminated.
[0067] FIG. 9 illustrates a system 900 according to an embodiment
of the invention. The system 900 is similar to system 400
illustrated in FIG. 4 and contains a number of components in
common. Those components which are common to both systems 400 and
900 are numbered with the same numbers in FIGS. 4 and 9 and will
not be described further.
[0068] One difference between systems 400 and 900 is that system
900 utilizes a water separator 931 in series with the carbon
dioxide membrane separator 426. The utilization of the water
separator 931 allows water to be removed from the portion of the
recycled fuel exhaust stream recycled to the fuel cell stack 106.
The removal of water from the recycled fuel exhaust stream
increases cell performance.
[0069] A purified (e.g., carbon dioxide depleted) recycled fuel
exhaust stream exits the carbon dioxide membrane separator 426 via
recycling conduit 928 and passes to the water separator 931. The
water separator 931 may be any type water separator, such as a
water condenser separator. The water separator 931 continuously
removes water from the recycled fuel exhaust stream entering via
recycling conduit 928. A drain on the water separator 936 may
provide the collected water to water conduit 933.
[0070] The purified recycled fuel exhaust stream exiting the water
separator 931 contains less water than the purified recycled fuel
exhaust stream that entered the water separator 931 via recycling
conduit 928. Compared to the fuel exhaust stream originally exiting
the fuel cell stack 106 via fuel exhaust conduit 110, the purified
recycled fuel exhaust stream exiting the water separator 931 via
recycling conduit 934 contains less water and less carbon dioxide
overall. The removal of carbon dioxide and water results in the
purified recycled fuel exhaust stream in recycling conduit 934
having an increased proportion of both hydrogen and carbon monoxide
as a percentage of volume when compared to the fuel exhaust stream
originally exiting the fuel cell stack 106 via the fuel exhaust
conduit 110.
[0071] The purified recycled fuel exhaust stream exits the water
separator 931 via recycling conduit 934 and the purified recycled
fuel exhaust stream is provided back to the fuel inlet stream by
the recycling conduit 934. The recycling of reduced carbon dioxide
fuel exhaust into the fuel inlet increases the performance of the
fuel cell stack 106 and the reduction of water optimizes the steam
to carbon ratio and increases cell performance.
[0072] In an alternative embodiment, (not shown), a carbon dioxide
membrane separator 926 described in connection with system 900 may
be combined with a water separator 936 in the same housing. In this
manner the separation of carbon dioxide would occur in the same
housing as the separation of water, but the carbon dioxide membrane
separator 926 and water separator 936 would remain separate
apparatuses.
[0073] FIG. 10 illustrates a system 1000 according to an embodiment
of the invention. The system 1000 is similar to system 300
illustrated in FIG. 3 and contains a number of components in
common. Those components which are common to both systems 300 and
1000 are numbered with the same numbers in FIGS. 3 and 10 and will
not be described further.
[0074] One difference between systems 300 and 1000 is that system
1000 utilizes spray humidifier 1028 to bias carbon dioxide
separator 326 by adding water to the collection side 326A of the
carbon dioxide separator 326, rather than the membrane humidifier
328 of system 300. Additionally, in system 1000 the air conduit 118
need not be connected to the spray humidifier 1042.
[0075] The spray humidifier 1028 is used to add water to the air
that will be input to the collection side 326A of the carbon
dioxide separator 326.
[0076] Air is input to the spray humidifier 1028 via air conduit
1038. Water may be input to the spray humidifier 1028 via a water
conduit 1042. Water may also be input to the spray humidifier via
water conduit 1033. Water is sprayed into the air input into the
spray humidifier 1028 and mixes with the air to produce humid air.
The now humid air passes to humid air conduit 330.
[0077] Humid air conduit 330 is coupled to the collection side 326A
of the carbon dioxide separator 326 and the humid air is used to
bias the separation of carbon dioxide by the carbon dioxide
separator 326. Where a traditional carbon dioxide separator
naturally selects for water in a reaction, the presence of water on
the collection side of the carbon separator reduces the selection
of water and increases the efficiency of the carbon dioxide
separator to select for carbon dioxide. In this manner the increase
amount of water in the air entering the carbon dioxide separator
326 biases the collection side 326A of the carbon dioxide separator
326 to select for carbon dioxide from the recycled fuel exhaust
stream.
[0078] The humid air and carbon dioxide mixture travels from the
carbon dioxide separator via carbon dioxide conduit 1032 to a
condenser 1031. The condenser 1031 removes a portion of the water
from the humid air and carbon dioxide mixture, and outputs carbon
dioxide and air via output conduit 1036. The water collected in the
condenser 1031 may be provided to water conduit 1033 and input to
the spray humidifier 1028.
[0079] FIG. 11 illustrates a system 1100 according to an embodiment
of the invention. The system 1100 is similar to system 700
illustrated in FIG. 7 and contains a number of components in
common. Those components which are common to both systems 700 and
1100 are numbered with the same numbers in FIGS. 7 and 11 and will
not be described further.
[0080] One difference between systems 700 and 1100 is that system
1100 utilizes spray humidifier 1028 to bias carbon dioxide
separator 326 by adding water to the collection side of the carbon
dioxide separator 326, rather than the membrane humidifier 328 of
system 700. Additionally, in system 1100 the air conduit 118 need
not be connected to the spray humidifier 1042 and contains two
water separators 731 and 1031. Water separator 731 is located at
the output of the product side 326B of the carbon dioxide separator
326 and water separator 1031 is located at the output of the
collection side 326A of the carbon dioxide separator 326. Thus,
system 1100 is a combination of systems 700 and 1000.
[0081] A drain on the water separator 730 may provide the collected
water to water conduit 733. Water conduit 733 is operatively
coupled to the spray humidifier 1028, and provides water to the
spray humidifier 1028.
[0082] The spray humidifier 1028 is used to add water to the air
that will be input to the collection side of the carbon dioxide
separator 326.
[0083] Air is input to the spray humidifier 1028 via air conduit
1038. Water may be input to the spray humidifier 1028 from the
water separator 731 via water conduit 733. Water may also be input
to the spray humidifier from condenser 1031 via water conduit 1033.
Water is sprayed into the air input into the spray humidifier 1028
and mixes with the air to produce humid air. The now humid air
passes to humid air conduit 330.
[0084] Humid air conduit 330 is coupled to the collection side 326A
of the carbon dioxide separator 326 and the humid air is used to
bias the separation of carbon dioxide by the carbon dioxide
separator 326. Where a traditional carbon dioxide separator
naturally selects for water in a reaction, the presence of water on
the collection side of the carbon separator reduces the selection
of water and increases the efficiency of the carbon dioxide
separator to select for carbon dioxide. In this manner the increase
amount of water in the air entering the collection side 326A of the
carbon dioxide separator 326 biases the carbon dioxide separator
326 to select for carbon dioxide from the recycled fuel exhaust
stream.
[0085] The humid air and carbon dioxide mixture travels from the
carbon dioxide separator via carbon dioxide conduit 1032 to a water
separator, such as a condenser 1031. The condenser 1031 removes a
portion of the water from the humid air and carbon dioxide mixture,
and outputs carbon dioxide and air via output conduit 1036. The
water collected in the condenser 1031 may be provided to water
conduit 1033 and input to the spray humidifier 1028.
[0086] FIG. 12 illustrates a system 1200 according to an embodiment
of the invention. The system 1200 is similar to system 800
illustrated in FIG. 8 and contains a number of components in
common. Those components which are common to both systems 800 and
1200 are numbered with the same numbers in FIGS. 8 and 12 and will
not be described further.
[0087] One difference between systems 800 and 1200 is that system
1200 utilizes spray humidifier 1028 to bias the combination carbon
dioxide and water separator 826 by adding water to the collection
side of the combination carbon dioxide and water separator 826,
rather than utilizing the membrane humidifier 328 of system 800.
Additionally, in system 1200 the air conduit 118 need not be
connected to the spray humidifier 1028. System 1200 is a
combination of systems 800 and 1000 in that it contains the
combination carbon dioxide and water separator 826 and the spray
humidifier 1028.
[0088] The spray humidifier 1028 is used to add water to the air
that will be input to the collection side of the carbon dioxide
separator 826.
[0089] The water and carbon dioxide removed from the combination
carbon dioxide and water separator 826 mixes with purge air
received from humid air conduit 330 and exits the combination
carbon dioxide and water separator 826 via carbon dioxide conduit
1232.
[0090] Air is input to the spray humidifier 1028 via air conduit
1038. Water may be input to the spray humidifier 1028 via a water
conduit 1233. Water is sprayed into the air input into the spray
humidifier 1028 and mixes with the air to produce humid air. The
now humid air passes to humid air conduit 330 to be provided to the
collection side of the carbon dioxide and water separator 826.
[0091] The humid air and carbon dioxide mixture travels from the
combination carbon dioxide and water separator 826 via carbon
dioxide conduit 1232 to a water separator, such as the condenser
1231. The condenser 1231 removes a portion of the water from the
humid air and carbon dioxide mixture, and outputs carbon dioxide
and air via output conduit 1236. The water collected in the
condenser 1231 may be provided to water conduit 1233 and input to
the spray humidifier 1028.
[0092] FIG. 13 illustrates a system 1300 according to an embodiment
of the invention. The system 1300 is similar to system 100
illustrated in FIG. 1 and contains a number of components in
common. Those components which are common to both systems 100 and
1300 are numbered with the same numbers in FIGS. 1 and 13 and will
not be described further.
[0093] One difference between systems 100 and 1300 is that system
1300 may utilize a water separator 1301 as opposed to a carbon
dioxide canister trap 126 or another carbon dioxide separator. The
utilization of the water separator 1301 allows water to be removed
from the portion of the recycled fuel exhaust stream recycled to
the fuel cell stack 106. In system 1300, the recirculation blower
122 is coupled to recycling conduit 120 to provide the recycled
fuel exhaust stream from recycling conduit 120 to a water separator
1301 via recycling conduit 124. Thus, in this embodiment, water
rather than carbon dioxide is removed from the fuel exhaust
stream.
[0094] The water separator 1301 may be any type water separator,
such as an air cooled water condenser separator where steam is
cooled to liquid water, which settles to the bottom of the
separator by gravity, while remaining gases (e.g., carbon monoxide,
carbon dioxide, hydrogen, etc) exit via recycling conduit 1305. The
water separator 1301 continuously removes water from the recycled
fuel exhaust stream entering via recycling conduit 124. A drain in
the water separator 1301 may provide the collected water to water
conduit 1303. Water conduit 1303 may discharge the collected water
away from the fuel inlet stream or additionally out of the system
1300. Preferably the water separator 1301 removes up to 65% of the
water from the recycled fuel exhaust stream. The water separator
1301 may remove less than 65%, such as about 1-50%, 50%-40%,
including 40%-30%, 30%-20%, 20%-10%, or 10%-1% of the water from
the recycled fuel exhaust stream.
[0095] The recycled fuel exhaust stream exiting the water separator
1301 contains less water than the recycled fuel exhaust stream that
entered the water separator 1301 via recycling conduit 124.
Compared to the fuel exhaust stream originally exiting the fuel
cell stack 106 via fuel exhaust conduit 110, the recycled fuel
exhaust stream exiting the water separator 1301 via recycling
conduit 1305 contains less water overall (i.e., is a drier recycled
fuel exhaust stream). The removal of water results in the drier
recycled fuel exhaust stream in recycling conduit 1305 having an
increased proportion of hydrogen, carbon monoxide, and carbon
dioxide as a percentage of volume when compared to the fuel exhaust
stream originally exiting the fuel cell stack 106 via the fuel
exhaust conduit 110.
[0096] The drier recycled fuel exhaust stream exits the water
separator 1301 via recycling conduit 1305 and the drier recycled
fuel exhaust stream is provided back to the fuel inlet stream by
the recycling conduit 1305. The removal of water from the recycled
fuel exhaust stream optimizes the steam to carbon ratio and
increases cell performance, and the recycling of fuel exhaust
containing less water into the fuel inlet increases the performance
of the fuel cell stack 106. SOFC fuel cells using natural gas fuel
produce chemical byproducts of two thirds water and one third
carbon dioxide. These byproducts dilute the fuel to the point that
it is not practical to function with a fuel utilization of greater
than approximately 88% including partial recirculation of the anode
exhaust. Separation and removal of a portion of the water in the
recirculated anode exhaust allows an increase in fuel utilization
to over 89%, such as 90-95%, such as about 95% and a resultant 3 to
4 efficiency points increase. Fuel cells generally degrade in
performance over time and produce more waste heat in the process.
This results in the need to combust less or no fuel for balancing
the heat loss and removal of water and/or carbon dioxide allows a
higher fuel utilization within the active fuel cells. Since both
the product water and the product carbon dioxide cause the same
negative Nernst voltage effect, the inventors realized that water,
being twice the volume of carbon dioxide, would have a bigger
impact in its removal than removing carbon dioxide. Water separated
from the fuel (anode) recirculation loop can allow fuel utilization
to be increased into the mid 90's percentile, e.g., such as 90-95%,
and efficiency gains up to about 4 points, but not exceeding about
64% based on the fuel LHV. Therefore, the water separator in the
anode recycle loop achieves up to about 95% fuel utilization by
increasing the recycle rate from 58% up to about 85% while removing
up to about 65% of the product water when the SOFC system requires
less fuel combustion for heat balance. This is accomplished while
maintaining the single pass fuel utilization at about 75% and the
fuel inlet oxygen to carbon ratio at 2.0.
[0097] In an alternative embodiment, all or a portion of the drier
recycled fuel exhaust stream may be passed to a hydrogen separator
1311. The hydrogen separator 1311 is optional and is preferably
omitted. A valve 1307 may direct all or a portion of the drier
recycled fuel exhaust stream from recycling conduit 1305 into
conduit 1309 and valve 1307 may direct all or a portion of the
drier recycled fuel exhaust stream from recycling conduit 1305 to
conduit 1308. Conduit 1309 may be coupled to air exhaust conduit
112 and may provide the drier recycled fuel exhaust stream to air
exhaust conduit 112 via which the drier recycled fuel exhaust
stream may be provided to the ATO reactor 116.
[0098] Conduit 1308 may be coupled to a hydrogen separator 1311.
Hydrogen separator 1311 may be any type hydrogen separator, such as
a cascaded electrochemical hydrogen pump separation unit which
electrochemically separates hydrogen from the drier recycled fuel
exhaust stream. The hydrogen separator 1311 may separate about 95%,
such as 95% to about 100% of the hydrogen contained in the drier
recycled fuel exhaust stream entering via conduit 1308. The
separated hydrogen may be provided to the fuel inlet stream by
hydrogen conduit 1313. The remaining gases in the drier recycled
fuel exhaust stream may exit the hydrogen separator 1311 via
conduit 1314 which may be coupled to conduit 1309. In this manner
the remaining gases in the drier recycled fuel exhaust stream may
be provided to the ATO reactor 116.
[0099] FIG. 14 illustrates a system 1400 according to an embodiment
of the invention. The system 1400 is a specific embodiment of
system 1300 illustrated in FIG. 13 and contains a number of
components in common. Those components which are common to both
systems 1300 and 1400 are numbered with the same numbers in FIGS.
13 and 14 and will not be described further.
[0100] System 1400 is a specific embodiment of system 1300 in which
a water membrane separator 1402 biased by air is used. The air flow
controlled selective water vapor membrane separator 1402 preferably
removes excess water to maintain the fuel inlet oxygen to carbon
ration at 2.0 and may discharge the water vapor into the
atmosphere. The utilization of the water membrane separator 1402
biased by air allows water to be removed from the portion of the
recycled fuel exhaust stream recycled to the fuel cell stack 106.
The water membrane separator 1402 continuously removes water from
the recycled fuel exhaust stream entering via recycling conduit
124.
[0101] Water membrane separator 1402 may comprise a polymeric
membrane separator. The membrane 1404 of water membrane separator
1402 may be a Nafion.RTM. membrane. For example, one separator made
by Perma Pure, LLC is based on Nafion.RTM. membrane tubes within a
316 stainless steel housing. The Nafion.RTM. is specified by its
manufacturer DuPont to operate up to 190C. When used with gasses as
a dryer, it is specified by Perma Pure to operate at temperatures
up to 150C. A pair of one foot long drying units at about 2.5
inches in diameter operating in a vertical parallel arrangement has
acceptable pressure drop and drying capability. The water membrane
separator 1402 may be oriented in any direction. In a preferred
embodiment the water membrane separator 1402 may be a vertically
positioned tubular membrane separator (i.e., positioned such that
the central axis of the membrane tube is vertical in relation to
the ground). The selective water vapor membrane separator
embodiment has the advantages of being low cost, low parasitic
power, easy to integrate, compatible with carbon dioxide
sequestration, and discharges the water vapor into the atmosphere.
Water may be collected by the water membrane separator 1402 from
recycling conduit 124 on the product side 1402B of the water
membrane separator 1402. Water permeates across the membrane 1404
from the product side 1402B to collection side 1402A of water
membrane separator 1402. The partial pressure of the water in the
product side 1402B of the water membrane separator 1402 drives
diffusion of the water across the membrane 1404 to the collection
side 1402A of the water membrane separator 1402. Preferably the
water membrane separator 1402 removes substantially 50% of the
water from the recycled fuel exhaust stream. The water membrane
separator 1402 may remove up to 65%, such as about 1-50%, 50%-40%,
40%-30%, 30%-20%, 20%-10%, or 10%-1% of the water from the recycled
fuel exhaust stream.
[0102] The drier recycled fuel exhaust stream exiting the water
membrane separator 1402 contains less water than the recycled fuel
exhaust stream that entered the water membrane separator 1402 via
recycling conduit 124. Compared to the fuel exhaust stream
originally exiting the fuel cell stack 106 via fuel exhaust conduit
110, the drier recycled fuel exhaust stream exiting the water
membrane separator 1402 via recycling conduit 1305 contains less
water overall. The removal of water results in the drier recycled
fuel exhaust stream in recycling conduit 1305 having an increased
proportion of hydrogen, carbon monoxide, and carbon dioxide as a
percentage of volume when compared to the fuel exhaust stream
originally exiting the fuel cell stack 106 via the fuel exhaust
conduit 110.
[0103] The drier recycled fuel exhaust stream exits the water
membrane separator 1402 from the product side 1402B via recycling
conduit 1305 and the drier recycled fuel exhaust stream is provided
back to the fuel inlet stream by the recycling conduit 1305.
[0104] Air may be provided to the collection side 1402A of the
water membrane separator 1402 via air conduit 1408 which is
operatively coupled to the collection side 1402A of the water
membrane separator 1402. An air blower (not shown) may be used to
blow air into conduit 1408. The air removes water from the
collection side 1402A of the water membrane separator 1402. The
water membrane separator 1402 is operatively coupled to discharge
conduit 1410 and the air and water mixture flows from the
collection side 1402A of the water membrane separator 1402 to the
discharge conduit 1410. Discharge conduit 1410 may discharge the
air and evaporated water mixture away from the fuel inlet stream or
additionally out of the system 1400, for example into the
atmosphere as humid air or water vapor and air. The addition of air
to the collection side 1402A of the water membrane separator 1402
biases the water membrane separator 1402 such that the partial
pressure of water on the collection side 1402A is less than the
partial pressure of water on the product side 1402B. The difference
in partial pressure drives the diffusion of water across the
membrane 1404 of the water membrane separator 1402.
[0105] FIGS. 13 and 14 illustrate embodiments of fuel cell systems
in which all the fuel exhaust is recycled into a water separator
before any fuel exhaust is provided into the fuel inlet stream. The
overall advantages of the embodiments of FIGS. 13 and 14 are to
increase the overall average efficiency of the SOFC system by up to
4 percentage points and extending the SOFC system lifetime at any
specific voltage level. Both embodiments have the advantage of
being able to use commercially available components to fashion the
system. The specific advantages of each embodiment are: the water
condenser separator 1302 embodiment of FIG. 13 has the advantages
of being low cost, low parasitic power, easy to integrate, and
compatible with carbon dioxide sequestration; and the selective
water vapor membrane separator 1402 embodiment of FIG. 14 has the
advantages of being low cost, low parasitic power, easy to
integrate, compatible with carbon dioxide sequestration, and
discharges the water vapor into the atmosphere.
[0106] FIG. 15 illustrates a system 1500 according to an embodiment
of the invention. The system 1500 is similar to system 400
illustrated in FIG. 4 and contains a number of components in
common. Those components which are common to both systems 400 and
1500 are numbered with the same numbers in FIGS. 4 and 15 and will
not be described further.
[0107] One difference between systems 400 and 1500 is that system
1500 utilizes a vacuum pump 1504 to remove separated carbon dioxide
from the collection side 426A of the carbon dioxide membrane
separator 426 rather than purge air. The utilization of a vacuum
pump 1504 may be more effective than purge air, and the parasitic
power draw of the vacuum pump 1504 may not be so large as to
overcome the benefit of using the vacuum pump 1504. An output
conduit 1502 may be operatively connected to the collection side
426A of the carbon dioxide membrane separator 426. The output
conduit 1502 may be operatively connected to the vacuum pump 1504.
An output conduit 1506 may be coupled to the vacuum pump 1504. In
operation, the vacuum pump 1504 may pull carbon dioxide from the
collection side 426A of the carbon dioxide membrane separator 426
via output conduit 1502.
[0108] In an alternative embodiment (not shown) nitrogen rather
than air may be used as the purge gas for carbon dioxide
separators. In another alternative embodiment (not shown) the
membrane of a carbon dioxide separator may include amine.
[0109] 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.
[0110] 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.
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