U.S. patent application number 11/099743 was filed with the patent office on 2006-10-12 for pem-sofc hybrid power generation systems.
Invention is credited to Malcolm James Grieve, Kaushik Rajashekara.
Application Number | 20060228593 11/099743 |
Document ID | / |
Family ID | 37083502 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060228593 |
Kind Code |
A1 |
Grieve; Malcolm James ; et
al. |
October 12, 2006 |
PEM-SOFC hybrid power generation systems
Abstract
A hybrid fuel cell system comprising a solid-oxide fuel cell
system, a proton exchange membrane fuel cell system, a hydrocarbon
reformer and a hydrogen separator. A large PEM provides output
power, such as motive power for a vehicle, using hydrogen storage
that may be resupplied from a separate hydrogen refilling station
or from the onboard reformer. The SOFC is preferably small and
provides heat and exhaust water that, when recycled into the
reformer, allow the reformer to operate endothermically without
requiring atmospheric air, thus excluding nitrogen from the
reformate stream. Alternatively, the reformer and SOFC are
stationary at a base station and the PEM is aboard the vehicle. The
SOFC and reformer have sufficient capacity to recharge hydrogen
storage in the vehicle in a relatively short period of time, such
as overnight.
Inventors: |
Grieve; Malcolm James;
(Fairport, NY) ; Rajashekara; Kaushik; (Carmel,
IN) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202
PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
37083502 |
Appl. No.: |
11/099743 |
Filed: |
April 6, 2005 |
Current U.S.
Class: |
429/9 ;
180/65.31; 429/411; 429/425; 429/492; 429/495; 429/515;
429/900 |
Current CPC
Class: |
H01M 8/2495 20130101;
Y02P 70/50 20151101; H01M 8/04156 20130101; Y02E 60/50 20130101;
Y02B 90/10 20130101; Y02T 90/40 20130101; H01M 8/1246 20130101;
H01M 8/0618 20130101; H01M 8/0668 20130101; H01M 16/006 20130101;
H01M 8/04208 20130101; H01M 8/04291 20130101; H01M 2250/10
20130101; H01M 8/04089 20130101; H01M 8/0662 20130101; H01M 2250/20
20130101; Y02E 60/10 20130101 |
Class at
Publication: |
429/009 ;
429/032; 429/019; 429/034; 429/017; 180/065.3 |
International
Class: |
H01M 16/00 20060101
H01M016/00; H01M 8/10 20060101 H01M008/10; H01M 8/12 20060101
H01M008/12; H01M 8/24 20060101 H01M008/24; H01M 8/06 20060101
H01M008/06; H01M 8/04 20060101 H01M008/04; B60L 11/18 20060101
B60L011/18 |
Claims
1. A hybrid fuel cell system, comprising: a) a catalytic
hydrocarbon reformer for reforming hydrocarbon fuel to produce fuel
gas; b) a hydrogen separator for receiving said fuel gas from said
reformer and forming a first fuel stream containing hydrogen and
carbon monoxide and a second fuel stream containing hydrogen; c) a
solid-oxide fuel cell system for receiving said first fuel stream;
and d) a proton exchange membrane fuel cell system for receiving
said second fuel stream.
2. A hybrid fuel cell system in accordance with claim 1 further
comprising: a) a compressor in said second fuel stream for
compressing said second fuel stream; and b) a first hydrogen
storage tank in flow communication with said compressor and said
proton exchange membrane fuel cell system for storing compressed
hydrogen received from said compressor and for supplying hydrogen
as fuel to said proton exchange membrane fuel cell system.
3. A hybrid fuel cell system in accordance with claim 2 wherein
said reformer, said hydrogen separator, said solid-oxide fuel cell
system, said proton exchange membrane fuel cell system, said
compressor, and said hydrogen storage tank are all mounted on one
of a platform selected from the group consisting of a motor
vehicle, a boat, a ship, an aircraft, a spacecraft and a
building.
4. A hybrid fuel cell system in accordance with claim 2 wherein
said reformer, said hydrogen separator, said solid-oxide fuel cell
system, and said first hydrogen storage tank define a stationary
base station, and wherein said proton exchange membrane fuel cell
system and a second hydrogen storage tank define a portable station
mounted on one of a portable platform selected from the group
consisting of a motor vehicle, a boat, a ship, an aircraft and a
spacecraft.
5. A hybrid fuel cell system in accordance with claim 1 further
comprising a first electrical storage device for receiving
electrical power from said solid-oxide fuel cell system and a
second electrical storage device for receiving electrical power
from said proton exchange membrane fuel cell system.
6. A hybrid fuel cell system in accordance with claim 5 wherein
said first electrical storage device has a voltage capacity of less
than 50 volts and wherein said second electrical storage device has
a voltage capacity greater than 50 volts.
7. A hybrid fuel cell system in accordance with claim 6 further
comprising a bi-directional DC/DC converter connected between said
first and second electrical storage devices.
8. A hybrid fuel cell system in accordance with claim 1 further
comprising a first stream of anode effluent from said solid-oxide
fuel cell system directed into an inlet of said reformer such that
said reforming proceeds endothermically.
9. A hybrid fuel cell system in accordance with claim 1 further
comprising a combustor for receiving a second stream of anode
effluent from said solid-oxide fuel cell system and combusting said
second stream to produce heat.
10. A hybrid fuel cell system in accordance with claim 1 wherein
the electrical output capacity of said solid-oxide fuel cell system
is less than the electrical output capacity of said proton exchange
membrane fuel cell system.
11. A hybrid fuel cell system in accordance with claim 10 wherein a
ratio of electrical output capacity of said solid-oxide fuel cell
system to the electrical output capacity of said proton exchange
membrane fuel cell system is between about 1:1 and about 1:100.
12. A method for producing electricity, comprising the steps of: a)
providing a hybrid fuel cell system including a catalytic
hydrocarbon reformer, a hydrogen separator, a solid-oxide fuel cell
system, and a proton exchange membrane fuel cell system; b)
producing reformate fuel gas in said reformer; c) separating said
reformate fuel gas in said hydrogen separator into a first stream
containing hydrogen and carbon monoxide and a second stream
containing hydrogen; d) directing said first stream into a SOFC
fuel cell of said solid-oxide fuel cell system to produce a first
electrical output and an anode exhaust stream; and e) directing
said second stream into said PEM fuel cell of a proton exchange
membrane fuel cell system to produce a second electrical output and
a cathode exhaust stream.
13. A method in accordance with claim 12 wherein said separating
step is carried out by a separating apparatus selected from the
group consisting of palladium membrane separator and pressure swing
adsorption separator.
14. A method in accordance with claim 12 comprising the further
steps of: a) recovering water from said cathode exhaust stream; and
b) supplying said recovered water to said hydrocarbon reformer to
assist in endothermic hydrocarbon reforming therein.
15. A method in accordance with claim 12 comprising the further
step of directing at least a portion of said anode exhaust stream
to an inlet of said hydrocarbon reformer.
16. A vehicle comprising a hybrid fuel cell system including a
catalytic hydrocarbon reformer for reforming hydrocarbon fuel to
produce fuel gas, a hydrogen separator for receiving said fuel gas
from said reformer and forming a first fuel stream containing
hydrogen and carbon monoxide and a second fuel stream containing
hydrogen, a solid-oxide fuel cell system for receiving said first
fuel stream and thereby producing a first electricity stream, and a
proton exchange membrane fuel cell system for receiving said second
fuel stream.
17. A vehicle in accordance with claim 16 wherein said hybrid fuel
cell system further comprises a first electrical storage device for
receiving said first electricity stream and a second electrical
storage device for receiving said second electricity stream,
wherein said first electrical storage device has a voltage capacity
of less than 50 volts and wherein said second storage battery has a
voltage capacity greater than 50 volts.
18. A vehicle in accordance with claim 17 wherein said first
electrical storage device supplies power to vehicle accessories and
wherein said second electrical storage device supplies power to at
least one electric drive motor for motivating said vehicle.
Description
TECHNICAL FIELD
[0001] The present invention relates to fuel cells; more
particularly, to solid-oxide fuel cells and proton exchange
membrane fuel cells; and most particularly, to a hybrid system
comprising a solid oxide fuel cell system and a proton exchange
membrane fuel cell system sharing a common hydrocarbon fuel
reformer.
BACKGROUND OF THE INVENTION
[0002] Fuel cells for combining hydrogen and oxygen to produce
electricity are well known. A first known class of fuel cells
includes a solid-oxide electrolyte layer through which oxygen ions
migrate from a cathode to combine with hydrogen, forming water at
the anode; such fuel cells are referred to in the art as
"solid-oxide" fuel cells (referred to herein as SOFC). A second
known class of fuel cells includes a membrane through which
hydrogen ions (protons) migrate from an anode to combine with
oxygen, forming water at the cathode; such fuel cells are referred
to in the art as proton exchange membrane fuel cells (referred to
herein as PEM). PEM are also known as polymer electrolyte membrane
fuel cells. In both classes of fuel cells, electrons flow through
an external circuit between the electrodes, doing electrical work
in a load in the circuit.
[0003] In the prior art, an SOFC is readily fueled by "reformate"
gas, which is the effluent from a catalytic hydrocarbon oxidizing
reformer, also referred to herein as "fuel gas". Reformate
typically includes amounts of carbon monoxide (CO) as fuel in
addition to molecular hydrogen. The reforming operation and the
fuel cell operation may be considered as first and second oxidative
steps of the hydrocarbon, resulting ultimately in water and carbon
dioxide. Both reactions are exothermic, and both are preferably
carried out at relatively high temperatures, for example, in the
range of 700.degree. C. to 1000.degree. C. An SOFC can use fuel gas
containing CO with the H.sub.2, the CO being oxidized to CO.sub.2,
whereas a PEM cannot oxidize CO; in fact, CO is a poison to the
catalysts in the PEM stack. Thus CO must be removed from a
reformate stream for PEM use (to near zero levels).
[0004] PEM and SOFC systems are being developed in the fuel cell
art for use in transportation applications, for both primary motive
power and for on-board power generation, as well as for stationary
applications such as building heating and water heating. A PEM
operates at about 100.degree. C. and has a very short start-up
period. The waste heat from a PEM is not of high quality because of
the relatively low operating temperature. Conversely, an SOFC
operates at about 800.degree. C. and has a relatively long start-up
period, but the waste heat from an SOFC is of higher quality
because of the higher operating temperature. Both SOFC and PEM
systems need about 10% of their power capability to power the
balance of plant loads, thus affecting their net electrical
capabilities.
[0005] What is needed in the art is a means for combining the
advantages and minimizing the drawbacks of an SOFC and a PEM in an
integrated system.
[0006] It is a principal object of the present invention to
integrate an SOFC system and a PEM system as a novel hybrid system,
and to fuel both from a common hydrocarbon reformer.
SUMMARY OF THE INVENTION
[0007] Briefly described, a hybrid fuel cell system in accordance
with the invention comprises a solid-oxide fuel cell system and a
proton exchange membrane fuel cell system. Preferably, both fuel
cell systems derive their fuel from a common catalytic hydrocarbon
reformer. The reformer is sized for a greater output than is
required by the SOFC alone, the excess capacity being available to
fuel the PEM. Recycling the high-temperature anode effluent of the
SOFC through the reformer provides both heat and water, enabling
the reformer to operate endothermically without requiring
atmospheric air, thus excluding nitrogen from the reformate stream.
This is a much more efficient way to provide a high-quality
hydrogen stream for the PEM than by using treated exothermic
reformate in the PEM as in the prior art.
[0008] In a first embodiment, a relatively large PEM provides the
motive power for a vehicle, using hydrogen stored on board the
vehicle. The hydrogen storage may be resupplied from a separate
hydrogen refilling station or from the onboard reformer and SOFC.
The SOFC is relatively small and provides sufficient heat and
exhaust water for recycle into the reformer that the reformer
operates endothermically to decompose the water and fuel without
atmospheric oxygen; thus, the reformate contains no nitrogen or
nitrogen oxides.
[0009] A second embodiment is similar to the first embodiment,
except that the SOFC is stationary at a base station and the PEM is
aboard a vehicle. The SOFC and reformer have sufficient capacity to
recharge the hydrogen storage in the vehicle in a relatively short
period of time, such as overnight. The SOFC also may be large
enough to provide electricity and air/water heating for a building,
such as a dwelling, as well as for supplying hydrogen to the PEM
system and charging batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0011] FIG. 1 is a schematic diagram of a first embodiment of a
hybrid reformer/SOFC/PEM system suitable for use on a PEM-powered
vehicle wherein both the SOFC and the PEM are onboard the vehicle;
and
[0012] FIG. 2 is a schematic diagram of a second embodiment of a
hybrid reformer/SOFC/PEM system wherein the SOFC is a stationary
base station and the PEM is disposed in a vehicle that docks at the
base station.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring to FIG. 1, a first embodiment 100 of a hybrid fuel
cell system in accordance with the invention comprises a
solid-oxide fuel cell system 200 and a proton exchange membrane
fuel cell system 300 supplied jointly by a catalytic hydrocarbon
reformer 400. System 100 is useful for generating electricity,
heat, and a by-product of pure hydrogen as described below. Both
SOFC system 200 and PEM system 300 are preferably as are well-known
in the prior art. Novelty in the present invention lies not in the
fuel cell systems themselves but rather in combining them to
provide an efficient, low-cost hybrid fuel cell system that
efficiently provides clean hydrogen fuel for powering the PEM.
[0014] SOFC 200 comprises an anode 200a and a cathode 200b that are
defined by a stack of a plurality of individual fuel cell elements,
for example, 60 SOFC fuel cell elements, in known fashion. Other
necessary balance of plant components such as heat exchangers,
manifolding, insulation, sensors and actuators etc., are not shown.
PEM 300 similarly comprises a stack of PEM fuel cell elements,
including a plurality of paired anodes 300a and cathodes 300b
(again, balance of plant components are not shown). A prior art
hydrogen membrane separator 500 is provided for removing CO from
the reformate fuel stream leading to the PEM, and a prior art post
combustor 600 is provided for burning exhaust fuel from the SOFC. A
hydrogen storage tank 700 is provided, along with a compressor 800.
Electrical storage devices (rechargeable batteries, capacitors or a
combination) 900, 901 receive the electrical output of the PEM and
SOFC, respectively and provide electrical power 304 to an
application 152 at high voltage levels and to an application 153 at
low voltage levels. A DC/DC converter 910 allows the bi-directional
conversion of power between the two voltages levels.
[0015] In first embodiment 100, SOFC 200 is preferably a relatively
small unit having, for example, about 5 kW electrical output
capacity or less, and PEM 300 is a relatively large unit having,
for example, about 30 kW electrical output capacity or greater.
System 100 may be considered, for example, an "extended range" PEM
unit wherein PEM is fueled from storage tank 700 which also may be
refilled "conventionally" from a hydrogen source 702, for example,
a hydrogen filling station (not shown).
[0016] In operation, reformer 400 receives hydrocarbon fuel 402 and
wet, recycled anode effluent 206 from SOFC 200 and catalytically,
and preferably endothermically, reforms fuel 402 into a fuel gas
reformate stream 404 comprising H.sub.2 and CO at an exhaust
temperature typically above about 700.degree. C. Within hydrogen
membrane separator 500, such as a palladium membrane separator or a
pressure swing adsorption (PSA) separator, a first portion 502 of
stream 404 passes through the separator, exiting as a pure hydrogen
stream. First portion 502 is compressed by compressor 800 to
provide a compressed stream 802 of hydrogen for storage in tank
700, either as compressed hydrogen or as a hydride 804, in known
fashion. Tank 700 also may be filled from a hydrogen source 702 as
described above. A metered hydrogen stream 806 is fed to the anode
side 300a of PEM 300, and a metered air stream 305 is fed to the
cathode side 300b of PEM 300, in known fashion. PEM 300 generates
heat 308, electric power 302 and an exhaust stream 306, containing
water, from the cathode side. This water may be condensed and
recirculated into reformer 400 (not shown) to augment endothermic
reforming and enhance hydrogen levels in reformate 404. In hydrogen
separator 500, a second portion 504 of reformate stream 404 sweeps
the rejected CO from the separator and passes into anode side 200a
of SOFC 200 where the H.sub.2 and CO contained therein reacts with
oxygen to produce electricity 208. Spent exhaust 210 and cathode
air 212 pass into combustor 600 wherein they are burned to generate
a high-temperature exhaust 602. This high-temperature exhaust may
be used optionally for driving a turbine 604, and residual thermal
energy 606 may be recovered as a co-product (for example for steam
generation, water heating, space heating etc.). Further, combustor
600 may be configured as a combustor/heat exchanger, and a blower
or compressor 608 may be employed to drive heated air 610 to the
cathode inlet of SOFC 200.
[0017] System 100 may be, for example, a fuel cell system onboard a
platform generally referred to as 150, including a motor vehicle
150a, boat 150b or ship 150c, aircraft 150d, spacecraft 150e, or
building 150f wherein PEM 300 is the high power source, operating
intermittently to supply electrical power 302 to electrical storage
device 900 which feeds power 304 to application 152 which may be
vehicle drives or other primary power consumers. System 100 can,
for example, extend the between-fillings range of an automotive
vehicle 150 by on-board generation of hydrogen 502. SOFC 200 does
the base load, heating, and hydrogen generation and may recharge
the high voltage electrical storage device via the DC/DC converter
910 at a low rate (when the PEM is off). PEM 300 and electrical
storage devices 900 do peak loads. During periods of low power
demand, PEM 300 may be shut down and the hydrogen supply may be
refueled via stream 502, 802. Self-refueling by generating hydrogen
onboard allows a smaller amount of hydrogen to be stored on a
vehicle, because the vehicle range is then largely determined by
the fuel capacity of a conventional hydrocarbon fuel tank (not
shown). However, when the hydrogen storage tank 700 and the
conventional fuel tank are both filled, a vehicle so equipped has a
greater range than when fueled by either one alone.
[0018] Only one reformer 400 is required for both fuel cell systems
200, 300 and it may be relatively small compared to the peak system
power because it may be sized to reflect little more than the
average power of the system. The reformer is sized for the SOFC
system plus an amount to produce the by-product hydrogen stream 502
to supply the PEM. This is especially attractive for residential
and light duty automotive systems where the average power is much
less than the peak power of the system. Because a PEM fuel cell can
start generating electricity much faster than an SOFC, the PEM 300
can provide initial power for all the accessories of the SOFC until
the SOFC gets up to operating temperature. In addition, the
high-temperature heat from the SOFC and combustor 600 may be used
for cogeneration or for heating purposes and optionally to maintain
the PEM fuel cell at a constant stand-by temperature.
[0019] In a motor vehicle example 150a, a known gasoline/electric
hybrid automobile comprises a low-voltage (14 V) system for
operating auxiliary motors, solenoids, lights, etc. and a
high-voltage (280 V) system for motive power via electric motors.
An internal combustion engine (ICE) starts and runs automatically
to recharge the main operating electrical storage devices as
needed. A hybrid fuel cell system in accordance with the invention
could replace the ICE. The auxiliary systems could run off of
electrical storage devices 901 and the electric drive motors off of
electrical storage devices 900. The SOFC 200 might be sized, for
example, to generate 2.0 kW @ 14 V, and the PEM sized to generate
60 kW @ 280 V, giving a power ratio of about 1:30 for SOFC:PEM.
[0020] The bi-directional DC/DC converter allows the vehicle to be
run very efficiently on power generated solely by the SOFC, with
the PEM powered down, at low speed driving such as in traffic,
wherein the output of the SOFC can be up-converted continuously
from high voltage electrical storage devices 901 to low voltage
electrical storage devices 900.
[0021] Bi-directional conversion is also very useful in starting
the vehicle after a prolonged shutdown, such as overnight, in cold
weather. The PEM can start quickly from its hydrogen storage tank
and down-convert power to help battery 901 operate the accessories
and get the SOFC running.
[0022] The low voltage system may move up to 42 V for higher end
vehicles in the future. One of the decision points for whether to
move to 42 V is the use of electric air-conditioning via the
lower-voltage storage device circuit. All other motors and
solenoids, for cooling fans, blowers, door locks, and the like, as
well as new functions such as drive-by-wire, brake-by-wire, and
steer-by-wire benefit in weight and efficiency from running at
higher voltage. Thus, a full-function luxury vehicle might generate
10 kW with an SOFC at 42 V, and 120 kW with a PEM at 420 V, giving
a power ratio of about 1:12 for SOFC:PEM.
[0023] SOFC:PEM power ratios between about 1:1 and about 1:100 are
most useful for applications of hybrid fuel cell systems in
accordance with the invention.
[0024] Referring to FIG. 2, a second embodiment 100' of a hybrid
fuel cell system in accordance with the invention is similar in
layout to first embodiment 100. However, SOFC 200, reformer 400,
hydrogen membrane separator 500, combustor 600, compressor 800, and
storage tank 700 together define a stationary base station 10; and
PEM 300, battery 900 and an onboard storage tank 806 define a
portable station 20. Preferably, SOFC 200 again is sized to have
relatively low electrical capacity, for example, 5 kW, and PEM 300
is sized to have relatively high capacity, for example 30 kW. The
difference from embodiment 100 is that the SOFC base station 10 is
carried on a stationary platform such as, for example, a residence
or place of business 12, whereas PEM 300 is carried aboard a
portable platform such as 150a, 150b, 150c, 150d and 150e. Thus,
base station 10 exists primarily as a source of pure hydrogen for
refilling a portable fuel tank 704 with onboard hydrogen 806 from
storage tank 700 via a coupling 706 (base station 10 and portable
station 20 being separable and joinable along line 701) during
periods when the portable platform is available to the base
station, for example, at nights or on weekends. Of course, portable
fuel tank 704 may also be refueled as in embodiment 100 from a
remote filling station 702. High grade waste heat from the SOFC may
be used for space heating, water heating, pool heating, and the
like. Because the PEMs in either of embodiments 100, 100' may be
refueled from either reformer 400 or from a remote hydrogen source
702, these hybrid systems are not dependent upon the availability
of a hydrogen-delivery infrastructure of filling stations, allowing
a gradual transition to such an evolving infrastructure while
operating on conventional hydrocarbon fuels via the reformer.
[0025] A hybrid fuel cell system in accordance with the invention
has several advantages over either an SOFC system or a PEM system
by itself.
[0026] a) The SOFC and PEM may be sized to obtain the best overall
efficiency based on their joint operation.
[0027] b) Only one reformer is required for both fuel cell
systems.
[0028] c) The reformer and hydrogen storage system may be
relatively small, sufficient for short term operation of the PEM at
high power, as would be useful for light duty vehicles or
residential power systems.
[0029] d) The PEM can provide essentially instantaneous power from
its associated battery; can begin producing its own power in a very
short time; and can assist in starting the SOFC, thereby minimizing
the battery storage requirements, which may be satisfied by a
peaking device such as an ultracapacitor, for example.
[0030] e) The SOFC may be allowed to run continuously at low power,
for perhaps several tens of thousands of hours, taking advantage of
the waste heat to drive a highly efficient endothermic reforming
process for the coproduction of H.sub.2 for fueling the PEM and
taking advantage of the lower grade exhaust heat for heating
functions (fitting an efficient cost and function profile for an
SOFC system).
[0031] f) The PEM is provided pure hydrogen for periodic operation
of up to several thousand hours at high power levels, in typical
residential or light duty vehicle applications, addressing the need
for pure hydrogen fuel, and taking advantage of the high power and
low cost potential of a PEM stack (while being realistic about its
durability).
[0032] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
* * * * *