U.S. patent application number 10/804342 was filed with the patent office on 2008-12-18 for turbocompressor impelling fuel recycle in fuel cell power plant.
Invention is credited to Henry G. Johnson, Michael L. Perry.
Application Number | 20080311454 10/804342 |
Document ID | / |
Family ID | 40118681 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080311454 |
Kind Code |
A1 |
Johnson; Henry G. ; et
al. |
December 18, 2008 |
TURBOCOMPRESSOR IMPELLING FUEL RECYCLE IN FUEL CELL POWER PLANT
Abstract
A fuel cell power plant (7, 7a) has a stack (8) fed
hydrogen-rich fuel gas from a source (14, 14a) with fuel recycle
(30, 34) through a compressor (20) of a turbocompressor (19) having
a turbine (17, 17a) driven either by high pressure hydrogen (14) or
air exhaust (41).
Inventors: |
Johnson; Henry G.; (Cobalt,
CT) ; Perry; Michael L.; (S. Glastonbury,
CT) |
Correspondence
Address: |
M. P. Williams
210 Main Street
Manchester
CT
06040
US
|
Family ID: |
40118681 |
Appl. No.: |
10/804342 |
Filed: |
March 19, 2004 |
Current U.S.
Class: |
429/413 ;
429/415 |
Current CPC
Class: |
H01M 8/04097 20130101;
H01M 8/04111 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
429/25 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Claims
1. A fuel cell power plant, comprising: a plurality of fuel cells,
each cell having an anode, a cathode and a proton exchange membrane
disposed between the anode and the cathode; fuel reactant flow
fields on an anode side of said membrane and oxidant reactant flow
fields on a cathode side of said membrane, each of said flow fields
having an inlet and an outlet; a source of hydrogen-rich fuel gas,
said hydrogen-rich fuel gas being applied to said fuel reactant
flow fields; a source providing oxidant reactant gas to said
oxidant flow fields; an impeller connected to at least some of said
fuel flow field outlets for pumping partially depleted fuel to at
least some of said fuel flow field inlets; said impeller comprising
a compressor of a turbocompressor, a turbine of which is driven by
said hydrogen-rich fuel gas.
2-3. (canceled)
4. A fuel cell power plant according to claim 1, wherein: said
impeller is connected between all of said fuel flow field outlets
and all of said fuel flow field inlets.
5-6. (canceled)
7. A fuel cell power plant, comprising: a plurality of fuel cells,
each cell having an anode, a cathode and a proton exchange membrane
disposed between the anode and the cathode; fuel reactant flow
fields on an anode side of said membrane and oxidant reactant flow
fields on a cathode side of said membrane, each of said flow fields
having an inlet and an outlet; a source of hydrogen-rich fuel gas,
said hydrogen-rich fuel gas being applied to said fuel reactant
flow fields; a source providing oxidant reactant gas to said
oxidant flow fields; an impeller connected to at least some of said
fuel flow field outlets for pumping partially depleted fuel to at
least some of said fuel flow field inlets; said impeller comprising
a compressor of a turbocompressor, a turbine of which is driven by
oxidant reactant gas flowing from said oxidant flow field
outlets.
8. A fuel cell power plant according to claim 7, wherein: said
source providing oxidant reactant gas is an air pump.
9. A fuel cell power plant according to claim 7 wherein: said
source providing oxidant reactant gas is an air blower.
10. A fuel cell power plant according to claim 7, wherein: said
impeller is connected between all of said fuel flow field outlets
and all of said fuel flow field inlets.
11. A fuel cell power plant, comprising: a plurality of fuel cells,
each cell having an anode, a cathode and a proton exchange membrane
disposed between the anode and the cathode; fuel reactant flow
fields on an anode side of said membrane and oxidant reactant flow
fields on a cathode side of said membrane, each of said flow fields
having an inlet and an outlet; a source of hydrogen-rich fuel gas,
said hydrogen-rich fuel gas being applied to said fuel reactant
flow fields; a source providing oxidant reactant gas to said
oxidant flow fields; an impeller connected to at least some of said
fuel flow field outlets for pumping partially depleted fuel to at
least some of said fuel flow field inlets; said impeller comprising
a compressor of a turbocompressor, a turbine of which is driven
directly by said hydrogen-rich fuel gas.
Description
TECHNICAL FIELD
[0001] This invention relates to the use of turbocompressors to
impel fuel recycle gas from fuel flow exits to fuel flow inlets,
the turbine being propelled either by (a) high pressure hydrogen
fuel or (b) oxidant flow field exhaust.
BACKGROUND ART
[0002] In order to achieve very high fuel utilization (such as
around 99%) in a fuel cell power plant, it is necessary to reduce
the amount of hydrogen exiting the fuel cell. However, attempts to
reach perfect utilization result in fuel starvation, typically in a
spotty fashion, at various locations within individual cells, and
in various cells. Recycling fuel, from the fuel flow field exits
back to the fuel flow field inlets, allows the overall fuel cell
stack utilization to be greater than the utilization in the fuel
cells. Recycling also tends to cause a more even distribution of
the fuel, and mitigates the effects of inert gases, such as
nitrogen which migrates from the anode through the porous
membrane.
[0003] Recycling the fuel requires a recycle blower or compressor
which must be powered by electricity generated by the fuel cell,
which is referred to as parasitic power. Further, pure hydrogen is
difficult to pump due to its low density, and the pump motor must
be appropriately rated to be non-sparking for safety.
DISCLOSURE OF INVENTION
[0004] Objects of the invention include: elimination of safety
concerns attendant traditional fuel recycle blowers; reducing or
eliminating parasitic power requirements for impelling fuel recycle
gas; a simpler, more reliable fuel recycle impeller; omitting a
powered motor in a recycle impeller; and improved implementation of
fuel cell stack fuel recycle.
[0005] According to the present invention, recycle fuel in a fuel
cell power plant is impelled by a compressor portion of a
turbocompressor, the turbine of which is driven either by (a) high
pressure hydrogen fuel or (b) exhaust from the oxidant flow field
exit.
[0006] In one embodiment, high pressure hydrogen from a tank system
drives the turbine, thereby totally eliminating any parasitic load
on the fuel cell power plant. In other embodiments, air exhaust is
used to operate a fuel recycle turbocompressor. Fuel cell stacks
employing water transport plates operating near atmospheric
pressure have a sufficiently low pressure drop across the oxidant
gas flow fields that the air exhaust has sufficient pressure to
operate the fuel recycle turbocompressor. The invention, however,
may be used in fuel cell stacks which employ pressurized oxidant
gas and having an air exhaust that is higher than ambient pressure.
Not only is this advantageous for driving a recycle
turbocompressor, but it is also advantageous from a water-balance
perspective since pressurized air at any given temperature, carries
less water vapor than ambient air; therefore, less water is lost
from the fuel cell stacks when pressurized air is used. The
invention can also be used with fuel cells operated at higher
temperature. The invention is particularly well suited for use
where oxidant gas stochiometry is well in excess of 100%. Thus,
even if use of the oxidant gas exhaust to drive the bypass fuel
impeller increases air blower parasitic power, it will only
increase very slightly.
[0007] Use of the invention may completely eliminate the need for a
conventional fuel recycle compressor with a drive motor, which is
advantageous with respect to system simplicity and system
safety.
[0008] Other objects, features and advantages of the present
invention will become more apparent in the light of the following
detailed description of exemplary embodiments thereof, as
illustrated in the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a simplified, stylized, schematic illustration of
a fuel cell stack according to the invention having recycle fuel
impelled by a turbocompressor which is driven by high pressure
hydrogen from a tank system.
[0010] FIG. 2 is a simplified, stylized, schematic illustration of
a fuel cell stack according to the invention having recycle fuel
impelled by a turbocompressor which is driven by the oxidant
exhaust of the fuel cell stack.
MODE(S) FOR CARRYING OUT THE INVENTION
[0011] Referring to FIG. 1, a fuel cell power plant 7 according to
the present invention includes a fuel cell stack 8 having a
plurality of fuel cells, each with an anode 9 and a cathode 10. As
is known, the anode is fed hydrogen-rich fuel, such as from a
source of pressurized hydrogen 14.
[0012] According to the invention, the hydrogen 14 is provided by a
conduit 16 to a compressor 17 of a turbocompressor 18, which drives
a shaft 19 which in turn drives a compressor 20. The flow from the
turbine 17 over a conduit 22 passes through a process-controlling
valve 23 which is responsive to a signal on a line 24 from a
controller 25. The correct amount of fuel is thus provided by the
valve 23 over a conduit 28 to the fuel flow fields within the anode
9 of each cell. The partially spent fuel exiting from the anode
flow fields into a conduit 30 may be expelled to ambient (or a
burner, as is known) through a valve 31 in response to a signal on
a line 32 from the controller 25, so as to purge the anode flow
fields in a conventional way, when necessary. The partially
depleted fuel in the conduit 30 is also provided by a conduit 34 to
the inlet of the compressor 20, the outlet of which on a conduit 35
is connected to the inlet conduit 28, thus providing the fuel
recycle function.
[0013] As is known, the cathode side of each fuel cell includes
oxidant reactant gas flow fields which in this embodiment receive
air over a conduit 38 from a pump 39 that is controlled by a signal
40 from the controller 25. The flow of air is also controlled by a
pressure-creating restriction, which may be a valve 42 controlled
by a signal on a line 43 from the controller 25, as is
conventional.
[0014] The stochiometry of oxidant flow can be controlled by the
valve 42 to suit the operational level (power output), which the
controller 25 determines by adjusting the amount of inlet fuel
through the valve 23. The embodiment of FIG. 1 operates passively
in that the more inlet fuel there is, the more bypass fuel there
will be, and the two are tied together by the turbocompressor
18.
[0015] A second embodiment is a fuel cell power plant 7a of the
invention illustrated in FIG. 2, fueled from a source 14a, may not
only be used with a high pressure source of hydrogen, but it also
may be used with hydrogen-rich reformate gas generated by a
reformer, as is known. In the embodiment of FIG. 2, the turbine 17a
of the turbocompressor 18a is driven by the exhaust in the conduit
41 from the cathode oxidant flow fields. In this case, the recycle
rate will be dependent upon the flow of air through the cathode
sides of the cells. As the current density varies, the recycle
rate, and therefore the recycle pressure will also vary. So long as
the components are selected and balanced to provide for a minimally
sufficient fuel recycle flow, the embodiment of FIG. 2 achieves the
advantages of eliminating the electric motor without unduly
affecting parasitic power, even if there is no high pressure
hydrogen source.
[0016] The turbocompressors of the present invention may be
utilized to impel recycle fuel to other than the first stage of
fuel flow fields as is described in copending U.S. patent
application Ser. No. 10/765,735 filed Jan. 27, 2004 and entitled
"Fuel Cell System Having Inlet Fuel to More Than One and/or Recycle
to Less Than All of the Fuel Fields".
[0017] The aforementioned patent applications is incorporated
herein by reference.
[0018] Thus, although the invention has been shown and described
with respect to exemplary embodiments thereof, it should be
understood by those skilled in the art that the foregoing and
various other changes, omissions and additions may be made therein
and thereto, without departing from the spirit and scope of the
invention.
* * * * *