Title of Invention	"A FUEL CELL SYSTEM AND A METHOD OF OPERATING THE SAME"
Abstract	A fuel cell System is provided that is capable of operating at high temperatures and near-ambient pressure with partial humidification of air supplied to the fuel cell stack. The fuel cells of the stack incorporate gas diffusion barrier layers at the cathode side thereof. The System includes a cooling loop for circulating a liquid coolant through the stack. In some embodiments, an incoming air stream is partially humidified with water vapor transferred from a cathode exhaust stream in a gas-exchange humidifier or enthalpy wheel. In other embodiments, a cathode recycle is employed to partially humidify the incoming air. The humidity of the air and cathode exhaust streams is maintained below a stack saturation point. Methods of operating the fuel cell System are also provided

Title of Invention

"A FUEL CELL SYSTEM AND A METHOD OF OPERATING THE SAME"

Abstract

A fuel cell System is provided that is capable of operating at high temperatures and near-ambient pressure with partial humidification of air supplied to the fuel cell stack. The fuel cells of the stack incorporate gas diffusion barrier layers at the cathode side thereof. The System includes a cooling loop for circulating a liquid coolant through the stack. In some embodiments, an incoming air stream is partially humidified with water vapor transferred from a cathode exhaust stream in a gas-exchange humidifier or enthalpy wheel. In other embodiments, a cathode recycle is employed to partially humidify the incoming air. The humidity of the air and cathode exhaust streams is maintained below a stack saturation point. Methods of operating the fuel cell System are also provided

Full Text	AMBIENT PRESSURE FUEL CELL SYSTEM EMPLOYING PARTIAL AIR HUMIDIFICATION CROSS-REFERENCE TO RELATED APPLICATION 5 This application claims the benefit of U.S. Provisional Patent Application No. 60/451,943 filed March 3, 2003, where this provisional application is incorporated herein by reference in its entirety. BACKGROUND OF THE INVENTION Field of the Invention 10 The present invention relates to fuel cell systems operating at or near ambient pressure. In particular, the present invention relates to fuel cell systems operating at or near ambient pressure with partial air humidification, and methods of operating such systems. Description of the Related Art 15 Fuel cells are known in the art. Fuel cells electrochemically react a fuel stream comprising hydrogen and an oxidant stream comprising oxygen to generate an electric current. Fuel cell electric power plants have been employed in transportation, portable and stationary applications. Water management issues are critical in polymer electrolyte membrane 20 (PEM) fuel cell operation. Humidification of the membrane is required to maintain optimal performance. As the water content of the membrane falls it loses the ability to transport protons, its electrical resistance increases, and fuel cell performance decreases and membrane failure may occur. To ensure adequate humidification of the membrane the reactant streams supplied to the fuel cell stack are typically humidified. At the same time, 1 WO 2004/079269 PCT/CA2004/000320 In other embodiments, the present fuel cell system comprises: a fuel cell stack with fuel cells having a cathode gas diffusion barrier means; a fuel system for supplying a fuel to the stack; supply means for supplying air to the stack at near-ambient pressure; humidification means for transferring water vapor from the cathode exhaust 5 stream with the air supplied to the stack; and, a coolant loop for circulating a liquid coolant through the stack. The present fuel cell system may be part of a power plant for use in vehicles; as part of a cogeneration system for stationary applications; or as part of a generator for portable power, back-up power orUPS applications. 10 In some embodiments, the present method comprises: supplying a stoichiometric excess of air to the stack at near-ambient pressure; supplying a cathode exhaust stream to a humidification device; maintaining the relative humidity of the air stream below a stack inlet saturation point; maintaining the relative humidity of the cathode exhaust stream below a stack inlet saturation point; and, operating the stack at a 15 temperature greater than about 75°C. BRIEF DESCRIPTION OF THE DRAWING(S) Figures 1 and 2 are schematic representations of embodiments of the present fuel cell system. In the drawings, identical reference numbers identify similar elements or 20 acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have 25 been solely selected for ease of recognition in the drawings. 5 WO 2004/079269 PCT/CA2004/000320 CLAIMS 1. A fuel cell system comprising: a fuel cell stack comprising a plurality of fuel cells, the fuel cells having a cathode gas diffusion barrier layer; a fuel system for supplying a fuel to the stack; a blower for supplying air p the stack at near-ambient pressure; a humidification device in fluid communication with an air stream supplied to the stack and a cathode exhaust stream exiting the stack for transferring water vapor from the. cathode exhaust stream to the air stream; and a coolant loop for circulating a liquid coolant through the stack. 2. The fuel cell system /of claim 1 wherein the blower is a variable speed blower. 3. The fuel cell system of claim 1, further comprising an air filter located upstream of the humidification device and in fluid communication therewith. 4. The fuel cell system of claim 1 wherein the humidification device comprises a gas-exchange humidifier. 5. The fuel cell system of claim 1 wherein the humidification device comprises an enthalpy wheel. 6. The fuel cell system of claim 1 wherein the blower is located downstream of the humidification device. 7. The fuel cell system of claim 1, further comprising a cathode recycle loop for returning at least a portion of the cathode exhaust stream to the fuel cell stack. 13 WO 2004/079269 PCT/CA2004/000320 8. The fuel cell system of claim 7, further comprising a damper disposed in the cathode recycle loop. 9. The fuel cell system of claim 7, further comprising a recycle blower disposed in the cathode recycle loop. 10. The fuel cell system of claim 7 wherein the cathode recycle loop is fluidly connected to the humidification device for supplying a remainder of the cathode exhaust stream thereto. 11. The fuel cell system of claim 1 wherein the fuel is substantially pure hydrogen. 12. The fuel cell system of claim 11 wherein the fuel supply system is dead- ended. 13. The fuel cell system of claim 11 wherein the fuel supply system comprises a hydrogen recycle loop. 14. The fuel cell system of claim 1 wherein the coolant loop farther comprises a heat exchanger. 15. The fuel cell system of claim 14 wherein the heat exchanger comprises a radiator. 16. The fuel cell system of claim I wherein the coolant is selected from the group consisting of deionized water, ethylene glycol and mixtures thereof. 14 WO 2004/079269 PCT/CA2004/000320 17. The fuel cell system of claim 1 wherein the gas diffusion barrier layer comprises an expanded graphite sheet material. 18. The fuel cell system of claim 1 wherein the gas diffusion barrier layer comprises a porous, electrically conductive material having a region filled with a solid, thereby reducing the porosity of the region. 19. The fuel cell system of claim 1 wherein the gas diffusion barrier layer comprises a laminate having a first layer interposed between a second layer and a fuel ceil membrane, the first layer having a lower permeability to water vapor relative to the second layer. 20. The fuel cell system of claim 1 wherein the gas diffusion barrier layer comprises a microporous membrane. 21. A method of operating a fuel cell system, the system including a fuel cell stack and the fuel cell stack including a plurality of fuel cells having a cathode gas diffusion barrier layer, the method comprising: supplying air to the stack at near-ambient pressure and a stoichiometry greater than 1; supplying a cathode exhaust stream to a humidification device; maintaining the relative humidity of the air below a stack inlet saturation point; maintaining the relative humidity of the cathode exhaust stream below a stack outlet saturation point; and operating the stack at a temperature greater than about 75 °C. 22. The method of claim 21 wherein the air is supplied to the stack at a pressure of about 20 mbar to about 50 mbar. 15 WO 2004/079269 PCT/CA2004/000320 23. The method of claim 21 wherein the air is supplied to the stack at a stoichiometry of about 1.2 to about 3.0. 24. The method of claim 21, further comprising increasing the air stoichiometry as a power output of the fuel cell system to an external load decreases. 25. The method of claim 21, further comprising decreasing the air stoichiometry as the stack temperature increases. 26. The method of claim 21, further comprising circulating a liquid coolant through the stack. 27. The method of claim 26, further comprising circulating the coolant through a heat exchanger. 28. The method of claim 21 wherein the air is supplied to the stack by a blower, the method further comprising: monitoring an operating parameter of the stack indicative of the stack temperature; and varying the speed of the blower in response to the monitored parameter. 29. The method of claim 21, further comprising returning at least a portion of the cathode exhaust stream to the stack. 30. The method of claim 29, further comprising: monitoring an operating parameter of the stack indicative of the stack temperature; and varying the portion of the cathode exhaust stream returned to the stack in response to the monitored parameter. 16 WO 2004/079269 PCT/CA2004/000320 31. A fuel cell system comprising: a fuel cell stack comprising a plurality of fuel cells,, the fuel cells having a cathode gas diffusion barrier means; a fuel system for supplying a fuel to the stack; supply means for supplying air to the stack at near-ambient pressure; humidification means for transferring water vapor from a cathode exhaust stream exiting the stack with an air stream supplied to the stack; and a coolant loop for circulating a liquid coolant through the stack. 32. The fuel cell system of claim 31, further comprising: a sensor for measuring an operating parameter indicative of an operating temperature of the stack; and control means adapted to receive an input from the sensor and control a stoichiometry of the air supplied to the stack by the supply means in response to the input. 33. The fuel cell system of claim 31, further comprising recycling means for returning at least a portion of the cathode exhaust stream to the stack. 34. The fuel cell system of claim 33, further comprising: a sensor for measuring an operating parameter indicative of an operating temperature of the stack; and control means adapted to receive an input from the sensor and, in response to the input, control at least one of a stoichiometry of the air supplied to the stack by the supply means and the portion of the cathode exhaust stream returned to the stack by the recycling means. 17 A fuel cell System is provided that is capable of operating at high temperatures and near-ambient pressure with partial humidification of air supplied to the fuel cell stack. The fuel cells of the stack incorporate gas diffusion barrier layers at the cathode side thereof. The System includes a cooling loop for circulating a liquid coolant through the stack. In some embodiments, an incoming air stream is partially humidified with water vapor transferred from a cathode exhaust stream in a gas-exchange humidifier or enthalpy wheel. In other embodiments, a cathode recycle is employed to partially humidify the incoming air. The humidity of the air and cathode exhaust streams is maintained below a stack saturation point. Methods of operating the fuel cell System are also provided

Full Text

AMBIENT PRESSURE FUEL CELL SYSTEM EMPLOYING PARTIAL AIR
HUMIDIFICATION
CROSS-REFERENCE TO RELATED APPLICATION
5 This application claims the benefit of U.S. Provisional Patent Application
No. 60/451,943 filed March 3, 2003, where this provisional application is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
10 The present invention relates to fuel cell systems operating at or near
ambient pressure. In particular, the present invention relates to fuel cell systems operating
at or near ambient pressure with partial air humidification, and methods of operating such
systems.
Description of the Related Art
15 Fuel cells are known in the art. Fuel cells electrochemically react a fuel
stream comprising hydrogen and an oxidant stream comprising oxygen to generate an
electric current. Fuel cell electric power plants have been employed in transportation,
portable and stationary applications.
Water management issues are critical in polymer electrolyte membrane
20 (PEM) fuel cell operation. Humidification of the membrane is required to maintain optimal
performance. As the water content of the membrane falls it loses the ability to transport
protons, its electrical resistance increases, and fuel cell performance decreases and
membrane failure may occur. To ensure adequate humidification of the membrane the
reactant streams supplied to the fuel cell stack are typically humidified. At the same time,
1

WO 2004/079269 PCT/CA2004/000320
In other embodiments, the present fuel cell system comprises: a fuel cell
stack with fuel cells having a cathode gas diffusion barrier means; a fuel system for
supplying a fuel to the stack; supply means for supplying air to the stack at near-ambient
pressure; humidification means for transferring water vapor from the cathode exhaust
5 stream with the air supplied to the stack; and, a coolant loop for circulating a liquid coolant
through the stack.
The present fuel cell system may be part of a power plant for use in
vehicles; as part of a cogeneration system for stationary applications; or as part of a
generator for portable power, back-up power orUPS applications.
10 In some embodiments, the present method comprises: supplying a
stoichiometric excess of air to the stack at near-ambient pressure; supplying a cathode
exhaust stream to a humidification device; maintaining the relative humidity of the air
stream below a stack inlet saturation point; maintaining the relative humidity of the cathode
exhaust stream below a stack inlet saturation point; and, operating the stack at a
15 temperature greater than about 75°C.
BRIEF DESCRIPTION OF THE DRAWING(S)
Figures 1 and 2 are schematic representations of embodiments of the present
fuel cell system.
In the drawings, identical reference numbers identify similar elements or
20 acts. The sizes and relative positions of elements in the drawings are not necessarily drawn
to scale. For example, the shapes of various elements and angles are not drawn to scale,
and some of these elements are arbitrarily enlarged and positioned to improve drawing
legibility. Further, the particular shapes of the elements as drawn, are not intended to
convey any information regarding the actual shape of the particular elements, and have
25 been solely selected for ease of recognition in the drawings.
5

WO 2004/079269 PCT/CA2004/000320
CLAIMS
1. A fuel cell system comprising:
a fuel cell stack comprising a plurality of fuel cells, the fuel cells having a cathode
gas diffusion barrier layer;
a fuel system for supplying a fuel to the stack;
a blower for supplying air p the stack at near-ambient pressure;
a humidification device in fluid communication with an air stream supplied to the
stack and a cathode exhaust stream exiting the stack for transferring water vapor from the.
cathode exhaust stream to the air stream; and
a coolant loop for circulating a liquid coolant through the stack.
2. The fuel cell system /of claim 1 wherein the blower is a variable speed
blower.
3. The fuel cell system of claim 1, further comprising an air filter located
upstream of the humidification device and in fluid communication therewith.
4. The fuel cell system of claim 1 wherein the humidification device
comprises a gas-exchange humidifier.
5. The fuel cell system of claim 1 wherein the humidification device
comprises an enthalpy wheel.
6. The fuel cell system of claim 1 wherein the blower is located downstream
of the humidification device.
7. The fuel cell system of claim 1, further comprising a cathode recycle loop
for returning at least a portion of the cathode exhaust stream to the fuel cell stack.
13

WO 2004/079269 PCT/CA2004/000320
8. The fuel cell system of claim 7, further comprising a damper disposed in
the cathode recycle loop.
9. The fuel cell system of claim 7, further comprising a recycle blower
disposed in the cathode recycle loop.
10. The fuel cell system of claim 7 wherein the cathode recycle loop is fluidly
connected to the humidification device for supplying a remainder of the cathode exhaust stream
thereto.
11. The fuel cell system of claim 1 wherein the fuel is substantially pure
hydrogen.
12. The fuel cell system of claim 11 wherein the fuel supply system is dead-
ended.
13. The fuel cell system of claim 11 wherein the fuel supply system comprises
a hydrogen recycle loop.
14. The fuel cell system of claim 1 wherein the coolant loop farther comprises
a heat exchanger.
15. The fuel cell system of claim 14 wherein the heat exchanger comprises a
radiator.
16. The fuel cell system of claim I wherein the coolant is selected from the
group consisting of deionized water, ethylene glycol and mixtures thereof.
14

WO 2004/079269 PCT/CA2004/000320
17. The fuel cell system of claim 1 wherein the gas diffusion barrier layer
comprises an expanded graphite sheet material.
18. The fuel cell system of claim 1 wherein the gas diffusion barrier layer
comprises a porous, electrically conductive material having a region filled with a solid, thereby
reducing the porosity of the region.
19. The fuel cell system of claim 1 wherein the gas diffusion barrier layer
comprises a laminate having a first layer interposed between a second layer and a fuel ceil
membrane, the first layer having a lower permeability to water vapor relative to the second layer.
20. The fuel cell system of claim 1 wherein the gas diffusion barrier layer
comprises a microporous membrane.
21. A method of operating a fuel cell system, the system including a fuel cell
stack and the fuel cell stack including a plurality of fuel cells having a cathode gas diffusion
barrier layer, the method comprising:
supplying air to the stack at near-ambient pressure and a stoichiometry greater
than 1;
supplying a cathode exhaust stream to a humidification device;
maintaining the relative humidity of the air below a stack inlet saturation point;
maintaining the relative humidity of the cathode exhaust stream below a stack
outlet saturation point; and
operating the stack at a temperature greater than about 75 °C.
22. The method of claim 21 wherein the air is supplied to the stack at a
pressure of about 20 mbar to about 50 mbar.
15

WO 2004/079269 PCT/CA2004/000320
23. The method of claim 21 wherein the air is supplied to the stack at a
stoichiometry of about 1.2 to about 3.0.
24. The method of claim 21, further comprising increasing the air
stoichiometry as a power output of the fuel cell system to an external load decreases.
25. The method of claim 21, further comprising decreasing the air
stoichiometry as the stack temperature increases.
26. The method of claim 21, further comprising circulating a liquid coolant
through the stack.
27. The method of claim 26, further comprising circulating the coolant
through a heat exchanger.
28. The method of claim 21 wherein the air is supplied to the stack by a
blower, the method further comprising:
monitoring an operating parameter of the stack indicative of the stack
temperature; and
varying the speed of the blower in response to the monitored parameter.
29. The method of claim 21, further comprising returning at least a portion of
the cathode exhaust stream to the stack.
30. The method of claim 29, further comprising:
monitoring an operating parameter of the stack indicative of the stack
temperature; and
varying the portion of the cathode exhaust stream returned to the stack in response
to the monitored parameter.
16

WO 2004/079269 PCT/CA2004/000320
31. A fuel cell system comprising:
a fuel cell stack comprising a plurality of fuel cells,, the fuel cells having a cathode
gas diffusion barrier means;
a fuel system for supplying a fuel to the stack;
supply means for supplying air to the stack at near-ambient pressure;
humidification means for transferring water vapor from a cathode exhaust stream
exiting the stack with an air stream supplied to the stack; and
a coolant loop for circulating a liquid coolant through the stack.
32. The fuel cell system of claim 31, further comprising:
a sensor for measuring an operating parameter indicative of an operating
temperature of the stack; and
control means adapted to receive an input from the sensor and control a
stoichiometry of the air supplied to the stack by the supply means in response to the input.
33. The fuel cell system of claim 31, further comprising recycling means for
returning at least a portion of the cathode exhaust stream to the stack.
34. The fuel cell system of claim 33, further comprising:
a sensor for measuring an operating parameter indicative of an operating
temperature of the stack; and
control means adapted to receive an input from the sensor and, in response to the
input, control at least one of a stoichiometry of the air supplied to the stack by the supply means
and the portion of the cathode exhaust stream returned to the stack by the recycling means.
17

A fuel cell System is provided that is capable of operating at high temperatures and near-ambient pressure with partial humidification of air supplied to the fuel cell stack. The fuel cells of the stack incorporate gas diffusion barrier layers at the cathode side thereof. The System includes a cooling loop for circulating a liquid coolant through the stack. In some embodiments, an incoming air stream is partially humidified with water vapor transferred from a cathode exhaust stream in a gas-exchange humidifier or enthalpy wheel. In other embodiments, a cathode recycle is employed to partially humidify the incoming air. The humidity of the air and cathode exhaust streams is maintained below a stack saturation point. Methods of operating the fuel cell System are also provided

Documents:

« Previous Patent

Next Patent »

Patent Number

216063

Indian Patent Application Number

01817/KOLNP/2005

PG Journal Number

10/2008

Publication Date

07-Mar-2008

Grant Date

06-Mar-2008

Date of Filing

13-Sep-2005

Name of Patentee

BALLARD POWER SYSTEMS INC.

Applicant Address

4343 NOTRH FRASER WAY, BURNABY, BRITISH COLUMBIA V5J 5J9, CANADA

Inventors:

#	Inventor's Name	Inventor's Address
1	SEDERQUIST, RICHARD, A.	68 WILDFLIWER LANE, MIDDLETOWN, CT 06457 MIDDLETOWN, CT 06457 UNITED STATES OF AMERICA
2	WELLS, BRIAN, W.	159 WEST 18TH AVENUE, VANCOUVER, BRITISH COLUMBIA V5Y 2A6, CANADA
3	MOSSMAN, ALEX	1572 EAST 10TH AVENUE, VANCOUVER, BRITISH COLUMBIA V5N 1X5, CANADA
4	LOUIE, CRAIG, R.	1405 INGLEWOOD AVENUE, WEST VANCOUVER, BRITISH COLUMBIA V7T 1Z2, CANADA

PCT International Classification Number

H01M 8/04

PCT International Application Number

PCT/CA2004/000320

PCT International Filing date

2004-03-03

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/451,943	2003-03-03	U.S.A.