Methods of operating fuel cells having closed reactant supply systems
View Patent ↗A fuel cell system is operated with the fuel supply pressure greater than the oxidant supply pressure to the fuel cell. This gives improved performance particularly when the fuel cell system is closed on the fuel side. The magnitude of fuel overpressure may be varied in accordance with variations in the fuel cell operating parameters.
1. A method for operating a fuel cell system comprising at least one fuel cell stack, the stack comprising at least one fuel cell, the fuel cell system further comprising a reactant supply system, the reactant supply system comprising a fuel passage for directing a fuel stream through the stack and an oxidant passage for directing an oxidant stream through the stack, the method comprising:
supplying the oxidant stream to the oxidant passage at an oxidant supply pressure; and
supplying the fuel stream to the fuel passage at a fuel supply pressure;
wherein the fuel supply pressure is at least 5 psig greater than the oxidant supply pressure at least some of the time and a fuel side of the reactant supply system is closed at least some of the time.
2. The method of claim 1 , wherein the at least one fuel cell is a solid polymer electrolyte fuel cell.
3. The method of claim 2 , wherein the fuel stream is hydrogen and the oxidant stream is air.
4. The method of claim 1 , wherein during operation the fuel supply pressure is always at least 5 psig greater than the oxidant supply pressure.
5. The method of claim 4 , further comprising:
varying the fuel supply pressure.
6. The method of claim 5 , wherein the fuel supply pressure is varied at a substantially constant frequency.
7. The method of claim 5 , wherein the fuel supply pressure is varied based on the power output of the fuel cell system.
8. The method of claim 5 , wherein the fuel cell system further comprises at least one sensor, and varying the fuel supply pressure comprises varying the fuel supply pressure based on an output of the sensor.
9. The method of claim 5 , further comprising:
monitoring a parameter indicative of fuel cell performance,
wherein the fuel supply pressure is varied based on the parameter indicative of fuel cell performance.
10. The method of claim 1 , further comprising:
varying the fuel supply pressure,
wherein the fuel supply pressure is intermittently at least 5 psig greater than the oxidant supply pressure.
11. The method of claim 10 , wherein the fuel supply pressure is varied at a substantially constant frequency.
12. The method of claim 10 , wherein the fuel supply pressure is at least 5 psig greater than the oxidant supply pressure during at least one of a shut-down phase and a start-up phase of the fuel cell system.
13. The method of claim 10 , wherein the fuel supply pressure is varied based on the power output of the fuel cell system.
14. The method of claim 10 , wherein the fuel cell system further comprises at least one sensor, and varying the fuel supply pressure comprises varying the fuel supply pressure based on an output of the sensor.
15. The method of claim 10 , further comprising:
monitoring a parameter indicative of fuel cell performance,
wherein the fuel supply pressure is varied based on the parameter indicative of fuel cell performance.
16. The method of claim 1 , wherein the fuel side of the reactant supply system is always closed.
17. The method of claim 1 , wherein the fuel side of the reactant supply system comprises a purge valve which is periodically opened to discharge a portion of the fuel stream from the stack.
18. The method of claim 1 , wherein the fuel side of the reactant supply system further comprises a recirculation loop and the method further comprises recirculating the fuel stream through the stack.
19. The method of claim 18 , wherein the fuel side of the reactant supply system further comprises a purge valve, and the method further comprises periodically opening the purge valve to discharge a portion of the fuel stream from the stack.
20. The method of claim 1 , wherein the fuel side of the reactant supply system is closed at a plurality of locations.
21. The method of claim 1 , wherein the stack comprises a plurality of fuel cells, and a fuel side of at least one fuel cell is dead-ended.
22. The method of claim 21 , wherein the fuel side of each fuel cell is dead-ended.
23. The method of claim 1 , wherein the fuel cell system comprises a primary stack and a secondary stack fluidly connected to receive the fuel stream in series downstream of the primary stack, wherein a fuel passage of the secondary stack is dead-ended at least some of the time.
24. The method of claim 1 , wherein the fuel supply pressure is between about 5 psig and 30 psig greater than the oxidant supply pressure.
25. The method of claim 1 , wherein the fuel supply pressure is at least 10 psig greater than the oxidant supply pressure.
26. The method of claim 1 , wherein the fuel supply pressure is at least 5 psig greater than the oxidant supply pressure when the fuel side of the reactant supply system is closed.