Fuel cell shutdown with steam purging
View Patent ↗The present invention relates to an apparatus for steam purging a solid oxide fuel cell stack. Purging the SOFC stack with steam has a physical flushing effect, removing carbon monoxide containing reformate and free oxygen gas from the anode area thereby reducing the potential for nickel oxide or nickel carbonyl formation.
1. A solid oxide fuel cell stack operative at a temperature of 600° C. to 1000° C. including a fuel delivery subsystem comprising a reformer, an air delivery subsystem capable of cooling the stack prior to purging the fuel delivery subsystem with steam, and having an anode comprising nickel, and a steam purge subsystem comprising:
(a) a water chamber or source connected to the fuel delivery subsystem upstream from the reformer; and
(b) a fail-safe mechanism configured to acurate the steam purge subsystem, comprising a salenoid valve connected to a power source, wherein the solenoid valve opens when power to the solenoid is disrupted, and pressurizing means for pressuring the water in a liquid state from the water chamber or source to the fuel delivery system.
2. The apparatus of claim 1 wherein the pressurizing means is contained within the water chamber.
3. The apparatus of claim 1 wherein the pressurizing means comprises a plunger biased with a spring.
4. The apparatus of claim 1 wherein the pressurizing means comprises an expandable resilient water bladder.
5. The apparatus of claim 1 further comprising a protective bed of sacrificial oxidizable material, disposed between the water source and the reformer.
6. The apparatus of claim 5 wherein the sacrificial oxidizable material comprises a metallic powder that upon oxidation increases hydrogen partial pressure and reduces oxygen partial pressure.
7. The apparatus of claim 1 further comprising control means configured to actuate the solenoid valve as a controlled response.
8. The apparatus of claim 7 wherein the controlled response is to a predetermined temperature of the solid oxide fuel cell stack.
9. The apparatus of claim 7 wherein the controlled response is to the elapse of a predetermined amount of time after the solid oxide fuel cell is shut down.
10. The apparatus of claim 7 wherein the controlled response is to a predetermined rate of fuel flow to the solid oxide fuel cell.