Apparatus for improving the cold starting capability of an electrochemical fuel cell
An electric power generation system has elements that improve the cold start capability and freeze tolerance of a constituent fuel cell stack cooperate to reduce the amount of water remaining within the passages of the stack. The system includes a purge system that is connectable to the oxidant supply, fuel supply and/or coolant passages upstream of the stack. When the stack is shut down, the stack is disconnected from an external circuit, and purge fluid is transmitted by the purge system through the stack before the stack falls below the freezing point of water. In systems where fuel and/or oxidant streams are humidified prior to entry into the stack, a humidifier bypass system may be provided in place of the purge system. The humidifier bypass system transmits reactant fluid to the stack in fluid isolation from the humidifier, so that the inlet reactant streams are unhumidified.
1. An electric power generation system comprising:
(a) a fuel cell stack connectable to an external electrical circuit for supplying electric current to said external circuit, said stack comprising at least one solid polymer fuel cell, and reactant stream passages for directing reactant streams through said at least one fuel cell;
(b) a humidifier in fluid communication with at least one of said reactant stream passages, for humidifying a reactant stream supplied to said stack; and
(c) a purge system comprising a humidifier bypass assembly comprising (1) at least one bypass conduit for directing said reactant stream to said stack in fluid isolation from said humidifier and (2) a bypass control device for selectively directing flow of said reactant stream to said stack through either of said humidifier and said humidifier bypass conduit; and
(d) a purge flow control device for actuating said bypass control device, after the supply of electric current from said stack to said external circuit has been interrupted, to direct flow of said reactant stream to said stack while bypassing said humidifier, such that water is purged from at least one of said reactant stream passages of said stack, whereby the amount of water remaining within said at least one reactant stream passage is reduced,
wherein said bypass control device comprises a bypass inlet valve connected to one of said reactant stream passages upstream of said humidifier, and a bypass outlet valve connected to one of said reactant stream passages downstream of said humidifier, and wherein said bypass conduit is connected to said bypass inlet and outlet valves.
2. The electric power generation system of claim 1 wherein said at least one bypass conduit comprises an inlet end connected to one of said reactant stream passages upstream of said humidifier, and an outlet end connected to one of said reactant stream passages downstream of said humidifier.
3. The electric power generation system of claim 1 wherein said at least one bypass conduit comprises an inlet end connectable to a reactant supply, and an outlet end connected to one of said reactant stream passages downstream of said humidifier.
4. The electric power generation system of claim 1 wherein said bypass control device further comprises a control unit communicative with said bypass inlet and outlet valves and with an input signal source.
5. The electric power generation system of claim 4 wherein said control unit is a microcontroller.
6. The electric power generation system of claim 1 wherein one of said reactant stream passages is an oxidant flow passage.
7. The electric power generation system of claim 1 wherein one of said reactant stream passages is a fuel flow passage.