Apparatus for improving the cold starting capability of an electrochemical fuel cell

Abstract

An electric power generation system has components that improve the cold start capability and freeze tolerance of a constituent fuel cell stack. The components 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, the fuel supply and/or the coolant passages upstream of the stack. When the stack is shut down, the stack is disconnected from an external circuit, and purge fluid is directed by the purge system through the stack before the stack falls below the freezing point of water. In systems where the fuel and/or oxidant streams are humidified prior to their introduction into the stack, a humidifier bypass system may be provided in place of the purge system. The humidifier bypass system directs reactant fluid to the stack in fluid isolation from the humidifier, so that the inlet reactant streams are unhumidified.

What is claimed is:  
     
         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 fluid stream passages for directing fluid streams through said at least one fuel cell; and    (b) a purge system comprising a purge conduit having an inlet end connectable to a purge fluid supply and an outlet end connected to at least one of said fluid stream passages, and a purge flow control device for controlling the flow of a pressurized purge fluid through said purge conduit such that water is capable of being purged from at least one of said fluid stream passages after a supply of electric current from said stack to said external circuit has been interrupted.    
     
     
         2 . The electric power generation system of    claim 1    wherein said fluid stream passages are reactant stream passages.  
     
     
         3 . The electric power generation system of    claim 2    wherein said reactant stream passages comprise oxidant stream passages.  
     
     
         4 . The electric power generation system of    claim 2    wherein said reactant stream passages comprise fuel stream passages.  
     
     
         5 . The electric power generation system of    claim 1    wherein said fluid stream passages comprise a coolant passage.  
     
     
         6 . The electric power generation system of    claim 1    wherein said purge flow control device comprises a control valve connected to said purge conduit.  
     
     
         7 . The electric power generation system of    claim 6    wherein said purge flow control device further comprises a control unit communicative with said control valve and with an input signal source.  
     
     
         8 . The electric power generation system of    claim 7    wherein said control unit is a microcontroller.  
     
     
         9 . The electric power generation system of    claim 1    wherein said purge system further comprises a pressure regulator associated with said purge conduit for regulating the pressure of said purge fluid from said purge fluid supply to said at least one reactant passage.  
     
     
         10 . The electric power generation system of    claim 1    wherein said purge fluid is inert.  
     
     
         11 . The electric power generation system of    claim 11    wherein said purge fluid is nitrogen.  
     
     
         12 . 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; and    (b) a humidifier in fluid communication with at least one of said reactant stream passages, for humidifying a reactant stream supplied to said fuel cell stack; and    (c) a humidifier bypass system comprising at least one bypass conduit for directing said reactant stream to said stack in fluid isolation from said humidifier and a bypass control device for selectively directing flow of said reactant stream to said fuel cell stack through either of said humidifier and said humidifier bypass conduit.    
     
     
         13 . The electric power generation system of    claim 12    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.  
     
     
         14 . The electric power generation system of    claim 12    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.  
     
     
         15 . The electric power generation system of    claim 12    wherein said control device is operable such that said reactant fluid is directed to said humidifier while electrical power is being generated by the stack and to said bypass conduit after a supply of electric current from said stack to said external circuit has been interrupted.  
     
     
         16 . The electric power generation system of    claim 15    wherein said bypass control device comprises a bypass inlet valve connected to one of said reactant passages upstream of said humidifier, and a bypass outlet valve connected to one of said reactant passages downstream of said humidifier, and wherein said bypass conduit is connected to said bypass inlet and outlet valves.  
     
     
         17 . The electric power generation system of    claim 16    wherein said bypass control device further comprises a control unit communicative with said bypass inlet and outlet valves and with an input signal source.  
     
     
         18 . The electric power generation system of    claim 18    wherein said control unit is a microcontroller.  
     
     
         19 . The electric power generation system of    claim 12    wherein one of said reactant passages is an oxidant flow passage.  
     
     
         20 . The electric power generation system of    claim 12    wherein one of said reactant passages is a fuel flow passage.  
     
     
         21 . 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 fluid stream passages for directing fluid streams through said at least one fuel cell; and    (b) a mechanism for directing the flow of a pressurized purge fluid from a purge fluid supply to at least one of said fluid stream passages such that water can be purged from said at least one purged fluid stream passage after a supply of electric current from said stack to said external circuit has been interrupted.    
     
     
         22 . 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) apparatus for humidifying at least one of said reactant streams supplied to said fuel cell stack; and    (c) a humidifier bypass system comprising apparatus for directing at least one of said reactant streams to said stack in fluid isolation from said humidifying apparatus, and apparatus for selectively directing flow of said reactant streams to said fuel cell stack through said humidifying apparatus or in fluid isolation from said humidifying apparatus.