Fuel cell system

Abstract

A fuel cell system is disclosed a fuel cell configured to generate electric power using an oxidizing gas supplied to a cathode of the fuel cell. In the fuel cell system, a combustible gas is filled and kept in the cathode after stop of power generation, and is thereafter diluted by an incombustible gas when the combustible gas is discharged to atmosphere.

1 . A fuel cell system comprising: 
 a fuel cell configured to generate electric power using an oxidizing gas supplied to a cathode of said fuel cell, wherein    a combustible gas is filled and kept in said cathode after stop of power generation, and is thereafter diluted by an incombustible gas when the combustible gas is discharged to atmosphere.    
     
     
         2 . The fuel cell system according to  claim 1 , wherein the combustible gas in a gas mixture containing the combustible gas and the incombustible gas is discharged to atmosphere in such a manner that the combustible gas is diluted to have a concentration lower than a combustion lower limit.  
     
     
         3 . The fuel cell system according to  claim 1 , further comprising: 
 an oxidizing gas supply device configured to supply the oxidizing gas;    an oxidizing gas passage through which the oxidizing gas supplied from said oxidizing gas supply device is guided to said cathode, and the oxidizing gas unconsumed in said cathode is discharged to atmosphere;    first and second oxidizing gas passage valves respectively provided at an upstream position and a downstream position of said cathode in a flow of the oxidizing gas, and configured to open and close said oxidizing gas passage;    a combustible gas supply device configured to supply the combustible gas to a portion of said oxidizing gas passage which is located between said first oxidizing gas passage valve and said cathode;    a diluting device configured to dilute the combustible gas purged from said cathode to a portion of said oxidizing gas passage which is located downstream of said cathode by the incombustible gas and to discharge the diluted combustible gas to atmosphere; and    a controller, wherein    in a stop operation of power generation in said fuel cell, said controller is configured to close said first oxidizing gas passage valve and to supply the combustible gas from said combustible gas supply device to said oxidizing gas passage to allow the combustible gas to be filled in said cathode, and to then close said second oxidizing gas passage valve to allow the combustible gas to be kept in said cathode, and    in a start operation of the power generation in said fuel cell, said controller is configured to open at least said first oxidizing gas passage valve to supply the oxidizing gas from said oxidizing gas supply device to said cathode through said oxidizing gas passage to purge the combustible gas filled in said cathode to the portion of said oxidizing gas passage which is located downstream of said cathode, and to cause said diluting device to dilute the purged combustible gas to be discharged to atmosphere.    
     
     
         4 . The fuel cell system according to  claim 3 , wherein the incombustible gas is the oxidizing gas.  
     
     
         5 . The fuel cell system according to  claim 4 , wherein said diluting device includes a cathode bypass passage configured to connect a portion of said oxidizing gas passage which is located upstream of said first oxidizing gas passage valve to a portion of said oxidizing gas passage which is located downstream of said second oxidizing gas passage valve, and a cathode bypass valve configured to open and close said cathode bypass passage, and 
 when the combustible gas filled and kept in said cathode is discharged, said first and second oxidizing gas passage valves are opened, and said cathode bypass valve is opened to allow the combustible gas exhausted to the portion of the oxidizing gas passage which is located downstream of said cathode to be mixed with and diluted by the oxidizing gas flowing through said cathode bypass passage, the diluted combustible gas being discharged to atmosphere.    
     
     
         6 . The fuel cell system according to  claim 5 , wherein a flow rate of the oxidizing gas flowing through said cathode bypass passage is controlled by adjusting passage resistance of said cathode bypass passage.  
     
     
         7 . The fuel cell system according to  claim 6 , wherein the flow rate of the oxidizing gas flowing through said cathode bypass passage is controlled by adjusting an aperture diameter of a cathode bypass valve which is said cathode bypass valve disposed in said cathode bypass passage.  
     
     
         8 . The fuel cell system according to  claim 4 , wherein said diluting device includes a cathode bypass passage configured to connect a portion of said oxidizing gas passage which is located upstream of said cathode to a portion of said oxidizing gas passage which is located downstream of said second oxidizing gas passage valve, and a dividing device disposed at a connecting portion between the portion of said oxidizing gas passage which is located upstream of the cathode and said cathode bypass passage, said dividing device being configured to open and close said oxidizing gas passage and to vary a ratio of a flow rate of the oxidizing gas flowing through said cathode bypass passage to a flow rate of the oxidizing gas flowing through said oxidizing gas passage as said diluting device and said first oxidizing gas passage valve, wherein 
 when the combustible gas filled and kept in said cathode is discharged, said second oxidizing gas passage valve is opened, and the combustible gas exhausted to the portion of said oxidizing gas passage which is located downstream of said cathode is mixed with and diluted by the oxidizing gas flowing through said cathode bypass passage in the ratio adjusted by said dividing device, the diluted combustible gas being discharged to atmosphere.    
     
     
         9 . The fuel cell system according to  claim 3 , wherein said diluting device includes a combustion air supply device configured to supply air to a flame burner of a combustor, a cathode combustion pipe configured to extend from a position of said oxidizing gas passage between said second oxidizing gas passage valve and said cathode and to be connected to said flame burner, and a combustion pipe valve configured to be opened and closed to open and close said cathode combustion pipe, and wherein 
 when the combustible gas filled and kept in said cathode is discharged, said second oxidizing gas passage valve is closed and said combustion pipe valve is opened, thereby allowing the combustible gas to be guided to said flame burner through said cathode combustion pipe and to be mixed with and diluted by the air supplied from said combustion air supply device, the diluted combustible gas being discharged to atmosphere.    
     
     
         10 . The fuel cell system according to  claim 9 , wherein the combustible gas is introduced to said flame burner during a stop period of combustion in said combustor.  
     
     
         11 . The fuel cell system according to  claim 3 , wherein said diluting device includes an exhaust pipe through which an exhaust gas generated by combustion in said combustor is guided to atmosphere, a cathode exhaust pipe configured to extend from a position of said oxidizing gas passage between said second oxidizing gas passage valve and said cathode and to be connected to the exhaust pipe, and an exhaust pipe valve configured to open and close said cathode exhaust pipe, and wherein 
 when the combustible gas filled and kept in said cathode is discharged, said second oxidizing gas passage valve is closed and said exhaust pipe valve is opened, thereby allowing the combustible gas to be guided to said exhaust pipe through said cathode exhaust pipe and to be mixed with and diluted by the exhaust gas, the diluted combustible gas being discharged to atmosphere.    
     
     
         12 . The fuel cell system according to  claim 3 , wherein said diluting device includes an exhaust pipe through which an exhaust gas generated by combustion in said combustor is guided to atmosphere, said exhaust pipe being connected to a portion of said oxidizing gas passage which is located downstream of said second oxidizing gas passage valve, and wherein 
 when the combustible gas filled and kept in said cathode is discharged, said second oxidizing gas passage valve is opened, thereby allowing the combustible gas to be guided to said exhaust pipe through said oxidizing gas passage and to be mixed with and diluted by the exhaust gas, the diluted combustible gas being discharged to atmosphere.    
     
     
         13 . The fuel cell system according to  claim 11 , wherein the combustible gas is introduced into said exhaust pipe during a combustion period of said combustor.  
     
     
         14 . The fuel cell system according to  claim 12 , wherein the combustible gas is introduced into said exhaust pipe during a combustion period of said combustor.  
     
     
         15 . The fuel cell system according to  claim 9 , wherein said combustor is configured to heat a fuel generator configured to generate a fuel gas from a feed gas.  
     
     
         16 . The fuel cell system according to  claim 11 , wherein said combustor is configured to heat a fuel generator configured to generate a fuel gas from a feed gas.  
     
     
         17 . The fuel cell system according to  claim 12 , wherein said combustor is configured to heat a fuel generator configured to generate a fuel gas from a feed gas.  
     
     
         18 . The fuel cell system according to  claim 1 , further comprising: 
 a fuel generator configured to generate a fuel gas from a feed gas, wherein the fuel gas is supplied from said fuel generator to an anode of said fuel cell to generate electric power, and the combustible gas is one of the feed gas and the fuel gas.    
     
     
         19 . The fuel cell system according to  claim 1 , further comprising: a hydrogen supply device configured to supply hydrogen, wherein the hydrogen is supplied from said hydrogen supply device to an anode of said fuel cell to generate electric power, and the combustible gas is hydrogen.