Method and apparatus for operating a solid-oxide fuel cell stack with a mixed ionic/electronic conducting electrolyte

Abstract

A method and apparatus for operating an intermediate-temperature solid-oxide fuel cell stack ( 10 ) with a mixed ionic/electronic conducting electrolyte in order to increase its efficiency. The required power output of the solid-oxide fuel cell stack ( 10 ) is determined and one or more operating conditions of the solid fuel cell stack ( 10 ) are controlled dependent upon the determined required power output. The operating conditions that are controlled may be at least one or the temperature of the fuel cell stack and the dilution of fuel delivered to the fuel cell stack.

1 - 22 . (canceled) 
     
     
         23 . A method of operating a variable power output solid oxide fuel cell stack comprising at least one solid oxide fuel cell having a mixed ionic/electronic conducting electrolyte, the method comprising the steps of:
 (a) determining a present power output and a required power output of said solid oxide fuel cell stack;   (b) comparing said determined present power output and required power output of said solid oxide fuel cell stack to determine a required change in the power output of said solid oxide fuel cell stack; and   (c) controlling at least one operating condition of said solid oxide fuel cell stack to effect said required change in power output, a required increase in power output including at least one of:
 (i) an increase in the temperature of said at least one solid oxide fuel cell; and 
 (ii) an increase in the concentration of fuel delivered to said solid oxide fuel cell, 
   
       and a required decrease in power output including at least one of:
 (i) a decrease in the temperature of said solid oxide fuel cell; and 
 (ii) a decrease in the concentration of fuel delivered to said solid oxide fuel cell. 
 
     
     
         24 . A method according to  claim 23 , wherein the temperature of the solid oxide fuel cell is maintained at 650° C. or below. 
     
     
         25 . A method according to  claim 23 , wherein the temperature of the solid oxide fuel cell is maintained at 600° C. or below. 
     
     
         26 . A method according to  claim 23 , wherein fuel delivered to the solid oxide fuel cell is diluted with a predetermined amount of steam, carbon dioxide, nitrogen or a mixture including steam, carbon dioxide and/or nitrogen. 
     
     
         27 . A method according to  claim 23 , wherein fuel delivered to the solid oxide fuel cell is diluted with a variable proportion of recycled exhaust gas from an anode side of the at least one fuel cell. 
     
     
         28 . A method according to  claim 23 , said at least one solid oxide fuel cell electrolyte including gadolinium-doped cerium oxide. 
     
     
         29 . A control system for a variable power output solid oxide fuel cell stack comprising at least one solid oxide fuel cell having a mixed ionic/electronic conducting electrolyte, the control system comprising:
 (a) a system adapted to determine a present power output and a required power output of said solid oxide fuel cell stack;   (b) a system adapted to compare a determined present power output and required power output of said solid oxide fuel cell stack to determine a required change in the power output of said solid oxide fuel cell stack; and   (c) a controller for controlling at least one operating condition of said solid oxide fuel cell stack to effect said required change in power output, said controller being arranged to effect a required increase in power output by controlling at least one of:
 (i) an increase in the temperature of said at least one solid oxide fuel cell; and 
 (ii) an increase in the concentration of fuel delivered to said solid oxide fuel cell, 
   
       and to effect a required decrease in power output by controlling at least one of:
 (i) a decrease in the temperature of said solid oxide fuel cell; and 
 (ii) a decrease in the concentration of fuel delivered to said solid oxide fuel cell. 
 
     
     
         30 . A control system according to  claim 29 , wherein the controller maintains the temperature of the stack at 650° C. or below. 
     
     
         31 . A control system according to  claim 29 , wherein the controller maintains the temperature of the stack at 600° C. or below. 
     
     
         32 . A control system according to  claim 29 , wherein the controller arranges the fuel delivered to the fuel cell stack to be diluted with a predetermined amount of steam, carbon dioxide, nitrogen or a mixture including steam, carbon dioxide and/or nitrogen. 
     
     
         33 . A control system according to  claim 29 , wherein the controller arranges the fuel delivered to the fuel cell stack to be diluted with a variable proportion of recycled exhaust gas from anode sides of the fuel cell stack. 
     
     
         34 . A fuel cell stack with mixed ionic/electronic conducting electrolytes including a control system according to  claim 29 .