Process for controlling the output of a selective oxidizer

In an improved method of controlling the composition of the output from a selective oxidizer in a fuel cell system, the fuel cell system including a steam reformer, a shift converter, a selective oxidizer and a fuel cell, the method including the steps of supplying a hydrocarbon fuel and steam to the steam reformer, steam reforming the hydrocarbon fuel, conveying the steam reformed fuel to the shift converter, shift converting the steam reformed fuel, conveying the shift converted fuel to the selective oxidizer, supplying air to the selective oxidizer, conveying the output of the selective oxidizer to the fuel cell, and supplying air to the fuel cell, the improvement comprising:

• sensing the operating temperature of the selective oxidizer;
• sensing the current output of the fuel cell;
• maintaining the operating temperature of the selective oxidizer within a narrow band selected to simultaneously minimize hydrogen consumption and maximize the conversion of carbon monoxide to carbon dioxide in the selective oxidizer by controlling the flow rate of the air to the selective oxidizer as a function of the operating temperature of the selective oxidizer and by biasing the flow rate of air to the selective oxidizer as a function of the current output of the fuel cell.