Patent ID: 7550214

Claim:
A fuel cell system comprising: a fuel gas supply unit supplying fuel gas; an oxidant gas supply unit supplying oxidant gas; a fuel cell stack that generates electric power upon electrochemical reaction between the fuel gas and the oxidant gas; a catalytic combustor combusting mixed gas comprising an anode off-gas discharged from an anode of the fuel cell stack and a cathode off-gas discharged from an cathode of the fuel cell stack; an anode off-gas control valve supplying the anode off-gas to the catalytic combustor; a cathode off-gas control valve supplying the cathode off-gas to the catalytic combustor; and a controller operative to control the anode off-gas control valve and the cathode off-gas control valve such that at least during an ignition period until the catalytic combustor is discriminated to be sufficiently activated from commencement of supplying the mixed gas to the catalytic combustor, an average fuel gas concentration of the mixed gas is maintained in a given range whereas after the ignition period has been elapsed, the mixed gas is available to be supplied to the catalytic combustor even if the average fuel gas concentration deviates from the given range.