Patent ID: 8557464

Claim:
A fuel cell system, comprising: a fuel cell; a fuel supply system for supplying fuel gas to an anode in said fuel cell; a circulation passage that mixes fuel off-gas exhausted from an anode exhaust port of said fuel cell with a new fuel gas from a fuel supply source and re-supplies it to an entry port of the anode; a shut-off valve provided in said circulation passage that, when open, emits said fuel off-gas to the outside of the system; and a regulating system which is programmed to adjust the amount of the new fuel gas to be supplied to said anode and to control the opening state of the shut-off valve, wherein said regulating system is programmed to control both a first operating mode, for providing higher levels of new fuel gas during fuel cell activation, and a second operating mode, for purging high levels of impurities from the circulation passage following a normal power generation mode, wherein during said first operating mode said shut-off valve is controlled to be in a closed state and the amount of new fuel gas supplied from said fuel supply is controlled to maintain an amount of the new fuel cell gas from said fuel supply source to said anode at a level higher than a new fuel gas supply amount set in response to an electric current generated by said fuel cell during normal power generation, wherein said first operating mode is maintained until a concentration of impurities in said fuel gas supplied to said anode falls below a previously set reference value, and wherein during said second operating mode said regulating system is programmed to reduce a new fuel gas supply amount from the amount provided during the normal power generation mode prior to opening the shut-off valve so as to reduce the amount of impurities in the circulation passage.