Patent ID: 7846596

Claim:
A fuel cell system comprising: a fuel cell which includes an anode electrode and a cathode electrode, and which is adapted to perform power generation by a chemical reaction of a fuel gas which is supplied to the anode electrode and an oxidizing agent gas which is supplied to the cathode electrode; a fuel gas supply path for supplying the fuel gas to the anode electrode; an oxidizing agent gas supply path for supplying the oxidizing agent gas to the cathode electrode; a fuel gas circulating path for returning an unreacted fuel gas, which has passed through the anode electrode, to an inlet side of the anode electrode; a discharge port element for discharging gas from an outlet side of the anode electrode to outside; fuel gas dilution means for diluting the fuel gas, which has passed through the discharge port element, by the oxidizing agent gas and for discharging it to outside; and anode purging means for introducing a dilution gas, which is different from the fuel gas, to the anode electrode side and for purging residual gases, which remain in the anode electrode and the fuel gas circulating path, through the discharge port element, wherein the discharge port element includes: a drain valve through which a residual water in the fuel gas circulating path is discharged; a purge valve through which water and other impurities, which reside in combination in the fuel gas circulating path when the fuel cell system is in operation, are discharged; an air discharge valve through which a gas to purge an inside of the fuel gas circulating path is discharged; three branch paths which include, respectively, the drain valve, the purge valve, and the air discharge valve, and a controller to control opening and closing of the drain valve, the purge valve, and the air discharge valve, respectively, wherein among the drain valve, the purge valve, and the air discharge valve, the drain valve has a smallest opening area, the purge valve has an intermediate opening area, and the air discharge valve has a largest opening area, and wherein the fuel cell system is arranged such that, when purging by the anode purging means, the flow volume of a gas flowing through the three branch paths is controlled by the controller so as to be gradually increased, and at the same time, dilution by the fuel gas dilution means is controlled by the controller so as to increase the flow volume of the gas flowing from the three branch paths to the fuel gas dilution means in accordance with reduction by the dilution gas in a hydrogen concentration of the residual gases remaining in the anode electrode, and thereby always regulating the hydrogen concentration of the fuel gas discharged from the fuel gas dilution means to a value below a predefined value.