Fuel cell system and method of operating the fuel cell system

A fuel cell system, comprising:

• a fuel cell stack for performing power generation by electrochemical reactions of a fuel gas and an oxygen-containing gas;
• a reforming unit for reforming a raw fuel to produce the fuel gas, and supplying the fuel gas to the fuel cell stack;
• a water supply unit for supplying water to the reforming unit;
• a raw fuel supply unit for supplying the raw fuel to the reforming unit, wherein the raw fuel supply unit includes a raw fuel supply channel connected to the reforming unit, a raw fuel supply apparatus for supplying the raw fuel to a desulfurizer, the desulfurizer for removing sulfur component from the raw fuel, and a flow rate meter for detecting a flow rate of the raw fuel,
• the raw fuel supply apparatus, the desulfurizer, and the flow rate meter are provided in the raw fuel supply channel such that the desulfurizer is provided downstream of the raw fuel supply apparatus, and the flow rate meter is provided downstream of the desulfurizer,
• the raw fuel supply channel including a first channel area provided upstream of the raw fuel supply apparatus, a second channel area provided downstream of the raw fuel supply apparatus and upstream of the flow rate meter, a bypass channel having both ends respectively connected to the first channel area and the second channel area, for bypassing at least the raw fuel supply apparatus, and an open/close valve for opening and closing the bypass channel based on a pressure in the first channel area and a pressure in the second channel area;
• and
• a control unit programmed to close the bypass channel by the open/close valve when the pressure in the first channel area is equal to the pressure in the second channel area, or when the pressure in the first channel area is larger than the pressure in the second channel area, and for opening the bypass channel by the open/close valve when the pressure in the first channel area is smaller than the pressure in the second channel area.