As a fuel cell, a system is known in which hydrogen is supplied as a fuel gas on a side of an anode and air is supplied as an oxidizing gas on a side of the cathode, with a membrane electrode assembly (MEA) therebetween, the membrane electrode assembly being a layered structure of a solid electrolytic membrane and a catalyst layer. In this fuel cell operating system, electric power is generated in the cell including the MEA through a reaction of the hydrogen and oxygen in the air, and water is discharged from the side of the cathode as a reaction product. In order to adjust an amount of air supplied to the side of the cathode, an adjusting valve, which is called a back pressure valve or a pressure adjusting valve, is provided at an exit on the side of the cathode of the fuel cell.
In addition, because the MEA is a layered structure of membranes, hydrogen may partially leak from the side of the anode to the side of the cathode. The leaked hydrogen and the unreacted hydrogen at the side of the anode are diluted by the air and are discharged. For this purpose, a bypass flow path is provided on the side of the cathode in order to distribute the air, which is the oxidizing gas, into the gas for reaction in the cell and the gas for dilution, and a bypass valve is provided on the bypass flow path.
For example, JP 2003-180006A discloses a regeneration braking system for a fuel cell vehicle which does not use an expensive battery pack. In this reference, a back pressure valve is provided between an exit of the fuel cell on the side of the cathode and an air release end, and a bypass valve which is a three-way valve for bypass to the air release end is provided between a compressor for supplying compressed air and the cathode.
As described, in a fuel cell operating system using hydrogen as a fuel gas, with operations of several valves along with the supply of hydrogen gas and the supply of the air, suitable extraction of generated power, discharge of water which is the reaction product of the power generation, and dilution of the discharge gas are achieved.
As described above, water, which is the reaction product, is present in the gas supply path of the fuel cell system. Because of this, the adjusting valve and the bypass valve provided on the gas supply path may be fixed in same place due to freezing or the like of the water by lowering of the environmental temperature, resulting in non-operation during activation.
As described, the adjusting valve and the bypass valve are used in a fuel cell operating system. Because a primary function of the bypass valve is to supply air for diluting the concentration of the hydrogen contained in the discharge gas, the bypass valve is in many cases completely closed during normal operation. Therefore, when water is present near the bypass valve, the water is frozen when the outside air temperature is reduced to subzero temperatures, and activating the bypass valve becomes difficult.
An object of the present invention is to provide a fuel cell operating system which can prevent freezing of the valve and a method of preventing fixation of the valve in the fuel cell operating system.