Method for Operating Fuel Gas Manufacturing Device

An method for operating a fuel gas manufacturing device that includes a desulfurizing unit that desulfurizes source gas that is heavy hydrocarbon gas, a reforming unit that reforms desulfurized source gas supplied from the desulfurizing unit by using water vapor to produce fuel gas that contains methane as a main component, a fuel gas return path for returning a portion of the fuel gas supplied from the reforming unit to the desulfurizing unit, and a moisture removing unit that removes moisture contained in the fuel gas supplied from the reforming unit, the operation method comprising

• when stopping operation while supply of the source gas to the desulfurizing unit is stopped, after supply of the source gas to the desulfurizing unit and discharge of the fuel gas to the outside are stopped, performing a standby operation process in which the fuel gas is circulated by a circulation driving unit in such a manner that the whole amount of the fuel gas passed through the moisture removing unit is circulated through a circulation gas path to return to the desulfurizing unit and the circulated fuel gas is heated by a heating unit to a set standby temperature to heat the reforming unit to a temperature that is equivalent to an operation temperature at which the reforming is performed, and supply of the water vapor is continued in a state where a supply amount of the water vapor is at least an amount with which carbon deposition due to thermal decomposition of the fuel gas can be prevented and is smaller than an amount that is supplied when the reforming is performed.