Hydrogen generation apparatus, fuel cell system and method of shutting down hydrogen generation apparatus

A method of operating a fuel cell system comprising a hydrogen generation apparatus which comprises a raw material supplier which supplies a raw material, a water supplier which supplies water, a reforming device having a reforming catalyst for generating a gas containing hydrogen through reforming reaction using the raw material and the water, a CO reducing device having a CO reducing catalyst for reducing carbon monoxide in the gas containing hydrogen delivered from the reforming device, a combustor which supplies heat necessary for the reforming reaction to the reforming device, a first air supplier which supplies air for combustion to the combustor, and a combustion exhaust gas path formed such that the combustion exhaust gas exhausted from the combustor makes heat exchange with the reforming device and then with the CO reducing device, and a fuel cell which generates electric power by using the gas containing hydrogen supplied from the hydrogen generation apparatus, the method comprising:

• a first step of stopping a combustion operation of the combustor;
• and
• a second step of allowing, by operating the first air supplier and supplying air through the combustion exhaust gas path, the supplied air to make heat exchange with the reforming device and then with the CO reducing device so that a temperature of a gas in the CO reducing device does not become equal to or lower than a dew point after shutdown of the combustion operation of the combustor and before a start of a purging operation to purge interiors of the reforming device and the CO reducing device with a replacement gas.