Fuel cell system and method of reprocessing off-gas

A method of reprocessing an off-gas, comprising using a fuel cell system comprising

• a fuel cell including an anode and a cathode in which the anode is supplied with a fuel gas,
• a fuel gas supply passage that is connected with the anode and is provided upstream of the fuel cell and allows the fuel gas to flow therethrough,
• an off-gas reprocessing unit that is provided downstream of the fuel cell and that at least partially removes at least one of steam or carbon dioxide from an off-gas discharged from the fuel cell, wherein reprocessing corresponds to a process for at least partially separating at least one of carbon dioxide or steam from the off-gas in the off-gas reprocessing unit, and
• a flow passage that is provided downstream of the off-gas reprocessing unit and that allows a reprocessed off-gas discharged from the off-gas reprocessing unit to flow therethrough,
• wherein the flow passage is connected between the off-gas reprocessing unit and the fuel gas supply passage to supply the anode via the fuel gas supply passage with the reprocessed off-gas,
• the method comprising a step of removing at least one of steam or carbon dioxide from the off-gas in the off-gas reprocessing unit, wherein by the step, a reaction constant Kpa of the following reaction A with respect to the reprocessed off-gas discharged from the off-gas reprocessing unit is modulated to 1.22 or more:
• Reaction A:
• CO+H2↔H2O+C (Solid)
• Reaction constant of Reaction A:
• Kpa═P(H2O)/[P(CO)xP(H2)]
• wherein P(H2O), P(CO), and P(H2) represent respective partial pressures of H2O, CO, and H2 in the reprocessed off-gas.