Fuel cell power generation system and operation stop method of the same

An operation stop method of a fuel cell power generation system including a fuel cell, the fuel cell including an electrolyte membrane, an anode, a cathode, a fuel gas channel through which a fuel gas is supplied to the anode, and an oxidizing gas channel through which an oxidizing gas is supplied to the cathode, the fuel cell being configured to generate electric power by causing a reaction between the fuel gas supplied to the anode and the oxidizing gas supplied to the cathode, the operation stop method comprising:

• a step (A) in which an output controller reduces an amount of electric power extracted from the fuel cell and then stops supplying the electric power to an external load;
• a step (C) in which either
• an oxidizing gas supply device stops supplying the oxidizing gas, an open-close mechanism closes a passage upstream from the oxidizing gas channel, and after the passage upstream from the oxidizing gas channel is closed, a raw material gas supply device and a water supply device stop when a predetermined period has elapsed, during which period the oxidizing gas in the oxidizing gas channel is consumed by the fuel gas that has cross-leaked to the oxidizing gas channel through the electrolyte membrane, or
• the oxidizing gas supply device stops supplying the oxidizing gas, the raw material gas supply device and the water supply device stop, the open-close mechanism closes the passage upstream from the oxidizing gas channel, and the predetermined period elapses, during which period the oxidizing gas in the oxidizing gas channel is consumed by the fuel gas that has cross-leaked to the oxidizing gas channel through the electrolyte membrane;
• and
• a step (D) in which the open-close mechanism closes a passage upstream from the fuel gas channel and a passage downstream from the fuel gas channel after the step (C), wherein
• after supply of the electric power to the external load is stopped, a period until the supply of the oxidizing gas is stopped is a period T represented by the following Equation (1):
• 3×A/FRa≦T≦5×A/Fra (1),
• where A represents a volume [L] of space sealed by a fuel gas supply open-close device and a fuel gas discharge open-close device, and
• FRa represents a flow rate [L/s] of the fuel gas that is generated by a fuel generator in a case where the amount of the electric power extracted from the fuel cell is set to a self sustained operation-enabled power amount.