Patent ID: 7595123

Claim:
A fuel cell system for generating electric power by supplying fuel fluid from a fuel tank to a fuel electrode of the cell and supplying air to an air electrode of the cell, the fuel cell system comprising: a fuel cell having a fuel electrode; first and second fuel tanks connected to opposite ends of the fuel electrode of the cell, the first and second fuel tanks for storing fuel fluid therein; pipe lines connected to the first and second fuel tanks, each pipe line having at least one air inlet/outlet and at least one fuel inlet/outlet; a pressurized air source; a first valve located in a first air flow path connected between the pressurized air source and the first fuel tank, the first valve for opening and closing the first air flow path; a second valve located in a second air flow path branched from the first air flow path at a point between the first valve and the first fuel tank, and connected to an atmosphere outside the fuel cell system, a third valve located in a third air flow path connected between the pressurized air source and the air inlet/outlet of the second fuel tank, a fourth valve located in a fourth air flow path branched from the third air flow path at a point between the third valve and the second fuel tank, and connected to an atmosphere outside the fuel cell system, the first, second, third, and fourth valves for switching between a first operation stage and a second operation stage, a first sensor for detecting a level of a fuel fluid in the first fuel tank; a second sensor for detecting a level of a fuel fluid in the second fuel tank; and a controller for instructing the first, second, third, and fourth valves to switch to the second stage when the second sensor detects a lowering of a liquid level in the second fuel tank, and instructing the first, second, third, and fourth valves to switch to the first stage when the first sensor detects a lowering of a liquid level in the first fuel tank, wherein the first and fourth valves close and the second and third valves open in the first stage, thereby providing pressurized air to the second fuel tank, transferring a fuel fluid from the second fuel tank to the first fuel tank via the fuel cell and, releasing air from the first fuel tank through the second valve to an atmosphere outside the fuel cell, and the first and fourth valves open and the second and third valves close in the second stage, thereby providing pressurized air to the first fuel tank, transferring a fuel fluid from the first fuel tank to the second fuel tank via the fuel cell, and releasing air from the second fuel tank to an atmosphere outside the fuel cell via the fourth valve.