Fuel cell system

1. A fuel cell system comprising:

a reformer which generates a hydrogen-containing fuel gas from a material gas and steam;

a fuel cell which generates electric power by using the hydrogen-containing fuel gas supplied from the reformer;

a water tank which stores water;

a water utilizing device which utilizes the water supplied from the water tank and is mechanically, directly or indirectly connected to at least one of the reformer and the fuel cell;

a first water supply unit disposed on a water passage extending from the water tank to the water utilizing device and which supplies the water in the water tank to the water utilizing device; and

a purifier which is disposed on the water passage and purifies the water flowing through the water passage, wherein:

the purifier is located lower than a full water level of the water tank, and the water in the water tank is supplied to the purifier by potential head water,

the first water supply unit includes a pump, and

the pump is disposed on the water passage between the purifier and the water tank.

2. The fuel cell system according to claim 1 , wherein:

the water passage extending from the purifier to the first water supply unit is a first water passage; and

an exhaust port provided in at least one of the purifier and the first water passage, the exhaust port discharging a gas in the purifier to the atmosphere.

3. The fuel cell system according to claim 2 , further comprising a degassing passage connecting the exhaust port and the water tank, wherein

the water tank is open to the atmosphere.

4. The fuel cell system according to claim 3 , wherein a first valve for opening and closing the degassing passage is disposed on the degassing passage.

5. The fuel cell system according to claim 4 , further comprising a controller, wherein:

the controller opens the first valve when performing a water filling operation of the purifier, and

the controller closes the first valve when performing a hydrogen generating operation of the reformer.

6. The fuel cell system according to claim 1 , wherein the water utilizing device is open to the atmosphere.

7. The fuel cell system according to claim 1 , wherein:

the purifier is provided downstream of the first water supply unit, and

the first water supply unit is disposed on the water passage such that when the water level of the water tank is the full water level, the first water supply unit is filled with the water by the weight of the water.

8. The fuel cell system according to claim 1 , further comprising a first water level detector which detects the water level of the purifier.

9. The fuel cell system according to claim 8 , wherein the first water level detector which detects the water level of the purifier by detecting the water level of the water tank.

10. The fuel cell system according to claim 9 , further comprising:

a water feed unit which supplies the water to the water tank; and

a controller, wherein

when the first water level detector detects an increase in the water level, the controller stops the water supply of the water feed unit.

11. The fuel cell system according to claim 10 , wherein when the first water level detector detects a decrease in the water level after the water supply of the water feed unit is stopped, the controller restarts the water supply of the water feed unit.

12. The fuel cell system according to claim 8 , wherein:

the water utilizing device is an evaporator which generates the steam; and

the water passage extending from the purifier to the evaporator is a second water passage,

the fuel cell system further comprising:

a third water passage which branches from the second water passage and includes an open end which is open to the atmosphere;

a first switching unit selectively connecting the first water supply unit to the evaporator and the open end of the third water passage; and

a controller, wherein

when the first water level detector detects that the water level of the purifier is the full water level, the controller activates the first water supply unit in a state where the first water supply unit and the open end of the third water passage are connected to each other by the first switching unit.

13. The fuel cell system according to claim 1 , wherein:

the water utilizing device is a cooling water tank which stores the water which is to be supplied through a cooling water passage to the fuel cell,

the fuel cell system further comprising:

an evaporator which generates the steam;

a second water level detector which detects the water level of the cooling water tank;

a fourth water passage which connects the cooling water passage and the evaporator;

a second water supply unit disposed on the fourth water passage which supplies the water to the evaporator;

a branch passage which branches from the fourth water passage and including an open end which is open to the atmosphere;

a second switching unit which connects the second water supply unit selectively to the evaporator and the open end of the branch passage; and

a controller, and

when the second water level detector detects that the water level of the cooling water tank is a predetermined water level, the controller activates the second water supply unit in a state where the second water supply unit and the open end of the branch passage are connected to each other by the second switching unit.

14. The fuel cell system according to claim 13 , further comprising a cooling water supply unit disposed on the cooling water passage which supplies the water in the cooling water tank to the fuel cell, wherein

the controller activates the second water supply unit and the cooling water supply unit.

15. The fuel cell system according to claim 1 , further comprising a water feed passage through which the water is supplied from outside the fuel cell system to the water tank.