Structure and method for optimizing system efficiency when operating an SOFC system with alcohol fuels

1. A method of operating a fuel cell system, comprising:

providing a fuel inlet stream from a fuel source into a fuel inlet conduit:

measuring, using a senor, a first water-to-fuel ratio of the fuel inlet stream in the fuel inlet conduit;

providing

a quantity of water into the fuel inlet conduit downstream from the sensor if the first water-to-fuel ratios is less than a predetermined water-to-fuel ratio; and

providing the fuel inlet stream into a fuel cell stack, wherein the fuel inlet stream comprises a second water-to-fuel ratio that is substantially equal to the predetermined water-to-fuel ratio;

wherein the step of providing the quantity of water downstream from the sensor comprises at least one of:

providing liquid water into the fuel inlet conduit downstream from the sensor and upstream from a heat exchanger in which the water and the fuel are vaporized; or

providing water vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized.

2. The method of claim 1 , wherein the step of providing the quantity of water comprises opening a water valve in a water inlet conduit downstream from the sensor if the first water-to-fuel ratio is less than the desired water-to-fuel ratio.

3. The method of claim 1 , wherein:

the fuel source comprises an alcohol fuel source; and

the sensor comprises an alcoholometer in the fuel inlet stream.

4. The method of claim 1 , wherein the step of providing the quantity of water downstream from the sensor comprises providing liquid water into the fuel inlet conduit downstream from the sensor and upstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is less than the desired water-to-fuel ratio.

5. The method of claim 1 , wherein the step of providing the quantity of water downstream from the sensor comprises providing water vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is less than the desired water-to-fuel ratio.

6. The method of claim 1 , wherein the fuel source comprises impure alcohol fuel comprising water and having a first water-to-fuel ratio.

7. The method of claim 6 , further comprising,

providing a quantity of purified fuel into the fuel inlet conduit if the first water-to-fuel ratio is greater than the desired water-to-fuel ratio.

8. The method of claim 7 , wherein the step of providing the quantity of purified comprises providing liquid fuel into the fuel inlet conduit downstream from the sensor and upstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is greater than the desired water-to-fuel ratio.

9. The method of claim 7 , wherein the step of providing the quantity of purified fuel comprises providing fuel vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is greater than the desired water-to-fuel ratio.

10. A method of operating a fuel cell system, comprising:

providing a fuel inlet stream from a fuel source into a fuel inlet conduit, wherein the fuel inlet stream provided from the fuel source comprises water and has a first water-to-fuel ratio;

measuring, using a sensor, the first water-to-fuel ratio of the fuel inlet stream in the fuel inlet conduit;

providing a quantity of water into the fuel inlet conduit downstream from the sensor if the first water-to-fuel ratio is less than a predetermined water-to-fuel ratio such that the fuel inlet stream comprises a second water-to-fuel ratio that is substantially equal to the predetermined water-to-fuel ratio and that is different from the first water-to-fuel ratio and

providing the fuel inlet stream having the second water-to-fuel ratio into a fuel cell stack,

wherein the step of providing the quantity of water downstream from the sensor comprises at least one of:

opening a water valve in a water inlet conduit to provide liquid water into the fuel inlet conduit downstream from the sensor and upstream from a heat exchanger in which the water and the fuel are vaporized; or

opening a water vapor valve in a water vapor inlet conduit to provide water vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized.

11. The method of claim 10 , wherein the step of providing the quantity of water downstream from the sensor comprises opening the water valve in the water inlet conduit to provide liquid water into the fuel inlet conduit downstream from the sensor and upstream from the heat exchanger if the first water-to-fuel ratio is less than the desired water-to-fuel ratio.

12. The method of claim 10 , wherein the step of providing the quantity of water downstream from the sensor comprises opening the water vapor valve in the water vapor inlet conduit to provide water vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is less than the desired water-to-fuel ratio.

13. The method of claim 10 , further comprising providing a quantity of purified fuel into the fuel inlet conduit if the first water-to-fuel ratio is greater than the predetermined water-to-fuel ratio such that the fuel inlet stream comprises a second water-to-fuel ratio that is substantially equal to a predetermined water-to-fuel ratio and that is different from the first water-to-fuel ratio.

14. The method of claim 13 , wherein the step of providing the quantity of purified fuel into the fuel inlet conduit occurs downstream from the sensor.

15. The method of claim 13 , wherein the step of providing the quantity of purified fuel downstream from the sensor comprises opening a fuel valve in a purified fuel inlet conduit to provide purified liquid fuel into the fuel inlet conduit downstream from the sensor and upstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is greater than the predetermined water-to-fuel ratio.

16. The method of claim 13 , wherein the step of providing the quantity of purified fuel downstream from the sensor comprises opening a fuel vapor valve in purified fuel vapor inlet conduit to provide purified fuel vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is greater than the predetermined water-to-fuel ratio.

17. The method of claim 10 , wherein the fuel comprises an alcohol fuel, and the sensor comprises an alcoholometer in the fuel inlet conduit.

18. The method of claim 5 , wherein the water vapor is supplied by an anode exhaust stream of the fuel cell stack.

19. The method of claim 9 , wherein the fuel vapor is supplied by an anode exhaust stream of the fuel cell stack.

20. The method of claim 12 , wherein the water vapor is supplied by an anode exhaust stream of the fuel cell stack.

21. The method of claim 16 , wherein the fuel vapor is supplied by an anode exhaust stream of the fuel cell stack.

22. A method of operating a fuel cell system, comprising:

providing a fuel inlet stream from a fuel source into a fuel inlet conduit;

measuring, using a sensor, a first water-to-fuel ratio of the fuel inlet stream in the fuel inlet Conduit;

providing a quantity of purified fuel into the fuel inlet conduit downstream from the sensor if the first water-to-fuel ratio is greater than a predetermined water-to-fuel ratio; and

providing the fuel inlet stream into a fuel cell stack, wherein the fuel inlet stream comprises a second water-to-fuel ratio that is substantially equal to the predetermined water-to-fuel ratio;

wherein the step of providing the quantity of purified fuel downstream from the sensor comprises at least one of:

providing liquid fuel into the fuel inlet conduit downstream from the sensor and upstream from a heat exchanger in which the water and the fuel are vaporized; or

providing fuel vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized.

23. The method of claim 22 , wherein the step of providing the quantity of purified fuel downstream from the sensor comprises providing liquid fuel into the fuel inlet conduit downstream from the sensor and upstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel ratio is greater than the predetermined water-to-fuel ratio.

24. The method of claim 22 , wherein the step of providing the quantity of purified fuel downstream from the sensor comprises providing fuel vapor into the fuel inlet conduit downstream from the sensor and downstream from the heat exchanger in which the water and the fuel are vaporized if the first water-to-fuel. ratio is greater than the predetermined water-to-fuel ratio.

25. The method of claim 22 , wherein:

the fuel source comprises an alcohol fuel source; and

the sensor comprises am alcoholometer in the fuel inlet stream.

26. The method of claim 25 , wherein the fuel source comprises impure alcohol fuel comprising water and having the first water-to-fuel ratio.