Fuel cell system with electrochemical anode exhaust recycling

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

providing a fuel inlet stream into a fuel cell stack, wherein the fuel cell stack is a solid oxide fuel cell stack;

operating the fuel cell stack to generate electricity and a hydrogen containing fuel exhaust stream;

lowering a temperature of a fuel exhaust stream to between 120° C. and 200° C. by exchanging heat with the fuel inlet stream and then with an air inlet stream;

passing the lower temperature fuel exhaust stream to a splitter;

passing a first portion of the lower temperature fuel exhaust stream to a high temperature, low hydration ion exchange membrane cell stack and a second portion of the lower temperature fuel exhaust stream into the fuel inlet stream;

separating at least a portion of hydrogen contained in the fuel exhaust stream using the high temperature, low hydration ion exchange membrane cell stack;

providing the hydrogen separated from the fuel exhaust stream into the fuel inlet stream; and

heating the air inlet stream, which is preheated by the fuel exhaust stream, using heat from an air exhaust stream;

wherein an AC electrical efficiency of the system is at least 50% and an effective fuel utilization is at least 94%.

2. The method of claim 1 , wherein the high temperature, low hydration ion exchange membrane cell stack comprises a stack of acid doped non-fluorinated ion exchange ionomer membrane cells.

3. The method of claim 2 , wherein each membrane of the membrane cells comprises a polybenzimidazole (PBI) membrane doped with sulfuric or phosphoric acid.

4. The method of claim 1 , wherein the step of lowering a temperature of the fuel exhaust stream to between 120° C. and 200° C. comprises lowering a temperature of the fuel exhaust stream to between 160° C. and 190° C.

5. The method of claim 1 , wherein the second portion of the lower temperature fuel exhaust stream is provided into the fuel inlet stream with a blower or compressor.

6. The method of claim 5 , wherein the blower or compressor is controlled to vary an amount of the fuel exhaust stream being provided into the fuel inlet stream based on at least one condition.

7. The method of claim 6 , wherein the at least one condition comprises a detected or observed condition of the system.

8. The method of claim 6 , wherein the at least one condition comprises previous calculations or conditions which require a temporal adjustment of an amount of hydrogen in the fuel inlet stream.

9. The method of claim 6 , wherein the at least one condition comprises a change in a price of electricity or hydrocarbon fuel compared to a price of hydrogen.

10. The method of claim 6 , wherein the at least one condition comprises a change in electricity demand by users of electricity generated by the system.