Fuel cell system with partial recycling of anode exhaust

• US 20100239924A1
• Filed: 07/24/2006
• Published: 09/23/2010
• Est. Priority Date: 07/25/2005
• Status: Active Grant

• Current Assignee: Bloom Energy Corporation
• Original Assignee: Bloom Energy Corporation
• Inventors: LeVan, M. Douglas, Mitlitsky, Fred, Finn, John, Venkataraman, Swaminathan, McElroy, James
• Granted Patent: US 9,911,989 B2
• Time in Patent Office: Days
• US Class Current: 429/423
• CPC Class Codes: H01M 2008/1293 Fuel cells with solid oxide electrolytes
• CPC Class Codes: H01M 8/04007 related to heat exchange
• CPC Class Codes: H01M 8/04097 with recycling of the reactants H01M8/04119, H01M8/04104 take precedence
• CPC Class Codes: H01M 8/04231 Purging of the reactants
• CPC Class Codes: H01M 8/0612 from carbon-containing material
• CPC Class Codes: H01M 8/0668 Removal of carbon monoxide or carbon dioxide
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A method of operating a fuel cell system includes providing a fuel inlet stream into a fuel cell stack, operating the fuel cell stack to generate electricity and a hydrogen containing fuel exhaust stream having a temperature above 200 C, lowering a temperature of the fuel exhaust stream to 200 C or less, separating the fuel exhaust stream into a first separated fuel exhaust stream and a second separated fuel exhaust stream, and recycling the first separated fuel exhaust stream into the fuel inlet stream.

Claims

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

providing a fuel inlet stream into a fuel cell stack;

operating the fuel cell stack to generate electricity and a fuel exhaust stream having a temperature above 200 C;

lowering a temperature of the fuel exhaust stream to 200 C or less;

separating the fuel exhaust stream into a first separated fuel exhaust stream and a second separated fuel exhaust stream; and

recycling the first separated fuel exhaust stream into the fuel inlet stream.

2. The method of claim 1, further comprising using a low temperature blower to controllably recycle the first separated fuel exhaust stream having a temperature of 200 C or less into the fuel inlet stream.

3. The method of claim 2, wherein:

the first separated fuel exhaust stream contains steam;

the fuel inlet stream comprises a hydrocarbon fuel inlet stream; and

the step of recycling comprises controllably recycling the first separated fuel exhaust stream into the fuel inlet stream to achieve a steam to carbon ratio of between 2;

1 and 2.3;

1 in the fuel inlet stream.

4. The method of claim 3, further comprising varying an amount of fuel exhaust being recycled into the fuel inlet stream to continuously maintain the steam to carbon ratio of between 2:

1 and 2.3;

1 in the fuel inlet stream during operation of the fuel cell stack.

5. The method of claim 4, wherein the fuel cell stack comprises a solid oxide fuel cell stack and the fuel inlet stream comprises a methane or a natural gas fuel inlet stream.

6. The method of claim 5, further comprising:

providing the fuel inlet stream into a reformer;

reforming the fuel inlet stream in the reformer;

providing the reformed fuel inlet stream into the fuel cell stack; and

using at least one of radiative, convective or conductive heat generated in the fuel cell stack or an air exhaust stream from the fuel cell stack to heat the reformer.

7. The method of claim 1, further comprising:

separating at least a portion of hydrogen contained in a second separated fuel exhaust stream;

and providing at least a portion of the separated hydrogen to at least one of a hydrogen using device, to a hydrogen storage vessel or into the fuel inlet stream.

8. The method of claim 7, wherein the step of separating at least a portion of hydrogen contained in a second separated fuel exhaust stream comprises using a partial pressure adsorption system or an electrochemical hydrogen pump to separate at least a portion of the hydrogen.

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

providing a fuel inlet stream into a fuel cell stack;

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

controllably separating the fuel exhaust stream into a first separated fuel exhaust stream and a second separated fuel exhaust stream; and

controllably recycling the first separated fuel exhaust stream into the fuel inlet stream.

10. The method of claim 9, wherein:

the fuel inlet stream comprises a hydrocarbon fuel inlet stream;

the fuel cell stack comprises a solid oxide fuel cell stack; and

the step of controllably recycling comprises controllably recycling the first\ separated fuel exhaust stream into the fuel inlet stream to achieve a steam to carbon ratio of between 2;

1 and 2.3;

1 in the fuel inlet stream.

11. The method of claim 10, further comprising varying an amount of fuel exhaust being recycled into the fuel inlet stream to continuously maintain the steam to carbon ratio of between 2:

1 and 2.3;

1 in the fuel inlet stream during operation of the fuel cell stack.

12. The method of claim 11, further comprising detecting at least one operating parameter of the fuel cell system and varying at least one of a ratio of the first separated fuel exhaust stream to the second separated fuel exhaust stream or an amount of the first separated fuel exhaust stream being recycled into the fuel inlet stream based on the step of detecting.

13. The method of claim 12, further comprising using a computer to control at least one of a multi-way valve used to controllably separate the fuel exhaust stream or a blower used to controllably recycle the first separated fuel exhaust stream.

14. The method of claim 9, further comprising lowering a temperature of the fuel exhaust stream to 200 C or less prior to the step of separating and using a low temperature blower to controllably recycle the first separated fuel exhaust stream having a temperature of 200 C or less into the fuel inlet stream.

15. The method of claim 9, further comprising:

providing the fuel inlet stream into a reformer;

reforming the fuel inlet stream in the reformer;

providing the reformed fuel inlet stream into the fuel cell stack; and

using at least one of radiative, convective or conductive heat generated in the fuel cell stack or an air exhaust stream from the fuel cell stack to heat the reformer.

16. A fuel cell system, comprising:

a high temperature fuel cell stack;

at least one device which is adapted to lower a temperature of a stack fuel exhaust stream from a temperature above 200 C to a temperature below 200 C;

a fuel exhaust splitter device which is adapted to separate the fuel exhaust stream into a first separated fuel exhaust stream and a second separated fuel exhaust stream; and

a low temperature blower adapted controllably recycle the first separated fuel exhaust stream having a temperature below 200 C into a fuel cell stack fuel inlet stream.

17. The device of claim 16, wherein:

the at least one device which is adapted to lower the temperature comprises a plurality of heat exchangers arranged so that the fuel exhaust stream passes through each heat exchanger in series;

the fuel exhaust splitter device comprises a computer or operator controlled multi-way valve; and

the fuel cell stack comprises a solid oxide fuel cell stack.

18. The device of claim 17, further comprising:

a hydrocarbon fuel inlet stream source;

a fuel reformer which is thermally integrated with the fuel cell stack to receive heat from the fuel cell stack;

a detector adapted to detect at least one operating parameter of the fuel cell system; and

a means for controlling least one of the low temperature blower or the multi-way valve to vary an amount of fuel exhaust being recycled into the fuel inlet stream to continuously maintain a steam to carbon ratio of between 2;

1 and 2.3;

1 in the fuel inlet stream during operation of the fuel cell stack based on information provided by the detector.

19. A fuel cell system, comprising:

a high temperature fuel cell stack;

a computer controlled multi-way valve which is adapted to controllably separate a fuel exhaust stream from the stack into a first separated fuel exhaust stream and a second separated fuel exhaust stream; and

a computer controlled blower adapted controllably recycle the first separated fuel exhaust stream into a fuel cell stack fuel inlet stream.

20. The system of claim 19, further comprising:

a hydrocarbon fuel inlet stream source;

a fuel reformer which is thermally integrated with the fuel cell stack to receive heat from the fuel cell stack;

a detector adapted to detect at least one operating parameter of the fuel cell system; and

a means for controlling least one of the blower or the multi-way valve to vary an amount of fuel exhaust being recycled into the fuel inlet stream to continuously maintain a steam to carbon ratio of between 2;

1 and 2.3;

1 in the fuel inlet stream during operation of the fuel cell stack based on information provided by the detector.