High temperature fuel cell system with integrated heat exchanger network

• US 20060251940A1
• Filed: 05/09/2005
• Published: 11/09/2006
• Est. Priority Date: 05/09/2005
• Status: Active Grant

• Current Assignee: Bloom Energy Corporation
• Original Assignee: Bloom Energy Corporation
• Inventors: Bandhauer, Todd M., Valensa, Jeroen, Reinke, Michael J.
• Granted Patent: US 7,858,256 B2
• Time in Patent Office: Days
• US Class Current: 429/414
• CPC Class Codes: F28D 9/0075 the plates having openings therein for circulation of the heat-exchange medium from one conduit to another
• CPC Class Codes: H01M 8/04014 Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
• CPC Class Codes: H01M 8/04097 with recycling of the reactants H01M8/04119, H01M8/04104 take precedence
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A fuel cell system (1) is provided and includes a fuel cell stack (3) and a heat transfer device (5) adapted to transfer heat from a cathode exhaust stream of the fuel cell stack (3) to water to be provided to a fuel inlet stream.

Claims

1. A fuel cell system, comprising:

a fuel cell stack; and

a heat transfer device adapted to transfer heat from a cathode exhaust stream of the fuel cell stack to water to be provided to a fuel inlet stream.

2. The system of claim 1, wherein the fuel cell stack comprises a solid oxide fuel cell stack.

3. The system of claim 1, wherein the heat transfer device comprises a water evaporator adapted to convert liquid water to steam, the evaporator comprising:

a first input operatively connected to a cathode exhaust outlet of the fuel cell stack;

a second input operatively connected to a water source; and

a first output operatively connected to a fuel inlet of the fuel cell stack.

4. The system of claim 3, further comprising a fuel preheater heat exchanger which comprises:

a first input operatively connected to the cathode exhaust outlet of the fuel cell stack;

a second input operatively connected to a fuel source; and

a first output operatively connected to a fuel cell stack.

5. The system of claim 4, wherein the fuel preheater heat exchanger is adapted to transfer heat from the cathode exhaust stream of the fuel cell stack to the fuel inlet stream being provided to the fuel cell stack.

6. The system of claim 5, wherein:

the evaporator comprises a co-flow evaporator in which the cathode exhaust stream and the water are adapted to flow in a same direction; and

an output of the evaporator is operatively connected to an inlet of the fuel preheater heat exchanger such that the cathode exhaust stream flows from the evaporator into the fuel preheater heat exchanger.

7. The system of claim 1, further comprising an air preheater which is adapted to preheat an air inlet stream using heat from an anode exhaust stream.

8. The system of claim 7, wherein the air preheater is adapted to partially condense the water vapor in the anode exhaust stream prior to the anode exhaust stream entering a condenser.

9. The system of claim 7, further comprising a cathode recuperator heat exchanger which has a size below a predetermined size, such that the cathode recuperator heat exchanger is adapted to provide the cathode exhaust stream exiting the cathode recuperator heat exchanger at a temperature of at least 200°

C.

10. A fuel cell system, comprising:

a fuel cell stack;

a first means for evaporating water to steam using heat from a fuel cell stack cathode exhaust stream; and

a second means for providing the steam into a fuel inlet stream being directed to the fuel cell stack.

11. The system of claim 10, further comprising:

a third means for heating an air inlet stream using the cathode exhaust stream upstream of evaporating the water and for providing an exiting cathode exhaust stream having a temperature of at least 200°

C. after heating the air inlet stream; and

a fourth means for heating the air inlet stream using a fuel cell stack anode exhaust stream prior to heating the air inlet stream using the cathode exhaust stream.

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

operating a fuel cell stack to generate electricity;

evaporating water to steam using heat from a fuel cell stack cathode exhaust stream; and

providing the steam into a fuel inlet stream being directed to the fuel cell stack.

13. The method of claim 12, wherein the fuel cell stack comprises a solid oxide fuel cell stack.

14. The method of claim 12, further comprising heating an air inlet stream using the cathode exhaust stream upstream of evaporating the water.

15. The method of claim 14, further comprising heating the air inlet stream using a fuel cell stack anode exhaust stream prior to heating the air inlet stream using the cathode exhaust stream.

16. The method of claim 15, further comprising partially condensing water vapor in the anode exhaust stream during the heating of the air inlet stream.

17. The method of claim 14, wherein the cathode exhaust stream has a temperature of at least 200°

C. after heating the air inlet stream.

18. The method of claim 12, further comprising preheating the fuel inlet stream with the cathode exhaust stream downstream of evaporating the water.

19. The method of claim 12, wherein the step of evaporating comprises flowing the cathode exhaust stream and the water in a same direction in an evaporator.

20. The method of claim 12, further comprising:

mixing the steam and the fuel inlet stream;

heating the steam and fuel mix using heat from a fuel cell stack anode exhaust stream; and

providing the steam and fuel mix into a reformer.

21. The method of claim 12, further comprising:

reforming the fuel comprising at least one of methane and natural gas in the reformer; and

providing the reformed fuel into the anode inlet of the fuel cell stack.

22. A fuel cell system, comprising:

a fuel cell stack; and

a concurrent flow water evaporator which is adapted to transfer heat from a cathode exhaust stream to water to be provided to a fuel inlet stream.

23. The system of claim 22 further comprising a fuel preheater, a cathode exhaust stream output of the evaporator operatively connected to the fuel preheater such that the cathode exhaust stream flows from the evaporator into the fuel preheater.

24. A fuel cell system, comprising:

a fuel cell stack; and

a first means for transferring heat from a cathode exhaust stream to water to be provided to a fuel inlet stream, such that the cathode exhaust stream and the water flow in a same direction in the first means.

25. The system of claim 24, wherein:

the first means comprises a means for providing the cathode exhaust stream into a fuel preheater.

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

flowing a cathode exhaust stream and a water stream in concurrent flow relationship;

evaporating the water to steam using heat from the cathode exhaust stream while flowing in said concurrent flow relationship; and

providing the steam into a fuel inlet stream being directed into a fuel cell stack.

27. The method of claim 26 further comprising:

heating a fuel flow using heat from the cathode exhaust stream after said evaporating step.

28. A fuel cell system, comprising:

a fuel cell stack;

a heat transfer device adapted to transfer heat from a cathode exhaust stream of the fuel cell stack to water to be provided to a fuel inlet stream;

an air preheater which is adapted to preheat an air inlet stream using heat from an anode exhaust stream; and

a cathode recuperator heat exchanger which is adapted to transfer heat from the cathode exhaust stream to the air inlet stream, the cathode recuperator heat exchanger operatively connected upstream from the heat transfer device with respect to the cathode exhaust stream and downstream from the air preheater with respect to the air inlet stream, and sized to provide a cathode exhaust stream to the heat transfer device at a sufficiently high temperature to allow for evaporation of the water in the heat transfer device.

29. The system of claim 28 wherein the cathode recuperator heat exchanger is sized to provide the cathode exhaust stream exiting the cathode recuperator heat exchanger at a temperature of at least 200°

C.