Dual function heat exchanger for start-up humidification and facility heating in SOFC system

• US 20080096073A1
• Filed: 10/10/2007
• Published: 04/24/2008
• Est. Priority Date: 10/23/2006
• Status: Active Grant

• Current Assignee: Bloom Energy Corporation
• Original Assignee: Bloom Energy Corporation
• Inventors: Venkataraman, Swaminathan
• Granted Patent: US 8,435,689 B2
• Time in Patent Office: Days
• US Class Current: 429/413
• CPC Class Codes: F28D 7/0016 the conduits for one medium or the conduits for both media being bent F28D7/0033 takes precedence
• CPC Class Codes: H01M 8/04014 Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
• CPC Class Codes: H01M 8/04141 by water containing exhaust gases
• CPC Class Codes: H01M 8/04225 during start-up
• CPC Class Codes: H01M 8/04302 applied during start-up
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A fuel cell system includes a fuel cell stack and a heat exchanger. The heat exchanger vaporizes water which is provided to the fuel cell stack during start-up of the fuel cell system and heats a heat transfer medium which is provided to a facility associated with the fuel cell system during steady-state operation of the fuel cell system.

Claims

1. A fuel cell system, comprising:

a fuel cell stack; and

a heat exchanger which in use vaporizes water which is provided to the fuel cell stack during start-up of the fuel cell system and heats a heat transfer medium which is provided to a facility associated with the fuel cell system during steady-state operation of the fuel cell system.

2. The system of claim 1, wherein:

the fuel cell stack comprises a SOFC stack; and

the heat exchanger comprises a first output which is fluidly connected to a fuel inlet conduit of the fuel cell stack and a second output which is fluidly connected to a heat transfer medium conduit being provided to the facility.

3. The system of claim 2, wherein a cathode exhaust conduit of the fuel cell stack is fluidly connected to an input of the heat exchanger.

4. The system of claim 3, further comprising a first output conduit which connects the first output of the heat exchanger to the fuel inlet conduit.

5. The system of claim 3, further comprising:

a hydrocarbon fuel source connected to an input of the fuel inlet conduit; and

an external or internal reformer connected to the output of the fuel inlet conduit.

6. The system of claim 1, further comprising:

a cathode exhaust conduit extending from a cathode exhaust of the fuel cell stack through the heat exchanger;

a process steam conduit which is thermally integrated with the cathode exhaust conduit in the heat exchanger, wherein an inlet of the process steam conduit is connected to a liquid water source and an outlet of the process steam conduit is fluidly connected to a fuel inlet conduit of the fuel cell stack; and

a heat transfer medium conduit which is thermally integrated with the cathode exhaust conduit in the heat exchanger, wherein an inlet of the heat transfer medium conduit is connected to a liquid water source and an outlet of the heat transfer medium conduit is fluidly connected to the facility heating system.

7. The system of claim 6, wherein the process steam conduit and the heat transfer medium conduit coil around the cathode exhaust conduit in the heat exchanger.

8. The system of claim 1, further comprising:

a cathode exhaust conduit extending from a cathode exhaust of the fuel cell stack through the heat exchanger; and

a steam conduit which is thermally integrated with the cathode exhaust conduit in the heat exchanger, wherein an inlet of the steam conduit is connected to a liquid water source, a first outlet of the steam conduit is fluidly connected to a fuel inlet conduit of the fuel cell stack, and a second outlet of the steam conduit is fluidly connected to the facility heating system.

9. The system of claim 8, wherein the steam conduit is coiled around the cathode exhaust conduit in the heat exchanger.

10. A fuel cell system, comprising:

a fuel cell stack; and

a means for vaporizing water which is provided to the fuel cell stack during start-up of the fuel cell stack and for heating a heat transfer medium which is provided to a facility associated with the fuel cell system during steady-state operation of the fuel cell stack.

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

during start-up of the fuel cell system, vaporizing liquid water in a heat exchanger using heat from a fuel cell stack of the fuel cell system, and providing steam generated in the heat exchanger into a hydrocarbon fuel inlet stream to form a humidified hydrocarbon fuel inlet stream; and

during steady-state operation of the fuel cell system, heating a heat transfer medium in the heat exchanger using heat from the fuel cell stack of the fuel cell system, and providing the heated heat transfer medium to a facility associated with the fuel cell system.

12. The method of claim 11, further comprising reforming the humidified hydrocarbon fuel inlet stream into a hydrogen containing fuel inlet stream, and providing the hydrogen containing fuel inlet stream to fuel cells of the fuel cell stack during the start-up of the fuel cell system.

13. The method of claim 12, further comprising using a cathode exhaust stream of the fuel cell stack to vaporize the water during the start-up of the fuel cell system and to heat the heat transfer medium during the steady-state operation of the fuel cell system.

14. The method of claim 13, wherein the heat transfer medium comprises water and the step of heating the heat transfer medium comprises vaporizing the water into steam or heating the water.

15. The method of claim 14, further comprising:

providing the cathode exhaust stream through a cathode exhaust conduit extending from a cathode exhaust of the fuel cell stack through the heat exchanger;

during the start-up of the fuel cell system, providing water through a process steam conduit which is thermally integrated with the cathode exhaust conduit in the heat exchanger, and providing the steam generated in the process steam conduit in the heat exchanger into the hydrocarbon fuel inlet stream; and

during the steady-state operation of the fuel cell system, providing water through a heat transfer medium conduit which is thermally integrated with the cathode exhaust conduit in the heat exchanger, and providing steam or hot water generated in the heat transfer medium conduit in the heat exchanger to a heating system of the facility.

16. The method of claim 15, wherein the process steam conduit and the heat transfer medium conduit coil around the cathode exhaust conduit in the heat exchanger.

17. The method of claim 14, further comprising:

providing the cathode exhaust stream through a cathode exhaust conduit extending from a cathode exhaust of the fuel cell stack through the heat exchanger;

during the start-up of the fuel cell system, providing water through a steam conduit which is thermally integrated with the cathode exhaust conduit in the heat exchanger, and providing the steam generated in the steam conduit in the heat exchanger into the hydrocarbon fuel inlet stream; and

during the steady-state operation of the fuel cell system, providing water through the steam conduit, and providing steam or hot water generated in the steam conduit in the heat exchanger to a heating system of the facility

18. The method of claim 17, wherein the steam conduit is coiled around the cathode exhaust conduit in the heat exchanger.

19. The method of claim 14, further comprising vaporizing liquid water in the heat exchanger and providing steam generated in the heat exchanger into the hydrocarbon fuel inlet stream to form a humidified hydrocarbon fuel inlet stream during the steady-state operation of the fuel cell system.

20. The method of claim 11, wherein the fuel cell stack comprises a SOFC stack.