Fuel cell power generation system and method of controlling the same

• US 5,462,815 A
• Filed: 08/19/1993
• Issued: 10/31/1995
• Est. Priority Date: 08/20/1992
• Status: Expired due to Fees

• Current Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Original Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Inventors: Horiuchi, Yoshimi
• Primary Examiner(s): KALAFUT, STEPHEN J
• Application Number:
  US08/108,447
• Time in Patent Office: 803 Days
• Field of Search: 429/22, 429/23, 429/13
• US Class Current: 429/415
• CPC Class Codes: H01M 8/04228 during shut-down
• CPC Class Codes: H01M 8/04246 Short circuiting means for defective fuel cells detection of defective fuel cells H01M8/04664, methods for shunting fuel cells H01M8/04955
• CPC Class Codes: H01M 8/04303 applied during shut-down
• CPC Class Codes: H01M 8/04679 of fuel cell stacks
• CPC Class Codes: H01M 8/04955 Shut-off or shut-down of fuel cells
• CPC Class Codes: H01M 8/0612 from carbon-containing material
• CPC Class Codes: H01M 8/0662 Treatment of gaseous reactants or gaseous residues, e.g. cleaning
• CPC Class Codes: H01M 8/249 comprising two or more groupings of fuel cells, e.g. modular assemblies
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y10S 429/90 Fuel cell including means for power conditioning, e.g. Conversion to ac

Abstract

A fuel cell power generation system includes a fuel cell subsystem having a plurality of fuel cell stacks connected in parallel to each other, a reformer, an oxidant gas feeder, a fuel gas exhaust conduit, an oxidant gas exhaust conduit, an inverter, shut-off valves, an exhaust fuel gas dilution conduit, and first and second bypass conduits. When a fuel cell stack is in an abnormal state or out of order and issues an abnormality signal, a part of reformed fuel from the reformer is bypassed through the first bypass conduit to the fuel gas exhaust conduit and diluted with an inert gas such as nitrogen gas from the exhaust fuel gas dilution conduit. The diluted gas is fed to the reformer. Also, air from the oxidant gas feeder, e.g., an air blower, is partly bypassed through the second bypass conduit and the oxidant gas exhaust conduit to the reformer.

Claims

1. A fuel cell power generation system, comprising:

a fuel cell subsystem including a plurality of fuel cell stacks connected in parallel with each other, each of said fuel cell stacks comprising at least one fuel cell and a dc breaker connected in series therewith;

a source of raw fuel gas;

a raw fuel gas feed conduit for feeding said raw fuel gas;

a reformer for forming fuel gas, said reformer having first, second and third inputs, and an output, the first input being connected to said source of raw fuel gas through said raw fuel gas feed conduit;

a fuel gas feed conduit interposed between the output of said reformer and said fuel cell stacks for feeding fuel gas to said fuel cell stacks, the fuel gas feed conduit having a fuel gas shut-off valve for each of said fuel cell stacks;

a fuel gas exhaust conduit connected to said fuel cell stacks and to the second input of said reformer, said fuel gas exhaust conduit having a fuel gas exhaust shut-off valve for each of said fuel cell stacks;

a source of oxidant gas;

an oxidant gas feed conduit for connecting said source of oxidant gas to said fuel cell stacks;

an oxidant gas exhaust conduit connected to said fuel cell stacks and to the third input of said reformer, said oxidant gas exhaust conduit having an oxidant gas exhaust shut-off valve for each of said fuel cells stacks;

said reformer receiving exhaust oxidant gas and exhaust fuel gases from said oxidant and fuel gas exhaust conduits, respectively, for reforming said exhaust fuel gas into said fuel gas and feeding said fuel gas to said fuel cell subsystem;

a first bypass conduit interposed between said reformer and said fuel gas exhaust conduit, said first bypass conduit having a first flow rate control valve therein;

a second bypass conduit interposed between said oxidant gas feed conduit and said oxidant gas exhaust conduit, said second bypass conduit having a second flow rate control valve therein;

a plurality of abnormality detectors, one of said detectors being connected to each of said fuel cell stacks for detecting the output thereof, each of said abnormality detectors generating a shut-off signal when the output of the fuel cell stack to which it is connected decreases to an amount below which the total load on said source of oxidant gas and on said reformer has reached a predetermined minimum value required for operation of said power generation system, said shut-off signal shutting the fuel gas, fuel gas exhaust, oxidant gas and oxidant gas exhaust shut-off valves, operating said first flow rate control valve to bypass a part of the fuel gas from said reformer to said fuel gas exhaust conduit, operating said second flow rate control valve to bypass a part of the oxidant gas from said source of oxidant gas to said oxidant gas exhaust conduit, and opening the dc breaker of the fuel cell stack connected to the abnormality detector which generated said shut-off signal; and

an inverter electrically connected in parallel with said at least one fuel cell of each of said fuel cell stacks, through said dc breaker, for converting a DC output of said fuel cells to an AC output.

2. The fuel cell power generation system as claimed in claim 1, wherein said source of oxidant gas is an air blower.

3. The fuel cell power generation system as claimed in claim 1, wherein said source of oxidant gas is a compressor.

4. The fuel cell power generation system as claimed in claim 1, further comprising a source of inert gas for diluting said exhaust fuel gas and a conduit connected to said source of inert gas for feeding said inert gas to said fuel gas exhaust conduit.

5. The fuel cell power generation system as claimed in claim 4, wherein said inert gas is nitrogen gas.

6. The fuel cell power generation system as claimed in claim 1, wherein each of said abnormality detectors has an operation mode judging means for judging whether said fuel cell subsystem is operating in a first output operation mode or a second output operation mode, said first output operation mode generating an output equal to or lower than a predetermined output, and said second output operation mode generating an output higher than said predetermined output, said predetermined output being equal to an amount below which the total load on said source of oxidant gas and on said reformer has reached a minimum value required for operation of said power generating system.

7. The fuel cell power generation system as claimed in claim 1, wherein said reformed gas is hydrogen gas.

8. A method of controlling a fuel cell power generation system comprising a plurality of fuel cell stacks each having at least one fuel cell and a dc breaker connected in series therewith, an abnormality detector associated with each of said fuel cell stacks, a reformer for feeding fuel gas to said fuel cell stacks, and means for feeding oxidant gas to said fuel cell stacks,

said method, upon issuance of an abnormality signal by the abnormality detector of a given fuel cell stack indicating that the given fuel cell stack has generated an output below a minimum value required for operation of the fuel cell power generation system, comprising the steps of:

opening the dc breaker of the given fuel cell stack and stopping the feeding of fuel gas and oxidant gas to the given fuel cell stack;

discharging a part of the fuel gas from the reformer to outside the power generation system; and

discharging a part of the oxidant gas to outside the power generation system.

9. The method claimed in claim 8 wherein said fuel cell power generation system further comprises first and second flow rate control valves, and wherein the amount of fuel gas and oxidant gas discharged to outside the system are controlled by the first and second flow rate control valves respectively.