System and method for networking electrochemical devices

• US 5,413,878 A
• Filed: 10/28/1993
• Issued: 05/09/1995
• Est. Priority Date: 10/28/1993
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Department Of Energy
• Inventors: Archer, David H., Wimer, John G., Williams, Mark C.
• Primary Examiner(s): LANGEL, WAYNE A
• Application Number:
  US08/142,563
• Time in Patent Office: 558 Days
• Field of Search: 429/32, 429/16, 429/17, 429/18
• US Class Current: 429/425
• CPC Class Codes: B01D 53/326 in electrochemical cells
• CPC Class Codes: C25B 15/00 Operating or servicing cells
• CPC Class Codes: H01M 2008/147 Fuel cells with molten carbonates
• CPC Class Codes: H01M 2300/0051 Carbonates
• CPC Class Codes: H01M 8/04014 Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
• CPC Class Codes: H01M 8/04022 Heating by combustion
• CPC Class Codes: H01M 8/04089 of gaseous reactants
• CPC Class Codes: H01M 8/0625 in a modular combined reactor/fuel cell structure
• 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

Abstract

An improved electrochemically active system and method including a plurality of electrochemical devices, such as fuel cells and fluid separation devices, in which the anode and cathode process-fluid flow chambers are connected in fluid-flow arrangements so that the operating parameters of each of said plurality of electrochemical devices which are dependent upon process-fluid parameters may be individually controlled to provide improved operating efficiency. The improvements in operation include improved power efficiency and improved fuel utilization in fuel cell power generating systems and reduced power consumption in fluid separation devices and the like through interstage process fluid parameter control for series networked electrochemical devices. The improved networking method includes recycling of various process flows to enhance the overall control scheme.

Claims

1. An electrochemically active system, comprising:

a plurality of electrochemical devices each having an ionically conductive membrane, a porous anode disposed in contact with said ionically conductive membrane on one side thereof, a porous cathode disposed in contact with said ionically conductive membrane on a side thereof opposite said one side of said ionically conductive membrane, an anode process-fluid flow chamber disposed in fluid communication with said anode on a surface thereof opposite the surface contacting said ionically conductive membrane, and a cathode process-fluid flow chamber disposed in fluid communication with said cathode on a surface thereof opposite the surface contacting said electrochemical membrane;

means for electrically connecting said plurality of electrochemical devices in series;

a cathode process-fluid communicating means for connecting said cathode process-fluid flow chambers of each of said plurality of electrochemical devices in a serial fluid-flow arrangement through each of said plurality of electrochemical devices;

an anode process fluid communicating means for connecting said anode process-fluid flow chambers of each of said plurality of electrochemical devices in a serial fluid-flow arrangement so that said plurality of electrochemical devices are connected in a networked serial flow arrangement; and

control means coupled with said anode and cathode process-fluid communicating means for separately controlling the process-fluid parameters of each of said plurality of electrochemical devices individually so that the operating efficiency of each of said plurality of electrochemical devices is improved, thereby improving the system efficiency.

2. An electrochemically active system as set forth in claim 1 wherein said plurality of electrochemical devices are fuel cells.

3. An electrochemically active system as set forth in claim 1 wherein said plurality of electrochemical devices are fluid separation devices.

4. An electrochemically active system as set forth in claim 2 wherein said fuel cells are molten carbonate fuel cells and further including a fuel inlet means for introducing a fuel stream containing hydrogen or its compounds into said anode process-fluid flow chamber of said networked fuel cells, and an oxidant inlet means for introducing a carbon dioxide and oxygen containing oxidant feed stream into said cathode process-fluid flow chamber of said networked fuel cells.

5. An electrochemically active system as set forth in claim 4 wherein said means for introducing a fuel stream includes means for introducing methane into said anode process-fluid flow chamber and wherein said molten carbonate fuel cells are internally reforming fuel cells wherein methane can be converted into a hydrogen containing fuel within said anode process-fluid flow chamber of each of said plurality of fuel cells and wherein said oxidant inlet means includes means for introducing air into said cathode process-fluid flow chamber.

6. An electrochemically active system as set forth in claim 5 wherein said control means includes means for introducing an amount of fuel to a first one of said networked fuel cells which is substantially greater than the amount consumed by said first one of said cells so that the voltage generated by said first one of said cells is greater than the remainder of said networked cells.

7. An electrochemically active system as set forth in claim 6 wherein said plurality of fuel cells is a plurality of N fuel cells each designed to consume essentially the same amount of fuel and wherein the amount of fuel introduced into said first one of said N plurality of fuel cells is about N times the amount of fuel to be consumed by one of said fuel cells so that the voltages generated by each cell in sequence is greater than the remaining ones of the sequence of said networked cells, thereby increasing the power output of said networked fuel cells.

8. An electrochemically active system as set forth in claim 7 wherein said anode process-fluid flow chambers of said plurality of fuel cells are connected in a serial fluid flow arrangement countercurrent to the direction of flow of said cathode process-fluid flow chambers of said plurality of fuel cells and wherein said control means further includes means for feeding forward a controlled portion of said methane fuel stream to aid in temperature control thereby reducing ohmic voltage losses, a cathode-to-cathode feedback means including a heat exchanger means for recycling a cooled portion of said oxidant stream through said cathode process-fluid flow chambers to remove heat from each of said cells of said network and to heat said oxidant feed stream, and an anode-to-cathode feed back means for feeding back a portion of said output fuel stream which includes CO₂ to said oxidant feed stream in an amount sufficient to raise the ratio of CO₂ to O₂ to a factor of about two.

9. An electrochemically active system as set forth in claim 8 wherein said control means further includes an anode-to-anode feedback means for feeding back a portion of the anode process-fluid stream containing steam formed as a result of anode reactions at the output of said Nth cell of said networked series of cells to the input fuel stream to promote reforming of the methane in said input fuel stream and prevent carbon deposition and to preheat fuel feed to a desired inlet temperature.

10. An electrochemically active system as set forth in claim 9 wherein said anode-to-cathode feed back means and said cathode-to-cathode feedback means further includes a combustor wherein cathode-to-cathode and anode-to-cathode feedback streams are combined to remove unburned fuel in said anode-to-cathode feedback stream and wherein an exhaust stream from said combustor forms an input stream to said heat exchanger so that the combined feedback stream can be cooled prior to being mixed with said oxidant input stream.

11. An electrochemically active system as set forth in claim 10 wherein said N plurality of cells are each formed of a fuel cell stack.

12. An electrochemically active system as set forth in claim 3 wherein said fluid separation devices are molten carbonate fluid separation devices for separating CO₂ and O₂ from a fluid stream forming a source gas stream and further including an inlet means for introducing said source gas stream into said cathode process-fluid flow chambers of said networked separation devices, and a separated stream outlet means for conveying the separated stream of CO₂ and O₂ from said anode process-fluid flow chamber of said networked separation devices.

13. An electrochemically active system as set forth in claim 12 wherein said anode process fluid communicating means includes means for connecting said anode process-fluid flow chambers of each of said plurality of separation devices in a serial fluid flow arrangement countercurrent to the flow direction of said cathode process fluid flow.

14. An electrochemically active system as set forth in claim 13 wherein said control means includes means for introducing an amount of CO₂ and O₂ to a first one of said networked separation devices which is substantially greater than the amount separated by said first one of said devices and a cooling means including a heat exchanger for continuously recirculating a portion of said separated stream passing through said anode process-fluid flow chamber through said heat exchanger.

15. A method for operating a networked plurality of electrochemically active devices wherein each of said devices includes an ionically conductive membrane, a porous anode disposed in contact with said ionically conductive membrane on one side thereof, a porous cathode disposed in contact with said ionically conductive membrane on a side thereof opposite said one side of said ionically conductive membrane, an anode process-fluid flow chamber disposed in fluid communication with said anode on a surface thereof opposite the surface contacting said ionically conductive membrane, and a cathode process-fluid flow chamber disposed in fluid communication with said cathode on a surface thereof opposite the surface contacting said electrochemical membrane and means for electrically connecting said plurality of electrochemically active devices in series, comprising the steps of:

flowing a cathode process-fluid through each of said cathode process-fluid flow chambers of each of said plurality of electrochemical devices in a serial fluid-flow arrangement;

flowing an anode process-fluid through said anode process-fluid flow chambers of each of said plurality of electrochemical devices in a serial fluid-flow arrangement so that said plurality of electrochemical devices are networked in a serial process flow arrangement; and

separately controlling the process-fluid parameters of each of said plurality of electrochemical devices individually so that the operating efficiency dependent on process fluid parameters of each of said plurality of electrochemical devices is improved, thereby improving the system efficiency.

16. A method for operating a networked plurality of electrochemically active devices as set forth in claim 15 wherein said plurality of electrochemical devices are molten carbonate fuel cells and said anode process fluid includes a fuel stream containing hydrogen or compounds thereof and said cathode process fluid includes an oxidant containing CO₂ and O₂.

17. A method for operating a plurality of electrochemically active devices as set forth in claim 16 wherein said fuel stream is methane and further including the step of reforming said methane to produce a hydrogen containing fuel within said anode process-fluid flow chamber.

18. A method for operating a plurality of electrochemically active devices as set forth in claim 17 wherein the amount of fuel supplied to said first one of said networked fuel cells is substantially greater than the amount consumed by said first one of said cells so that the voltage generated by said first cell is greater than the remainder of said networked cells.

19. A method for operating a plurality of electrochemically active devices as set forth in claim 18 wherein said step of flowing an anode process-fluid includes flowing said anode process-fluid through said anode process-fluid flow chambers of each of said plurality of fuel cells in a direction countercurrent to the direction of flow of said cathode process-fluid flow through said fuel cells and further including the step of feeding forward a controlled portion of said methane fuel stream to each of said anode process fluid flow channels of each of said plurality of fuel cells to aid in temperature control and thereby reducing ohmic voltage loses, recycling a cooled portion of said oxidant stream through said cathode process-fluid flow chambers to remove heat from each of said cells of said network and wherein said oxidant is air and further including the step of feeding back a portion of said output fuel stream which includes CO₂ to said oxidant input stream in an amount sufficient to raise the ratio of CO₂ and O₂ to a factor of about two.

20. A method for operating a plurality of electrochemically active devices as set forth in claim 19 further including the step of feeding back a portion of the anode process-fluid stream containing steam formed as a result of anode reactions at the output of the last cell of said networked series of cells to the input fuel stream to promote reforming of said methane in said input fuel stream, prevent carbon dioxide deposition and to heat said input fuel stream to a desired inlet temperature.

21. A method for operating a plurality of electrochemically active devices as set forth in claim 20 further including the step of combining a portion of the cathode process fluid stream output with said feedback portion of said output fuel stream through a combustor to remove unburned fuel and a heat exchanger so that the combined feedback stream is cooled prior to being mixed with said oxidant input stream.

22. A method for operating a plurality of electrochemically active devices as set forth in claim 21 further including the step of altering the composition of the oxidant stream flowing through said cathode process-fluid flow chambers by feeding forward a controlled portion of said oxidant feed to each of said plurality of networked devices and removing heat from the anode and cathode process-fluid flow streams between each one of said plurality of networked devices to maintain a desired maximum operating temperature for each of said devices so that ohmic voltage loses are reduced.

23. A method for operating a plurality of electrochemically active devices as set forth in claim 22 wherein said plurality of cells are each formed of a fuel cell stack.

24. A method for operating a plurality of electrochemically active devices as set forth in claim 15 wherein said devices are fluid separation devices.

25. A method for operating a plurality of electrochemically active devices as set forth in claim 24 wherein said devices are molten carbonate devices for separating CO₂ and O₂ from a fluid stream forming said cathode process fluid into said anode process-fluid flowing through said anode process-fluid flow chambers of said networked devices wherein said step of flowing a cathode process-fluid through said cathode process-fluid flow chambers includes the step of introducing an amount of CO₂ and O₂ to a first one of said networked separation devices which is substantially greater than the amount separated by said first one of said devices and said step of flowing an anode process fluid includes flowing said anode process fluid through said anode process fluid flow chambers of each of said plurality of separation devices in a direction countercurrent to the direction of flow of said cathode process-fluid flow through said devices and further including the step of recirculating a portion of said anode process-fluid flow through a heat exchanger to cool said anode process-fluid flow sufficient to maintain a desired operating temperature for said series networked devices.