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RESEARCH PAPERS

Dynamic Simulation of an Integrated Solid Oxide Fuel Cell System Including Current-Based Fuel Flow Control

[+] Author and Article Information
Fabian Mueller

Mechanical and Aerospace Engineering Department, National Fuel Cell Research Center, University of California, Irvine, CA 92697fm@nfcrc.uci.edu

Jacob Brouwer

Mechanical and Aerospace Engineering Department, National Fuel Cell Research Center, University of California, Irvine, CA 92697jb@nfcrc.uci.edu

Faryar Jabbari

Mechanical and Aerospace Engineering Department, National Fuel Cell Research Center, University of California, Irvine, CA 92697fjabbari@uci.edu

Scott Samuelsen

Mechanical and Aerospace Engineering Department, National Fuel Cell Research Center, University of California, Irvine, CA 92697gss@uci.edu

J. Fuel Cell Sci. Technol 3(2), 144-154 (Oct 11, 2005) (11 pages) doi:10.1115/1.2174063 History: Received July 19, 2005; Revised October 11, 2005

A two-dimensional dynamic model was created for a Siemens Westinghouse type tubular solid oxide fuel cell (SOFC). This SOFC model was integrated with simulation modules for other system components (e.g., reformer, combustion chamber, and dissipater) to comprise a system model that can simulate an integrated 25kw SOFC system located at the University of California, Irvine. A comparison of steady-state model results to data suggests that the integrated model can well predict actual system power performance to within 3%, and temperature to within 5%. In addition, the model predictions well characterize observed voltage and temperature transients that are representative of tubular SOFC system performance. The characteristic voltage transient due to changes in SOFC hydrogen concentration has a time scale that is shown to be on the order of seconds while the characteristic temperature transient is on the order of hours. Voltage transients due to hydrogen concentration change are investigated in detail. Particularly, the results reinforce the importance of maintaining fuel utilization during transient operation. The model is shown to be a useful tool for investigating the impacts of component response characteristics on overall system dynamic performance. Current-based flow control (CBFC), a control strategy of changing the fuel flow rate in proportion to the fuel cell current is tested and shown to be highly effective. The results further demonstrate the impact of fuel flow delay that may result from slow dynamic responses of control valves, and that such flow delays impose major limitations on the system transient response capability.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flow schematic of 25kW integrated system model, after Siemens Westinghouse Power Corporation

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Figure 2

Schematic of the annular geometry external steam reformer, showing model nodes, and internal flow configuration

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Figure 3

Schematic of modeled heat transfer network within the external steam reformer

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Figure 4

Schematic of a Siemens Westinghouse tubular SOFC, showing model nodes, and internal flow configuration

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Figure 5

Schematic of modeled heat transfer network within the tubular SOFC

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Figure 6

Comparison of power and temperature data to system simulation output results

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Figure 7

Typical open loop response of power, voltage, current, fuel utilization, center cell temperature, and fuel cell exit hydrogen concentration following a load resistance drop of 5%. Data normalized to initial steady state conditions.

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Figure 8

Typical open loop response of power, voltage, current, fuel utilization, center cell temperature, and fuel cell exit hydrogen concentration following a load resistance drop of 5%. Data normalized to initial steady state conditions.

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Figure 9

Comparison of the power and fuel utilization results from the open loop (open) and current-based flow control (CBFC) system dynamic response

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Figure 10

Power and fuel utilization transients from the open loop (open) and current-based flow control (CBFC) following a simulated instantaneous 2.2% change in power

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Figure 11

Power and fuel utilization transients, due to flow delay in current-based flow control strategy following a large instantaneous power change

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