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Research Papers

Performance Evaluation of Dynamic Model of Compact Heat Exchange Reformer for High-Temperature Fuel Cell Systems

[+] Author and Article Information
Jeongpill Ki

e-mail: jeong.ki@mavs.uta.edu

Daejong Kim

e-mail: daejongkim@uta.edu
Mechanical and Aerospace Engineering,
The University of Texas at Arlington,
500 W. 1st Street,
Arlington, TX 76019

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY. Manuscript received April 29, 2013; final manuscript received July 29, 2013; published online October 22, 2013. Editor: Nigel M. Sammes.

J. Fuel Cell Sci. Technol 11(1), 011006 (Oct 22, 2013) (9 pages) Paper No: FC-13-1040; doi: 10.1115/1.4025524 History: Received April 29, 2013; Revised July 29, 2013

Solid oxide fuel cell (SOFC) systems are the most advanced power generation system with the highest thermal efficiency. The current trend of research on the SOFC systems is focused on multikilowatt scale systems, which require either internal reforming within the stack or a compact external reformer. Even if the internal reforming within the SOFC stack allows compact system configuration, it causes significant and complicated temperature gradients within the stack, due to endothermic reforming reactions and exothermic electrochemical reactions. As an alternative solution to the internal reforming, an external compact heat exchange reformer (CHER) is investigated in this work. The CHER is based on a typical plate-fin counterflow or coflow heat exchanger platform, and it can save space without causing large thermal stress and degradation to the SOFC stack (i.e., eventually reducing the overall system cost). In this work, a previously developed transient dynamic model of the CHER is validated by experiments. An experimental apparatus, which comprises the CHER, air heater, gas heater, steam generator, several mass flow controllers, and controller cabinet, was designed to investigate steady state reforming performance of the CHER for various hot air inlet temperatures (thermal energy source) and steam to carbon ratios (SCRs). The transient thermal dynamics of the CHER was also measured and compared with simulations when the CHER is used as a heat exchanger with inert gas. The measured transient dynamics of CHER matches very well with simulations, validating the heat transfer model within the CHER. The measured molar fractions of reformate gases at steady state also agree well with the simulations validating the used reaction kinetics. The transient CHER model can be easily integrated into a total integrated SOFC system, and the model can be also used for optimal design of similar CHERs and provides a guideline to select optimal operating conditions of the CHERs and the integrated SOFC system.

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References

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Figures

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Fig. 1

Stages of the SOFC system, CHER: compact heat exchange reformer, CI: cathode inlet plenum, CE: cathode exit plenum, AI: anode inlet plenum, AE: anode exit plenum, COMB: combustor, M/C: mixing chamber, HEX: heat exchanger, adopted from Fig. 1 of Ref. [22]. (a) Stage 1: SOFC stack start-up with combustor. (b) Stage 2: initiation of anode fuel line and start to generate electrical power. (c) Stage 3: normal operation.

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Fig. 2

Configuration of the CHER and flow directions of gases; (a) compact heat exchange reformer (CHER) and flow directions of gases and (b) components of the CHER

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Fig. 3

Flow direction of both the air and FSM along y-coordinate

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Fig. 4

The CHER test rig. (a) Schematic diagram, GC: gas chromatography, T: thermocouple. (b) Photo of air heater and controller. (c) Photo of gas heater and steam generator.

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Fig. 5

CHER inlet pressures of hot air and N2: measured and interpolated. (a) Pressure of hot air at inlet. (b) Pressure of N2 at inlet.

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Fig. 6

CHER inlet temperatures of hot air and N2: measured and interpolated. (a) Temperature of hot air at inlet. (b) Temperature of N2 at inlet.

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Fig. 7

Comparison of transient response of CHER when it is operated as heat exchanger without reforming reaction when the measured thermal boundary conditions shown in Figs. 5 and 6 are applied. (a) Exit temperature of hot air side. (b) Exit temperature of cold air side.

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Fig. 8

Comparison of molar fraction (not including steam) for each species between the experiment and transient simulation for different temperatures

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Fig. 9

Comparison of molar fraction (not including steam) for each species between the experiment and transient simulation for different SCRs

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Fig. 10

Comparison of measured temperature with the simulation, where arrows show the flow direction of both the hot air and FSM

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Fig. 11

Simulated molar fractions of H2 in each control volume along flow direction

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Fig. 12

Simulated molar fraction of each species at the reformer exit for different FSM mass flow rates when air flow rate is 1 g/s

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Fig. 13

Simulated mass flow rate of H2 at the reformer exit for different FSM mass flow rates

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