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Research Papers

Performance of an Integrated Microtubular Fuel Reformer and Solid Oxide Fuel Cell System

[+] Author and Article Information
John R. Izzo, Aldo A. Peracchio

Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Storrs, CT 06269-3139

Wilson K. S. Chiu1

Department of Mechanical Engineering, University of Connecticut, 191 Auditorium Road, Storrs, CT 06269-3139wchiu@engr.uconn.edu

1

Corresponding author.

J. Fuel Cell Sci. Technol 7(3), 031017 (Mar 16, 2010) (9 pages) doi:10.1115/1.3211098 History: Received December 10, 2008; Revised January 07, 2009; Published March 16, 2010; Online March 16, 2010

A numerical model is developed to study the performance of an integrated tubular fuel reformer and solid oxide fuel cell (SOFC) system. The model is used to study how the physical dimensions of the reformer, gas composition and the species flow rates of a methane feed stream undergoing autothermal reforming (ATR) affect the performance of an SOFC. The temperature in the reformer changes significantly due to the heat of reaction, and the reaction rates are very sensitive to the temperature and species concentrations. Therefore, it is necessary to couple the heat and mass transfer to accurately model the species conversion of the reformate stream. The reactions in the SOFC contribute much less to the temperature distribution than in the reformer and therefore the heat transfer in the SOFC is not necessary to model. A packed bed reactor is used to describe the reformer, where the chemical mechanism and kinetics are taken from the literature for nickel catalyst on a gamma alumina support. Heat transfer in the reformer’s gas and solid catalyst phases are coupled while the gas phase in the SOFC is at a uniform temperature. The SOFC gas species are modeled using a plug flow reactor. The models are in good agreement with experimental data. It is observed that the reformer temperature decreases with an increase in the reformer inlet water-to-fuel ratio and there is a slight decrease in the voltage of the SOFC from higher water content but an increase in limiting current density from a higher hydrogen production. The numerical results show that the flow rates and reformer length are critical design parameters because if not properly designed they can lead to incomplete conversion of the methane fuel to hydrogen in the reformer, which has the greatest impact on the SOFC performance in the integrated ATR reformer and SOFC system.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of integrated reformer and SOFC system. Dimensions of the reformer were modified from Ref. 14 to model the integrated system.

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Figure 2

Autothermal reformer validation for the (a) temperature and (b) outlet flow rates of hydrogen and total dry gas. Both cases are run with a constant A/F=3 over a range of W/F from 1 to 2.5. The lines represent numerically predicted values while the symbols represent experimentally determined data values (14).

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Figure 3

Species conversion in reformer with a uniform temperature of 773 K in (a) and 973 K in (b) to isolate the temperature dependence on reaction rates and fuel conversion. The methane conversion nearly doubled, hydrogen yield more than doubled and the total outlet flow rate increased by 31%.

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Figure 4

Species conversion in reformer with an inlet methane flow rate of (a) 1000 SCCM and (b) 3000 SCCM

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Figure 5

Model validation performed against experimental data from a tubular SOFC provided by AMI (18). Symbols represent experimental data and lines are numerically predicted values, where the solid and dotted lines correspond to the voltage and power density, respectively.

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Figure 6

Results from an integrated system run at a methane inlet flow rate of 7 SCCM with A/F=3 and W/F=2, for varying reformer length. Species flow rates at the outlet of the reformer are plotted against the physical length of the reformer in (a) and the predicted polarization curves are shown for specified reformer lengths in (b).

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Figure 7

Study on the variation of W/F into the reformer with a constant A/F=3 where the reformer temperature is plotted in (a) and the tubular SOFC polarization curves in (b). It is shown that an increase in W/F decreases the temperature in the reformer and the operating voltage of the SOFC. A noticeable effect on the polarization occurs in the limiting current density, which increases with higher W/F ratios.

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