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TECHNICAL PAPERS

Modeling of a Solid Oxide Fuel Cell Fueled by Methane: Analysis of Carbon Deposition

[+] Author and Article Information
J.-M. Klein1

 Laboratoire d’Electrochimie et de Physico-Chimie des Matériaux et des Interfaces (LEPMI), UMR 5631 CNRS-INPG-UJF, ENSEEG, BP 75, 38402 Saint Martin d’Hères, Francejean-marie.klein@lepmi.inpg.fr

Y. Bultel

 Laboratoire d’Electrochimie et de Physico-Chimie des Matériaux et des Interfaces (LEPMI), UMR 5631 CNRS-INPG-UJF, ENSEEG, BP 75, 38402 Saint Martin d’Hères, Franceyann.bultel@lepmi.inpg.fr

M. Pons

 Laboratoire de Thermodynamique et de Physicochimie Métallurgique (LTPCM), UMR 5614 CNRS-INPG-UJF, ENSEEG, BP 75, 38402 Saint Martin d’Hères, France

P. Ozil

 Laboratoire d’Electrochimie et de Physico-Chimie des Matériaux et des Interfaces (LEPMI), UMR 5631 CNRS-INPG-UJF, ENSEEG, BP 75, 38402 Saint Martin d’Hères, France

1

Corresponding author.

J. Fuel Cell Sci. Technol 4(4), 425-434 (May 30, 2006) (10 pages) doi:10.1115/1.2759504 History: Received November 29, 2005; Revised May 30, 2006

Natural gas appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems. It mainly consists of methane, which can be converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. However, a major limitation to DIR is carbon formation within the ceramic layers at intermediate temperatures. This paper proposes a model solution using the CFD-ACE software package to simulate the behavior of a tubular SOFC. A detailed thermodynamic analysis is carried out to predict the boundary of carbon formation for SOFCs fueled by methane. Thermodynamic equilibrium calculations that take into account Boudouard and methane cracking reactions allow us to investigate the occurrence of carbon formation. This possibility is discussed from the values of driving forces for carbon deposition defined as α=PCO2(KBPCO2) and β=PH22(KCPCH4), from the equilibrium constants KB and KC of the Boudouard and cracking reactions, and from the partial pressure Pi of species i. Simulations allow the calculation of the distributions of partial pressures for all the gas species (CH4, H2, CO, CO2, and H2O), current densities, and potentials of both electronic and ionic phases within the anode part (i.e., gas channel and Cermet anode). Finally, a mapping of α and β values enables us to predict the predominant zones where carbon formation is favorable (α or β<1) or unfavorable (α or β>1) according to the calculation based on thermodynamic equilibrium. With regard to the values of these different coefficients, we can say that a carbon formation can be supposed for temperature less than 800°C and for ratios xH2OxCH4 smaller than 1.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Geometry of the tubular SOFC cell

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Figure 2

DIR of methane by steam

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Figure 3

Mole fraction of methane

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Figure 4

Mole fraction of dihydrogen

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Figure 5

Mole fraction of dioxygen

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Figure 6

Distribution of the α value

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Figure 7

Distribution of the β value

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Figure 8

Distribution of the γ value

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Figure 9

Distribution of the γ coefficient along the fuel cell for four temperatures. (∎) 1273K, (●) 1173K, (×) 1073K, (▴) 973K, and (◆) carbon deposition limit.

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Figure 10

Distribution of the γ coefficient along the cell for three ratios. (◆) R=3, (●) R=1, and (▴) R=0.4.

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Figure 11

Carbon deposition limit for ten ratios, xH2O∕xCH4

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