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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

## Abstract

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 $xH2O∕xCH4$ smaller than 1.

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## Figures

Figure 1

Geometry of the tubular SOFC cell

Figure 2

DIR of methane by steam

Figure 3

Mole fraction of methane

Figure 4

Mole fraction of dihydrogen

Figure 5

Mole fraction of dioxygen

Figure 6

Distribution of the α value

Figure 7

Distribution of the β value

Figure 8

Distribution of the γ value

Figure 9

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

Figure 10

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

Figure 11

Carbon deposition limit for ten ratios, xH2O∕xCH4

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