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

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.

Assessment of finite volume modeling approaches for intermediate temperature Solid Oxide Fuel Cells working with CO-rich syngas fuels

“…1a; the various terms of electrochemical equations and the resulting current flow are related only to H 2 oxidation [10,11,14,26], On the contrary, when direct CO oxidation is considered, the equivalent electric circuit changes into the one shown in Fig. 1b.…”

“…The formation of solid carbon has to be prevented to avoid fast degradation of the cell and a relevant cell voltage drop. A comprehensive discussion of the phenomena and the effect on cell performance and the strategies to limit carbon formation are reported in Miao et al [25]; moreover, Klein et al [26] discussed the effect of syngas composition and current density from a qualitative point of view, with the calculation of the a coefficients for the Boudouard (E4) and methane cracking (E3) reactions, expressed by:…”

Three-dimensional numerical and experimental investigation of an industrial-sized SOFC fueled by diesel reformat – Part II: Detailed reforming chemistry and carbon deposition analysis

“…Klein et al [28] and Vakouftsi et al [29] numerically studied possible carbon deposition on solid oxide fuel cells anodes (tubular [28] and planar [29]) by calculating the thermodynamic activity of the methane cracking and boudouard reaction. Furthermore, they combined both activites to assess the influence of both reactions at the same time.…”

An On‐Demand Safety Gas Generator for Solid Oxide Fuel Cell and Electrolyzer Systems

“…The fuel gas would be, for example, natural gas (NG), as its availability is mostly high. Higher hydrocarbons within the fuel are challenging because they decompose at temperatures above 150°C and promote carbon formation in the system [28]. This blocks the gas pipes, increases the pressure drop and can cause leaks.…”