Mathematical Modeling of a Porous Media Burner Based Methane Flame Fuel Cell

Abstract

A detailed two-dimensional axisymmetric computational model of a flame fuel cell (FFC) unit was developed and presented. The FFC unit is based on the integration of a fuel-rich methane flame in a porous media burner and a micro-tubular solid oxide fuel cell (SOFC). The model considered the coupling effects of the chemical reactions and electrochemical reactions and the heat-transport, masstransport and charge -transport processes in the FFC. The simulated temperature distribution and electrochemical characteristics showed good agreement with experimental data. The coupling mechanism of the fuel-rich flame and the SOFC anode were clarified. The Ni catalyst in the anode and the electrochemical reactions promoted the conversion of CH 4 in porous media fuel-rich combustion. A flame fuel cell (FFC) is a novel kind of solid oxide fuel cell (SOFC) in which a fuel-rich flame is directly integrated with an SOFC. 1 The fuel-rich flame acts as a partial oxidation reformer for the SOFC at the anode to convert C x H y to CO and H 2 . Meanwhile, it also provides heat for the SOFC to start up and operate. [2][3][4] FFCs have emerged as an attractive system owing to its simple setup and rapid startup. Until now, FFCs were investigated using various combustion concepts and different SOFC configurations. [5][6][7][8][9][10][11][12][13][14][15] The effects of operational conditions on FFC performance were studied and discussed in these early experimental studies. In a previous study, an FFC unit was implemented and studied by integrating a porous media burner with a micro-tubular SOFC. 16 In an FFC unit, the anode of the micro-tubular SOFC is directly integrated with the fuel-rich flame. The chemical and electrochemical reactions, as well as the heat transport, are coupled between the anode and the fuel-rich flame. The coupling effects will further influence the combustion characteristics of the porous media burner as well as the electrochemical performance of the SOFC. However, it is a difficult task to clarify the coupling effects via experimental methods due to the chemical and thermal complexity within the FFC unit. 17 Consequently, a modeling technique is necessary to clarify the complex physical and chemical processes.Compared with the vast number of experimental studies on FFCs, numerical studies have been relatively lacking. Vogler et al. developed a computational model of an FFC based on a flat-flame burner and a planar SOFC. 17 They found that the products of the electrochemical conversion in the SOFC did not influence the flame, and that the flame and the SOFC were chemically decoupled. However, this conclusion was drawn given the fact that a stagnation flame takes place at a certain flamelet that was far away from the SOFC. However, when a porous media burner was applied in the FFC unit, the fuel-rich combustion exhausts flowed along the anode of the micro-tubular SOFC, and chemical reactions still occurred due to the high temperature of the SOFC region.To that end, a modeling approach was undertaken to investigate the...