Investigation of carbon deposition behavior on ferritic alloys in low S/C ratio using direct heating method

Preventing the deposition of carbon is one of the main challenges to achieving highly efficient operation of solid oxide fuel cell (SOFC) systems in low steam/carbon (S/C) environments. The carbon deposition can easily occur in the fuel gas supply line, when humidified methane with a S/C ratio of less than 1 is used as a fuel. By preventing this carbon deposition, it should be possible to develop robust SOFC systems with a high fuel to electricity conversion efficiency. Typically, ferritic Cr₂O₃- and Al₂O₃-forming alloys are the materials of choice for fuel gas supply lines in SOFC stacks and systems. This study therefore investigates the carbon deposition behavior on the oxide scale formed on me surface of such alloys, in order to clarify the mechanism of the carbon deposition. To achieve this, samples of ZMG232L and NCA-1 were directly heated up to 1173 K in the stream of a CH₄-H₂O gas mixture (S/C=0.02). The results show the A1₂O₃ scale on NCA-l has a higher tolerance for the carbon deposition than the Cr₂O₃ scale on ZMG232L. On the basis of this, it is proposed that the optimized oxide scale on the alloy surface can effectively restrict carbon deposition in the low S/C environments.