Experimental study of anode gas recycling on efficiency of SOFC

Anode gas recycling is desirable in solid oxide fuel cell (SOFC) systems in order to provide water for steam reforming reactions and to simplify the system architecture. Possible benefits can also be achieved for the electrical efficiency and lifetime. By recycling a certain amount of unused fuel back to the SOFC, higher efficiencies at low fuel utilizations can be achieved as the current efficiency is increased. However, the recycling dilutes the inlet fuel as the partial pressures of the reactive components, i.e. hydrogen, carbon monoxide and methane, are decreased. The diluted fuel results in decreased cell voltage and thus decreases the voltage efficiency. In this study, the magnitude of these counter effects on the electrical efficiency is experimentally studied. The effect of the auxiliary power losses, resulting e.g. from the power consumption of a recycle pump or from the need of excess air for cooling, on the overall efficiency are excluded from the study.