Extensive analysis of SOFC fed by direct syngas at different anodic compositions by using two numerical approaches

The paper presents an extensive analysis of the techno-energy performance of SOFC, when directly fed by syngas of different compositions. An ad hoc numerical modeling is developed and then run in a Matlab calculation environment. The model considers coupled site chemical reactions and multi-species gas diffusion in gases and electrodes, and considers the concurrent electroreactions of hydrogen and carbon monoxide, as well as the kinetics of the internal thermochemical processes. The numerical modeling deals with two approaches: the WGS_SOFC_Model and the DIR_SOFC model, suitable for predicting SOFC behavior with the absence and presence of methane respectively. The analyses are based on the assessment of the main output variables of the fuel cell, voltage, power density, electric efficiency vs the current density simulated, and by varying the input parameters, fuel composition, inlet gas temperature and SOFC excercise pressure, while calculating the composition of the output gas. A wide-ranging carbon deposition analysis completes the overall assessment. It is based on pressure, temperature and additional steam to carbon ratio as control parameters, and is aimed at finding the thermodynamic conditions and so the operative region that staves off the undesired phenomenon. Temperature increase affects SOFC energy performance as well as pressure positively. Electric efficiency is about 45-50% for high quality syngases, while about 30% for lower quality ones. The parallel carbon deposition analysis reveals that a working region of compromise must be detected, since increasing a control variable does not ensure an overall improvement. This evidence is more noticeable in syngases with significant methane content meaning the cracking carbon deposition is difficult to control. The numerical modeling presented, and so the overall analysis performed, is aimed to set a valid tool to come to the comprehension of the conditions of feeding and of excercise of SOFC, and to find the solution to excercise the electrochemical device efficiently and safely.