Transient Analysis of Solid Oxide Fuel Cell Hybrids. Part B: Anode Recirculation Model

The aim of this work is the transient analysis of hybrid systems based on high-temperature Solid Oxide Fuel Cells (SOFC). The cell models were presented and discussed in Part A of this work. In this part attention is focused on the anode recirculation system. In a SOFC hybrid system it is necessary to recirculate part of the exhaust gas in order to maintain a proper value for the Steam To-Carbon Ratio and to support the reforming reactions. This is carried out with an ejector, which exploits the pressure energy of the fuel to recirculate part of the anodic exhausts to fuel cell anodic side. Initially, a “dynamic” stand-alone ejector model is presented and validated for the analysis of unsteady flows. Particular attention was paid to the effect of time variation in the mixture composition, creating a general model for the unsteady simulation of flows with variable composition. To analyze the whole anodic circuit the “dynamic” model was simplified to the “lumped volume” model, which, even if it cannot properly analyze supersonic flows and shock waves, considerably reduces calculation time. So, it is suitable for transient system simulations, generally longer than a few minutes. The “lumped volume” model has been tested with the “dynamic” model and it has been used for the anodic recirculation system time-dependent simulations.