Early start-up of solid oxide fuel cell hybrid systems with ejector cathodic recirculation: experimental results and model verification

A new test rig, founded in part by Rolls-Royce Fuel Cell Systems Limited, by the EU integrated project ‘FELICITAS’, and by the national project PRIN-2005, has been designed and built at the University of Genova to study different early start-up layouts and strategies for solid oxide fuel cell (SOFC) hybrid systems, using ejector-based cathodic recirculation. The test rig, which is flexible enough to analyse different emulated turbomachine layout (single shaft, two shafts, regenerated cycles or not, and so forth), different ejector configurations, and different stack arrangements, is unique. It also allows the early start-up performance to be fully investigated with particular attention to the analysis of the hybrid system fluid dynamic behaviour when the stack is off and the control system operates at critical conditions. The experiments have been carried out using a patented start-up combustor emulator (outlet temperature higher than 950°C), and monitoring the pressure and temperature quick rise to prevent mechanical and thermal stress to the fuel cell stack and to maintain turbomachine stability. The experimental results have also been used to verify the time-dependent hybrid system models based on TPG-TRANSEO tool. The results show good agreement with experimental data. This is essential to increase confidence with predictive time-dependent simulation tools during the start-up phase, where experimental data are hardly available and fuel cell materials may operate under risky conditions.