Effect of fuel composition fluctuation on the safety performance of an IT-SOFC/GT hybrid system

Fuel composition fluctuation could result in operation performance degradation caused by a potential failure of component or system. Therefore, this work elaborated the safe characteristic and load performance of an intermediate-temperature solid oxide fuel cell (IT-SOFC) and gas turbine (GT) hybrid system using gasified biomass gas when the composition fluctuates. The malfunction restrictions of components (such as fuel cell thermal crack, compressor surge, reformer carbon deposition) were considered in this research. Results show that the hybrid system has a high efficiency 60.78% at the design point using gasified wood chip gas, which is a useful reference for small distributed power stations. H2 concentration variation is the most influential factor to the hybrid system output power and efficiency, followed by CH4, and then CO. System efficiency increases significantly with H2 concentration increase, while decrease slightly with CO and CH4 increase. For the system safety operation: ⅰ) when the H2 and CH4 fluctuates to relative proportion 90% and 97%, respectively, the reformer will suffer from the potential failure of carbon deposition; ⅱ) when H2 increases to 116%, the TIT exceeds the upper limit 1223 K, which causes the turbine blade to burn down because of over temperature. For the effect of water variation, the system output power and efficiency will be improved with water reduction, and the efficiency can even reach up to 64.85%. However, the reformer can't work safely due to the severe shortage of water for the reforming reactions.