Dynamic Response of Fuel Cell Gas Turbine Hybrid to Fuel Composition Changes using Hardware-based Simulations

The solid oxide fuel cell gas turbine hybrid system (SOFC/GT) is an exciting new approach to producing electricity with high efficiency and lower environmental impacts than conventional power plants. One of its key strengths is the potential for fuel flexibility, which is the ability to transition between different kinds or qualities of fuels during operation. However, there has been very little research into the dynamic performance of SOFC/GT systems in response to changes in fuel. Therefore, the open loop behaviour of SOFC/GT systems in response to fuel composition transients was experimentally investigated. In this study, hardware-based simulations were used to study transitions between using coal-derived syngas and humidified methane. A hybrid test facility at the U.S Department of Energy, National Energy Technology Laboratory, Morgantown, West Virginia, was used to adequately capture the coupling of fuel cell stacks (simulated with hardware driven by a real time dynamic model) and a gas turbine system (from actual equipment) during transient events. Given the dynamic trajectories of key process variables, the impact on the hybrid system was quantified via transfer functions. The results show that the open-loop dynamic behaviour exhibited significant inverse response which limited the range of transitions that could be achieved safely without damage to various system components such as the compressor or fuel cells. However, the results also showed that if a control system could be designed which limited the impact of the inverse response, then transitions between even very different kinds of fuels could potentially be achieved without operational problems. The resulting transient information will be used to develop a new control system for thermal management of SOFC/GT hybrid systems in future work.