Experimental analysis of a pressurized 30 kW SOFC system with fuel gas recirculation at reaction temperature

Solid oxide cells (SOCs) are flexible and efficient energy conversion devices. Due to their multiple usage possibilities, like electricity generation and syngas production, they can support the global energy transition. However, to play a significant role in the future energy system SOC reactors have to reach the megawatt and multi-megawatt range. To address process system issues expected in the higher power range, a 30 kW solid oxide fuel cell (SOFC) system with multiple reactors was set up at the German Aerospace Center in Stuttgart, Germany. This system can be operated under pressure and is equipped with a recirculation blower that recirculates the fuel electrode off-gas at reaction temperature. The system can be used to investigate the behavior of multi-reactor modules in a process system. Multi-reactors are necessary for scaling to higher power ranges and behave differently compared to single reactors. Furthermore, the test rig is capable of emulating gas turbine (GT) components to investigate the operation of a SOFC reactor in a GT/SOFC hybrid power plant. This work will present experimental results to help clarify the above mentioned multireactor issues. The focus will be on the heat losses and unequal flow distribution inside the reactor, which result in different temperature and reactant conversion rates for the single reactors. Various methods, like fuel and pressure variation, are used to characterize these effects. It will be shown how these effects limit the operability of the system and affect the design and operation of process systems. Furthermore, it will be analyzed how process systems should be designed and operated to overcome these problems. Control approaches that improve operability are elaborated and their impact is discussed. Assuming that similar multi-reactor modules will constitute the building blocks of future multi-megawatt systems, generic operation strategies that are derived from the extensive experiments are presented