Simulation of an Innovative Startup Phase for SOFC Hybrid Systems Based on Recompression Technology: Emulator Test Rig

This paper presents a novel startup approach for solid oxide fuel cell (SOFC) hybrid systems (HSs) based on recompression technology. This startup approach shows a novel method of managing a complete plant to obtain better performance, which is always also a difficult task for equipment manufactures. The research activities were carried out using the HS emulator rig located in Savona (Italy) and developed by the Thermochemical Power Group (TPG) of the University of Genoa. The test rig consists of three integrated technologies: a 100 kWe recuperated microturbine modified for external connections, a high temperature modular vessel necessary to emulate the dimensions of an SOFC stack, and, for air recompression, a turbocharger necessary to increase fuel cell pressure (using part of the recuperator outlet flow) as required for efficiency increase and to manage the cathodic recirculation. It was necessary to develop a theoretical model in order to prevent abnormal plant startup conditions as well as motivated by economic considerations. This transient model of the emulator rig was developed using Matlab®-Simulink® environment to study the time-dependent (including the control system aspects) behavior during the entire system (emulator equipped with the turbocharger) startup condition. The results obtained were able to demonstrate that the HS startup phase can be safely managed with better performance developing a new control logic. In detail, the startup phase reported in this paper shows that all important parameters were always inside acceptable operating zones (surge margin kept above 1.1, turbine outlet temperature (TOT), and fuel flow maintained lower than 918.15 K and 7.7 g/s, respectively).