Optimal technology for fuel cell systems
Even if solid oxide fuel cell (SOFC) technology is still immature compared to proton exchange membrane and molten carbonate fuel cell technology, it may have more applications than the latter two. SOFC technology based on lower-cost ceramic materials could be competitive with conventional technologies. SOFCs with efficiencies above 60 % in electric power generation and higher than 90 % for cogeneration of heat and power are possible. However, high efficiency, as well as reliability and long operating lifetime, must be ensured to achieve widespread market penetration. The EU-funded project CATION (Cathode subsystem development and optimisation) was initiated to optimise the cathode subsystem. Consisting of a cathode, the side where air enters and waste gas is expelled, and an anode, a solid oxide electrolyte between them, this subsystem largely defines the electric efficiency of the whole SOFC system. Project partners focused on improving fluid supply and thermal management as well as the cathode subsystem, including components such as heat exchangers, burners and blowers. The goal was to reach an electrical efficiency of 55 % and 40 000 hours of operation for a stationary 250 kW SOFC system. Following a thorough evaluation of different alternatives for the cathode subsystem, system modelling and reliability analysis led to modified layouts for ejector and modular stack structure. Additional tools were developed to optimise the recuperator core and scientists tested new cathode and burner concepts. Investigations pointed to the most suitable solutions, namely recirculation by ejector and air-in-series. The cathode ejector was chosen based on its superiority in critical aspects, such as sensitivity to stack quality deviations and operability and controllability. The anode subsystem of SOFCs was optimised in parallel in the framework of the EU-funded project ASSENT. Building on the experience with 50 kW demonstration systems, the CATION and ASSENT projects have resulted in solutions promising a 250 kW system in line with the objectives of Europe's energy policy.
Keywords
Fuel cell, solid oxide fuel cell, SOFC, electric power generation, cathode subsystem
