Comparison of a fuel-driven and steam-driven ejector in solid oxide fuel cell systems with anode off-gas recirculation: Part-load behavior

• We model an SOFC system with anode off-gas recirculation.
• A steam and fuel driven ejector are used for recirculation.
• Carbon formation limits the part load of a fuel driven ejector system.
• The condensation temperature limits the part load of a steam driven ejector system.
• A steam driven concept increases the electrical efficiency.

This paper investigates the use of ejectors for recirculating anode off-gas in an SOFC system, focusing on the part-load capability of two different systems. In the first system, recirculation was enabled by a fuel-driven ejector. The part-load threshold of this system was determined by carbon formation and was 77.8% assuming a fuel utilization of 70% and suitable ejector geometry. The second system was based on a steam-driven ejector. The simulation results for this system showed an improved part-load capability of 37.8% as well as a slightly improved electrical efficiency. Here, the minimal part load was determined by the condensation temperature of the condenser used in the system.