System model and performance analysis of a solid oxide fuel cell system self-humidified with anode off-gas recycling

Abstract

Recycling the anode off-gas of the solid oxide fuel cells can effectively improve the system fuel utilization (Uf,sys) under a low stack fuel utilization (Uf,1), prolonging the service life and reducing the power generation cost. A compact self-humidified anode off-gas recycle (SAOR) system fueled by natural gas is proposed and analyzed. Clear mathematical relationships for key physical quantities in all system components are derived. Analytical expressions concerning the controllable parameters, Uf,sys and the recycling ratio (λ), and the controlling targets, Uf,1 and the oxygen to carbon ratio, are presented to facilitate the accurate system control for high efficiency and moderate Uf,1 and free of carbon deposition. The core system model is found to agree very well with multiple sets of available experimental data. The SAOR system performance for representative fuel flow rates and Uf,1 and for all λ are presented. The results show the SAOR system can achieve a DC efficiency similar to, but with Uf,1 10% lower than the best known non-SAOR system, demonstrating the presumed superiority of SAOR system. The SAOR system is a promising low cost design capable of achieving high efficiency and durability and should be pursuit for commercial development.