Efficient 5 kW-class solid oxide fuel cell (SOFC) hotbox design with off gas integration for power generation

This research addressed the challenge of enhancing the efficiency and compactness of a 5-kW class solid oxide fuel cell hotbox system for power generation. The novelty of this work lies in the design a state-of-the-art hotbox that incorporates components such as a steam generator, an air heat exchanger, a reformer, a start-after burner, and anode off-gas recycling within a compact setup. Experimental and modeling analyses were conducted to investigate the effects of critical operational variables, namely, the steam-to-carbon ratio, operating temperature, anode off-gas recycling ratio, and current density, on the system’s efficiency. It was found that at an 85 % recycling ratio, the system operates without needing an external steam supply. The results indicate that implementing a 75 % anode off-gas recycling ratio in the system boosts its electrical efficiency from 39.30 % to approximately 51.09 %, marking a significant 30 % increase. The optimal conditions were a 50 % anode off-gas recycling ratio, 1023.15 K operating temperature, and 3.0 steam-to-carbon ratio. Meeting these conditions, the system’s electrical efficiency was 47.7 %, which ensured efficient operation, effective thermal management, and safety. This study is expected to help optimize the design and operating parameters to maximize compact solid oxide fuel cell system performance, improve durability and minimize cost.