High-efficiency ammonia-fed solid oxide fuel cell systems for distributed power generation

Abstract

Ammonia can be considered as an alternative fuel for solid oxide fuel cells (SOFCs) because it is carbon-free, it can be easily stored, and it has a high volumetric energy density. Several large-scale ammonia-fed SOFC systems have been investigated. However, small-scale systems that are applicable for distributed power generation have not been extensively studied. Therefore, we propose three small-scale ammonia-fed SOFC systems, and compare the performance of these systems with that of a standalone SOFC system. The first system is an internal combustion engine combined with an SOFC, which is termed as a SOFC-engine hybrid system. It has a simple construction and it recovers energy from anode off-gas. In the case of the second system, the water was removed from the anode off-gas to enhance the hydrogen molar fraction before supplying it to the stack. In the third system, an internal combustion engine was integrated with a recirculation SOFC system as a combination of the two above systems. An SOFC system was modeled and validated with experimental data. It was observed that the engine enhances the system efficiency by 6.2% point compared with that of the standalone SOFC system. The recirculation using a water condensation system resulted in an increase in the system efficiency to 67.4% owing to the recirculation of rich-hydrogen gas. The SOFC-engine recirculation system exhibits a higher efficiency than that of the second system. However, the maximum efficiency was 67.5%, which is slightly higher than that of the recirculation system. The obtained results proofed that NH3-fed SOFC is totally difference with others and these finding can be effectively used in further developing ammonia-fueled SOFC system.