Thermodynamic analysis of an SOFC-GT-ORC integrated power system with liquefied natural gas as heat sink

To recover the waste heat from solid oxide fuel cell (SOFC) and improve the overall electrical efficiency, a new integrated power system driven by SOFC is proposed to achieve the cascade energy utilization. This system integrates an SOFC-GT system with an organic Rankine cycle (ORC) using liquefied natural gas (LNG) as heat sink to recover the cryogenic energy of LNG. Based on the mathematical model, a parametric analysis is conducted to examine the effects of some key thermodynamic parameters on the system performance. The results indicate that the overall electrical efficiency of 67% can be easily achieved for the current system, which can be further improved with parametric optimization. An increase in fuel flow rate of SOFC can raise the net power output, but it has a negative effect on SOFC and overall electrical efficiency. The compressor pressure ratio contributes to an increase in SOFC and overall electrical efficiency, which are contrary to the effects of air flow rate and steam-to-carbon ratio. Under the given conditions, compared with the Kalina sub-system, the ORC sub-system produces 12.6% more power output by utilizing the cryogenic energy of LNG with simple configuration.