High-efficiency conversion of natural gas fuel to power by an integrated system of SOFC, HCCI engine, and waste heat recovery: Thermodynamic and thermo-economic analyses

A novel natural gas utilization system for power generation including solid oxide fuel cell (SOFC) and homogeneous charge compression ignition (HCCI) engine is proposed and modeled to evaluate the thermodynamic and thermo-economic performance in this paper. The results show that the SOFC-HCCI engine hybrid system has a net electrical efficiency of approximately 59% and the exergy efficiency of 53.5%, both of which are more than single fuel cell system and comparable to other hybrid fuel cell systems. It is also found that the SOFC contributes to the total power of 80% and has a relatively low exergy destruction. Through the parametric analysis, the power distribution between SOFC and engine can be adjusted by controlling SOFC fuel utilization to optimize the system overall performance. Besides, the specific electric energy cost of the proposed hybrid system is calculated to be 6.91 cent/kW h, which is comparable to the specific cost of electric power (6.92 cent/kW h) generating from a biogas-fueled fuel cell hybrid system. The payback period and annual return on investment can reach 1.53 year and about 6.41%. These results reveal that the proposed conversion technology of natural gas fuel to power is efficient and economical, which could be a promising natural gas fuel utilization.