Thermo-economic analysis and optimization of combined PERC - ORC - LNG power system for diesel engine waste heat recovery

Abstract

In order to recover diesel engine exhaust gas waste heat, a new configuration consisting of screw expander based Partial Evaporation Rankine Cycle (PERC) combined with Organic Rankine Cycle (ORC) and Liquefied Natural Gas (LNG) power system is proposed and its performance is investigated from thermo-economic viewpoint. In studied system, a heat exchanger preparing domestic hot water is considered to recover the residual waste heat after PERC evaporator and thermo-economic performance of the system is investigated for 6 various organic fluids in ORC. Also, parametric analysis is performed to assess the effects of PERC evaporation temperature, PERC expander inlet steam quality and ORC condensation temperature on system performance. Finally, multi objective optimization is used to find the favorable performance point of system. LNG and PERC systems have a proper operation respectively from energy and exergoeconomic viewpoints. Also, ORC condenser has the highest total cost rate. System optimization results show that using isopentane fluid leads to the highest net power output and total cost rate respectively equal to 178.6 kW and 19.3 $/h and using toluene fluid leads to the lowest net power output and total cost rate that are respectively equal to 154.7 kw and 17.36 $/h.