Thermo-economic optimization of an ORC system for a dual-fuel marine engine

In this study, thermodynamic, economic and environmental analyses of the scavenge air cooling water driven waste heat recovery system (WHRS) based on organic Rankine cycle (ORC) are conducted for a dual-fuel marine engine integrated with the EGR unit. R245fa, R236ea, R600a, R601a, R1234ze and R1234yf are selected as the working fluids. Thermo-economic performances of the fluids are analyzed, optimized and compared under various engine operating conditions. In addition, the mass and volume of the system along with the safety factors of the working fluids are evaluated to judge the physical applicability of the system for ships. According to the results, scavenge air has a significant amount of waste heat at medium and heavy loads and switching the engine mode remarkably affects the performance of the WHRS. R601a shows the best thermo-economic performance, however, considering the applicability of the system R236ea is the most suitable working fluid for the ORC WHRS.