The potential of exhaust waste heat recovery (WHR) from marine diesel engines via organic rankine cycle

Highlights: • This study examines the waste heat recovery using Organic Rankine Cycle. • This study proves the mass flow rate and temperature difference influences the results. • Finally Synechococcus PCC 7002 presents the highest efficiency of nett power output. -- Abstract: The rise of fuel prices due to the depletion of fossil fuel energy and unlimited carbon dioxide let-off are creating a renewed interest in techniques to increase the thermal efficiency of marine diesel engines. One promising mechanism to achieve improvement in system thermal efficiency is the conversion of engine waste heat to a more useful form of energy, either mechanical energy or electrical energy. Thus, this study investigates the potential of exhaust waste heat recovery from marine diesel engines using bioethanol production from selected microalgae as the working fluid via organic Rankine cycle (ORC). It also examines the system thermal efficiency and determines the pinch temperature of the plant. The microalgae Dunaliella tertiolecta, Chlamydomonas fasciata Ettl 437 and Synechococcus PCC 7002 are chosen as bioethanol producers based on the high yield of production. The maximum net power output and high system thermal efficiency are chosen as the evaluation criteria to select the microalgae with the best performance. The results demonstrate that among the three selected microalgae, Synechococcus PCC 7002 shows the highest efficiency of approximately 2.28% for the mass flowrate of exhaust gas of 4189 kgh⁻¹, while the net power output was approximately 5.10 kW.