EVALUATING THE WASTE HEAT SOURCES IN A VERY LARGE CRUDE CARRIER AND THE POTENTIAL INTEGRATION OF ORGANIC RANKINE CYCLE CONFIGURATIONS

Decarbonizing the shipping industry is gaining increasing attention, with the Waste Heat Recovery (WHR) technologies being in the spotlight as fuel saving solutions for marine engines. Although many studies focus on assessing of recovered energy from marine main engines using Organic Rankine Cycle (ORC) systems, only a few investigations deal with the overall waste heat potential of the vessel, considering also the auxiliary diesel generator sets. In this work, the waste heat potential of the heat sources available from the main engine and the auxiliary gensets are examined as functions of the engine loads in different sailing and laden conditions by applying real long-term operational data of a case study Very Large Crude Carrier (VLCC). A direct and an indirect method, with respect to the heat balance, are followed to estimate the exhaust gas waste heat. In particular, the former method is developed using the measured temperature values, while the latter one introduces the exhaust gas mass flow rates estimated indirectly by the measured fuel oil consumption. Furthermore, two rcORC configurations are proposed to determine the achievable energy recovery by exploiting the major waste streams of the main engine and auxiliary gensets. Two methods are evaluated: (i) utilizing only the exhaust gases of the main engine to evaporate the ORC working fluid, and (ii) utilizing the exhaust gases of both main engine and auxiliary gensets. The simulations based on the real exhaust gas temperature measurements for the mean engine load during sailing indicate that the rcORC power output can be estimated equal to 530 kW, being increased up to 653 kW and 741 kW due to the diesel gensets integration, for R245fa and R1233zd(E) as the selected ORC working fluids, correspondingly.