Thermal design and analysis of an organic rankine cycle system utilizing the main engine and cargo oil pump turbine based waste heats in a large tanker ship

The utilization of main engine-based waste heat sources using organic Rankine cycle (ORC) systems is only available during the navigation phases of marine vessels, which leads to reductions in the system uptake time and economic viability of the investment during cargo loading/discharging operations and waiting periods in ports. The novel perspective of this study is to propose the cargo oil pump turbine (COPT) based waste heat as a utilizable source, which has not been introduced in the literature yet, and show the economic viability of ORC systems for tanker ships. In this regard, a new waste heat recovery system specifically designed for a reference crude oil tanker ship was introduced that can utilize both main engine-based waste heat during navigation and COPT-based waste heat during cargo discharge operations. The optimal heat exchanger network of the main engine and COPT-based waste heats was designed using pinch point analysis method for achieving optimum waste heat recovery. Energy and exergy analyses were conducted for the proposed ORC integrated waste heat recovery system for both navigation and discharge operation modes of the ship. The economic performance of the ORC system was further assessed by calculating payback periods and levelized energy costs for eleven design points. The highest energy conversion efficiency (16.2%) was achieved when the ORC condenser outlet temperature was taken as 15 °C for R1233zd(E). COPT based waste heat reduced the levelized energy cost of the system by at least 8.9% and the minimum levelized energy cost value was obtained as 0.1307. The best economic performance was yielded with COPT utilization at design point 9 with a payback period of 6.2 years, which was reduced by at least 0.7 years with the utilization of COPT based waste heat.