Study of Waste Heat Recovery Systems in Marine Engines: Potential for Energy Savings and Emission Reduction

Abstract

The shipping industry faces increasing pressure to reduce greenhouse gas emissions while maintaining operational efficiency. This study evaluates the energy-saving potential of an Organic Rankine Cycle (ORC) system for waste heat recovery from a 21,840 kW MAN 8S65ME-C8.6 main marine diesel engine during a realistic 1,610.7-nautical-mile coastal voyage from Dalian to Qinzhou, China. R245fa was utilized as the working fluid, with the main engine operating at various loading conditions (50% and 90%) and seawater temperatures (10-30°C). A steady-state thermodynamic model using MATLAB® with CoolProp™ library was developed and validated against published benchmarks. The analysis integrates exhaust gas and jacket cooling water as dual heat sources, post-boiler steam, and various sulfur fuel qualities under IMO MARPOL regulations. Results indicate that LSFO significantly outperforms HSFO for waste heat recovery, delivering 753.1 kW net power output (68% higher than HSFO) at 90% load, with thermal efficiencies of 11.31% and 10.86% respectively. The ORC system produces 121 MWh per voyage, replacing 8% of auxiliary power demands. CO₂ reduction reaches 62.1 tons per voyage for LSFO in winter conditions, aligning with IMO's 40% reduction target by 2030. Seawater temperature variation from 10°C to 30°C reduces ORC power output by approximately 7%, highlighting the importance of seasonal considerations in system design. This research provides a validated, open-source computational framework for marine waste heat recovery assessment and demonstrates that ORC technology offers a practical pathway for improving marine engine efficiency while reducing emissions.