Cycle analysis and environmental assessments of cascade organic rankine cycle on diesel engine ships

Abstract

This study investigates the application of organic Rankine cycle (ORC) on ships to reduce fuel oil consumption and assess improvements in the Energy Efficiency Existing Ship Index (EEXI), and carbon intensity indicator (CII). A cascade ORC(C-ORC) configuration is designed to utilize the exhaust gas from a diesel engine.

Thermodynamic simulation identified a combination of toluene and R1233zd as the optimal working fluids for the C-ORC. Exergy analysis was conducted to evaluate the performance difference between the C-ORC system and a version with an internal heat exchanger (C-IHX ORC). The results showed a maximum exergy efficiency of 56.78 % for the C-IHX ORC, compared to 49.33 % for the C-ORC. Further evaluations of the C-IHX ORC, including fuel savings, energy generation, EEXI, and CII, demonstrated that average vessel fuel consumption decreased by 1.02 %, and average attained EEXI improved by 0.93 %. Additionally, the attained CII value was enhanced by 0.98 % on average, depending on operating loads and traveled distances. Although the improvements of EEXI, and CII offered were modest, they present the potential for further enhancement through the utilization of additional waste heat sources, such as economizer steam, and jacket cooling water.