Thermo-Economic Analysis and Optimization through Genetic Algorithm of a Dual-Loop Regenerative Supercritical CO₂ Brayton Cycle/ORC System Coupled to the Main Diesel Engine of a Bulk Carrier

In the present study, an energy and exergy analysis of a dual-loop regenerative supercritical CO2 Brayton cycle (RSCBC)/ORC system, which harvests waste heat from the exhaust gases and the intercooler of a main marine diesel engine of a bulk carrier, was performed. A thermal analysis was also conducted to calculate the main dimensions of the heat exchangers of the bottoming system. An economic analysis was performed to calculate the capital cost of each component of the bottoming cycle, the total capital cost of the RSCBC/ORC installation, and the electricity production cost (EPC). An integrated thermo-economic model was developed comprised of the thermodynamic model, the heat transfer analysis model, and the economic analysis model. A genetic optimization algorithm was imposed to the thermo-economic model, and it was used to run various scenarios with variable dual loop cycle parameters and as main objective to minimize the EPC of the proposed system. The optimum RSCBC/ORC system was then used to perform a mission analysis of 7500 hours of the examined bulk carrier to calculate the fuel savings, and the CO2 and SO2 emission savings for maritime fuels with different bunkering costs. The results showed that the proposed marine RSCBC/ORC system can result in considerable fuel savings from the auxiliary engines. The proposed RSCBC/ORC system can result in the significant reduction of a bulk carrier CO2 and SO2 emissions. Finally, it was found that the fuel bunker cost directly affects the capital cost and the payback period of the waste heat recovery installation.