Performance analysis and optimization of an electricity-cooling cogeneration system for waste heat recovery of marine engine

Abstract

Recovering the waste heat is meaningful for reducing the fuel consumption and pollution emissions of marine engine (ME). This paper proposes a system to efficiently convert the waste heat of the exhaust gas (EG) and jacket cooling water (JCW) of ME into electrical and cooling energies largely required on the ship. The proposed waste heat recovery system containes three sub-cycles, namely, the steam Rankine cycle (RC), organic Rankine cycle (ORC) and absorption refrigeration cycle (ARC), which perform well in the utilization of high-, medium- and low-temperature heat sources, respectively. The RC is combined with the ORC to recover waste heat from EG. The RC uses a portion of the JCW as a working fluid, while the remaining portion of the JCW is gradually utilized by the ARC and ORC as a driving heat source and a preheating source, respectively. The thermodynamic performance of the proposed waste heat recovery system (WHRS) was evaluated. Furthermore, the effects of the parameters including evaporation pressure, superheat and engine load on WHRS performance were analyzed for design optimization. The designed WHRS can output 7620 kW electricity and 2940 kW cooling energy under the rated operating conditions of the engine which improves the thermal efficiency of the engine by 10.5%, while WHRSs based on single RC and the dual loop ORC can only improve the efficiency by 5.3% and 7.3%, respectively.