Design and partial load operation optimization of integrated ship energy system based on supercritical CO2 waste heat recovery cycle

Abstract

In the present work, a supercritical CO2 cycle, designed for recovering waste heat originating specifically from heavy-duty turbocharged diesel engines, constitutes the basis of an integrated energy system. The purpose of this system is to cover the time-varying power loads required during the operation of ships, appearing in diverse forms of energy (propulsive/mechanical, electrical, thermal). Optimization procedures are applied for the determination of the optimal design and of the optimal operational characteristics of the CO2 cycle during partial loading conditions. Appropriate techno-economic criteria are used for evaluating the optimality of the proposed engineering solutions. The effects of the added capital costs of the CO2 cycle on its useful power output are investigated, while the temporal variations of the energy loads are appropriately taken into account in the determination of the optimum CO2 cycle design characteristics. The inclusion of the CO2 cycle is economically justified, while a reduction of operational fuel costs from 5.8% to 6.3 % is achieved for a typical yearly energy profile, according to the optimal allocation of the useful power produced by the CO2 waste heat recovery cycle towards the propulsive or electric loads.