Exergoeconomic analysis and multi-objective optimization of a marine engine waste heat driven RO desalination system integrated with an organic Rankine cycle using zeotropic working fluid

Abstract

In order to waste heat recovery from a marine heavy duty diesel engine, a cogeneration system based on a series two-stage organic Rankine cycle (STORC) using a zeotropic mixture as the working fluid integrated with a reverse osmosis desalination (RO) unit is proposed for producing the consumed electricity and fresh water of a ship. The proposed system is simulated thermodynamically and a detailed energy, exergy and exergoeconomic analysis is conducted. Moreover, to identify the optimal values of the design parameters, including the evaporator 1 pressure, evaporator 2 pressure, seawater salinity and volumetric flow rate of the fresh water, multi-objective optimization with respect to the maximization of the exergy efficiency and minimization of the total product unit cost of the system is carried out. The exergoeconomic analysis results show that the evaporator 2 pressure is a very effective parameter on the system performance, so that for a specific thermodynamic operating condition of the system, there is an optimum value of the evaporator 2 pressure which leads to the total product unit cost minimization. The optimization results reveal that at the final optimum design point obtained by Pareto frontier, the values of the objective functions are gained 37.04% and 59.106$/GJ, respectively.