Multi-objective optimization of a combined cycle using exergetic and exergoeconomic approaches

A parametric study is conducted for a combined cycle which combines a Gas Turbine-Modular Helium Reactor (GT-MHR) and two Organic Rankine Cycles (ORCs) to reveal the influences of decision parameters on the performance and total cost of the cycle. Two ORCs are operated from GT-MHR waste heat. Also, in order to optimize the system from both thermodynamic and economic aspects, a multi-objective optimization strategy is applied. The purpose of the optimization is to maximize the exergy efficiency and to minimize the total cost rate of the system. The selected decision variables in optimization process are the compressor pressure ratio, temperatures of inlet turbine and evaporators, temperature difference in the evaporator and degree of superheat at the inlet of the ORC turbines. After optimization, the exergy efficiency reaches 50.20% compared to 49.84% of the base case. Furthermore, it approximately reduces the capital expense by 2.4%. Distribution of the decision variables for the Pareto optimal front reveals that the degree of superheat at the inlet of the both ORC turbines has a tendency of being almost lowest value. However, the other variables reveal contrast process on the exchange between thermodynamic and economic aspects.