Multi-objective optimization study of Organic Rankine Cycle system driven by combined grain drying waste heat and solar energy

This study proposes an Organic Rankine Cycle system based on a multi-energy complementary strategy, which couples the residual heat from grain drying with solar energy to achieve energy cascade utilization. The system adopts two heat source configuration modes: series and parallel. A thermodynamic-economic-environmental comprehensive evaluation model is constructed using MATLAB. Six working fluids (R1233zd, R601a, R601, isohexane, hexane, and benzene) are selected to systematically evaluate the effects of key parameters - including four heat source parameters and two Organic Rankine Cycle side parameters - on system performance metrics: exergy efficiency, levelized cost of energy, and Emission Rate of Carbon Dioxide.The hybrid Decision Making Trial and Evaluation Laboratory-Analytic Network Process method is employed to quantify interdependencies and establish objective weights, revealing that system exergy efficiency is the foundational metric (centrality: 4.801506, causality: 0.750033). The resulting weights (levelized cost of energy: 0.337614, exergy efficiency: 0.333045, Emission Rate of Carbon Dioxide: 0.329341) indicate a balanced prioritization with a slight emphasis on economic performance. A multi-objective multi-criteria decision-making framework, integrating Co-evolutionary Multi-Objective Particle Swarm Optimization-Technique for Order Preference by Similarity to Ideal Solution, is then established to determine the global optimum. Optimization results demonstrate that the series configuration with R1233zd constitutes the global optimum, yielding an exergy efficiency of 26.15 % and an levelized cost of energy of 0.25 $/kWh and an annual CO2 reduction of 135.72 t. A general comparison reveals that, excluding the global optimum (R1233zd), the parallel mode offers superior thermo-economic performance, whereas the series mode consistently provides better environmental performance.