Parametric analysis and thermo-economical optimization of a Supercritical-Subcritical organic Rankine cycle for waste heat utilization

Abstract

The Supercritical-Subcritical organic Rankine cycle could combine the superiorities of supercritical ORC and dual-pressure organic Rankine cycle to recover more heat and improve the system performance. The parametric analysis and thermo-economical optimization of a Supercritical-Subcritical organic Rankine cycle using R1234ze has been investigated in this study. The effects of five key operation parameters on the thermodynamic performance and economical factor are examined. A single-objective optimization for maximizing net work output, maximizing exergy efficiency and minimizing UAsys (heat transfer requirement) is examined and compared. The bi-objective optimization for maximizing exergy efficiency and minimizing UAsys simultaneously is also addressed. Research demonstrates that the net output power increases first and then decreases as supercritical stage temperature and supercritical stage pressure. UAsys decreases first and then increases with the supercritical stage temperature. The lower UAsys does not mean the higher net power output or exergy efficiency. A higher supercritical stage pressure and temperature are detrimental to system economic performance, while a higher condensation temperature can benefit improving system economic performance. The Pareto-optimal solutions for exergy efficiency and UAsys are 61.25% and 20.08 kW/K, respectively.