Thermodynamic Performance Comparison of Single-pressure and Dual-pressure Evaporation Organic Rankine Cycles Using R1234ze(E)

Abstract

The organic Rankine cycle (ORC) presents a great potential in the efficient heat–power conversion of low and medium temperature (<350°C) thermal energy. Dual-pressure evaporation ORCs can significantly reduce the exergy loss in the endothermic process. While, variations of optimal cycle parameters and the superiority in the thermodynamic performance compared with the single-pressure evaporation ORC remain indeterminate for various heat source temperatures. This paper focuses on the dual-pressure evaporation ORC using R1234ze(E) driven by the 100–200°C heat sources without the outlet temperature limit. Two-stage evaporation pressures and the high-pressure evaporator outlet temperature were optimized, and the system thermodynamic performance was compared with that of the single-pressure evaporation ORC. Results show that the maximum net power output of the dual-pressure evaporation ORC system is generally larger than that of the single-pressure evaporation ORC system for the heat source temperature below 150°C. The heat source temperature is lower, the increment of the maximum net power output is generally larger; and the maximum increment is 24.3%. When the endothermic process minimal temperature difference of the single-pressure evaporation ORC occurs at the evaporation bubble point, the dual-pressure evaporation ORC generally can further increase the system net power output.