Techno-thermodynamic multi-objective optimization of organic Ranckine cycles for waste heat recovery

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.

Organic Rankine cycles (ORC) are considered a mature technology in waste heat recovery applications. Yet, many of the commercially available implementations have comparable design characteristics. They operate under subcritical regime and only few working fluids are considered. In this work, three ORC configurations are analyzed on thermodynamic and technical grounds. The cycles under consideration are the subcritical cycle (SCORC), the transcritical cycle (TCORC) and the partial evaporation cycle (PEORC). Technical design constraints on the expander generally limit the cycles which can be considered feasible. Yet, their impact on the optimization process is not clear. Therefore, in this work, the technical performance criteria are optimized in conjunction with maximization of the net power output. Thus the investigation results in a multi-objective optimization strategy. The proposed strategy is performed on two representative but distinctive waste heat recovery cases. The results of the investigation are particularly useful for manufacturers of ORCs. The thermodynamic performance of the cycles is compared under equal boundary conditions, expander criteria are taken into account, actual cases are used and a ranking is created.