The use of mixtures as working fluids of organic Rankine cycle (ORC) waste heat recovery (WHR) power plants has been proposed in the past to improve the matching between the temperature profile of the hot and the cold streams of condensers and evaporators, and the possible increase in thermodynamic efficiency of the system. The goal of this study was to assess the benefits in terms of efficiency, environmental (GWP) and operational safety (flammability) that can be obtained by selecting binary mixtures as working fluids in air-cooled ORC bottoming power plants of medium-capacity industrial gas turbines. Furthermore, two thermodynamic cycle configurations were analyzed, namely the simple and the split-cycle configuration. The benchmark case is a combined cycle power plant formed by an industrial gas turbine and an air-cooled recuperated ORC power unit with cyclopentane as the working fluid. The results of this study indicate that binary mixtures provide the designer with a wider choice of optimal working fluids, however, in the case of the simple-cycle configuration, the improvement in terms of combined cycle efficiency over the benchmark case is rather limited. The so-called split-cycle configuration leads to a general performance enhancement especially in combination with working fluid blends. Furthermore, this cycle configuration enables the use of environmentally and operationally safe working fluids if compared to cyclopentane, with no penalty in terms of combined cycle efficiency.     «

The use of mixtures as working fluids of organic Rankine cycle (ORC) waste heat recovery (WHR) power plants has been proposed in the past to improve the matching between the temperature profile of the hot and the cold streams of condensers and evaporators, and the possible increase in thermodynamic efficiency of the system. The goal of this study was to assess the benefits in terms of efficiency, environmental (GWP) and operational safety (flammability) that can be obtained by selecting binary m...     »