INTEGRATED DESIGN OF WORKING FLUID MIXTURES AND ORGANIC RANKINE CYCLES (ORC) IN THE CONTINUOUS-MOLECULAR TARGETING (COMT) FRAMEWORK

asme-orc2015 Tracking Number 76

Organic Rankine Cycles (ORCs) provide power by exploiting low-temperature heat of renewable sources or waste heat. To enhance the efficiency of ORCs, binary mixtures have been proposed as working fluids. Using a working fluid mixture leads to a temperature glide during evaporation and condensation and thus to a better match between the temperature profile of the heat source and the working fluid. We present a method for the integrated optimization the working fluid mixture, i.e., its components and its composition, and the ORC process parameters. Mixture properties are calculated by the PC-SAFT equation of state. In our design framework, the so-called continuous-molecular targeting (CoMT), the pure component parameters are relaxed in the optimization to allow for a simultaneous optimization of the working fluid mixture and the process. However, the resulting optimal mixture components do in general not coincide with any real fluid. Real fluids are identified in the second step of the CoMT framework, the structure-mapping. In this paper, only the CoMT optimization is employed to quantify the potential benefit of working fluid mixtures. The results show that mixtures are not always beneficial and that their benefit depends on the conditions under which the ORC system is finally installed.