Simultaneous optimization of working fluid and process for Organic Rankine Cycles (ORCs) using PC-SAFT.

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Abstract

Organic Rankine Cycles (ORCs) generate power from lowtemperature heat. To make best use of the diverse lowtemperature heat sources, the cycle is tailored to each application. The objective is to maximize process performance by optimizing both, process parameters and the working fluid. Today, process optimization and working fluid selection are addressed separately in a twostep approach: working fluids are selected using heuristic knowledge; subsequently, the process is optimized. Such an approach can lead to suboptimal solutions, since the optimal fluid might be excluded by the heuristics. We therefore present a framework for the holistic design of ORCs enabling the simultaneous optimization of process and working fluid based on process performance. The simultaneous optimization is achieved by exploiting the rich molecular picture underlying the PCSAFT equation of state in a continuousmolecular targeting approach (CoMTCAMD). To allow for the prediction of caloric properties, a quantitative structureproperty relationship (QSPR) for the ideal gas heat capacity is proposed that relies on pure component parameters of PCSAFT. The framework is used for the optimization of a geothermal ORC in a case study. A sound holistic design of process and working fluid is achieved.