Integrated thermo-economic design of processes and molecules using PC-SAFT

Abstract

The right choice of molecules is often crucial for the ultimate success or failure of energy and chemical conversion processes, e.g., refrigerants for cooling systems. However, choosing the right molecule for a process is challenging as the choice of molecules depends directly on the design of the process itself and vice versa. The ultimate success of a process can only be ensured if molecules are assessed on process level considering the inherent thermo-economic trade-off between operating cost and capital investment of the process. To capture all thermo-economic trade-offs, the molecule has thus to be designed simultaneously with the process. To tackle the challenge of choosing the right molecule, this thesis presents a systematic method for the integrated thermo-economic design of molecules and processes. For this purpose, computer-aided molecular design is directly integrated into process design. Thereby, novel molecules can be designed in silico and assessed on the process level. The link between process and molecule is modeled in a thermodynamically consistent way, using the physically-based PC-SAFT equation of state. Besides the design of pure molecules, the method enables also the design of mixtures. To quantify the economic performance of molecules, the design of the process flowsheet and the sizing of the equipment are directly integrated into the design problem. Thereby, the molecule design captures the inherent thermo-economic trade-off between operating cost and capital investment of the process. To provide a user-friendly application for a large user community, the presented method is integrated into a commercial flowsheeting software enabling the definition of the process flowsheet based on model libraries and drag-and-drop flowsheeting. The presented design method identifies the thermo-economically optimal molecule or mixture jointly with the optimal process settings, equipment sizes, and flowsheet. The method is exemplified for the integrated design of Organic Rankine Cycles. The results demonstrate the strong interaction between molecule and process highlighting the need for a systematic integrated design. The presented design method enables a systematic design linking all scales from molecule to economics to ensure the ultimate success of energy and chemical conversion processes.