Cfd Simulation Of A Solid-Liquid Counter-Current Screw Extractor

More efficient processes to obtain artemisinin from Artemisia annua leaves via a solid-liquid extraction process are desirable, since artemisinin is increasingly needed as anti-malaria drug. As a substitute for conventional batch extraction technology, continuously operated counter-current processes are highly attractive for that purpose. To get first a better understanding of the hydrodynamics controlling the extraction, a multiphase 3D computational fluid dynamics (CFD) simulation model has been developed in the present project. It relies on the Volume of Fluid (VoF) model, leading to a purely Eulerian description of the flow. Using VoF, the distribution of the different phases within the screw extractor can be obtained. When varying the two inlet flow rates, different residence times for the liquid and the solid phases are obtained. This is particularly important, since the residence time is the most important process parameter to adjust. Currently, the predicted residence times for the liquid solvent amount to only one third of the experimentally determined values. However, accurate measurements are difficult, the assessment of residence times is different in the experiments and in the simulations, and the numerical model does not consider mass exchange processes between the phases yet. In spite of this discrepancy, a very good qualitative agreement is obtained, and these first results can be used to support the development of a compartment model, able to capture later both hydrodynamic and mass exchange processes with short computational times.