Settler with drop-size distributions
Wide drop-size distributions in settler design are especially encountered, if the system has increased viscosity. Such systems are to be expected in the future, especially in the context of raw-material change from fossil to biobased feedstock. The wide drop-size distribution creates specific design challenges, because often a primary phase separation occurs, leaving behind a turbid continuous phase, which actually still contains a significant fraction of drop phase. These small drops at a low phase fraction sediment slowly and do not coalesce among each other. Thus, their separation requires significant additional settling time. The goal is to predict the remaining drop-phase fraction as a function of time and height to allow safe settler design.
A drop-based simulation tool has been developed, which allows accounting for arbitrary drop-size distributions, and which can consider several dispersed phases including their interactions. This allows describing systems, where coalescence happens during sedimentation, which leads to curved sedimentation curves. Other interactions like adsorption between solid particles and the drops can in principle be described as well, which may be used to describe crud formation. The simulation also allows accounting for centrifugal forces, which depend on the radial position in the centrifugal extractor considered. It has e.g. be shown that it is efficient to leave a significant fraction of the centrifugal settler volume at its center empty, especially if also the small drops are to be separated.
Current focus is on further developing the simulation tool and on validating the individual models applied.
Publications
- N. Kopriwa, A. Pfennig: Characterization of Coalescence in Extraction Equipment Based on Lab-Scale Experiments. Solvent Extr. Ion Exc. 34(7) (2016) 622-642.
- M. Henschke, L.H. Schlieper, A. Pfennig: Determination of a coalescence parameter from batch-settling experiments. Chem. Eng. J. 85 (2002) 369–378.
- L. Schlieper, M. Chatterjee, M. Henschke, A. Pfennig: Liquid-Liquid Phase Separation in Gravity Settler with Inclined Plates. AIChE J. 50(4) (2004) 802-811.
Contact(s) : David Leleu
