Dilution and flocculation prediction of a pilot-scale thickener feedwell by hybrid modelling approach

Abstract

Dilution plays a significant role in the flocculation process, which relies on the structure and dimensions of the dilution port. The dilution port was optimized by the hybrid modelling approach between Response Surface Methodology (RSM) and Computational Fluid Dynamics (CFD), considering the interactive impact of sidewall immersion length (L), reference angle (α) to bending pipe, and width of the cuboid (W). Batch simulation tests were performed to explore the effect of structure and dimension on dilution quantity. A quadratic regression model forecasted the optimal feedwell would be capable of a self-diluting water volume of 1.53 L/s compared to the basic case of negative1.32 L/s, and the α was most sensitive factor that influence the dilution quantity. Subsequently, the flow characteristics and flocculation performance were compared between the two cases using the coupled CFD-Population Balance Model (PBM) approach. Results showed that the outer well was subdivided into four zones following the predicted variation of floc size along the vertical direction. The optimal case exhibited better flocculation performance than the basic case evaluated by the mean floc size distribution in and around the feedwell, thereby guiding the design of feedwell dilution ports for enhancing the flocculation performance.