(438f) Characterization of Gas Dispersion Behavior in Flotation Cells Using Coupled CFD-PBM and Direct PBM Approaches
Accurate predictions of Sauter mean diameter (SMD) of dispersed phase (gas) is necessary to facilitate accurate predictions of flotation kinetics in the flotation cells. Previous studies have shown the presence of spatial non-uniformity in bubble size distribution (BSD) for both lab- and pilot-scale flotation cells. In this study, we aim to use coupled computational fluid dynamics (CFD) and population balance modeling (PBM) approach to predict the distribution of SMD in generic flotation cells. The dynamics of multiphase flow is modeled using Eulerian-Eulerian approach and BSD is obtained by using quadrature method of moments (QMOM). Only binary breakage and coalescence processes of gas bubbles are considered. Coalescence rate is modeled using Coulaloglou and Tavlarides model (1977), while breakage rate and daughter size distribution are modeled using Laakkonen (2007) model. A moment correction procedure proposed by McGraw (2012) is used to identify and correct invalid moment sequences in each computational cell. The numerical approach applied in this work is validated by comparing the numerical predictions against published BSD in stirred tanks. Using the coupled CFD-PBM approach, overall gas holdup and SMD for flotation cell are obtained. Furthermore, flotation cell is also modeled as a homogeneous well-mixed reactor, and the resulting population balance equation (PBE) is solved using high-order moment conserving method of classes (HMMC) technique. Different breakage and coalescence models are tested, and their effect on final BSD and SMD are investigated. Finally, the predictions obtained from coupled CFD-PBM and HMMC techniques are compared for the entire cell.