CFD simulation on influence of suspended solid particles on bubbles' coalescence rate in flotation cell

Abstract

A computational fluid dynamics (CFD) model was used to investigate the influence of solid concentration on bubbles' coalescence rate in flotation cell using Eulerian–Eulerian approach. CFD simulations were performed with AVL-FIRE 2009.2, and the existing flow field was modelled for two-phase (gas–liquid) and three-phase (gas–liquid–solids). The liquid phase was treated as a continuum and the gas phase (bubbles) and solid particles were considered as dispersed phases. The population balance equation for bubble break-up and bubble coalescence rate and the interfacial exchange of mass and momentum as well as bubble–particle attachment and detachment have been included in the CFD code by writing subroutines in FORTRAN. This investigation focused on studying the effect of solid particle on bubble break-up and bubble coalescence rate in the flotation cell at different superficial gas velocity values. The results predict that the presence of solid particles reduced the gas holdup in a flotation column. With the increase of the superficial gas velocity the size of gas bubble that were generated inside the cell decreased, leading to increased gas holdup. The result also shows that the Sauter mean diameter of bubbles decreases with the increase of solid concentration. Reasonably good agreement was obtained between simulation and experimental results for the effect of solid concentration on gas hold-up and axial pressure profile. In the current study, the froth zone was neglected, only the pulp zone was simulated. This is a deficiency of the present model, as the pulp is only one part of the flotation process, and it is physically linked to the froth. However, the model is a step towards gaining a complete view to describing the processes within a flotation cell through inspect the impact of presence of solid particles on the bubble coalescence rate under the different operation conditions.