CFD study of liquid drainage in flotation foams

Abstract

Abstract Froth flotation is a separation process used in a number of applications worldwide. Recycled paper deinking, water purification, bitumen recovery from oil sands and, in particular, mineral separation, benefit from this industrial operation. The complex phenomena occurring within the froth phase of a flotation cell, however, are not entirely understood. The flow patterns of the froth, the drainage of liquid within the system and the behaviour of solid particles, represent a challenge for both experimental and numerical studies. State of the art Computational Fluid Dynamics (CFD) techniques can be used to assess the performance of flotation tanks in order to achieve better equipment design and enhanced operations. This work makes use of mathematical models for foam flow and liquid drainage in two-phase foams implemented in Fluidity, a finite element code which incorporates anisotropic adaptive remeshing. Adaptivity is an important feature for improving the computational cost of modelling these systems, as there are boundary layers present in the process whose size is independent of the scale of the flotation tank being modelled. Potential flow theory, previously shown to adequately represent the flow of froths in flotation tanks, has been used to obtain the velocity and trajectory of the foam, whilst the equations for liquid drainage in foams have been extended to consider transient simulations in up to three dimensions. In addition, the flexibility offered by the Finite Element Method in terms of the selection of the element types has been exploited, and mixed elements are employed to accurately represent the fields of interest. This work presents results from numerical investigations of a large laboratory scale flotation tank and discusses important aspects of the model that make it suitable for studying industrial processes involving the drainage of liquid through flowing foams.