Abstract
A new boundary condition treatment has been devised for two-phase flow numerical simulations in a self-aerated minerals flotation machine and applied to a Wemco 0.8 m3 pilot cell. Airflow rate is not specified a priori but is predicted by the simulations as well as power consumption. Time-dependent simulations of two-phase flow in flotation machines are essential to understanding flow behavior and physics in self-aerated machines such as the Wemco machines. In this paper, simulations have been conducted for three different uniform bubble sizes (db = 0.5, 0.7 and 1.0 mm) to study the effects of bubble size on air holdup and hydrodynamics in Wemco pilot cells. Moreover, a computational fluid dynamics (CFD)-based flotation model has been developed to predict the pulp recovery rate of minerals from a flotation cell for different bubble sizes, different particle sizes and particle size distribution. The model uses a first-order rate equation, where models for probabilities of collision, adhesion and stabilization and collisions frequency estimated by Zaitchik-2010 model are used for the calculation of rate constant. Spatial distributions of dissipation rate and air volume fraction (also called void fraction) determined by the two-phase simulations are the input for the flotation kinetics model. The average pulp recovery rate has been calculated locally for different uniform bubble and particle diameters. The CFD-based flotation kinetics model is also used to predict pulp recovery rate in the presence of particle size distribution. Particle number density pdf and the data generated for single particle size are used to compute the recovery rate for a specific mean particle diameter. Our computational model gives a figure of merit for the recovery rate of a flotation machine, and as such can be used to assess incremental design improvements as well as design of new machines.
Highlights
Mineral flotation machines are classified into two main types; forced air and self-aerated machines.Wemco machines are widely used self-aerated machines where no air pumping mechanism is required, which simplifies flotation plant design and operation
Following Koh and Schwarz [13], we model the flotation kinetics as a first-order rate process, which is given by the fundamental equation:
We demonstrate the viability of computational fluid dynamics (CFD)-based flotation model as a tool to evaluate the performance of flotation machines and provide detailed hydrodynamic and kinetics data that can help improve the design of such machines
Summary
Mineral flotation machines are classified into two main types; forced air and self-aerated machines. Even two-phase flow simulations of flotation machines are time consuming and require large computational resources. Bubble size is one of the most important parameters that affect the air holdup of the pulp phase. A spectrum of bubble sizes exists in flotation machines depending on air flow rate and turbulence parameters. To predict such bubble size distribution, another set of equations that describes a population balance can be solved in the course of CFD simulation (Kerdouss et al [3]). Wemco 0.8 m3 that provide the hydrodynamic data and air volume fraction spatial distribution for uniform bubble size in the pulp phase.
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