cfd simulation of single-phase flow in flotation cells: effect of impeller blade shape, clearance, and reynolds number - sciencedirect
A series of numerical simulations of turbulent single-phase flows are performed to understand the flow and mixing characteristics in a laboratory scale flotation tank. Four impeller blade shapes covering a wide range of surface areas and lip lengths are considered to highlight and contrast the flow behavior predicted in the impeller stream. The mean flow close to the impeller is fully characterized by considering velocity components along the axial direction at different radial locations. Normalized results suggest the development of a comparatively stronger axial velocity component for a blade design with the smallest lip length, called big-tip impeller here. Normalized turbulent kinetic energy profiles close to the impeller reveal the existence of an asymmetric trailing vortex pair. The highest turbulence kinetic energy dissipation rates are observed close to the impeller blades and stator walls where the radial jet strikes the stator walls periodically. Furthermore, liquid phase mixing in the flotation cell is studied using transient scalar tracing simulations providing mixing time data. Finally, pumping capacity and efficiency of different impeller designs are calculated based on which the impeller blade design with a rectangular blade design is found to perform most efficiently.
a review of cfd modelling studies on the flotation process - sciencedirect
CFD modelling studies on the flotation process are reviewed.Advances in the flotation equipment modelling are analysed.CFD methods for determining the effect of hydrodynamics are summarized.Recommendations for future progresses are made.
A comprehensive review of the published literature regarding the computational fluid dynamics (CFD) modelling of the flotation process is presented. The detailed principles, mechanism and operation of the flotation process are discussed focusing mainly on the hydrodynamic aspect which is required for the successful operation of the flotation cell.
The kinetic modelling of flotation process has been reviewed in detail in three major flotation equipment namely mechanically agitated flotation cell, flotation column and dissolved air flotation. The advances made in the modelling and simulations of the equipment have been critically analyzed. Specific emphasis is given on the bubble-particle interactions and the effect of turbulence on these interactions. An attempt has been made to correlate the model parameters with the turbulence parameters. A thorough discussion is presented to highlight strengths and weaknesses of currently used CFD models and the recent developments in the numerical simulation tools for better understanding of the process. Finally, recommendations have been made for the future progress based on the analysis of the previous work.
hydrodynamic study of a phosphate flotation cell by cfd approach - sciencedirect
The impeller rotational speed increases the consumed power.The solid volume fraction increases the consumed power.The mixing time is independent from the impeller rotational speed.The solid distribution within the flotation cell is not homogeneous.
The flotation is a widely used separation process. Its efficiency is evaluated essentially through the purification and mass recovery yields. Since this unit operation occurs in liquid medium in the presence of air, the involved interactions are highly influenced by the hydrodynamics flow parameters. Therefore, a rigorous hydrodynamic investigation is required to ensure an optimal performance , . In this work, the key hydrodynamic parameters that impact the flotation efficiency were investigated. For this purpose, we assimilated the flotation cell to a stirred tank, then we treated two separate cases of hydrodynamic flow using the computational fluid dynamics (CFD) approach. The first one is the single phase flow and the second is the multiphase flow where we took into consideration phosphate rock (solid particles) suspended in the liquid phase (water). To model and study this kind of complex hydrodynamic flows, we adopted the EulerianEulerian approach, which allowed us to investigate the principal hydrodynamics criteria that can afford optimal operating parameters. These parameters are: the dissipated power, the pumping flow, the number of power, the number of pumping, the mixing time and solid homogenization in the flotation cell fluid sheath. For these performance criteria, the CFD results are in good agreement with those published in experimental studies , .
cfd model of a self-aerating flotation cell - sciencedirect
The effect of impeller speed on the air flow in a self-aerated Denver laboratory flotation cell was investigated using computational modelling. Air is induced into the slurry by the impeller's rotating action. The rate of air flow is determined by the suction pressure created by the impeller, the hydrostatic head of the slurry and the frictional losses along the delivery shaft from the inlet valve to the impeller. From two-phase simulations of the flotation cell at varying impeller speeds, the predicted air flow rates have been found to compare favourably against measured values reported in the literature. The effect of increasing impeller speed is to increase the air flow rate and gas holdup in the cell. Simulations with flotation kinetics showed that the gravitational force acting on the attached particles is significant. The effect is a decrease in the bubble rise velocity which in turn affects the flotation rate as predicted by the model. The effects of the local turbulence level on the local attachment rate and bubble loading have been discussed and quantified.
cfd modelling of bubbleparticle attachments in flotation cells - sciencedirect
In recent years, computational fluid dynamic (CFD) modelling of mechanically stirred flotation cells has been used to study the complexity of the flow within the cells. In CFD modelling, the flotation cell is discretized into individual finite volumes where local values of flow properties are calculated. The flotation effect is studied as three sub-processes including collision, attachment and detachment. In the present work, these sub-processes are modelled in a laboratory flotation cell. The flotation kinetics involving a population balance for particles in a semi-batch process has been developed.
From turbulent collision models, the local rates of bubbleparticle encounters have been estimated from the local turbulent velocities. The probabilities of collision, adhesion and stabilization have been calculated at each location in the flotation cell. The net rate of attachment, after accounting for detachments, has been used in the kinetic model involving transient CFD simulations with removal of bubbleparticle aggregates to the froth layer.
Comparison of the predicted fraction of particles remaining in the cell and the fraction of free particles to the total number of particles remaining in the cell indicates that the particle recovery rate to the pulpfroth interface is much slower than the net attachment rates. For the case studied, the results indicate that the bubbles are loaded with particles quite quickly, and that the bubble surface area flux is the limiting factor in the recovery rate at the froth interface. This explains why the relationship between flotation rate and bubble surface area flux is generally used as a criterion for designing flotation cells. The predicted flotation rate constants also indicate that fine and large particles do not float as well as intermediate sized particles of 120240m range. This is consistent with the flotation recovery generally observed in flotation practice. The magnitude of the flotation rate constants obtained by CFD modelling indicates that transport rates of the bubbleparticle aggregates to the froth layer contribute quite significantly to the overall flotation rate and this is likely to be the case especially in plant-scale equipment.