Modeling Erosion Wear Rates in Slurry Flotation Cells
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TECHNICAL ARTICLE—PEER-REVIEWED
Modeling Erosion Wear Rates in Slurry Flotation Cells M. G. Lipsett • V. Bhushan
Submitted: 8 July 2011 / Published online: 11 August 2011 ASM International 2011
Abstract In processes using slurry as the working fluid, wear due to solid particles impinging on elements of the process units is a serious reliability issue. This study considers modeling wear damage in flotation cells, which are widely used in mineral processing. Flotation cells are typically cylindrical vessels where an impeller is used to agitate the fluid, enabling the liberation of the minerals from the slurry. Some solids, particularly those entrained in the impeller stream, can impact on the wall of the cell, leading to material loss and eventually to loss of structural integrity. The problem of predicting the remaining life of the unit due to erosion requires understanding of various sub-processes: flow modeling, particle–fluid interaction, energy interactions at the surface, and the mechanism of erosion itself. In this study, empirically developed equations for the flow field of cylindrical mixing vessel with a Rushton turbine are used in formulating a model relating and the damage accumulation rate to a simple set of measurable variables. To validate a model, a PIV technique was used to measure velocities in the flow field and near the wall on a physical model of the cell with transparent walls and particles that match the refractive index of the fluid. An Eulerian–Langrangian approach has been used to determine the particle trajectories and the effect of a squeeze film is incorporated into the model to modify the velocity distribution of particles prior to impacts. An analytical model based on equations of impulse and momentum for a particle of any shape striking a flat massive surface has been used to describe
M. G. Lipsett (&) V. Bhushan Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6R 1Z1, Canada e-mail: [email protected]
the energy lost at the walls. Finally, a damage model is developed that takes into account impact velocity, attack angle, properties of the impinging particles and the surface. This model is verified against a second physical model that measures material loss rate at different locations within the cell. Keywords Damage modeling Flotation cells Slurry Wear Particle–fluid interactions Particle image velocimetry
Introduction Slurry systems are critical elements in many industrial processes, and yet there is a lack of understanding of the effect of process conditions on damage accumulation. Damage can accumulate by erosion, erosion–corrosion, impact, and even scaling. Variability in process conditions makes condition monitoring and predictive modeling highly challenging. The key elements of a slurry system for a mineral processing operation are shown in Fig. 1. In general, there is a comminution or crushing step to take particles down to a small enough size for hydraulic transport, followed by slurry preparation and screening, and then pipeline t
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