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UBC Theses and Dissertations

DEM simulation and analysis of operating parameters on grinding performance of a vertical stirred media mill Hou, Yu


Stirred media mills have been increasingly used in ultra-fine grinding. The VXPmill is a vertical high speed stirred media mill for grinding mineral ores with high efficiency. Since it is a new technology in the industry, there is little understanding on the breakage kinetics of the mill. In order to gain more knowledge about the VXPmill, computer modelling of the mill was performed. Laboratory grinding trials were also conducted on a pilot scale mill to provide more information about the mill’s capability, as well as verify simulation results. DEM (Discrete Element Method) is a powerful tool in predicting particle behaviour, which is ideal for the study of stirred media milling. The CFD (Computational Fluid Dynamics) is used to model the motion of slurry by numerically solving the Navier–Stokes equations facilitated with the Volume of Fluid (VOF) and multiphase flow models. Simulation results suggested that a velocity gradient exists in the fluid field and grinding media in the mill. The highest grinding media velocity was reached near the disc edge in the horizontal direction and near the bottom of the mill in vertical direction. Those are the most active grinding zones in a vertical stirred mill. Different operating parameters such as stirrer rotational speed, slurry solid content and slurry viscosity have an influence on mill performance. Simulation results show that operating the mill at a high impeller speed helps to improve mineral liberation, while at too high impeller speed leads to a waste of electric energy without much improvement in mineral liberation. As well, a mid-level slurry solid content (15% v/v to 30% v/v) was found to achieve the best energy utilization during grinding. The slurry viscosity should be kept low to minimize the effect of high shear stress in the slurry. The influence of various operating parameters can be combined into the ‘stress intensity’ which describes the capability of a stirred media mill. Operating parameters also have an influence on the magnitude of force magnitude between grinding media which will result in different breakage mechanism. Fracture breakage mechanism plays a more important role than attrition in VXPmill.

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