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UBC Theses and Dissertations

Optimization of design and operation parameters of vertical stirred mill using DEM approach Kenawi, Marawan A.


Fine ore grinding is a relatively new technology in the industry, generally operated in stirred media mills filled with grinding media and a mixture of water and ore particles known as slurry. Stirred mills have been increasingly used in ultra-fine grinding circuits. However, there is limited understanding of the influence of many process and design parameters on the mill’s performance. To gain more knowledge about those parameters, this study focuses on the development and validation of DEM numerical models, which are then used to evaluate the design of FLSmidth's VXPmill and identify its critical process parameters. Laboratory experiments and material parameters calibration tests were conducted on a pilot-scale 10 liters mill to validate the numerical model and provide more insight into the mill operation, mixing pattern, and power consumption. This thesis focuses on the analysis and optimization of the key operating and design parameters and investigates their effects on the kinetic energy, collision efficiency, abrasive wear rate, and momentum transfer rate to the media inside the vertical stirred mill. A Lagrangian numerical model based on the discrete element method (DEM) is developed and used to gain a fundamental understanding of the dynamic behavior of grinding media in the mill. Specifically, the distribution of stress intensity levels inside the mill for different grinding media properties, rotational velocities, and mill designs was investigated in depth. Various configurations of a selection of parameters are studied, both design and operational. Operation parameters such as stirrer speed, media load, size, and density are examined individually and concurrently. The general trend of the results shows an increase in kinetic and collision energies as the input variables are increased, while also an increase in power consumption and liner wear is observed. A design of experiment study considered gradual improvements to the original design of the VXP10 mill rotor. The study examined variations in the disc geometry, spacing, and hole size and number. The design parameter study considered introducing vertical impellers to improve the momentum transfer to the media particles. The results from this design of experiments allowed the development of various alternative rotor designs to the VXP10.

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