Power Distribution of various Rotor Configurations in a Vertical Stirred Mill determined with DEM

Abstract

Vertical stirred milling is a well-recognized technology for fine grinding applications in the mineral processing industry. It is increasingly used due to the higher energy efficiency compared to horizontal mills. Vertical arrangement leads to high grinding intensity and power draw in the bottom grinding chambers, thus bottom rotors may wear out more than upper rotors. Modelling power draw is of great interest proven by the effort in previous work. An analytical power model for this type of mills based on measurement data was developed by Heath et al. [1] and a particle-based approach was presented by Larsson et al. [2]. In this contribution a DEM model to determine the torque distribution along the shaft for every grinding compartment in a vertical stirred mill with castellated rotors [3] is presented. Different rotor configurations are evaluated, whereby the rotors vary in diameter, alignment and spacing. An optimized configuration with a combination of different rotors could be developed, which leads to a more even power distribution and a significant reduction of load on the bottom rotors. Simulations also reveal particle dynamics, which explain field experience in terms of wear. Furthermore, the influence of grinding media filling level on power draw is investigated. Higher filling levels increase power draw following an exponential trend. This model allows to optimize the rotor configuration along the shaft, which has a strong impact on rotor and liner wear, critically influencing operational costs

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