Discrete element method - computational fluid dynamics modelling of flow behaviour in a stirred mill - effect of operation conditions

Stirred mills are increasingly used in the mineral industry for a range of milling duties from fine to coarse grinding. This work investigated the particle and fluid flow in a stirred mill using a combined discrete element method (DEM) and computational fluid dynamics (CFD) approach. The effect of operation conditions such as mill loading and disc rotation speed was studied. The flow properties were analysed in terms of flow velocity, power draw, collision frequency and collision energy. Both particle and fluid flows showed different flow patterns at different mill loadings. Higher mill loading showed an increased collision frequency and decreased collision energy within the particle flow. The regions with high impact energy were also observed near the disc and mill chamber at a high loading. Both collision energy and collision frequency increased with increasing mill speed. Energy consumption increased faster with mill loading than total impact energy, which reduced mill energy efficiency. The results obtained for the particle-fluid system were qualitatively comparable with those obtained from dry systems under similar operating conditions. The findings would be useful to understand and optimise operation condition for improved grinding performance.