Prediction of 3D slurry flow within the grinding chamber and discharge from a pilot scale SAG mill

Slurry flow, including flow through the charge in the grinding chamber, through the discharge grates, along the pulp lifters and its discharge from the mill is an important contributor to the efficiency of the grinding process within a SAG mill. Poor transport of finer ground material can adversely affect grinding leading to excess energy consumption and over-grinding of fine material. This paper uses a 1-way coupled DEM–SPH method in three dimensions to analyse the full slurry flow for a 1.8 m diameter by 0.6 m long AG/SAG pilot mill. This provides detailed information on the internal flow of slurry within a SAG mill, including the prediction of dry regions and of slurry pooling. The importance of the end walls in generating complex three dimensional recirculation patterns in the charge and its influence on axial flow is demonstrated. Such a full 3D analysis ensures that the slurry is presented to the grate with a realistic spatial distribution and allows prediction of the flow through the grates and then within the pulp chamber. The rate of filling of the pulp chambers, the point of initiation of flow down along the rising pulp lifters, back flow into the grinding chamber and flow onto the discharge cone are all investigated. It is shown that the end wall lifters are critical to the flow through the grate generating pumping and shadowing effects which produce strongly non-uniform flow through different grate panels.

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► One-way coupled SPH–DEM models can predict the flow of solids and fluid charge in SAG mills.
► End walls and worn shell liners create significant axial flow and recirculation in a SAG mill charge.
► Slurry flow through the grate and along the pulp lifters and discharge from the mill can be predicted.
► End wall lifters are critical to grate flow producing non-uniform flow through different panels.