Modelling the influence on power draw of the slurry phase in Autogenous (AG), Semi-autogenous (SAG) and ball mills

• The power draw has been modelled by assuming it is a separate phase to the solids.
• The hold-up has been to slurry flow and the design of the mill discharge mechanism.
• The resultant model accurately reproduces the observed trends in mill power draw.

The slurry level in AG/SAG and ball mills has an influence on their power draw, which in some instances can be profound. This is particularly the case with so-called slurry pooling in AG/SAG mills which can result in significant lowering of power draw. From a predictive viewpoint there are currently no published models that explicitly describe the influence of slurry level on power draw and the relationship between slurry level, slurry flow and pulp lifter design. Citic SMCC Process Technology Pty Ltd has developed such a model and in this paper its structure is described. Examples are given of both AG/SAG and ball mills of how the model responds to changes in slurry level. These examples are used to explain the observed phenomena of slurry pooling and the decrease in power draw observed in ball mills after start-up when feed is first introduced into the mill.