Analysis of power draw in ball mills by the discrete element method

Ball mills, like other comminution devices, consume large amounts of energy. Mill operators often have to assess the power draft of mills for an entirely different set of operating conditions or for a reconfigured circuit. It is shown that the power draft can be accurately predicted from analysis of the motion of the charge. The motion of the charge is rigorously simulated with a numerical technique known as Discrete Element Method (DEM). In this technique, the coordinates and velocities of each individual ball are computed From a knowledge of forces arising when balls collide with each other and with mill shell and lifter walls. First, simulation results on a wide range of ball mills are compared with available experimental data. Then the power draft predictions as a function of a few operating variables are shown. The unique feature of this method is that the mill power can be predicted for a mixture of ball sizes, different lifter geometry and lifter spacing, which is absent in other methods proposed in the literature. (C) 1999 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.