Modelling comminution devices using DEM

Particle size reduction, or milling, is an essential component of mineral p rocessing and is important in other industry sectors. This needs to be done as efficiently as possible, maximizing mill throughput while minimizing op erating costs. Such milling processes typically use only 1-5 per cent of th e supplied energy for particle breakage, which leaves room for improvement. In discrete element modelling (DEM) of granular hows the trajectories, ori entations and spins of all the particles and objects in the system are calc ulated and their interactions with other particles and with their environme nt are predicted. It is necessary to simulate particles of many different s izes and densities interacting with complex-shaped objects moving in differ ent ways. Particle flows in three types of mills; a 5 m ball mill, a 10 mm SAG mill and a 15 cm diameter centrifugal mill are predicted. Charge behavi our, torque and power draw are analysed for a range of rotation rates from 50 to 130 per cent of the critical speed for the ball mill. Sensitivity of the results to material properties and size distribution are examined. Radi al size segregation is shown to occur and increases strongly with min speed . Charge motion and power consumption for the SAG mill are predicted. Compa rison of simulated flow patterns for the centrifugal mill with high-speed e xperimental photographs reveals dose agreement. The limitations and restric tions of this type of DEM model are discussed in detail. Copyright (C) 2001 John Whey & Sons, Ltd.