A REVIEW OF DEPOSIT VELOCITY PREDICTION METHODS FOR MEDIUM PARTICLE SIZE SLURRIES IN PIPES

Methods of predicting the deposit velocity for wide particle size slurries with maximum particle size up to about 1 mm and maximum d50 size around 0.3 mm are outlined. These slurries generally possess non-Newtonian properties, typically modelled as Bingham plastics, and typically flow pseudo-homogeneously in turbulent flow down to the deposit velocity. Because they flow pseudo-homogeneously, pressure gradient prediction is relatively easy once a suitable operating velocity is selected. Consequently, the deposit velocity is the most important parameter as it determines the operating velocity. Beginning with Durand and Condolios [6], the historical development of the major methods for predicting the deposit velocity for mono-size particles in water are first reviewed, and their advantages and limitations discussed. Methods of extending predictions to mono-size particles in viscous Newtonian fluids are then reviewed. Next, prediction techniques relevant to deposition are reviewed for non-Newtonian slurries. These include prediction of the transition velocity between laminar and turbulent flow, and the critical pressure gradient required to prevent deposition under laminar flow conditions. Finally, these prediction techniques are combined to apply to minus 1 mm, wide size distribution, viscous slurries, commonly encountered in the mining industry. Two deposit velocity prediction techniques for these types of slurries are discussed. The first technique, based on determining the inherent viscosity of the slurry and assuming the weighted mean particle size of the total slurry represented the relevant coarse particle dimension, was found to predict performance in an operating 593 mm ID pipeline. The second technique, based on assuming the minus 75 µm portion represented the “carrier” fluid and assuming the median size of the plus 75 µm portion represented the relevant coarse particle dimension, was found to give very good predictions of the observed deposition trends of Goosen and Paterson [8] for a minus 300 µm gold tailings tested in 100 mm, 152 mm and 242 mm test loops.