Abstract

Hydrocyclones are used for classification purposes in the mining and mineral processing industries. According to their geometry and under certain operating conditions, hydrocyclones may present roping, which is a defective operation. Studies have related the roping phenomena to many variables such as hydrocyclone geometry and operating conditions. Some authors established a connection between the solids concentration of the feed and the discharge as one of the factors that generate roping. Other authors presented factors such as the apex and the vortex finder diameters, inlet pressure and the relationship between roping generation and the air core. This research aims to study the effect of inlet pressure and particle size distribution in the feed on roping in hydrocyclones. We develop a model using computational fluid dynamics (CFD) in order to study a 75-mm hydrocyclone operating with a variable flowrate and fed with two different materials. Each material is characterized by five granular phases interacting with each other and the model is validated by comparison with experimental data. The turbulence is treated using the Reynolds Stress Model (RSM) and the Eulerian Multiphase Model is used for the interactions between phases. The granular phases are described by the kinetic theory of granular flows (KTGF). The characteristics studied were: (i) air core and material distribution inside the hydrocyclone, (ii) underflow shape and spray angle, (iii) flow and solid concentrations, (iv) efficiency curve and separation size and (v) particle size distribution in the underflow and the cut sizes. According to the results, the particle size distribution of material in the feed has a direct impact on underflow behavior; when operating with coarser material the device tends to rope as the spray angle decreases. The same happens with an increase in the feed pressure. The roping condition generated by the coarse material directly affects the efficiency of the hydrocyclone, triggering an increase in separation size. The underflow particle size distribution tends to be coarser with an increase in the inlet pressure. When the inlet pressure decreases, the overflow particle distribution tends to be finer.