Particle scale modelling of the multiphase flow in a dense medium cyclone: Effect of medium-to-coal ratio

The effect of solids loading ratio or the medium-to-coal (M:C) ratio is the most important operational parameter of the Dense Medium Cyclones (DMC) that are widely used in the coal industry to upgrade the run-of-mine coal by separating gangue from product coal. However, its effect is still not well understood so far, since the flow pattern within a DMC is complicated due to the size and density distributions of the feed and process medium solids, and the turbulent vortex formed. Recently, it is shown that the particle-laden flow in a DMC can be modelled by the so-called combined Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) (CFD-DEM) in which the flow of coal particles is modelled by DEM which applies Newton's laws of motion to individual particles and that of medium flow by the conventional CFD which solves the local-averaged Navier-Stokes equations, allowing consideration of particle-fluid mutual interaction and particle-particle collisions. In this work, the effect of medium-to-coal (M:C) ratio is studied by a two-way coupling CFD-DEM approach for a large diameter DMC. The flow structure, and particle-particle and particle-fluid forces are analysed to understand the fundamentals governing this effect. The results suggest that the solids volume fraction of 20% (or M:C ratio of 4 by volume) is a critical point for the DMC performance under the conditions considered.