Particle scale modelling of the multiphase flow in a dense medium cyclone: Effect of fluctuation of solids flowrate

Dense medium cyclone (DMC) is widely used to upgrade run-of-mine coal in the coal industry. The flow dynamics/fluctuation in a DMC is important but has not been studied previously. In this work, the dynamics is studied by numerically with special reference to the effect of the fluctuation of solid mass flowrate. The simulation is carried out by use of a combined approach of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). In the model, the motion of discrete mineral particle phase is obtained by DEM which applies Newton’s equations of motion to every individual particle and the flow of medium (mixture of water, air and fine magnetites) phase by the traditional CFD which solves the Navier–Stokes equations at a computational cell scale. The simulated results are analysed in terms of medium and coal flow patterns, and particle–fluid, particle–particle and particle–wall interaction forces. It is shown that under high fluctuation frequency and current conditions, the performance of DMC is not sensitive to both the fluctuation amplitude and period of coal flow at the DMC inlet. However, under low fluctuation frequency, as fluctuation amplitude increases, the separation performance deteriorates slightly and the flow is obviously affected at the spigot. A notable finding is that the near-gravity particles that tend to reside at the spigot and/or have longer residence time in the DMC would be affected more than other particles. The work shows that this two-way coupled CFD–DEM model could be a useful tool to study the dynamics of the flow in DMCs.

The flow instability in a dense medium cyclone is investigated with special reference to the effect of solids fluctuation at feed by means of the CFD–DEM approach. Spatial distributions of the time-averaged particle–particle interaction intensity at a central section being normal to the inlet of the DMC when the M:C ratio fluctuation period is constant (=30 s) for different M:C fluctuation amplitude : (a), 10%; (b), 30%; and (c), 50%.Figure optionsDownload as PowerPoint slideHighlights
► Solids flow fluctuation in a dense medium cyclone (DMC) is investigated numerically.
► The flow and performance is sensitive to low fluctuation frequency.
► Major effects are found in the cone region in a DMC, and near-gravity particles.
► The proposed model should be useful for future studies of DMC dynamics.