Numerical studies of multiphase flow and separation performance of natural medium cyclones for recovering waste coal

Coal has been a major energy resource worldwide for many years and will continue to be in the foreseeing future. One of the major by-products of using coal is the redundant colliery spoil heaps that are harmful to environments. This problem can be overcome in a relatively economical way by using a newly developed technology, i.e., the Nature Medium Cyclone (NMC) technology which makes use of fine dirty particles in the feed rather than magnetite particles to form the medium phase. The current understanding on the flow and performance of NMCs are extremely limited. In this work, the flow in an NMC is studied by using a combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) (CFD-DEM) where the flow of coal particles is modelled by DEM and that of medium flow by conventional CFD. The simulated results are compared favourably with physical experiments and the effects of two of the most important operational parameters, i.e., medium velocity and medium-to-coal ratio (M:C ratio) at the NMC inlet, are investigated numerically.