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Dense medium cyclone (DMC) is a high-tonnage device that is widely used to upgrade run-of-mine coal in the coal industry. It is known that the complicated multiphase flow in the DMC is technically difficult and expensive to experimentally investigate. In recent years, with the development of computational technology, various mathematical models based on the flow fundamentals such as computational fluid dynamics (CFD) and its combination with discrete element method (DEM) have been shown to be effective in overcoming this difficulty. In practice, the material properties fed in the DMC such as coal particle density and size distribution and their interaction are important variables affecting the DMC performance. Particularly, many problems frequently confronted in the operation of DMCs (e.g., vortex finder/spigot overloading, surging and system instability) are basically related to these variables. Although many studies have been done to help understand the underlying mechanisms, no systematic study has been made to examine the effects of these variables on DMC performance. In this work, the effects of particle density and size distribution and their interaction are systematically studied using a previously developed CFD-DEM model. In particular, Johnson s SB function, which is able to describe a wide range of distribution, is employed to represent the particle density and/or size distribution. The simulation results are analysed in terms of medium and particle flow patterns, particle-fluid, particle-particle and particle-wall interaction forces to elucidate the mechanisms. Based on the newly obtained CFD-DEM results in this thesis, a previously developed PC-based DMC model, which can readily run on a personal computer (PC), to predict the DMC performance as a function of a range of variables in an easy, fast and cost-effective way, is further developed and extended. Finally, the extended PC-based model is used to optimize the DMC designs for coal preparation through representative examples, in comparison with several typical designs in the industry. In addition, some new rules for DMC scale-up are proposed to meet industrial needs. It is shown that the developed PC-based model can indeed offer a cost-effective way to design, operate and optimize DMC process under different conditions.

Dense medium cyclone (DMC) units have been extensively used to upgrade run-of-mine coal in the contemporary coal preparation industry. In the past decades, development of DMCs has been mostly based on empirical methods, however, this would not give rise to the much enhanced understanding of the fundamentals of DMC under diverse conditions, and the consequences often have limited applicability. Recently, mathematical modeling was used to improve the understanding of DMCs (Suasnabar and Fletcher, 1999 ; Brennan, 2003 ; Narasimha et al., 2006). Specially, Wang (2009) and Chu (2010) carried out systemically numerical studies on the multiphase flow of DMC by use of computational fluid dynamics (CFD) and discrete element method (DEM). In this work, a statistic method, i.e., nonlinear curve fitting and multiple-regression procedure are repeated to analyse the CFD and CFD-DEM simulation data generated at the University of New South Wales, resulting in a set of empirical equations in which the performance of the DMC is a function of the geometrical, material and operational conditions. By use of the obtained equations, a robust and readily usable PC-based simulator of dense medium cyclone is developed to examine the performance of DMCs in a fast and easy way. The proposed computer model can investigate the effects of key variables related to the operational conditions, geometry and material properties on DMC flow and performance. In order to validate this computer model, comparisons of the effect of some key variables between the formulated empirical model and experimental results have been carried out. Qualitative agreements between predicted results with those measured are obtained in various aspects, such as the effect of some key variables on the performance of DMCs, and already established trends in literature. Moreover, it is shown that the developed computer model can quantitatively predict the operation of DMCs, and is superior to other empirical models reported in the literature in terms of simplicity, generality and accuracy. A comprehensive parametric study is carried out by use of the PC-based simulator, which explores the effects related to geometrical conditions, operational conditions and material properties on DMC flow and performance. The obtained relationship among the key variables could be used to facilitate engineering application and as a guide in the control, design and optimization of DMC units in coal preparation industry.