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Kuang S.,University of New South Wales | Qi Z.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
Minerals Engineering | Year: 2014

A computational fluid dynamics (CFD) model is proposed to describe the multiphase flow in a dense-medium cyclone (DMC). In this model, the volume of fluid (VOF) multiphase model is first used to determine the initial shape and position of the air core, and then the so called mixture model is employed to describe the flows of the medium, coal particles and air, where the turbulence is described by the Reynolds stress model. The validity of the proposed approach is verified by the reasonably good agreement between the measured and calculated results in terms of separation efficiency. On this base, this model is used to quantify the effects of the ratios of spigot to vortex finder diameters (U:O) and medium to coal (M:C) on performance. The results are shown to be generally comparable to those reported in the literature. It reveals that when vortex finder or spigot diameter is varied at the same U:O ratio, the offset and medium split nearly remain the same, however, the coal feed rate and Ep are different under the conditions considered. It is also shown that the fish-hook phenomenon is observed when spigot diameter is equal to or slightly larger than vortex finder diameter, and a normal operation becomes less stable with decreasing U:O ratio. The key phenomena predicted are explained by the calculated inner flows. © 2013 Elsevier Ltd. All rights reserved. Source


Chu K.W.,University of New South Wales | Kuang S.B.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
Minerals Engineering | Year: 2014

Dense medium cyclone (DMC) is a high-tonnage device that is widely used to upgrade run-of-mine coal in modern coal preparation plants. It is known that wear is one of the problems in the operation of DMCs, but it is not well understood. In this work, the wear rate of DMC walls due to the impact of coal particles is predicted by a combined computational fluid dynamics and discrete element method (CFD-DEM) approach, using the Finnie wear model from the literature. In the CFD-DEM model, DEM is used to model the motion of discrete coal particles by applying Newton's laws of motion and CFD is used to model the motion of the slurry medium by numerically solving the local-averaged Navier-Stokes equations together with the volume of fluid (VOF) and mixture multiphase flow models. According to the Finnie wear model, the wear rate is calculated according to the impact angle of particles on the wall, particle velocity during an impact and the yield stress of wall material; the relevant particle-scale information can be readily obtained from the CFD-DEM simulation. The numerical results show that the severe wear locations are generally the inside wall of the spigot and the outside wall of the vortex finder. The wear rate depends on both the operational conditions and solids properties. It increases generally with the decrease of medium-to-coal (M:C) ratio. For a given constant M:C ratio, the wear rate for thermal coal is higher than that for coking coal, especially at the spigot. Large particles may cause a non-symmetric wear rate due to the gravity effect. The effect of a worn spigot wall on the multiphase flow and separation performance is also studied. This work suggests that the proposed approach could be a useful tool to study the effect of wear in DMCs under different conditions. © 2013 Elsevier Ltd. All rights reserved. Source


Chen J.,University of New South Wales | Chu K.W.,University of New South Wales | Zou R.P.,University of New South Wales | Yu A.B.,University of New South Wales | And 3 more authors.
Minerals Engineering | Year: 2014

The dense medium cyclone (DMC) is a high-tonnage device widely used to upgrade run-of-mine coal in the modern coal industry. It is known that a small improvement on the performance of DMC may greatly enhance industrial profitability. Therefore, it is very useful to develop an effective method to help optimize the design and operation of DMCs. Recently, based on the numerical experiments performed by Computational Fluid Dynamics and its combination with Discrete Element Method; the authors have established a PC-based mathematical model that looks promising to achieve this design and operational goal. In this paper, the authors will first discuss how to use this model to design high capacity or high efficiency DMCs for coal preparation through representative examples, in comparison with several typical designs in the industry. Some rules for DMC scale-up are then proposed for general application. The results further demonstrate that this DMC model can indeed offer a convenient way for optimum design and/or operation of DMCs under different conditions. © 2013 Elsevier Ltd. All rights reserved. Source


Wang B.,Lanzhou University | Wang B.,University of New South Wales | Chu K.W.,University of New South Wales | Yu A.B.,University of New South Wales | And 3 more authors.
Minerals Engineering | Year: 2011

This paper presents a numerical study of the gas-liquid-solid flow in 1000 mm dense medium cyclones (DMCs) with different body dimensions, which includes the spigot diameter, cylinder length, cone length and inlet size by means of a computer model which we recently proposed. In this model, mixture multiphase model is used to describe the flow of the dense medium (comprising finely ground magnetite contaminated with non-magnetic material in water) and the air core, where the turbulence is described by the well-established Reynolds Stress Model. The stochastic Lagrangian Particle Tracking method is used to simulate the flow of coal particles. It is found that the spigot size is very sensitive to the performance. The operational head and medium split reporting to overflow, decrease dramatically as the spigot diameter increases. The density differential decreases rapidly, and then passes through a minimum and increases slowly. The long body including cylinder and cone is helpful to particle separation, particularly for fine and heavy particles. The inlet size plays a remarkable role on the performance on DMCs. The operational head, the density differential and the medium split increase dramatically as the inlet size decreases. Both the upward flow and the downward flow become very strong in the DMC with a small inlet when medium feed rate is constant, which results in a very low Ep. © 2010 Elsevier Ltd. All rights reserved. Source


Wang B.,University of New South Wales | Chu K.W.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
AIP Conference Proceedings | Year: 2010

A mathematical model is proposed to describe the multiphase flow in a 1000 mm industrial dense medium cyclone (DMC). In this model, a Mixture Multiphase model is employed to describe the flow of the dense medium (comprising finely ground magnetite contaminated with non-magnetic material in water) and the air core, where the turbulence is described by the well established Reynolds Stress Model. The stochastic Lagrangian Particle Tracking model is used to simulate the flow of coal particles. The proposed approach is qualitatively validated using literature and industrial data and then used to study the effect of the vortex finder configuration including the vortex finder length and diameter. The results show that the operational head, density differential and the medium split reporting to overflow increase to a maximum and then decrease as the vortex finder length increases. Because of the effect of the short circuit flow, the vortex finder in DMC cannot be too short or too long. As the vortex finder diameter increases, the operating head decreases and the density differential and the medium split increases dramatically. A high medium tangential velocity distribution is found in the DMC with a thin vortex finder, which results in a high pressure gradient force on coal particles and reduced separating efficiencies. © 2010 American Institute of Physics. Source

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