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Chen J.,University of New South Wales | Chen J.,Monash University | Chu K.,University of New South Wales | Chu K.,Monash University | And 6 more authors.
Minerals Engineering | Year: 2015

Dense medium cyclone (DMC) is a high-tonnage device that is widely used to upgrade run-of-mine coal in the 0.5-50mm size range. It is known that the performance of a DMC depends on the coal particle size distribution but quantitative relationships have not been established yet. In this work, the effect of the particle size distribution in a DMC is studied in detail using the combined Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). In particular, Johnson's SB function, which is capable of representing a wide range of size distributions, is employed to describe the particle size distribution of coal. The function has two parameters, i.e., particle median size d0.5 and distribution parameter σj, for a given size range. It is found that for a constant σj, the operational head and medium differential decrease dramatically, and the separation efficiency deteriorates rapidly when d0.5 increases from 6 to 40mm. For a constant d0.5, the DMC performance is sensitive to σj, particularly when d0.5 and σj are small. Both the medium differential and split decrease at first and then almost remain constant as σj increases from 0.4 to 1.0, and the separation performance follows the similar trend as well. The simulation results are also analysed in terms of medium and particle flow patterns, particle-fluid, particle-particle and particle-wall interaction forces to elucidate the underlying mechanism. For example, the decrease of pressure gradient force and viscous drag force represents the loss of swirling energy and then contributes to the drop of operational pressure and worse separation efficiency. The results should be useful to better design and control DMC operations, particularly for various coal types with different particle size distributions. © 2015.


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.


Ghodrat M.,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

Hydrocyclones generally follow a conventional design and may have some limitations on separation performance. This paper presents a numerical study of hydrocyclones with different conical configurations by a recently developed computational fluid dynamics method. The feed solids concentration considered is up to 30% (by volume), which is well beyond the range reported before. The numerical results show that the cyclone performance is sensitive to both the length and shape of the conical section, as well as the feed solids concentration. A longer conical section length leads to decreased inlet pressure drop, cut size d50, and Ecart probable Ep, and at the same time, an increased water split (thus larger by-pass effect). When conical shape varies from the concave to convex styles gradually, a compromised optimum performance is observed for the cyclone with a convex cone, resulting in a minimum Ep and relatively small inlet pressure drop and water split. Almost all these effects are pronounced with increasing feed solids concentration. Based on the numerical experiments, a new hydrocyclone featured with a long convex cone is proposed. It can improve the performance of the conventional cyclone at all the feed solids concentrations considered. © 2013 Elsevier Ltd. All rights reserved.


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.


Ghodrat M.,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

This paper presents a numerical study of the multiphase flow and performance of hydrocyclone by means of two-fluid model, with special reference to the effects of diameter, length and shape of vortex finder at a wide range of feed solids concentrations. The considered shapes include the conventional cylindrical style and the new conical and inverse conical styles. The simulation results are analysed with respect to cyclone flow and performance in term of cut size d50, water split, Ecart probable Ep and inlet pressure drop. It is shown that when vortex finder diameter or shape varies, a compromised optimum performance can be identified, resulting in relatively small inlet pressure drop, Ep, and water split. Both d50 and Ep are more sensitive to feed solids concentration than inlet pressure drop and water split. Overall, the effect of vortex finder length on the separation efficiency of particles is much less significant than diameter and shape, which shows opposite trends at low and high feed solids concentrations. All these results can be well explained using the predicted tangential and axial velocities and solid volume fraction. © 2014 Elsevier Ltd. All rights reserved.


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.


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.


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.


Ghodrat M.,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.
Industrial and Engineering Chemistry Research | Year: 2013

This paper presents a numerical study of multiphase flow in hydrocyclones with different configurations of cyclone size and spigot diameter. This is done by a recently developed mixture multiphase flow model. In the model, the strong swirling flow of the cyclone is modeled using the Reynolds stress model. The interface between liquid and air core and the particle flow are both modeled using the so-called mixture model. The solid properties are described by the kinetic theory. The applicability of the proposed model has been verified by the good agreement between the measured and predicted results in a previous study. It is here used to study the effects of cyclone size and spigot diameter when feed solids concentration is up to 30% (by volume), which is well beyond the range reported before. The flow features predicted are examined in terms of the flow field, pressure drop, and amount of water split to underflow, separation efficiency and underflow discharge type. The simulation results show that the multiphase flow in a hydrocyclone varies with cyclone size or spigot diameter, leading to a different performance. A smaller cyclone results in an increased cut size, a decreased pressure drop and a sharper separation, and, at the same time, an increased water split (thus worse bypass effect) and a more possibly unstable operation associated with rope discharge, particularly at relatively high feed solids concentrations. Both large and small spigot diameters may lead to poor separation performance. Accordingly, an optimum spigot diameter can be identified depending on feed solids concentration. It is also shown that for all the considered hydrocyclones, a better separation performance and a smoother running state can be achieved by the operation at a lower feed solid concentration. © 2013 American Chemical Society.


Chen J.,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: 2013

Dense medium cyclone (DMC) is widely used to upgrade the run-of-mine coal in the coal industry. It is known that the amount of near gravity material (NGM) fed into a DMC is an important parameter since it may cause problems such as vortex finder/spigot overloading, surging phenomenon, and system instability. Until now, the underlying mechanism of this phenomenon is not well understood. Here, this phenomenon is studied numerically using a previously developed method of combined computational fluid dynamics and discrete element method (CFD-DEM), facilitated by a "parcel-particle" model to account for fine particles. The simulated results are analyzed for fundamental understanding, in terms of medium and coal flow patterns, particle-fluid, particle-particle and particle-wall interaction forces. It is found that the amount of NGM has a significant effect on the stability inside a DMC. When there are excessive NGM fed into a DMC, the solid concentration below the vortex finder increases drastically, resulting in high local tangential particle-fluid and particleparticle interaction forces. Correspondingly, the pressure drop is high there, and so is the pressure gradient force. This unstable flow structure has been identified as a cause of the vortex finder overloading phenomenon in the DMC operation. © 2013 AIP Publishing LLC.

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