Dense Medium Cyclone Research Articles

Separation of coal with a top size of up to 6 mm in a full-scale REFLUX™ Classifier

ABSTRACT A 2 m diameter REFLUX™ Classifier was tested on coal feeds up to 6 mm top size. Solids feed rate was varied from 50 to 160 t/h at suspension concentrations up to 37 wt.% solids. Performance was consistent, with product ashes below 10 wt.% for +1 mm particles and reject ashes usually exceeding 70 wt.%. The density cut point could be freely varied and decreased with particle size to the power −0.114. Ep values less than 0.10 were obtained on the composite +0.5 mm material. Ep varied with particle size to the power −0.963. Hence, beneficiation performance for −4.0 + 0.50 mm material approached that of large dense medium cyclones (DMCs). Hence, REFLUX™ Classifiers could be used to increase the capacity of existing plants with minimal capital expenditure. The primary screen aperture size could be raised to around 4 mm, which should significantly increase screen capacity. The +4.0 mm fraction could be sent to the existing DMC circuit, which with a lower fines loading would have increased capacity and medium recovery. The −4.0 mm fraction could be sent to a REFLUX™ Classifier and if required its overflow could then be sent to a flotation circuit.

Particle size-included partition curve model of dense medium cyclones

ABSTRACT The partition curve of dense medium cyclones (DMCs) has been extensively investigated. Most of the existing models are merely used to simulate the density distribution at the same size fraction. However, when the particle size varies, the models are no longer applicable to the new separation. To solve this problem, first, the effects of coal slime size in the suspension and feed coal size on the separation performance of DMCs were discussed. We found that with an increase in the coal slime size, the separation deteriorated and the cut density increased slightly, whereas an opposite trend occurred in the case of feed coal size. Then, a new partition curve model with a compound input of the density and particle size for DMC was presented. The model took the form , where x indicates density, y indicates particle size and a, b, c m, n are constants. The results of comparison between our experiment and other plant data demonstrated the effectiveness of the model as all the predicted partition curves approximated to the actual ones. Further, the model could be applied to simulate the separation performance of DMCs with different coal slime sizes in the suspension and feed coal size simultaneously. The model can be used to describe the complex separation behaviors of DMCs with varying particle size.

Effect of coaxial electromagnetic field on separation density of dense-medium cyclone

To decrease the separation density of a dense-medium cyclone by using an online control method, a coaxial coil was placed outside the lower cone position of the dense-medium cyclone, and a separation test of coal with a size of 0–3 mm was performed in a coaxial magnetic field. Subsequently, the density composition of the separation products was determined through a float-and-sink analysis. Further, the magnetic force of the dense-medium particles in a magnetic field generated by the coil was analyzed through the Ansoft software. The results showed that dense-medium particles were attracted into the underflow by the downward axial magnetic field force. Therefore, the separation density of the dense-medium cyclone can be decreased in the magnetic field created by the coil with large passing currents (i.e. 12.5–20 A). Hence, this study may provide a new method to control the separation density of dense-medium cyclones, which has a considerable significance to improve the automation of coal preparation plants.

Statistical studies on high ash Indian coal crushed to (−3 mm) using 76 mm dense medium cyclone

ABSTRACT The present paper deals with the results obtained for a 76 mm diameter Dense Medium Cyclone treating high ash Indian coals possessing difficult washing characteristics, coal crushed to −3 mm for improved liberation and better end utilization. The key influential parameters like the diameter of outlets and feed medium density were considered for analyzing their influences on yield and quality of the product. During this study, the influence of other variables such as magnetite to coal ratio, cyclone dimensions, feed pressure, medium properties, and feed rates were kept constant. The results of the test obtained thereof were analyzed for estimation of yield and ash content. In this paper, a comparative study of the parameter using an artificial neural network and the approach of response surface methodology (RSM) based on Box Behnken Design has been used. From both, the methodology separate equation has been developed for the prediction of quality and quantity of washed coal with the level of variables studied. The result shows that the artificial neural network implemented is able to provide a higher rate of accuracy than that of RSM. The yield % values predicted through ANN shows good agreement with the achieved experimental values (R2 0.9970) and demonstrated an improved correlation than RSM (R2 0.9831). Similar findings were observed for ash content (R2 0.9992) using ANN and found to be higher than RSM (R2 0.9698). Sensitivity analysis performed using the ANN model indicated that the Feed Medium Density is the most significant followed by the Vortex Finder Diameter and Spigot Diameter. A similar finding was also observed from the RSM-BBD for both the yield and ash content.

Application of a biconical dense medium cyclone to pre-treat a low-grade Pb-Zn sulfide ore

Application of a biconical dense medium cyclone to pre-treat a low-grade Pb-Zn sulfide ore

Preliminary optimisation study on integrating mining with gravity separation

ABSTRACTOptimisation studies on integrating different procedures in mining and mineral processing have an increasing popularity in recent years, and most of them focus on the mine-mill or mine-flotation integration. However, few optimisation studies on integrating mining with gravity separation are found. The gravity separation plays a vital role in coal preparation, which also makes the related integration study necessary. In this work, an optimisation study on integrating mining with gravity separation is first carried out, which contributes to proposing the optimal cut point (the density at which 50% of the feed report to underflow) for gravity separation and the coal seam mass ratio for mining. Specifically, a simplified optimisation model includes separations in dense medium cyclones, dense medium shallow grooves, and spiral separators is developed. Then the Differential Evolution algorithm is employed to obtain the solution that has the maximum economic profit. Finally, the organic efficiency is utilised to evaluate this optimisation. The validation results indicate that the developed optimisation model and the adopted algorithm are applicable. Even though it is a simplified model, it is supposed to provide a preliminary optimisation scheme for integrating mining with gravity separation.

A new partition curve model of dense-medium cyclone based on process parameters

ABSTRACT The partition curve of gravity separation has been widely investigated, but few studies have established the models directly based on the operating conditions. A new model was proposed to predict the distribution rates of anthracite in a coal preparation plant with a compound input of density and process parameters. These included the density of dense-medium suspension d, the content of magnetic substance c, the inlet pressure of dense-medium suspension p and the coal feed rate r. The model took the following form: , where , indicate functions of the separation density δp and probable error Ep , respectively. The effects of each process parameter on the model were discussed, and their behaviors were in accordance with the knowledge of the dense-medium cyclone. It was proved that the proposed model performed better around the cut point of the curve compared with the previous method by means of solving the coefficients of partition curve equations. It was also more instructional and easier to use for field operators as it met their operating habits. It provided a foundation of real-time predictive control for dense-medium cyclones in coal preparation plants.

The beneficiation of tailing of coal preparation plant by heavy-medium cyclone

Dense-medium cyclones have been used for beneficiation of fine particles of coal. In this study, the usability of cyclones in the beneficiation of tailings of a coal preparation plant was investigated. For this purpose, separation tests were conducted using spiral concentrator and heavy medium cyclones with the specific weight of medium 1.3–1.8 (g/cm3) on different grading fractions of tailing in an industrial scale (the weight of tail sample was five tons). Spiral concentrator was utilized to beneficiate particles smaller than 1 mm. In order to evaluate the efficiency of cyclones, sink and float experiments using a specific weight of 1.3, 1.5, 1.7 and 1.9 g/cm3, were conducted on a pilot scale. Based on the obtained results, the recovery of floated materials in cyclones with the specific weight of 1.40, 1.47 and 1.55 g/cm3 are 17.75%, 33.80%, and 50%, respectively. Also, the cut point (ρ50), which is the relative density at which particles report equally to the both products are 1.40, 1.67 and 1.86 g/cm3. The probable errors of separation for defined specific weights for cyclones are 0.080, 0.085 and 0.030, respectively. Also, the coefficients of variation was calculated to be 0.20, 0.12 and 0.03. Finally, it could be said that the performance of a cyclone with a heavy medium of 1.40 g/cm3 specific weight is desirable compared with other specific weights.

Numerical simulation of near-gravity coal particle behavior in a dense medium cyclone using a mixture model coupled with a discrete phase model

ABSTRACT In general, the washing of coal is greatly influenced by the amount of near-gravity material (NGM) present at the desired cut density. It is observed that the presence of a high percentage of NGM coal results in significant misplacement of particles to wrong products and reduces the separation efficiency of dense medium cyclone (DMC). In this work, an attempt is made to study the behavior of different sizes of NGM coal particles at three feed relative densities inside 350 mm DMC using a discrete phase model (DPM) superimposed on the magnetite medium segregation simulated by modified mixture model. The Reynolds stress model (RSM) is used to resolve turbulence. The DPM is adopted to track different sizes and densities of coal particles, and then a partition curve is constructed to calculate the Ecart probable (Ep) error, percent misplacement, and imperfection. The results show that the lighter and heavier density coal particles away from the separation cut density exhibit very short residence times. Fine-sized coal particles close to the cut density have a significant misplacement compared to the coarse-sized particles having the same density. It is also observed that NGM coal particles show very long residence times irrespective of size.

A study of dense-medium cyclone inner-wall abrasion based on ultrasonic phased array technology

Directing at the problem that dense-medium cyclone is abraded by materials while conventional detection method can’t make real-time and highly efficient detection of defects, this paper introduced working process and imaging principle of ultrasonic phased array technology in details. And then through experimental research of dense-medium cyclone model, it drew the conclusion that ultrasonic phased array technology could conduct real-time imaging display of dense-medium cyclone inner-wall abrasion defects and the error was within 8%.

Comparative Study of Separation Performance of a Spiral and Dense-medium Cyclone on Cleaning Coal

ABSTRACT Spiral separators and dense-medium cyclones (DMCs) are widely used for separation of −1 + 0.125 mm fine coal. In this study, testing was carried out using −1 + 0.125 mm fine coal with low near density material to produce a concentrate, using both a spiral and DMC. Clean coal with 8.31% ash content was obtained with the spiral at 37.39% yield, 47.76% combustible recovery and 0.150 Ep value. For the DMC, the combustible recovery of clean coal at the ash of 8.31% ash was improved to 80.84% at 62.98% yield, and 0.118 Ep value. The advantage of the DMC is further proved by analysis using Fuerstenau upgrading curves.

Application of density tracers in a dense medium circuit: A case study

Density tracers are often used to identify the separation efficiency of mineral processing equipment and the overall plant performance in several mineral and coal applications. In a 700 t/h coal washing plant in Turkey, comprising dense medium drums and dense medium cyclones, a plant audit was conducted using density tracers. In this study, the data obtained from the dense medium cyclone and drum circuits during the plant survey are presented. Besides the detailed separation behavior of the particles in the drums and cyclones, some variables affecting the performance such as particle retention, separation cut-point and separation efficiency are also discussed. Based on the efficiency data from the plant audit, the mass balance of the plant was obtained using an in-house-developed coal washing plant simulator (LAVE) by using the size-by-size washability data of the run-of-mine (ROM) coal and the plant control room data.

Separation of 0.75–0.125 mm Fine Coal Using the Cylindrical Section of a 710/500 mm Three-Product Dense Medium Cyclone

ABSTRACTDense medium cyclone is effective in beneficiation of fine coal with great separation precision. Small-diameter cyclones (usually 150 mm to 350 mm) are preferred in industrial applications. But the handling capacity of a small cyclone is low, which brings about the problems of maintain and operation. The separation efficiency of large-diameter cyclones with greater handling capability in fine coal treatment is questionable. In this study, the cylindrical section of a 710/500 mm three-product cyclone was adopted to treat 0.75–0.125 mm fine coal, where the cylinder-cone cyclone was a surge section. Influence of inlet pressure and feed rate were studied in an industrial environment. According to the results, the separation efficiency was sharp at relatively low feed pressures (110 KPa to 160 KPa). The separation effect increased with the feed rate. The favorable Ecart probable (Ep) value of 0.054 was obtained at an inlet pressure of 120 KPa and a feed rate of 42 t/h. Results of the studies showed that large-diameter cyclones will be applicable for fine coal treatment. These results will be significant for fine coal with a high content of near-density material.

A Dual-Loop Control System for Dense Medium Coal Washing Processes With Sampled and Delayed Measurements

A dual closed-loop control system is developed for a dense medium coal washing process. The controller is designed to improve the separation efficiency and energy efficiency of the dense medium cyclone coal beneficiation process simultaneously making use of a model predictive control method and a pumped-storage system (PSS). In the dual-loop control, the outer loop is designed for medium density profile optimization and the inner loop is used for actuator control of the medium supplying circuit, considering the interplay of the energy efficiency and separation efficiency. Mathematical models of the PSS and the magnetite recycle process of the dense medium circuit are developed and employed in the design of the advanced controller. The effectiveness of the designed control system is demonstrated by simulations based on operational data from a South African coal beneficiation plant.

The dense medium cyclone – past, present and future

Since the dense medium cyclone (DMC) was first patented in the 1940s it has become the process of choice in coal preparation, and is also widely used for upgrading iron ore and in the pre-concentration of diamonds and metalliferous and industrial minerals. It is in every sense a mature technology. This paper summarises the history of the process, considers its current status in mineral and coal processing, and suggests ways in which the process might evolve. Aspects reviewed include the process principles, process models, the importance of medium behaviour, particle size limitations, process analysis, instrumentation and control, and increases in scale. Particular attention is given to the potential for the use of larger cyclones at lower heads in mineral separations, as practiced in the coal industry. Using operating examples and published modelling results, the paper makes the case that these conditions will work in minerals too, and should be adopted. This will significantly improve the economics of DMC mineral separations at a time when pre-concentration is becoming more important for upgrading lower grade ores.

Understand solids loading effects in a dense medium cyclone: Effect of particle size by a CFD-DEM method

Industrial cyclones, such as gas, hydro and dense medium, are widely used in chemical, mineral and process industries to separate particles from fluids or classify particles by size, density or other solid properties. It is well known that the loading of particles can significantly affect fluid flow in such cyclones but the specific effect can be confusing due to a limited fundamental understanding of the working mechanisms involved. In this work, the problem is partially tackled by analysing the influence of particles of different size on the medium flow in a dense medium cyclone (DMC) by using a combined approach of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) (CFD-DEM). In the CFD-DEM model, CFD is used to model the motion of slurry medium by numerically solving the local-averaged Navier-Stokes equations at a computational cell scale, facilitated by the Volume of Fluid (VOF) and Mixture multiphase models. DEM is then used to model the motion of discrete particles by applying Newton's laws of motion, facilitated by a coarse-grained (CG) method to model small coal particles. It is found that both the particle and medium flows are sensitive to the particle size. The most notable finding is that spatial distributions of solid flow patterns form due to particles of different size have different trajectories in the cyclone. These lead to significant different distribution of volumetric particle-fluid interaction forces which cause different effects on the fluid flow. The findings are useful for developing a better understanding the working mechanisms of solids loading effects in DMCs and also in other similar swirling multiphase flow systems.

Structure and Optimization of a Two-Stage Equal-Density Dense Medium Cyclone

On the basis of the components of the raw feed, two basic conditions need be met to prepare super-low-ash coal: High-density components (+1.55 kg/L) need be preremoved, and the separation accuracy should not exceed 0.015. Two-stage equal-density dense medium cyclones were developed to improve the separation accuracy. The research was applied to commercial production in the Taixi coal preparation plant, where super-low-ash coal with Ad (ash content) < 2.00% was prepared with good economic benefits. The actual industrial production results showed that the two-stage equal-density separation is advantageous to the production of super-low-ash coal. The separation accuracy (Ecart probability) reached 0.015, and the failure-free operation time was more than 10000 h. As a result, the reliability and economic performance of industrial super-low-ash coal production are improved, which will further promote the development of coal-based materials.

Computational Fluid Dynamic study on the effect of near gravity material on dense medium cyclone treating coal using Discrete Phase Model and Algebraic Slip mixture multiphase model

In this paper, the effect of near gravity material at desired separation density during the coal washing is studied. It is believed that the Dense Medium Separation of coal particles in the presence of high percentage of near gravity material, results in a significant misplacement of coal particles to wrong products. However the performance of dense medium cyclone does not merely depend on the total amount of near gravity materials but also on their distribution as well as on their quality. This paper deals with numerical simulation of magnetite medium segregation and coal partitioning handled in a 350 mm dense medium cyclone. Volume of Fluid coupled with Reynolds Stress Model is used to resolve the two-phase air-core and turbulence. Algebraic Slip mixture multiphase model with the granular options are considered to predict magnetite medium segregation. Medium segregation results are validated against Gamma Ray Tomography measurements. Further, Discrete Phase Model is used to track the coal particles. Residence Time Distribution of different size and density coal particles are also estimated using Discrete Phase Model. Additionally, Algebraic Slip mixture model is also utilised to simulate magnetite and coal particle segregation at different near gravity material proportions. Discrepancies in the coal particle behaviour at different near gravity material content are explained using locus of zero vertical velocities, mixture density, coal volume fractions.

Beneficiation of oxide ores using dense medium cyclones. A simulation study

Beneficiation of oxide ores using dense medium cyclones. A simulation study

Systematic study of the effect of particle density distribution on the flow and performance of a dense medium cyclone

Dense medium cyclone (DMC) is widely used to upgrade run-of-mine coal in modern coal preparation plants. The flow within it is very complicated, with multi-phases involved including air, water, coal and magnetic/non-magnetic particles of different sizes, densities and other properties. In this work, the effect of coal particle density distribution, one of the most important variables and highly related to coal type, is systematically studied using a combined approach of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). In particular, the so called Johnson's SB function, which can describe a wide range of distributions, is employed to represent different particle density distributions. For a given density range, the function is characterized by two parameters: median particle density ρ0.5 and distribution parameter σj, with the latter describes the spread of the distribution. The effects of the two parameters on the flow and performance of a typical DMC are quantified. Moreover, their implication to practical operation, e.g. when the amount of near gravity material is high, is discussed. The results are also analysed in terms of the medium and particle flow fields, particle-fluid, particle-particle and particle-wall interaction forces to understand the fundamentals of the operation. The results obtained in this work should be useful to the design and control of DMC operations with different coal density distributions or coal types.