The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform

Malcolm Powell - One of the best experts on this subject based on the ideXlab platform.

  • Estimating energy in grinding using DEM modelling
    Minerals Engineering, 2015
    Co-Authors: Nirmal Weerasekara, Lian X. Liu, Malcolm Powell
    Abstract:

    The latest state of the art on Discrete Element Method (DEM) and the increased computational power are capable of incorporating and resolving complex physics in comminution devices such as tumbling Mills. A full 3D simulation providing a comprehensive prediction of bulk particle dynamics in a grinding Mill is now possible using the latest DEM software tools. This paper explores the breakage environment in Mills using DEM techniques, and how these techniques may be expanded to provide more useful data for Mill and comminution device modelling. A campaign of DEM simulations were performed by varying the Mill size and Charge particle size distribution to explore and understand the breakage environment in Mills using DEM techniques. Analysis of each Mill was conducted through consideration of the total energy dissipation and the nature of the collision environment that leads to comminution. The DEM simulations show that the Mill Charge particle size distribution has a strong influence on the Mill input power and on the way the energy is distributed across the Charge. The smaller particles experience higher energies while the larger experience less, but this variation is strongly dependent on the Mill size. The results also showed that the average particle collision energy increases with increasing Mill size, whereas its distribution over particle size is strongly influenced by the Mill content particle size distribution. The simulations also captured the energy distribution within different regions of the tumbling Charge, with the toe impact region having higher impact energies and the bulk shear region having higher tangential energies. Regardless of the Mill size most of the energy is consumed by the particles in the mid-size range, which has the highest percentage mass of the total Charge distribution.

  • Experimental observations of lifter parameters and Mill operation on power draw and liner impact loading
    Minerals Engineering, 2010
    Co-Authors: M. Rezaeizadeh, Majid Fooladi, Malcolm Powell, Shahla Mansouri
    Abstract:

    In mineral processing the Mill power plays a major role in the economics of the process and is a critical design criterion. The Mill power is influenced by a range of parameters such as: Charge and slurry filling, number and geometry of lifters, and Mill speed. Deriving the optimum conditions of these parameters should lead to efficient Mill operation. Additionally, the optimum utilization of the impact loads that are affected by Charge and slurry filling, number of lifters, geometry of lifter and Mill speed should result in increased Milling efficiency. In this work the influence of these operating parameters were investigated using a laboratory experimental Mill. It is found that the power, are affected by number of lifters, lifter height, Mill Charge and Mill speed. Overall the results showed that increasing the Mill velocity, number of lifters, and height of lifter and significantly decreasing the Mill Charge filling results in a higher impact value and impact frequency that may also increase overall efficiency. A simple linear regression relationship has been demonstrated for Mill power as a function of lifter spacing (S/H) and Mill speed. These parameters give an indication of the possible optimum Mill operating conditions in an idealised condition.

  • An experimental investigation of the effects of operating parameters on the wear of lifters in tumbling Mills
    Minerals Engineering, 2010
    Co-Authors: M. Rezaeizadeh, Majid Fooladi, Malcolm Powell, Nirmal Weerasekara
    Abstract:

    Lifters are usually used with Mill liners to extend their life and to enhance the grinding and crushing efficiency. Although the lifters are durable wear parts but they will gradually worn and consequently their dimensions change during the course of operation. These changes in dimensions have a significant influence on the overall economic performance of the Mills. Therefore, it is useful to know the relationship between the Mill operation and the lifter profile, and the influence of lifter wear on the change in lifter profile. In this work, a laboratory Mill which is capable of producing the required impact and abrasion grinding was operated both wet and dry. Many factors were varied such as: velocity, Charge, ore size and different material for the lifters. Also the wear rate on the top and face of lifters are compared in the different conditions. It is found that the Mill Charge and the Mill speed significantly affect the wear rate. Also, the results showed how size distribution affects the wear rate. The results can be interpreted in terms of the wear process in industrial scale Mills over different operating conditions. The experimental results provide the possibility of including the lifter wear in optimising Mill performance.

  • Contributions to the experimental validation of the discrete element method applied to tumbling Mills
    Engineering Computations, 2004
    Co-Authors: Andrew Mcbride, Malcolm Powell, Indresan Govender, T.j. Cloete
    Abstract:

    Accurate 3D experimental particle trajectory data, acquired from a laboratory tumbling Mill using bi‐planar X‐ray filming, are used to validate the discrete element method (DEM). Novel numerical characterisation techniques are presented that provide a basis for comparing the experimental and simulated Charge behaviour. These techniques are based on fundamental conservation principles, and provide robust, new interpretations of Charge behaviour that are free of operator bias. Two‐ and three‐dimensional DEM simulations of the experimental tumbling Mill are performed, and the relative merits of each discussed. The results indicate that in its current form DEM can simulate some of the salient features of the tumbling Mill Charge, however, comparison with the experiment indicate that the technique requires refinement to adequately simulate all aspects of the system.

Johnny Tshibangu Kalala - One of the best experts on this subject based on the ideXlab platform.

  • Discrete element method modelling of forces and wear on Mill lifters in dry ball mining
    2009
    Co-Authors: Johnny Tshibangu Kalala
    Abstract:

    Since the beginning of the last century, many studies have been performed in order to improve our understanding on the Milling process. Recently, Mishra and Rajamani (1992) applied the Discrete Element Method (DEM) to solve the Milling problem. Since then, this method gained considerable success due to its ability to predict load motion and power draw by tumbling Mills as affected by operating conditions. The application of this method at an industrial stage requires a more rigorous validation in order to produce realistic output. Lifter profiles play a key role in the performance of tumbling Mills since they influence the motion of Mill Charge. Since lifters change profiles during their useful life due to wear, the performance of tumbling Mills will correspondingly vary as a function of time. There is therefore a need to predict forces and wear on Mill lifters in order not only to chose or design an initial lifter profile which optimizes tumbling Mills performance over the lifters’ useful life but also to evaluate lifter replacement time and type and also modifications which can be performed on lifters and/or operating Mill conditions in order to extend the lifters’ useful life. Despite the importance related to this subject, few works has been done in this field. In this thesis, we firstly assess the ability of the Discrete Element Method to model the tangential and normal forces exerted by the Mill Charge on lifters. Data from an experimental two-dimensional Mill designed in order to record the normal and tangential forces exerted on an instrumented lifter were available. The measured results obtained at different speeds and percentages of filling have been compared to the Discrete Element Method simulated results in the same conditions. A good agreement has been found between the experimental and the simulated results in terms of toe, shoulder positions and amplitude of forces.

  • Discrete element method (DEM) modelling of evolving Mill liner profiles due to wear. Part I: DEM validation
    Minerals Engineering, 2005
    Co-Authors: Johnny Tshibangu Kalala, Murray M. Bwalya, Michael H. Moys
    Abstract:

    Since the early 1990s the discrete element method (DEM) gained considerable success in its ability to predict the power draw and the load behaviour in Mills as affected by operating conditions. The DEM can also be used to design Milling equipment and predict the breakage of particles. A detailed validation of this method is required in order to produce accurate results. In this paper, we assess the ability of the DEM to predict forces exerted by the Mill Charge on liners. Data obtained on an experimental two-dimensional Mill designed in order to record the normal and tangential forces exerted on an instrumented lifter bar was available. The measured results are compared to the DEM simulated results. Good agreement has been found in terms of amplitude of forces and positions of shoulder and toe at low speed.

M. Anibal Valenzuela - One of the best experts on this subject based on the ideXlab platform.

  • Robust Estimation and Protection of Locked Charge in Grinding Mills
    IEEE Transactions on Industry Applications, 2017
    Co-Authors: Pablo Castro Palavicino, M. Anibal Valenzuela
    Abstract:

    The most critical equipment in mining concentrator plants is the grinding Mill. One very important Charge condition that can produce a catastrophic failure during the starting of grinding Mills is the compacting of the load inside the Mill, especially after long downtimes. This condition is usually named frozen Charge. The load remains locked to the Mill shell and after a half-turn drops damaging the Mill body and bearings. Therefore, the Mill protection system must give an early detection of this condition and abort the start before the compacted Mill Charge falls hitting the bottom of the Mill shell. This paper presents the development of a robust estimation and protection algorithm of locked Charge condition based on drive and process signals. The proposed algorithm includes a locked Charge model that permits to define torque, root mean square (rms) current, and power thresholds for the existing starting Charge conditions, and compares the locked Charge signals to the online estimation of drive variables. This comparison is used to detect the beginning of Charge cascading and the threshold values are used to command the termination of the start-up. Proposed algorithm was evaluated using field records of an 8.2 MW semiautogenous Mill drive confirming its ability to handle startups with different Charge conditions.

  • IAS - Robust estimation and protection of locked Charge in grinding Mills
    2015 IEEE Industry Applications Society Annual Meeting, 2015
    Co-Authors: P. Pablo Castro, M. Anibal Valenzuela
    Abstract:

    One very important Charge condition that can produce a catastrophic failure during the starting of grinding Mills is the compacting of the load inside the Mill, especially after long downtimes. This condition is usually named frozen load and the load remains locked to the Mill shell and after a half turn drops damaging the Mill body and bearings. Therefore, the Mill protection system must give an early detection of this condition and aborts the start before the compacted Mill Charge falls hitting the bottom of the Mill shell. Actual protection schemes against locked load use fix torque or current trip values and do not consider the effect of the specific Charge inside the Mill on each startup. This paper presents the development of a robust estimation and protection algorithm of locked load condition based on drive and process signals. The proposed algorithm includes a locked load model used to define torque, rms current and power thresholds for the existing starting Charge conditions, and compares the locked load signals to the online estimation of drive variables. This comparison is used to detect the beginning of Charge cascading, and the threshold values are used to command the starting abortion. Main advantage of the proposed protection algorithm is that considers the effect of the Mill Charge and Charge position, and therefore gives an accurate and safe detection of locked load for any Charge condition during the Mill starting. Proposed algorithm was evaluated using field records of an 8.2 MW semi-autogenous (SAG) Mill drive confirming its ability to handle startups with different Charge conditions.

Paul W. Cleary - One of the best experts on this subject based on the ideXlab platform.

  • Prediction of slurry transport in SAG Mills using SPH fluid flow in a dynamic DEM based porous media
    Minerals Engineering, 2006
    Co-Authors: Paul W. Cleary, Matt Sinnott, Rob Morrison
    Abstract:

    DEM modelling of the motion of coarse fractions of the Charge inside SAG Mills has now been well established for more than a decade. In these models the effect of slurry has broadly been ignored due to its complexity. Smoothed particle hydrodynamics (SPH) provides a particle based method for modelling complex free surface fluid flows and is well suited to modelling fluid flow in Mills. Previous modelling has demonstrated the powerful ability of SPH to capture dynamic fluid flow effects such as lifters crashing into slurry pools, fluid draining from lifters, flow through grates and pulp lifter disCharge. However, all these examples were limited by the ability to model only the slurry in the Mill without the Charge. In this paper, we represent the Charge as a dynamic porous media through which the SPH fluid is then able to flow. The porous media properties (specifically the spatial distribution of porosity and velocity) are predicted by time averaging the Mill Charge predicted using a large scale DEM model. This allows prediction of transient and steady state slurry distributions in the Mill and allows its variation with operating parameters, slurry viscosity and slurry volume, to be explored. © 2006.

  • Centrifugal Mill Charge motion and power draw: comparison of DEM predictions with experiment
    International Journal of Mineral Processing, 2000
    Co-Authors: Paul W. Cleary, David I. Hoyer
    Abstract:

    The ongoing need to improve the efficiency and performance of grinding Mills requires more detailed understanding of the dynamics of the Charge behaviour. Discrete Element Methods (DEM) for simulating the flow of granular materials are increasingly being used to model such Mills in order to extend this understanding. An essential part of this process is the validation of predictions from such models. Here we present detailed comparisons of the Charge behaviour in a centrifugal Mill predicted by DEM with high speed photographs obtained in an experimental Mill. Excellent correspondence is generally obtained both for the Charge motion and the power predictions.

Indresan Govender - One of the best experts on this subject based on the ideXlab platform.

  • Circulation rate modelling of Mill Charge using position emission particle tracking
    Minerals Engineering, 2011
    Co-Authors: D.v.v. Kallon, Indresan Govender, Aubrey Mainza
    Abstract:

    Abstract A model linking the circulation rate of Charge particles with physical Mill parameters (load fraction, shoulder angle and friction) has been developed and tested using experimental data derived from positron emission particle tracking (PEPT). The model parameters are obtained directly from the in situ flow field of the PEPT tracer particles. The model formulation, methodology for model parameter correlations and comparison of circulation rate model with direct measurement from PEPT forms the focus of this paper.

  • Characterising porosity of multi-component mixtures in rotary Mills
    Minerals Engineering, 2011
    Co-Authors: K. Sichalwe, Indresan Govender, Aubrey Mainza
    Abstract:

    Abstract The measurement of porosity presents a significant challenge in modelling of slurry transport in rotary Mills. This is due to the aggressive environment within rotary Mills. In this paper, a method of measuring the porosity of Mill Charge, using the positron emission particle tracking (PEPT) technique, is presented. In this work, multiple particles are tracked, in turn. The packing density of each size component is proportional to the residence time distribution of its representative tracer particle, based on the ergodicity of the system. The Charge porosity is a linear combination of the packing densities of individual components. The porosity is modelled as a function of Mill geometric and operating parameters—Mill speed and filling fraction. The results show correlations between porosity distribution and operating parameters.

  • Contributions to the experimental validation of the discrete element method applied to tumbling Mills
    Engineering Computations, 2004
    Co-Authors: Andrew Mcbride, Malcolm Powell, Indresan Govender, T.j. Cloete
    Abstract:

    Accurate 3D experimental particle trajectory data, acquired from a laboratory tumbling Mill using bi‐planar X‐ray filming, are used to validate the discrete element method (DEM). Novel numerical characterisation techniques are presented that provide a basis for comparing the experimental and simulated Charge behaviour. These techniques are based on fundamental conservation principles, and provide robust, new interpretations of Charge behaviour that are free of operator bias. Two‐ and three‐dimensional DEM simulations of the experimental tumbling Mill are performed, and the relative merits of each discussed. The results indicate that in its current form DEM can simulate some of the salient features of the tumbling Mill Charge, however, comparison with the experiment indicate that the technique requires refinement to adequately simulate all aspects of the system.