Size Reduction Operations Research Articles

Simulating large-diameter industrial ball mills from batch-grinding tests

Phenomenological models of ball milling are routinely used to optimize size reduction operations. A usual method adopted in the minerals industry relies on batch-grinding tests to calibrate models in a population balance model formulation describing the breakage behaviour and then scale-up the breakage parameters using an energy-based relationship. Despite the important advances and application of these methods, their application in describing grinding in large-diameter (>7.5 m) mills has not been widely demonstrated. The work demonstrates the calibration of industrial-scale ball mill model parameters from laboratory milling tests on Platinum Group Metals (PGM) and Itabirite iron ores. Minor fine-tunning of a single model parameter was required to simulate the large-diameter industrial mills, demonstrating the validity of the approach for ores as distinct as PGM and Itabirite iron ores. Estimation of the Arbiter Flow Number below 4.1 showed a regular slurry transport for all mills studied. This model can then be used in optimization of the ball mill performance.

Design of Multiband, Reconfigurable Coplanar Meander Antenna for WLAN Applications

This paper presents the implementation of Reconfigurable, Planar Meander Antenna operates at 2.45 GHz and 5.12 GHz for WLAN applications. In the proposed work the planar meander antenna is designed using FR4 substrate. In the meander antenna the varactor diodes are incorporated in the appropriate arm positions to achieve reconfigurability. In this, reconfigurability is accomplished using frequency tuning. Also, the principle of reconfigurability in meander antenna focuses size reduction and dual band operations. The meander structure is characterized for its operating frequency. A parametric study is done for finding the resonance in the appropriate arm positions of the meander antenna. The varactor diodes fixed meander antenna is tested using network analyzer. The comparison is made for the antenna designs of with and without varactor diodes for the establishment of reconfigurability. The effects of active components are ignored. The proposed antenna design is validated for its concurrence in both simulation and experimentation. The arm and the behavior of the frequency tuning is tested using the network analyzer. The reflection coefficient is -23.66dB and -18.41dB at 2.45 GHz and 5.1 GHz respectively. The overall size of the meander antenna is reduced by 76%. VSWR of the proposed antenna is 1.

Comparing modeling approaches in simulating a continuous pilot-scale wet vertical stirred mill using PBM-DEM-CFD

Vertical stirred mills have become increasingly popular in size reduction operations in the fine and ultrafine range, being normally used in industry in continuous operation. The present work describes the application of a mechanistic mill modeling approach based on the population balance (PBM) to describe the performance of a pilot-scale gravity-induced continuous stirred mill using 6 mm steel grinding media. At first, DEM and coupled DEM-CFD were compared in simulation of the mill, clearly demonstrating the significant effect of incorporating explicitly the fluid flow in describing the motion of the grinding media. The work then uses data from the stirred mill grinding calcite in multiple passes for model calibration and validation, besides breakage parameters from previous studies. It shows that the population balance-based mechanistic mill model predictions vary depending on the number of mixers-in-series used to predict product size, but that are capable of describing very well the milling operation considering the mill as three perfectly mixed grinding zones in series.

Prediction of Particle Size Distribution of Mill Products Using Artificial Neural Networks

High energy consumption in size reduction operations is one of the most significant issues concerning the sustainability of raw material beneficiation. Thus, process optimization should be done to reduce energy consumption. This study aimed to investigate the applicability of artificial neural networks (ANNs) to predict the particle size distributions (PSDs) of mill products. PSD is one of the key sources of information after milling since it significantly affects the subsequent beneficiation processes. Thus, precise PSD prediction can contribute to process optimization and energy consumption reduction by avoiding over-grinding. In this study, coal particles (−2 mm) were ground with a rod mill under different conditions, and their PSDs were measured. The variables studied included volume% (vol.%) of feed (coal particle), vol.% rod load, and grinding time. Our supervised ANN models were developed to predict PSDs and trained by experimental data sets. The trained models were verified with the other experimental data sets. The results showed that the PSDs predicted by ANN fitted very well with the experimental data after the training. Root mean squared error (RMSE) was calculated for each milling condition, with results between 0.165 and 0.965. Also, the developed ANN models can predict the PSDs of ground products under different milling conditions (i.e., vol.% feed, vol.% rod load, and grinding time). The results confirmed the applicability of ANNs to predict PSD and, thus the potential contribution to reducing energy consumption by optimizing the grinding conditions.

Reprocessing of magnesite beneficiation waste to recover mineral value and minimise environmental footprint

The current paper deals with the re-processing of mineralised mine waste from magnesite processing operations aiming at the recovery of the value. Two cases of mineralised waste were examined. First, waste derived from the removal of “fine” before hand-sorting, with particle size of -40 mm; this waste is usually stockpiled, comprises mostly of relatively coarse particles and is of relatively high-grade in magnesite. The separation methods applied were sorting, sink-float tests and magnetic separation. In general, the results from the application of physical separation methods were satisfactory. Commercial concentrates were obtained from sorting with MgCO3-grade ranging between 94 and 97% MgCO3 and yield about 46%; in case of mixing concentrate with middling, yield rises to 58-64% while grade slightly drops to 91-94%. Equally satisfactory were the results from sink-float separation at sp.gr. 2.88 (grade 95%, yield 45%) but questions arise from the small sp.gr. difference of magnesite and gangues. Finally, the less satisfactory results obtained from magnetic separation (grade around 80-85%, yield 33-65%) may be due to inefficient particles liberation and higher magnetic field is maybe required. Second, mineralised waste consisting of fine particles from size reduction operations were tested. These fines were processed with selective magnetic coating as well as co-agglomeration / magnetic separation techniques. In general, the results of physicochemical processing of fines were very encouraging both on single minerals and their artificial mixtures. In case of magnetic coating, the effect of pH, collector concentration and kerosene dose was studied first on single minerals. Optimum results were obtained for pH=9, dodecylamine solution 4.5x10-5 M and kerosene 2.5 L/t. Tests on artificial mineral mixtures at optimum conditions and magnetic separation at 0.8 A resulted in non-magnetic product with MgCO3-grade higher than 99%. The parameters examined in co-agglomeration / magnetic separation tests were the same as with magnetic coating. Best conditions for co-agglomeration on single minerals were pH=8, dodecylamine 2 kg/t, kerosene 4 L/t. Tests on mineral mixture reveals that the MgCO3-grade increases with dodecylamine but the yield drops.

Relationships between particle breakage characteristics and comminution response of fine iron ore concentrates

Production of iron ore pellets typically requires regrinding of the iron ore concentrates. Although these concentrates are produced following close control of chemical composition, substantial differences may exist in their response to the size reduction operations that are used prior to pellet formation in the pelletizing disc or drum. Establishing relationships between some intrinsic characteristics of these concentrates and their response to size reduction is, therefore, worthwhile. Single-particle breakage testing has long been used to characterize the material intrinsic response to comminution. However, application of traditional breakage tests to iron ore concentrates is not possible, given their fine sizes. The present work analyzes the application of recent single-particle testing methods that are suitable for particles in the –150 µm size range to characterize breakage of four iron ore concentrates from Brazil. The response of particles when assembled in beds is then analyzed in great detail through piston-and-die testing, as well as by comminution tests in a bench-scale ball mill and high-pressure grinding rolls. Relationships between the results in the various devices, which represent the different levels of particle interaction, have been analyzed in light of their energy utilization. Furthermore, implications of differences in particle characteristics on the differences observed in breakage response are also analysed.

Correlating common breakage modes with impact breakage and ball milling of cement clinker and chromite

Understanding the mechanisms of the breakage of ore particles is important to predict the particle size distribution in size reduction operations. This paper aims to show the presence of common breakage modes in impact breakage and ball milling of the cement clinker and chromite samples. For that purpose, narrow size fractions of the two samples were broken in a drop-weight tester or ball mill by changing the degree of applied energy. Then the resultant size distributions were evaluated to seek evidence for the common breakage modes. The results showed that increasing the breakage energy will produce a systematic change in the shapes of the size distributions, suggesting a sequential set of breakage modes. The breakage is initially due to tensile stresses at low breakage energies and compressive stresses at high breakage energies. Further studies should be done to assess if these breakage modes occur at size-reduction of different ores.

A Mathematical modeling and Simulation Analysis of Lattice reduction algorithms for large MIMO detections

Abstract – This paper analyses the performance of Multiple Input Multiple Output (MIMO) wireless communication system by combining it with an efficient algorithm Diagonal Reduction (DR). DR is a powerful tool to achieve more efficiently a high performance with less complexity. This paper proposes a DR algorithm in order to reduce its complexity named Greedy Diagonal Reduction (GDR) algorithm which gives reduced complexity with efficient performance at the receiver using the MATLAB communication tool box version 7.0 as a simulation tool. From the simulation results of various reduction algorithms it is observed that, DR can reduce the number of iterations using size reduction operations. Proposed DR algorithm gives identical Bit Error Rate (BER) performance with LLL algorithms when applied to Successive Interference cancellation (SIC) decoding. Greedy DR reduces the computational complexity in Multiple Input Multiple Output systems by improving the efficiency in terms of size reduction operations. Sphere Decoding (SD) technique gives better BER performance on comparing with Successive Interference cancellation decoding technique.

Treatment of Leather Effluents and Waste Using Fungi

Leather industry plays an important role in the economic development of the country and the wastewater from this industry is a major source of pollution among all industrial sectors considering both volume and composition of effluent. During leather processing, a number of size reduction, levelling and purification operations are carried out which results in generation of untanned and tanned proteinaceous waste materials which pose as a major environmental problem if not managed effectively. Large-scale production systems are adopted for leather processing and so this industry receives focus of environmentalists and society. Consequently, tremendous pressure is exerted by various pollution regulatory bodies to treat the effluents before disposal. The tannery effluents contain tannins, high suspended solids, and dissolved solids, BOD and some inorganic compounds such as chlorides, sulphides, sulphates, sodium and some toxic heavy metals, which affect the environment. Thus there is a need for innovative treatment technologies for the removal of these heavy metal ions from wastewater. Numerous physical and chemical methods such as screening, flow equalization, primary sedimentation, chemical flocculation, aerobic activated sludge treatment, secondary sedimentation have been employed for the disposal of wastes. These methods are very expensive and therefore the most reliable way seems to be the biological treatment using microorganisms that serve as efficient detoxifiers of pollutants. Fungi contribute a major role in the reduction of pollution by possessing superior aptitudes to produce a large variety of extracellular proteins, organic acids and other metabolites, and for their capacity to adapt to severe environmental constraints. Fungi are mainly used in leather production in different steps like soaking, dehairing, bating, dyeing, degreasing or in effluent and proteinaceous solid wastes treatment. During the bating process, fungi remove the degraded hairs and epidermis and promote the removal of nonstructural proteins and help on carbohydrates removal. Free mycelia, mycelia pellets, immobilized fungi or their enzymes have been reported in treatment of leather effluents. Thus the use of fungi to treat leather effluent is cost effective and therefore highly suitable for reduction of pollutant load of tannery effluents.

A Diagonal Lattice Reduction Algorithm for MIMO Detection

Recently, an efficient lattice reduction method, called the effective LLL (ELLL) algorithm, was presented for the detection of multiinput multioutput (MIMO) systems. In this letter, a novel lattice reduction criterion, called diagonal reduction, is proposed. The diagonal reduction is weaker than the ELLL reduction, however, like the ELLL reduction, it has identical performance with the LLL reduction when applied for the sphere decoding and successive interference cancelation (SIC) decoding. It improves the efficiency of the ELLL algorithm by significantly reducing the size-reduction operations. Furthermore, we present a greedy column traverse strategy, which reduces the column swap operations in addition to the size-reduction operations.

Identification of the breakage rate and distribution parameters in a non-linear population balance model for batch milling

Non-linear population balance models (PBMs), which have been recently introduced due to the limitations of the classical linear time-invariant (LTINV) model, account for multi-particle interactions and thus are capable of predicting many types of complex non-first order breakage kinetics during size reduction operations. No attempt has been made in the literature to estimate the non-linear model parameters by fitting the model to experimental data and to discriminate various models based on statistical analysis. In this study, a fully numerical back-calculation method was developed in the Matlab environment to determine the model parameters of the non-linear PBM. Not only does the back-calculation method identify the parameters of complicated non-linear PBMs, but also it gives the goodness of fit and certainty of the parameters. The performance of the back-calculation method was first assessed on computer-generated batch milling data with and without random error. The back-calculation method was then applied to experimental batch milling data exhibiting non-first order effects using both the LTINV model and two separate non-linear models. The back-calculation method was able to correctly determine the model parameters of relatively small sets of batch milling data with random errors. Applied to experimental batch milling data, the back-calculation method with a two-parameter non-linear model yielded parameters with reasonable certainty and accurately predicted the slowing-down phenomenon during dry batch milling. This study encourages experimenters to use advanced non-linear population balance models along with the back-calculation method toward estimating the breakage rate and distribution parameters from dense batch milling data sets.

Recovery and utilization of proteinous wastes of leather making: a review

Hides and skins, by-product of the meat industry is converted into a value added product namely leather by the tanners. Tanning essentially is the process of converting raw hides and skins into imputrescible substance. The tanning process has number of steps and generates significant quantities of by products and wastes. These solid and liquid wastes pose major environmental problem if not managed effectively. Large–scale production systems are adopted for leather processing in clusters and therefore, the industry receives focus of environmentalists and society. Consequently tremendous pressure is exerted by various pollution regulatory bodies. The hides and skins, after trimming, removal of flesh and fat, are treated with chemicals, which cross-link the collagen fibers to form a stable, durable material. The chemicals used may be derived from traditional vegetable products, or inorganic metal salts. During leather processing number of size reduction, leveling and purification operations are carried out which results in generation of untanned and tanned proteinous waste materials. In this paper, various recovery processes and utilization methodologies of proteinous solid wastes, emanating from leather processing operations prior to tanning is reviewed.

Optimization of Miscanthus Harvesting and Handling as an Energy Crop: BioFeed Model Application

The success of the bioenergy sector depends significantly on ensuring efficient and sustainable biomass feedstock production and provision, which requires a comprehensive systems theory based approach. BioFeed is a system-level model that has been proposed to optimize the feedstock production and provision activities. It has been applied in the past to study switchgrass production in Illinois. This work presents recent additions to the BioFeed model to enable a more accurate representation of various biomass production activities for energy crops. While maintaining the original model framework that focuses on farm-level design and operational issues in addition to storage and transportation logistics, new biomass packing and size reduction operations such as pelletization and grinding have been added. The selection and operation of biomass handling equipment such as loaders, unloaders, and in-field transportation equipment have also been incorporated. The addition of these new operations created the challenge of ensuring the logical validity of the operational sequence during model simulation. A superstructure of all possible operational sequences was developed, and the biomass form at the output of every piece of equipment was tracked to ensure appropriate equipment selection. The model was then applied to a case study of Miscanthus production as the energy crop in southern Illinois. The results showed that the optimized delivered cost based on existing technology was about $45 Mg-1. Biomass packing and storage were important components of the total cost distribution. The potential alternatives to reduce the delivered cost included using a single-pass mowing and baling operation, increasing the packing throughput capacity, and extending the harvesting window.

Energy absorbed in breakage of single particles in drop weight testing

Drop weight tests are a useful tool to determine energy-size reduction relationships for breakage of particulate materials. Their use in modeling and simulation of size reduction operations has increased significantly in recent years. The main limitation of the classical drop weight test lies in the fact that it does not allow the direct measurement of the fraction of the input energy that is used in particle breakage (called comminution energy). A procedure that overcomes this limitation through the calculation of the comminution energy and the coefficient of restitution in drop weight tests is proposed in the present study. It uses force-time histories of the entire event measured in a modified drop weight apparatus, the Ultrafast Load Cell, along with assumptions of conservation of energy and momentum during impact. Calculations using the procedure have been compared to measurements of the coefficient of restitution using high-speed video, and the agreement is excellent. Experimental results show that the fraction of the input energy that is actually used in particle breakage increases with an increase in relative impact energy and decreases for more elastic and crystalline materials.

Grinding behaviour of coal in different size-reduction systems

It was found that it is easer to grind some coals in ball-race mills and others in tube mills. In this paper, simple laboratory methods are presented for evaluation of the grinding behavior of five coals in two different size-reduction operations. The tests proved that certain coals are better ground by impact than attrition and vice versa.

The tensile properties of frozen and thawed lean beef

The tensile properties of frozen beef are relevant to many size reduction operations in frozen meat processing. The tensile properties of lean beef aligned both along, and perpendicular to, the fibre direction have been studied over the temperature range +10°C to −30°C and over a range of strain rates. Strain rate had an effect on tensile strength and other tensile parameters for frozen beef with either fibre orientation. Two distinct types of behaviour were observed. At the higher temperatures (e.g. −5°C and −10°C for beef oriented perpendicular to the fibre direction) there was a rise in tensile strength with increase in strain rate. This viscoelastic fracture behaviour can be attributed to the viscoelastic character of meat proteins and also to the plasticity of ice. At the lower temperatures (e.g. −15°C to −30°C for beef oriented perpendicular to the fibre direction) there was a decrease in tensile strength with increase in strain rate. This fracture behaviour can be attributed to the brittleness of ice. Temperature had a marked effect on all tensile parameters. The maximum tensile strength at most strain rates occurred in the temperature range −10°C to −20°C, and the strength was lower at −30°C than at −20°C.

A New Theory of Size Reduction

Since Rittinger proposed his theory on size reduction in 1867, a number of theories for size reduction have been developed empirically as well as semi-empirically and theoretically. Among these theories, Rittinger's theory, Kick's theory and Bond's theory have been widely referred to. However, many examples of discrepancies between these theories and actual size reduction operations have been experienced.The present authors studied theoretically the fracture phenomena experienced in the size reduction process, particularly the mechanism of fracture, from the material strength point of view. According to this theory, the energy required for size reduction is proportional to the 3 (1-2/β) th power of particle size and the square of tensile strength, as well as inversely proportional to Young's modulus where β being coefficient of uniformity when the “size effect” of tensile strength is taken into consideration.This theory is sufficiently general to incorporate all the three older theories mentioned above, and may permit an accurate calculation to be made for a selected size reduction operation from simple laboratory test information on rock specimens.

Rheology in dispersion testing and mill base formulation optimization

Rheology offers only slight advantages in terms of mill base formulation, because of the comparatively low shear rates available on existing viscometers and the considerable changes in mill base rheology which occur during the milling cycle. These changes can however be utilised as a means of dispersion testing and satisfactory and reproducible “milling isotherms” can be obtained for a wide variety of dispersion and size reduction operations. It would seem possible to characterise grinding and dispersion by changes in mill base rheology in that grinding shows an increase in non-Newtonian characteristics whereas dispersion shows a decrease in these characteristics. Care must be taken to ensure that controlled pretreatment of the samples is adopted be ore satisfactory results can be ensured, but extensive storage periods tend to magnify differences between samples.