Mill Power Research Articles

Assessing the stirred mill design space

In the context of the mining industry, smaller grain size and other mineralogical characteristics have motivated the need to grind finer. In order to address this need, the interest in fine grinding technologies has grown over the last 20years as is illustrated by a growing body of knowledge on stirred milling. Emphasis in recent years has been on the use of computationally intensive modeling and simulation methods such as the discrete element method (DEM) and computational fluid dynamics (CFDs). However, due to the computational requirements of these two methods, initiating a study that spans the stirred mill design space would take a lot of computational effort and time. Therefore the goal of this paper is to propose and apply a simplified stirred mill model that will then be used to assess configurations in the stirred mill design space.To this end, a stirred mill model was proposed based on the assumption that the main if not only mechanism of ore breakage is shear. As the basis of this model is the fluid mechanics definition of shear stress, the stirred mill power model became a function of viscosity, mill speed and a new parameter called shear volume. An initial validation using published data indicated the shear based power model correlated well with measured power.Establishing a morphological chart to delimit the stirred mill design space indicated that 24 design and operating conditions can be assess using the established shear volume measure. The results indicated for the mill configurations tested that a change in stirred mill liner design can potentially increase shear volume and power from 14% to 290% as compared to smooth chamber liners.

Analysis and validation of a run-of-mine ore grinding mill circuit model for process control

A simple and novel non-linear model of a run-of-mine ore grinding mill circuit, developed for process control and estimation purposes, is validated. The model makes use of the minimum number of states and parameters necessary to produce responses that are qualitatively accurate. It consists of separate feeder, mill, sump and hydrocyclone modules that can be connected to model different circuit configurations. The model uses five states: rocks, solids, fines, water and steel balls. Rocks are defined as too large to be discharged from the mill, whereas solids, defined as particles small enough to leave the mill, consist of out-of-specification coarse ore and in-specification fine ore fractions. The model incorporates a unique prediction of the rheology of the slurry within the mill. A new hydrocyclone model is also presented.The model parameters are fitted to an existing plant’s sampling campaign data and a step-wise procedure is given to fit the model to steady-state data. Simulation test results of the model are compared to sampling campaign data of the same plant at different steady-state conditions. The model shows promise in estimating important process variables such as mill power and product particle size and is deemed suitable for process control studies.

Integrated Economic Equilibrium and Life Cycle Assessment Modeling for Policy‐based Consequential LCA

SummaryConsequential life cycle assessment (CLCA) has emerged as a tool for estimating environmental impacts of changes in product systems that go beyond physical relationships accounted for in attributional LCA (ALCA). This study builds on recent efforts to use more complex economic models for policy‐based CLCA. A partial market equilibrium (PME) model, called the U.S. Forest Products Module (USFPM), is combined with LCA to analyze an energy demand scenario in which wood use increases 400 million cubic meters in the United States for ethanol production. Several types of indirect economic and environmental impacts are identified and estimated using USFPM‐LCA. A key finding is that if wood use for biofuels increases to high levels and mill residue is used for biofuels and replaced by natural gas for heat and power in forest products mills, then the increased greenhouse gas emissions from natural gas could offset reductions obtained by substituting biofuels for gasoline. Such high levels of biofuel demand, however, appear to have relatively low environmental impacts across related forest product sectors.

Predicting the effect of operating and design variables on breakage rates using the mechanistic ball mill model

Batch grinding tests have been a very good tool to aid in understanding the effect of design and operating variables in ball milling, as well as in providing data for a couple of successful scale-up methods. Recently, a mechanistic model of the ball mill has been proposed, and the present paper describes its application in the simulation of batch mills operating under a range conditions. First-order breakage rates have been estimated using data from these simulations, and used to investigate the effect of operating and design variables in milling. Predictions using the mechanistic model are then compared to those using the scale-up relationships proposed by Austin and collaborators and Herbst and Fuerstenau. The trends predicted using the mechanistic model are in general agreement with the empirical models. Good correlation has also been observed between the simulated specific breakage rates and the specific mill power, which is in agreement with the scale-up method proposed by Herbst and Fuerstenau.

Tom Sparling-Engineer and Entrepreneur [History

This paper is a biographical note on Tom Sparling, and his work as an engineer and entrepreneur. He was nationally known for electrical power and control systems for military facilities, high-rise buildings, and steel and flour mills.

The Experimental Research on the Variable Loading System of LM18.20 Coal Mill

The paper research the loading methods of medium-speed coal mill and the variable loading system of LM18.20 coal mill. The experiment result has shown that using variable hydraulic loading system can make the coal mill running steadily with stable output under varies output conditions; and the mill's loading range is extended; the mill power consumption and wear rate of grinding parts are reduced.

The Experimental Research on the Variable Loading System of LM18.20 Coal Mill

The paper research the loading methods of medium-speed coal mill and the variable loading system of LM18.20 coal mill. The experiment result has shown that using variable hydraulic loading system can make the coal mill running steadily with stable output under varies output conditions; and the mill's loading range is extended; the mill power consumption and wear rate of grinding parts are reduced.

Power Factor Improvement In Wind Mill Power Station Using TCC

Power Factor Improvement In Wind Mill Power Station Using TCC

Influence of wood properties and technological parameters of processing on cutting power in milling of thermally modified beechwood

The paper presents results of influence of thermal modification on cutting power required for milling wood processing. The experiment was conducted for the different treatment temperatures (170?C, 190?C and 210?C) and different technological parameters of processing (feed and cutting depth). Cutting powers during milling were measured on four groups of beech wood samples, dimensions 35?16?400 mm, separately for heartwood and sapwood. The following mechanical and physical properties of the processed samples were tested: bending properties (modulus of rupture and modulus of elasticity), cross-sectional and tangential hardness, and air-dry density. The measuring device used for measuring, monitoring and displaying cutting power was developed at the Wood Machining Centre at the Faculty of Forestry in Belgrade. The results point out the differences in the powers required for processing heat-treated wood compared to untreated wood. The analysis shows that with the increase in treatment temperature, the required cutting powers decrease.

Analysis of energy–size reduction relationships in batch tumbling ball mills

A theoretical energy–size reduction relationship is derived for tumbling ball mills based on a solution of the integro-differential equation of comminution kinetics, in which the proportional relationship is applied between the grinding rate constant and the net mill power. The derived formula is similar to an empirical energy law, d W ∝ d x r / x r i , where W is the specific energy input, x r is the particle size of product and the exponent i is shown to be a variable depending upon the ground material, the type of mill and the method to measure energy. Derived results are confirmed with reported data in reasonable agreement. Also, the Bond's energy law is examined and a method for the correction of the Bond work index is discussed.

Mechanochemical Synthesis and Characteristics of Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>

This paper presents a novel mechanochemical synthesis technique for making nano-structured Pb(Mg1/3Nb2/3)O3 (PMN) ferroelectric material without annealing treatment in a much shorter time and at much lower temperature than those reported in the literature, by using the starting precursors MgO, PbO, and Nb2O5. Specimens of various milling time (3-6h) are characterized from XRD patterns to track and analyze the synthesizing procedure of this mechanochemical processing route. The time used to make the desired PMN powders varies with different milling power. When the constituent oxides were mechanically activated at 1.8KW milling power for 6h, the perovskite phase PMN powder was obtained; while it was formed when milling at 3KW for only 3h. Typical SEM images of the as-received PMN powders show that the powders are aggregated of nano-particles of about 100nm in size.

Spreadsheet-based modeling of liner wear impact on charge motion in tumbling mills

Grinding remains the major constituent of the total cost of processing minerals in most applications. Charge motion is one of the key parameters affecting grinding efficiency and mill power draw. Although there have been numerous investigations on the effect of liner design on charge motion, the effect of charge profile due to liner wear during mill operation along the mill length has not received much attention. In this research, Powell’s analytical approach to calculate the charge trajectory with respect to the liner profile was used to develop a software based on Microsoft Excel© . As a case study, the liner wear profile of the Sarcheshmeh copper complex SAG mill was used to model the liner wear rate and calculate the changes of lifter face angle and lifter height during mill operation. Results were then used to determine charge motion in the SAG mill at any given operation time. The results indicated that after 4000 h of operation the lifters face angle increased from 14° to 47.1° and the height of lifters decreased from 15.2 to 5.8 cm. Modeling charge motion in the mill after 3000 h of operation showed 34° difference between the maximum and minimum of angles of impact along the mill length due to the nonuniform wear profile. It was also found that the variation in the pattern of the charge motion depends on the mill working hours and the distance of the desired point from the feed end. It was determined that the ratio of spacing to the height of lifters (S/H) plays an important role in the grinding efficiency and throughput. After 4000 h of operation, S/H ratio of the Sarcheshmeh SAG mill increased from 1.7 to 4.6.

Experimental observations of lifter parameters and mill operation on power draw and liner impact loading

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.

Relation between mechanochemical dechlorination rate of polyvinyl chloride and mill power consumption

A sample of polyvinyl chloride (PVC) powder was milled with CaO powder in a planetary mill for various mill operational parameters. The milled product consisted of dechlorinated hydrocarbon and water-soluble CaOHCl. The dechlorination rate of PVC was determined by the concentration of Cl− ions measured in solution after dispersing the milled product in water. To evaluate the power consumption during PVC dechlorination, the mill power consumption was measured during each experimental run. In addition, media motion during planetary milling was simulated using the discrete element method (DEM), enabling calculation of the mill power consumption. The power consumption calculated by the DEM simulation compared well with the power consumption measured experimentally. The dechlorination rate correlated well with the specific mill power consumption, regardless of the sample weight. The dechlorination rate of PVC when milled with oyster shells (CaCO3) was observed to be faster than that of the PVC/CaO system, and oyster shells could be used as a reactant for the treatment of PVC wastes. This work should be useful for the design of a reactor for the dechlorination of PVC.

Estimation of tool wear based on adaptive sensor fusion of force and power in face milling

Sensor fusion of multi-sensory measurements is believed to enhance accuracy of tool condition monitoring methods for sensor signals which are at least partly complementary. In this paper, a novel statistic based on the least squared error criteria is used to evaluate performances of models arising from sensor fusion. An adaptive sensor fusion of cutting force and electrical power signals, which performs optimally even in case of failure in any acquiring channel, is proposed. Combinations of signal processing techniques are used to extract accurate and robust features, which are refined by feature space filtering techniques to obtain improved and robust estimators of tool wear. It is shown that the model using sensor fusion of force and power produces superior results to those using single measurements. Error bounds of the estimates are also provided as prediction limits. Significant improvements are obtained compared to the existing methods in terms of accuracy and robustness.

Field-scale investigation of pulverized coal mill power consumption

Twenty field-scale tests were conducted in a 28 MW pulverized coal power plant in Healy, Alaska, to examine mill power consumption in relation to coal grind size. The intent in this field-scale study was to verify if grind size truly impacted power consumption by a detectable amount. The regression model developed from the data indicates that grind size does impact mill power consumption, with finer grinds consuming significantly more power than coarser grinds. However, other factors such as coal hardness (i.e. the lower the Hardgrove Grindability Index, or the harder the coal, the higher the power consumption) and mill throughput (i.e., the higher the throughput, the higher the power consumption) had to be included before the impact of grind size could be isolated. It was also observed that combining amperage and flow rate into a single parameter, i.e., specific amperage, hurt modeling. Cost analysis based on the regression model indicate a power savings of $19,972 per year if the coal were ground to 50% passing 76 {mu}m rather than the industry standard of 70% passing 76 {mu}m. The study also demonstrated that size reduction constituted a significant portion of the power consumption.

Calculus of the Required Driving Power for Tube Ball Mills

This paper presents the determining of the necessary driving power for tube ball mills, regarding frequently used working conditions: by rolling balls and by falling down balls, on parabolic trajectory. To make easier the calculation of driving power, the established correlations where used in Blanc formula.

Particle filling and size effects on the ball load behaviour and power in a dry pilot mill: Experimental study

The ball load behaviour in a pilot mill is studied under conditions of increasing particle filling, for coarse silica feed (0.8–1.8 mm) and fine silica feed (0.075–0.3 mm), at the mill speeds of 63, 78, 88 and 98% of the critical. An inductive probe is used to obtain the ball load behaviour independent of particles present in the mill. The difference in mill power draw obtained from the coarse and fine particle charges are explained via their load behaviour signals. The effect of particle filling and size on the ball load behaviour is quantified through the toe and shoulder angular positions. Radial segregation of the coarse silica particles to the periphery of the charge occurs. A radial segregation index related to the extent of drop in the inductive probe's signal has been defined and used to quantify radial segregation as a function of particle filling and mill speed.

Varied charge-transfer complex crystals formed between diols and benzoquinone in the solid and solution states

Co-grinding of crystals of diols (electron donor) and benzoquinone (BQ, electron acceptor), and in some cases with crystals of a third aromatic compound, produces charge transfer (CT) complex crystals in the solid state without going through an obvious amorphous state, followed by a change in colour and in powder X-ray diffraction patterns. A milling power above a threshold is required for the new CT complex crystal formation, however, in some cases simple mixing of pulverized crystals is good enough to initiate the transformation. On exposing the CT complex crystals to air, without any mechanochemical force, they revert to the starting diol crystals by losing sublimable BQ molecules, rearranging hydrogen bonds and establishing a three-dimensional periodicity. Remarkably, solid-state and conventional solution crystallization give different results, i.e., formation or non-formation of CT complex crystals, or formation of different crystals with different colours. The phenomenon is surprisingly frequent and all three two-component CT systems and six out of the nine three-component systems investigated, exhibit different crystallization behaviour. A quartet structure where two BQ molecules are sandwiched by two naphthols was formed in the crystal obtained from solid-state crystallization. A new triplet CT complex structure in which a BQ is sandwiched by a naphthol and a biphenyl is also reported.

Modeling of energy loss to the environment from a grinding mill. Part I: Motivation, literature survey and pilot plant measurements

Grinding mills are generally very inefficient, difficult to control and costly, in terms of both steel and power consumption. Improved understanding of temperature behaviour in milling circuits can be used in the model-based control of milling circuits. The emphasis in this work is to develop a model for the overall heat transfer coefficient as a function of the load volume, mill speed and design of mill shell/liner using the energy balances in order to model energy loss from the mill. The energy loss via convection through the mill shell is accounted for by quantifying the overall heat transfer coefficient of the shell. The ambient temperature allows the model to account for convective loss. Firstly the models of temperature behaviour are developed followed by the development of the model for the overall heat transfer coefficient for the pilot dry batch mill. The practical aspects of the work involved the measurement of the temperatures of the mill load, air above the load, the liners, mill shell and the environmental temperature. Other measurements were: mill power and sound energy from the mill. Energy balances are performed around the entire mill. The model for the heat transfer process is parameterized in Part II.