Dry Mills Research Articles

Assessing the Effects of Material Properties on Load Behavior in Dry Ball Mills Using DEM

Understanding how the mill load behaves is crucial for enhancing ball mill effectiveness. This study aimed to create a discrete element method (DEM) model to simulate the motion charge in ball mills and to analyze how the simulation material properties affected the load behavior. The steel balls were modelled as a collection of distinct particles, each of which was subject to Newton’s laws of motion and tracked in a Lagrangian manner. Hertzian contact law was used to describe inter-particle collisions. Then, this numerical model was coded using the open-source C++ program LAMMPS Improved for General Granular and Granular Heat Transfer Simulation (LIGGGHTS) to mimic laboratory and pilot-scale ball mills. The load positions measured from the DEM simulations were compared to the published experimental data and empirical models of comparable laboratory and pilot-scale experiments to validate the findings. The angular shoulder position ranged between 137° to 154° for the range of Young’s modulus of 0.5 to 1000 MN/mm2. Angular shoulder and toe positions had a variation of less than 10% from the laboratory and pilot-scale experimental data. The outcomes demonstrated a significant relationship between load position and material characteristics such as Young's modulus in DEM simulation. This preliminary model can be used for choosing the appropriate material parameters for ball mills both with DEM and coupled CFD–DEM multiphase simulations. This assessment concluded that material properties affect the load behavior in computer simulations of ball mills.

A cell-based PBM for continuous open-circuit dry milling: Impact of axial mixing, nonlinear breakage, and screen size

This theoretical study examined the impact of the degree of mixing, nonlinear particle breakage, and screen opening size on the particle size distribution (PSD) and mass hold-up in continuous dry mills with internal classification. A cell-based population balance model (PBM) incorporating a non-ideal screen model was formulated, wherein the back-mixing ratio and number of cells modulated the extent of axial mixing. The set of differential–algebraic equations (DAEs) was solved for the spatio-temporal evolution of the PSD in the mill and the product stream. The simulation results suggest that a smaller screen opening delayed the attainment of the steady state, increased the hold-up, and yielded a finer product PSD. The cushioning action of fines resulted in a coarser product PSD; however, a screen with a smaller opening mitigated this effect. The cell-based PBM predicted various features of experimental milling observations while providing insights into the mixing–nonlinear breakage–classification interplay.

Study on the Effects of Grinding Factor and Scaling up in Grinding Using Horizontal Dry Bead Mill

Effect of grinding factor and scaling up were carried out by grinding using horizontal dry bead mill. For the experiments, 2 sizes of horizontal dry bead mills with different capacities, lab and manufacturing scale, were used to study scaling up and down. The grinding experiments were performed by changing each typical grinding factor for bead mills, including the agitator peripheral speed, bead packing density, bead diameter, and material feeding speed. This set of experiments was conducted for 3 kinds of materials, silica sand of natural inorganic materials, alumina of synthetic inorganic materials, and activated carbon of organic materials. As a result, common for all materials, similar rules were found between the particle size and specific energy, the amount of mechanical energy per unit amount of material. In addition, these rules were applicable for the different-size mills, indicating that the scale can be controlled by the rules and specific energy. Also, it is revealed that when using a single type of material, changing the bead diameter changes the energy efficiency, indicating that using small-diameter bead was effective for efficient grinding.

On dry SAG mills end liners: Physical modeling, DEM-based characterization and industrial outcomes of a new design

The role of end liners in dry SAG mills with the objective of obtaining a thorough understanding of the effects of end liners design on the load trajectory and SAG mill performance was experimentally studied. The test works were conducted in a scale down mill with a diameter of 1 m. It was shown that the liner in the first and the last 20% of the mill length which were under the protection of the deflector liners experienced no deformation. To improve the grinding efficiency, a new design using low profile end liners incorporating radial ribs of proper height was investigated. The results indicated that the new lower height profile deflectors and 15.5 mm-height (14.5 cm in industrial scale) radial ribs improved the mill performance. A new liner design was proposed by decreasing the number of liners in each slice from 5 to 4 pieces. The thickness of the inner head liners reduced from 45 cm to 30 cm and the outer deflector liners were replaced by 14.5 cm radial ribs. The distance between feed and discharge end liners increased from 115 to 176 cm resulting in an increase of 53% in the effective mill length. The weight and volume of new end liners decreased by 9 and 23%, respectively. Installation of the new liners in Aerofall SAG mills increased the throughput from 441 to 465 t/h, decreased the product size from 519 to 480 μm and decreased the amount of recycled material from the SAG mill product from 10 to 6%. The most significant improvement was observed in the liner life; an increase of 50– 200% in liner life depending on the location of end liners was achieved. The relining time also reduced by 37.5% with the new liners.

Development of a laboratory scale continuous dry stirred media mill

Stirred media mills are widely operated in the industry for the production of fine ground materials. The application of the mill type in dry mode came to the front in the recent years. Most of the operating dry mills have vertical orientation, however the horizontal type mills are also available on the market now, and some research is still ongoing for the development of this mill type. In the present study two development phase of a laboratory scale continuous dry, horizontal stirred media mill is presented. In the first phase the working principle of the mill, the air flow rate and feed rate were investigated. Later based on the operational experience and earlier results of the grinding experiments the mill has undergone significant changes resulted in a significant increase in the amount of air flow rate through the mill. The measurement results of the second phase led to that the mill has a significantly higher air flow rate and stable constant feed rate, however the control of the air flow during operation is essential to achieve the required product particle size.

Insights into advanced ball mill modelling through discrete element simulations

Important advances have been made in understanding ball milling during the last 25 years or so, a great part of it owing to the widespread application of the discrete element method (DEM), which is now an integral part of several advanced ball mill models. These models, however, must rely on assumptions regarding the mill mechanical environment that can help make the problem more manageable. The paper analyzes the validity of some assumptions that have been the basis of several advanced ball mill models by conducting DEM simulations of dry batch mills including both grinding media and particles. The validity of the assumption of perfect mixing of grinding media and particles, as well as of simulating exclusively the grinding media in order to collect the collision energy information for prediction of breakage and, thus, saving computational effort, are analyzed in great detail. It is concluded that the assumption of perfect mixing in the radial direction is generally valid, except for mill frequencies that are unusually high and exceedingly large ratios of mean ball and particle sizes being ground. It is also observed that a fraction of the number of collisions inside the mill do not involve particles, so that an empirical expression that is based on the ratio of surface areas of the ball and particle charge is proposed to estimate such proportion of unsuccessful collisions. Finally, a model from the authorś laboratory, that assumes that each collision in the mill will involve a monolayer bed of particles, is tested, demonstrating reasonable agreement when compared to simulations.

ANALISIS RANTAI NILAI AGROINDUSTRI SAGU DI KABUPATEN KEPULAUAN MERANTI

Sago industries in Kepulauan Meranti holds an important position in driving the local economy. Around 80,000-90,000 tons of sago starch are produced annually by sago mills generally located in rural areas . Almost all of the sago starch production from the Kepulauan Meranti is sent out of the region as raw material for the next industry. Lack of market information related to price, quality, quantity and types of products that the market wants makes the sago industry only rely on information from the midleman. Sago has significant value to be utilized into various commercial products such as modified starch, glucose, food thickener, noodles and biscuits. The purpose of this study were (1) to map the sago industry value chain and (2) to identify the distribution of values to the actors involved. Data collection includes key informant interviews, focus group discussions, observation and collection of related documents. Data analysis used includes value chain analysis, marketing margin analysis and value added analysis. The results of this study indicated that there are various actors involved in the sago industry value chain starting from seed suppliers, sago smallholders, PT. NSP, log traders, wet sago mills, dry sago mills, glass noodles factories, home industries, Harmonis Cooperatives, individual distributors and PT. Saweri Gading. In the wet sago value chain, PT. Saweri Gading obtained a higher marketing margin than the sago mills, with a margin of Rp 2,000 per kg. In the dry sago value chain, sago mills actors obtained a margin of Rp 4,600 per kg. The results of the value added analysis showed that glass noodles products have value added of Rp 3,450 per kg, the highest value added compared to other sago industry products. Key words : Kepulauan Meranti, sago industry, value added, value chain

Processing of Moringa leaves as natural source of nutrients by optimization of drying and grinding mechanism

AbstractIn this study, Moringa leaves were processed in two steps (1) drying and (2) grinding. In the first step, leaves were dried with different drying treatments including conventional, laboratory and advanced methods to optimize drying conditions in terms of maximum nutrients preservation and color quality. During the second step, leaves were ground with three different grinding mills including hammer, dry, and cutter mills to study the effect of grinding mechanism in combination with particles size and moisture content on the flowability of the powder. The flowability was measured using conventional and advanced methods including Carr Index and Cohesion Index. Oven drying at 50 °C was found to be the optimum conditions in terms of maximum nutrients and color preservation of Moringa leaves. The grinding mechanism having a substantial impact on the flowability of the powder produced in different types of mills. The effect of moisture content and particle size on Moringa leaves powder was also investigated and found that moisture content directly affects the flowability of Moringa leaves powder followed by particles size and shape. We have also noted powder sample prepared by the impact mechanism (hammer mill) with particle size 50 µm and moisture content 5% having appreciable flowability as compared to the samples processed by cutting (dry mill) and shattering (cutter mill) mechanisms. This study conveys an ultimate understanding regarding processing (drying and grinding) of Moringa leaves powder.Practical ApplicationsDried Moringa is restricted to use as dietary purposes because of its unpleasant taste, which becomes further bitter after drying procedure. Therefore, powder of Moringa leaves can be processed into different forms such as tablet, capsules and cereal formulations. For this purpose, a comprehensive study has been carried out to increase the understanding of drying and flow characteristics of Moringa (leaves and powder) using different drying and grinding mechanisms. The findings of this study regarding drying treatments, nutrients preservation, flowability and different grinding mechanisms can also be applied to other herbs and leaves. A correlation between Carr Index and Cohesion Index established successfully. This study will be helpful to conduct further research in food processing because Carr Index is simple and easy to measure as compared to Cohesion Index that requires both texture and powder flow analyzers.

Techno-Economic Analysis of Integrating First and Second-Generation Ethanol Production Using Filamentous Fungi: An Industrial Case Study

The 2nd generation plants producing ethanol from lignocelluloses demand risky and high investment costs. This paper presents the energy- and economical evaluations for integrating lignocellulose in current 1st generation dry mill ethanol processes, using filamentous fungi. Dry mills use grains and have mills, liquefactions, saccharifications, fermentation, and distillation to produce ethanol, while their stillage passes centrifugation, and evaporation to recycle the water and dry the cake and evaporated syrup into animal feed. In this work, a bioreactor was considered to cultivate fungi on the stillage either before or after the centrifugation step together with pretreated lignocellulosic wheat bran. The results showed that the integrated 1st and 2nd generation ethanol process requires a capital investment of 77 million USD, which could yield NPV of 162 million USD after 20 years. Compared to the fungal cultivation on thin stillage modified 1st generation process, the integrated process resulted in 53 million USD higher NPV. The energy analysis showed that the thin stillage modified 1st generation process could reduce the overall energy consumption by 2.5% and increase the ethanol production by 4%. Such modifications in the 1st generation processes and integration concepts could be interesting for the ethanol industries, as integrating lignocelluloses to their existing setup requires less capital investment.

An experimental study on the ultra-fine grinding of gypsum ore in a dry ball mill

Gypsum is a crystalline form of hydrated calcium sulfate (CaSO4·2H20) generally used in cements and plasters in the construction industry, though also in paints, fertilizers, medicines, papers, and textiles. For use in these materials, gypsum must be ground finely (<100μm), if not ultra-finely (<10μm), for which ball mills are most effective. Despite gypsum's widespread use and the regular need to grind it, studies concerning the grinding of gypsum ore remain scarce. In response, in this study, we have systematically investigated how certain grinding parameters (i.e., mill speed, ball filling ratio, ball size distribution, powder filling ratio, grinding aid ratio, and grinding time) of conventional dry ball mills affect the grindability of gypsum ore. We determined the properties of the micronized gypsum products obtained in optimal grinding conditions, and the results showed that the dry ball mill grinding process can effectively produce ultra-fine gypsum products.

G0900205 リング型粉砕媒体を持つ乾式微粉砕機の木質バイオマス粉砕特性の検討

We examined the pulverizing characteristics of woody biomass by three defferent sizes of dry mills with ring-type pulverizing media. This type of mills have many pulverizing rings in the inside of the pulverizing cylindrical chambers and these rings roll and rotate in me chambers by external vibration. Woody biomass are pulverized by this high rotational centrifugal force. Two kinds of woody biomass: cedar and douglas fir were used for pulverizing tests of these mills. Pulverizing energy consumption of each of mills was inversely proportional to the amount of input materials. When the amount was too large, the pulverizing was no longer proceeding. The study of the pulverizing characteristics of small and large dry mills leaded to the definite relationship between the pulverizing energy consumption and saccharification efficiency of woody biomass. The relationship was independent of the physical size of mills. Input power per area of pulverizing chamber is about 15 kw/m^2. Then, it was estimated that woody powder was heated by large pressure from pulverizing rings and the average temperature of this woody powder layer achieved at about 300 centigrade.

Integration of the first and second generation bioethanol processes and the importance of by-products

Lignocellulosic ethanol has obstacles in the investment costs and uncertainties in the process. One solution is to integrate it with the running dry mills of ethanol from grains. However, the economy of these mills, which dominate the world market, are dependent on their by-products DDGS (Distiller’s Dried Grains and Solubles), sold as animal feed. The quality of DDGS therefore must not be negatively influenced by the integration. This puts restraints on the choice of pretreatment of lignocelluloses and utilizing the pentose sugars by food-grade microorganisms. The proposed solution is to use food related filamentous Zygomycetes and Ascomycetes fungi, and to produce fungal biomass as a high-grade animal feed from the residues after the distillation (stillage). This also has the potential to improve the first generation process by increasing the amount of the thin stillage directly sent back into the process, and by decreasing the evaporator based problems.

Understanding the evolution of environmental and energy performance of the US corn ethanol industry: evaluation of selected metrics

AbstractThroughout the past two decades, numerous studies characterized the greenhouse gas (GHG) emissions and net energy balance of corn ethanol production in the USA. A wide range of reported values resulted from differences in the vintage of the data used to evaluate the ethanol conversion technology and the agricultural practices of corn production, which evolved substantially during the rapid growth phase of the industry. Methodological differences in life cycle assessments also caused the reported values to vary widely. With corn dry mills growing from 30% of total installed ethanol production capacity in 1990 to 80–90% from 2006 to 2011, we document the evolution of this industry using vintage‐specific data to analyze selected energy and environmental metrics, including GHG emissions, fossil energy use, direct land use, and GHG emissions reduction per hectare of land harvested for ethanol production. Our estimates indicate that production and use of corn ethanol emitted 44% fewer GHG emissions, consumed 54% less fossil energy and required 44% less land in 2010 compared to 1990 (on a life cycle basis). Our review and analysis point to strategies for reducing the carbon footprint of the corn dry mill industry by building on the progress already achieved. Using biomass (e.g. residues from corn production) for process heat or combined heat and power is one such strategy. Additional environmental benefits are projected from the adoption of integrated gasification combined cycle technology (using corn residues), which leads to energy‐self‐sufficient mills or net electricity producers depending on the power system configuration. © 2013 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Axial transport in dry ball mills

Ball mills are used for grinding of rocks, cement clinker and limestone from 10 to 100 mm feed sizes down to sub-millimetre product. They are typically rotating cylinders with diameters from 3 to 6 m and lengths from 6 to 12 m. The flow of particulate solids within these mills can be modelled using the discrete element method (DEM). Typically, such modelling is done for short durations of a few mill revolutions and either in two dimensions or using thin three-dimensional slices through the center of the mill with periodic boundary conditions in the axial direction. This facilitates an understanding of the radial motion of the charge, estimation of power draw and of liner wear, but it cannot provide information about axial transport within the mill. In this paper, we examine the axial transport in dry ball mills. This requires simulation of the entire mill and the full volume of the charge for significant periods of time (thousands of revolutions). We use a simple model for grate discharge that allows prediction of the time varying axial distribution of different particle sizes within a discharging ball mill. The distributions of sub-grate size ‘fines’ is shown to satisfy a one-dimensional diffusion equation with the diffusion coefficient decreasing with grate size. A pulse test, where a single mass of fines in injected at the feed end, is able to quantify the residence time distribution of the fines.

Radial mixing of particles in a dry batch ball mill

Poor mixing in dry ball mills can lead to insufficient presentation of fine particles to the classifying air, overgrinding of particles and wastage of energy in a ball mill. A video capture method has been used to study radial mixing kinetics in a dry batch ball mill. Experiments were conducted in a ball mill with PVC plastic powders being used as particles so that the effect of size reduction could be neglected. Radial mixing in ball mills was studied at typical industrial speeds of 75%, 80% and 90% of critical. The rate of particle mixing was observed to increase with increasing mill speed. A simplified mathematical model is presented that can be used to predict the radial mixing of particles in a ball mill. A parameter, k, was used to quantify the kinetics of mixing as affected by the mill's speed.

An experiment study of hard coating and cutting fluid effect in milling aluminum alloy

This paper investigates the cutting performance of a tungsten carbide end mill with hard coating and a sulfurous boric acid ester cutting fluid in milling A6061P-T651 aluminum alloy. The experiments were conducted to compare the milling force responses and flank wear under various cutting conditions. The results indicate that adding sulfurous boric acid ester cutting fluid decreases tool wear by 12.5% for hard coating tungsten carbide end mills and decreases the milling force by 10%. Besides, the average values of side and end flank wear of TiAlN-surface multilayer end mills can be decreased 38.7% and 68.7% respectively compared with uncoated and dry end mills.

Isolation in cell culture and detection by PCR‐based technology of IPNV‐like virus from leucocytes of carrier turbot, Scophthalmus maximus (L.)

A non-destructive procedure was utilized to determine the infectious pancreatic necrosis virus (IPNV) status of an apparently healthy turbot broodstock. Blood samples were used to detect IPNV by reverse transcriptase-polymerase chain reaction (RT-PCR), Southern blot hybridization and nested PCR. In addition, viral isolation from turbot leucocytes was performed. Around 22% of the fish were IPNV positive by RT-PCR, and this increased to close to 60% when nested PCR was performed. The present report supports the use of blood samples for the detection of IPNV-like viruses in brood fish. In addition, we demonstrate that it is possible to isolate the virus from the blood of carrier fish, as a non-lethal detection method, although it is much less sensitive than RT-PCR and nested PCR as a IPNV-like strain was isolated from only five of the 15 blood sample pools assayed. The viral isolate was identified as type Dry Mills (genogroup I) by means of restriction fragment length polymorphisms and DNA sequencing.

Plant size: Capital cost relationships in the dry mill ethanol industry

Estimates suggest that capital costs typically increase less than proportionately with plant capacity in the dry mill ethanol industry because the estimated power factor is 0.836. However, capital costs increase more rapidly for ethanol than for a typical processing enterprise, judging by the average 0.6 factor rule. Some estimates also suggest a phase of decreasing unit costs followed by a phase of increasing costs. Nonetheless dry mills could be somewhat larger than the current industry standard, unless other scarce factors limit capacity expansion. Despite the statistical significance of an average cost-size relationship, average capital cost for plant of a given size at a particular location is still highly variable due to costs associated with unique circumstances, possibly water availability, utility access and environmental compliance.

Molecular characterization of birnaviruses isolated from wild marine fishes at the Flemish Cap (Newfoundland)

Several isolates of aquatic birnaviruses were recovered from different species of wild fish caught in the Flemish Cap, a Newfoundland fishery close to the Atlantic coast of Canada. The nucleotide sequence of a region of the NS gene was identical among the isolates and was most similar to the Dry Mills and West Buxton reference strains of infectious pancreatic necrosis virus (IPNV). Phylogenetic analysis of the sequence of a region of the VP2 gene demonstrated that the isolates were most closely aligned with the American strains of IPNV serotype A1. Electron microscopy of virus structures clarified and concentrated from cultures of infected chinook salmon embryo (CHSE-214) cells revealed a majority of typical IPNV-like icosahedral particles, as well as a low proportion of type I tubules having a diameter of approximately 55 nm and a variable length of up to 2 microm. The tubules could be propagated in cell cultures, but always in the presence of low proportions of icosahedral particles. Cloning of selected isolates by serial dilution yielded preparations with a high proportion of the tubular structures with a density in CsCl gradients of approximately 1.30 g cm(-3). Polyacrylamide gel electrophoresis revealed the material in the band was composed of the IPNV pVP2 and VP2 proteins.

Technical note Cr(VI) generation during milling

An investigation of the dry milling of chromite at a ferroalloy producer revealed high Cr(VI) concentrations in the milled ore. This promted further investigation into the possible generation of Cr(VI) during milling. Experiments conducted in the laboratory proved that Cr(VI) is generated during dry milling. This fact implies that the health of workers on and around such milling installations could be compromised. Leaching of Cr(VI) from settled dust originating from dry mills could also lead to soil and groundwater contamination. Due to the vast differences in toxicity of Cr(III) and Cr(VI), chemical analysis is often required to distinguish between these two oxidation states. However, pulverising or milling of samples during sample preparation, which is common practise for solids, could lead to misleading analytical results. This investigation proved that even material that initially contained no Cr(VI) could be regarded as toxic if treated incorrectly.