Ground Particles Research Articles

Data-based equation to predict power and energy input for grinding wheat straw, corn stover, switchgrass, miscanthus, and canola straw

This study investigated size reduction of five herbaceous species: wheat straw, corn stover, switchgrass, miscanthus, and canola straw. The biomass samples were air-dried to moisture content of 10%. The instantaneous power input to grind the material was recorded. Grinding wheat straw, corn stover, and canola straw using a 3.2 mm screen inside the hammer mill consumed 32 to 35 kWh/t whereas grinding switchgrass and miscanthus on the same screen used 22 kWh/t of energy. All five biomass samples required almost the same amount of energy input (13 to 20 kWh/t) when a 6.4 mm screen was installed in the hammer mill. Some species like corn stover produced strings of fiber causing blockage of the inlet to the grinder. A linear relation was developed between geometric mean diameter (dgw) of the ground particles and the screen size (SS). The screen size inside the hammer mill was used as the representative size of the particles. The Rittinger equation was fitted to the size data to estimate the equation constant kR from energy input vs. screen size. The kR value ranged from 96 to 267 J mm/g depending on the species.

Minimum fluidization velocity of ground chip and ground pellet particles of woody biomass

The present work reports the hydrodynamic properties of ground chip (GC) and ground pellet (GP) particles of pine wood. Ground particles are made by grinding whole wood chips and whole wood pellets in a hammer mill equipped with a 3.2mm screen. The average diameter of the particles measured by using image processing is 0.75mm for GC particles and 1.31mm for GP particles. The average density of particles is 1.33g/cm3 for GC and 1.43g/cm3 for GP. Pressure drop versus the air flow across a bed of particles is measured and the parameters of Ergun equation are estimated. GP particles have a minimum fluidization velocity of 15.2cm/s which is much higher than the minimum fluidization velocity of GC particles at 8.5cm/s. Both GC and GP particles undergo channeling and bed separation during fluidization. No bubbling regime was observed.

ИССЛЕДОВАНИЕ ИНТЕНСИВНОСТИ ГИДРОМОНИТОРНОЙ ОТБОЙКИ ПОРОД

В статье рассмотрено влияние содержания тонкодисперсных грунтовых частиц в напорной воде на силу удара струи гидромонитора о забой. По результатам моделирования в лабораторных условиях составлена математическая модель расчета силы удара струи о забой. Произведено сравнение с известными зависимостями.

Sedimentation assisted preparation of ground particles of silica monolith and their C18 modification resulting in a chromatographic phase of improved separation efficiency

The sedimentation procedure has been adopted in production of ground silica monolith particles to improve chromatographic separation efficiency of the resultant phase. First, silica monolith particles have been successfully prepared in a large scale by a sol-gel process followed by grinding. The particles after calcination were separated by sedimentation into three zones using an Imhoff sedimentation cone. The particles of the bottom zone were derivatized with a C18 ligand and end-capped. The sedimentation process was found to not only eliminate troublesome minute particles but also narrow down the particle size distribution. The resultant phase was packed in glass lined stainless steel micro-columns. The average number of theoretical plates (N) of the columns for a test mixture was 47,000 and 29,300 for the 300 and 150mm columns (1mm internal diameter), corresponding to 157,000/m and 195,000/m, respectively.

Development of empirical drying correlations for ground wood chip and ground wood pellet particles

ABSTRACTIn this research, the drying rates of ground chip and ground pellet particles of pine were investigated. Pulp wood chips and whole pellets were ground in a hammer mill. Grinder screens with perforations 3.2, 6.3, 12.7, and 25.4 mm were installed in the hammer mill to produce a range of ground particle sizes. Particle size of ground chips had a broad range of 0.25–6 mm, while pellet particles had a smaller range of 0.5–2 mm. Initial moisture contents of ground particles were conditioned to 0.1, 0.3, and 0.5 (dry mass basis) using sprayed water. The moistened particles were dried isothermally in a thin-layer dryer set at the temperatures of 50, 100, 150, and 200°C. Chip particles dried faster than pellet particles of the same particle sizes. In addition to water loss, the particles exposed to a temperature of 200°C lost 3–7% of their dry mass. Smaller particles lost more dry mass than larger particles. The modeling revealed that the drying constants of pellet particles are less than those of chip particles with the same particle size.

A combined experimental and DEM approach to determine the breakage of particles in an impact mill

Population balance models (PBMs) are widely used to predict particle size variation in grinding. An accurate determination of particle breakage and selection functions in PBMs requires detailed knowledge on the stress causing particle breakage. This study proposed a combined experimental and numerical approach to determine the two functions. In the physical experiments, the breakage of individual iron ore particles in a Fritsch impact mill with different mill speeds was investigated and the product sizes were analysed. The simulations based on the discrete element method (DEM) were carried out under similar conditions to examine the dynamics of the particles inside the mill, such as number of impacts, impact velocity and impact angle. The simulation results showed that most of the particles experienced multiple impacts before they were ejected from the mill. The first impacts occurred at low impact energy which had no contribution to particle breakage. The second and third impacts, on the other hand, posed high impact energy on the particles and were the main cause of particle breakage. Based on the simulation results and the experimental data, two semi-empirical selection and breakage functions were determined. The accuracy of the equations was confirmed by applying them to predicting the size distribution of ground particles under different mill conditions.

Effect of design and operational parameters on particle morphology in ball mills

Different factors involving in grinding of ore cause various breakage mechanisms. These different mechanisms differ the morphology of ground particles. In this study, the effect of ball mill types, feed sizes, and ball surface area have been investigated on the morphology of ground quartz particles using MBL cruise optical microscope and Olympus E-510 camera. Measured two-dimensional particle projection was expressed mathematically such as circularity, roundness and aspect ratio by ImageJ software. >20,000 particles were morphologically measured for image analysis. Results show that circularity and roundness of ground particles are enhanced in an ordinary ball mill equipped with smooth liner (OBM). While higher aspect ratio of ground particles are achieved in cylindrical ball mill equipped with wavy liner (CBM). Consequently, the dominant breakage mechanism for OBM and CBM are abrasion and impact, respectively. Circularity and roundness values of coarse-grained ground particles are more than fine-grained particles. The increase of ball surface area causes the increase of circularity as well as roundness values and the decrease of aspect ratio value.

Influence of Cryogenic Attrition Ball Milling on the Particle Size of Microcrystalline Cellulose at Different Moisture Contents

In this study the effect of attrition ball milling on cellulose particle size distribution was studied. The effect of moisture content of cellulose and grinding time were examined and grinding was carried out at room temperature and under cryogenic conditions, as well. The grinds obtained were studied with electron microscope, and the characteristic dimensions of ground particles were determined using image processing software. Results revealed that effective size decrease of cellulose particles was achieved at low moisture content at room temperature, while under cryogenic conditions high moisture content was necessary, i.e. frozen moisture enhances grinding efficiency in the latter case.

ジェットミル粉砕プロセスにおける粒子径分布のリアルタイムモニター

The optimum parameters for grindings by a jet mill is determined by many experiments, changing parameters, such as the feeding speed, the inlet pressure, and measure the particle size distribution of the corrected powder. This process takes long time and work load. To reduce this optimization time, in-line monitoring of the particle size distribution for the jet mill process was investigated. We could successfully monitor the particle size distribution of the ground particles, just after the jet mill process, using an in-line laser diffraction measurement system. A proportional relationship was observed between the supplying speed of the material, and the Volume based median diameter, Dv50 of the ground powder. When we changed the feed rate step by step, we could see the Dv50 value was changed with those steps.

Size, shape and flow characterization of ground wood chip and ground wood pellet particles

Size, shape and density of biomass particles influence their transportation, fluidization, rates of drying and thermal decomposition. Pelleting wood particles increases the particle density and reduces the variability of physical properties among biomass particles. In this study, pine chips prepared for pulping and commercially produced pine pellets were ground in a hammer mill using grinder screens of 3.2, 6.3, 12.7 and 25.4mm perforations. Pellets consumed about 7 times lower specific grinding energy than chips to produce the same size of particles. Grinding pellets produced the smaller particles with narrower size distribution than grinding chips. Derived shape factors in digital image analysis showed that chip particles were rectangular and had the aspect ratios about one third of pellet particles. Pellet particles were more circular shape. The mechanical sieving underestimated the actual particle size and did not represent the size of particles correctly. Instead, digital imaging is preferred. Angle of repose and compressibility tests represented the flow properties of ground particles. Pellet particles made a less compacted bulk, had lower cohesion and did flow easier in a pile of particles. Particle shape affected the flow properties more than particle size.

Dependence of morphology on anionic flotation of alumina

Morphological features of particles upon size reduction affect flotation recoveries in terms of kinetics, bubble-particle interactions and even suspension properties. The significance of surface roughness and shape factor of particles on flotation recovery and their underlying mechanism has been shown to be of importance. Towards this aim, a series of micro-flotation tests have been performed with original, ground and ground-abraded alumina particles in the presence of sodium dodecyl sulfate collector in order to demonstrate the influence of morphological features on flotation recoveries. The flotation results are discussed with the help of literature data on shape and roughness of various types of particles.

ABS/HIPS blends obtained from WEEE: Influence of processing conditions and composition

ABSTRACTThe recycling of acrylonitrile–butadiene–styrene (ABS) and high‐impact polystyrene (HIPS) from postconsumer electronic equipment housing was investigated. A preliminary study of shot size and particle size effects on the mechanical properties of ABS/HIPS (50/50) blends obtained directly via injection molding was conducted. Injection‐molded specimens of ABS/HIPS blends, obtained at different compositions with or without previous extrusion, were subjected to mechanical, thermal, and morphological testing. Preliminary studies showed that a smaller particle size resulted in higher tensile and impact strength, regardless of the shot size used during injection molding. ABS/HIPS blends obtained using previous extrusion presented a slight increase in Young's modulus and a decrease in elongation at break and impact strength. The increase in glass‐transition temperature related to the Polybutadiene (PB) phases of these blends indicated a possible increase in crosslinking structures during extrusion. In addition, these blends showed a coarse and heterogeneous morphology, suggesting that ABS did not completely mix with HIPS. Compared to processing conditions, the blend composition appeared to have a much stronger effect on the mechanical properties. The results obtained suggest the possibility of obtaining ABS/HIPS blends directly via injection molding as long as small ground particles are used. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43831.

Size Reduction Characteristics of Yellow Poplar in a Laboratory Knife Mill

ABSTRACT Size reduction is one of the major pre-processing operations in using biomass as a source of energy or rawmaterials for forest products industry. The grinding characteristics of dried yellow poplar wood chips wereinvestigated using laboratory knife mill with three different screen aperture diameters to provide the basicinformation for the optimizing of size reduction processes in biomass industry. Average specific energy con-sumptions were 0.157, 0.137, and 0.093 Wh/g for the screen aperture diameters of 5.0, 7.5, and 9.0 mm, respectively. According to the results of size distribution analysis of ground particles, the sizes of the most of ground particles were much smaller than the aperture diameters of the screens installed on knife mill used in this study. Keywords : size reduction, biomass, knife mill, specific energy consumption for milling, particle size distribution, Liriodendron tulipifera L. 1 Date Received November 19, 2015, Date Accepted December 28, 2015 2 College of Agriculture and Life Science, Chonnam National University, Gwangju 61186, Republic of Korea

An assessment of triboelectrification effects on co-ground solid dispersions of carbamazepine

One of strategies adopted to improve the dissolution rates of poorly soluble drugs is by co-grinding the drug with a hydrophilic carrier. However, the introduction of mechanical forces during the grinding process can lead to changes in the physicochemical characteristics as well as an increase in the surface free energy of the ground particles, which causes an alteration in the electrostatic properties of these particles. The solid state characteristics of glucosamine hydrochloride (GLU) and carbamazepine (CBZ) and their co-ground mixtures were studied using DSC, XRPD and SEM. These revealed that polymorphic transformations occurred due to the grinding process. The influence of grinding time on the triboelectrification properties of the formulations was also studied. Both pure CBZ and GLU powders were predominantly electro-positively charged and their charging properties increased with increasing grinding time. CBZ:GLU physical mixtures exhibited complicated bipolar charging behaviour, however, when subjected to grinding, these mixtures demonstrated mainly electronegative charge properties. The influence of both grinding time and CBZ content within CBZ:GLU mixtures was examined. The value of net-electronegative-charge density of CBZ:GLU mixtures was shown to increase with grinding time and/or when increasing the percentage proportion of CBZ up to 30% w:w. This study helps to provide information about the handling of these formulations and gives a formulator tools to ascertain appropriate ratios for handling and possible simultaneous dissolution improvements.

Effect of roughness and shape factor on flotation characteristics of glass beads

Abstract The effect of surface roughness and shape factor on behavior of particles in flotation has been investigated. Surface roughness of various degrees was applied on spherical glass beads of −150 +106 μm by means of acid etching. The same procedure was also performed on ground glass beads of the same size interval with different shape factors. The effect of these variations on surface morphology of particles was investigated in terms of flotation recovery, contact angle, and bubble-particle attachment. An Atomic Force Microscope (AFM) was used for surface roughness characterizations and a correction methodology on roughness measurements of spherical particles is proposed. A digital image analyzer was used for shape factor characterizations. It is shown that increase in surface roughness improves the flotation recovery, contact angle, and bubble attachment. Shape factor, however, was found to be more predominant in flotation and bubble attachment. This is attributed to the effect of sharp edges of ground particles which triggers the film rupture process and shortens the attachment time.

낙엽송 반탄화 바이오매스를 이용한 고밀도 고형연료 생산

본 연구에서는 반탄화된 낙엽송 칩을 분쇄한 후 그 입자를 이용한 펠릿성형에서 함수율과 입자크기의 영향을 반탄화 조건(<TEX>$220^{\circ}C$</TEX>-50분, <TEX>$250^{\circ}C$</TEX>-50분, <TEX>$250^{\circ}C$</TEX>-120분)에 따라 조사하였다. 반탄화 후 함수율은 0.69~1.75%로 반탄화 처리전의 5.26%보다 낮았으나, 회분이나 발열량은 증가하였다. 또한 반탄화에 의한 중량감소율은 크게 증가하였는데 이는 헤미셀룰로오스의 분해가 활발하게 일어났기 때문으로 생각된다. 반탄화 낙엽송 칩에 포함된 탄소함량은 반탄화 처리 전 낙엽송 칩과 비교하여 증가하였으며 수소와 산소함량은 감소하였다. 반탄화 낙엽송 칩에 포함된 리그닌과 글루칸 함량은 반탄화 정도가 증가할수록 증가하였으며 헤미셀룰로오스는 감소하였다. 반탄화 칩을 분쇄하여 입자크기분포를 비교한 결과 높은 반탄화 조건은 낮은 반탄화 조건에서보다 1 mm 이하의 미세분 함량이 높았고 <TEX>$500{\AA}$</TEX> 이상의 macropore가 생성되었다. 반탄화 분쇄 입자를 이용한 펠릿성형 과정에서 입자크기와 관계없이 반탄화 분쇄 입자의 함수율이 증가할수록 투입된 반탄화 분쇄 입자가 받는 압력은 감소하였으며 펠릿길이는 증가하였다. In this study, the effects of moisture content and particles size of ground particles of torrefied larch chips on the pelletizing process were investigated depending on torrefaction conditions (<TEX>$220^{\circ}C$</TEX>-50 min, <TEX>$250^{\circ}C$</TEX>-50 min, <TEX>$250^{\circ}C$</TEX>-120 min). The moisture content in the torrefied chip decreased to 0.69~1.75%, while ash content and calorific value increased compared to untreated chip. In addition, weight loss significantly increased during torrefaction due to hemicellulose degradation. The carbon content in torrefied larch chip increased compare to untreated larch chip, while the hydrogen and oxygen contents decreased. The lignin and glucan contents in torrefied larch chip increased with increasing severity of the torrefaction condition, while hemicellulose decreased. In the particle size distribution of ground particles of torrefied larch chip, larch torrefied at severe conditions was found to produce smaller particles (~1 mm) than that of the larch torrefied at mild conditions. Macropore (over <TEX>$500{\AA}$</TEX>) in the torrefied particle was produced during torrefaction. During the pelletizing using ground particles of torrefied larch chip, the pressure needed in pelletizing decreased and pellet length increased with increasing moisture content, regardless of the particle size.

Optimization of supercritical fluid extraction: Polydisperse packed beds and variable flow rates

This theoretical study examines variable-in-time flow rates v(t) and different ways of packing polydisperse ensemble of ground particles as controls in supercritical fluid extraction (SFE) to maximize the extraction yield. The so-called packing function χ is introduced to describe the local particle-size distribution in the pack along the extraction vessel. The research is based on the modified shrinking-core (SC) model for the mass transfer inside particles and assumes the pseudo-steady solvent flow in the SFE vessel. It is rigorously proven that for any variable flow rate v(t) and overall particle-size distribution F, the corresponding locally-monodisperse stratified (LMS) packing χ0 maximizes the current amount of extracted solute, while the appropriate filtration policy extends the domain of efficient particle-size distributions. Sufficient conditions that guarantee a certain extraction degree at a fixed time are deduced and formulated in terms of F-distribution. Being of obvious practical significance for finely ground substrates, optimization is shown to be rather limited for relatively big particles (commonly used in laboratory experiments), and only longer extraction times, higher oil solubility and diffusion rates allow noticeable increase in the extraction yield in this case.

MODELING OF SIZE REDUCTION, PARTICLE SIZE ANALYSIS AND FLOW CHARACTERISATION OF SPICE POWDERS GROUND IN HAMMER AND PIN MILLS

Comparative study using Rosin-Rammler-Sperling-Bennet (RRSB) and Rosin-Rammler model parameters, including particle size analysis and flow characterization helps in identifying whether hammer mill or pin mill is suitable for grinding three selected spices, namely, cinnamon, coriander and turmeric. Model parameters like degree of uniformity in size and statistical average diameter of ground products, mean sizes of ground particles, Bond’s work index, specific energy consumption for grinding, and flow characteristics indicate cinnamon and coriander are suitable for grinding with hammer mill while turmeric is suitable for grinding with pin mill.

Impact of mechanochemical effect on chalcopyrite leaching

Stirred milling is an enabling technology to process low grade finely disseminated ore bodies. Besides size reduction, stirred mill has the ability to deliver high energy to particles which facilitate crystal structure distortion. High energy stirred milling experiments (up to 300kWh/t) were carried out on chalcopyrite concentrate. The media size, mill speed and slurry % solids were kept constant in this experiment. The only operational variable is milling time that results different levels of specific energy. The feed and ground particles were characterized for particle size distribution and mineral phase analysis (XRD). Mechanochemical effect was quantified by calculating the degree of crystallinity, crystallite size and lattice strain. The feed and ground sample undergo leaching test in five different lixiviants. The lixiviants chosen were sulphuric acid, hydrochloric acid, nitric acid, ferric sulfate and ferric chloride. The minimum particle size and degree of crystallinity obtained were 3.7μm and 42% respectively at 113kWh/t. Ferric chloride exhibits the highest Cu dissolution (up to 75%) when it was ground at 113kWh/t. Based on the results, this paper has suggested two circuit layouts that may assist mechanochemical effect in order to enhance leaching. Mechanochemical effect exhibited during high energy fine grinding enhances downstream processes i.e. leaching. This is not taken into consideration when evaluating the efficiency of the milling circuit. In the future the milling circuit efficiency should take into consideration the reduction in particle size and mechanochemical effect during milling circuit efficiency evaluation.

Dynamic image based shape analysis of hard and lignite coal particles ground by laboratory ball and gyro mills

A new real-time 3D dynamic image analysis system was used to measure the particle shapes of different type of coal samples (lignite and hard coals) ground by different mills (ball and gyro mills). Shape factors such as circularity, ellipse aspect ratio (EAR), bounding rectangle aspect ratio (BRAR) and Feret aspect ratio (FAR) described the results. At least 6400 particles were measured for each mill product indicating the accuracy of the results achieved with 99% statistical significance. Although experiments were performed on different ranked coal samples, there is a clear difference in the particle shapes generated by the grinding methods tested. Results indicated that the ball mill ground particles had the highest aspect ratios (EAR, BRAR, and FAR) with the lowest circularity. However, the gyro mill produced particles with highest circularity along with the lowest aspect ratios. Thus ball milled particles had the highest elongated particles with the lowest rounded particles. On the other hand, gyro mill products included the highest rounded particles and the lowest elongated particles. This relative difference in shape was attributed to the difference in grinding action involved in the ball and gyro mills. Results will find applications in various coal characterization, preparation, and utilization processes.