Jet Mill Research Articles

Study on the pozzolanic activity of ultrafine circulating fluidized-bed fly ash prepared by jet mill

The pozzolanic activity of ultrafine circulating fluidized-bed (CFB) fly ash prepared by jet mill has been investigated in this research. The ultrafine powder properties and the hydration heat release process of the cement blended with ultrafine CFB fly ash have been obtained. Furthermore, the dissolution characteristics of SiO2 and Al2O3, the Ca2+ absorption capacity in saturated Ca(OH)2 solution, and the polymerization degree of Si-O and Al-O polyhedrons have been studied to further clarify the mechanism of ultrafine grinding on pozzolanic activity. Compared to raw CFB fly ash (RCFA), the particle morphology, the pore structure of ultrafine CFB fly ash (UCFA, D50 ≤ 5 μm), and the pozzolanic activity of UCFA are significantly improved. The hydration rate of cement blended with UCFA is accelerated, and the total heat release is close to that of pure cement within 72 h. Ultrafine grinding increases the SiO2 and Al2O3 dissolution rate of CFB fly ash and Ca2+ absorption capacity in saturated Ca(OH)2 solution, mainly due to the decrease of polymerization degree of Si-O and Al-O polyhedrons and particle size of CFB fly ash.

Understanding Crystal Cleavability and Physical Properties of Crystal Surfaces Using in Silico Simulation.

In the drug formulation process, compound dissolution rate and wettability may be improved by grinding. However, there is no method to understand the effects of the wettability of the crystal facets of the ground product. Here, acetylsalicylic acid (ASA) was used to evaluate the changes in crystal morphology and dissolution rate by jet milling using powder X-ray diffraction and in silico simulation. Several cleavage facets were observed in cube crystals, and the (0 0 2) facet was observed in plate crystals. Furthermore, the dissolution rate of the ground samples per unit area decreased with the cleavage of the (1 0 0) and (0 0 2) facets. The polar surface energy of the ground sample decreased with increasing grinding pressure. The simulation results showed that the absolute attachment energy of the (1 0 0) and (0 0 2) facets was lower than that of the other crystal facets. Moreover, atoms with low polarity were present on the crystal surface of (0 0 2). The wettability and dissolution rate of the (0 0 2) facet were worse than those of the (1 0 0) facet. It was suggested that the dissolution rate of the ground sample was affected by the wettability of the crystal facet caused by the cleavage. The cleavability and wettability may be understood by simulation.

Assessment of Chokeberry Powders Quality Obtained Using an Innovative Fluidized-Bed Jet Milling and Drying Method with Pre-Drying Compared with Convection Drying

There is a need and great interest among food producers in obtaining powders from fruit and vegetables of both high nutritional value and sensory qualities superior to those hitherto obtained by convection drying (CD) and spray drying methods and cheaper to prepare than the sublimation method. This study is focused on whether powders can be obtained from fruit berries with a sticky structure, using the chokeberry (Aronia melanocarpa) as a test example, by a combined fluidized-bed jet milling and drying (FBJD) of pre-dried fruit by CD to an adequate water activity (aw). The pre-drying step reduced sticking between fruit particles during the simultaneous drying and grinding processes of the FBJD method in order to obtain powders of desired granulation. Three different pre-drying temperatures of 50, 60, and 70 °C were tested for levels of microorganisms in chokeberries at a water activity of 0.4. Vitamin C content and antioxidant properties were also examined along with polyphenol separation. Fruit pre-dried at 60–70 °C had significantly higher vitamin C and polyphenolic content and greater antioxidant properties than those pre-dried at 50 °C. Further studies were thus undertaken on powders pre-dried at 70 °C in which antioxidant properties, vitamin C, and polyphenols content were also compared with CD obtained powders. The FBJD method combined with CD pre-drying proved superior to just using the CD method, where powders had a greater preservation of vitamin C at 84% (CD powders 35%), a 12% higher total polyphenol content, and a 10% higher antioxidant activity. The test method also uses a much shorter drying time than the CD method, because the grinding of the hard-textured material takes only few minutes.

Automatic control of jet grinding on the basis of acoustic monitoring of mill operating zones

Purpose. Increasing the jet mill productivity by use of automatic control of the grinding chamber filling level based on the acoustic monitoring results of the jet grinding process. Methodology. Simulation is performed in MATLAB. Acoustic signals of the mill operating zones are used to determine the grinding process parameters. Findings. A simulation model of the automatic jet mill control system is created, which takes into account the inertia of material flows in the grinding chamber and classifier, as well as the main disturbing influences on the process of forming the mill output flow. To analyze the control process, there are three main parts the information component (regulator and technical means of automation), a set of mathematical models that describe the physical processes in the grinding chamber and in the classifier. A study on the automatic control process of the grinding chamber filling is made under the condition of determining the controlled value indirectly through spectral analysis of the acoustic signal in the mill. The insignificant influence of perturbations on the controlled quantity due to very slow filling of the chamber with material in comparison with the period of stream fluctuations at a chamber entrance owing to perturbation action is shown. Originality. For the first time the possibility has been proved of using a relay regulator in control of the grinding chamber filling, determined indirectly through spectral analysis of the acoustic signal in a jet mill. The efficiency of the mill operation at automatic control of the grinding chamber filling according to the relay law is investigated. Practical value. It is shown that with the transition from automated to automatic control of the grinding chamber filling, the mill productivity increases by 1015%. The obtained results are used to build a system of automatic jet mill control.

Investigate the effect of process parameters of magnetic inductively assisted spark plasma sintering (SPS) of iron oxide (Fe3O4) on microstructure behaviour – Part I

Abstract A new magnetically assisted spark plasma sintering as a novel method of adding a continuous intensive magnetic field during the sintering process was briefly introduced as an alternative method of traditional SPS in which the sintering process passed through several processes started with jet milling, aligning, densifying, and then ended up with sintering during the production of a material with excellent magnetic, electrical, and mechanical properties. Furthermore, the use of an external magnetic field parallel with the sintering process leads to a shortening of these processes in addition to driving the molten metal in a certain way for grain refinement and grain re-orientated, resulted in the reduction of porosities and cavities. In this paper (Part I) Iron oxide (Fe3O4) nanopowder has been characterized to study the sintering process's effect on microstructure behavior using FESEM, XRD, XPS, and VSM. Based on the results obtained, Fe3O4 has cubic shaped particles with an average size of 100–200 nm, and the indexed peaks are (1 1 1), (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1), and (4 0 0), which confirmed with the standard.

Analysis of hold-up and grinding pressure in a spiral jet mill using CFD-DEM

A spiral jet mill was simulated using Discrete Element Method modelling and Computational Fluid Dynamics. The particle behaviour and fluid motion were analysed as a function of hold-up and grinding pressure. Particle collision energy was predicted to be prevalent along the bed surface and in front of the grinding jets, as shown through the collision data recorded. The bed itself affects the fluid flow field, as momentum is transferred to the particles. Increasing the grinding pressure does not result in a proportional increase in the kinetic energy of the particle system, as the high pressure jets begin to penetrate the bed with greater ease. The particle bed moves as ‘plug-flow’, with the layers of the bed closest to chamber wall.

Identification of factors to reduce the energy costs of dispersing in jets

This paper reports the operational indicators for industrial-sized jet grinding plants (JGP). The dependences of specific energy consumption on productivity have been generalized. The technological patterns in the working process were considered in terms of reducing energy costs using the operation of gas-jet and steam-jet mills at the Vilnohirsk Mining and Metallurgical Plant (VMMP) involved in crushing zircon to 60 µm as an example. The acoustic activity in the grinding area has been studied relative to the concentration of μ and in combination with the technological assessment of the mill’s performance. A broadband piezo sensor was used in the assessment of acoustic emission (AE). It is shown that the acoustic activity of the grinding zone contains information about the effects of dispersion and energy costs for grinding, which makes it possible to estimate and minimize the specific energy costs. It has been established that the principal factors of JGP energy intensity are the initial temperature of the energy carrier, which sets the speed of the jet, and the concentration of solid phase in the jet, which changes the effects of dispersing. A technique has been proposed for the current assessment of energy costs in the working process of dispersion based on the experimental acoustic data and a pattern of the acoustic dimensional effect. The estimated acoustic indicators of the energy cost of a jet mill for the conditions of VMMP were derived. To reduce the energy cost of dispersion (γs@0.42 J/cm2), the effect of adjusting the loading of jets to γN@1.8 J/pulse is employed. Thus, this study has investigated the dispersal of solid loose material in jets with the involvement of acoustic information about the operation of jet mills, which makes it possible to comprehensively assess and minimize (optimize) the specific energy costs of grinding

Eulerian Multiphase Simulation of the Particle Dynamics in a Fluidized Bed Opposed Gas Jet Mill

The compressible and turbulent gas–solid multiphase flow inside a fluidized bed opposed jet mill was systematically investigated through numerical simulations using the Euler–Euler approach along with the kinetic theory of granular flow and frictional models. The solid holdup and nozzle inlet air velocity effects on the gas–solid dynamics were assessed through a detailed analysis of the time-averaged volume fraction, the time-averaged velocity, the time-averaged streamlines, and the time-averaged vector field distributions of both phases. The simulated results were compared with the experimental observations available in the literature. The numerical simulations contributed to a better understanding of the particle–flow dynamics in a fluidized bed opposed gas jet mill which are of fundamental importance for the milling process performance.

ОСОБЕННОСТИ ПРОЦЕССОВ ГИДРАТАЦИИ ВЯЖУЩИХ КОМПОЗИЦИЙ С ИСПОЛЬЗОВАНИЕМ ОТХОДОВ ВСПУЧЕННОГО ПЕРЛИТОВОГО ПЕСКА

The results of studying the processes of hydration of binder compositions obtained at different ratios of cement and waste of expanded perlite sand (from 5 to 10%), in a vortex jet mill, under different modes of mechanical and chemical activation - from one to three passes are presented. Comprehensive studies of hydration products by X-ray phase analysis and electron microscopy indicate that the use of highly dispersed wastes from the production of expanded perlite sand in binding compositions allows an increase in the content of hydrated neoplasms due to an increase in the degree of hydration of the main clinker phases, as well as due to the pozzolanic activity of these wastes. The contact zone between the hydrated compounds and the remnants of the grains of the original cements has a special effect on the formation of a high-strength structure of the cement stone. The structure formation of a cement stone depends on a number of factors, which can be influenced by various technological methods. When designing compositions of cement composites, it is necessary to ensure that hydration products in the created system are present along with low-basic calcium hydrosilicates and high-basic ones. Their ratio should be such that carbonization does not reduce the volume of the formed crystalline phase of the cement stone. The composition of the hydration products determines the level of supersaturation of the solution, the type and number of impurities soluble in water, the duration of the hydration process, etc. The chemistry of the reactions of the hydrated system changes accordingly. It is found that the intensity of the diffraction maxima, indicating the presence of highly basic calcium hydrosilicates in the compositions that underwent mechanical activation, increases by 18% in comparison with the ordinary PC. The strength characteristics of Portland cements, which have undergone mechanical activation, increase up to 15% compared to the original PC. The most rational binder composition is established in terms of composition (No. 6), mechanical activation and maximum compressive strength at 28 days of age – 69.1 MPa.

Jet milling conditions impact on wheat flour particle size

Jet milling is an emerging, size reduction technique for producing superfine powders in one-step process. The aim of the present article was the research about the efficiency of jet milling process on the wheat flour micronization. A mathematical power model is proposed to describe the effect of feed rate and air pressure on the final flour particle size and energy consumption. A sample of soft wheat flour was grοund using a jet mill at different feed rate (FR) and air pressure (AP) (2–18 kg/h at 4 and 8 bar, respectively). Τhe decrease in FR and further increase in AP resulted in finer flour reaching the lowest value of 10.62 μm. The energy-size reduction equations revealed that the particle size, as well as the energy consumption, were mainly influenced by FR and to a lower extent by AP. FR of 70% was the limit for energy efficient grinding. Α short grinding at high FR and AP is also preferable as damaged starch content was lower.

On the Structural and Magnetic Properties of Mn-Bi Alloy Jet Milled at Different Feed Rates

Mn50Bi50 alloy was prepared using arc melting method with subsequent homogenization treatment. The homogenized alloy was crushed and subjected to jet mill at different feed rates. The weight fraction of the LTP MnBi phase determined by the Rietveld refinement of the XRD pattern was found to be 89% in the as-homogenized and crushed alloy. The crushed alloy was subjected to jet milling at different feed rates from 0.5 to 1.5 g/min. Structural studies show that increase in feed rate leads to phase decomposition. Magnetic studies show that as-homogenized crushed alloy exhibits a magnetization of 60 emu/g. Jet milling leads to increase in coercivity and a decrease in magnetization. However, it was found that increase in the feed rate during jet milling leads to decrease of both coercivity and magnetization. Microstructural studies show that jet milling leads to decrease in particle size. Jet milling done at a lower feed rate helps in yielding the lowest average particle size compared to remaining feed rates in the Mn-Bi alloy. The spin reorientation transition temperature of the Mn-Bi alloy decreases with jet milling and varies at different feed rates. The coercivity of the Mn-Bi powder jet milled with a lower feed rate increases from 14.7 kOe at room temperature to 19.4 kOe at 400 K.

Amplification of Vitamin D2 in the White Button Mushroom (Agaricus bisporus) by UV-B Irradiation and Jet-Milling for Its Potential Use as a Functional Ingredient.

The objective of this study was to amplify vitamin D2 in white button mushrooms using ultraviolet (UV-B) irradiation and to prepare a vitamin D2-fortified superfine mushroom powder through jet milling. Mushrooms irradiated with UV-B for 30 min had a vitamin D2 concentration of 8.19 μg/g, an amount about 400 times greater than that of the control (0.02 μg/g). The vitamin D2-fortified mushrooms were then freeze-dried and conventionally ground or jet-milled to obtain coarse (Dv50 = 231 μm), fine (Dv50 = 106.3 μm), and superfine (Dv50 = 7.1 μm) powders. The vitamin D2 content was retained during the preparation of the powders. The physical characteristics were evaluated by scanning electron microscopy and hydration properties. The superfine powder of vitamin D2-amplified mushrooms was suitable for use as a functional ingredient because its roughness was significantly reduced, and it had a neutral aroma and taste as determined by descriptive analysis.

Analysis of grinding in a spiral jet mill. Part 1: Batch grinding

Jet milling is widely used in several industrial applications to produce fine particles with a narrow size distribution. We studied by means of experiments, the influence of grinding pressure, holdup and milling time on the performance of a spiral air jet-mill operating in a batch mode, with respect to the particles. The experimental results indicated that a uni-modal size distribution of feed particles yields trimodal particle size distributions. The data for variation of the mean particle size and specific surface area with energy supplied collapsed to a curve for all the cases studied, indicating that mean size is primarily dependent on the energy supplied. A population balance model for the dynamics of the batch milling process, based on empirical breakage functions is developed, which describes the experimental results quite well. The form of the breakage functions provides an insight into the mechanisms of breakage of particles.

Mechanochemical and Size Reduction Machines for Biorefining.

In recent years, we have witnessed an increasing interest in the application of mechanochemical methods for processing materials in biomass refining techniques. Grinding and mechanical pretreatment are very popular methods utilized to enhance the reactivity of polymers and plant raw materials; however, the choice of devices and their modes of action is often performed through trial and error. An inadequate choice of equipment often results in inefficient grinding, low reactivity of the product, excess energy expenditure, and significant wear of the equipment. In the present review, modern equipment employing various types of mechanical impacts, which show the highest promise for mechanochemical pretreatment of plant raw materials, is examined and compared—disc mills, attritors and bead mills, ball mills, planetary mills, vibration and vibrocentrifugal mills, roller and centrifugal roller mills, extruders, hammer mills, knife mills, pin mills, disintegrators, and jet mills. The properly chosen type of mechanochemical activation (and equipment) allows an energetically and economically sound enhancement of the reactivity of solid-phase polymers by increasing the effective surface area accessible to reagents, reducing the amount of crystalline regions and the diffusion coefficient, disordering the supramolecular structure of the material, and mechanochemically reacting with the target substances.

Inhalable Hydroxychloroquine Powders for Potential Treatment of COVID-19.

Background: Hydroxychloroquine (HCQ) is one of the repurposed drugs proposed for the treatment of coronavirus disease 2019 (COVID-19). However, all the published clinical trials involve oral administration of the drug, although the disease is primarily a respiratory one. Direct inhaled delivery could reduce the side effects associated with oral use and ensure a high concentration of the drug in the lungs. In this study, inhalable HCQ powders were prepared and characterized for potential COVID-19 therapy. Methods: Hydroxychloroquine sulfate (HCQ-sul) was jet milled (JM) followed by conditioning by storage at different relative humidities (43%, 53%, 58%, and 75% RHs) for 7 days. The solid-state properties, including particle morphology and size distribution, crystallinity, and vapor moisture profiles of HCQ-sul samples, were characterized by scanning electron microscopy, laser diffraction, X-ray powder diffraction, differential scanning calorimetry, thermogravimetric analysis, and dynamic water vapor sorption. The aerosol performance of the HCQ-sul powders was assessed using a medium-high resistance Osmohaler coupling to a next-generation impactor (NGI) at a flow rate of 60 L/min. Results: The jet-milled powder showed a volume median diameter of 1.7 μm (span 1.5) and retained the same crystalline form as the raw HCQ-sul. A small amount of amorphous materials was present in the jet-milled HCQ-sul, which was convertible to the stable, crystalline state after conditioning at 53%, 58%, and 75% RH. The recovered fine particle fraction (FPF)recovered and the emitted fine particle fraction (FPFemitted) of the HCQ-sul sample immediately after jet milling and the samples after conditioning at 43%, 53%, and 58% RH were similar at ∼43% and 61%, respectively. In contrast, the sample having conditioned at 75%RH showed lower corresponding values at 33% and 26% respectively, due to the formation of solid bridges caused by excessive moisture. Conclusion: Inhalable crystalline powders of HCQ-sul were successfully prepared, which can be used for clinical testing as a potential inhaled COVID-19 treatment.

Micronized whole wheat flour and xylanase application: dough properties and bread quality.

The micronization process by jet mill of whole wheat flour in addition to xylanase application may be used to improve dough properties and baking quality. This study aimed to evaluate the dough formation and bakery performance of whole wheat flour micronized using jet mill and having different particle sizes and xylanase content A decrease in particle size increased water absorption and increased dough stability by 3.7 units. Increase in xylanase content decreased the dough stability and mixture tolerance, resulting in reduced strength. Although the dough quality reduced, this was not evident in bread quality. In bread, the increase in xylanase content increased the specific volume and improved the texture profile. The 158 and 261μm particle sizes with 60 and 100mgkg-1 xylanase content reduced the undesirable effects of fibers in the dough, which may lead to improved bread making, thus enhancing improved consumer acceptance.

Ejector jet mill with external pressure

Jet mills are used to produce fine products in many industries. Spiral jet mills and fluidized bed jet mills are widely used. They differ in that the destruction of particles occurs as a result of the abrasion process. The use of impact ejector jet mills is limited by a relatively low consumable concentration of material. When the consumable concentration of the material increases the acceleration speed of particles and the material grinding degree decrease. To eliminate this disadvantage a new method and design of an ejector jet mill for fine grinding of bulk materials has been developed (patent of Russian Federation No. 2711252). The technological process occurs at excessive external pressure of the ejected gas. It is shown that it is feasible to increase the pressure at the beginning of the acceleration tube when the pressures ratio of the working and secondary gas is higher than the critical one. It increases the consumption concentration of bulk material and the acceleration speed of crushed particles. This allows reducing the specific energy consumption and increasing the grinding degree. Experimental studies have confirmed an increase in the consumption concentration by 1.6–1.9 times and an increase in the grinding degree by 1.3–1.7 times compared to a typical ejector jet mill.

Calculation of a closed grinding cycle in a jet mill with two classifiers

The matrix calculation method is successfully used for calculating the closed cycle in a jet mill. In the traditional closed-cycle scheme of a jet mill, a dynamic centrifugal classifier is used for fine separation of the grinding product. The circulation load can be up to 5 or more. This involves using a high-performance classifier the cost of which will be a significant share of the total installation cost. In addition, the dynamic classifier rotor wear is proportional to the quantity of material, i.e. performance. To eliminate these shortcomings a closed loop scheme with two consecutive classifiers is proposed within the framework of the matrix model. Moreover, the first classifier must be of the pass-through type and the second is of the dynamic one. The use of this scheme in mica production allowed reducing the circulation load on the second centrifugal dynamic classifier for fine separation of the material by two times. Equations that allow determining the granulometric composition and mass yield of separation products, the multiplicity of circulation, the load on the mill and classifiers are obtained. The mathematical model proposed permits to calculate the optimal separation limits of each classifier.

Synthesis of layered silicon-graphene hetero-structures by wet jet milling for high capacity anodes in Li-ion batteries

While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries (LIBs), implementing a large-scale production method that can be easily transferred to industry, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in LIBs. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g−1 after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g−1). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05–1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g−1) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density LIBs for multiple device applications.

Вплив місця розташування елементу керування газовими потоками в ежекторному вузлі на характер течії потоку

This article is devoted to a numerical simulation of the flow in a jet mill ejector equipped with a gas flow control element. This element is a channel wherefrom an additional gas flow enters the accelerating tube of the ejector. The gas flows in the mill ejector are controlled using the energy of additional gas flows, thus increasing the velocity of the main flow at the outlet of the ejector accelerating tube and producing a protective layer around the tube walls to prevent their wear. At the same time, there is no substantiation for the choice of optimal control parameters, a methodology, or scientific methods for gas flow control in the ejector channels. The purpose of this work is to investigate the effect of the location of the gas flow control element on gas-dynamic ejector performance and the flow pattern in the ejector channels. A numerical study was carried out using the Ansys Fluent software package and the SST k-? turbulence model. In the course of the study, the pressure of the additional gas flow and the distance from the accelerating tube inlet to the energy carrier supply channel were varied. The angle of the additional gas flow was 20 ?. The numerical simulation gave flow patterns in the ejector as a function of the location of the gas flow control element. Streamlines of the additional gas flow were constructed. The article presents the average flow velocity at the accelerating tube outlet and the energy carrier flow rate as a function of the pressure of the additional flow of the energy carrier and the location of the gas flow control element and the maximum values of the average outlet velocity for given pressure ranges. The article substantiates the choice of the gas flow control parameters that maximize the velocity of the mixed flow at the accelerating tube outlet at a minimum gas flow rate. The results may be used in improving material processing technologies.