In this paper the general features, behavior and application possibilities of motionless mixers in mixing and treatments of bulk solids are overviewed, summarizing the results published during the last three decades. Working principles, mechanisms, performance, modeling and applications of these devices are described. Related topics, such as use in particle coating, pneumatic conveying, contacting, flow improvement, bulk volume reduction, and dust separation are also summarized.
Gas-phase synthesis is a well-known chemical manufacturing technique for an extensive variety of nano-sized particles. Since the potential of ultra-fine and especially nano-sized particles in high-performance applications has been identified, the scientific and commercial interest has increased immensely, disclosing this field as a most important technology of the future. The paper will present the basics of the gas-phase synthesis and particle formation process including the relation between the principal process conditions and the product characteristics. Moreover, several reactor technologies such as flame, hot-wall, plasma and laser reactors will be introduced and their specific advantages will be pointed out. Precise process control is crucial in order to meet stringent specifications regarding the particles’ chemical composition and morphology. In addition, the paper will deal with some special nanoscaled gas-phase products of high innovative potential and their functional contribution in various applications.
This paper provides a concise review of the contributions to research in sedimentation and thickening that were made during the 20th century, starting from the invention of the Dorr thickener in 1905. The different steps of progress that were made in understanding batch sedimentation and continuous thickening processes in mineral processing are reviewed. A major breakthrough was Kynch’s kinematic sedimentation theory published in 1952. The authors’ own contributions to sedimentation and thickening research are summarized, including the development of the appropriate mathematical framework for Kynch’s theory and its extensions to continuous sedimentation and to polydisperse suspensions of spheres. An even more general model framework is provided by the phenomenological theory of sedimentation, which permits the description and simulation of the transient behavior of flocculent suspensions.
Because proteins and peptides are poorly absorbed through the gastrointestinal tract, the lungs are a promising organ for administering these substances because of their large inner surface area, thin epithelium, and relatively low protease activity. Pulmonary absorption rate constants are inversely related to molecular weights. Adding an absorption enhancer is a promising method to increase systemic bioavailability of inhaled peptides and proteins. The local lung toxicity of soluble powder seems to be minimal. Spray drying is a useful and widely applied technique to prepare powders for inhalation, and supercritical fluids have recently been used for producing such powders. Selecting operating conditions and adding proper additives such as sugars yields hollow porous particles, which are easily dispersed and avoid phagocytic clearance in the lungs, with maximized chemical and physical stability.
In recent years, the functions of porous ceramics such as light weight, thermal insulation, permeability, separation, adsorption, and sound absorption have been paid attention. They are applied to materials for environmental improvement, materials for energy system, biomechanical materials, spatial materials and so on. In conjunction with this, many synthesis and fabrication methods for not only porous ceramics in the usual macropore range, but also those in the mesopore and micropore ranges were reported. The functions and fabrication methods of porous materials are closely related to pore size and structure. In this paper we reviewed recent synthesis and fabrication methods for porous materials across a wide range from nanometer to millimeter pore sizes while also touching upon material functions.
The effect of an increase in gravitational force on the separation of a binary (different densities) mixture of particles in a centrifugal separator is investigated. An algorithm calculates the effect an increase in gravity has on improving separation using established particulately fluidised bed models. These results are compared to separation data generated by a continuous centrifugal separator.
A stochastic approach has been taken to examine the flow behaviour of particles in a vibrated granular bed. The coordinates of a single grain were determined as a function of time using the technique of positron emission particle tracking. Following a particle for extended periods allowed a detailed representation of the displacement probability density to be built up. This showed that, initially, particles dispersed according to a Gaussian law, but that the variation in the solid fraction of grains, their granular temperature and the presence of walls meant that significant distortions were observed over longer timescales. The determination of the displacement probability density allowed the spatial distribution of the granular temperature and the diffusion coefficient to be measured in both mono- and bi-disperse granular systems.
Results from an experimental investigation of the development of cake resistance during filtration assisted by vibration are presented and the vibration conditions that lead to improved filtration rates are identified. It is shown that vibration is a possible technique to increase the rate of filtration. However, a critical acceleration that is dependent on the vibration frequency and solids mass in the cake must be exceeded for filtration to be enhanced, otherwise the rate of filtration is slowed. Changes in the visual structure of the “cake” with vibration acceleration are described and related to changes in the “cake” resistance.
The effects of wall inclinations and wall imperfections at the onset of granular flow in a silo are numerically studied. The calculations were carried out for the onset of quasi-static mass flow in a silo with a controlled outlet velocity along the entire bottom. In the analysis, a finite element method and a polar hypoplastic constitutive law were used. A polar hypoplastic law describes the salient properties of granular bodies. FE calculations were performed with a plane strain silo with parallel walls, slightly convergent walls, slightly divergent walls, and parallel and convergent walls. The influence of a wall imperfection directed inwards and a wall imperfection directed outwards in a silo with parallel walls was also analysed. The FE results showed a large sensitivity of stresses in bulk solids due to the change of the direction of shear deformation along the silo wall.
The attenuation of a beam of X-rays as it passes through a body has been used for over 100 years in diagnostic medicine. A more recent application of the technique has been in the study of industrial-type units such as gas-solid fluidized beds, and this paper reviews this application in the analysis of the hydrodynamic features of bubbling and circulating fluidized beds. The measurement of jet penetration into bubbling beds and the study of bubble slurry columns are also considered. The equipment used and its methods of operation are described and the salient results of the more revealing investigations are summarised both from a qualitative and a quantitative viewpoint.
The combination of mechanochemical activation and self-propagating high-temperature synthesis (SHS) have widened the possibilities for both methods. For metallic systems, the investigation showed that a short-term mechanochemical activation of heterophase SHS products leads to single-phase and ultrafine intermetallides obtained from the elements by mechanical alloying. It was demonstrated that metastable phases, usually obtained by mechanical alloying, can be obtained from the equilibrium intermetallic compounds synthesized by SHS. Besides this, the investigations showed that preliminary mechanical activation, during which layered composites are formed from the initial elements, allows one to extend the concentration limits of SHS processes up to a solid solution region. The preliminary mechanical activation also allows production of single-phase ultrafine complex oxides.
Coating sand and granular activated carbon with iron aluminum hydroxides changed the zeta potential of these filtration media from negative to positive at pH 6–9, while also significantly improving removal of viruses (MS2, PRD1, Polio1). A quaternary ammonium based coating on sand also increased zeta potential, but led to limited improvement in virus removal. The coated activated carbon was effective in both columns and faucet filters. Performance of faucet filters decreased slightly (e.g., 98% removal initially vs. 89% removal after 1 month) with time. The chemical costs of coating would add approximately 10% to the cost of water delivered by large-scale municipal systems, whereas coating chemical costs would add less than 1% to the cost of water treated by point-of-use faucet filters. The improvement in virus removal performance gained by use of coated filter media provides a significant benefit to the consumer in terms of increased microbiological quality at a modest-to-negligible increase in cost.
In this paper we study the consolidation behavior of inhomogeneous granular beds of elasto-plastic particles by means of a discrete-continuum formulation, which systematically bridges the micro and meso scales. The methodology is particularly suitable for describing the post-rearrangement regime where consolidation proceeds mostly by elastic and inelastic deformation. This formulation is able to provide the quantitative estimates of the evolution of macroscopic variables, such as pressure and density, while following microlevel processes, such as local coordination number and loading paths. This methodology is used to simulate binary mixtures composed by particles with different nonlinear properties. The predictions are in general agreement with the experimental data during both loading and unloading cycle.
Comparative analysis between salmeterol xinafoate (SX) powders was carried out to define quantitatively the solid-state and surface particle properties relevant to formulation of these materials into dry powder respiratory drug delivery systems. SX powders were prepared in supercritical CO2 using a single-step crystallization process (Solution Enhanced Dispersion by Supercritical fluids, SEDS™), the volume mean diameter and deagglomeration behaviour of pure drug compound were optimised for respiratory applications. This compound together with reference samples of starting granulated material and micronised powder were used in analytical studies which involved assessment of polymorphic purity and crystallinity (domain size and strain) using high-resolution X-ray powder diffraction, determination of powder surface energetics using inverse gas chromatography (IGC), electrostatic charge and adhesion measurements. The supercritically-processed powders showed low surface energy, low strain, higher crystallinity and higher polymorphic purity than both granulated and micronised powders and resulted in reduced agglomeration, electrostatic charge and adhesion of this powder.
The evolution of particle shape during the course of comminution processes has been investigated. Shape is characterized using a variety of quantitative shape descriptors determined from particle profiles obtained by image analysis. Descriptors related to particle elongation, roundness and angularity are emphasized. Distributions of the descriptors have been determined for a range of particle sizes, for different extents of grinding for various equipment types. For a given descriptor, the distributions of measured values generally follow a consistent pattern (often roughly log normal). Typically, the means and standard deviations show progressive changes as grinding time increases. For the most part, prolonged exposure to the grinding environment leads to rounding of the particles.
Segregation is important in many bulk handling industries due to its impact on product quality and mixing. Previous studies have focused on quantifying segregation as a coefficient for a particular process. Although this has provided insights into the effect of segregation during particular processes, it has not provided a rational approach to understanding the phenomena of segregation. Toward this end, a vertically oriented segregation shear cell was designed, fabricated and used to test the response of binary mixtures of spherical glass beads. Three size ratios of 10.9:1, 8.7:1, and 5.1:1 were used in this study. Variables such as strain, strain rate (i.e., cycle speed) and bed depth were used to quantify size-segregation characteristics under different input energies. Size ratio was the most dominant variable that affected the percolation rate of fines through a bed of coarse particles. Based on the differences in percolation between the smaller ratio of 5.1:1 and larger ratios of 8.7:1 and 10.9:1, there are indications of a critical size ratio that determines the mechanism of percolation. Two mechanisms were observed. First, the larger size ratios exhibited an initial free-fall discharge of fines at the beginning of the test. This initial discharge was followed by a diffusive behavior, i.e., monotonically increasing trend that approaches an asymptotic value. The smaller ratio did not exhibit the initial discharge and the responses were described adequately by the diffusive behavior. Strain also had an effect. Input energy, as related to strain, was found to be critical in the type of percolation exhibited, i.e., the presence or absence of an initial rapid discharge. For the size ratio of 10.9:1, the amount of input energy was critical because the size of the fine particles was near the size of the coarse bed pore space. When the input energy was below a critical limit, mechanical arching was occurring. Although, the input energy is a function of bed depth and strain rate, these parameters did not influence the results outside random behavior.
The Julius Kruttschnitt Mineral Research Centre (JKMRC) has been involved in the study and modelling of industrial autogenous (AG) and semi-autogenous (SAG) mills for over 25 years. Recent research at the JKMRC has developed a new AG/SAG mill model which is based on charge dynamics. The model relates charge motion and composition to power draw and size reduction. Size reduction is described by considering impact and attrition/abrasion as separate processes. These are linked to energy available in the mill, the charge size distribution and the relative motion of the grinding media. Ore specific energy-breakage are described using laboratory data which are obtained from breakage tests over a wide range of energies and particle sizes. Slurry transport is described using the JKMRC’s latest model which incorporates the effect of grate design. This paper describes the overall structure of the model together with its main sub-processes.
We developed an apparatus that uses the direct separation method to measure adhesive force between fine particles, and between a fine particle and a flat-surface substrate. This apparatus was able to measure adhesive force with high resolution (approximately 2 nN) and monitor the behavior of each particle with a microscope and image analyzer when separating particles from each other, and to calculate the adhesive force of the particles. Of the organic particles tested (corn starch, potato starch, and lactose), potato starch had the highest adhesive force, while lactose had the lowest adhesive force toward flat-surface substrates. The diameter and size distribution of fine particles clearly affected their adhesive force.
†This report was originally printed in J. Soc. Powder Technology, Japan. 37(9), 658-664 (2000) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
A continuous reactor was developed for industrial production of monodispersed alumina particles from metal alkoxide. Taylor vortex flows were used for solution mixing. Each of the Taylor vortices functioned as a batch reaction vessel. Monodispersed spherical alumina particles were prepared by hydrolyzing aluminum alkoxide in a mixture of octanol and acetonitrile. The particles were continuously produced for 5 h by using this reactor. Particle size and distribution were comparable to those obtained by batch processing. We investigated the effects of Taylor number (Ta) and residence time on the particle size, particle size distribution, yield, and particle number density of monodispersed alumina particles, which were obtained at Ta numbers from 50 to 150.
†This report was originally printed in J. Soc. Powder Technology, Japan. 37(10), 722-727 (2000) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
Electrostatic atomization is a method typically used to produce fine liquid droplets with diameters between ten and several hundred micrometers and a relatively narrow size distribution. This method is simple but its mechanism is not yet fully understood. Our research involved producing fine silica particles by forming droplets of water glass no. 3 using electrostatic atomization, then dehydrating them and removing their sodium ions. The atomization state was classified into three modes according to applied voltage: dripping, uniform cone-jet, and discharge modes. Uniformly sized droplets were produced only with the uniform cone-jet mode at a positive high voltage. The mean volume diameter of silica particles could be estimated as a function of flow rate and applied voltage, as well as the surface tension, viscosity, and conductivity of the water glass solution.
†This report was originally printed in J. Soc. Powder Technology, Japan. 38(2), 90-96 (2001) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
We examined the flocculation of suspended particles using a thermosensitive polymer which undergoes a reversible hydrophilic/hydrophobic transition when heating or cooling its aqueous solution. As a thermosensitive polymer poly(N-isopropylacrylamide) (polyNIPAM), whose transition temperature is about 32°C, was used. Flocculation experiments were performed by the jar test using kaolin suspension. In the case of operating temperature lower than the transition temperature of poly-NIPAM, there was an optimum polymer dosage, and by dosing excessively kaolin particles were dispersed stably in the same manner as conventional polymeric flocculants. However, floc formation was observed by heating the suspension above the transition temperature under the excess polymer dosage. Furthermore, by cooling the floc-containing suspension down to below the transition temperature again, the flocs were disorganized to the particles. These phenomena show that the floc formation caused by heating to above the transition temperature is due to the hydrophobic interaction of polyNIPAM molecules adsorbed on the particles.
†This report was originally printed in Kagaku Kogaku Ronbunshu, 26(5), 734-737 (2000) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.
Spherically agglomerated crystals of ascorbic acid for direct tableting were successfully prepared by the spherical crystallization technique. This agglomeration dramatically improved the micromeritic and compaction properties of the original ascorbic acid crystals. The dominating mechanisms that improved compaction properties of the spherically agglomerated crystals depended on their fragmentation and plastic deformation during compaction. Support for this mechanism existed because the compacted agglomerated crystals had higher stress relaxation and lower elastic recovery than the original crystals. Spherically agglomerated crystals were tableted directly without capping by using a single-punch tableting machine under dynamic compaction, although the tensile strength of tablets with spherically agglomerated crystals decreased when the compression speed increased.
†This report was originally printed in J. Soc. Powder Technology, Japan. 38(3), 160-168 (2001) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
The objective of this study is to investigate the relation between the flocculation and dispersion of Al2O3, TiO2 and Fe2O3 particles and the properties of solvents such as dielectric constant and solubility parameters. The median diameter of these metal oxide particles was measured in many organic solvents. The effect of the kind of solvent on the flocculation/dispersion behavior of metal oxide particles was evaluated from these results. Hansen’s solubility parameters with three dimensions were applied to the evaluation of the flocculation/dispersion behavior for fine metal oxide particles in organic solvents. The numeral balance among the Hansen’s solubility parameters of various solvents was plotted in a triangular chart, and then the points of solvents with similar median diameter of the particle were linked. In the triangular chart, these linked lines were not intersected each other and there was the specific point at which the best dispersibility of the particles was obtained.
†This report was originally printed in Kagaku Kougaku Ronbunshu, 27(4), 497-501 (2001) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.