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In this study, the impact of different vibrational modes on the fluidization characteristics of cohesive micro- and nano-silica powder was examined. Fractional pressure drop, bed expansion measurements, and X-ray imaging were utilized to characterize the fluidization quality. The densities of the emulsion phase at the top and bottom of the column were quantified and compared, providing insights into the solid distribution within the fluidized bed. In the absence of vibration, neither powder could be fluidized within the considered range of superficial gas velocities. Vertical vibration was found to initiate fluidization for both powders. In contrast, elliptical vibration failed to overcome the channelling behavior when fluidizing the micro-powder. For nano-powder, combined channelling and powder compaction occurred when the bed was subjected to elliptical vibration. For the micro-powder, it was observed that bed homogeneity was independent of vertical vibration intensity but improved with increasing superficial gas velocity. For nano-powder, intensifying vertical vibration led to segregation, likely due to agglomerate densification. Furthermore, fractional pressure drop measurements proved to be a strong tool in assessing fluidization quality, providing insights that could not be attained by conventional indicators. • Fractional pressure drop data provides a strong indication of the solid distribution within fluidized beds of cohesive powder. • Occurrence of channelling can be interpreted from fractional pressure drop measurements. • Elliptical vibration is insufficient to disrupt gas channels in micro-powder beds. • Elliptical vibration compacts sections of nano-powder and depresses fluidization. [ABSTRACT FROM AUTHOR]

Highlights • A novel continuum theory accurately predicts aggregation in a gas-solid flow. • The continuum theory accurately predicts entrainment of cohesive particles. • Aggregation leads to increased granular temperature and breakup of agglomerates. Abstract In this work, a continuum theory for cohesive particles developed recently (Kellogg et al., 2017) is applied to lightly-cohesive particles in an unbounded, gas-solid riser. The novelty of this recent theory is its fundamental incorporation of the effects of the granular temperature (i.e., continuum measure of impact velocity) and the material and cohesion properties on the rates of aggregation and breakage of agglomerates. Here, we extend this theory to multiphase systems and place particular emphasis on its ability to predict entrainment rate, as past empirical correlations vary by orders of magnitude when applied to the same system (Chew et al., 2015). Specifically, continuum predictions of entrainment rates and agglomerate fraction are compared with Discrete Element Method (DEM) simulations of lightly-cohesive particles in a gas-solid flow. The agreement obtained for these quantities provides preliminary validation for the use of the continuum theory for cohesive particles in gas-solid flows. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights: • Activation energy and stable energy increase with the separation distance between particles. • Activation separation distance and critical separation distance are directly proportional to particle radius. • Equilibrium energy is a quadratic function of particle radius. • Agglomeration of non-wetted solid particles in the high temperature melt is derived from the cavitation between particles. Abstract Based on the bridge cavitation theory, the free energy variation during the cavitation between two non-wetted solid particles in a high temperature melt was investigated. The activation state and the stable state were achieved at the maximum and the minimum of the free energy curve varying with the neck radius, respectively. Increasing the separation distance between particles, both the activation energy and the stable energy increased. The activation separation distance was defined as the separation distance at which the extremum of the total free energy with respect to the neck radius had disappeared and the critical separation distance was derived by equaling the free energy before and after the cavitation. When particles were contacting, an equilibrium state was obtained as the system energy reached its minimum value. The equilibrium energy was the energy when the energy drop for the cavitation reached its maximum value. It is novel for the present study to find that both the activation separation distance and the critical separation distance were directly proportional to the radius of particles. Meanwhile, the equilibrium energy was a quadratic function of the particle radius. In the case of the cavitation between two 5.0 μm alumina particles in the molten steel, the activation separation distance, the critical separation distance and the equilibrium energy were 0.96 μm, 0.73 μm and 17.75 × 10−12 J, respectively. Furthermore, a comparison between the calculation and experimental results showed a good agreement. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al 2 O 3 film was coated on nickel phyllosilicate by atomic layer deposition method. • NiSiO 3 @5Al 2 O 3 -R 600 catalysts showed good performance for CO 2 thermal hydrogenation. • Al 2 O 3 film inhibits the agglomeration of Ni particles during high-temperature reduction. • XPS and DFT results indicate the electronic interaction between ALD-Al 2 O 3 and Ni. • High-pressure DRIFTS showed HCOO* species were key intermediates to produce CH 4. Herein, NiSiO 3 @Al 2 O 3 catalysts were prepared by encapsulating Al 2 O 3 films on nickel phyllosilicate nanosheets via atomic layer deposition (ALD) technique, and used for CO 2 hydrogenation reaction. The NiSiO 3 -R 600 catalyst without Al 2 O 3 films underwent serious agglomeration of Ni particles after H 2 reduction at 600 °C, leading to poor CO 2 conversion of 22.6%. In comparison, CO 2 conversion over NiSiO 3 @5Al 2 O 3 -R 600 catalyst reached 66.9% due to that the ALD-Al 2 O 3 film can effectively alleviate the agglomeration of Ni particles (6.3 vs. 22.1 nm). Furthermore, the electronic interaction between Al 2 O 3 and the metallic nickel site was confirmed by both XPS spectroscopy and DFT calculations. The chemisorption behaviors of probe molecules on the catalyst surface also prove the better dispersion of metallic Ni sites in the presence of the ALD-Al 2 O 3 layer. Moreover, in-situ DRIFTS characterization indicates that the presence of ALD-Al 2 O 3 film promoted the hydrogenation of HCOO* to CH 3 O*, which then increased the CO 2 conversion and CH 4 selectivity. [ABSTRACT FROM AUTHOR]

While particulate products are often characterized by their median diameter or the width of the particle size distribution, information is rarely given about the agglomeration degree of the product. To obtain this information, a tool combining image analysis and discriminant factorial analysis (DFA) was introduced in previous works. The accuracy of that method depended on the number of image descriptors selected, i.e. measurements describing each particle: few image descriptors resulted in rather poor classification while too many lead to an overfitting of the data. The aim of this study is twofold: First, we want to compare the classification accuracy of artificial neural networks (ANN) and DFA which, contrary to ANN, forms linear classifiers. Second, we want to provide an easy-to-implement procedure for generating particle classifiers. We used a qualitative measure called Proportional Similarity to test whether a subset selection of image descriptors was necessary to avoid an overfitting. The influence of the training set size was investigated as well as the transferability of the classifier on data obtained under different experimental conditions. The chemical systems used were l -alanine/water and adipic acid/water and the classes considered were single crystals, agglomerates, and gas bubbles. The results show that an ANN classifier provides higher accuracy and is more effective when only few image descriptors are available while DFA is simpler to create. Moreover, we show good transferability of classifiers trained on data of different experimental conditions. Based on our results, we provide guidelines for classification of particulate systems. [ABSTRACT FROM AUTHOR]

Particle agglomeration, wall deposition and resuspension are inherent to many industries and natural processes, and often inter-connected. This work looks into their relation in a confined particle laden swirling flow. It investigates how the size of detergent powder spray dried in a swirl counter-current tower responds to changes in the air flow. Four sets of sprays are investigated under varying combinations of air temperature and velocity that cause the same evaporation. The use of high air velocities accumulates more of the droplets and dry powder in the chamber swirling faster, but it leads to creation of a finer product. Particle-particle and particle-wall contacts are made more frequent and energetic but in turn the swirl troughs the solids to the wall where deposits constantly form and break. Past PIV and tracer studies revealed that the rates of deposition and resuspension are balanced; the data discussed here indicate that the dynamic nature of the deposits is a major contributor to particle formation. In contrast with the usual assumption, the product size seems driven not by inter-particle contacts in airborne state but the ability of the solids to gain kinetic energy and break up a collection of clusters layering on the wall. As a result, the dryer performance becomes driven by the dynamic of deposition and resuspension. This paper studies the efficiency of limiting operation strategies and shows that a low temperature design concept is better suited to control fouling phenomena and improve capacity and energy consumption. [ABSTRACT FROM AUTHOR]

In froth flotation, fine hydrophobic particles selectively attach to the surface of air bubbles, in turn rising through the liquid and then more slowly as part of the foam that emerges from the system. This paper proposes a paradigm shift from the traditional use of air bubbles as the hydrophobic separation medium to potentially a far more powerful version that utilises a novel hydrophobic binder, a concentrated water in oil emulsion. We show empirically the oil consumption increases linearly with the specific surface area of the particles, with an average oil film thickness of 178 nm for fine coal particles, well below the level required for conventional oil agglomeration. The new approach is ultrafast, achieving agglomeration within seconds under batch conditions, with strong selectivity. We also show for the first time continuous steady state agglomeration can be achieved by simply passing the feed and binder suspensions through a partially closed ball valve. Here the residence time through the valve is less than 0.1 s. And, by subjecting the agglomerated product to further shear, the emulsion is inverted, releasing bound water. Pressure driven filtration then delivers remarkably low product moistures. Operational aspects of this new technology are discussed. [ABSTRACT FROM AUTHOR]

Hydrates of light hydrocarbons are frequently formed during the subsea petroleum production. These crystalline ice-like solids may accumulate at concentrations sensitive from the flow assurance point of view, increasing the overall pumping costs and imposing sufficient risk of the pipe blockage. Modern trend in the assessment of hydrate-related risks is the development of numerical models of multiphase flows laden by hydrates. The present paper describes a computational fluid dynamic (CFD) model capable to simulate turbulent slurry of oil, water and gas hydrates. The population balance technique (PBM) coupled with CFD enables to predict such details of the process as the formation of hydrate phase, agglomeration of formed solids and granular interactions within the hydrate phase. The simulation results, validated with experimental data in terms of the slurry rheology, highlight flow patterns for a pipe system typical in oil industry. The model is in addition compared to the hydrate kinetics model from Colorado School of Mines (CSMHyK). [ABSTRACT FROM AUTHOR]

Simulations of wet fluidized beds of particles in small periodic domains have been carried out using a CFD-DEM approach. A liquid bridge forms upon particle–particle collision, which then ruptures when the particle separation exceeds a critical distance. The simulations take into account only the surface tension force of attraction due to the liquid bridge. Increasing the strength of cohesion leads to larger agglomerates, and correspondingly, higher gas velocities are required to fully support the particles. The slip velocity results from the simulations have been correlated in terms of a Bond number characterizing the strength of cohesion, volume of liquid in the bridge, and particle volume fraction. The CFD-DEM results are systematically coarse-grained to expose the dependence of the filtered drag coefficient on Eulerian filter size, surface tension forces, liquid loading, and solids loading in wet gas–solid fluidized beds. [ABSTRACT FROM AUTHOR]

• New analytical expression for particle (collision) speed in collision-dominated fluidized beds. • Combines kinetic theory of particle collisions with fluid-particle drag. • Accommodates collective/correlated particle motion in the bed. • Validated by comparing to computational fluid dynamics (CFD) - discrete element method (DEM) • Provides rapid prediction as well as a basis for understanding particle speed. The target of this method is gas–solid fluidized beds, in which the particles progressively become coated with liquid or generally become sticky for any reason. Previous studies have shown that the restitution coefficient of wet particle collisions depends on the speed at which the particles collide. Moreover, below a critical collision speed, the particles fail to rebound at all. Therefore, predicting particle collision speeds is important. Current methods to predict collision speeds are computationally expensive. The present method provides an analytical expression for particle collision speed, making it convenient for evaluating the potential for agglomeration. Moreover, it provides a basis for understanding the speed of particle motion in fluidized beds—usually only accessible through time-consuming numerical simulations—by anticipating the outcome of what is largely a repetitive computation of particle–particle collision and re-acceleration by the gas flow. The method combines the mean free time between inelastic particle collisions (with provision for collective particle motion), which cause them to lose kinetic energy, and the drag force by the turbulent gas flow on the particles, which accelerates them prior to their next collision. To validate the method, the results are compared to corresponding computational fluid dynamics (CFD) - discrete element method (DEM) calculations. [ABSTRACT FROM AUTHOR]

An understanding of agglomeration in multiphase flows by means of capillary bridges is important for various technical applications. One of the key parameters that describe the process is the probability of agglomeration, usually termed collision efficiency. In the present paper we study the collision efficiency by using Eulerian–Lagrangian computational fluid dynamics (CFD) modelling. The analysis evaluates the dependence of the collision efficiency on various dimensionless parameters that describe the process, including, among others: Reynolds number, bridge capillary number and wetting angle. In addition we further develop a theoretical expression for a priori engineering estimates of the collision efficiency. This expression is validated against numerical, theoretical and experimental results. [ABSTRACT FROM AUTHOR]

This study uses the Eulerian-Lagrangian multiphase particle-in-cell (MP-PIC) approach, adopted in the computational particle fluid dynamics (CPFD) code, Barracuda Virtual Reactor®, to simulate the injection of a gas–liquid spray into a gas–solid fluidized bed. The model accounts for evaporation of volatile liquid in the form of individually moving droplets and thin films distributed on the surface of the solid bed particles. Comparison with previously reported temperature measurements for varying spray nozzle gas-to-liquid ratios suggests that the model is capable of predicting the overall features of the gas temperature distributions within the injection region at injection velocities of less than 50 m/s. Locally observed discrepancies between experimental and simulated temperature profiles are likely related to the presence of wet particle agglomerates in the spray region, as suggested by a developed energy dissipation model that, combined with the MP-PIC model, predicts the location and extent of agglomeration in the fluidized bed. [ABSTRACT FROM AUTHOR]

The present paper proposes a model for agglomeration of solid particles covered with a liquid flocculant. Rather then being derived by time-consuming numerical simulations of collision dynamics as the particles are in contact, the model is based on analytic relations: thus the computational cost is significantly reduced. The model was implemented into a computer code simulating a set of particles using the Eulerian–Lagrangian approach, that is, it forms an attractive alternative to Distinct Element Modelling (DEM). Moreover numerical simulations in a shear-flow system were done and the results were compared with a theoretical model. [ABSTRACT FROM AUTHOR]

The effects of evaporation and the presence of agglomerating nanoparticles on the oscillation characteristics of pendant droplets are studied experimentally using ethanol and aqueous nanoalumina suspension, respectively. Axisymmetric oscillations induced by a round air jet are considered. Wavelet transform of the time evolution of the 2nd modal coefficient revealed that while a continuous increase in the natural frequency of the droplet occurs with time due to the diameter regression induced by vaporization in the case of ethanol droplet, no such change in resonant frequency occurs in the case of the agglomerating droplet. However, a gradual reduction in the oscillation amplitude ensues as the agglomeration becomes dominant. [ABSTRACT FROM AUTHOR]

Abstract: A surfactant is used to reduce the agglomeration of iron catalysts during the synthesis of carbon nanotubes (CNTs) and their assembly by chemical vapor deposition. The agglomeration of iron catalysts during synthesis affects the CNT diameter and number of CNT walls. Also, the agglomerated catalysts within the CNT assembly indicate an inefficient reaction of catalysts during the CNT synthesis. In this study, the non-ionic surfactant, polysorbate, is added to the CNT synthesis solution in varying amounts from 0 to 3.0wt%. The effects of the surfactant are closely related to the crystalline perfection, diameter, and number of walls of CNTs synthesized under different concentrations of the surfactant. Here, 1.0wt% surfactant is the most favorable concentration to achieve crystalline perfection. When the surfactant is added at more than 1.0wt%, amorphous carbons increase, although the agglomeration of iron catalysts continues to decrease. The simple addition of this surfactant can facilitate the development of the CNT assemblies that have high mechanical and electrical properties. [Copyright &y& Elsevier]

Abstract: Suspensions of non-spherical particles are commonly encountered in the flow procedures used in material processing industries and biological applications. The rheological properties of these suspensions are influenced by both the dynamics and the orientation of the suspended particles, which is a characteristic that can be affected by hydrodynamic interactions. The rheology and dynamics of a suspension of spherical doublets in bounded flow between plane parallel walls were examined using the Stokesian Dynamics simulation method. The doublets consisted of two rigid spheres connected by inter-particle forces. These doublets are commonly observed in the agglomeration of particles during the processing of suspensions. The simulations were performed for particles undergoing both simple shear and pressure driven flow between two parallel walls. For all concentrations, the viscosity of the suspension of doublets was observed to be higher than the values determined for spherical particles. The wall normal stresses were similar for both types of suspensions. In addition to the shear and normal stresses, the velocity and concentration profiles in simple shear and pressure driven flow in the channel were also studied. In pressure driven flow, the shear induced migration observed with the doublets was similar to the behaviour observed with the spherical particles. Compared with the suspension of spherical particles in pressure driven flow, the maximum centreline concentration for the doublets always exhibited a lower value. An analysis of the orientation parameter indicated that the doublets near the wall were aligned in the flow direction, with the particles in the centre of the channels exhibiting random orientations. [Copyright &y& Elsevier]

Abstract: When growing crystals aggregate, they do so at a rate that depends on the frequency of collisions and the efficiency of those collisions. In this paper we revisit the work of Mumtaz to show from first principles that the efficiency depends on Mumtaz's dimensionless strength, M. Mumtaz's original work was restricted to collisions between particles of the same size, to failure under simple tension and to collisions originating with a point of contact. The current work extends that approach to include polydisperse systems, shear stress and linear contacts. In all cases studied the location of the efficiency curve is at M of O(1), while the spread of efficiency depends on the mechanism of failure and the contact geometry. To a first approximation the efficiency of collision of two colliding particles depends on the geometric mean of their sizes. The work presented here provides aggregation kinetics at a point in a crystallizer. Further experimental work is required to determine which failure mechanism is appropriate, the relevant materials properties and an appropriate method for averaging over a vessel. [Copyright &y& Elsevier]

Abstract: To develop a microscopic understanding of the role of cyclic fluidization and compaction in making spherical and dense granules by Pressure Swing Granulation, numerical simulation was conducted with our private code (SAFIRE21) using realistic parameter values determined by a micro-particle interaction analyzer. The values of the spring constant and coefficient restitution obtained from this experimental measurement were 300–790N/m and 0.9 respectively. The results obtained by the discrete element method simulation showed that collision frequency and collision force in a fluidized bed were insufficient to cause deformation of the granules but were significant in shaping the granules spherically. [Copyright &y& Elsevier]

Abstract: Agglomeration of fine mineral particle into robust and porous granules is an essential precursor to heap leaching and valuable metal recovery from low grade lateritic ores. In this paper, isothermal, batch agglomeration behavior of selected model clay (kaolinite and smectite) and oxide (hematite and quartz) minerals which constitute the predominant host gangue phases of typical low-grade nickel (Ni) lateritic ores is investigated. Specifically, the influential role of feed particle size and mineralogy on H2SO4 binder dosage requirement and agglomeration behavior was studied. Granules of 5–40mm size range were produced within 8–14min and their mechanical/structural properties examined. The results showed that for equivalent wetting and saturation, finer feed particles required higher binder dosage and led to dry agglomerates of higher compressive strength and re-wetting stability in acidic solution than coarser feed particles. Furthermore, binder dosages required for effective agglomeration were greater for the clays than the oxide minerals. Quartz, kaolinite and smectite displayed markedly slower growth behavior in comparison with hematite. The internal micro-structural analysis showed that the pore volumes (porosities) of the oxide granules were noticeably more than those of the clay granules these increased markedly (20–30% for clays and 30–40% for oxides) upon drying due to stresses/strains resulting from particle shrinkage after solvent (water) loss. Agglomerate dry compressive strengths for kaolinite and hematite were found to be similar and greater than those for quartz and smectite whilst the corresponding re-wetting stability decreased in the order: kaolinite>quartz>hematite=smectite. These findings, which indicate that the correlation between granule mineralogy, structural and behavior is quite complex, provide a useful basis for benchmarking the agglomeration behavior and granule properties of lateritic mineral ores. [Copyright &y& Elsevier]

Abstract: Amine oxides are an alternative, non-ionic class of gas hydrate anti-agglomerant (AA) surfactants that are potentially more environmentally-friendly than cationic surfactant AAs. These classes of AAs work by interacting with hydrate crystal surfaces. Recently, we reported on the clathrate hydrate crystal growth inhibition of monoamine oxides using Structure II (SII) tetrahydrofuran (THF) hydrate (Kelland et al., 2012). It was determined that the best hydrate crystal growth inhibition was provided by amine oxides with n-butyl, n-pentyl or iso-pentyl groups, with tributylamine oxide being the best homofunctional trialkylamine oxide investigated. However, replacement of one butyl group with a larger group, forming the tail of an AA surfactant, lowered the inhibition significantly which could have consequences for the use of mono-amine oxides as AAs. We have now investigated bis-amine oxides and discovered that they can give even greater THF hydrate crystal growth inhibition than mono-amine oxides, particularly when the amine oxides have the correct size alkyl groups and are an optimum distance apart. The optimum alkyl group was found to be n-butyl and the optimum distance for bis-amine oxides is with a chain of 5–6 sp3 carbon atoms separating the nitrogen atoms. Alternatively, a heteroatom can be placed in this spacer chain, for example a third nitrogen atom, such as for alkylated derivatives of diethylenetriamine. These results mean that the use of bis-amine oxide surfactants could potentially lead to improved AA performance compared to mono-amine surfactants because of their greater adsorption onto hydrate surfaces. They may also act as improved synergists for polymeric kinetic inhibitors of natural gas hydrates. [Copyright &y& Elsevier]

Abstract: Good fluidization was generally established when fine and light catalyst particles were fluidized. However, a large decrease in the fluidization quality was observed when two types of particles composed of different materials were mixed and fluidized, even though good fluidization was established with each type of particle alones. Formation of gas channeling was observed for binary mixtures of particles in a two-dimensional (2D) fluidized bed. In a three-dimensional (3D) bed, measurement of the pressure fluctuation showed that abnormal fluidization occurred due to mixing of the particles. In addition, measurements of the minimum fluidization velocity and emulsion phase expansion indicated that particle agglomeration occurred. The phenomena observed in the fluidized bed with the mixture of particles are quite similar to those observed for Group C particles. On the basis of the direction of the electrostatic charge, the particles were separated using electrodes installed above the fluidized bed surface. It was confirmed that one type of particle was positively charged and the other was negatively charged. Thus, it was concluded from these results that the bipolar charging caused by the difference in chemical composition of the particles induced the agglomeration phenomena and poor fluidization. [Copyright &y& Elsevier]

Abstract: A series of tris(dialkylamino)cyclopropenium chloride salts with different alkyl groups of up to 5 carbon atoms has been synthesised and their performance studied as low dosage hydrate inhibitors for the first time. We have investigated the ability of these organic salts to inhibit the growth of tetrahydrofuran (THF) hydrate crystals. The hexa-n-butylated derivative gave the best crystal growth inhibition, with a similar performance to tetrabutylammonium bromide (TBAB). The hexa-pentylated derivatives (both normal and iso) were found to be water-insoluble. Sparingly soluble cyclopropenium derivatives with a 2:1 mixture of di-n-pentylamino:diethylamino groups gave poor THF hydrate crystal growth inhibition. This series of cyclopropenium salts was also investigated for their ability to act as synergists for the kinetic hydrate inhibitor (KHI), polyvinylcaprolactam (PVCap). In a series of high pressure rocking cell tests using a structure II-forming natural gas mixture, the hexa-butylated cyclopropenium derivative performed well, but the best synergist was the cyclopropenium derivative with a 2:1 mixture of di-iso- and di-n-pentylamino:diethylamino groups. As has been shown in previous work with the synergism of tetraalkylammonium salts with PVCap (P.C. Chua, M.A. Kelland, 2012. Energy Fuels 26, 1160), we presume that adsorption onto hydrate crystal surfaces is not the only KHI mechanism operating and that perturbing the water structure and thus the nucleation of gas hydrates with the cyclopropenium salts is also a key KHI mechanism. [Copyright &y& Elsevier]

Abstract: In the past studies, MHz-order ultrasound has been frequently employed in the ultrasound separation techniques and the flocculation mechanism of particles due to the acoustic radiation force has been reported. The previous separation technique, however, is applicable to particles with diameters similar to a wavelength of the irradiated ultrasound or with smaller diameters than that. Hence, particles which are larger than μm-order in diameter are difficult to be manipulated with MHz-band ultrasound. In the present study, to clarify an unknown flocculation mechanism of the particles in an ultrapure water under kHz-band ultrasound irradiation, we quantitatively discussed an interaction between the particle motion and the acoustic cavitation bubble motion based on the experimental results. First, we successfully captured the particle motion and acoustic-cavitation-oriented bubble motion simultaneously by using a high-speed video camera. Second, we measured the distribution of the sound pressure in the water phase and discussed the relationship between that of the sound pressure and the motion of the particle and the acoustic cavitation bubble. Finally, we investigated the effects of the gravity force, the acoustic radiation force and the spatial heterogeneity of the pressure acting on the particle. By combining the results, we found out that an acoustic-cavitation-oriented bubble adhered to the particle and the particles moved toward the pressure anti-nodes of the standing wave by the acoustic radiation force acting on the adhering acoustic-cavitation-oriented bubble. [Copyright &y& Elsevier]

Abstract: Control of nucleation in wet granulation often determines the size and structure of the final granules. After a decade of research, our knowledge of “immersion nucleation”, where a large droplet engulfs fine particles, is relatively well established. However, far less is known about the second mechanism called “distribution nucleation”, where the powder particles are gradually coated by a layer of small droplets. In this paper, the similarities between particle coating and granulation were used to define the five steps of distribution nucleation. A Bernoulli model was developed to describe the fractional surface coating F, and a new dimensionless parameter, the particle coating number Φ p , was defined as the ratio of the theoretical area coated by the drops, assuming no overlap, to the total surface area of the particle. The particle coating number was experimentally validated by adding drops randomly over the surface of a particle and measuring the fractional surface coating using image analysis. Standard ping pong balls (40mm diameter) plus four sizes of foam balls ranging from 20 to 50mm diameter were coated with either small or large drops of melted PEG1000. The results demonstrated that the particle coating number Φ p can be used to predict the fractional surface coverage F using simple, known parameters (without any fitting coefficients), and was able to account for differences in particle size and drop size. Deviations in the experimental data from the theoretical predictions were observed, and attributed to drop spreading and merging and heat conduction into the particle, which all affect the experimental drop footprint area. When the effective footprint area was used as a fitting parameter all the experimental data collapsed onto a single line, demonstrating that the particle coating number captures the key coating coverage behaviour. The particle coating number can also be used to predict the effect of changing particle size, surface area, liquid level, or drop size on the coating fraction, which is in turn known to be linked to granulation kinetics. The particle coating number opens up new options for granulation process control, and is expected to be valuable in a variety of particle wetting and coating applications where small drops are distributed over larger particles. [Copyright &y& Elsevier]

Abstract: Disentanglement, dispersion of CNTs without attrition and efficient interfacial interaction with polymer chains are a major challenge in developing CNT/polymer composites. In the present device the mixture of highly viscous polyphosphoric acid (PPA) and entangled MWCNTs fills a hollow cylinder where a perforated piston, encasing micro-grids, is axially translating, oscillating and simultaneously rotating. This generates an extensional-shear-spiralling flow, magnified in the entrance/exit zone of the grid micro-openings, the smallest having diameter of 40μm. The reciprocating action forces the agglomerates to cross the grid many times, while the oscillation reduces effectively the clogging of the grid. Flow micro-splitting and recombination, across millions of micro-openings in a time dependent regime, facilitated erosion and collision mechanisms to prevail, leading to a gradual CNT deagglomeration–dispersion without CNT attrition. The resulting high multi-directional-rotational flow generated the conditions for efficient functionalisation. [Copyright &y& Elsevier]

Abstract: The fluid, particle and collision dynamics inside a fluidised bed granulator are described in detail using coupled DEM-CFD simulations. Three different granulator configurations are compared in terms of their particle–particle interactions, using criteria such as the average particle velocity, angular velocity, average particle–particle and particle–wall collision velocity and the collision frequency. From these measures the agglomeration probability, the breakage and growth rate and the agglomerate strength can be assessed. Depending on the required product properties the results highlight advantages of specific granulator geometries. The top-spray granulator is the simplest device and is often used for large-scale granulation processes in the food and fertilizer industries, but wetting intensity and growth rate are relatively low compared to the other configurations investigated in this work. The spouted bed has the most intensive gas–liquid–solid contact and produces compact and dense agglomerates. Both the agglomeration probability and the breakage rate are very high. The Wurster-coater achieves the fastest growth rate for the applied process conditions and is characterised by homogeneous cyclic particle wetting and a low breakage rate. The simulation results are confirmed by lab scale batch agglomeration experiments using maltodextrin DE21, a model substance for amorphous food powders. It can be concluded that the DEM model offers large potential for process intensification by investigating the effect of geometry modifications on the fluid and particle dynamics and on the homogeneity of particle wetting. This is shown exemplarily for fluidised bed agglomeration. [Copyright &y& Elsevier]

Abstract: In this work, a nucleation model that includes nuclei breakage/fragmentation is proposed. The model is based on the nucleation model of Hapgood and the Stokes deformation number calculated from the granule dynamic yield strength from the previously reported granule breakage work. It is proposed that breakage or fragmentation of primary nuclei from binder spray will occur if the Stokes deformation number exceeds a certain critical number. In the case where breakage occurs the model for secondary nuclei size distribution is proposed. To validate the model, the characteristics of the primary nuclei formed from nickel laterite ores with diluted sulphuric solutions as a binder were investigated. The nuclei were produced by dropping the binder solution onto a stationary powder bed. The mechanical integrity of the primary nuclei formed, the relationship between the nuclei diameter and binder drop diameter were studied. The Stokes deformation numbers for nickel laterite powders with different particle size in a lab scale drum granulator were calculated and the nuclei size distributions with different nickel laterite feed powders are predicted. [Copyright &y& Elsevier]

Abstract: A promising method for continuous wet granulation is to pass powdered solids and binder through a twin-screw extruder, usually, as in this case, with co-rotating screws. In the current work, the relationship between operating conditions and product granule properties has been investigated using the same materials (microcrystalline cellulose and polyethylene glycol) as in an earlier study of conventional batch granulation using a high shear mixer-granulator (Tu et al., 2009), enabling a direct comparison to be made. Two extruder configurations were used: with barrel diameter/length dimensions of 16mm/16mm and 16mm/64mm. Two regimes (granulation and extrusion) were recognised for the short mixing geometry, while three regimes (granulation, extrusion and blockage) were recognised for the long mixing geometry and the staggered geometry. The resulting regime maps suggest that optimal granulation (narrow granule size distribution and large mean granule size) can be achieved with a higher liquid-to-solid ratio and a higher screw speed. The uniformity of size distribution can be improved by reprocessing and/or more aggressive mixing. [Copyright &y& Elsevier]

Abstract: The memory effect for cyclopentane hydrate formation has been investigated for various degrees of superheating and time periods. It was found that provided the superheating above the equilibrium temperature for cyclopentane hydrates (7.7°C) was no more than 2–3°C, we could consistently obtain hydrates much faster during cooling to 0.0°C than if hydrates were formed from the liquids for the first time. The memory effect did not always disappear with as much as 8.4°C superheating for 20min, or with 1.5°C superheating for 20h. It was also found that transference of a small amount of water from melted cyclopentane hydrates (made with no more than 2–3°C superheating) to a much larger amount of fresh water and cyclopentane, with no previous cyclopentane history, initiated cyclopentane hydrate formation significantly faster than using the unspiked fresh water alone. This suggests that the memory effect is in the bulk water phase and is probably due to residual clathrate hydrate structure. [Copyright &y& Elsevier]

Abstract: Batch process of silica precipitation was investigated experimentally and interpreted based on available theories and models. Silica was manufactured by neutralization of dilute sodium silicate solution with sulphuric acid in a baffled stirred tank reactor of diameter D T =145mm. Effects of pH, temperature, silica and electrolyte (NaCl) concentration were investigated. Particle size measurements were performed using a Malvern Zetasizer ZS ZEN 3500. Effects of process conditions on agglomeration of silica particles and stabilization of the silica nano-particle suspensions were interpreted using the DLVO based theories and models of surface composition. The stability ratio and surface composition were expressed in terms of the properties of the solution. Results of theoretical investigations together with experimental data show that effects resulting from colloidal forces including repulsion and attraction are not enough to explain aggregation phenomena and thus effects resulting from surface reactions should be considered in modeling as well. [Copyright &y& Elsevier]

Abstract: Unwanted agglomeration, especially in highly concentrated submicron and nano- particle suspensions, can rapidly change the physical product properties of produced particles. Knowledge of the agglomeration kinetics and mechanisms is crucial to achieve control over this secondary sub-process of particle formation. To obtain this kinetics a new measurement method is presented to monitor the shear induced agglomeration behavior of submicron barium sulfate particles while passing a narrow pipe. The residence time, i.e. agglomeration time was varied with the pipe length at constant suspension flow rate. Before measurement, the particle suspension was stabilized by rapid mixing with a dispersing agent. Based on measured agglomerate size distribution, the agglomeration behavior is discussed in terms of non-turbulent flow in a narrow pipe. Barium sulfate agglomeration in a simple shear flow could be monitored on submicron scale. The effect of steric stabilization to reduce or prevent agglomeration was shown and quantified. The controlling mechanism for agglomeration in a pipe is identified based on the hydrodynamic characteristics. The adhesion probability was found to decrease with agglomerate size. [Copyright &y& Elsevier]

Abstract: The solution of a bivariate population balance equation (PBE) for aggregation of particles necessitates a large 2-d domain to be covered. A correspondingly large number of discretized equations for particle populations on pivots (representative sizes for bins) are solved, although at the end only a relatively small number of pivots are found to participate in the evolution process. In the present work, we initiate solution of the governing PBE on a small set of pivots that can represent the initial size distribution. New pivots are added to expand the computational domain in directions in which the evolving size distribution advances. A self-sufficient set of rules is developed to automate the addition of pivots, taken from an underlying X-grid formed by intersection of the lines of constant composition and constant particle mass. In order to test the robustness of the rule-set, simulations carried out with pivotwise expansion of X-grid are compared with those obtained using sufficiently large fixed X-grids for a number of composition independent and composition dependent aggregation kernels and initial conditions. The two techniques lead to identical predictions, with the former requiring only a fraction of the computational effort. The rule-set automatically reduces aggregation of particles of same composition to a 1-d problem. A midway change in the direction of expansion of domain, effected by the addition of particles of different mean composition, is captured correctly by the rule-set. The evolving shape of a computational domain carries with it the signature of the aggregation process, which can be insightful in complex and time dependent aggregation conditions. [Copyright &y& Elsevier]

Abstract: The production and stabilization of crystalline pharmaceutical suspensions, an area of great importance to the pharmaceutical industry, was investigated through exploration of the ability of surfactants and polymers to affect the growth and stability of poorly water soluble pharmaceutical crystals on a molecular scale using molecular dynamics simulations coupled with anti-solvent crystallizations. Griseofulvin, a model poorly soluble drug, was simulated in an aqueous system containing individual non-ionic surfactant Tween 80, polymer HPMC, polymer Pullulan, and anionic surfactant SDS, as well as binary surfactant–polymer mixtures. To evaluate the stability and growth potential of the crystals, the interfacial binding energies between three elementary faces were calculated and compared, based on which HPMC was determined to be the most effective individual additive of those tested. Additionally, the potential synergism of additives was evaluated by the simulation of binary mixtures containing each of the non-ionic additives with the anionic surfactant SDS at different starting configurations. The combination of HPMC with SDS proved to be the most effective and significantly greater than HPMC when used alone. Simulation results were validated by observing both crystal growth rates, as well as final particle sizes of griseofulvin crystals grown using an antisolvent crystallization in the presence of individual and mixtures of additives, suggesting that the simulation approach may be used as a screening tool for selection of additives. [Copyright &y& Elsevier]

Abstract: The objective of this work was to characterize a sub-micron grinding process in a wet ball mill including the agglomeration of fines inside the grinding chamber. To do so a population balance model has been developed. A Dynomill ball mill was used and the grinding medium consisted of zirconium oxide beads. The product under investigation was poorly water-soluble. The particle size distribution of the initial powder ranged from 1 to 100um. Laser diffraction was used to analyze the particle size distribution. During grinding the average particle diameter of a particulate product is reduced to a minimum value. These grinding experiments showed that for a specific product this minimum value is a fixed constant within the range of tested operating conditions. This minimum average particle diameter could be influenced by modification of the particle surface properties with surface active agents. The minimum mass mean particle diameter is a result of grinding and simultaneous agglomeration of broken particles. To build a representative model, a dynamic population balance model was developed. The crystallite size as measured with X-Ray diffraction was chosen as the minimum achievable particle size by grinding. Simulations showed that the applied population balance model is an adequate tool to forecast the evolution of the particle size reduction process and the time required to reach the final product specifications. The product could be defined as “very brittle” using the approach from and . The shear induced by the translation movements of the grinding medium beads was thus enough to break the particles. The median particle size of the broken particles (x 50) was plotted as function of the number of stress events (SN) in the mill. This number of stress events was calculated for one initial product particle. That is the representative number of stresses that needs to be applied on an initial particle to break it into fractions with the desired fine particle size. SN is proportional to the number of media contacts and their frequency, and the probability that a media contact leads to particle breakage. That frequency of media contact is defined as the angular rotation speed (ω) of the mill corrected by an efficiency factor (γ F ). The stress number SN is characteristic of the ground product. The efficiency factor γ F describes the efficiency with which the impellor transfers its energy to the grinding medium. γ F was a function of the mill design and more specifically the impellor shape. Factor γ F is taken as the surface of the impellor in contact with the grinding media. This approach leads to a general representation of the grinding profile of the studied product in a stirred media mill. [Copyright &y& Elsevier]

Abstract: Pulverized coal is important for gasification to convert carbonaceous fuel to gaseous products with a usable heating value; it is cohesive with a poor flowability, typical of Group C powders. The fluidization behaviors of pulverized coal in a fluidization column and in a Perspex hopper were investigated. The pulverized coal was extremely hard to be fluidized and its experimental incipient fluidizing velocity was much larger than expected. The discharge of pulverized coal from a carbon steel hopper under several aeration rates was studied. Four flow regions were developed, and the major phenomena that occurred during the discharge were analyzed. The mechanism of aerated discharge was probably the integration of various effects, all of which were confirmed by the experimental data. [Copyright &y& Elsevier]

Abstract: A new structured discretization of 2D space, named X-discretization, is proposed to solve bivariate population balance equations using the framework of minimal internal consistency of discretization of Chakraborty and Kumar [2007, A new framework for solution of multidimensional population balance equations. Chem. Eng. Sci. 62, 4112–4125] for breakup and aggregation of particles. The 2D space of particle constituents (internal attributes) is discretized into bins by using arbitrarily spaced constant composition radial lines and constant mass lines of slope −1. The quadrilaterals are triangulated by using straight lines pointing towards the mean composition line. The monotonicity of the new discretization makes is quite easy to implement, like a rectangular grid but with significantly reduced numerical dispersion. We use the new discretization of space to automate the expansion and contraction of the computational domain for the aggregation process, corresponding to the formation of larger particles and the disappearance of smaller particles by adding and removing the constant mass lines at the boundaries. The results show that the predictions of particle size distribution on fixed X-grid are in better agreement with the analytical solution than those obtained with the earlier techniques. The simulations carried out with expansion and/or contraction of the computational domain as population evolves show that the proposed strategy of evolving the computational domain with the aggregation process brings down the computational effort quite substantially; larger the extent of evolution, greater is the reduction in computational effort. [Copyright &y& Elsevier]

Abstract: Small quaternary ammonium salts, particularly with butyl or pentyl groups, have been shown previously to be good Structure II tetrahydrofuran hydrate crystal growth inhibitors. This ability has been exploited in their use as synergists for certain kinetic hydrate inhibitor polymers, and in the design of commercial gas hydrate anti-agglomerants. We have now investigated the effect of bis- and polyquaternary ammonium salts, in which all the nitrogen atoms are in the backbone of the molecule, on the crystal growth of tetrahydrofuran hydrates. The results are compared with those of monomeric quaternary compounds previously reported. The new compounds tested contain 2 to over 100 quaternary centres with various structural geometries including linear and branched polymers. The size of the alkyl groups on the nitrogen atoms was varied and contained from 2 to 6 carbon atoms. Improved performance over monoquaternary ammonium salts was obtained with both bis-quaternary and polyquaternary ammonium products. The optimal distance between the nitrogen atoms in bis-quaternary ammonium salts for best THF hydrate inhibition appears to be with a chain of 6–8 aliphatic carbon atoms. [Copyright &y& Elsevier]

Abstract: There have been significant advances in the understanding of wet granulation processes. Foam granulation is the latest development and an emerging area of interest for pharmaceutical manufacturing. Single foam penetration experiments were carried out on static powder beds, followed by short-nucleation experiments (where nuclei are formed by a nucleation-only mechanism) and full foam granulation experiments (where nucleation, growth and breakage are occurring simultaneously). All experiments were performed with lactose monohydrate powder using a 5L high shear mixer–granulator. The foam penetration/dispersion behaviour was examined and the granule size distributions were investigated as a function of foam quality (83–97% FQ), impeller speed (105–515rpm) and wet massing period (0–4min). Nucleation in foam granulation is postulated to undergo either “foam drainage” or “mechanical dispersion” controlled mechanisms. For “foam drainage” mechanism, the foam penetrates the powder bed to form coarse and broad granule size distributions. For “mechanical dispersion” mechanism, the wetting and nucleation conditions are governed by the powder mixing conditions and similar granule size distributions are produced. Regardless of the mechanism, the initial wetting and nucleation behaviour controls the initial nuclei size distribution, and this initial distribution is retained in the final granule size distribution. This work demonstrated the critical importance of the nucleation and binder distribution in determining the granule size distributions for foam granulation process. [Copyright &y& Elsevier]

Abstract: Nanomaterial suspensions with different dopant types and compositions were investigated to examine their effects on agglomeration through the measurement of hydrodynamic diameter (HD), surface charge, and isoelectric point (IEP). Four different types of nanoparticles, all synthesized by a flame aerosol reactor, were considered for the analysis. The nanoparticles considered were pristine TiO2, Cu–TiO2, V–TiO2, and Pt–TiO2 with dopant concentrations ranging from 1 to 6wt%. Measurements were conducted over a broad range of pH (3–11) and ionic strengths (0.001–0.1M) to understand the roles of pH and ionic strength (IS) on dispersion characteristics. Calculations were made using the classical DLVO theory to explain the agglomeration behavior. The results indicate that dopant addition can change surface charge, hydrodynamic diameter, and shift the IEP to higher or lower pH than pristine TiO2, depending on the type of dopant and composition. Vanadium and platinum doping shifted the IEP to lower pH values, whereas copper doping shifted it to higher pH values. For each of the nanoparticles considered, pH and IS were found to have significant effects on the surface charge and HD, which were also verified by calculation from DLVO theory. [Copyright &y& Elsevier]

Abstract: A 26mm N.B. horizontal pipe loop has been used to study the transport velocity of aqueous dispersions of colloidal silica. At low electrolyte concentrations the silica spheres form a stable dispersion, while at high electrolyte concentration particle aggregates are readily formed. Two measurement techniques have been used to study the critical transport velocity; (i) flow visualisation, and (ii) ultrasonic Doppler velocity profiling. Both measurement techniques show agreement in identifying the critical transport velocity. The study has shown that the critical transport velocity can be reduced when the suspension is transformed from a dispersed (d 50=0.8μm) to an aggregated (d 50=4.6μm) state. Such behaviour is related to the introduction of inter-floc flow through aggregates, enhancing the turbulence intensity of the fluid. [Copyright &y& Elsevier]

Abstract: The effect of the primary particle porosity during the formation of agglomerates in spray fluidized beds is presented in this study. The method is based on the single micro-interactions occurring within the fluidized bed such as inter-particle collisions, droplet spread on the particle surface, aging of the deposited droplets and particle coalescence. The porous character of the particles is expected to directly affect the aging process of the deposited binder layer by penetration into the pores of the substrate. The droplet penetration process is experimentally analyzed by single droplet deposition on spherical, porous alumina particles. The results indicate that the penetration process is mainly governed by the viscosity of the liquid and that at relatively low viscosities, droplet penetration is fast. For highly viscous liquids, the penetration velocity slows down and an additional mechanism, namely drying becomes important. A combined imbibition–drying model is developed and included into a comprehensive stochastic agglomeration model that allows the simulation of agglomerate formation in a batch process. Lab-scale agglomeration experiments with porous and non-porous particles are carried out in an attempt to validate the general tendencies predicted by the main agglomeration model. The results show that the agglomeration rate for porous particles is significantly reduced due to the losses of deposited droplets into the pores of the primary particles; this tendency is much more pronounced at low binder viscosities. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to characterise the cohesive behaviour of powders by measuring aerosolisation at a sequence of different flow rates, i.e. flow titration. Salbutamol sulphate and Lactohale 300 were model cohesive materials. Laser diffraction particle sizing of the aerosolised plume provided in-situ, real time particle size distributions of the aerosolised powder dispersed at increasing flow rates, from 30 to 180Lmin−1. Relative de-agglomeration was determined from the cumulative particle size of the aerosolised powder less than 5.4μm compared with the full availability of particles in that size range. Relative de-agglomeration-flow rate profiles were modelled using a non-linear least squares regression to fit an empirical 3-parameter sigmoidal equation; the parameters of the sigmoid were estimated from the data. Relative de-agglomeration–flow rate titration profiles and their estimated parameters were obtained to define the different de-agglomeration mechanisms of the two cohesive powders. Salbutamol sulphate showed a maximum percent de-agglomeration of 54.9%, compared with Lactohale 300 which was only 29.5%. Lactohale 300 gave 50% of its maximum de-agglomeration at a flow rate of 48.0Lmin−1 while the equivalent for Salbutamol sulphate was 113.8Lmin−1. Salbutamol sulphate and Lactohale 300 demonstrated different patterns of dispersion in relation to de-agglomeration mechanism. This approach to characterising the aerosolisation processes has significant application in designing formulation and processing strategies for pharmaceutical inhalation drug delivery. [Copyright &y& Elsevier]

Abstract: The Chemical Reactor Engineering Center – Gas Solid – Optiprobes (CREC-GS-Optiprobe) can be used to determine particle cluster properties in down flow reactors. These properties include solid hold-up, cluster size and cluster velocity. Critical to this task is the determination of the “focal region”. It is established in this study that the CREC-GS Optiprobes display an “effective focal region” smaller than the focal region calculated using geometrical and optical considerations. In this respect, an “effective focal region” of 118μm with a standard deviation of 34μm is established on the basis of different considerations including experimental observations. The existence of this “effective focal region” is most valuable in downer units given it makes the CREC-Optiprobe a suitable tool for measurements of clusters sizes with an average diameter of 84μm FCC particles as well as local solid concentration. [Copyright &y& Elsevier]

Abstract: New data are reported on the filtration of binary fibre/titania (rutile) mixtures. The combined use of the Kozeny–Carman equation and Darcy’s law is presented and discussed in relation to application in the filtration of binary mixtures. Upon close study, this approach is shown to have its limitations, particularly when significant aggregation takes place between the two solids species. The difficulties in overcoming these limitations from a purely fundamental basis are highlighted, and a semi-empirical model is presented and discussed. This model appears to represent the specific resistance trend with solids composition reasonably well for a wide range of binary mixture filtration data. [Copyright &y& Elsevier]

Abstract: Fluid flow and charge transport in nanoporous packed beds are closely interrelated due to the formation of the electrochemical double layers on the solid–liquid interfaces, thus giving reason to the term electrohydrodynamic transport. This interrelation results from the formation of electrochemical double layers on the particle surfaces. The electrohydrodynamic transport thus depends on the physicochemical properties of the packed bed, as well as on the on its pore structure, which is also determined by the physicochemical properties. Despite its promising commercial applications, the electrohydrodynamic transport in nanoporous structures is only partly understood. This study presents an empirical model for the hydraulic permeability of packed beds and a capillary model for the interaction of mass and charge transport. The capillary model permits to separate between structural and physicochemical influences, based on experimentally determined parameters. A numerical investigation of the formation and hydraulic permeation of packed beds confirms the empirical model for the hydraulic permeability and gives further insight into the structure of the packed beds. [ABSTRACT FROM AUTHOR]

Abstract: Wet granule breakage is a significant mechanism, particularly in high shear mixer granulation. This paper presents a study of the wet breakage mechanism using a Breakage Only Granulator. Granules with varying powder and liquid binder properties were created using single drop nucleation. These granules were inserted in a Breakage Only Granulator, a high shear mixer granulator with non-granulating cohesive sand as the bulk medium. Two different impellers were used at impeller speeds of 500 and 750rpm. An 11° beveled edge impeller was used to create both impact and shear in the granulator, and a flat plate impeller was used to minimize impact and maximize shear in the granulator. The fraction of granules which broke during the granulation process was used as a measure of granule breakage within the granulator. These results were compared with Stokes deformation numbers calculated using mean dynamic peak flow stresses measured in unconfined uni-axial compression tests. Results for the beveled edge impeller blade show increasing breakage with increasing Stokes deformation number. Significant breakage was observed at high Stokes deformation number. Increasing impeller speed increased the magnitude of breakage. The Stokes deformations number appears to be a reasonable predictor for granule breakage within the granulator. Results for the flat plate impeller show very little breakage at 500rpm, and significant breakage for only one formulation at 750rpm. This suggests that either impact is dominant over shear for breakage within the granulator, or that the two impeller designs give substantially different collision velocities in the granulator. The impeller speed, type and shape have a profound effect on granule breakage in high shear mixer granulators. [ABSTRACT FROM AUTHOR]

Abstract: Agglomeration occurring during fluidized bed incineration not only causes the fluidization characteristics to change and the system to unexpectedly shut down, but it also leads to the generation of secondary pollutants such as heavy metals. Accordingly, the aim of this study is to estimate the mechanisms of particle agglomeration in fluidized bed incineration. Experiments are carried out, including a pilot-scale fluidized bed test and a laboratory furnace test. Thermodynamic equilibrium simulations are also considered. In addition, the speciation of agglomerates is determined from the analysis of the laboratory furnace using X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and field emission scanning electron microscopy/energy dispersive spectrometry (FESEM–EDS). The experimental results reveal that higher concentrations of metals are emitted when defluidization occurs. When we compare the results from two different agglomeration inhibitors, the Al-based additive is shown to achieve higher levels of inhibition versus a Ca-based additive. In addition, the results from our simulation illustrate that the heavy metals Pb, Cr, and Cd have different affinities with Na, Si, Al, and Ca, which causes different emission behaviors during the agglomeration inhibition processes. Good agreement is observed among the experimental data, the agglomerate characterization, and the thermodynamic equilibrium simulations. The primary mechanisms of both particle agglomeration and the emission of heavy metals are also established. [Copyright &y& Elsevier]

Abstract: The crystallization kinetics of aluminium hydroxide from the sodium aluminate solution reacted with sodium bicarbonate were systematically investigated in a steady-state MSMPR (mixed-suspension mixed-product removal) crystallizer for the first time, and the expressions of the nucleation rate, growth rate and the agglomeration kernel of aluminium hydroxide were successfully regressed. The aluminium hydroxide particles precipitated from the reactive system are identified as gibbsite by XRD and SEM examinations. The volume growth rate order of gibbsite with respect to the relative supersaturation of the solution is above the linear growth rate order, and the spiral growth mechanism for the growth of the basal face of gibbsite in the reactive system was further identified by the growth rate, morphology analysis as well as the calculated surface entropy factor. The secondary nucleation rate of gibbsite from the reactive system is three to four orders of magnitude larger than that from seeded process reported in the only available literature reference. The agglomeration kernel of gibbsite in the reactive system increases linearly with growth rate and residence time, and the positive order about 0.55 of magma density is thoroughly different from the negative order of magma density for gibbsite agglomeration in seeded process presented in the literature. [Copyright &y& Elsevier]

Abstract: A simplified mathematical model and numerical simulations of the governing Navier–Stokes equations are used to predict the shape evolution, rupture distance, and liquid distribution of stretching pendular liquid bridges between two equal-sized spherical solid particles. In the simplified model, the bridge shape is approximated with a parabola, and it is assumed that the surface tension effects dominate the viscous, inertial, and gravitational effects. For the numerical simulations, a commercial Computational Fluid Dynamics (CFD) software package – FLUENT – is used. The rupture distance predictions obtained with both models are compared with experimental data and a reasonable agreement is found. The results of the numerical investigations show that for simulations with negligible viscous, inertial, and gravitational effects, the rupture distance approaches an asymptotic value, which is close to the value predicted by the simplified model. The bridge profiles predicted using the simplified model and the numerical simulation are compared. It is found that a second-order polynomial appropriately represents the stable bridge shape for particles with identical contact angles; however, for liquid bridges between particles with different contact angles, the numerical simulations of the governing Navier–Stokes equations should be used. [Copyright &y& Elsevier]