Agglomeration Of Fine Particles Research Articles

In vitro cytotoxicity of carbon black nanoparticles synthesized from solution plasma on human lung fibroblast cells

Carbon black nanoparticles (CB-NPs) have been synthesized from liquid benzene by a solution plasma method at room temperature and atmospheric pressure. The morphological observation by scanning electron microscopy revealed the agglomeration of aggregated fine particles. The synthesized CB-NPs were predominantly amorphous as confirmed by X-ray diffraction. The in vitro cytotoxicity of CB-NPs on the human lung fibroblast (MRC-5) cell line was assessed by the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and systematically compared with those of two types of commercial carbon blacks (i.e., Vulcan XC-72 and Ketjenblack EC-600JD). Cell viabilities were studied at different concentrations of 32.5, 65, 125, and 250 µg/mL. It was found that the CB-NPs derived from solution plasma exhibited a lower cytotoxicity on the MRC-5 cells than the other two comparative carbon blacks. The viability of MRC-5 cells exposed to CB-NPs remained higher than 90% even at a high concentration of 250 µg/mL. This result preliminarily confirmed the biosafety and potential use of CB-NPs in the field of biological applications.

Hydrophobic agglomeration of talc fines in aqueous suspensions

In this work, hydrophobic agglomeration of fine talc particles in aqueous solutions under mechanical conditioning and without any addition of surfactants has been experimentally studied. A method of in-situ measurement of turbidity of flocs suspension in the settlement process has been applied, and the turbidity as a function of settling time has been attempted to fit a certain function so as to assess the hydrophobic agglomeration behaviors. Effects of kerosene dosages, stirring rate, and wettability of talc particles on the hydrophobic agglomeration behaviors have been investigated. The results show that the addition of kerosene can greatly enhance the aggregation of colloidal talc in aqueous suspensions. Besides, the stirring strength and duration make an enormous influence on the aggregation through providing the kinetic energy for overcoming the energy barrier between the approaching particles. It is also found that the wettability of talc is closely related to the aggregation degree. More hydrophobic talc particles show a much stronger aggregation behaviors.

Pbm/les numerical simulation of vortex structure and fine particles agglomeration in three-dimensional plate jet

The emission of fine particles has caused serious environmental problems due to the characteristics and the low removal efficiency of fine particles. The turbulent agglomeration is one of the most promising precondition techniques for guiding the growth and reunion of fine particles into larger particles, which is convenient to be captured by conventional precipitators when the size of particles increases to about 1·10-6 m. This paper sets up a three-dimensional plane jet as a subject, we use the method of Population balance model (PBM) and Large eddy simulation (LES) to analyse the agglomeration of fine particles in this model. Furthermore, a study of the distribution of particle size via turbulent aggregation kernel function is presented. There are two main parameters which related to enlargement of fine particles, including the flow field of gas and the jet velocity. The simulated results show that there is a close relationship between particle distribution and jet vortex field. The agglomeration effect of fine particles increases with the increasing of jet velocity, and the influence of jet velocity is not obvious for particle enlargement.

A novel Lagrangian agglomerate structure model

Agglomeration of fine particles in fluid flows is important for many processes in powder handling or production. In order to accurately perform numerical calculations of such processes models are needed which realistically describe particle agglomeration. For applications in the frame of an Euler/Lagrange approach such a model was developed which allows predicting the agglomerate structure and its behaviour in the point-particle approximation. The detection of collisions between primary particles or particles and agglomerates is realised by the stochastic collision model. The collision point on the particle or agglomerate surface is generated by accounting for the impact efficiency. The developed structure model is based on storing location vectors from the reference primary particle to all other particles collected in the agglomerate which is still treated as point-mass. Thereby the structure and porosity of the agglomerate is known and an equivalent agglomerate diameter (e.g. gyration diameter) is obtained. With this information the fluid dynamic forces acting on the agglomerates can be predicted correctly as well as the appropriate collision cross-section is used in the collision modelling. For testing the novel agglomerate structure model, fine particle agglomeration in homogeneous isotropic turbulence is calculated considering different properties of the primary particles or droplets. In the case of dry solid particles the van der Waals adhesion force is considered and based on an energy balance the possibility of particle sticking or rebound is calculated. Moreover, high viscous droplets are considered as primary particles, a situation also found in spray dying. For such cases the penetration of two primary particles or a primary particle and a stochastically selected primary particle within an agglomerate is modelled. The structure of the agglomerates produced under these different situations and for mono- and poly-sized primary particles are analysed and compared, using for example gyration diameter, porosity of convex hull and fractal dimension. These results demonstrate that the developed novel agglomerate structure model is applicable in the frame of an Euler/Lagrange approach and provides appropriate results.

The filler effect: The influence of filler content and type on the hydration rate of tricalcium silicate

AbstractThe partial replacement of ordinary portland cement (OPC) by fine mineral fillers accelerates the rate of hydration reactions. This acceleration, known as the filler effect, has been attributed to enhanced heterogeneous nucleation of C‐S‐H on the extra surface provided by fillers. This study isolates the cause of the filler effect by examining how the composition and replacement levels of two filler agents influence the hydration of tricalcium silicate (T1‐Ca3SiO5; C3S), a polymorph of the major phase in ordinary portland cement (OPC). For a unit increase in surface area of the filler, C3S reaction rates increase far less than expected. This is because the agglomeration of fine filler particles can render up to 65% of their surface area unavailable for C‐S‐H nucleation. By analysis of mixtures with equal surface areas, it is hypothesized that limestone is a superior filler as compared to quartz due to the sorption of its aqueous CO32− ions by the C‐S‐H—which in turn releases OH− species to increase the driving force for C‐S‐H growth. This hypothesis is supported by kinetic data of C3S hydration occurring in the presence of CO32− and SO42− ions provisioned by readily soluble salts. Contrary to prior investigations, these results suggest that differences in heterogeneous nucleation of the C‐S‐H on filler particle surfaces, caused due to differences in their interfacial properties, have little if any effect on C3S hydration kinetics.

Electric agglomeration modes of coal-fired fly-ash particles with water droplet humidification

Electric agglomeration is a useful method to improve fly-ash particle collection efficiency in traditional electrostatic precipitators (ESPs) by increasing particle diameter and achieving particle pre-charging. In this study, a laboratory agglomerator, which consisted of a pre-charging region and a static mixer, was designed and tested for fine particle agglomeration. The pre-charging provided both positive and negative discharges in parallel channels. Fine water droplets were used to enhance particle agglomeration and collection efficiency in a downstream small ESP. The operating effects were evaluated under various applied voltages and droplet concentrations. Experimental results showed that the presence of water droplets effectively improved coal-fired particle agglomeration, pre-charging, and collection in the ESP. The total number collection efficiency improved from 53.91% to 86.02% compared with the condition without the agglomerator. In addition, a novel sampling method was used to observe agglomerated particles using scanning electron microscopy, and theoretical adhesive force analysis supported the proposal of a series of power-plant particle electric agglomeration modes.

Novel Single-Step Combustion Synthesis of Nanocrystalline MgFe2O4 Materials Using Hexamethylenetetramine as a Fuel: Properties and Features

In this work, a novel combustion synthesis of nanocrystalline MgFe2O4 materials using hexamethylenetetramine as a fuel is reported. The properties and features of as-prepared MgFe2O4 materials were evaluated by X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometer, UV-vis and Fourier transform infrared spectroscopic techniques, and field emission scanning electron microscope. The as-prepared MgFe2O4 materials crystallized in cubic spinel phase with an average crystalline of 26.34 and 21.54 nm for the samples obtained at pH = 1 and 10, respectively. It is evident from the room temperature (300 K) field (±15 kOe) dependence magnetization measurements that the saturation magnetization of the MgFe2O4 materials is 25.86 emu/g and 9.98 emu/g for pH = 1 and 10, respectively. For the as-prepared MgFe2O4 materials, the agglomeration of fine particles is seen through a micro-image under higher magnification. The FT-IR spectra reveal a typical metal–oxygen absorption band at ∼568 cm−1 for the as-prepared MgFe2O4 materials which suggest the intrinsic stretching vibration of the metal (Fe–O) at the tetrahedral site.

Agglomeration and capture of fine particles in the coupling effect of pulsed corona discharge and acoustic wave enhanced by spray droplets

Fine particles from industrial processes are considered to be potentially harmful to humans and environment, and massive amounts of fine particles are continuously emitted into the air due to the low removal efficiency of current conventional dust capture devices. A novel pretreatment process using the coupling effect of pulsed corona discharge and acoustic waves enhanced by spray droplets for fine particle agglomeration and capture was investigated in this study. The application of pulsed corona discharge in an acoustic field led to an increase in the efficiency of fine particle agglomeration to 74.7%, and the improvement was much more obvious for low frequency acoustic waves. The spray flow rate delivered by the spray nozzles with a size of 0.30mm or 0.40mm was incrementally increased. Furthermore, the penetration efficiency initially decreased, then increased, and finally decreased when droplets were sprayed in either a pulsed corona discharge field or an acoustic wave field. The penetration efficiency of fine particles substantially decreased to 10% with the enhancement of spray droplets coupled with both a pulsed corona discharge and an acoustic wave, both at their most efficient settings. The penetration efficiency further decreased with the addition of sodium dodecyl sulfonic salt surfactant to the spray droplets, in particular, at a concentration of 0.3%.

Effects of turbulent intensity on nano-PMMA flame propagation behaviors

Experiments with different ignition delay times (td) corresponding to different residual turbulent intensities after dispersion were conducted to reveal the effects of turbulent intensity on nano-PMMA flame propagation behaviors. The residual vertical root-mean-square (RMS) turbulent velocities and RMS vorticities measured by a particle image velocimetry system (PIV) at td = 0.9 s, 1.0 s and 1.1 s were 0.22 m/s, 0.16 m/s, and 0.15 m/s and 50.40/s, 38.23/s, and 36.68/s, respectively. It was indicated that the residual turbulent intensity in the combustion space decayed with increasing ignition delay time. One-hundred nanometer PMMA dust flames with a nominal concentration of 450 g/m3 were approximately spherical in shape and propagated continuously after ignition at different ignition delay times. As time proceeded, the flame front of td = 0.9 s was still smooth, whereas the flame fronts of td = 1.0 s and 1.1 s were irregular due to the dominant effects of flame self-instability against the residual turbulence. The average pulsating flame propagation velocities of td = 0.9 s, 1.0 s and 1.1 s were 0.67 m/s, 0.54 m/s and 0.44 m/s, respectively. The pulsating level was enhanced by extending the ignition delay time due to the weaker residual turbulent intensity compared with the turbulence induced by the dust flame self-instability. In addition, the suspended particle size distribution was measured by a Phase Doppler Particle Analyzer (PDPA). It was found that the effective suspended particles existed as agglomerates of fine particles rather than as the primary particles themselves.

A study of the redistribution of fines between carriers in adhesive particle mixing using image analysis with coloured tracers

Understanding the dynamics and kinetics of mixing mechanisms, i.e. random mixing, de-agglomeration, adhesion, and redistribution, is critical in order to achieve a structure of interest in adhesive particle mixing. In this work, the redistribution of fines between carrier particles, one of the key mechanisms in establishing a homogeneous mixture, was investigated. Coloured carriers (tracers) and image analysis utilizing CIELCH colour space are used as a tool to assess the dynamics of such a mechanism via the evolution of the colour of blends. It is found that, in a high shear mixer, redistribution quickly reaches a pseudo-steady state within a time scale that is of the same order of magnitude as that of random mixing. Considering all the governing mechanisms necessary to achieve an adhesive mixture, it is concluded that the de-agglomeration of fine-particle agglomerates is the rate-limiting step. This work also demonstrates that the redistribution of fines is influenced by the structure of fines on carrier surfaces resulting from processing conditions. This finding supports the fact that beside material properties, blending conditions, e.g. mixing speed and time, are crucial as regards the structure of adhesive mixtures for inhalation.

A Versatile Combustion Synthesis and Properties of Nickel Oxide (NiO) Nanoparticles

We report here a simple solution combustion synthesis of nickel oxide (NiO) nanoparticles by using urea as a fuel and nickel nitrate as an oxidizer. The structural, morphological, optical, and magnetic properties of NiO nanoparticles were investigated by X-ray diffraction (XRD); highresolution scanning electron microscopy (HRSEM); Fourier transform infrared (FT-IR), nearinfrared (NIR), and UV-vis spectroscopic techniques; and vibrating sample magnetometer. The combustion-synthesized NiO nanoparticles have a cubic structure with an average crystalline size of ∼8 nm without any impurity. The agglomeration of fine particles with particle sizes in the range of 19.5 ∼22.4 nm is seen by HRSEM images. The FT-IR spectrum of NiO nanoparticles reveals that an absorption band at ∼493 cm −1 is due to the bending vibration of NiO phase. The NIR spectrum exhibits poor NIR reflectivity of the combustion product, NiO. The as-prepared combustion product was black in color in contrast to the usual light green color. The room-temperature magnetization of the as-prepared NiO nanoparticles reveals an antiferromagnetic behavior.

Morphology study on the depleted uranium as hydriding/dehydriding cycles

Depleted Uranium (DU) is one of the strongest candidates as a getter material of hydrogen isotopes in the nuclear fusion reactor. In this work, small DU lump specimen with 99.8% purity was prepared for observation of morphology variation as hydriding/dehydriding cycles. Hydriding/dehydriding of DU was carried out more than 10 cycles for powder preparation. The pulverized DU specimen was safely handled in the glove box under Argon gas condition to minimize contact with oxygen and humidity. The morphology change according to hydriding/dehydriding cycles was observed by visual cell reactor, optical microscope and scanning electron microscope. The first hydriding of the small DU sample has progressed slowly with surface enlargement and volume expansion as time passes. After third hydriding/dehydriding cycles, most of DU was pulverized. The powder fineness of DU developed as hydriding/dehydriding cycle progresses. But the agglomerates of fine DU particles were observed. It was confirmed that the DU particles exist as porous agglomerates. And the particle agglomerate shows poor fluidity and even has the cohesive force.

Effect of synthesis on the purity and particle size of ZrB2 powder

In the present investigation, an attempt has been made to prepare ZrB2 powder by self-propagating high temperature synthesis (SHS) technique. The effect of synthesis on the purity and morphology of powder is investigated. A stoichiometric mixture of ZrO2, H3BO3 and Mg powder is synthesised in a resistance heating tubular furnace with continuous flow of high pure argon gas. The synthesis is also carried out with NaCl as a diluent. The MgO is leached out from the as-synthsised powder. Phase analysis of powder is performed by X-ray diffraction (XRD). Laser beam scattering technique is used to measure the particle size distribution. The morphology of powder is characterized by scanning and transmission electron microscopes. The XRD results show the presence of significant amount of unreacted ZrO2 phase in the product. The product is mixed with calculated amount of magnesium and boric acid and the mixture is synthesised further. There is a significant decrease of unreacted ZrO2 in the product after double synthesis. The SEM images show the presence of agglomeration of fine particles, whereas the TEM images show the decrease of particle size after double synthesis. To understand the synthesis process, the individual synthesis of ZrO2-Mg and H3BO3-Mg are also performed.

Experimental investigation of aerodynamic agglomeration of fine ash particles from a 330 MW PC-fired boiler

This paper reports the experimental investigation of fine particle agglomeration through an in-situ trial on aerodynamic agglomerators installed in front of the electrostatic precipitator (ESP) of a 330MW PC-fired (i.e. pulverized-coal-fired) boiler. It is demonstrated that the agglomerators greatly reduce the fine particles entering the ESP. In particular, for the present case, the fine particles of the aerodynamic diameter ⩽2.5μm (PM2.5) and those ⩽10μm (PM10) are found to decrease 56.2% and 50.6%, hence reducing the overall particle concentration by 26.3mg/Nm3 at the outlet of the ESP. Also, the mercury concentration of 891.08ng/g obtained in the ash from hoppers of the ESP with the agglomerators is 26.4% higher than that of the ESP without agglomerator. Therefore, the application of aerodynamic agglomerators is believed to reduce both emissions of fine particles and mercury from the flue gas of PC-fired boilers. In addition, the reason for the above observations is also explored in the paper.

Multilayer adhering model for holdup and separation behavior of fine particles in a powder-particle fluidized bed

Time variation of the holdup of fine particles in a powder-particle fluidized bed was formulated on the basis of a multilayer adhering model. Unsteady-state experiments using a fluidized bed of 550μm-silica sand, limestone, and glass beads were conducted under different operating conditions, changing the inlet concentration of aerosol fines (aluminum hydroxide), superficial gas velocity, and particle size of the fines (0.5 to 3μm). The multilayer adhering model provided nearly the same value as that experimentally obtained. The model was modified so as to interpret numerous separable layers, which were subjected to being removed as fine-particle agglomerates. A change in the mechanism of the elutriation of fine particles with the size of fine particles was explained.

Mechanistic time scales in adhesive mixing investigated by dry particle sizing

This study exploits the mechanisms governing blending of adhesive mixtures, i.e. random mixing, de-agglomeration and adhesion, and their relative importance to achieve mixing homogeneity. To this end, blending of micronized particles (fines) with carrier particles was carried out using a high shear mixer. Dry particle sizing using laser diffraction coupled with a strong powder dispersion unit was employed to measure the fines content in samples collected during mixing, and hence to assess blend homogeneity. The method was also employed to evaluate the relative strength of the agglomerates present in the fines. Particle sizing using a non-destructive imaging technique was used to monitor changes in particle size during blending. It could be shown that the de-agglomeration of the fine-particle agglomerates is the slowest mechanism and hence the rate-limiting step as regards achieving a homogeneous adhesive mixture. Consequently, a longer mixing time is needed for blending of larger agglomerates. Being fast, simple and reproducible, the laser diffraction technique was shown to be an efficient method for measurement of fine particle content and homogeneity of a mixture, while the non-destructive image analysis was able to give relevant information on the rate of de-agglomeration of the fine-particle agglomerates as well as on the size of the resulting carrier-fine particle assemblies.

Laboratory Investigation on Residual Strength of Reclaimed Asphalt Mixture for Cold Mix Recycling

The purpose of this study is to evaluate the residual strength of reclaimed asphalt pavement (RAP) to understand the strength forming mechanism of RAP in cold recycled asphalt mixture. The mechanical properties of the RAP were investigated as compared to the properties of pure aggregates. Triaxial shear tests were conducted to analyze the residual cohesion of asphalt binder in the RAP. The gradation and specific surface area of RAP were analyzed to understand the agglomeration structure of coarse RAP particles. Splitting strength of cement-RAP mixtures was tested as compared to cement-aggregate mixtures. It can be concluded that the RAP in the cold recycled asphalt mixture does not act exactly like ＂black color＂ aggregates. The aged asphalt in the RAP has active cohesion although its cohesion strength is much lower than the binder in the hot-mix asphalt mixture. The coarse RAP particles formed by agglomeration of fine particles and the aged binder have important influences on the strength of cold recycled asphalt mixtures. The cement-RAP mixture has much lower splitting strength than the cement-aggregate mixture with the same gradation and cement content. It is important to add new aggregate into the recycled mixture to increase the effective aggregate surface area that can be coated with the new binder.

Preliminary Experimental Study of Acoustic Agglomeration of Coal-fired Fine Particles

Respirable particulate matter, especially fine particles are doing great harm to human health and the environment nowadays, but the removal efficiency of traditional dust removal devices for PM2.5 is quite low. Acoustic agglomeration is a pretreatment technology of dust removal which uses sound wave with high intensity to make fine particles get agglomerate and grow up, and improves the efficiency of traditional dust removal devices for PM2.5 and thus reduces the concentration of fine particle emissions. In this paper, the experimental set-up of acoustic agglomeration is designed and reconstructed. Coal-fired ashes are mixed with air to simulate aerosol emissions from coal-fired power plants. A travelling wave acoustic field is generated in a vertical agglomeration chamber in which the residence time of the aerosol is around 4s. Preliminary experimental study of the influence of acoustic frequency, SPL and the initial concentration of aerosol on the acoustic agglomeration is conducted. It is found that the efficiency of agglomeration is very sensitive to the change of acoustic frequency and there exists an optimal frequency which in this paper is 1400Hz. The effect of acoustic agglomeration has a linear relationship with SPL and it is enhanced with the increase of SPL. The increase of the initial number concentration of aerosol can also enhance the agglomeration effect, but the rate of the increase of the agglomeration effect decreases while the initial concentration is getting bigger. When the acoustic frequency is 1400Hz, the SPL is 142dB and the initial concentration is 4.04×105cm-3, the number concentration of aerosol can be reduced to 35% of the initial value.

ICOPE-15-C071 The study on agglomeration and removal of fine particles in wet phase transition condensation process

ICOPE-15-C071 The study on agglomeration and removal of fine particles in wet phase transition condensation process

Recent Advances in the Development and Application of Power Plate Transducers in Dense Gas Extraction and Aerosol Agglomeration Processes

Power ultrasound (PU) is an emerging, innovative, energy saving and environmental friendly technology that is generating a great interest in sectors such as food and pharmaceutical industries, green chemistry, environmental pollution, and other processes, where sustainable and energy efficient methods are required to improve and/or produce specific effects. Two typical effects of PU are the enhancement of mass transfer in gases and liquids, and the induction of particle agglomeration in aerosols. These effects are activated by a variety of mechanisms associated to the nonlinear propagation of high amplitude ultrasonic waves such as diffusion, agitation, entrainment, turbulence, etc. During the last years a great effort has been jointly made by the Spanish National Research Council (CSIC) and the company Pusonics towards introducing novel processes into the market based on airborne ultrasonic plate transducers. This technology was specifically developed for the treatment of gas and multiphasic media characterized by low specific acoustic impedance and high acoustic absorption. Different strategies have been developed to mitigate the effects of the nonlinear dynamic behavior of such ultrasonic piezoelectric transducers in order to enhance and stabilize their response at operational power conditions. This work deals with the latter advances in the mitigation of nonlinear problems found in power transducers; besides it describes two applications assisted by ultrasound developed at semi-industrial and laboratory scales and consisting in extraction via dense gases and particle agglomeration. Dense Gas Extraction (DGE) assisted by PU is a new process with a potential to enhance the extraction kinetics with supercritical CO2. Acoustic agglomeration of fine aerosol particles has a great potential for the treatment of air pollution problems generated by particulate materials. Experimental and numerical results in both processes will be shown and discussed.