Influence of the interaction between binder and powders on melt agglomeration behavior in a high-shear mixer

The purpose of this study was to investigate the effects of the different surface properties of powders on granular agglomeration in a high-shear mixer. Polyethylene glycol 6000 (PEG 6000) was used as the melting binder. Three different powders, with mean granule sizes of 75-150 μm were used as the raw materials: calcium carbonate, calcium sulfate, and sodium carbonate. The wetting properties of the raw materials were measured with a contact angle instrument. The results indicate that the speed at which the droplets sink into the powder bed and the contact angle of binder droplets on the powder surface play important roles in determining the progress of the agglomeration process. Several types of agglomeration were found: a slurry state, heterogeneous nucleation, snowballing, and induction growth behavior. Heterogeneous dispersion leads to induction behavior and subsequent growth, but a homogeneous dispersion leads to little or no nucleation and growth of agglomerate size.     

Influence of co-current spray drying conditions on agglomeration of melamine-formaldehyde microcapsules

The drying of microcapsules causes agglomeration and oversized agglomerates disturb fiber melt spinning. In this study, three parameters in co-current spray drying were studied and their influence on agglomeration was established with a morphological analysis, granulometric analysis, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). The results showed that the inlet temperature, feed rate, and dry matter content have a significant influence on agglomeration; thus, their optimal combination was determined. In these conditions, the microcapsules were dried and applied in fibers.     

Influence of macromixing on powder formation in a reactive coaxial jet

This paper deals with an experimental study and a modelling of the formation of particles in a reactive gaseous jet. Particles result from the gas-phase hydrolysis of tin tetrachloride in a turbulent coaxial jet. In presented experiments, the influence of velocities of gases and nozzle shape on particle size distributions has been studied. Experimental distributions have been evaluated by in situ light-scattering measurements. Theoretical particle size distributions resulting from a simple model are compared to experimental measurements. Results show that particles do not seem to grow only by agglomeration and mixing near the nozzle may strongly influence final particle size distributions. In fact, the development of mixing layers near the nozzle appears to have little effect on particle size distributions, so that mesomixing could be the major phenomenon.     

Influence of material properties on the agglomeration of water-soluble amorphous particles

The viscosity and elasticity of particles influence their agglomeration behaviour. Such mechanical particle properties are determined by the supra-molecular and microscopic structure of the particles and process conditions such as temperature, humidity and strain rate or frequency.Most food powders are composed of amorphous water soluble substances. Accordingly spray dried dextrose syrup is used as a model substance for the current study.Such amorphous water-soluble substances show visco-elastic behaviour and depending on strain rate, temperature and moisture content, either the viscous or the elastic properties dominate their material behaviour. The viscous behaviour of a material can be characterised through its shear or its complex viscosity. The materials viscosity affects all types of agglomeration processes. The complex viscosity can be measured by Dynamic Mechanical Thermal Analysis (DMTA) while the shear viscosity is typically determined using a rotational viscometer. Alternatively it is possible to estimate the viscosity based on the difference between glass transition and process temperature.In the current study the glass transition temperature of spray dried dextrose syrup (DE21) is measured for different moisture contents and the obtained data are used for estimating the viscosity. In addition, the viscosity of the dextrose syrup powder at different temperature/moisture/frequency combinations is determined for higher viscosities by DMTA or measured for the lower viscosity range using a rotational viscometer. The obtained data are used to predict growth and pressure agglomeration processes such as fluid bed agglomeration and tabletting.     

Influence of liquid binder dispersion on agglomeration in an intensive mixer

In industrial scale mixer granulation, liquid binder is usually sprayed onto the agitated powder bed by means of a nozzle in order to enhance the agglomeration process. The early stage of this process, where granule nuclei are formed and grow, is not well understood. As it is desirable to model the agglomeration state right from the beginning of the process for the purposes of control and modeling, this nucleation step is therefore an important field of interest.To investigate the influence of binder droplet size on the nucleation stage of the agglomeration process, experiments were carried out with lactose and water in an intensive mixer. Water was sprayed in to the mixer with different nozzles to vary the size of the produced droplets. As a comparison, water was also directly poured into the turning mixer. Samples of the produced granules were taken at specific time intervals and analysed for size and water content. As the experiments were focused on examining short granulation times, the first samples were taken after only half of the water was added.Particle size distribution and liquid distribution in the wet granule samples were analyzed. It was found, that the droplet size of the binder liquid has great influence on agglomerate size and binder distribution at short mixing times, with increasing time, the mechanical stresses acting in the mixer becomes more and more dominating in the process. Preliminary comparisons are also carried out with single drop penetration tests in an attempt to correlate drop size to penetration time and also to produced granule size.In conclusion this paper studies the effect of different drop size conditions and subsequent spray flux on the behaviour of the nucleation and the early stages of the agglomeration process. The context of these findings for agglomeration in an intensive mixer is examined.     

The effect of glass transition on the desired and undesired agglomeration of amorphous food powders

In the food manufacturing and pharmaceutical industry several agglomeration technologies are applied: fluidised bed agglomeration, steam jet agglomeration, agglomeration during drying and pressure agglomeration like extrusion, roller compaction or tabletting. In addition, caking or sticking of amorphous substances, which is a kind of undesired agglomeration, is frequently observed.Any desired or undesired agglomeration of amorphous substances is dependent on the mechanical properties of the entire particle or the particle surface. Changes in the mechanical properties of the material are linked to changes in moisture and temperature and can be predicted by applying the glass transition concept. Using this concept it is possible to estimate the viscosity and the Young's modulus for a given amorphous substance while knowing their glass transition temperature in dependence on the water content.Knowing the viscosity and the Young's modulus and applying equations derived from the sintering technology or the theory of viscoelasticity it is possible to define suitable conditions for most of the agglomeration processes mentioned above.     

Modelling of multiple-mechanism agglomeration in a crystallization process

A three-level agglomeration model coupled with crystal growth is developed. It accounts for Brownian, laminar, and turbulent agglomeration. The desupersaturation profiles, the particle size distributions, the average sizes, and variances (or standard deviations), as well as the instantaneous agglomeration degrees for each mechanism, can be calculated as functions of time. The model is applied to the crystallization of an amorphous solid into a crystalline polymorph in a batch crystallizer. A runaway phenomenon is detected for agglomeration when crystals are switching over from the Brownian regime to the laminar one: this switchover significantly affects the desupersaturation curve and the crystal shapes.     

不凝气体对蒸汽射流冷凝影响的数值研究

通过二维轴对称数值模型研究了空气等不凝性气体对蒸汽射流与过冷水直接接触冷凝行为和传热特性的影响。采用CFX中的欧拉-欧拉双流体模型,结合热相变模型计算蒸汽的冷凝量、组分传递模型计算混合气体中组分的变化量;喷嘴出口的气体质量流量为300 kg/(m²·s),不凝气体含量在15%以内。结果表明,不凝气体阻碍了蒸汽与过冷水直接接触,形成热阻,恶化了冷凝传热,且热阻随不凝气体含量增加而增加;冷凝速率随不凝气体含量增加而减小;射流区长度随不凝气体含量增加而增加;不凝气体的存在,使水蒸气不能被完全冷凝,而剩余水蒸气的含量与初始不凝气体含量无关。     

Numerical investigation of influence of non-condensable gas on steam jet condensation

The influence of non-condensable gas on the direct contact condensing behavior and heat transfer characteristics of steam jet in subcooled water is investigated by two-dimensional axisymmetric numerical model. Based on Euler-Euler two-fluid model in CFX, the steam condensation is calculated with thermal phase change model. The composition variation of steam-air mixture is realized using species transport equation for the gas phase. The gas mass flow at nozzle outlet is 300 kg/(m²·s), and non-condensable gas is within 15%. The results show that non-condensable gas obstructs the direct contact between steam and subcooled water, forming the thermal resistance and deteriorating the condensation heat transfer. The thermal resistance and the length of jet region increase with the increase of non-condensable gas. While the condensation rate decreases with the increase of non-condensable gas. The presence of non-condensable gas prevents vapor from being condensed completely, and the remaining vapor is independent of the original non-condensable gas.     

Population balance modelling for a flow induced phase inversion based granulation in a two-dimensional rotating agglomerator

A novel two-dimensional rotating agglomerator was developed to carry out the flow induced phase inversion (FIPI) based granulation. The process in this agglomerator shows that a continuous paste flow (mixed with liquid binder and primary particles) is extruded into the interstice of two relatively rotating disks, as the paste becomes solidified due to the loss of heat to the disks, it is then broken into granules by the shearing force imposed by the rotating disk. Experimental measurements have shown that the size of these granules is enlarged along the positive radial direction of the disks. It is also found that these granules contain approximately the same quantity of binder in terms of its volume fraction. The paper thus proposes a population balance (PB) model to describe the growth of the granules by considering a size independent agglomeration kernel. The PB simulated results are found to be well capable of describing the change of the particle size distribution (PSD) of the granules in the radial direction. This study also proposes a velocity profile for the paste flow and attempts to establish a quantitative relationship between the granulation rate and the deformation rate as this would help us understand the mechanism of the agglomeration. It is hoped that this study would be used to improve the design of the agglomerator and to assure the control of the process and the granular product quality.     

Formation of bed agglomeration in a fluidized multi-waste incinerator

A case study was carried out to investigate the bed agglomeration observed in a fluidized bed incinerator when burning blends of three wastes (carbon soot, biosludge and fuel oil). Several instrumental approaches were employed (i.e. XRF, SEM, XRD, and ICP-AES) to identify the bed materials (fresh sand and degrader sand) and clinkers formed in the full-scale incinerator tests. Several elements (V, Al, S, Na, Fe, Ni, P, and Cl), which normally are associated with the formation of low melting point compounds, were found in the waste blends at high content levels. The clinker bridges were identified to be associated with Al, Fe, V, K, Na, S, Ni, and Si elements.The effects of temperature and blending ratio were investigated in a muffle furnace. Carbon soot is believed to be more susceptible to the clinker formation than the other two fuels. Thermodynamic multi-phase multi-component equilibrium calculations predict that the main low melting point species could be Al₂(SO₄)₃, Fe₂(SO₄)₃, Na₂SO₄, NaCl, Na₂SiO₃ and V₂O₅. This information is useful to understand the chemistry of clinker formation. Also, it helps to develop methods for the control and possible elimination of the agglomeration problem for the design fuels.     

纳米颗粒在制备过程中团聚现象的研究进展

综述了纳米颗粒的制备方法,分析了纳米颗粒在制备过程中的团聚机理及防止团聚的技术;认为采用某些方法可以有效地防止团聚,防团聚技术的研究将是研究者的主要任务。     

Effects of different nano-agglomerated powders on the microstructures of PS-PVD YSZ coatings

Plasma spray physical vapor deposition (PS-PVD) is a technology that combines the advantages of traditional atmospheric plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD). As the feedstock of the PS-PVD, nano-agglomerated powder is critical on determining the microstructure of the obtained coating. In this study, a method to characterize the cohesion of nano-agglomerated powders was investigated. The nano-agglomerated powders fractured into smaller particles under ultrasonic waves. Their particle size distributions were measured to quantitatively compare their cohesiveness. The change rate in the percentage of powders with particle size less than 5 μm was selected as the value for the cohesion comparison. A high change rate corresponded to a faster fracture and lower powder cohesion. Furthermore, the fracture behavior and heat and mass transfer process of nano-agglomerated powders in the plasma torch were studied by combining 3-D simulation and observation of the microstructures of PS-PVD coatings sprayed with different powders. To obtain a quasi-columnar coating, the nano-agglomerated powder required high cohesion. Finally, a suitable powder was selected and quasi-columnar structure coatings were obtained by optimizing the PS-PVD parameters.     

The sintering temperature of ash, agglomeration, and defluidisation in a bench scale PFBC

Five Australian black coals were studied in a bench scale pressurised fluidised bed combustor (PFBC) to investigate the agglomeration propensity. It was found that coals with higher proportions of calcium aluminosilicate showed higher propensity for agglomeration and defluidisation. The pressure-drop sintering technique can predict the agglomeration propensity for coals. Samples with a sintering temperature lower than the operating temperature of the PFBC showed agglomeration. The laboratory ash can be a good representative of the PFBC ash when studying agglomeration and defluidisation.     

Optimization of some parameters on agglomeration performance of Zonguldak bituminous coal by oil agglomeration

In this study, the optimization of some parameters on agglomeration performance of Zonguldak bituminous coal by oil agglomeration was discussed. A three-level Box-Behnken design combining with a response surface methodology (RSM) and quadratic programming (QP) were employed for modeling and optimization some operations parameters on oil agglomeration performance. The relationship between the responses, i.e., grade and recovery, and four process parameters, i.e., amount of oil, agitation time, agitation rate and solid content were presented as empirical model equations for both grade and recovery on oil agglomeration. The model equations were then optimized individually using the quadratic programming method to maximize both for grade and recovery within the experimental range studied. The optimum conditions were found to be 14.61% for amount of oil, 8.94 min for agitation time, 1554 rpm for agitation rate and 5% for solid content to achieve the maximum grade. The maximum model prediction of 0.650 grade at these optimum conditions is higher than any value obtained in the initial tests conducted. Similarly, the conditions for maximum recovery were found to be 20.60% for amount of oil, 5 min for agitation time, 1800 rpm for agitation rate and 19.48% for solid content with a prediction of 96.90% recovery, which is also higher than any other recovery obtained in the initial tests conducted.     

水蒸气超音速流动中非平衡相变的温度特性

引入水蒸气非平衡相变的动力模型和水蒸气真实物性模型的基础上,建立了水蒸气超音速非平衡流动的守恒型数值计算模型,采用对激波捕捉具有高精度和高分辨率的Roe-FDS格式进行计算,数值求解了水蒸气超音速流动过程中的非平衡相变及凝结激波现象。着重研究了水蒸气超音速非平衡凝结相变的温度特性,归纳了水蒸气超音速非平衡流动的凝结特性随温度的变化规律,归纳了蒸汽温度变化对核化凝结、激波形态的影响规律。研究发现,入口温度对蒸汽超音速流动中的非平衡相变具有显著的影响,进口温度越低,非平衡核化凝结爆发的越早,产生的液滴粒径越大;随着进口温度的升高,非平衡凝结相变的起始点逐渐向喷管出口方向移动,蒸汽需要在缩放喷管中加速膨胀到较高马赫数下达到较高的过饱和度和过冷度时才能产生核化凝结,而成核率也相应较高。     

Gas–solid adhesion and solid–solid agglomeration of carbon supported catalysts in three phase slurry reactors

In the study of three phase slurry reactors the slurry phase is conventionally treated as a quasi homogeneous liquid phase with altered sorption and reaction capacity due to the presence of catalyst particles. This approach may be utterly wrong in any case where phase segregation of the solid takes place. This phenomenon is relatively little studied and it will be demonstrated that it may have a considerable impact on the operation of three phase reactors. Two examples of segregation, i.e. gas–solid adhesion and solid–solid agglomeration, are to be discussed. Taking the example of carbon and alumina supported palladium catalysts employed in the hydrogenation of methyl acrylate towards methyl propionate, the segregation of the catalyst phase by adhesion to gas bubbles is studied. This adhesion may take place up to complete coverage of the gas bubbles but it may also be entirely absent. A quantitative model is developed based on the film theory, the particle to bubble collision probability and the impact of the size of adhering particles on the effective film thickness. This model is used to describe adhesion under non-stagnant conditions and the impact it has on the overall G–L mass transfer rates. The conversion rate of a mass transfer limited model reaction, i.e. the hydrogenation of methyl acrylate to methyl propionate, is studied in a stirred tank reactor for two different catalysts (Pd/C and Pd/Al₂O₃) in order to verify the model. It is quantitatively demonstrated that G–L mass transfer rates may be increased considerably as a result of adhesion. The second, closely related, phenomenon studied is the segregation of the solid and liquid phase by agglomeration of the catalyst particles. This behaviour is of particular importance as it leads to a substantial increase in the effective particle size resulting in a decreased conversion rate.     

Investigation of the effect of agglomeration time, pH and various salts on the cleaning of Zonguldak bituminous coal by oil agglomeration

In this study, the effects of bridging liquid concentration, agglomeration time, pH and various salts on the combustible recovery and ash contents of the agglomerated products have been investigated. Kerosene was used as bridging liquid. The optimum values of kerosene concentration, pH and agglomeration time have been determined as 20 wt%, 7.5 and 15 min, respectively. Metallic salts, such as FeSO₄, NaCl, FeCl₃, Al₂(SO₄)₃ were used in the experiments in which the effects of salts were investigated. While the combustible recovery slightly increased depending on the increase in the concentration of NaCl, very small decreases have been recorded in the recoveries depending on the increase in the concentration of the FeCl₃. A considerable reduction occurs in the agglomeration recovery with the increasing concentration of FeSO₄, while the combustible recovery slightly decreases at low concentration of Al₂(SO₄)₃.     

Fully coupled LES-DEM of particle interaction and agglomeration in a turbulent channel flow

Coupled large eddy simulation and the discrete element method are applied to study turbulent particle–laden flows, including particle dispersion and agglomeration, in a channel. The particle–particle interaction model is based on the Hertz–Mindlin approach with Johnson–Kendall–Roberts cohesion to allow the simulation of van der Waals forces in a dry air flow. The influence of different particle surface energies, and the impact of fluid turbulence, on agglomeration behaviour are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with a positive relationship observed between the two. Particle agglomeration is found to be enhanced in two separate regions within the channel. First, in the near-wall region due to the high particle concentration there driven by turbophoresis, and secondly in the buffer region where the high turbulence intensity enhances particle–particle interactions.     

Influence of a Lipid Phase on the Physical Properties of Spray‐Dried Maltodextrin Powders

Maltodextrin powders containing 5, 10, 15, 20 and 25 % from three different palm oil fractions were produced by spray‐drying emulsions with 30 wt % total solids content. The effect of the lipid phase on the characteristics of the particles was evaluated. Oilless spray‐dried particles presented a smaller average size and reduced wettability as compared to the commercial product. An increase in fat content resulted in a decrease in true density while the Hausner Ratio and average diameter of the particles increased. The powders containing palm olefins (melting points, 14 °C and 18 °C) were stickier than the product containing stearin (melting point, 51 °C).