双螺杆湿法制粒关键质量属性调控机理模拟研究

针对我国造粒工艺存在关键质量属性（粒径分布均匀性、颗粒表观质量和制粒收率）难以调控的行业共性问题,基于Edinburgh Elastic?Plastic Adhesion接触模型,构建了连续异向啮合双螺杆高剪切湿法制粒过程的仿真方法,模拟研究了过程参数?粒径分布均匀性和收率的协同耦合演化规律,以此诠释了双螺杆湿法制粒关键质量属性的调控机理。结果表明,连续异向啮合双螺杆高剪切湿法制粒机能制备表面光滑的球化颗粒,粒径与粉体喂料速度呈正关联关系,而与螺杆转速呈负关联关系,制粒收率与粉体喂料速度、螺杆转速均呈现先增后减的演化规律;在粉体喂料速度为360 kg/h或螺杆转速为1 400 r/min时,制粒收率处于最佳状态,其最优制粒收率值分别为87.9 %和83.91 %;制粒粒径主要受控于颗粒平均停留时间和持有颗粒质量,且呈正关联关系,以此提出了通过粉体失重喂料装置螺杆和异向啮合双螺杆高剪切湿法制粒机螺杆的变频转速控制,在线实时调控合格颗粒粒径和收率的技术方法。     

TiO2悬浮液颗粒团聚机理及团聚分形特征研究

本文实验测试不同浓度TiO2悬浮液的相关参数,包括颗粒粒径、电导率、介电常数、表面电势、颗粒的Zeta电势等,计算了不同浓度悬浮液颗粒间作用势能,分析了颗粒团聚机理及悬浮液的稳定性.用光学显微镜观察不同浓度悬浮液团聚体的形貌.在此基础上,从团聚体的自相似性、实验获得团聚体的形貌出发,分析了团聚体的分形特征,并用分形软件计算了不同浓度悬浮液团聚体的分形维数.     

球磨过程对ZrO2粉末团聚的影响

本文采用两种不粒度的工业３ｍｏｌ％Ｙ２Ｏ３－ＺｒＯ２粉为原料，研究球磨过程对粉末粒度和ＺrＯ２粉末团聚系数的影响。实验表明：球磨能使大团聚粒子破碎，平均粒径减少 ，团聚系数降低，粉末粒度均匀， 球磨时间的延长，粉末平均粒径细化速度减慢。ＺrＯ２团聚粒子破碎过程将发生四方相t向单斜相m的相变。     

金银花提取物成型干燥过程研究

采用系统设计和分析方法,通过对金银花提取物的浓缩液在流化床干燥制粒机中的干燥制粒实验,得出了进风温度、进风量、喷雾空气压力、喷雾速度等主要参数的优化值;通过对FL-5型沸腾制粒机的改造,达到了改善颗粒均匀度的目的。     

大蒜提取物沸腾干燥过程研究

采用系统设计和分析方法,通过对大蒜提取物的浓缩液在流化床干燥制粒机中的干燥制粒实验,得出了进风温度、进风量、喷雾空气压力、喷雾速度等主要参数的优化值;通过对FL-5型沸腾制粒机的改造,达到了改善颗粒的均匀度的目的.     

球磨过程对ZrO2粉末团聚的影响

本文采用两种不同粒度的工业３ｍｏｌ％Ｙ２Ｏ３－ＺｒＯ２粉为原料，研究了球磨过程对粉末粒度和ＺｒＯ２粉末团聚系数（ｄ５０／ｄＢＥＴ）的影响，实验结果表明：球磨能使大团聚粒子破碎，平均粒径减少，团聚系数降低，粉末粒度更均匀，随着球磨时间的延长，粉末平均粒径细化速度减慢，ＺｒＯ２团聚粒子破碎过程中将发生ｔ－ｍ相变。     

金银花提取物制粒工艺研究

通过采用系统设计和分析方法,在流化床干燥制粒机中对金银花提取物的浓缩液进行了干燥制粒实验,得到了进风温度、进风量、喷雾空气压力、喷雾速度等主要工艺参数的优化值;通过对FL-5型沸腾制粒机的改造,达到了改善颗粒均匀度的目的.     

球形团聚硼颗粒制备工艺的优化

通过正交实验,对溶剂蒸发法制备球形团聚硼颗粒的工艺参数进行优化,研究了固化温度和固化时间对球形团聚硼颗粒的形态、平均粒径大小及其分布的影响,用扫描电子显微镜观察了球形团聚硼粉的外观形态。结果表明,团聚硼粒子的形态圆整,粒径可控且分布均匀。最佳制备工艺条件为:搅伴速度70 r/m in,工艺温度20℃,硼粉与黏合剂的质量比为9∶1,固化温度70℃,固化时间7 d。     

大蒜提取物成型制粒过程研究

通过对大蒜中超氧化物歧化酶的提取,并将提取物的浓缩液在流化床干燥制粒机中进行干燥制粒实验,得出了进风温度、进风量、喷雾空气压力、喷雾速度等主要参数的优化值。针对实验中存在的问题,通过对FL-5型沸腾制粒机结构的改造,改善了所制颗粒的均匀度,通过对喷头结构的改造,改善了流化床干燥制粒机的操作性能。     

回转圆筒内固体颗粒径向偏析的研究

混合固体颗粒在回转圆筒内运动时要发生径向偏析，笔者认为颗粒的渗流以及粗细颗粒的流动性不同是引起颗粒偏折的主要原因。本文通过实验得到了筒体转速及填充系数对偏析的影响。     

Agglomeration during the Drying of Fine Silica Powders, Part II: The Role of Particle Solubility

The effect of particle solubility and the dissolution rate on agglomeration was studied by drying silica and titania particles from aqueous slurries with pH values in the range of 2–12. The agglomerate strength and strength distribution were measured by a calibrated ultrasonic force, and the strength increased as the solubility and dissolution rate increased. Two silica powders of different particle size (60 nm and 500 nm) were studied, and smaller-sized particles formed stronger agglomerates. The drying rate of the powders was varied by using spray drying and tray drying, and slower drying was shown to lead to higher agglomerate strength. The agglomerate strength of titania powder (insoluble in water) was independent of pH, whereas the agglomerate strength of silica was dependent on pH. It was concluded that the solubility and dissolution rate are important parameters that govern the strength of agglomerates.     

密相流化床中介尺度流动结构的流体力学特性研究

在一套流化床冷模实验装置中对黄沙颗粒和黄沙-硅微粉 （20 μm）混合颗粒进行实验。测量固含率时间序列信号并进行统计分析,提出并建立复杂光纤脉动信号的解耦方法,实现稠密气固流中介尺度流动结构的准确识别。基于统计矩一致性原理提出气泡阈值的计算方法,通过遍历法确定气泡阈值。对气泡阈值变化规律进行分析,发现加入细颗粒有助于改善流化质量,随表观气速的增加,气泡阈值减小。对气泡、乳化和聚团三相的相分率进行统计,发现在黄沙颗粒中加入少量（5%,质量分数）细颗粒能够显著改善流化质量,细颗粒添加量过多时（10%）,对流化质量的改善将减弱。对气泡的流体力学特性进行分析,发现加入10%硅微粉后,气泡弦长增大,频率降低,速度略有降低。对颗粒聚团流体力学特性进行分析,发现随硅微粉含量增加,表观气速对聚团速度的影响减弱,聚团弦长略有减小。加入5%硅微粉后,颗粒聚团的出现频率较小且径向上分布均一。加入10%硅微粉后,聚团频率有所增大,说明加入过多硅微粉会促进聚团的形成。     

A numerical study on agglomerate formation in a fluidized bed of fine cohesive particles

Two-dimensional (2D) DEM simulation was conducted to investigate the mechanism of agglomeration in a fluidized bed of cohesive fine particles. For the present simulation, granules were numerically generated from Geldart group C particles starting from initial agglomerates of an intermediate size. Particle pressure and agglomerate sizes were measured numerically. The behavior of agglomerates around a bubble were tracked in detail. Breakage of agglomerates above a bubble as assumed in the development of the Iwadate and Horio (Powder Technol. 100 (1998a) 223) model (I–H model) was numerically confirmed. Spots of high in-bed compression force, where agglomerate growth is supposed to take place, was clearly observed in the wake region below each bubble. Numerical results for agglomerate sizes compared fairly well with those predicted by the I–H model redeveloped for 2D cases to validate its mechanistic picture for agglomerate size determination.     

Flotation of Fine Gold Particles by the Assistance of Coal-Oil Agglomerates

This paper describes the use of coal-oil agglomerates in flotation to increase the gold recovery from an ore containing fine gold particles. The effects of operating parameters on gold flotation recovery such as oil type, particle size of agglomerating material, agglomerate/ore and oil/ore ratios were investigated. The studies showed that petroleum oils are more effective than vegetable oils in oil agglomeration of Kozlu coal and coal-oil assisted gold flotation. Gold recovery can be increased using a higher amount of agglomerates in the process; however, gold grade of the flotation concentrates is reduced significantly. The use of bridging oil at high concentrations in the agglomeration process provides high-grade gold concentrates, but lower recoveries. The utilization of coarser coal particles in the coal-oil agglomeration stage leads to higher selectivity and recovery values for gold particles.     

Agglomeration modeling of small and large particles by a diffusion theory approach

The interaction particle‐binder during the wet granulation process plays a major role in the agglomeration of particles. This interaction has been modeled by a force balance acting on the particle where the binder's viscous force increases the strength of liquid bridge and facilitates the particle agglomeration. In this work, agglomeration kernels based on Brownian movement approach of small particles in the binder layer, the size ratio between particles (monodispersed and polydispersed), and binder's viscous forces were considered to model the wet granulation process of pharmaceutical powders in a laboratory‐scale high shear mixer. The assumptions of no‐stationary and pseudostationary behavior were suitable to describe the growth kinetics of the two stages (fast and slow) observed. A volume ratio of 150 between large and small particles produces the most effective granulation growth. The developed kernels were tested simulating experimental data obtained from a high shear mixer. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

声场流化床中超细颗粒聚团受力与尺寸

在内径40 mm的流化床中,采用平均粒径为7.4 mm的超细铁矿颗粒进行声场流态化实验. 结果显示,聚团尺寸随声压级增大逐渐减小,在固定声压级的条件下存在最优声波频率,本实验为130 Hz. 由铁矿颗粒声场流态化中聚团受力分析提出聚团受力平衡模型,当促进聚团破碎的力和促进聚团形成的力相等时,计算出一定频率不同声压级下的聚团尺寸,在频率130 Hz、声压120.5 db下,根据模型计算得到的聚团直径为384 mm,而通过最小流化速度计算值为367 mm,二者较接近.     

New perspectives on capturing particle agglomerates in CFD modeling of spray dryers

Abstract

Current computational fluid dynamic (CFD) models of spray dryers lack the capability to predict the structure of the agglomerates formed; loose or compact agglomerates. This is mainly due to the conventional simplistic approach in numerically “fusing” of the colliding particles forming the agglomerate. A new theoretical treatment is introduced in this work, suitable for implementation in CFD simulations, which numerically fuses the particles and yet retain information on the structure of the agglomerate. This new theoretical treatment is based on tracking the reduction of the agglomerate surface area as the agglomerate is progressively formed. Analysis revealed that the reduction in the agglomerate surface area exhibits a unified correlation with the degree of compactness of the agglomerate. Further analysis comparing this new approach to the conventional numerical fusing of the particles revealed inherent numerical discrepancies, which has not been noted in the literature before. Understanding these discrepancies will provide clarity to the interpretation of the modelling and simulation of spray drying particle agglomeration in CFD. Moreover, this work lays the groundwork for a more comprehensive CFD model for agglomeration which can be potentially utilized to predict final powder properties.     

Agglomeration of fine particles subjected to centripetal compaction

Agglomeration is a common phenomenon in many processes. The mechanical properties of agglomerates strongly depend on their structures. This paper presents a numerical study of the agglomeration of fine particles down to 1 μm in size based on the discrete element method. The agglomerates were formed with particles initially generated randomly in a spherical space and then packed under an assumed centripetal force. Agglomerate structure, packing density, coordination number and tensile strength were analysed with particular reference to the effect of particle size associated with the van der Waals attraction. The results showed that both the packing density and coordination number of the agglomerates decay exponentially to their limits as agglomerate size increases. The tensile strength of the agglomerates was calculated from the simulations and shown to decrease with the increase of particle size. The strength was also estimated from the Rumpf model supported by the empirical equations formulated based on the present simulation results. The good agreement between the results from the simulations and the estimation indicates that the equations are useful to facilitate engineering applications.     

Experimental and theoretical study on the agglomeration arising from fluidization of cohesive particles—effects of mechanical vibration

A novel technique that can prevent the disruption of agglomerates when sampling the agglomerates from a fluidized bed has been developed and has been applied to the investigation of the agglomeration behaviour of cohesive particles during fluidization with and without mechanical vibration. A new model for the prediction of agglomerate size has also been established on the basis of the energy balance between the agglomerate collision energy, the energy due to cohesive forces and the energy generated by vibration. The accuracy of the model is tested by comparing the theoretical results with the experimental data obtained both in the present work and in the literature. Effects of gas velocity and mechanical vibration on agglomeration for two cohesive (Geldart group C) powders in fluidization are examined experimentally and theoretically. The experimental results prove that mechanical vibration can significantly reduce both the average size and the degree of the size-segregation of the agglomerates throughout the whole bed. However, the experiments also reveal that the mean agglomerate size decreases initially with the vibration intensity, but increases gradually as the vibration intensity exceeds a critical value. This suggests that the vibration cannot only facilitate breaking the agglomerates due to the increased agglomerate collision energy but can also favour the growth of the agglomerates due to the enhanced contacting probability between particles and/or agglomerates. Both the experimental and theoretical results show that a higher gas velocity leads to a smaller agglomerate size.     

超细粉在声场导向管喷流床中的聚团尺寸预测模型

超细粉的流化性能与聚团尺寸密切相关。通过分析超细粉聚团在声场导向管喷流床中的形成过程,提出了高速射流的剪切作用和聚团间的碰撞作用是决定聚团尺寸的主要原因。在此基础上,结合聚团在射流剪切过程和聚团间碰撞过程中的力平衡分析,建立了声场导向管喷流床中聚团尺寸分布的预测模型;并运用这一模型成功预测了不同射流气速下,超细TiO₂颗粒在声场导向管喷流床中的聚团平均直径和聚团尺寸分布。