Effect of operating conditions and design parameters in a continuous powder mixer

An experimental investigation was carried out to study the mixing performance and flow behavior in a continuous powder mixer for a typical pharmaceutical mixture. Blender performance, characterized by the relative standard deviation (RSD) of composition of blend samples taken at the blender discharge and by the variance reduction ratio (VRR) of the blender, was measured as a function of impeller rotation rate, flow rate and blade configuration. The flow behavior in the continuous mixer was characterized using the residence time distribution (RTD) and powder hold-up measurements. To quantify the strain applied to the powder in the blender, the number of blade passes experienced by the powder in the blender was calculated using the residence time measurements. The relationship between different experimental parameters and mean residence time and mean centered variance was examined. The mixing performance was largely dominated by the material properties of the mixture, which had a larger effect than the ingredient flow rate variability contributed by the feeders. Holdup was strongly dependent on impeller rotation rate; as impeller rotation rate increased, holdup (and therefore, residence time) decreased sharply. As a result, intermediate rotation rates showed the best mixing performance. Blade configuration affected performance as well; blade patterns where some of the blades push the powder backwards improved the mixing performance.     

Impact of process parameters on critical performance attributes of a continuous blender—A DEM‐based study

A discrete element method‐based computational study carried out to study the effect of impeller design, speed, and input feed rate on the performance of a continuous powder blender is presented. The blender performance was characterized using the mean particle residence time, the residence time distribution, the number of blade passes experienced by the powder, and the mean centered variance. The powder residence time decreased with increasing impeller speed; however, the number of blade passes experienced a maximum at an intermediate speed. The effects of feed rate and impeller design were more prominent at lower speeds. Lower feed rate resulted in the powder experiencing higher number of blade passes. The number of blade passes was also higher for the alternate blade pattern when compared to the forward pattern. The computational findings were compared with an experimental study which showed that the model captured the essential flow dynamics well. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

钛白粉生产闪蒸干燥机旋转叶片的改造

介绍了对金红石钛白粉生产设备闪蒸干燥机进行改造以提高产能的改造过程。调整了筒体倒锥体的角度及环缝隙的距离，并改进了搅拌器的分散叶片的结构和制作。改造后，产量提高3倍，能耗降低了60％，取得了较好效益。     

组合桨搅拌器的宏观混合特性

分别以浓度为１％，２％，３％，３．５％的羧甲基纤维素溶液为实验，采用测温法，测定了正交双层三角桨－单螺带桨，正交双层三角桨－内外单螺带桨．锚式桨－三叶推进器．锚式桨－内外单螺带４种组合桨拌器的宏观混合时间，无量钢数Ｃ１，Ｃ２，Ｃ３，Ｃ４综合评判了它们的宏观混合性能，实验证明，前２种组合桨搅拌器在不同流域内都使搅拌介质达到良好的宏观混合，且功率消耗低，混合效率高，具有明显的节能优势，对搅拌变粘度体系     

固体碱渣解聚均质器结构试验与数值模拟

制碱工业过程产生大量碱渣等废弃物,固体碱渣再利用是化工行业技术难题。本文以某化工股份有限公司氨碱法制碱过程中产生的固体碱渣为研究对象,数值模拟研究了影响均质器内浆液分布均匀性的变化因素,通过试验验证了均质器的最佳结构特征。结果表明：固体碱渣的粒度小,具有溶胶的性质,经过压滤机压滤过后的碱渣,粒子重新团聚,硬度大、不易破碎、解聚;提高均质器的搅拌器转速对流体的流动速度及均质效果有很大改善,但并不能完全消除死区;相比于局部立式搅拌桨叶结构,采用立式搅拌桨结构的均质效果明显,且功耗更小;增加导流板结构,与未加装前相比,功耗降低,综合考虑确定均质器的搅拌器采用立式桨+平直桨+导流板的混合型桨叶结构,有利于提高碱渣再利用的经济性。本文研究结果可为固体碱渣制备脱硫剂的工业应用奠定基础。     

制备工艺对微乳化柴油稳定性能的影响

为了考察制备工艺对微乳化柴油稳定性能的影响,采用单因素变化试验和正交试验设计安排试验,系统分析了制备微乳化柴油时的温度、搅拌速度、搅拌方式、试剂的添加顺序以及各工序搅拌时间对其稳定性能的影响。结果表明:温度为25～35℃,搅拌速度为300～500r/m in,添加顺序为乳化剂和柴油先混合,再加入水,最后加入助乳剂,各工序搅拌时间均为5m in时所制备的微乳化柴油稳定性好。结论为制备微乳化柴油时温度、搅拌速度、搅拌时间以及添加顺序对其稳定性能影响较大,搅拌方式对其稳定性能影响较小。     

The thermodynamics of high shear blending

As a key constituent in many aerosol powder formulations, the properties of inhaled lactose greatly influence the overall performance of the pharmaceutical powder in inhalers. The interparticle forces defining pharmaceutical performance are markedly affected by the energy input during the high shear blending process. By conducting a number of lactose blending experiments in a small-scale pharmaceutical high shear blender, heat generation in lactose during blending was studied and shown to be consistently predictable. Experiments were then conducted in a larger high shear blender to quantify the energy input into powder using an energy balance equation. A set of relations were developed requiring only the powder temperature and jacket water temperature to approximate energy input into lactose at a given impeller speed and blend time in a high shear blending process. Additionally, this study sets out to substantiate the assumptions made in the proposed energy balance model. These experiments could not identify all possible sources of error; however, evidence is presented suggesting that energy input due to impeller shaft heating is negligible. As a result, the set of relations should be applicable for any high shear blender, given a constant blade size and shape. This analysis of powder heating with respect to blending parameters could be applied to tune blending parameters to minimize powder heating and the resulting change in powder properties. These experiments have provided the framework to understand power input in high shear blending for a range of blend parameters.     

稀土异戊橡胶聚合工艺分析

从稀土异戊二烯聚合反应动力学出发,以2万t/a异戊橡胶生产装置为例,对其聚合单元首釜进行热稳定性分析,发现缩短原料在第一聚合釜内的停留时间,能够降低第一聚合釜的转化率,可以有效地提高第一聚合釜的热稳定性;对不同形式的搅拌器对釜内物料的返混效果进行了比较,采用内外反向双螺带聚合釜,釜内温度梯度小,催化剂浓度和活性均匀,避免了局部温度和催化剂浓度过高;优化第一与第二聚合釜之间管线走向,可以在一定程度缓解首釜至二釜之间管线挂胶的情况。     

Predicting cone-in-cone blender efficiencies from key material properties

Blending of powders and granular materials is a critical unit operation in many industries, yet the ability to predict blending effectiveness lags well behind our ability to create new and novel blenders. As a result of this, production plants must rely on vendor blending tests conducted on small scale model blenders to determine if their specific material will work in the proposed blender design. Once these blending tests are conducted, engineers must then use past experience and conservative design practices to scale-up to full scale units at process flow rates.The difficulty in predicting blending efficiencies arises from the fact that blending performance depends on basic material properties, blender geometry, blender flow rates, and blender operation parameters. These effects are convoluted during blending operation. Successful scale-up would require understanding how to separate the influence of these four effects. If this could be accomplished, blender performance could be determined by measuring simple material properties, predicting blender velocity profiles, and computing blender efficiencies from predicted velocity patterns. This method would allow separation of factors affecting blender performance and provide a means of reliable scale-up using simple material properties and specified blenders geometries.This paper presents a methodology of predicting blender performance in simple in-bin blenders using easily measured material properties. It discusses blender optimization and determines the influence of gas pressure gradients on blender flow and operation. The specific blender analyzed is the cone-in-cone blender and the analysis suggests that blender performance depends on wall friction parameters for conditions where input concentration fluctuations occupy much of the blender volume. However, blending action appears to be independent of friction angle for conditions where there are many concentration fluctuations within a blender volume. The analysis also shows that gas pressure gradients can lead to stagnant region formation.     

Melt flow indexer evidence of high‐temperature transitions in molten high‐density polyethylenes

A melt flow indexer (MFI) was used to investigate high‐temperature transitions in melts of high‐density polyethylene (HDPE). The MFI data were obtained in the range 190–230°C. These transitions were found in the MFI at about 210 and 225°C and reproduced in a Haake melt blender. Polystyrene was used in the blender experiment to demonstrate typical amorphous behavior. For HDPE melts, the MFI–temperature behavior and the torque–temperature data of the blender were found to be alternative images of the same anomalous temperature dependency in the range 210–225°C. Also, the Haake melt blender was able to reproduce the 150°C transition observed by Kolnaar and Keller in the extrusion of HDPE. Regardless of the simplicity of the MFI device, results are in agreement with our previous DSC findings. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1309–1313, 2004     

A statistical method for velocity detection in moving powder beds using image analysis

An existing method to measure particle velocity is particle image velocimetry which requires presence of tracer materials. This method of contrast enhancement is not always applicable in an industrial setting. Therefore a method to assess the movement of small, structures has been introduced, called powder surface velocimetry (PSV). The principle of PSV is to follow the movement of small structures on the surface of the powder bed. The displacement of the structure is correlated with velocity. The rate of the blade of a blender was quantified to assess the validity of PSV. Next the powder surface velocity of lactose 100 M was measured by PSV and was found to be in line with expected values and flow regimes. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Treatment of soybean oil soapstock to reduce pollution

Often soapstock is acidulated to convert this byproduct of vegetable oil refining to a salable commodity. The acidic waste water from this treatment constitutes a significant part of the environmental pollution from refineries. A process of neutralizing and drying was investigated as a nonpolluting method for upgrading soybean oil soapstock. Neutralization with sulfuric acid was conducted in a ribbon blender. The neutral soapstock was dried to ca. 4% moisture, either batchwise in a natural circulation evaporator or continuously in a scraped film evaporator. The product is liquid while hot but solidifies to a waxy solid when cooled to room temperature. When added to a standard broiler ration, the feed efficiency and rate of gain of chickens equaled that obtained with a commercial feed fat added at the same level. The soapstock products fed, which contained 200–300 ppm xanthophyll, gave significantly better shank pigmentation than the commercial fat, which contained 3 ppm. Presented at the AOCS Meeting, Los Angeles, April 1972. N. Market. Nutr. Res. Div., ARS, USDA.     

Theory of blending in single inlet flow systems

Good design requires that the fluctuations in concentration which occur at the output of a blending device be small. Using the criterion of minimum variance of the output concentration, it is shown that blender performance depends only on the residence time distribution of the blender and the autocovariance function of the input concentration. The optimal blender design is found for the case of rapid uncorrelated fluctuations at the inlet, and nearly ohtimal blender designs are found for input fluctuation which are autocorrelated over a moderate time interval. A general method for blender design is given using discrete time increments.     

Investigation into microstructure of carbon nanotube multi-yarn

Structural analysis at the nano and micro scale was performed on a carbon nanotube (CNT) multi-yarn. The yarns were made by a process of drawing CNTs into a ribbon and twisting the ribbon into a yarn. Scanning electron microscopy (SEM) was used to view the exterior of the yarn. Polarized microscopy was used to examine details of the 1-yarn, and it also identified ribbon–ribbon boundaries. Further examination of interior structure was done by NanoCT scans which showed that folding of the ribbons had occurred causing complicated structures. The interior folding was found by milling into the yarn with a focus ion beam gun (FIB) and imaging with SEM. These different methods thus provided various microstructural details (structure, ribbon–ribbon boundary, folding and void fraction) of CNT multi-yarn which could be used to compare with other yarns fabricated with different procedures/sources as well to provide parameters for analytical tools. Further, these microstructural details can be related to macro mechanical and physical properties.     

Which impeller should be chosen for efficient solid–liquid mixing in the laminar and transitional regime?

The vast majority of solid–liquid mixing studies have focused on high Reynolds number applications with configurations and impeller geometries adapted to this type of regime. However, the mixing of particles in a viscous fluid is an essential element of many contemporary industries. We used the computational fluid dynamics-discrete element method model previously developed in our group to investigate solid–liquid mixing with close-clearance impellers in the laminar regime of operation. We compared different geometries, that is, the double helical ribbon, anchor, Paravisc™, and Maxblend™ impellers. We investigated the impact of fluid viscosity and compared the results with those obtained with the pitched blade turbine, a more commonly used impeller, based on power consumption for equivalent mixing states. This study highlights that the higher the viscosity of the fluid, the more interesting it is to use close-clearance impellers for their ability to generate a strong shear stress and a strong bulk flow in the entire vessel.     

果汁机外罩壳注射模设计

根据某品牌果汁机外罩壳的形状特点,详细分析了其模具的结构和工作原理,设计了具有前模内滑块、斜滑块、穿孔滑块,后模滑块、斜顶等抽芯机构的注射模具,实现了外罩壳的注射成型。     

Characterization of continuous convective powder mixing processes

The Process Analytical Technology (PAT) initiative has encouraged the development of new technology to improve upon the current manufacturing paradigm. As a result substantial attention has recently focused on continuous processing due to the ability to control disturbances online, avoiding the loss of processing materials and enabling effective process scale-up. In this paper, a pharmaceutical formulation is blended using a continuous flow “high shear” mixer utilizing different operating and design parameters. The mixing efficiency is characterized by extracting samples at the discharge of the blender, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Operational conditions such as the inclination angle of the mixer and impeller rotation rate were investigated and showed to affect the mean residence time. The effects of mixer angle, agitation speed, number of blades, blade angle, number of passes through the mixer on the mixing performance of a powder continuous convective mixer are also examined and shown to affect mixing performance whereas the cohesive properties of the material did not significantly affect the mixing operation.     

烷氧基化釜式反应器设计探讨

合理地进行烷氧基化釜式反应器的设计,对于提高非离子表面活性剂和聚氨酯聚醚生产能力和产品质量具有显著意义。因此本文从流程设计、反应器的结构尺寸、搅拌器的型式选择、搅拌器的功率计算、反应器的传质以及反应器的传热等方面详细论述了烷氧基化釜式反应器的设计过程。     

A study of the mixing and segregation mechanisms in the Bohle Tote blender via DEM simulations

The flow of spherical particles in a tumbling blender is investigated using discrete element methods (DEM). Simulations are performed on a collection of particles that are mono-disperse and bi-disperse in size. The mono-disperse system is primarily used to assess the quality of mixing as a function of fill level and time. Results reveal that radial convection is faster than axial dispersion transport. This slow dispersive process hinders mixing performance in this geometry. We also find that both axial dispersion and radial convection worsen as the blender fill level is increased. This trend is corroborated by recent laboratory experiments performed in an identical geometry. Particle velocity profiles indicate that the flow is composed of two regions: i) a high velocity layer cascading atop ii) a nearly ‘solid body’ rotation region. Segregating mechanisms are investigated using bi-disperse systems, which show that small particles segregate in pockets at both extremes of the axis of rotation.     

Mixing in the transition flow regime with helical ribbon agitators

The effects of the non-Newtonian properties on the effective deformation rate, mixing and circulation times and flow behaviour have been investigated in the transition flow regime of mixing systems. Based on the equivalent Couette flow, three models are proposed and are shown to predict similar and drastic increases of the effective deformation rate with the impeller rotational speed in the transition regime. The predictions are shown to fit very well data obtained for various non-Newtonian fluids mixed with helical ribbon agitators, and with literature data for anchor, blade turbine and flat disc agitators. The elasticity along with shear-thinning properties appear to have slight effects on the dimensionless mixing and circulation times in the transition regime, whereas their effects in the laminar regime are quite drastic, as reported by others.