Experimental study on fluidization of fine powders in rotating drums with various wall friction and baffled rotating drums

Fine powders were found to be fluidized in a rotating drum by internal cycling gas by the drum rotation. It is essentially a fluidized bed without requiring any external fluidizing gas. Such a rotating drum can be regarded as a new gasless fluidized bed for fine powders in contrast to a traditional fluidized bed, possibly leading to a considerable amount of energy savings. In addition, the fluidization quality of fine powders was found to be further improved with the assistance of drum rotation because of the shearing movement among particles that eliminates channeling and cracks and possibly also breaks agglomerates. Five regimes were identified in the rotating drum including slipping, avalanching-sliding, aerated, fluidization and re-compacted regimes. It was also found that drum wall friction plays an important role to fluidize fine powders because the friction carries particles to the freeboard, leading to gas cycling that fluidizes the powders. As well, three types of specially designed baffles were utilized to promote powder fluidization in rotating drums. These baffles effectively bring an early onset of all the regimes in rotating drums by reducing powder-wall slipping, carrying particles and bringing additional gas to the powders.     

Formation of deagglomerated PLGA particles and PLGA-coated ultra fine powders by rapid expansion of supercritical solution with ethanol cosolvent

Rapid expansion of supercritical solution (RESS) was used for preparing polymer particles and polymer coating of ultra fine powders. The polymer of pharmaceutical interest was Poly(lactic-co-glycolic acid) (PLGA with PLA: PGA ratio of 85: 15 and MW of 50,000–75,000) and the simulated core particles were 1.4-μm SiO₂ and 70-nm TiO₂ particles. The supercritical solution was prepared by dissolving PLGA in supercritical carbon dioxide with ethanol as a cosolvent. Supercritical solution of CO₂-PLGA was sprayed through capillary nozzles to ambient conditions, resulting in formation of submicron PLGA particles. Similarly, rapid expansion of supercritical solution of CO₂-PLGA suspended with the core particles could provide solvent evaporation and deposition of submicron PLGA particles on the surface of the core particles, resulting in the formation of coating films on dispersed particles of SiO₂ and agglomerates of TiO₂. The influences of the core particle size, spray nozzle diameter as well as powder-to-polymer weight ratio were also investigated and discussed with respect to the coating performance.     

护肝片改薄膜包衣生产工艺研究

为了解决糖衣片在临床使用中出现的问题,改变了包衣工艺,建立了护肝片薄膜包衣的最佳工艺条件并考察其稳定性。将护肝片的包衣工艺由糖衣改为薄膜衣,通过正交试验确定护肝片薄膜包衣的最佳包衣液浓度、喷量、喷雾风速温度,并用加速试验法和室温留样考察其稳定性。在包衣液浓度为13%、包衣液喷速为140 g/min、进风温度为75℃的条件下生产的薄膜衣片质量最佳,且按2010药典检验其稳定性合格。结果表明,此制备工艺稳定,可用于护肝薄膜衣片的工业生产。     

Fine particle coating by a novel rotating fluidized bed coater

Fine particle coating has been conducted by using a novel rotating fluidized bed coater. The coater consists of a plenum chamber and a horizontal porous cylindrical air distributor, which rotates around its axis of symmetry inside the plenum chamber. Cohesive fine cornstarch (mass median diameter of 15 μm), a Geldart Group C powder, was used as core particle and an aqueous solution of hydroxypropylcellulose (HPC-L) was sprayed onto the cornstarch to generate a film coating. Fine particle coating was conducted under various coating levels (wt.% HPC-L) and the particle size distribution of the coated particles, release rate of an aqueous pigment (food blue No. 1), which had been pre-coated onto the initial cornstarch, and the degree of agglomeration were investigated. The relationship between the coating level and the physical properties of the coated particles was analyzed. The results indicated that coating of cohesive fine cornstarch with HPC-L could be achieved, producing a favorable prolonged release property with almost maintaining the individual single particle.     

用石蜡-CO_2超临界流体快速膨胀在流化床中进行细颗粒包覆

对超临界流体快速膨胀技术在流化床中进行细颗粒的表面包覆进行了研究 ,以实现细颗粒中关键成分的有效控制释放 .实验研究了含有包覆剂———石蜡的超临界二氧化碳流体通过微细喷嘴快速膨胀到装有细颗粒的流化床中 ,膨胀射流中所产生的微核在细颗粒表面均匀沉积 ,形成细颗粒表面薄层包覆 .结果分析表明 ,超临界流体快速膨胀前的温度是包覆过程的关键参数 ,通过控制操作过程参数可以获得良好的包覆结果     

Batch drying kinetics of corn in a novel rotating jet spouted bed

The batch drying kinetics of corn as a test material were investigated experimentally in a novel rotating jet spouted bed (RJSB) using both continuous and intermittent (on/off) spouting and heating schemes. The parameters investigated include inlet air temperature, bed height, superficial air velocity, nozzle diameter, distributor rotational speed and intermittency of spouting and heat input. The results indicate that the drying kinetics are comparable with conventional spouted and fluidized beds for slow drying materials and that intermittent drying can save up to 40% of the thermal energy as well as air consumption with better quality product.     

Evaluation of the morphological and release characteristics of coated fertilizer granules produced in a Wurster fluidized bed

In the present study, coated fertilizer granules were produced in a Wurster chamber of a fluidized-bed equipment for controlled-release agrochemical applications. The coating material was a commercially available latex of poly(vinylidene-chloride). The influence of the process parameters (e.g., spray rate of the polymer latex, fluidization air velocity, distance of the partition from the air inlet and perforation percentage of the plate at the air inlet) on the morphology and quality of the coating was thoroughly investigated. The surface characteristics of the coated fertilizer granules were examined by scanning electron microscopy (SEM). The release rate of the fertilizer's nutrients from the coated granules was determined by kinetic-release experiments carried out in distilled water. Depending on the selected process conditions, the coating thickness could vary from 25 to 65 μm, while the surface of the coated granules changed from completely smooth to rough and porous. It was shown that by suitable selection of the coating conditions in the Wurster process, controlled-release fertilizers exhibiting prolonged release profiles could be produced.     

Behavior of Ultrafine versus Superfine Powders in a Binary‐Mixture Semi‐Batch Circulating Fluidized Bed

The solid circulation rates of a binary mixture of ultrafine or superfine Al(OH)₃ powders and fluidized catalytic cracking (FCC) particles were investigated in a semi‐batch circulating fluidized bed. The circulation rates were measured at different loadings of fine powders and different equilibrium water contents of the FCC particles. At a certain loading of ultrafine powders, the circulation rates were much smaller than in the presence of the superfine powders. The circulation rates were controlled by the strong cohesive property of the ultrafine powders, irrespective of the water contents of the FCC particles. Slight increases in the circulation rates were observed during fluidization of the ultrafine powders, even at higher equilibrium water contents of the FCC particles.     

Artificial Neural Network Modeling of the Deposition Rate of Lactose Powder in Spray Dryers

A spray dryer is the ideal equipment for the production of food powders because it can easily impart well-defined end product characteristics such as moisture content, particle size, porosity, and bulk density. Wall deposition of particles in spray dryers is a key processing problem and an understanding of wall deposition can guide the selection of operating conditions to minimize this problem. The stickiness of powders causes the deposition of particles on the wall. Operating parameters such as inlet air temperature and feed flow rate affect the air temperature and humidity inside the dryer, which together with the addition of drying aids can affect the stickiness and moisture content of the product and hence its deposition on the wall. In this article, an artificial neural network (ANN) method was used to model the effects of inlet air temperature, feed flow rate, and maltodextrin ratio on wall deposition flux and moisture content of lactose-rich products. An ANN trained by back-propagation algorithms was developed to predict two performance indices based on the three input variables. The results showed good agreement between predicted results using the ANN and the measured data taken under the same conditions. The optimum condition found by the ANN for minimum moisture content and minimum wall deposition rate for lactose-rich feed was inlet air temperature of 140°C, feed rate of 23 mL/min, and maltodextrin ratio of 45%. The ANN technology has been shown to be an excellent investigative and predictive tool for spray drying of lactose-rich products.     

A Taguchi approach production of spray-dried whey powder enriched with nanoencapsulated vitamin D3

Abstract

The objective of the present study was to investigate the effect of inlet air temperature of spray drying and different combinations of carrier agents (maltodextrin (MD), gum Arabic (GA), modified starch (MS), and whey protein concentrate (WPC)) on the physicochemical characteristics of spray-dried whey powder, enriched with vitamin D₃ to improve its usage as a functional ingredient. Firstly, vitamin D₃ was nanoencapsulated by nanoliposome prepared with egg yolk lecithin, sesame oil, and glycerol through thin-film dispersion method. The mean particle size of prepared nanoliposomes was 140?nm. Then, the prepared nanocarriers loaded with vitamin D₃ were added into the feed solution and dried through spray dryer. The effect of carrier agent types and inlet air temperature on the physicochemical (moisture content, solubility, porosity, color, and powder yield) and microstructure properties of obtained spray-dried powders were investigated. The optimal carrier agents and condition of spray drying were selected by Taguchi design. Our results showed that the inlet air temperature and carrier agent had significant effects on the characterization of powders. Powders produced by 2% WPC, 3% MS, and 25% MD at 170?°C inlet air temperature showed the highest powder yield (96.4%). Also, the morphology of powders was affected by carrier agent types; increase in MD concentration in feed solution causes to create smoother and spherical spray-dried powder particles.     

Mathematical Model for Batch Drying in an Inert Medium Fluidized Bed

A modified three-phase model is proposed for batch drying of fine powders in an inert medium fluidized bed. The overall heat and mass transfer coefficients between the interstitial gas and solid phases have been determined by the proposed surface-stripping model in which the Biot number is a governing parameter. The effects of gas velocity, inlet gas temperature and mass ratio of starch to inert particles on the drying characteristics of starch in a 0.083 m ID × 0.80 m high medium fluidized bed have been determined. Based on the proposed model, the internal resistance of mass transfer at the powder is equal to the external resistance. The model predicts well the bed temperature, humidity of outlet gas, moisture content of solid particles, heat and mass transfer in an inert medium fluidized bed.     

细颗粒的团聚流态化及其判定

本文在考查了不同细颗粒的流态化过程及物料的气动特性与粘附力关系的基础上，提出了当量流态化的概念；实验发现聚团密度的减小是改善细颗粒流化性能的一种有效途径；根据气动情况下不同的成团结果，把细颗粒的聚团流态化分成了三类：沟流；似A类聚团流态化；似B／D类聚团流态化；同时，结合实验结果，给出了不同细颗粒聚团流态化类型的定量判据     

非磁性粘性颗粒在添加磁性大颗粒磁场流化床中的流化性能

通过添加磁性大颗粒，破碎活塞及沟流，显著改善了非磁性粘性颗粒在磁场流化床中的流化性能。为了评价非磁性粘性颗粒在磁场流化床中的流化性能，测量了最小流化速度、床层压力降和床膨胀高度。实验结果表明，非磁性粘性颗粒的最小流化速度，由于添加磁性大颗粒，而显著降低。磁性大颗粒添加量对非磁性粘性颗粒的最小流化速度有较大影响，随磁性大颗粒添加量的增加，最小流化速度降低，但当磁性大颗粒添加量增大到40％后，非磁性粘性颗粒和磁性大颗粒的混合物的最小流化速度就不再降低。     

Experimental investigation of a rotating fluidized bed in a static geometry

Rotating fluidized beds in a static geometry are based on the new concept of injecting the fluidization gas tangentially in the fluidization chamber, via multiple gas inlet slots in its cylindrical outer wall. The tangential injection of the fluidization gas fluidizes the particles tangentially and induces a rotating motion, generating a centrifugal field. Radial fluidization of the particle bed is created by introducing a radially inwards motion of the fluidization gas, towards a centrally positioned chimney. Correctly balancing the centrifugal force and the radial gas-solid drag force requires an optimization of the fluidization chamber design for each given type of particles. Solids feeding and removal can be continuous, via one of the end plates of the fluidization chamber.The fluidization behavior of both large diameter, low density polymer particles and small diameter, higher density salt particles is investigated at different solids loadings in a 24 cm diameter, 13.5 cm long non-optimized fluidization chamber. Scale-up to a 36 cm diameter fluidization chamber is illustrated.Provided that the solids loading is sufficiently high, a stable rotating fluidized bed in a static geometry is obtained. This requires to minimize the solids losses via the chimney. With the polymer particles, a dense and uniform bed is observed, whereas with the salt particles a less dense and less uniform bubbling bed is observed. Solids losses via the chimney are much more pronounced with the salt than with the polymer particles.Slugging and channeling occur at too low solids loadings. The hydrostatic gas phase pressure profiles along the outer cylindrical wall of the fluidization chamber are a good indicator of the particle bed uniformity and of channeling and slugging. The fluidization gas flow rate has only a minor effect on the occurrence of channeling and slugging, the solids loading in the fluidization chamber being the determining factor for obtaining a stable and uniform rotating fluidized bed in a static geometry.     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

细颗粒振动流态化行为的二维床观察

本文利用一种新型复合振动充化装置，使在一般操作条件下无法实现正常流化的细颗粒床层处于良好的流化状态。通过观察发现，振动的引入可以破坏沟流的存在而使细颗粒流化；其振动流化有三种存在形式，提出了振动流化的物理模型和流化相同，可以解释细颗流化状态与振动条件及其物性的关系。     

Modification and re-interpretation of Geldart's classification of powders

In developing his powder classification, Geldart [D. Geldart, Powder Technol. 7 (1973) 285.] employed fluidization data obtained only at ambient temperature and pressure and from beds fluidized only with air. Unfortunately, industrial applications of fluidized bed technology invariably are at elevated pressure and temperature and with fluidizing gas other than air. Geldart classification of powders does not apply at elevated pressure and temperature. There are ample evidences reported in the literature indicating that normally Geldart Group B powders at ambient conditions, such as polymer particles, can behave like a Group A powder under polymerization conditions at elevated pressure and moderate temperature with substantial emulsion-phase expansion, relatively small bubbles, smooth fluidization, and reduced gas bypassing [J.R. Grace, Can. J. Chem. Eng. 64 (1986) 353; I.D. Burdett, R.S. Elsinger, P. Cai, K.H. Lee, Gas-phase fluidization technology for production of polyolefins, in Fluidization X, Eds. M. Kwauk, J. Li, W.C. Yang, 2001, pp. 39-52; P.N. Rowe, P.U. Foscolo, A.C. Hoffmann, J.G. Yates, X-ray observation of gas fluidized beds under pressure, in Fluidization IV, Eds. D. Kunii, R. Toei, 1983, pp. 53-60]. Similar findings were also reported for Geldart Group B powders fluidized by supercritical carbon dioxide at elevated pressures [C. Vogt, R. Schreiber, J. Werther, G. Brunner, Fluidization at supercritical fluid conditions, in Fluidization X, Eds. M. Kwauk, J. Li, W.C. Yang, 2001, pp. 117-124; C. Vogt, R. Schreiber, G. Brunner, J. Werther, Powder Technol. 158 (2005) 102; D. Liu, M. Kwauk, H. Li, Chem. Eng. Sci. 51 (1996) 4045; M. Poletto, P. Salatino, L. Massimilla, Chem. Eng. Sci. 48 (1993) 617; A. Marzocchella, P. Salatino, AIChE J. 46 (2000) 901].The original Geldart's classification is modified and re-interpreted in this paper by plotting a dimensionless density against the Archimedes number. The new parameters allow powders with different properties fluidized at different pressures and temperatures with gases of different properties to be plotted in the same graph. The proposed modification successfully transforms the normally Geldart Group B particles at ambient conditions to Group A classification when fluidized at elevated pressure and temperature. The selection of these two parameters, the dimensionless density and the Archimedes number, for plotting is not arbitrary, however. The experimental and theoretical development is discussed.     

Effects of Spray-Drying Conditions on the Physicochemical Properties of Blackberry Powder

The purpose of this work was to study the effects of spray-drying conditions on the physicochemical characteristics of blackberry powder using a central composite rotatable design. Inlet air temperature (140–180°C) and maltodextrin concentration (5–25%) were employed as independent variables. Moisture content, hygroscopicity, anthocyanin retention, color, powder morphology, and particle size were analyzed. A higher inlet air temperature significantly increased the hygroscopicity of the powder, decreased its moisture content, and led to the formation of larger particles with smooth surfaces. Powders produced with higher maltodextrin concentrations were less hygroscopic, slightly lighter and less red, and had a lower moisture content. Anthocyanin retention was mainly affected by drying temperature due to the heat sensitivity of the pigment. The optimal processing conditions were an inlet air temperature of 140–150°C and maltodextrin concentration of 5–7%. Overall, these results indicate that good quality powders can be obtained by spray drying, with potential applications for the food industry.     

Drying of Sodium Acetate in a Pulsed Fluid Bed Dryer

Sodium acetate crystals obtained from the reaction of acetic acid with sodium hydroxide are usually dried in rotary or fluidized beds. In this study, a batch pulsed fluid bed dryer with a 0.18 m² cross‐sectional area was used in an attempt to reduce energy consumption and increase productivity. Drying curves of sodium acetate were determined for different conditions: inlet air temperature of 65 and 80 °C and pulsation frequency of 0 rpm (conventional fluidized bed), 500 and 900 rpm (pulsed fluid bed). A 2² factorial design was used to analyze the results. The intermittent flow helped to break agglomerates and provided better contact between particles and the gas. Drying rates were higher under pulsed fluidization when compared to conventional fluidization. Conventional fluidized bed drying consumed 2.5 times more energy at 80 °C. The influence of temperature on the drying rate was also evident.     

Fluidization of fine particles in a sound field and identification of group C/A particles using acoustic waves

Effects of sound field on the fluidization of fine particles have been comprehensively examined by using fine powders (4.8-65 μm average in size) including Al₂O₃, TiO₂, glass beads and FCC catalyst. It is found that the fluidization quality of fine particles can be enhanced with the assistance of a sound field, resulting in higher pressure drops and a lower u_mf. The effect of sound on the fluidization of fine particles is strongly dependent on the particle properties (Geldart type and particle size) as well as the parameters of the sound field such as sound pressure level (or intensity) and frequency. Given a fixed sound frequency, the effect becomes more significant at a higher sound pressure level. For the present sound-aided fluidized bed system, there is a resonant frequency at about 100-110 Hz, at which the effectiveness of the sound wave in improving fluidization of fine particles is most remarkable. In addition, based on the different attenuation features of sonic waves in the gas-solid suspension of group C and A particles, a novel acoustic method is explored to distinguish group C from group A particles.