Analysis of particle rotation in fluidized bed by use of discrete particle model

The particle rotation was found important in the fluidized bed when the heterogeneous structures appeared. Some researches show that Magnus lift force might play an pivotal role in fluid-solid system, especially when the particles have fast rotation speed. As the Magnus lift force is acted at the single particle level, a pseudo two-dimensional discrete particle model (DPM) was used to investigate the influence of Magnus lift force in fluidized bed. The rotational Reynolds number (Re_r) bases on the angular velocity and the diameter of the spheres is used to characterize the rotational movement of particles. We studied the influence of Magnus lift force for particles with rotational Reynolds number in the range of 1–100. Our results show that the influence of Magnus lift force is enhanced with a higher Re_r. Magnus lift force affects the movement of particles in both radial and axial directions while Re_r is high. However, in low Re_r case it can be neglected in computational simulation model. This indicates the introduction of Magnus lift force may improve the discrete particle model only in high Re_r case and Magnus effect should be considered in real gas-solid two phase system when the particle rotational speed is high.     

Horizontal particle mixing in a free fluidized bed

Horizontal particle diffusion in free fluidized beds is investigated experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 5, pp. 767–773, May, 1982.     

Shell porosity in spray fluidized bed coating with suspensions

An experimental study regarding spray fluidized bed coating with aqueous suspensions is presented. The dependency of coating shell morphology on drying parameters, atomization pressure and composition of suspension is investigated. The results are compared to existing work regarding spray fluidized bed coating with aqueous solutions of crystalline material. Contrary to coating with solutions, coating shell smoothness and porosity does not depend on drying conditions. Nevertheless, atomizing pressure and mass fraction of solids in suspension have large influence on coating shell morphology. High atomization pressures, leading to small droplets, result in smooth coating surfaces and low shell porosities. A similar trend is observed for a low mass fraction of solids in the suspension.     

The calculation of particle trajectories in fluidized bed apparatus

The problem arising in investigations of chlorination of polymers in a boiling bed was formulated in [1,2]. It was found necessary to take into consideration the trajectories of particles and to introduce a certain special measure in the space of these trajectories. The method of solving this problem is presented together with the results of calculations for two separate variants.     

Determination of particle velocity in a fluidized bed by the labeled atom method

The distribution of vertical and horizontal particle velocity in a fluidized bed has been investigated. The experimental results are presented below.     

CFD-DEM study on the mixing characteristics of binary particle systems in a fluidized bed of refuse-derived fuel

The fluidization of quartz in the fluidized bed has great influence on the combustion and gasification of refuse-derived fuel (RDF). The combined computational fluid dynamics (CFD) and discrete element method (DEM) approach was used to explore the gas-solid hydrodynamics and mixing characteristics in a three-dimensional fluidized bed. All numerical analyses were performed referring to the experiments (Goldschmidt, Beetstra, and Kuipers 2004 Goldschmidt, M. J. V., R. Beetstra, and J. A. M. Kuipers. 2004. Hydrodynamic modelling of dense gas-fluidised beds: Comparison and validation of 3D discrete particle and continuum models. Powder Technology 142 (1):23–47. doi:10.1016/j.powtec.2004.02.020[Crossref], [Web of Science ®] , [Google Scholar]). The simulation results indicated that the quartz volume fraction agrees well with the experimental data. Furthermore, the cylinder-shaped RDF particles can mix well with the quartz particles as they were added from upside. For binary systems, it is necessary to investigate solid flow characteristics as well as pressure drops and examine the influence of superficial gas velocity on the solid mixing. Two main parameters are discussed: mixing degree and the time required to reach the steady state. It is also found that inlet gas velocity and particle properties (particle density ratio, shape and size) are significant factors on particle mixing in a fluidized bed.     

Alumina coating on dense tungsten powder by fluidized bed metal organic chemical vapour deposition

In order to study the feasibility of coating very dense powders by alumina using Fluidized Bed Metal Organic Chemical Vapour Deposition (FB-MOCVD), experiments were performed on a commercial tungsten powder, 75 microm in median volume diameter and 19,300 kg/m3 in grain density. The first part of the work was dedicated to the experimental study of the tungsten powder fluidization using argon as carrier gas at room temperature and at 400 degrees C. Due to the very high density of the tungsten powder, leading to low initial fixed bed heights and low bed expansions, different weights of powder were tested in order to reach satisfactory temperature profiles along the fluidized bed. Then, using argon as a fluidized bed former and aluminium acetylacetonate Al(C5O2H7)3 as a single source precursor, alumina thin films were deposited on tungsten particles at a low temperature range (e.g., 370-420 degrees C) by FB-MOCVD. The influence of the weight of powder, bed temperature and run duration was studied. Characterizations of the obtained samples were performed by various techniques including scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (EDS) analyses, Field Emission Gun SEM (FEG-SEM) and Fourier Transform InfraRed (FT-IR) spectroscopy. The different analyses indicated that tungsten particles were uniformly coated by a continuous alumina thin film. The thickness of the film ranged between 25 and 80 nm, depending on the coating conditions. The alumina thin films were amorphous and contained carbon contamination. This latter may correspond to the adsorption of species resulting from incomplete decomposition of the precursor at so low deposition temperature.     

热熔融流化床液固接触包衣特性的CFD-DEM模拟

为了研究热熔融流化床包衣的影响因素,优化包衣过程,采用计算流体力学(CFD)与离散单元法(DEM)耦合的方法,在4种流化速度下(u_(mf),1. 5 u_(mf),2. 5 u_(mf),3. 5 u_(mf))模拟熔融液滴与流化粉体的接触过程;研究热熔融流化床包衣过程中的参数变化对包衣过程的影响。结果表明,当液滴与粉体接触成粒时,产生聚并和破碎现象;顶喷流化床比中喷流化床的液滴与粉体的接触次数更多更充分;较理想的流化速度为1. 5 u_(mf)。     

Choice of optimum particle diameter for heat exchange in a fluidized bed

It was shown experimentally and by calculation that in heat transfer between an isothermal wall and a fluidized bed with all the heat removed by the fluidizing agent, the assumed transfer coefficientas and the maximum flux Q vary widely with increase in particle size of fine grained materials.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 5, pp. 800–806, November, 1973.     

基于DEM模拟液固流化床粒度级配对颗粒流动特性的影响

采用离散单元方法(DEM)对三维液固流化床进行数值模拟。考虑润滑力的作用,对比二元混合、窄级配和宽级配3种粒度级配方式对颗粒分布、速度、温度波动和混合程度的影响。分析结果表明:大颗粒有向床层下部运动的趋势,而小颗粒则有向床层上部聚集的趋势;与窄级配相比,二元混合和宽级配的轴向速度在不同高度上差异较明显,且颗粒温度波动也较小,颗粒更加容易出现偏析;2种颗粒粒径差距越大,越容易分离,而粒径越接近,越难分离,混合程度越好。     

Mass transfer at a moving particle in a fluidized bed of coarse material

An experimental study has been made of mass transfer to a moving particle in the fluidized bed of coarse inert material. The experimental results are presented in terms of dimensionless relationships.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 2, pp. 235–242, August, 1984.     

Study the particle loss from vortex chamber fluidized bed with different conditions

Vortex chamber fluidized bed (VCFB) is a novel type of fluidized bed which has many advantages compare to conventional fluidized beds due to its high-G operation. Hence, the VCFB can replace the conventional fluidized bed for process intensification. However, particle loss at the initial stage of particle injection from VCFB is an important issue which may prevent the particle bed formation inside the VCFB. Therefore, the quality of the fluidized bed will largely depends upon it. The present work aims to study the particle loss from a VCFB at the beginning of particle injection by varying different conditions such as particle feeding location, number of feeding points and particle diameter. A three-dimensional computational fluid dynamics (CFD) model of the VCFB is developed and the particle loss is studied numerically. It is observed that particle loss is minimal when particles are injected from the rear wall of the vortex chamber. Particle loss increases with increasing the number of particle injection points and particle diameter.     

Study of heat exchange between a model particle and a fluidized bed

An experimental study is made of heat exchange between an unsecured model particle and a fluidized bed. The test data is generalized with a dimensionless relation.     

Particle dynamics in a multi-staged fluidized bed: Particle transport behavior on micro-scale by discrete particle modelling

This work studies the particle exchange rates in horizontal fluidized beds equipped with different weir designs between compartments. These particle exchange rates provide information on the axial dispersion of the solid material within the process. For this purpose discrete particle modelling (DPM) was used to determine the particle exchange on microscopic level. This method uses a coupled CFD-DEM approach to observe particle dynamics in a fluid field. The model was validated against exchange rates in a lab-scale setup as determined by Particle Tracking Velocimetry (PTV) with very good quantitative agreement, showing the suitability of the method for the evaluation of weir designs. Simulations were performed for different weir designs and under variation of the hold-up mass, the feed rate and gas velocity to predict their transport behavior in a pilot-scale 3D horizontal fluidized bed. The results indicate that the solids transport behavior is strongly dependent on the used weir design and the main driving force for the particle transport that can be influenced by the process conditions. The installation of weirs between two compartments induces a transport resistance, while the base type without the installation of a weir between the two chambers represents the fastest possibility for mixing the particles of a two-compartment system. It has been observed that the general trend shows higher particle recirculation rates for the overflow weir and base configuration (no weir), whereas the underflow and sideflow weir applications improve the solids transport through the horizontal fluidized bed.     

Experimental study and particle population modeling of coating in a jet-fluidized bed

The present work focuses on the study of a bottom-spray fluidized-bed coater in the absence of any liquid (solvent) evaporation. The main objective is to point out and model the effect of operating conditions on the coating efficiency and the coating mass content distribution of particles. A fluidized bed with a bottom-placed spraying nozzle situated in the middle of a perforated distributor plate was used. The experimental results showed that increasing the jet and fluidizing gas flow rates improve the quality of coating, but there is a limitation for the binder flow rate which is dependent on the bed size and jet gas flow rate. Based on the experimental results, an empirical function was derived to predict the coating efficiency in different operating conditions and this function was also used in the mathematical model. Furthermore, a mathematical model was derived based on the population balance equations for two different zones in the bed. The model could predict the coating mass content distribution and the effect of different operating conditions during the process.     

Quantitative analysis of film coating in a fluidized bed process by in-line NIR spectrometry and multivariate batch calibration

A method is described which enables real-time analysis of film coating on pharmaceutical pellets during an industrial manufacturing process. Measurements were conducted on the solid particulate material by near-infrared (NIR) spectrometry utilizing a diffuse reflectance fiber-optic probe positioned inside a fluidized bed process vessel. Time series of NIR spectra from 11 batches generated a three-way data matrix that was unfolded and modeled by partial least squares (PLS) in a multivariate batch calibration. The process conditions were deliberately varied according to an experimental design. This yielded good predictability of the coating thickness with a best model fit, R2 = 0.97, for one PLS-projection, and a root-mean-square error of calibration = 2.2 microm (range tested 0-50 microm). The regression vector was shown to be highly influenced by responses that are both direct (aliphatic C-H stretch overtones) and indirect (aromatic C-H stretch overtones), from film component and core material, respectively. The impact of different data pre-treatment methods on the normalization of the regression vector is reported. Justification of the process calibration approach is emphasized by good correlation between values predicted from NIR data and reference image analysis data on dissected pellets and a theoretical nonlinear coating thickness growth model. General aspects of in-line NIR on solids and multivariate batch calibration are discussed.     

致密SiC包覆层低温流化床化学气相沉积制备及形成机制

一般致密SiC材料的制备需要极高的温度,而降低制备温度一直是SiC制备领域的重要研究方向。采用流化床化学气相沉积法,在球形二氧化锆陶瓷颗粒上制备了厚度为几十微米的SiC包覆层。通过对不同温度SiC包覆层的显微形貌及微观结构变化规律研究,给出了沉积效率变化规律,发现低温产物富硅,而高温产物富碳。对不同氩气含量的实验研究发现,氩气的加入可以促进沉积反应向富碳方向移动,从而可以在显著降低温度的条件下制备出致密SiC包覆层。综合实验结果给出了流化床化学气相沉积方法在不同温度及氩气浓度条件下制备SiC的物相分布图。      

Particle granulation in fluidized bed

A mechanism of particle granulation in a wet fluidized bed is proposed on the basis of experimental data, and test calculations are performed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 1, pp. 112–116, July, 1991.     

Optimization and characterization of direct coating for ibuprofen particles using a composite fluidized bed

Ibuprofen particles (mean particle size, 27 μm and melting point, 76 °C) as core materials were directly coated with a water-soluble polymer. The primary particles were preserved using a composite fluidized bed with a dispersing mechanism at the bottom of the fluidized bed apparatus. Coated primary particles were obtained under the following 3 conditions: (1) Setting the spray air flow rate at 10 L/min from the initial to 2% coating, (2) adding the low-viscosity water-soluble polymer macrogol 6000 to the hypromellose coating solution, and (3) changing the spray air flow rate to 15 L/min from 2% coating. The particles obtained were confirmed to be coated primary particles by scanning electron microscopy of their cross sections prepared by the cryo-focused ion beam method. The dissolution test showed a marked improvement in the solubility of ibuprofen from the coated primary particles compared with that of a physical mixture. In conclusion, the optimization of the direct coating process made it possible to undertake primary particle coating of a raw material that has a low melting point and a particle size of not more than 50 μm. Primary particle coating contributes to improvements in the physicochemical properties of drugs.     

The effect of ash and filter media characteristics on particle filtration efficiency in fluidized bed

The phenomenon of filtering particles by a fluidized bed is complex and the parameters that affect the control efficiency of filtration have not yet been clarified. The major objective of the study focuses on the effect of characteristics of ash and filter media on filtration efficiency in a fluidized bed. The performance of the fluidized bed for removal of particles in flue gas at various fluidized operating conditions, and then the mechanisms of collecting particles were studied. The evaluated parameters included (1) various ashes (coal ash and incinerator ash); (2) bed material size; (3) operating gas velocity; and (4) bed temperature. The results indicate that the removal efficiency of coal ash increases initially with gas velocity, then decreases gradually as velocity exceeds some specific value. Furthermore, the removal of coal ash enhance with silica sand size decreasing. When the fluidized bed is operated at high temperature, diffusion is a more important mechanism than at room temperature especially for small particles. Although the inertial impaction is the main collection mechanism, the "bounce off" effect when the particles collide with the bed material could reduce the removal efficiency significantly. Because of layer inversion in fluidized bed, the removal efficiency of incinerator ash is decreased with increasing of gas velocity.