Classification of Fine Particles Using the Hydrodynamic Forces in the Boundary Layer of a Membrane

The wet classification of particles < 10 μm is a complex process that has been researched for many years. In this study, the usage of a modified cross‐flow filtration process as a classification process was investigated. With this process, particles in a fine micrometer range can be separated from suspensions. The upper particle size is dependent on hydrodynamic forces. The experimental results were compared with different hydrodynamic force models to predict upper size. The influence of the permeate flux and the particle concentration in the feed on the upper particle size is studied.     

Development of a high-performance cake-less continuous filtration system

A new cake-less continuous filtration system with a rotating disk filter and slurry prepared in a well-dispersed state is discussed in this paper. It is expected that the new system can concentrate a feed suspension much more than traditional filtration systems and that the concentrate can be discharged by the filtration pressure without a scraping device. We tried to filter some difficult to filter materials such as sericite, hydrolyzed cellulose, pulp wastewater and algal suspension. Concentrated slurries of sericite and hydrolyzed cellulose were discharged at the 35 vol% and 12 mass%, respectively. The algal suspension and the pulp wastewater were concentrated up to 8 times more than the concentration of feed suspensions. The concentrates of every sample retained fluidity and flowed out of the new system by way of the filtration pressure.In this system, it was shown that the filtration flux increased with the rotation speed. At lower rotation speeds, the filtration flux was independent of pressure. Conversely at higher rotation speeds, the filtration flux increased along with the pressure. This dependency was clearer in the case of the large disk than when the small disk was used. We also proposed a model for a sweeping mechanism in this system which is explained in the above results.     

Synthesis of submicron barium carbonate using a high-gravity technique

The purpose of this study was to build a platform for producing fine particles by applying a high-gravity (higee) technique to achieve reactive precipitation. Barium carbonate was chosen as a model compound and was produced in a spinning disk reactor (SDR), which is one type of higee equipment, via a carbonation route and a once-through mode. For size measurement, a suitable dispersion method was developed to obtain reproducible particle size data, using a laser-light analyzer. Several factors that affected the particle size of barium carbonate, including the CO₂ flow rate, the feed rate of Ba(OH)₂ slurry, the rotation speed, and the solid-content of feed slurry, were investigated. A high rotating speed and low feeding rate of slurry yielded small particles. The optimum solid-content of feeding slurry for obtaining small particles was also determined. However, the effect of the CO₂ flow rate on the particle size of the product was not significant.     

Numerical Modeling of Particle Dynamics in a Cylindrical Chamber Containing a Rotating Disk

Numerical modeling was performed to study the submicron particle dynamics in a confined flow field containing a rotating disk, temperature gradient, and various inlet gas flow rates. The Lagrangian model was employed to compute particle trajectories under the temperature gradient, disk rotation speed, and inlet gas flow rate effects. The trajectories of particles with diameters of 1 μm, 0.1 μm, and 0.01 μm were examined in this study. When the inlet gas temperature was lower than that of the disk, particle-free zones were created due to upward thermophoretic force for 1 μm and 0.1 μm particles. Disk rotation was found to depress the size of the particle-free zone. Particle deposition onto the disk for 0.01 μm particles was possible because of the Brownian motion effect. A detailed evaluation of the particle-free zone size as a function of the temperature gradient, disk rotation speed, and inlet gas flow rate was performed. When the inlet gas temperature was higher than the disk temperature, particle deposition onto the disk was enhanced due to the downward thermophoretic force for 1 μm and 0.1 μm particles. Disk rotation was found to increase the deposition rate. For 0.01 μm particles, Brownian motion was more important than thermophoretic force in controlling particle behavior. The particle deposition rates as a function of the temperature gradient, disk rotation speed, and inlet gas flow rate were performed.     

涡流空气分级机工艺参数对窄级别产品粒径分布和产率的影响

在建立涡流空气分级机的窄级别实验系统的基础上,为了研究工艺参数对窄级别产品粒径分布和产率的影响,确定了以两级分级机的转笼转速差和第二级分级机的二次风速为实验因素,以产品的粒径分布曲线为实验指标,对涡流空气分级机的窄级别实验系统进行实验。实验结果表明,随着转速差的减小,产品的粒径分布曲线变窄;随着二次风速的增大,产品中的细粉含量减少,粒径分布曲线变窄。进一步研究了窄级别产品的产率、均匀度和转速差的关系。结果表明,窄级别产品的产率随转速差的减小而降低,均匀度随转速差的减小而增加。发现存在一个最佳转速差?n0,在这个转速差?n0下得到的产品能同时满足物料的均匀度和产率的要求。实验结果对窄级别产品的制备具有一定的指导意义。     

Spray Drying of Mannitol as a Drug Carrier—The Impact of Process Parameters on Product Properties

Powders intended for the use in dry powder inhalers have to fulfill specific product properties, which must be closely controlled in order to ensure reproducible and efficient dosing. Spray drying is an ideal technique for the preparation of such powders for several reasons. The aim of this work was to investigate the influence of spray-drying process parameters on relevant product properties, namely, surface topography, size, breaking strength, and polymorphism of mannitol carrier particles intended for the use in dry powder inhalers. In order to address this question, a full-factorial design with four factors at two levels was used. The four factors were feed concentration (10 and 20% [w/w]), gas heater temperature (170 and 190°C), feed rate (10 and 20 L/h), and atomizer rotation speed (6,300 and 8,100 rpm). The liquid spray was carefully analyzed to better understand the dependence of the particle size of the final product on the former droplet size. High gas heater temperatures and low feed rates, corresponding to high outlet temperatures of the dryer (96–98°C), led to smoother particles with surfaces consisting of smaller crystals compared to those achieved at low outlet temperatures (74–75°C), due to lower gas heater temperatures and higher feed rates. A high solution concentration of the feed also resulted in the formation of comparably rougher surfaces than a low feed concentration. Spray-dried particles showed a volume-weighted mean particle size of 71.4–90.0 µm and narrow particle size distributions. The mean particle size was influenced by the atomizer rotation speed and feed concentration. Higher rotation speeds and lower feed concentrations resulted in smaller particles. Breaking strength of the dried particles was significantly influenced by gas heater temperature and feed rate. High gas heater temperatures increased the breaking strength, whereas high feed rates decreased it. No influence of the process parameters on the polymorphism was observed. All products were crystalline, consisting of at least 96.9% of mannitol crystal modification I.     

On the Relation between Filtrate Flux and Particle Concentration in Batch Cross flow Micro filtration

Abstract

The relation between the filtrate flux and particle concentration in batch cross flow micro filtration is investigated using a model based on classical filtration theory and the Kern–-Seaton theory of surface fouling. The model, which includes the effects of cake compressibility but not of membrane fouling, is solved for both laminar and turbulent tangential flows. It is found that the sole effect of cake compressibility is to reduce the flux without altering the general shape of the flux versus concentration curve. Fluxes which increase with increasing concentration are shown to be a result of enhanced cake removal due to the increased wall shear stress brought about by increased suspension viscosity. A sigmoidal relation between flux and concentration is reproduced by the model only if there is a reduction in the cake removal rate as the tangential flow regime changes from turbulent to laminar.     

采用超高分子量聚乙烯过滤介质强化过滤过程的研究

采用颗粒烧结法制备的超高分子量聚乙烯过滤介质,对用途广泛、难过滤的一种无机盐醋酸钙物料做了动态强化过滤过程研究。在对3种超高分子量聚乙烯过滤介质表征的基础上,考察了不同操作压力、旋转速度、固含量、操作温度等对过滤过程的影响。研究表明,过滤通量随着过滤介质孔径增大、压力增大、温度升高、固含量降低均有所增加,截留效果较好,滤液浊度都在30.0 NTU以下,实现了有效的过滤分离,可供技术工程化应用研究参考。     

湍流促进器对液固一体式膜反应器中膜过滤性能影响的研究

以改善液固一体式膜反应器中膜过滤性能为目的,设计了3种外置式湍流促进器进行膜过滤强化实验,考察了湍流促进器的构型、旋转速度等因素对膜通量的影响。结果表明,旋转的湍流促进器可以明显地提高膜通量,其中推进式湍流促进器的强化效果最明显;随着湍流促进器旋转速度的增加,膜通量也相应增加;采用该湍流促进器可以进行高悬浮液质量浓度的膜过滤强化实验。     

分层填料对旋转填料床气相流场影响的数值模拟

通过设计简化的分层填料旋转床(SP-RPB)模型,采用计算流体力学方法(CFD)对比同尺寸旋转填料床(RPB)的稳态气相流场。分析转速和进料速度对气相压力、相对速度及湍动能分布的影响,同时还考察了单位丝网圈上的压降情况。结果表明,在气体进入各级填料位置的相对速度出现峰值,湍动能分布与之相同,各峰的出现位置仅由填料位置决定,两者共同表明SP-RPB具有多个端效应区域。转速增加对相对速度峰值大小有更明显的提升,较大的进料速度使填料内气体的速度波动更大,也使湍动能的峰值有所增加。由于SP-RPB内填料厚度较RPB变薄,从整个设备范围上看,SP-RPB表现出更低的压降。进气速度提高和转速降低使SP-RPB两层填料间的高压范围变窄,但SP-RPB的单位丝网圈数压降更大。     

The use of dean vortices for crossflow microfiltration: basic principles and further investigation

The effect of Dean vortices on the filtration flux and efficiency of crossflow microfiltration processes in sinusoidal curved and helically coiled tubular membranes was investigated by several research groups. Experimental results are presented showing an enhanced filtrate flux and efficiency of the filtration process. CFD simulations were performed, revealing two important effects of secondary flow: an increased wall shear stress causing a reduced particle deposition and an enhanced mass transfer between the boundary layer and the bulk phase.     

Fouling Control in a Submerged Flat Sheet Membrane System: Part I – Bubbling and Hydrodynamic Effects

Abstract

Submerged flat sheet membranes are mostly used in membrane bioreactors for wastewater treatment. The major problems for these modules are concentration polarization and subsequent fouling. By using gas‐liquid two‐phase flow, these problems can be ameliorated. This paper describes a study of the use of gas‐liquid two‐phase flow as a fouling control mechanism for submerged flat sheet membrane bioreactors. The effect of various hydrodynamic factors such as airflow rate, nozzle size, intermittent filtration, channel gap width, feed concentration, imposed flux, and the use of membrane baffles were investigated. Experiments conducted on model feeds showed that fouling reduction increased with air flow rate up to a given value and beyond this flowrate no further enhancement was achieved. The effect of bubbling was also found to increase with nozzle size at constant airflow. Using intermittent filtration as an operating strategy was found to be more effective than continuous filtration and it also reduced energy requirements. The study showed the importance of the size of the gap between the submerged flat sheet membranes. As the gap was increased from 7 mm to 14 mm, the fouling became worse and the degree of fouling reduction by two‐phase flow decreased by at least 40% based on suction pressure rise (dTMP/dt). This is the first study which has reported the effects of baffles in improving air distribution across a flat sheet submerged membrane. It was found that baffles could decrease the rate of fouling by at least a factor of 2.0 based on the dTMP/dt data, and significantly increase critical flux.     

Flow of slightly settling slurries in a horizontal rotary drum

An experimental study was conducted to examine the flow of slightly settling slurries in a horizontal rotary drum. The effects of the slurry flow rate, feed solids concentration, particle settling velocity and drum rotational speed on the hold-up solids concentration were investigated. At low drum speeds, the hold-up solids concentration was much higher than that of the feed. However, at higher drum speeds, the hold-up solids concentration approached that in the feed. At a given drum speed, the hold-up solids concentration was found to vary linearly with the feed solids concentration. A semi-empirical correlation was developed to predict the hold-up solids concentration using the drum Froude number, the single particle drag coefficient and a dimensionless slurry feed rate.     

Unsteady-State Permeate Flux of Crossflow Microfiltration: Effect of Particle Size Distribution

Abstract

A mathematical model based on a hydrodynamic theory and mass balance was developed for the prediction of the unsteady-state permeate flux in crossflow microfiltration under the influence of particle size distribution. Experiments were also conducted in a membrane filtration cell to verify this model. Spherical polystyrene latex particles of 0.303, 0.606, and 1.020 μm were used to make suspensions of various particle size distributions. The flow of the suspension in the channel of the filtration cell was controlled under the laminar flow region. It was found that the unsteady-state permeate flux increased as the mean particle size of the suspension was increased. Moreover, the model predicted satisfactorily the unsteady-state permeate flux under the effect of particle size distribution.     

微悬浮法制备有机颜料微胶囊中的粒径调控

为调控有机颜料微胶囊的粒径及其分布,在分析微悬浮聚合过程粒径变化的基础上,系统研究了微悬浮聚合工艺(均质化剪切速率、搅拌速率)和配方(有机颜料、分散剂含量)对颜料微胶囊粒径的影响。发现当搅拌速率为250 r·min^-1时,单体液滴的融合和乳胶粒的粘并现象均较少,聚合体系可较稳定地保持均质化单体液滴的尺寸。分散剂磷酸三钙TCP用量对体系稳定性影响明显,但其粒径调控能力有限。均质化强度对微胶囊粒径影响明显,具有较好的调控能力,而颜料含量对微胶囊粒径的影响较少。因而通过聚合工艺和配方的综合调节,可制得一系列颜料含量高、粒径分布窄、粒径可调范围较大的"石榴状"有机颜料微胶囊。     

往复旋转中空纤维膜处理脱脂奶水溶液

采用一种往复旋转中空纤维膜超滤装置处理脱脂奶水溶液,考察了该膜过滤装置的结构参数、膜组件旋转参数以及料液的特征参数等对膜渗透通量衰减的影响。结果表明,旋转角速度越大,膜丝距中空轴轴心越远,往复旋转中空纤维膜的剪切强化作用越好;往复旋转周期的优化则需考虑如何使料液流场流速与膜丝转速之间的矢量迭加在膜表面产生的速度梯度更大,单纯增大或减小旋转周期均会弱化剪切强化的效果。在同样操作参数下,往复旋转方式比死端过滤及单向旋转方式的膜过滤更利于延缓膜通量衰减。     

Microfiltration of yeast cells in an internal filter reactor

Microfiltration was carried out in a newly-developed internal filter reactor system (stainless steel membrane filter, pore size=2 or 10 μm) using yeast cells ofSaccharomyces cerevisiae ATCC 24858, industrialS. cerevisiae, and recombinant yeast RH 51. The filter performance was measured in terms of filtrate flux and retention coefficient of cell, and was highly influenced by agitation speed and cell concentration. Both gel polarization model and solid flux model failed to predict the filtration behavior in the internal filter system. An empirical equation was obtained to correlate filtrate flux as a function of agitation speed and cell concentration. Retention coefficient with a filter of 2 Μm pore size was found more than 95%, and the filter was suitable for the yeast cell separation.     

Comparison of the filtration characteristics between biological powdered activated carbon sludge and activated sludge in submerged membrane bioreactors

The filtration performances of submerged membrane bioreactors (SMBR) with and without the addition of powdered activated carbon (PAC) were investigated respectively under the same feed and operation conditions. A series of experiments were conducted to analyze near-critical flux, effect of air-scouring rate and time of stable filtration operation of both systems. The experimental results demonstrated that pronounced flux enhancement was achieved by adding 1.2 g/L PAC. The near-critical flux for the biological powdered activated carbon (BPAC) system was about 32% higher than that for the activated sludge (AS) system. Increasing the air-scouring rate led to a more significant flux improvement for the BPAC system compared to the AS system. Long-term operation indicated that, at constant flux, the TMP increasing rate of the BPAC system could be lagged and thus cause the extension of operating intervals about 1.8 times compared to the AS system. Quantitative calculations showed the total hydraulic resistance of the BPAC system was about 44% lower than that of the AS system, and this decrease was mainly caused by the reduction in cake resistance. Analyses were then made from various aspects such as floc size distribution and apparent viscosity of the mixed liquor to elucidate the major factors giving rise to different filtration characteristics.     

Unsteady-State Permeate Flux of Crossflow Microfiltration

Abstract

In this study a membrane filtration cell was installed to investigate the variation of permeate flux with filtration time under various operating conditions including crossflow velocity, pressure drop, particle concentration, membrane pore size, particle size, pH, and electrolyte concentration. The dimensions of the filtration channel in the CFMF cell were 6 cm x 0.6 cm x 0.036 cm, and the flow of the suspension in the channel was controlled under the laminar flow region. Spherical polystyrene latex particles of 0.303, 0.606, and 1.020 μm were used as the suspension particles in the experiments. The density of the particles was 1.05 g/cm³. It was found that the unsteady-state permeate flux increased with an increase in particle size, membrane pore size, or crossflow velocity, but decreased with an increase in particle concentration or electrolyte concentration in the suspension. A mathematical model based on mass balance and hydrodynamic theory was developed in this study. In addition, the effect of cake growth and particle concentration decline during experiments on the permeate flux were also considered in this model. This model predicts satisfactorily the unsteady-state permeate flux of CFMF under various operating conditions.     

液体燃料合成浆态反应器内部过滤的研究

在液体燃料合成浆态搅拌反应器中设置了以金属烧结板为过滤介质的内过滤器,实现固液分离。研究了压降、温度、搅拌转速、固含率、过滤介质孔径及颗粒粒径对过滤速率的影响。实验结果表明:在浆态反应器中进行内过滤可以得到澄清稳定的滤液;随着操作进行,滤饼厚度达到动态平衡,过滤速率最终趋于稳定;过滤速率随着压降、温度、过滤介质孔径、颗粒粒径的增大及搅拌转速、固含率的减小而增大。应用因次分析法建立过滤模型,通过麦夸特算法对实验数据进行最优拟合得到模型的参数值,统计检验以及模型计算值与实验值的比较表明该模型可靠。