Particle Deposition in Laminar Crossflow Filtration of Power Law Slurry

Abstract

A theoretical model for predicting the probability of particle deposition in crossflow filtration of power law slurry is developed. The model is based on the critical angle of friction between depositing particles, which can be estimated by analyzing the forces exerted on the particles. The binding force between the particles due to polymer adsorption plays an important role in the particle deposition. The smaller the flow behavior index of the slurry is, the larger the binding force and the higher the probability of particle deposition will be. The effects of operating conditions such as the crossflow velocity of the slurry and the filtration rate on the probability of particle deposition are also discussed in depth. The calculated values of the probability of particle deposition agree fairly well with the experimental data. A program is designed to simulate the packing structure and the porosity at the cake surface. The porosity increases not only with the increase of the crossflow velocity, but also with the increase of the flow behavior index of the power law slurry.     

Dimensional Analysis of Crossflow Microfiltration Data

Abstract

A new approach to correlating crossflow microfiltration (CFMF) data based on dimensional analysis is presented. The steady state flux was assumed to be a function of the trans‐membrane pressure (ΔP), the crossflow velocity (u), the particle concentration (c), filtrate viscosity (μ), and membrane resistance (R _m). Correlations of the form J/u=K(ΔP/cu ²) ^a (ΔP/μuR _m) ^b were tested on three sets of published data: one for CFMF of dried yeast suspensions in a laminar flow hollow fiber module, one for dried yeast suspensions in a turbulent flow tubular module and one for suspensions of latex particles in a laminar flow flat sheet module. The R ² values for the fits of the correlations to the data were 0.98, 0.94, and 0.91 respectively.     

管式膜十字流微滤过程分析

分析了管式膜器中过滤悬浮液从膜管外壁向内壁渗透过滤的过程。以流体力学分析为基础 ,利用力平衡原理和多孔介质渗透定律 ,分析了该结构的过滤特性和滤饼形成特点及规律。     

十字流微滤过滤机理研究评述

近年来，膜分离过程中的十字流微滤机理研究在国外非常活跃，在预测过滤速率，动态滤饼的形成，提出了一些新观点和新的机理，加深了对十字流过滤通量下降和膜污染的认识和理解。本文介绍了这些理论和实验研究的成果。     

The Removal of Submicron Particles in Liquid-Based Cleaning

Megasonic cleaning is one of the most widely used wet-cleaning processes in the semiconductor, hard disk and flat panel display industries. Presented results involve different and new techniques for introducing the high frequency ultrasonic energy in the cleaning bath. The effects of power, temperature and time on the removal efficiency of Si₃N₄ particles in the size range from 0.1 μm to 1.0 μm from silicon wafers are presented. Results show that removal efficiencies near 100% for silicon nitride particles using deionized water could be achieved under the right conditions. The megasonic input power has a greater effect on the removal efficiency than does temperature.     

Use of Chemical Species as Dynamic Membranes with Crossflow Microfiltration

ABSTRACT

The feasibility of utilizing the phenomenon of dynamic membrane formation with crossflow microfiltration in treating domestic wastewater was investigated. The primary membrane, used throughout the investigation, was made of woven polyester. Different chemical species, such as CaCO₃, FeCl₃, and NaAIO₂, were used in forming dynamic membranes on top of the primary membrane. Secondary effluent from a domestic activated sludge wastewater treatment plant was treated. A calcium carbonate dynamic membrane produced a stabilized permeate flux of 90 L/m²·h, with a permeate turbidity of 0.21 Nephelometric Turbidity Unit (NTU), at optimum conditions. Ferric chloride produced optimum results when it was mixed with tap water. A permeate flux and turbidity of 70 L/m²-h and 0.16 NTU, respectively, were obtained. Sodium aluminate produced a stabilized permeate flux of 77 L/m²·h when it was mixed with tap water during the formation of the dynamic membrane. The permeate turbidity was 0.16 NTU. The fouling mechanism of the three dynamic membranes was investigated, and empirical models were produced.     

Modelling the Effect of Particle Size in Microfiltration

Abstract

Particle deposition at the filter surface in microfiltration is studied to better understand the effect of particle size on cake morphology and permeability reduction. Numerical simulations are carried out on a Hele Shaw cell which consists of a representative unit element of a two dimensional spatially periodic flat plate with pores. The particle concentration in the fluid is assumed to be low so that particles enter one by one into the computation domain. Particles follow the flow streamlines under creeping flow conditions from a random initial location until they are subjected to physico‐chemical interactions near the filter surface or a particle already deposited. The computational domain consists of two regions: a fluid region and a porous medium region, i.e. the particle cake. The flow over the two regions of the Hele Shaw cell is computed using the Darcy model, including the variations of the permeability field due to the cake formation. Results show that both the permeability and the filtration efficiency are affected significantly by particle size.     

颗粒粒径和膜孔径对陶瓷膜微滤微米级颗粒悬浮液的影响

通过测定颗粒悬浮液通过陶瓷微滤膜时的参透通量及污染阻力,确定了陶瓷膜处理微米级颗粒悬浮液时,颗粒粒径和膜孔径对微滤过程的影响和膜污染机理,获得了微米级颗粒悬浮液微滤过程中膜孔径的选择方法。     

Recent Theoretical Results for Nonequilibrium Deposition of Submicron Particles

Selected theoretical developments in modeling of deposition of sub-micrometer size (submicron) particles on solid surfaces, with and without surface diffusion, of interest in colloid, polymer, and certain biological systems, are surveyed. We review deposition processes involving extended objects, with jamming and its interplay with in-surface diffusion yielding interesting dynamics of approach to the large-time state. Mean-field and low-density approximation schemes can be used in many instances for short and intermediate times, in large enough dimensions, and for particle sizes larger than few lattice units. Random sequential adsorption models are appropriate for higher particle densities (larger times). Added diffusion allows formation of denser deposits and leads to power-law large-time behavior which, in one dimension (linear substrate, such as DNA), was related to diffusion-limited reactions, while in two dimensions (planar substrate), was associated with evolution of the domain-wall and defect network, reminiscent of equilibrium ordering processes.     

Recent Theoretical Results for Nonequilibrium Deposition of Submicron Particles

Selected theoretical developments in modeling of deposition of sub-micrometer size (submicron) particles on solid surfaces, with and without surface diffusion, of interest in colloid, polymer, and certain biological systems, are surveyed. We review deposition processes involving extended objects, with jamming and its interplay with in-surface diffusion yielding interesting dynamics of approach to the large-time state. Mean-field and low-density approximation schemes can be used in many instances for short and intermediate times, in large enough dimensions, and for particle sizes larger than few lattice units. Random sequential adsorption models are appropriate for higher particle densities (larger times). Added diffusion allows formation of denser deposits and leads to power-law large-time behavior which, in one dimension (linear substrate, such as DNA), was related to diffusion-limited reactions, while in two dimensions (planar substrate), was associated with evolution of the domain-wall and defect network, reminiscent of equilibrium ordering processes.     

The Effect of Large Particles on Microfiltration of Small Particles

The effects of the presence of large latex (1 m) particles on the microfiltration of small gold (50 nm) colloidal suspensions have been investigated using hydrophobic 0.22 m polyvinylidene fluoride (GVHP) micro-filtration (MF) membranes. Gold sol was filtered through the membrane with or without prefiltration of latex suspension. The characteristics of the cake formed on the membrane surface depends not only on the intrinsic properties of the particles in the feed but also depends on the nature of the mixture. The type of cake formation (e.g. a cake of small particles on the top of large particles or a cake of mixed particles) affects the cake properties due to the combination effect. This can be explained by the type of filling of the voidage between large particles with small particles. Various combinations of these particles result in cakes with different resistances. The understanding of the combination effect and the type of cake formation has a potential application for fouling minimization.Fouling is surprisingly serious in microfiltration of the feeds containing mixed particles. Separation of large particles prior to the microfiltration of suspension of small particles can reduce cake resistance and minimize fouling.     

去除亚微米粉尘的旋风除尘系统开发

本文开发出了亚微米粉尘的旋风除尘系统——环流循环除尘系统。并通过实验测试了该除尘系统的性能。结果表明 ,亚微米粉尘的旋风除尘系统的分割直径 d50 达到了 0 .5 μm～ 0 .7μm,压降小于 35 0 0 Pa,只比常规旋风除尘器的单台压降略高。该工艺系统可使半密闭和开放式电石炉气达到环保排放标准 ,亦能保证密闭电石炉除尘的需要 ,且可用于水泥立窑、锅炉等窑炉除尘     

陶瓷微滤膜处理钛白粉水洗液的过程强化研究

本文采用湍流促进器和反冲对陶瓷膜处理钛白粉水洗液的微滤过程进行了强化研究。实验和以上两种方法均不同程度地提高了渗透通量,降低了能耗。考察卫湍流促进器结构参数和反冲持续时间、压力、周期对强化效果的影响,确定了合适的湍流促进器结构参数和反冲条件,并对反冲的重复性进行了实验考察。     

微米与亚微米级的液固与气固混合物的一种新型分离技术

微米与亚微米级的液固与气固混合物的高效分离非常困难。目前工业生产上普遍使用的各种传统分离技术,其分离效率均不高。本文给出一种新的分离技术——高分子烧结精密微孔过滤技术(由烧结微孔过滤介质、精密微孔过滤机、辅助装置及不同的应用方法组成)能对这些混合物进行高效分离,能得到干的滤饼。除了过滤效率高外,其操作还非常简便,占地面积较小,动力消耗较少,操作成本与投资费均较低。该技术已在国内许多工业生产与废水处理中获得广泛应用。     

旋转流强化管式膜微滤过程中分离因数研究

分离因数是影响旋转流强化管式膜微滤过程的关键操作变量之一。本文首先对管式膜分离器内分离因数的分布特征进行了研究,然后,不仅从理论上研究了分离因数对过滤过程行为的影响,而且进行了探讨分离因数对过滤性能影响的试验研究。结果表明,管式膜分离器内分离因数沿轴向从顶部到底部呈迅速减小的分布特征;分离因数的增大,可使过滤过程推动力提高,并使外旋流时过滤过程中固相颗粒不易向膜面迁移并沉积,但加剧了内旋流时过滤过程中固相颗粒向膜面迁移并沉积的趋势;在悬浮液固相浓度保持一定时,过滤通量随分离因数的增大而提高     

陶瓷微滤膜回收钛白粉水洗液中TiO2颗粒中试与现场考核

对陶瓷微滤膜回收钛白粉水洗液中二氧化钛粒子进行了中试实验和现场考核 ,考察了错流速度、浓度对渗透通量的影响及湍流促进器对微滤过程的强化效果 ;建立了日处理 15 0t废水的陶瓷膜回收钛白粉成套装置 ,并对该装置进行了现场运行性能考察和经济核算。实验结果表明 ,采用陶瓷膜微滤技术回收钛白粉水洗液中二氧化钛粒子不仅在技术上是可行的 ,在经济上也是合理的。     

溶液环境对陶瓷膜微滤微米级颗粒悬浮液的影响

本文研究了溶液环境对陶瓷微滤膜处理微米,亚微米级颗粒悬浮液过程的影响,通过测定电解质溶液种类,浓度对微滤过程渗透通量的影响,及溶液环境对微滤过程影响随颗粒粒径,膜孔径的变化,确定了溶液环境对微滤过程的影响主要是由于其引起了颗粒表面Ｚｅｔａ电位的变化,改变了颗粒在溶液中的分散情况,并引起了决定膜通量的颗粒粒径／膜孔径比值的变化,从而改变了微滤过程。     

Cross-Flow Microfiltration of Bacillus Subtilis Broths under Various Culture Times

Bacillus subtilis broths under different culture times are filtered in a cross-flow microfilter. The operating condition effects, such as cross-flow velocity, transmembrane pressure, and broth culture time, on the filtration flux, cake properties, and extracellular polymeric substances (EPS) transmissions are discussed thoroughly. The culture broths contain B. subtilis cells and EPS which is characterized as polysaccharides (hydrocarbons) and proteins. An increase in broth culture time leads to higher concentrations of cells, soluble and extractable EPS. The total protein to polysaccharide concentration ratio in the broths is ca 0.2. However, the soluble polysaccharide concentration is 10-fold higher than that of soluble proteins. The filtration flux increases with increasing cross-flow velocity or transmembrane pressure. However, the impact of cross-flow velocity is more significant. The filter cake resistance formed by B. subtilis cells and EPS flocs plays the most important role in determining the overall filtration resistance. The mass and average specific filtration resistance of cake can be estimated using a force balance model and empirical equations. The cake structure and thickness are analyzed using SEM. A thicker and more compact cake may be formed under longer broth culture time. Most soluble polysaccharide and protein molecules have the opportunity to penetrate through the cake and membrane into the filtrate because the solute transmissions are measured as high as 0.75–1.0. The influences of operating conditions on the polysaccharide and protein transmissions are negligible. Therefore, to enhance filtration flux by increasing transmembrane pressure or cross-flow velocity is beneficial to improve separation efficiency, especially by increasing cross-flow velocity.     

超重力辅助溶剂-反溶剂重结晶法制备亚微米级RDX

为了获得粒径分布均匀的细化RDX,在超重力反应器中,以丙酮-水作为溶剂-反溶剂重结晶体系,添加聚乙烯吡咯烷酮(PVP)作为表面活性剂,制备了亚微米级RDX。研究了RDX溶液浓度、PVP含量以及超重力反应器转速对RDX形貌和尺寸的影响,获得最优工艺条件,利用SEM、XRD和FT-IR对其形貌、晶体结构和分子结构进行了表征,并采用DSC研究了RDX的热分解过程。结果表明,在RDX溶液浓度为0.04g/mL、PVP浓度为0.2g/L、超重力反应器转速为1500r/min时,制备了平均粒径为0.54μm的亚微米级RDX,细化处理未改变RDX的晶型;与原料RDX相比,亚微米级RDX的分解峰温提前了1.2℃,热分解活化能从180~250kJ/mol降至约150kJ/mol。     

海水淡化系统中微滤膜的污染和清洗

该文依托浙江某电厂海水淡化系统中微滤装置在不同运行工况下的水质数据,对微滤膜的污染成因与清洗方法进行探讨与研究,分析了不同清洗方法对微滤膜性能恢复的影响。在综合考虑各种工程因素的基础上,提出了微滤膜日常运行维护方案,有效延长微滤膜清洗周期。