Enhancement of fine particle filtration with efficient humidification

Filtration is one of the most effective methods to remove suspended fine particles from air. In filtration processes,pressure drop of compact dust cake causes problems in efficiency and economy, which has received increasing attention and still remains challenging. In this study, we developed a novel technique to intensify the filtration of fine particles with efficient humidification. Two strategies for humidification, including ultrasonic atomization and steam humidification(controlling of ambient humidity), were employed and proved to be both effective. The regeneration frequency of the filter could be reduced by 55% with ultrasonic atomization, while steam humidification could lead to a 78% reduction in regeneration frequency. The effect of operating conditions on pressure drop and the mass loading during filtration were investigated. The dust cake showed a loose and porous structure with an optimized droplet-to-particle ratio. With the ratio of 1.53 and 0.0282, the maximum mass loading was 552 g·m-2upon the ultrasonic atomization and 720 g·m-2upon the steam humidification. The results show that humidification could slow down the increase of pressure drop during filtration and improve the efficiency of process.     

硅藻土-木桨纤维为助滤剂强化过滤过程的研究(英文)

In this paper, a study to enhance the filtration for solid/liquid materials difficult to be filtered, such as highly viscous, highly compactible or gel like materials, is presented. Filter aids diatomaceous earth and wood pulp cellulose are used to enhance the filtration by improving filter cake structure and properties in the filtration of a biological health product and a highly viscous chemical fiber polymer melt product. The property of solid/liquid systems, filtration at different flow rates, specific cake resistance, cake wetness, filtration rate, filtrate turbidity for filter aid selection and evaluation, and operation optimization are investigated. The results are successfully applied to industrial process, and can be used as a reference for similar filtration applications.     

Effect of Coagulant Agents on Oily Wastewater Treatment Performance Using Mullite Ceramic MF Membranes： Experimental and Modeling Studies

In this paper, fouling mechanisms of mullite ceramic membranes for treatment of oily wastewaters in hybrid coagulation-microfiltration （MF） process presented. Hermia＇s models for cross flow filtration were used to investigate the fouling mechanisms of membranes with various coagulating chemicals concentrations. Four coagu lating chemicals （FeC12.4H20, FeSO4.7H20, A1C13-6H20 and A12（SO4）3.18H20） plus Ca（OH）2 of the same concen- tration were evaluated in the coagulation-MF hybrid process with different concentrations （0, 50 mg.L-1, 100 mg.L-1 and 200 mg.L-1）. To determine whether the data agree with models under consideration, the coefficients of determination （R2） of all models were compared with one another. In addition, average prediction errors of models were calculated. The results showed that cake filtration model can be applied for prediction of permeation flux decline for MF and coagulation-（MF） hybrid process with the best average error equal to 0.09%. Results indicated that pore blocking behavior changes as time of filtration increases, and one model cannot predict pore blocking behavior in all filtration time with very good precision.     

用于TS-1催化苯酚羟基化的一体式催化/膜过滤系统的模型研究

This research is focused on the development of a simple design model of the submerged catalysis/ membrane filtration (catalysis/MF) system for phenol hydroxylation over TS-1 based on the material balance of the phenol under steady state and the reported kinetic studies. Based on the developed model, the theoretical phenol conversions at steady state could be calculated using the kinetic parameters obtained from the previous batch ex-periments. The theoretical conversions are in good agreement with the experimental data obtained in the submerged catalysis/MF system within relative error of ±5%. The model can be used to determine the optimal experimental conditions to carry out the phenol hydroxylation over TS-1 in the submerged catalysis/MF system.     

基于详细反应机理的富燃多孔燃烧制氢的计算流体力学模拟

Computational fluid dynamics （CFD） combined with detailed chemical kinetics was employed to model the filtration combustion of a mixture of methane/air in a packed bed of uniform 3 mm diameter alumina spherical particles. The standard k-ε turbulence model and a methane oxidation mechanism with 23 species and 39 elemental reactions were used. Various equivalence ratios （1.47, 1.88, 2.12 and 2.35） were studied. The numerical results showed good agreement with the experimental data. For ultra-rich mixtures, the combustion temperature exceeds the adiabatic value by hundreds of centigrade degrees. Syngas （hydrogen and carbon monoxide） can be obtained up to a mole fraction of 23%. The numerical results also showed that the combination of CFD with detailed chemical kinetics gives good performance for modeling the pseudo-homogeneous flames of methane in porous media.     

MATHEMATICAL MODELING OF NON-CATALYTIC LIQUID-SOLID REACTION AND ITS SOLUTION BY ORTHOGONAL COLLOCATION

The mathematical model of non-catalytic liquid-solid diffusion reactions discussed in this paper can be applied to quite different cases. The models in the literature such as unreacted shrinking core model, two stage model and homogeneous model can be considered as special cases of the above model which has been derived for leaching vanadium from steel slag with sodium carbonate and]or sodium bicarbonate solution reacting with two components in the slag simultaneously. The vanadium leaching reaction is inhibited by the solid product formed during the reaction. The power law equation can be used to represent the kinetic experimental data of leaching reaction. The model equations have been solved by orthogonal collocation and semi-implicit Runge-Kutta method. The parameters of the model have been estimated by the complex method. The calculated results based on this model is in good agreement with experimental data.     

混凝耦合多孔陶瓷膜净化河水简

Membrane filtration technology combined with coagulation is widely used to purify river water. In this study, micro filtration （MF） and ultrafiltration （UF） ceramic membranes were combined with coagulation to treat local river water located at Xinghua, Jiangsu province, China. The operation parameters, fouling mechanism and pilot-scale tests were investigated. The results show that the pore size of membrane has small effect on the pseudo-steady flux for dead-end filtration, and the increase of flux in MF process is more than that in UF process for cross-flow filtration with the same increase of cross-flow velocity. The membrane pore size has little influence on the water quality. The analysis on membrane fouling mechanism shows that the cake filtrationhas significant in fluence on the pseudo-steady flux and water quality for the membrane with pore size of 50, 200 and 500 nm. For the membrane with pore size of 200 nm and backwashing employed in our pilot study, a constant flux of 150 L-m^-2-h^-1 was reached during stable operation, with the removal efficiency of turbidity, total organic carbon （TOC） and UV254 higher than 99%, 45% and 48%, respectively. The study demonstrates that coagulation-porous ceramic membrane hybrid process is a reliable method for river water purification.     

HYDRODYNAMICS AND AXIAL MIXING OF LIQUIDSOLID SYSTEM IN OPEN TURBINE ROTATING DISC CONTACTOR

The open turbine rotating disc contactor (OTRDC) has been installed simply by adding three narrow strips to the lower surface of each rotating disc in the rotating disc contactor (RDC), so it can be used for the system with high solid particle content. Hydrodynamics and axial mixing have been investigated in a 0.152m diameter OTRDC of different compartment height for the system of tap water and quartz particles. A model has been developed to describe the flow of liquid and solid phases. The solid phase holdup can be calculated satisfactorily according to the model equations. Axial mixing data have been treated by the backflow model and the correlations for predicting backflow ratios of liquid and solid phases in OTRDC have been presented.     

Development of separation sharpness model for hydrocyclone

Hydrocyclones are mechanical devices used in classifying and separating many different types of materials. A classification function of the hydrocyclone has been continually developed for solid–liquid separation. In the classification process of solids from liquids, it is desirable to reduce the amount of misplaced material; therefore, the separation sharpness, α(alpha), is a parameter that helps in evaluating misplaced material and has been developed as a model to help the designer predict the performance of the classification. However, the problem with the separation sharpness model is that it cannot be used outside the range of conditions under which it was developed. Therefore, this research aimed to develop the separation sharpness model to predict more accurately and cover a wide range of conditions using the multiple linear regression method. The new regression model of separation sharpness was based on a wide range of both experimental and industrial data-sets of 431 tests collaborating with the additional experiments of 117 tests that were obtained from a total of 548 tests. The new model of separation sharpness can be used in the range of 30–762 mm hydrocyclone body diameters and feed solid concentrations in the range of 0.5 wt%–80 wt%. When compared with the experimental separation sharpness, the accuracy of the separation sharpness model prediction has an error of 4.53% and ~ of 0.973.     

Kinetic Treatment for copolymerization of styrene or methyl methacrylate with N-phenylmaleimide

Shirota‘s kinetic model and our kinetic model were used to treat the kinetic data of styrene (St) and N-phenylmaleimide (PMI) copolymerization in which chaxge-transfer complex (CTC) was formed. The results obtained by Shirota‘s kinetic model were disagreed with the experiments and the experimental phenomena could not be explained. The kinetic data of all feed fractions can be treated with our kinetic model, and the experimental phenomena can be explained from the propagation constants and reactivity ratios. Our kinetic model is also suitable for the kinetic data of methyl methacrylate (MMA) and PMI copolymerization in which CTC can not be formed.     

高粘度物料滤饼沟流的形成与特征

描述和分析了滤饼横向沟流和纵向大毛细管的形成和发展特征,横向沟流以毛细管入口处结构剪切破坏为基本特征,而纵向大毛细管的形成及进一步扩大,对过滤质量立即产生破坏性影响。滤饼二端的压差与流量过大或剧烈波动是这 2种特殊现象的根本原因。通过对毛细管中非牛顿流动分析,滤饼二端压差与流量的乘积与毛细管内的剪切应力、剪切速率的关系得到初步明确。     

微米级高分子精密过滤技术及其在精细化工、水处理与环保领域的应用

微米级高分子精密过滤既能澄清过滤 ,也能滤饼过滤 ,还能卸干滤饼 ,过滤介质能高效再生 ,耐化学性能好 ,是一种使用寿命长的新型过滤技术。主要介绍了该技术的组成特点及其在精细化工、水处理及环保领域的主要应用。     

高效节能过滤技术与强化过滤过程的途径

叙述了国内外过滤与分离技术的发展和趋势。介绍了在节能型压榨过滤、陶瓷过滤、纳米过滤等3种节能型过滤技术的研究进展与结果;并针对难过滤物料及高精度过滤与分离的要求,分析了难过滤物料的特点,针对酶解液过滤的应用实例,提出了改善物料性质和强化过滤的有效途径,即添加助滤剂进行掺浆过滤,降低比阻,控制滤饼厚度,降低滤饼阻力的薄层滤饼过滤,这2种强化过滤技术的集成应用于某个难过滤物料分离的应用实例。     

The Role of Polysaccharide on the Filtration of Microbial Cells

The role of polysaccharide on the “dead-end” microfiltration of microbial cells is studied. Yeast and blue dextran are used as typical samples of microbial cells and polysaccharide, respectively. The filter cake becomes more compressible in the early periods of filtration and exhibits much higher filtration resistance when dextran molecules co-exist in the cake structure. A cake compression mechanism is proposed to explain the pressure effects on the cake structure and filtration resistance. For the two-component cakes, the dextran molecules deform easily even under a pressure as low as 30 kPa, while significant yeast deformation is observed when pressure is higher than 100 kPa. It is attributed to the depletion of most solid compressive pressures by deformed dextran molecules. The cake porosity data indicate that the cake compressibility is higher under low filtration pressure, and blue dextran plays a significant role on the cake structure and occupies a considerable volume in the cake. A resistance model is also derived for understanding the relationship between the average specific cake filtration resistance and filtration pressure. The cake filtration resistance is determined by the effective volume fraction of each component in cake and nearly the same as that of blue dextran under low pressure.     

Cake properties of nanocolloid evaluated by variable pressure filtration associated with reduction in cake surface area

A potential method has been developed for evaluating simultaneously both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as bovine serum albumin solution and silica sol. The method consists of variable pressure filtration followed by constant pressure filtration. The relation between the average specific cake resistance and the pressure drop across the cake was determined from the evolution of the filtration rate with time in the course of the variable pressure filtration period, based on the compressible cake filtration model. The average porosity was evaluated from the significant flux decline caused by a sudden reduction in the cake surface area in the middle of the constant pressure filtration period. The pressure dependences of both the average specific cake resistance and average cake porosity were obtained from only two runs which differed from each other in the pressure profiles. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3869–3877, 2014     

Modeling of Particle Fouling and Membrane Blocking in Submerged Membrane Filtration

Abstract

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is also derived. In order to estimate the shear stress acting on the membrane surface, the diameter, shape, and rising velocity of air bubbles are analyzed based on hydrodynamics. Once the model coefficients are obtained, the pseudo‐steady filtration flux under various conditions can be estimated by the proposed model and the basic filtration equation. The calculated results agree fairly well with the available experimental data.     

动态膜的形成机理及其水处理性能研究

以陶瓷管为载体,对高岭土动态膜的形成及其污水处理性能进行了详细的研究.实验中采用错流过滤方式涂膜,考查了跨膜压差、涂膜液浓度、错流速度及涂制时间等对动态膜形成的影响.通过对实验数据分析可知,动态膜形成初期10～13 min,膜的形成过程可用标准过滤模型描述,在此期间颗粒堵塞载体膜管孔道,致使渗透液通量急剧减小;之后,膜的形成过程符合滤饼过滤模型,这一阶段颗粒主要在载体膜管内壁面沉积,渗透液通量缓慢下降直至基本稳定.制备的动态膜可用于处理城市污水厂二级出水,动态膜对浊度去除率基本上为100%,对COD也有一定的去除作用.     

Measurements and evaluation of concentration distributions in filter cake formed in dead-end ultrafiltration of protein solutions

To clarify the internal structures of the filter cake formed on the membrane surface in protein ultrafiltration, a method has been developed for measuring the variations of protein concentration across the filter cake on the basis of the principle of inclined ultrafiltration, where the membrane was inclined and a large amount of filter cake was formed, and the results were compared with the calculations based on a compressible cake filtration model, which explicitly took the non-homogeneity and the compressibility of the filter cake into account. The experimental results obtained from ultrafiltration of bovine serum albumin (BSA) solutions under constant pressure conditions clearly demonstrated that the filter cake tended to have a much more compact structure at the membrane in comparison with a relatively loose condition at the surface. It was also found that the thickness of the filter cake formed on the membrane increased as the filtration progressed. Further, the effects of pH and the solute concentration in the feed solution on the structure of the filter cake have been examined experimentally. The measured concentration distributions accorded well with the calculated results based on a compressible cake filtration model. This study revealed that the dynamic deposition behaviors of the protein molecules in dead-end ultrafiltration could be accurately described by a compressible cake filtration model.     

空气过滤形成滤饼的模拟研究

提出了一个新的模型,用于预测空气过滤中捕集效率和滤饼层空隙率。模型中粒子的产生符合正态分布,其落点符合随机均匀分布。模型预测的捕集效率随粒径和孔径比的增大而增大,滤饼层空隙率随粒径和孔径比的增大而减小。粒子的分散度对滤饼结构的影响较小。     

Empirical Modelling of Cake Washing in a Pressure Filter

The focus of this article is on empirical modelling of filter cake washing. The filtration experiments introduced in this paper were conducted by using a pilot-scale (0.1 m²) filter press according to the basic principles of factorial designs. Five different variables of the filtration, pressing, cake washing, and air drying stages were considered in the tests and the examined product characteristics were the overall capacity of the filter and the purity of the cake. The results obtained from the tests were used for creating different kinds of regression models for explaining the influence of the studied variables on the success of the cake washing process. The goal of the modelling strategy for the cake washing was to determine the simplest empirical models and compare these with theoretical equations complemented with linear terms. It was found that the empirical equation could model the results more accurately than the theory-based equations could.