Comparison of Different Pitch Lengths on Static Promoters for Flux Enhancement in Tubular Ceramic Membrane

Abstract

The use of turbulence promoters in membrane based processes have been investigated and are increasingly been used in industrial applications to minimize fouling and enhance the membrane flux. The efficiency of crossflow microfiltration is limited by membrane fouling and concentration polarization leading to flux decline during operation. A detailed study was carried out in the microfiltration of yeast suspensions using an in‐house rig and three different static turbulence promoters of varying pitch lengths. The design of the promoters incorporates a helical thread around the length of the insert, which induces turbulent flow through the membrane. This promotes good mixing of the feed fluid and minimizes concentration polarization effects. The testing of tubular membranes with the static inserts has been carried out and the results are included in the report. The pitch lengths used were 7 mm, 10 mm, and 14 mm and the parameters investigated included temperature, CFV, concentration of feed suspension and pressure. The flux decline data was recorded over a 50 minute filtration cycle and the cleaning protocol was employed after every cycle to restore the permeability of the membrane. A comparison of the membrane performance and efficiency of the three swirls inserts of varying pitch lengths together with a comparison of the degree of total, reversible, and irreversible fouling data amongst others are reported and discussed. The results obtained during the investigations of flux enhancement via static turbulence promoters into the tubular membranes are presented and are selected to differentiate the efficiency of the inserts and the degree of fouling associated with them.     

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。     

The effects of performance and cleaning cycles of new tubular ceramic microfiltration membrane fouled with a model yeast suspension

The efficiency of crossflow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The experiments that were carried out in the laboratory were conducted to determine and investigate the performance, behaviour and the fouling susceptibility of new ceramic tubular microfiltration membranes during the crossflow filtration of yeast suspensions. The tubular membranes of nominal pore size 0.5 microns were fouled over a varied range of concentration, temperatures, pH, crossflow velocities and system pressures. The typical filtration conditions were at a temperature of 25°C, a system pressure of 1.5 bar and a concentration of 0.03 g/L yeast suspension. These parameters varied during subsequent investigations. After each experiment, the membrane and the rig were cleaned using a three stage cleaning process and was reused in order to replicate industrial filtration conditions. The effects of repeated fouling and cleaning cycles upon membrane flux over time and cleaning efficiency are investigated and their influence over time is also documented. For every experiment, the flux data was recorded over a 50 min period and the membrane was changed after the PWF declined considerably due to excessive fouling over time. Chemical cleaning consisted of a sequential application of a 1% caustic solution through the rig followed by a 2% hypochlorite solution and a 2% nitric solution, all at 50°C. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was developed and established, there appeared to be a leveling of permeate flux. The experimental results are presented in the report and the flux values at different conditions are presented.     

陶瓷膜构型对错流微滤酵母悬浮液性能的影响

采用3种构型的陶瓷微滤膜元件对酵母悬浮液进行错流过滤实验,考察陶瓷膜元件的构型对于其错流过滤性能的影响。结果表明:减小陶瓷膜元件的通道直径可以提高料液在膜表面的剪切力,有助于提高过滤稳定通量和临界压力,在3 m/s膜面流速、0.1 MPa跨膜压差条件下,单管、19通道、55通道的稳定通量分别为96、128、196 L/(m2.h);在3 m/s膜面流速条件下,3种陶瓷膜元件的临界压力分别约为0.15、0.2、0.2 MPa。另外,减小通道直径还可以减小滤饼层的比阻,有利于降低过滤阻力;与提高膜面流速来增大过滤通量的方法相比,减小陶瓷膜的通道直径具有能耗较小的优点。     

Flux Improvement during Cross-flow Microfiltration of Wheat Starch Suspension using Turbulence Promoter

The objective of this study was to investigate the effects of the process variables (transmembrane pressure, flow rate, and concentration) on the permeate flux during the microfiltration of model starch suspensions, and to determine the conditions under which the use of Kenics statics mixer as a turbulence promoter is justified. A response surface methodology was used to examine the influence of the selected operating conditions on starch suspension microfiltration using a single channel ceramic membrane with 200 nm pore size. The experimental results clearly show that the improved performance of starch suspension cross-flow microfiltration can be obtained by using a Kenics static mixer, especially at lower flow rates. Compared to the operation without the turbulence promoter, the average permeate flux improvement during the filtration period ranged from 30% to 230%. As a result of the statistical analysis, the optimal conditions for starch suspension microfiltration were determined and applied to microfiltration of starch industry wastewater.     

Tubular Membrane Filtration with A Side Stream and its Intermittent Backwash Operation

The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux.     

湍流促进器强化微滤过程的实验与CFD模拟研究(英文)

This paper reports experimental and computational fluid dynamics(CFD) studies on the performance of microfiltration enhanced by a helical screw insert.The experimental results show that the use of turbulence pro-moter can improve the permeate flux of membrane in the crossflow microfiltration of calcium carbonate suspension,and flux improvement efficiency is strongly influenced by operation conditions.The energy consumption analysis indicates that the enhanced membrane system is more energy saving at higher feed concentrations.To explore the intrinsic mechanism of flux enhancement by a helical screw insert,three-dimensional CFD simulation of fluid flow was implemented.It reveals that hydrodynamic characteristics of fluid flow inside the channel are entirely changed by the turbulence promoter.The rotational flow pattern increases the scouring effect on the tube wall,reducing the particle deposition on the membrane surface.The absence of stagnant regions and high wall shear stress are respon-sible for the enhanced filtration performance.No secondary flow is generated in the channel,owing to the streamline shape of helical screw insert,so that the enhanced performance is achieved at relatively low energy consumption.     

集成反应器微滤过程中湍流促进器的研究

采用湍流促进器对陶瓷膜分离TiO2超细粒子悬浆液微滤过程进行了强化研究。考察了湍流促进器结构参数对强化过程的影响,确定了合适的湍流促进器为螺旋式湍流促进器,其结构参数为螺杆直径2 mm,螺距20 mm;探讨了湍流促进器的强化机理,同时对湍流促进器的有效性进行了实验考察。研究表明,采用这种方法提高了渗透通量。     

往复旋转管式陶瓷膜超滤脱脂奶水溶液的研究

往复旋转管式陶瓷膜过滤系统通过膜组件往复旋转在膜表面反复产生高剪切率,达到减缓膜污染的效果。在相同操作条件下,与单向旋转过滤和死端过滤相比较,往复旋转过滤具有更好的减缓膜污染的作用。本实验利用往复旋转膜过滤装置超滤脱脂奶水溶液,考察了各种参数对该膜系统过滤特性的影响。实验结果表明,料液浓度增大,膜通量减小;过高的操作压差将会抑制膜通量增加;旋转速度增大,膜表面剪切强化作用增强,膜通量相应增大;膜稳态通量随往复旋转周期增大呈现先增大后减小的趋势。当料液速度达到膜组件转速时,瞬时反方向旋转膜组件,膜表面产生最大的剪切率,膜稳态通量也达到最大值。能耗分析表明,往复旋转过滤较单向旋转过滤单位通量能耗低。     

Fabrication of low-cost ceramic ultrafiltration membrane made from bentonite clay and its application for soluble dyes removal

This work reports the preparation and the characterization of low-cost ultrafiltration bentonite membrane deposited on ceramic perlite support. The bentonite layer was obtained by spin-coating process of colloidal solution with different bentonite contents ranging from 0.25 to 1.50 wt.%, followed by sintering at 500 °C. It was confirmed that optimized membrane prepared with 0.75 wt.% of bentonite is homogeneous and exhibits a good adhesion on perlite support. Furthermore, the membrane has a thickness of 6 μm, a pore size of 13 nm and a permeability of 30 L/h.m².bar. In addition, the filtration performance of bentonite membrane was evaluated by tangential filtration of Direct Red 80 and Rhodamine B solutions under pressure of 4 bar. The effect of filtration time and initial feed concentration on flux and rejection was studied and showed that the rejection of Direct Red 80 and Rhodamine B could achieve value of 97.0 and 80.1 % respectively.     

附加湍流器强化陶瓷膜微滤过程的研究

通过在管式陶瓷膜内设置不同结构形式的湍流器，试验和比较了不同主体流速和膜滤压差等工艺条件下的膜滤速率及能耗，分析了湍流器所产生的强化膜滤过程的效果以及试验条件下的一般规律。     

面向过程的陶瓷膜材料设计理论与方法(Ⅰ)膜性能与微观结构关系模型的建立

提出了面向过程的陶瓷膜设计基本研究框架,分析了膜的孔径分布与悬浮液颗粒体系粒径分布对过滤过程的影响,提出采用堵塞因子来表征膜的初始堵塞污染情况,建立了颗粒体系微滤过程中的膜微观结构与性能关系新模型,不仅可以计算膜通量随时间的变化,且能预测陶瓷膜结构参数对膜通量的影响.模拟结果与实验值有较好的一致性.     

面向过程的陶瓷膜材料设计理论与方法(Ⅰ)膜性能与微观结构关系模型的建立

提出了面向过程的陶瓷膜设计基本研究框架 ,分析了膜的孔径分布与悬浮液颗粒体系粒径分布对过滤过程的影响 ,提出采用堵塞因子来表征膜的初始堵塞污染情况 ,建立了颗粒体系微滤过程中的膜微观结构与性能关系新模型 ,不仅可以计算膜通量随时间的变化 ,且能预测陶瓷膜结构参数对膜通量的影响 .模拟结果与实验值有较好的一致性     

陶瓷膜分离CaCO_3悬浆液强化过程的研究

在固定反冲条件下,研究了螺旋型湍流促进器及其螺杆直径、螺间距等参数对19通道无机陶瓷膜分离轻质碳酸钙悬浆液的强化过程,确定了湍流促进器的优化设计参数,并在优化条件下,对操作压力、操作温度、膜面流量和溶液浓度等操作条件进行了研究。     

Separation of non-sucrose compounds from sugar-beet syrup by ultrafiltration with ceramic membrane containing static mixer

The aim of this work was to investigate possible improvement of non-sucrose compounds separation from the syrup of raw brown sugar by application of a static mixer in an ultrafiltration process. The static mixer was expected to reduce the concentration polarization and fouling of the membrane. Non-affinated B sugar from the second stage of crystallization, diluted to 60°Bx dry matter, was used for preparing the solution subjected to the ultrafiltration. The cross-flow filtration, at a laboratory level, was carried out on the tubular ceramic membrane (Schumasiv Pall, USA), with a pore diameter of 5 nm. The separation was performed under various working conditions, with and without the presence of static mixer. The effect of turbulence promotion on filtration performances was investigated by using Kenics static mixer (FMX8124-AC, Omega). The process efficiency was quantified through the achieved values of the permeate flux, its colour and dry matter content, while the working factors were: fluid flow-rate, temperature, transmembrane pressure (TMP) and process duration. The positive effects of mixer application were proved.     

弹状流对陶瓷膜超滤葡聚糖水溶液的影响

为降低膜污染和浓差极化需维持较高膜面流速,能耗较高。将气升式外循环引入膜过程,可有效降低浓差极化和能耗。实验考察了曝气量对渗透通量的影响,当曝气量为400 L·h^-1时,与相同液速条件下单相流错流过滤相比较,膜通量提升87%;进一步增大曝气量,膜通量增加趋势变缓。对气升式膜过滤过程的水力学特性进行了研究,在弹状流条件下,气液两相流可有效提高膜面剪切力,增强膜面传质。在较低流速下,曝气可有效降低膜污染阻力,提高膜通量。结合气液两相流理论和膜过滤阻力模型,分析了弹状流提升膜通量的机理。     

Use of a Rotating Filter to Enhance Ceramic Membrane Filtration Performance of Latex Dispersions

Abstract

The performances of both the tangential crossflow system and the rotating system with a tubular microfiltration ceramic membrance were investigated experimentally in the separation of latex dispersions. In addition, the shear rate at the membrane surface for azimuthal flow in an annulus with a porous wall on the rotating inner cylinder was solved for the narrow-gap approximation. In contrast to the tangential crossflow system, the rotary system was characterized by a significantly higher flux. The increase in the membrane flux was achieved at shear rates less than those for the crossflow system investigated.     

Experimental study on the enhancement of yeast microfiltration with gas sparging

Gas‐sparged microfiltration experiments with baker's yeast suspensions were performed using a 0.15 µm PCI multi‐tubular membrane module. The permeate flux and the enhancement from gas sparging were measured over the following operational parameter ranges: yeast suspension concentration 0.01–10% (wt), transmembrane pressure 0.5–4.0 bar, liquid crossflow velocity 0.36–1.8 ms^?1, gas superficial velocity 0.18–1.02 ms^?1. It was demonstrated that injecting air to create a gas–liquid two‐phase crossflow operation can significantly increase the permeate flux. The observed enhancement, resulting from injecting a relatively small amount of gas with a superficial velocity of 0.18 ms^?1, ranges from 10% when fouling is insignificant to 135% when fouling tendency is severe. Controlled pulse injection leads to further increase in permeate flux. Examining the dependence of permeate flux on transmembrane pressure, it is clearly demonstrated that the injection of gas will elevate the value of the limiting flux. There is also evidence to show that the value of critical flux is increased when gas injection is applied. Further quantitative analysis will be performed in our future work. © 2001 Society of Chemical Industry     

Benefits of High Shear Rate Dynamic Nanofiltration and Reverse Osmosis: A Review

Dynamic filtration permits to increase permeate flux and membrane selectivity, as compared to crossflow filtration. It consists in creating the shear rate by a disk rotating near the membrane or by rotating or vibrating the membrane, avoiding the need for large feed flow rates. The benefits of high shear rates are important in microfiltration and ultrafiltration, but they are even larger in nanofiltration (NF) and reverse osmosis (RO). The reduction in concentration polarization by high shear rate can increase the permeate flux by a ratio of 3 to 5 as compared to a spiral wound module and augments also solutes rejection as their diffusive transfer through the membrane is reduced by a factor of 4 to 5. This paper describes available dynamic filtration modules suitable for NF and RO and reviews the treatment of dairy effluents, desalination, oil emulsions, and oligosaccharides recovery using a rotating disk module or a VSEP module with vibrating membranes and compares their performances with those of crossflow filtration. These examples confirm the high potential of dynamic NF and RO when operated at high shear rate and high TMP. The availability of large rotating NF ceramic membrane disks could permit the fabrication of highly efficient modules.     

Application of UNIQUAC and SVM to ultrafiltration for modeling ternary mixtures of oil, FAME and methanol

To describe a membrane separator for ternary mixtures of oil-FAME-MeOH, two models of UNIQUAC and support vector machine (SVM) are developed for the permeate composition and permeate flux, respectively. The UNIQUAC model is used to represent the liquid-liquid phase equilibrium of oil-FAME-MeOH. Its prediction results are consistent with the experimental data measured at the temperatures of 293, 313 and 333 K, respectively. For this two-phase system, experimental results show that the oil-rich phase can be rejected by the ceramic membrane while the methanol-rich phase permeates through the membrane. The permeate composition is mainly determined by the feed bulk concentration, and therefore is consistent with the concentration of the methanol-rich phase predicted by the UNIQUAC model. On the other hand, the permeate flux under various operating conditions, such as feed concentrations, temperatures, inlet flow rates and transmembrane pressures, is modeled by the SVM algorithm. Unlike the general data-based neural network model, SVM is especially valuable in the present crossflow filtration problem of small sample sizes. By combining UNIQUAC and SVM with the experimental ultrafiltration of biodiesel mixtures, the predicted membrane separator performance shows no significant lack of fit, and continuous production of biodiesel with both high purity and maximal productivity is also discussed.