中空纤维膜外压全量过滤动态过程的数值模拟

建立了中空纤维膜外压式全量过滤的CFD模型,模拟膜丝长度、直径、渗透系数、装填密度、污染指数以及跨膜压差不同条件,得到通量分布和产水量的动态演变过程。研究结果表明:通量分布会随着过滤的进行而逐渐变得均匀,这种通量分布的自我调节作用在膜丝较长、较细,渗透性较好,装填密度较高,污染指数较高以及跨膜压差较高时更为明显;产水流量的倒数与累积产水量呈线性关系,但由于通量分布不均匀并且均匀性演变,这种线性关系区别于传统滤饼过滤模型;通过数据拟合得到了适用于中空纤维外压式全量操作的滤饼过滤关联式,可用于预测组件的性能和指导组件的设计。     

膜丝非均匀排布中空纤维膜组件内流场的模拟

本文建立了中空纤维膜组件外压式死端过滤的纯水过滤CFD模型,模拟得到了膜丝不同装填方式下组件内流场以及组件的产水性能。以膜丝均匀装填的组件为参照对象,分别考察了膜丝装填由壳体向内逐渐紧密,由壳体向内逐渐稀疏,以及随机装填的三种组件。结果表明,各个组件不同位置的压力场差别较小,而速度场随着高度而变化;膜丝排布由组件壳体边缘向中心逐渐稀疏的组件产水效率高于其他三个组件,单膜丝平均产水流量比最小值高出约10.9%。     

连续微滤用于海水净化的运行条件优化

采用连续微滤技术进行反渗透海水淡化预处理中试,通过正交实验考察连续微滤前处理工艺、过滤模式及膜通量、运行时间、反洗通量、反洗时间等运行条件对产水水质、单位净产水量跨膜压差增长量及产水率的影响,并对运行条件进行优化。结果表明,前处理工艺、膜通量和运行时间是影响单位净产水量跨膜压差增长量的显著因素,而过滤模式是影响产水率的主要因素。"混凝-沉淀-砂滤"作为前处理工艺可有效减少连续微滤进水的悬浮物含量;对外压式中空纤维膜而言,错流过滤减轻膜污染的效果不明显,宜采用死端过滤模式;其他优化运行参数为:通量40L/(m~2·h),运行时间30 min,反洗通量60 L/(m~2·h),反洗时间60 s。     

气液两相流对中空纤维膜错流过滤过程的影响

采用聚偏氟乙烯(PVDF)中空纤维膜进行错流过滤试验,以中空纤维膜组件的膜通量、浑浊度以及高锰酸盐指数(CODMn)的截留率为考察指标,通过在过滤时添加曝气形成气液两相流,研究在气液两相流条件下曝气量、进水流量、跨膜压差等参数对中空纤维膜错流过滤过程的影响.试验结果表明:在一定范围内,膜通量随着曝气量增大而增大,曝气量...     

混凝-超滤工艺中膜污染和膜清洗试验研究

以重庆江河水源水为研究对象,考察混凝-超滤工艺膜污染情况。结果表明,在超滤膜膜组件处理江河水的过程中,随着膜组件运行时间的延长,膜组件会出现一定程度的污染状况,其跨膜压差的增加和膜通量的下降表现了膜污染程度。通过混凝-平板式膜滤组合工艺处理水样运行25 min,跨膜压差上升量占总上升量的73%,之后随着过滤时间的延长跨膜压差呈现上升趋势,并且上升较为缓慢,通过物理清洗膜通量可恢复为到原始通量的94%。通过混凝-中空纤维式超滤组合工艺处理水样运行15 min,膜压差上升量占总上升量的82%,之后随着过滤时间的延长跨膜压差呈现上升趋势,且上升较为缓慢,通过物理清洗膜通量可恢复为到原始通量的98.5%。     

内外压式超滤组件在火电厂循环冷却排污水处理中的应用比较

分别选取一种内压式和一种外压式中空纤维超滤膜组件,从超滤膜材质、运行参数和出水水质等方面对这2种组件在火电厂循环冷却排污水反渗透预处理中的应用进行了中试规模的研究。结果表明:外压式组件在跨膜压差和膜通量上要优于外压式,而2种组件出水水质基本一致。因此,外压式膜组件更适合于火电厂循环冷却排污水反渗透预处理的工艺。     

内外压式超滤组件在反渗透预处理中的应用比较

分别选取一种内压式和一种外压式中空纤维膜超滤组件,从超滤膜材质、运行参数和出水水质等方面对这2种组件在海水淡化反渗透预处理中的应用做了比较。结果表明:由于超滤膜的材料不同,使得2种组件运行工艺有较大差异:内压式组件在跨膜压差和膜通量方面要好于外压式组件,而2种组件出水水质在同一水平上。在进水浊度小于20NTU时,内压式膜组件更适合作为反渗透的预处理工艺。     

两种内压式超滤膜组件在反渗透预处理中的应用

选取两种内压式中空纤维超滤膜组件,从膜材质、运行参数和出水水质等方面对这两种组件在海水淡化反渗透预处理中的应用进行比较。结果表明：2#膜组件跨膜压差和膜通量的稳定性较1#组件好,两种膜组件出水水质比较接近,但2#膜出水水质稳定性较1#膜好。     

两种内压式超滤膜组件在反渗透预处理中的应用

选取两种内压式中空纤维超滤膜组件,从膜材质、运行参数和出水水质等方面对这两种组件在海水淡化反渗透预处理中的应用进行比较。结果表明:2#膜组件跨膜压差和膜通量的稳定性较1#组件好,两种膜组件出水水质比较接近,但2#膜出水水质稳定性较1#膜好。在进水浊度小于20NTU时,2#膜组件更适合应用于反渗透的预处理工艺。     

一种基于膜污染指数的超滤膜污染评价方法

利用浸没式中空纤维膜小试系统,基于膜污染指数（FI）建立超滤膜污染的评价和试验方法。通过试验考察超滤膜污染变化规律,以及运行周期对膜污染指数计算的影响,并确定计算膜污染指数的运行周期;并对膜污染指数评价方法的可重复性进行检验：对化学清洗前后膜污染指数进行比较。试验表明,在过滤初期,滤饼污染和吸附污染并存,所以初期水力不可逆膜污染指数（HIFI）增长较快;中期超滤膜的吸附能力不断减弱,膜污染主要是滤饼污染,所以膜污染较为稳定：后期跨膜压力过大,压缩滤饼层,减小滤饼孔隙率,增加滤饼阻力,所以HIFI有所增加。同时短期的膜污染试验可以用来反映长期的膜污染情况,该超滤膜污染的评价方法重复性好,污染后的超滤膜经过化学清洗后。可以重复利用。     

Modeling of fouling layer deposition in cross-flow microfiltration during tomato juice clarification

The effect of parameters, such as transmembrane pressure and axial flow rate, on membrane fouling during tomato juice clarification were studied by cross-flow microfiltration using flat sheet polyvinylidenefluoride membranes. The effect of fouling on permeate flux was modeled using a classical constant pressure dead-end filtration equation and its modified form for cross-flow filtration. The main physico-chemical properties of tomato juice were evaluated. The clarified juice was very similar to the feed except for insoluble solids and lycopene, which were concentrated in the retentate. Cake formation was identified as the main reason for flux decline. At different axial flow rates, the fouling mechanism evolves from cake filtration to an intermediate pore blocking mechanism with increasing pressure.     

Variations in backwash efficiency during colloidal filtration of hollow-fiber microfiltration membranes

A series of filtration experiments was performed systematically to investigate physical and chemical factors affecting the efficiency of backwashing during microfiltration of colloidal suspensions. In this study, all experiments were conducted in dead-end filtration mode utilizing an outside-in, hollow-fiber module with a nominal pore size of 0.1 μm. Silica particles (mean diameter = 0.14 μm) were used as model colloids. Using a flux decline model based on the Happel's cell for the hydraulic resistance of the particle layer, the cake structure was determined from experimental fouling data and then correlated to backwash efficiency. Modeling of experimental data revealed no noticeable changes in cake layer structure when feed particle concentration and operating pressure increased. Specifically, the packing density of the cake layer (1-cake porosity) in the cake layer ranged from 0.66 to 0.67, which corresponds well to random packing density. However, the particle packing density increased drastically with ionic strength. The results of backwashing experiments demonstrated that the efficiency of backwashing decreased significantly with increasing solution ionic strength, while backwash efficiency did not vary when particle concentration and operating pressure increased. This finding suggests that backwash efficiency is closely related to the structure of the cake layer formed during particle filtration. More densely packed cake layers were formed under high ionic strength, and consequently less flux was recovered per given backwash volume during backwashing.     

Transient Simulation of Hollow‐Fiber Membrane Filtration with Nonuniform Permeability Distribution

Transient simulation of filtration in hollow‐fiber membranes with nonuniform permeability distribution was conducted. The diversity of permeability distributions caused different initial flux and transmembrane pressure distributions. Manipulating the permeability distribution enables a hollow‐fiber membrane to achieve its maximum volumetric flow rate. During solid‐liquid separation, the inter‐adjustment between flux and cake distributions improved their uniformities simultaneously. The reciprocal of the volumetric flow rate of the membranes all increased linearly with water production. Severely nonuniform permeability distribution caused low water production. The numerical results could be applicable to account for the non‐ideal performance of industrial hollow‐fiber membrane modules.     

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。     

Filtering surface water with a polyurethane-based hollow fiber membrane: effects of operating pressure on membrane fouling

Membrane fouling seriously restricts applications of membrane technology. A novel strategy was ap-plied in this study to retard membrane fouling by changing operating pressure with the pressure responsibility membrane. A polyurethane-based hollow fiber membrane was used to treat surface water for evaluating the effect of operating pressure on membrane fouling. Some bench-scale tests in dead-end mode were carried out. In the experi-ments without backwashing, as operating pressure increased, severe membrane fouling occurred on membrane sur-face, while the permeate quality was improved obviously, which is considered to be due to shrinkage deformation. The total resistance, irreversible resistance and reversible resistance under different backwash pressures were de-termined in filtration/backwashing test. With the increase of backwash pressure, the total resistance decreased, and more importantly, the irreversible resistance also decreased, which implies that small particles deposited inside membrane pores and cake layers on membrane surface are effectively removed. Similar results could be obtained in mass balance tests. The results of the present study indicate that the application of pressure responsibility membrane in surface water treatment may be an effective strategy for reducing membrane fouling.     

Three‐dimensional simulation of the time‐dependent fluid flow and fouling behavior in an industrial hollow fiber membrane module

A novel three‐dimensional CFD model has been developed on the basis of fluid flow in the shell and lumen sides, and permeation and fouling behavior in the porous membrane zone. The simulated 25‐min dead‐end outside‐in filtration process showed that the energy consumed by the inlet manifold decreases during the constant pressure filtration. The velocity and pressure distributions in the module change with time. Flux distribution both in the axial and radial directions becomes increasingly more uniform, so does the cake distribution. Flux distribution and cake distribution inter‐adjust each other in different modes. A correlation equation has been developed to describe the relationship between the volumetric flow rate and accumulated water production. The correlation equation with simple experiment enables the dynamic evolution of energy consumed by shell inlet manifold to be presented, which can be the criterion of how well the shell inlet manifold or module has been designed. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2655–2669, 2018     

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.     

Development of the MFI-UF in constant flux filtration

The MFI-UF, based on cake filtration, was developed to measure and predict the particulate fouling potential of feedwater to membrane filtration installations. The MFI-UF is determined in constant pressure filtration with the flux deceasing during the test. However, many membrane systems, e.g., reverse osmosis (RO), operate at constant flux with pressure increasing when fouling occurs. As both pressure and flux contribute to cake compression, determining the MFI-UF in constant flux with correction to the flux of an RO system is expected to more closely simulate particulate fouling Therefore, this research investigated the development of the MFI-UF test in constant flux filtration applying low (tap water) and high fouling (diluted canal water) feedwater. Preliminary experiments were promising; the fouling index (I) (and hence the MFI-UF) of all feedwater could be determined within 2 h under constant flux filtration. Cake filtration was demonstrated as (1) a minimum in the fouling indexvs time plot and (2) by linearity of the fouling index with feedwater particulate concentration. The fouling index increased with increasing applied flux due to cake compression. Further investigation at higher and lower applied flux is required to identify a reference test flux and to develop a method to correct the fouling index to the reference test flux and/or the flux of a membrane filtration system The fouling index can then be applied in a model to predict fouling.     

Flux enhancement with glass ball inserted membrane module for the ultrafiltration of dextran solution

The glass-ball-inserted membrane module has been designed to enhance the filtration of a flat-sheet membrane. Three different modes of filtration experiments were conducted and compared to demonstrate the flux enhancement due to the presence of glass balls: normal dead-end filtration, vortex flow filtration, and enhanced vortex flow filtration using glass balls. In the case of enhanced vortex flow filtration, the permeate flux was found to be three times as large as that of dead-end filtration and two times larger than vortex flow filtration. In addition, the flux decline was observed to be relatively low. The effect of the amount of glass balls on the permeate flux was also investigated by changing the glass ball volume fraction from 0.059 to 0.356. It has been observed that the permeate flux shows a maximum value of the volume fraction of 0.119. For the glass-ball-inserted membrane module, the permeate flux tends to increase with the feed flow rate.     

Measurements of Growth Rate of Filter Cake in Vertical Single-Pass Ultrafiltration Using Hollow Fiber Membrane Module

Vertical ultrafiltration experiments of silica colloid and bovine serum albumin solution were conducted in the single-pass mode by using a hollow fiber membrane module and beneficial in measuring the time evolution of the growth rate of the filter cake during filtration. The extremely small mass flux of the concentrate enabled us to highly concentrate the feed solution on the principle of vertical ultrafiltration in which the filter cake formed on the membrane surface is exfoliated continuously. Both growth and re-entrainment rates of the filter cake formed in vertical ultrafiltration were evaluated from the experimental data of the filtration rate and the mass fraction ratio of the concentrate on the basis of the mass balance within the hollow fiber membrane module. As a consequence, it was found that the re-entrainment rate of the filter cake increased almost linearly with the filtration time in the initial period of filtration and then tended to rapidly approach a constant value. The filter cake stopped growing under this dynamically balanced condition. The variations of the average specific resistance of the filter cake with time were also determined from the time evolutions of both the filtration rate and the growth rate of the filter cake.