基于FBG传感的正渗透膜界面剪切力变化特性

针对正渗透(FO)过程中膜面剪切力的分布式测量问题,基于光纤光栅(FBG)传感技术提出一种膜面剪切力的实时测量方法。研究了不同入口流速对剪切力分布、水通量和反向盐通量的影响,并对膜面的水力学特性进行分析。结果表明,FBG技术能够较好地给出FO膜组件表面流速的变化状况。膜面各位置的剪切力均呈现周期性的变化,在FO膜表面切向方向上,剪切力呈现空间分布的不均匀变化,直接导致了渗透通量的变化。增大入口流速能有效地改善膜面各位置的冲刷作用,但采用较大的入口流速才能使膜面距离入口较远位置的剪切力得到明显的提高。膜组件两侧剪切力的同步增加有利于提高膜通量,但单纯增加剪切力并不能更好地减缓浓差极化而提高水通量。     

操作条件对正渗透分离性能的影响

正渗透是以渗透压差为驱动力的新型膜分离过程。采用水流分布较佳的膜池结构,研究了膜朝向、流动方式对正渗透水通量性能的影响,结果表明PRO模式（当膜的活性层朝向驱动液时）的水通量明显高于FO模式（当膜的活性层朝向原料液时）,但其衰减程度较大;在溶液浓度差相同的条件下,逆流操作更利于水通量的提高。针对FO模式和逆流条件,探讨了溶液温度对水通量和反向盐通量的影响,结果表明：膜两侧溶液温度同步升高时,正渗透过程的水通量和反向盐通量均增加,且水通量的增加幅度大于反向盐通量;单侧增加溶液的温度时,驱动液侧温度升高对水通量性能的提升效果优于原料液侧。综合考虑过程能耗和系统性能,认为单独升高驱动液温度更具实用价值。     

壳聚糖复合正渗透膜及其分离乳化油废水研究

研究以壳聚糖(CS)为正渗透(FO)膜成膜材料,以聚酯筛网为支撑材料,经过交联、碱液浸泡得到CS复合FO膜(CS-FO膜)。并将其用于石油醚乳化油废水的分离。结果表明,该CS-FO膜分离层为单一均质膜,具有良好的热稳定性和亲水性;该膜具有良好的渗透性能,以NaCl为驱动液时,其平均渗透水通量可达30 L/(m~2·h),截盐率可达到97%。分离乳化油废水时,膜面流速和乳化油废水含量均会影响膜的分离性能,膜面流速越大膜的渗透通量越大;废水乳化油含量越高,膜的通量越低。对质量浓度1.0 g/L的乳化油废水连续分离5 h后其水通量可维持在12L/(m~2·h),对乳化油的截留率可达到96.8%,这说明该FO膜在分离乳化油废水方面具有一定的应用前景。     

渗透模式影响纳米涂层修饰陶瓷微滤膜分离性能的研究

研究了膜分离技术处理含油废水存在因油滴变形引起的膜堵塞问题。为减少膜污染,使用在市场上销售氧化铝微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,具有良好的效果。考虑其工业应用条件,重点研究了循环模式（模拟大量废水处理）和浓缩模式（模拟少量废水处理）对膜渗透通量的影响。结果表明：循环模式下料液的油浓度为恒定的,纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m／s时,修饰陶瓷膜的最大渗透通量为280L／（m^2·h）,油截留率为96．4％。在浓缩模式下,料液的油浓度随渗透液的排出呈指数性增加,随着油浓度的增加,渗透通量持续衰减,油截留率持续上升。当油浓度达到一定程度后,修饰陶瓷微滤膜不能有效地实现稳定含油废水的油水分离。     

正渗透膜过程中临界通量的影响因素

临界通量是膜过程中一种重要的污染特性指标。采用阶梯汲取液浓度递增法测定不同污染物、架桥离子浓度及膜面流速对正渗透(FO)膜过程临界通量的影响。结果表明,海藻酸钠(SA)、腐殖酸(HA)及二氧化硅(SiO2)污染时FO膜临界通量值分别为29.32, 46.35和32.17 L/(m2?h);随Ca2+浓度由0 mmol/L增大至10 mmol/L,SA污染下FO膜的临界通量由29.22 L/(m2?h)显著降低至9.48 L/(m2?h),原因为Ca2+与SA分子中的羧基的螯合作用及Ca2+在膜?污染物之间的架桥作用;此外,当膜面流速从5 cm/s增至15 cm/s时,SA-Ca2+污染下的FO膜临界通量由9.48 L/(m2?h)提高至31.59 L/(m2?h),表明改善膜表面湍动有利于提高临界通量,扩大操作通量范围。     

温度对正向渗透的影响机制与数值模拟

正向渗透(FO)是一种以溶液自身渗透压作为推动力的膜分离技术。温度对溶液、膜的性质以及溶液与膜之间的相互作用有很大影响,进而影响FO的水通量。利用数值模拟与试验研究了温度对FO性能的影响。结果表明,当膜两侧等温时,FO水通量随着温度的升高而增大;当膜两侧不等温时,原液(FS)一侧温度的影响比提取液(DS)一侧更大,主要是因为温度升高降低了溶液黏度,强化了过膜扩散过程,而温度对DS渗透压的影响不明显。在不同温度条件下,FO水通量和热通量随流量的增大而增大,主要是由于流速的增大压缩膜表面的流体边界层,强化了传质和传热过程。     

利用多效膜蒸馏技术浓缩硫酸和磷酸水溶液

利用自制中空纤维气隙式多效膜蒸馏组件进行了多效膜蒸馏过程浓缩稀硫酸和磷酸溶液的研究, 考察了膜入口温度、料液进口浓度和料液流量对渗透通量和造水比的影响。结果表明,膜入口温度升高时渗透通量和造水比增加;料液流量增加,渗透通量增加,而造水比随之降低;料液酸浓度增加,渗透通量和造水比均随之下降,且硫酸的影响更为显著。实验过程中渗透通量和造水比最高可达5.3 L/(m²·h)和11.5。在适当的操作条件下,该过程可将质量分数(下同)为2%的稀硫酸或稀磷酸溶液浓缩至40%以上,且渗透液最大的电导率仍小于200 μS/cm。以10%的硫酸溶液为料液,利用2个不同的膜组件进行了持续30 d的多效膜蒸馏过程稳定性实验研究,实验期间所用膜组件操作性能没有明显下降,没有观察到膜渗漏现象。     

聚偏氟乙烯中空纤维膜蒸馏性能研究

采用疏水性聚偏氟乙烯(PVDF)中空纤维微孔膜,以3.5%的NaCl水溶液为测试液,进行直接接触膜蒸馏(DCMD)脱盐过程研究.考察了盐水温度、流速、PVDF膜的壁厚、内径、组件长度及封装分率等因素对DCMD过程性能的影响.结果表明:盐水温度、流速提高都有利于提高DCMD过程的通量;随中空纤维膜壁厚增加,通量逐渐降低;内径从0.5mm增加到1.0mm,通量略有提高,且壁厚较薄的膜,内径变化对通量的影响较明显;膜组件长度、装填分率增加,产水通量降低但组件产水总量提高.截留率受操作条件、膜和组件结构的影响较小,基本保持在99.99%,产水电导率<4μS/cm.     

荷电中空纤维复合膜及其正渗透性能研究

以聚丙烯中空纤维微滤膜为底膜、羧甲基纤维素钠为功能材料、氯化铁为交联剂,采用溶液涂覆-交联工艺制备了表面荷电的中空纤维复合膜,将该中空纤维复合膜用于正渗透(FO)过程,研究了汲取液盐含量、原料液流速等对FO通量的影响。结果表明,制备的荷电中空纤维复合膜可用于FO过程,以蒸馏水为原料液、Na2SO4水溶液为汲取液,采用PRO模式进行FO试验,当原料液与汲取液体积流量均为15 mL/min、汲取液浓度为0.5 mol/L时,FO水通量为12.3 L/(m2.h),盐通量与水通量的比为1.42 g/L。     

纳米ZrO2修饰Al2O3微滤膜处理废冷却液的实验研究

膜分离技术处理含油废水表现出明显的技术优势,其应用还应解决膜表面易被污染,分离效果逐渐下降的问题,主要原因是由于油滴的易变形性引起的膜堵塞。为解决膜渗透通量与膜选择性的矛盾,本文在市售Al2O3微滤膜孔道表面制备纳米ZrO2涂层,利用纳米涂层改变微滤膜的表面亲水憎油性,阻止油滴的变形。研究了陶瓷膜修饰条件和膜过滤操作参数对膜渗透通量的影响,结果表明:纳米涂层能有效提高微滤膜的渗透通量。膜面流速的增加在一定程度上能提高膜渗透通量,但超过一定程度后,增加不明显。当膜面流速为7m/s,修饰陶瓷膜的最大渗透通量为280 L.m-2.h-1,油截留率为96.4%。纳米涂层修饰微滤膜具有良好的抗油滴污染性能,能有效实现稳定含油废水的油水分离。     

Assessment of hydraulic performance and fouling control caused by pulse flow in hollow fiber membrane module

To shed light on the effect of pulse flow on shear force and membrane fouling, the pulse frequency and flow velocity based on fiber Bragg grating (FBG) sensing technology were studied. The results show that there is a threshold for this synergy between the pulse frequency and flow velocity, which forms more easily at a high pulse frequency and low flow velocity. Moreover, the transition from pulse flow to continuous flow affects the shear force distribution with the membrane module height. Besides, at the same volumetric flow, Re gradually reaches a plateau as the pulse frequency increases from 1 to 5 Hz, and the membrane fouling control has a better flux recovery, which can reach a maximum of 28.89%. Finally, the results also show that the combined effect of high pulse frequency and low flow velocity would be higher than that of low pulse frequency and high flow velocity.     

柱式膜组件结构的CFD优化设计

采用Euler模型与多孔介质模型对不同结构的柱式膜组件内的流体流动进行了计算模拟。研究了曝气孔数目（开孔率为1.92%保持不变）与膜组件高度对膜组件膜丝填充区域内的气液两相分布、壁面剪应力、湍流黏度以及液相速度场的影响。计算模拟数据与实验结果吻合良好。计算模拟表明：通过减小曝气孔直径,增加曝气孔数目的方式能够促进气液两相流场与液相速度场的均匀分布,以及壁面剪应力与湍流黏度的增强;增加膜组件的高度,有利于增加单支膜组件膜面积的同时充分利用曝气擦洗过程中气液两相流对膜丝壁面进行高效的气擦洗。综合考虑膜组件的安装运输、膜丝通量分布以及能耗等因素,对于直径250 mm的膜组件采用曝气孔的直径为6.32 mm,数目为30个,长度在2~2.5 m之间为最优。     

旋流强化中空纤维膜组件结构优化及壳程流动研究

提出并优化了一种旋转流强化的膜组件水力学模型。Box-Behnken方法用于进口直径、进口长度、膜壳高度、进/出口端管长度、球突结构直径,进出口倾斜角度的多参数的实验设计,获得了响应变量最优的膜组件设计方案。通过雷诺应力RSM湍流模型与基于Euler-Lagrange算法的离散相DPM模型的耦合计算,模拟研究了三维模型内液固两相流的颗粒停留时间分布、流体力学特征。模拟结果显示,旋流强化的膜组件壳程的速度分布更加均匀,膜面剪切应力高;湍流耗散率、涡量分布不同于传统膜组件。实验结果证实,优化后的膜组件具有高产水量、低压力降,膜污染速率低的特点。     

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.     

Investigation on removing recalcitrant toxic organic polluters in coking wastewater by forward osmosis

Investigation was made on the efficiency of two commercial membranes in removing via forward osmosis (FO) the low molecular weight organic compounds typical of coking wastewater. The membranes were supplied by Poten and HTI companies. The organics in the simulated coking water were indole and pyrridine. Under FO mode, the rejection to the organics by Poten membrane was around 50%, whereas that for HTI membrane was obviously higher, ranging from 65% to 74%. The response of the two membranes in terms of Water flux and reverse salt flux (RSF) towards changing feed/draw solution (DS) flow rates in FO mode showed similar tendency, but different degree. Generally, the flux in FO using HTI membranes was lower. For HTI membrane, FO operated with pressure retarded osmosis (PRO) mode was also performed and the overall rejection of the organics was slightly lower than that in FO mode. In the long term FO test within 15 days, both Poten and HTI membranes displayed flux reduction and rejection enhancement. But the variation with Poten membrane was much more obvious. Discussion was carried out about the reasons and the mechanisms behind the FO performance difference between two membranes and the variation in flux and rejection with operation conditions. Characterizations by SEM, FTIR, AFM, XRD and XPS were tried to support the proposed explanations.     

An agent-based simulation with NetLogo platform to evaluate forward osmosis process (PRO Mode)

Forward osmosis (FO), as an emerging technology, is influenced by different factors such as operating conditions, module characteristics, and membrane properties. The general aim of this study was to develop a suitable (flexible, comprehensive, and convenient to use) computational tool which is able to simulate osmosis through an asymmetric membrane oriented in pressure retarded osmosis (PRO) mode in a wide variety of scenarios. For this purpose, an agent-based model was created in NetLogo platform, which is an easy-to-use application environment with graphical visualization abilities and well suited for modeling a complex system evolving over time. The simulation results were validated with empirical data obtained from literature and a great agreement was observed. The effect of various parameters on process performance was investigated in terms of temperature, cross-flow velocity, length of the module, pure water permeability coefficient, and structural parameter of the membrane. Results demonstrated that the increase in all parameters, except structural parameter of the membrane and the length of module led to the increase of average water flux. Moreover, nine different draw solutes were selected in order to assess the influence of net bulk osmotic pressure difference between the draw solution (DS) and feed solution (FS) (known as the driving force of FO process) on water flux. Based on the findings of this paper, the performance of FO process (PRO mode) can be efficiently evaluated using the NetLogo platform.     

Evaluation of hollow fiber T-type zeolite membrane modules for ethanol dehydration

This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concen-tration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle. Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.     

CFD analysis for the geometry effect of disc-type membrane module on separation performance

A disc-type Pd-Au membrane module was considered, and a computational fluid dynamics (CFD) model was developed to describe the actual flow dynamics and the distribution of H₂ flux over the membrane. When the membrane size was increased to develop a module with a large separation capacity, the feed flow rate per unit membrane area decreased, indicating loss of utilization of the membrane area. To increase the utilization, the sizes of the feed inlet tube and retentate tube were varied (cases 1 and 2, respectively). The CFD simulation showed that the feed flow rates per unit membrane area increased by ca. 8% and 10%, respectively, whereas a change in the geometry from circular to a rectangle with rounded edges (case 3) resulted in an increase of approximately 19%. A change in the ratio of the edges (case 4) had a slight influence on the separation performance. The distribution of H₂ flux where the geometries in cases 1–3 were combined clearly revealed that most of the membrane area was used to permeate H₂; as a result, the number of membranes decreased by approximately 88% upon increasing their size, while the total membrane area remained the same. This indicated improved utilization of the membrane. The proposed approach is expected to be useful for acquiring valuable information on the design of a membrane module with a large separation capacity.