膜蒸馏脱盐过程膜润湿的研究进展

膜蒸馏（MD）适合在偏远地区小规模制备淡水,有脱盐率高、接近常压操作、可利用太阳能等优势。但MD膜润湿影响了装置的运行稳定性,是制约MD脱盐应用的重要因素之一。本文介绍了MD膜润湿的评价方法,包括测定透水压力、临界膜孔润湿深度及可视化在线监测膜润湿进程等;简述了膜污染、MD操作变量、膜蒸馏形式及不同结垢晶体各因素对膜润湿的影响;从防垢和强化通量、掌握合适的膜清洗周期、物理干预及提升MD膜性能等方面分析了抑制膜润湿的措施;并分析了一些脱盐实验时间较长的MD膜润湿情况;指出具有自清洁性的光催化膜及防垢性能更强的双疏膜和Janus膜,具有抑制MD膜润湿的巨大潜力。本文有助于对脱盐过程中MD膜润湿的预测和有效控制。     

太阳能膜蒸馏技术研究进展

介绍了太阳能膜蒸馏技术的原理、特点等,总结分析了国内外太阳能膜蒸馏技术的发展现状,展望了该技术的发展方向,新型膜材料的研发、太阳能膜蒸馏系统的连续稳定运行、提高系统耦合性为今后的研究方向。     

低温膜蒸馏及其过程模拟

采用聚丙烯中空纤维膜对纯水介质膜蒸馏、冷侧盐水循环有温差膜蒸馏及等温渗透膜蒸馏进行了实验研究,建立了描述膜蒸馏过程的传质及传热数学模型,以实验数据为基础对模型中的参数进行了回归并对数学模型进行了计算机数值求解,计算结果与实验数据吻合较好     

膜蒸馏的开发和利用研究

膜蒸馏是在迅速发展的膜分离技术中,极有发展前途的新型分离技术。膜蒸馏是膜技术和蒸发过程结合的新型膜分离过程。具有相态变化。它利用疏水性微孔膜提供很大的传质表面来实现水溶液汽化和传质的分离过程。其传质推动力是膜热侧和冷侧水溶液间的温度差所引起传递组份的气相分压差。     

新型气隙式膜蒸馏组件脱盐过程

利用基于聚丙烯中空纤维膜和聚丙烯中空纤维换热管的新型能量回收式膜组件(AGMD-HF),以70 g·L^-1的氯化钠溶液为研究对象,考察了膜组件长度和膜孔径大小对膜组件脱盐性能的影响。为直接衡量操作条件、组件参数以及温差、浓差极化现象对传质系数的影响,引入总传质系数,并研究进料温度和膜孔径对总传质系数的影响。实验结果表明,总传质系数随着温度的升高、膜孔径的增大而增大,提高膜孔径可有效提高总传质系数,同时可有效提高通量和造水比。通量随组件长度的增大而减小,而造水比增大,因此在应用过程中可综合考虑通量和造水比以便选择合适的组件长度。     

膜蒸馏脱盐中膜污染与膜润湿的研究进展

膜蒸馏作为一种脱盐的新兴技术受到广泛关注。然而,因为实际水质组分复杂,可能含有如表面活性剂、油类物质、易结垢盐和有机溶剂等污染物,导致一般疏水膜在长时间运行情况下极易发生膜污染或者膜润湿,最终造成膜通量或截留性能降低。本文首先简述了不同种类的膜污染和膜润湿的特点及形成原因,并分析了膜污染和膜润湿之间的区别和联系。对膜蒸馏过程中膜污染和膜润湿的监测和预测手段进行了简要介绍,最后针对膜蒸馏脱盐过程,重点介绍了近几年国内外预防膜污染和膜润湿的研究进展。研究者一般从污染物与疏水膜的相互作用力着手对疏水膜进行表面改性制备全疏膜和Janus复合膜,避免污染物在膜面的吸附以及抑制表面或孔道润湿。越来越多的研究人员采用致密亲水膜的渗透汽化脱盐来从根本上避免疏水膜带来的润湿。除此之外,对进料液进行预处理也能显著延迟膜的污染和润湿,如混凝/沉淀、膜过滤、煮沸、pH调控等,还可通过改变进料方式、辅助外加磁场等措施控制膜表面局部区域的流体力学状态,减少污染物的附着。适当的膜后处理措施也能恢复膜性能。最后,文章指出了解决膜蒸馏中膜污染和膜润湿的研究方向。     

鼓气减压膜蒸馏过程研究

设计了新型鼓气减压膜蒸馏(AVMD)过程,在原水进入疏水膜组件前鼓入低压压缩空气,形成气液混合流进入疏水膜组件,在疏水膜组件的产汽出口外接负压系统,构成AVMD系统.采用疏水性聚偏氟乙烯中空纤维微孔膜,以自来水为测试液,研究了鼓气强度、进料温度、流速、冷侧真空度对AVMD过程性能的影响,考察了AVMD对不同NaCl含量溶液的分离性能.结果表明,随着鼓气量、进料液温度、流速,真空度的提高,AVMD过程通量有明显的增加,而产水电导率始终低于0.3 mS·m~(-1).当进料液温度70℃,冷侧真空度85 kPa,进料流速1.33 m·s~(-1)时,AVMD过程膜通量可高达45 kg·m~(-2)·h~(-1),而相同实验条件下减压膜蒸馏(VMD)过程的通量约为30 kg·m~(-2)·h~(-1).     

中空纤维空气隙式膜蒸馏海水淡化过程的性能模拟与优化

利用响应曲面法(RSM),以模拟标准海水(质量分数3.5%)为进水对中空纤维空气隙式膜蒸馏(AGMD-HF)海水淡化过程的影响因子和膜通量指标进行了模拟优化。通过面向中心复合设计法(CCD)实现了基于热料液进水温度、冷凝液进水温度和料液流量的实验优化设计,并建立了响应值与影响因子之间的二次多项式回归模型。方差分析(ANOVA)、RSM分析及实验响应值与预测值的对比验证了该模型对影响因子和膜通量模拟优化的可信度。进一步地,通过期望函数的引入确定了各影响因子最佳水平,并利用太阳能加热驱动过程实验进行验证。结果表明,ANOVA的决定系数R²达到0.986,p值则低于0.0001;实验膜通量与预测值平均误差仅为6.95%,产水电导率始终保持在10 μS·cm^-1以下,脱盐率稳定在99.99%以上;最佳影响因子水平分别为83.5℃、13.2℃和60.2 L·h^-1,在此条件下太阳能加热驱动过程膜通量达到6.47 L·m^-2·h^-1。该实验不仅为潜在可行的规模放大过程提供了可参照的操作参数,而且表明将太阳能引入AGMD-HF海水淡化过程具有很强的实际应用潜力。     

膜蒸馏技术最新研究应用进展

膜蒸馏是一种热驱动的新型分离技术,可使蒸汽分子在膜两侧的压力梯度作用下通过膜孔迁移至膜外侧并冷凝下来。本文简要介绍了膜蒸馏的热质传递原理以及直接接触式、气隙式、气扫式、真空式等几种主要膜蒸馏装置的特点。综述分析了膜蒸馏的相关研究进展,包括:膜蒸馏的操作及膜特性参数的影响机理研究;更多高性能的膜材料的研制;对膜污染在工艺与操作参数方面的改进;通过能源利用与组件优化强化膜蒸馏过程等。概述了膜蒸馏在海水脱盐制备纯水、食品工业中果汁浓缩及酒精发酵、化学可挥发性物质的分离以及有毒有害废水处理方面的最新应用。最后,进一步指出过程参数的综合影响、膜材料的商业化、膜组件设计以及过程热效率是目前阻碍膜蒸馏工业化应用的主要问题。展望了加强能源研究、专注于商业用膜的研发、较多关注于其他膜蒸馏过程以及系统角度的优化分析是膜蒸馏技术未来的发展方向。     

疏水石墨烯膜的制备及其用于膜蒸馏脱盐的研究进展

膜蒸馏技术由于理论截盐率高、操作条件温和及对盐浓度灵敏度低等优势,在脱盐领域中展现出巨大潜力。近年来,人们开始关注石墨烯材料在膜蒸馏脱盐领域中的应用。本文首先概述膜蒸馏技术的基本原理及常用膜材料;接着介绍石墨烯的疏水性质和疏水石墨烯膜的制备;再详细综述石墨烯混合基质膜、石墨烯复合膜及石墨烯纯膜这三类疏水石墨烯膜在膜蒸馏脱盐中的应用;最后总结疏水石墨烯用于膜蒸馏脱盐面临的主要挑战及未来研究方向。     

Efficiencies of Sieve Tray Distillation Columns by CFD Simulation

A 3‐D two‐fluid CFD model in the Eulerian‐Eulerian framework was developed to predict the hydrodynamics and heat and mass transfer of sieve trays. Interaction between the two phases occurs via interphase momentum and heat and mass transfer. The tray geometries are based on the large rectangular tray of Dribika and Biddulph and FRI commercial‐scale sieve tray of Yanagi and Sakata. In this work a CFD simulation is developed to give predictions of the fluid flow patterns, hydraulics, and mass transfer efficiency of distillation sieve trays including a downcomer. The main objective has been to find the extent to which CFD can be used as a design and prediction tool for real behavior, concentration and temperature distributions, and efficiencies of industrial trays. Despite the use of simple correlations for closure models, the efficiencies obtained are very close to experimental data. The results show that values of point efficiency vary with position on the tray because of variation of affecting parameters, such as velocities, temperature and concentration gradients, and interfacial area. The simulation results show that CFD can be used as a powerful tool in tray design and analysis, and can be considered as a new approach for efficiency calculations and as a new tool for testing mixing models in both phases. CFD can be used as a “virtual experiment” to simulate tray behavior under operating conditions.     

曝气膜生物反应器的CFD模拟

利用Fluent软件对曝气膜生物反应器中气液两相流动进行模拟计算,探讨了进气气泡的直径、进气速度及膜纤维束的长度等因素对膜生物反应器内液体流动、气体分布的影响.结果表明,减小气泡的直径并适当增大进气速度、膜纤维束长度可以有效提高膜生物反应器内气体的分布和液体与气体的接触,从而促进气液两相进行高效的传质.     

规整填料内气液两相流动与传质的计算传质学模型

Detailed investigation of flow behavior in structured packing distillation columns is of great importance in accurate prediction of process efficiency and development of more efficient and optimal equipment internals. In this study, a three-dimensional two-phase flow model based on VOF method for simulating the hydrodynamics and mass-transfer behavior in a typical representative unit of the structured packing is developed. In the proposed model, the model is used for the closure of turbulent mass transfer equation. By solving the proposed model, the velocity distribution, phase fraction profile and concentration field are obtained. Using these data, the total liquid holdup, the wetted area and the separation efficiency [height equivalent to a theoretical plate (HETP)] are estimated. For testing the model validation, the simulated HETPs are compared with our previous experimental data obtained in a 150 mm-diameter column containing Mellapak 350Y operating at the pressures of 0.6-1.8 MPa. The compari-son shows that they are in satisfactory agreement, with an average absolute deviation (AAD) of 25.4%.     

Design and Analysis of a Submerged Membrane Reactor by CFD Simulation

CFD was applied to demonstrate the effect of reactor configurations on the fluid flow pattern in submerged membrane reactors. A mixture model, a realizable k‐? model, and the multiple reference frame (MRF) technique were employed to simulate the solid‐liquid turbulent flow. Influences of the introduction of a ceramic membrane, the relative position between ceramic membrane and impeller, and the types of impeller on velocity profiles and concentration distributions were systematically discussed. These simulation results were validated qualitatively with experimental data for various reactor configurations.     

Coupled Phenomena Membrane Distillation and Osmotic Distillation through a Porous Hydrophobic Membrane

Abstract

Water transport in the vapor phase through a porous hydrophobic membrane has been studied in different experimental situations. Pure water and/or different aqueous solutions of sodium chloride, ranging from 0.5 to 5 mol/L, were employed on both sides of the membrane. The experiments were carried out under temperature differences varying between 5 and 30 K, and at mean temperatures varying between 20 and 40[ddot]C. The stirring rate was varied between 0 and 350 rpm. The results were interpreted based on the existence of unstirred polarization layers.     

CFD Simulation of Mass Transfer Efficiency and Pressure Drop in a Structured Packed Distillation Column

The pressure drop and mass transfer efficiency for two‐phase flow in a structured packed column were simulated using a commercial CFD package, CFX version 10. The distillation of the methanol/isopropanol system was carried out in a 0.073 m diameter column, with an element composed of a ceramic structured packing and 0.053 m in height. The Height Equivalent to Theoretical Plate (HETP) value varied from 0.106–0.146 m. Pressure drop experiments were measured with an air/water system. The pressure drops at the flooding and loading points were ca. 173 and 580 Pa/m of packing, respectively. HETPs and pressure drops calculated from the Computational Fluid Dynamics (CFD) model were compared to their experimental counterparts. The average relative error between CFD predictions and the experimental data for the prediction of dry pressure drop, irrigated pressure drop and mass transfer efficiency are 20.3 %, 23 % and 9.15 %, respectively. In all cases, the CFD predictions show a good agreement with the experimental data, indicating that CFD is a reliable, cost saving and suitable technique for the design and optimization of separation processes.     

Simulation of Membrane Distillation for Purifying Water Containing 1,1,1‐Trichloroethane

Vacuum membrane distillation is modeled for the purification of water containing organic matter. The separation medium is a hollow‐fiber membrane contactor that is simplified to a two‐dimensional structure with a single porous membrane wall. The model considers the transport phenomena of a vacuum membrane distillation system in porous media, in which the aqueous volatile organic solution was considered as an incompressible and steady fluid. The numerical simulation of the two‐dimensional model of vacuum membrane distillation for an aqueous solution of 1,1,1‐trichloroethane was established under steady state. The effects of the bulk feed temperature and the feed flow rate on the percentage of 1,1,1‐trichloroethane removal from an aqueous solution are discussed.     

CFD模拟在卷式反渗透膜性能优化中的研究进展

反渗透工艺在世界范围内广泛应用于海水淡化、废水处理和医药生产等领域.计算流体力学(CFD)的模拟能描述出多种流体的流动、传质和传热等相关物理过程,可以在反渗透膜组件的模拟中可视化流体流动情况和膜污染情况,对膜组件的设计与应用过程具有指导意义.文中综述了卷式反渗透膜组件中的流道隔网优化和膜污染过程的CFD模拟研究进展,以及一些特殊形式膜组件中CFD的应用可行性和成果,并提出了CFD模拟应用于优化反渗透膜性能可能的研究方向.     

CFD Simulation of the Heat and Mass Transfer Process during Centrifugal Short‐Path Distillation

Numerical simulation was carried out for a centrifugal short‐path distillation arrangement using the computational fluid dynamics technology. Both two phases and interfacial transport were taken into account with an attempt to explore the heat and mass transport in the film body and the interface. The model tried to provide a general method to study the short‐path distillation in various situations. The effects of feed flow rates, feed and heating wall temperature controlling the development of the temperature and concentration along the axial and radial direction were investigated. On the basis of the simulation results, detailed characteristics such as distribution of temperature and concentration, heat and mass transfer coefficient throughout the liquid film can be described.     

Vapor Permeate Characteristics of Membrane Distillation

Abstract

To study the permeate characteristics of membrane distillation considering heat and mass transfers and concentration polarization, theoretical and experimental studies were performed. To understand the effect of concentration polarization, concentrated solutions of LiBr and H₂SO₄ were used as feed. The permeate flux was found to be proportional to the vapor pressure difference between the feed and cooled surface and decreased with increasing concentration because of the concentration and temperature polarization. Furthermore, when considering the heat and mass transfers and concentration polarization, the permeate flux could be estimated accurately.