Innovative hydrophobic/hydrophilic perfluoropolyether(PFPE)/polyvinylidene fluoride(PVDF)composite membrane for vacuum membrane distillation

Though membrane distillation(MD)has gained more and more attention in the field of desalination,the wetting phenomenon was still a non-negligible problem.In this work,a method combined dip-coating and UV in situ polymerization for preparing hydrophobic/hydrophilic perfluoropolyether(PFPE)/polyvinylidene fluoride composite membranes.This composite membrane consisted of a top thin hydrophobic coating layer and hydrophilic substrate membrane.In terms of anti-wetting properties,contact angle and liquid entry pressure of all composite membranes(except for those based on 0.45μm)exceeded 160°and 0.3 MPa,respectively.In particular,the desalination performance was tested in vacuum membrane distillation tests by feeding 3.5%(mass)saline solution(NaCl)at 60℃.The composite membranes with larger support pore size and lower PFPE content had higher membrane distillation flux.And for stability tests(testing the 0.22μm membrane coated by 5%(mass)PFPE),the highest MD flux29.08 kg·m^(-2)·h^(-1) and stable salt rejection(over 99.99%)during the period.Except that,the effects of coating material concentration and pore sizes of substrate membrane were also investigated for surface morphology and topography,porosity,mechanical strength and pore size characteristics.This work provided a simple and effective alternative to prepare excellent hydrophobic composite membranes for MD applications.

Numerical Analysis of Conjugated Heat and Mass Transfer of Helical Hollow Fiber Membrane Tube Bank for Seawater Distillation

A numerical study on the conjugated heat-mass transfer of helical hollow fiber membrane tube bank(HFMTB)for seawater desalination was carried out.Physical and mathematical models of fluid flow,temperature and humidity distribution were constructed to investigate the influences of flow type,Reynolds number,and temperature on the conjugated heat-mass transfer performance of hollow fibers in the distillation membrane module.The conjugated heat-mass transfer characteristics of HFMTB were discussed by utilizing the friction coefficient,Nusselt number(Nu),and Sherwood number(Sh).Results demonstrate that a distillation efficiency enhancement of 29%compared to the straight HFMTB has been detected for four-helical HFMTB configuration,though the friction coefficient of such a module is about 4 times of their straight counterparts.The values of average Nu and Sh numbers are increasing with tube number,which improves distillation efficiency.The effect of flow type has been studied by employing the upstream and downstream flows to the double-helical HFMTB,demonstrating upstream flow type is more conducive to the heat-mass transfer process.Both the outlet air humidity(ω)and distillation efficiency(η)decrease with the air-side Reynolds number(Rea)and inlet air temperature in the helical HFMTB while increasing with the solution-side Reynolds number(Re_(S))and inlet solution temperature.Overall,the obtained results indicate that helical HFMTB applying upstream flow has great potential to achieve high-performance SGMD for seawater desalination.It is anticipated that the present work can assist in a better understanding of the membrane desalination process in HFMTB and thus provide theoretical suggestions for further optimization and development.

Incorporation of 3-dimensional lycopodium with hydrophobic nature and interconnected nano-channels into polyvinylidene fluoride membranes for desalination applications by vacuum membrane distillation

In the present research,for the first time,lycopodium as a novel nanofiller was incorporated into a polyvinylidene fluoride matrix to fabricate lycopodium/polyvinylidene fluoride flat-sheet membrane for desalination applications by vacuum membrane distillation process.The prepared lycopodium/polyvinylidene fluoride membranes and lycopodium were characterized by field emission scanning electron microscopy,X-ray diffraction,Fourier transform infrared,energy dispersive X-ray,and mapping analyses.Water contact angle and liquid entry pressure measurements were also performed.Response surface methodology was applied to optimize membrane structure and performance.The optimized lycopodium/polyvinylidene fluoride membrane exhibits superior performance compared to the neat polyvinylidene fluoride membrane in terms of flux,salt rejection,water contact angle,and hydrophobicity.In vacuum membrane distillation experiments,using a 15000 ppm NaCl solution as a feed at 70℃,the neat polyvinylidene fluoride membrane,optimum membrane,and agglomerated membrane(with high lycopodium loading)demonstrated 3.80,25.20,and 14.83 LMH flux and 63.30%,99.99%,99.96%salt rejection,respectively.This improvement in flux and salt rejection of the optimized membrane was related to the presence of lycopodium with hydrophobic nature and interconnected nano-channels in membrane structure.It was found that lycopodium,as the most hydrophobic material,effectively influences the membrane performance and structure for membrane distillation applications.

炼化企业中低温多效蒸馏海水淡化技术的应用

低温多效蒸馏海水淡化技术是一种利用水平管降膜蒸发器或竖直管蒸发器串联并划分为若干效组,以一定量的输入蒸汽作为热源,经多次蒸发、冷凝,利用二次蒸汽潜热,得到多倍加热蒸汽量的蒸馏海水的海水淡化技术。该技术具有传热效率高、产品水质好、负荷调节范围大、工艺温度低等特点,可用于发电厂、化工厂、低温核反应堆等领域,是国际主流海水淡化技术之一。文章结合某炼化企业节能降耗中低温多效蒸馏海水淡化技术创新应用,分析了该技术应用经济效益,并对技术应用前景进行展望,以期促进该技术推广应用和创新发展。

太阳能驱动膜蒸馏中光热疏水膜研究进展

太阳能驱动膜蒸馏技术是目前膜蒸馏领域的研究热点,光热疏水膜的性能直接决定其光热转换效率和运行成本。本文综述了适用于太阳能驱动膜蒸馏技术的光热疏水膜制备方法及其脱盐效能;重点分析了不同种类光热疏水膜的渗透性能和光热转换性能;指出了光热疏水膜结构和性质对其SMD性能的影响,并提出了其优化策略。

疏水微孔膜蒸馏膜的应用进展

膜蒸馏作为一种热法与膜法耦合的高效分离技术,在海水淡化、工业废水处理等多个领域都具有广阔的应用前景.然而膜蒸馏在实际应用中存在疏水膜的润湿、污染、结垢等瓶颈,以及能量利用效率低、实际通量低等问题,尚未得到大规模的应用推广.本文从膜蒸馏技术的简要介绍出发,总结了膜蒸馏技术的发展历程.之后综述了膜蒸馏技术在国内外企业的商业应用情况,分析了疏水微孔膜蒸馏膜在多个水处理领域的应用潜力.最后总结了制约膜蒸馏应用的主要问题,并探讨了膜蒸馏的未来发展方向.

海水淡化膜蒸馏膜的研究现状与展望

海水淡化技术(热法和膜法)是一项有望使人类摆脱淡水资源短缺困境的有效方法,其中,膜蒸馏技术是一种能源消耗低、脱盐能力强且有望实现淡水经济可持续生产的新型膜分离技术,但是膜蒸馏性能在很大程度上受膜污染与温度极化的制约,严重阻碍了其规模化应用,为此,研究人员围绕膜改性做了系列研究,以提高膜抗污染性并最大限度地降低温度极化。从阻碍膜蒸馏发展的问题入手,简要介绍了膜污染与温度极化及其对膜蒸馏造成的不利影响,综合分析了当前通过构造特殊润湿性表面抵抗膜污染以及利用限域加热降低/消除温度极化的研究现状,并指出当今膜蒸馏膜面临的问题,认为未来对于膜蒸馏膜的研究应从以下几方面开展:1)选用高导热/高光吸收的材料制造有限域加热功能并具有特殊润湿性表面的膜;2)设计能够适应多元污染物进料液的膜蒸馏膜;3)构筑一体化的具有高导热/光吸收性亲水层的Janus膜。

低温多效蒸馏海水淡化与汽轮机耦合技术应用

介绍了一种低温多效蒸馏(LT-MED)海水淡化与汽轮机耦合技术,分析了汽轮机排汽参数的精准控制、海水淡化装置与汽轮机可靠隔断、海水淡化装置与汽轮发电机的协同控制等。某钢铁公司的应用结果表明LT-MED海水淡化与汽轮机耦合系统整体热量利用效率达到81.5%以上,海水淡化蒸汽成本降低了60%左右。

Effect of Complex Parameters of Porous Media on Desalination Performance in Air-Gap Diffusion Distillation Based on Multiple Regression Analysis

Air-Gap Diffusion Distillation(AGDD) is a new technology aiming at solving the problem of the safety of drinking water for residents in remote areas that uses a super hydrophilic porous medium as the hot channel and evaporation surface. In the experiment, it was found that the parameters of porous media have a significant influence on the desalination(evaporation) efficiency of AGDD. Although porous media are widely used as evaporation components, the factors affecting their evaporation efficiency are not fully understood. The evaporation process in super hydrophilic porous media is rarely discussed. A large number of experiments have been carried out based on AGDD. The introduction of statistical methods solves the problem that experiments cannot distinguish the contribution of complex parameters of porous media to evaporation efficiency. Stepwise regression analysis is used to reduce the dimensionality of the independent variables and construct regression equations(coefficient of determination R~2 reached 81.3%-96.8%). Evaporation flux correlations and dimensionless mass transfer correlations are established based on porous media parameters. We found that the surface evaporation of super hydrophilic porous media can be divided into three stages: diffusion evaporation, capillary evaporation, and thermal evaporation. The evaporation efficiency of these three stages is controlled by the vapor diffusion process resistance, capillary force, and energy supply. At low saturation, evaporation efficiency is limited by the resistance of the vapor diffusion process. The evaporation efficiency of the porous media is affected predominantly by the pore size, the specific surface area, porosity and the characteristic length. At high saturation, the evaporation efficiency becomes influenced primarily by the permeability. A small thickness and a high hydrophilicity also improve the evaporation efficiency.

漂浮式聚光升膜多效太阳能蒸馏器的性能研究

提出一种漂浮在海面上进行淡化产水的聚光升膜多效太阳能蒸馏器,该淡化装置包含一个抛物面聚光镜和多个垂直布置的蒸发-冷凝单元。采用吸水芯作为蒸发器,利用毛细吸力使海水形成上升的液膜,有效减少了加热损失。建立理论模型分析装置内部的传热传质过程。通过实验研究不同运行参数对装置温度、产水量和比能耗的影响。室内稳态研究结果表明,当太阳辐照度为900 W/m^(2)时,蒸馏器内部温差为56.9℃,产水率可达到2.64 kg/(m^(2)·h)。在户外平均太阳辐照度为603.7 W/m^(2)的条件下,装置一天产水量为5.3 kg/(m^(2)·d),日平均比能耗为1591.6 kJ/kg。

基于冷冻过程的脱盐研究进展

冷冻脱盐是海水淡化的一种理论方法,具有运行温度低、不易结垢、腐蚀小的优点。但由于存在冷源耗能和脱盐率不高的问题,冷冻脱盐未能应用于工业生产。许多学者对冷冻脱盐进行了理论与实验研究,试图找到降低冷源能耗和提高脱盐率的方法,为冷冻脱盐的工业应用提供技术支持。对近年来学者们在冷冻过程参数对冰脱盐效果的影响、降低冰盐度的方法及影响因素以及冷冻法与膜法、热法结合提高产水率、降低能耗等方面开展的研究工作进行了综述。

太阳能热脱盐的途径和应用研究

太阳能热脱盐(Solar thermal desalination,STD)是一种极具潜力的低能耗、可持续海水淡化新方法,可用于在能源基础设施不完备的干旱地区生产清洁淡水。目前,通过改进太阳能吸收材料和系统设计来提高STD效率受到越来越多的关注。系统地介绍了各类高效光热转换材料的特点及其在利用太阳辐射进行海水淡化方面的应用,然后从隔热结构和冷凝结构设计等不同的角度讨论了STD系统的热能管控措施,并进一步阐明了潜热回收的重要性,最后,总结了STD系统工艺现有的局限性和提高STD系统脱盐效率的有效途径,并对STD系统的实用性和经济性进行了展望,以期为开发更高产水率、更低能耗的可再生能源脱盐新工艺提供参考。

基于余热利用的热泵辅助单效压气蒸馏系统

基于国内外水资源短缺以及换流阀余热浪费严重的问题,提出了一种以热泵循环为辅助热源的新型单效压汽蒸馏海水淡化系统(HP-SEMVC),根据热力学定律和热经济模型,从系统能耗、㶲损和经济成本等角度对系统的进行优化分析,获得系统最优工况,并与传统压气蒸馏海水淡化系统进行比较。分析表明,HP-SEMVC是一种节能的海水淡化技术,与纯单效系统相比,可使系统GOR提高40%。明显改善了系统的㶲损分布,系统㶲效率提高约1.397~1.511个百分点,整体上与多效蒸馏系统相当甚至更优。在日产水量为100~5000m^(3)的范围内,制水成本可降低14.18%~21.24%。HP-SEMVC组合系统很好的弥补了传统单效机械压气蒸馏系统的不足,为实现我国“双碳”目标提供新思路。

Review:Solar Still with Additional Condenser

Getting consumable water to individuals has been a continuous challenge worldwide.Contaminated or non⁃purified water sources are responsible for the bulk of human illnesses.The demand for water purification that does not harm the biological system is urgent.Sun⁃based desalination is one of the effective water purification methods creating ultra⁃pure refined water.Sun⁃based still refining frameworks offer maintainable devices for a freshwater generation.Diverse plans were tried by analysts to move forward the efficiency of sun⁃powered still.According to the experiments,solar still coordinates outside or inside the condenser is considered to be a valid and successful plan.This survey hopes to show,explain,and study the performance of several solar stills combined with diverse condenser designs.

操作条件对真空膜蒸馏过程影响的实验及模拟研究

真空膜蒸馏(VMD)技术具有膜通量大、操作压力低、能耗低等优点,在海水淡化领域中占有重要的地位。本文分别研究了真空度、流速和进料液温度等外界条件对膜通量的影响。结果表明,随着真空度、流速和进料液温度的提高,膜通量逐渐增大。同时,利用计算流体力学(CFD)软件对真空膜蒸馏过程进行了模拟,并通过编写用户自定义函数(UDF)进行了数值仿真。结果表明,仿真数据与实验数据吻合较好。因此,UDF可以进一步用于中空纤维膜组件的放大模拟,以减少工程应用中复杂情况下的实验误差。

页岩气压裂返排液真空多效膜蒸馏脱盐处理与现场试验

开展了使用真空多效膜蒸馏处理页岩气压裂返排液的现场试验研究,考察了处理前后原水、浓缩液、淡水产水的TDS、COD、氯化物等11项指标的变化情况及进水含盐量变化对膜蒸馏处理的影响,运行过程中对装置进行30 d的热端及冷端压力监测。结果表明,膜蒸馏具有较好的离子及有机物截留效果,运行较为稳定,随着试验进程推进,膜与物料接触侧发生结垢现象,由于其耐酸碱的特性,经过化学清洗,热端及冷端压力差得以有效恢复。优化运行参数,收水率最高达87.8%,浓缩液最高含盐量可达到29%。装置处理后的淡水水质较好,出水COD、氯化物浓度分别为5、102 mg/L,满足外排标准中对应指标的要求。

膜蒸馏技术简述及其应用前景

膜蒸馏是一种以蒸汽压差为推动力的新型分离技术,与传统蒸馏方法和其他膜分离技术相比,具有运行压力低、运行温度低、分离效率高等优点,可充分利用太阳能、废热和余热等热源。广泛用于海水淡化、超纯水的制备、挥发性物质水溶液的浓缩、结晶和分离等方面。本文主要介绍了直接接触式、气隙式、气扫式、真空式四种膜蒸馏装置,以及膜蒸馏技术的前景。随着膜蒸馏技术的不断发展,将在应用领域和分离重组技术领域给人类带来新的认识。

Harvesting net power and desalinating water by pressure-retarded membrane distillation

Pressure-retarded membrane distillation(PRMD)can convert low-grade heat to useful work by harvesting the pressure energy of the condensation liquid on the cold side.In this study,a new type of PRMD system for combined freshwater and power production was proposed.For this configuration,the thermal energy of the phase change is transported to the interface mainly by conduction rather than convection,which significantly reduces the pump power loss of the liquid flow.In addition,it also utilizes a multistage structure to regenerate heat with low pump power loss.The experimental results showed that,for a module with a heating area of 1.0 m^(2),this system can produce 188 L of freshwater and 27.8 kJ of power each day when operating between 80℃ and 40℃.The water and power densities of the PRMD configuration would be affected by saline ions in the feed liquid,air resistance in the evaporation chamber,membrane wetting,and membrane compaction.The experimental and molecular dynamics simulation results indicated that a higher temperature difference or working temperature will significantly improve the desalination and power generation rates because of the increased mass transfer driving force of the vapor gradient.This study proved that it is possible for a PRMD system to simultaneously obtain net power and freshwater using low-grade heat as the only energy input.Nevertheless,the liquid supply,working pressure,and membrane properties should be improved to achieve better performance.