【作者】 田瑞；

【导师】 刘进荣；

【作者基本信息】 内蒙古工业大学 ， 化学工艺， 2008， 博士

【摘要】 空气隙膜蒸馏是一种新型的膜蒸馏技术,它除了具有一般膜蒸馏具有的可用低品位能源、常温常压操作、蒸馏液纯度极高、蒸馏液不发生化学反应等优点外,空气隙膜蒸馏还由于热液蒸汽与冷却液不直接接触,而具有蒸馏液可单独收集及热效率高的特有优点,应用领域更为广泛,特别适用于有腐蚀性溶质或溶剂的提取以及对放射性废液处理,海水淡化、地下水处理和饮用水制备等,这是其它蒸馏或分离技术无法替代的。膜蒸馏的主要缺点是蒸馏通量小,如能发展一种高通量的空气隙膜蒸馏组件,其蒸馏通量能接近或超过直接接触式膜蒸馏通量,对空气隙膜蒸馏系统的应用推广很有意义。提高膜蒸馏通量可从开发新膜和设计新的膜组件以提高传热传质效率两方面共同解决。本文发展了一种新型高通量空气隙膜蒸馏组件,其特点是采用可调切向旋流供液改善膜面温度和浓度极化,采用很小的空气间隙使膜面可与冷壁部分接触以减小空气隙的传热传质阻力、提高传热传质效率;本文揭示了这种新型膜组件的传热传质机理,建立了相应的传热传质模型及数值分析软件和优化设计方法,并有实验考核。1、改进并完善了高通量空气隙膜蒸馏实验系统。该实验系统是在原第二代膜蒸馏实验系统的基础上,增大了热溶液循环系统流量调节范围和多支路调节供给功能;研制了制冷循环及其控制系统,解决了冷端工质温度不稳定问题;增设了可调节的多点温度量测装置,并改用多通道智能数据测试仪及计算机数据采集和处理系统以提高温度量测及整体的实验量测精度。2、发展了一种新型高通量空气隙膜蒸馏组件。设计并制作了旋转切向入流膜组件,大大改善了温度和浓度极化现象,提高了传热传质效率,有利于提高膜蒸馏通量,并在冷工质容腔的冷壁设计了三角形的沟槽,在加快水蒸汽冷凝的同时,使冷凝液沿三角形沟槽迅速流出。并采用小间隙及膜与冷壁部分接触以减小空气隙的传热传质阻力,从而显著提高了蒸馏通量。3、实验研究表明,在一定的切向入流条件下,膜面接触率为70～80%左右时,得到较为理想的实验效果。采用这种新的膜组件的空气隙膜蒸馏系统,如用自来水作为热溶液、间隙为1mm,冷热水温差为65℃时蒸馏通量可高达120kg/m2h,而传统的空气隙膜蒸馏系统(间隙为4mm)的最大蒸馏通量仅为28kg/m2h;本文还做了热溶液为15%的浓盐水和苦咸水的膜蒸馏通量实验,得到类似结果。同时还进一步考核了采用超声激励的方法,以达到膜蒸馏的过程强化,实现提高膜蒸馏通量的目的,实验结果表明,具有超声激励的膜蒸馏方法仍有一定的研究应用价值;运用Fluent软件对空气隙膜蒸馏热容腔内的流场情况进行了模拟计算,分析比较了无切向入流管与有切向入流管及切向入流管位置的不同对膜面冲刷的不同影响。结果表明,切向入流增大了流体对膜面的冲刷,从而有利于膜面热侧温度边界层和浓度边界层的破坏,有利于提高膜通量。4、本文建立了高通量的空气隙膜蒸馏系统一种新的传热传质模型。所建立的传热传质模型,其特点是考虑空气隙内蒸汽冷凝及膜面与冷壁部分接触对传热传质的影响。用此模型对六个膜面与冷壁有不同间隙厚度和不同接触程度的膜组件系统预测得到的膜蒸馏通量与实验值误差除个别点外均小于10%;预测得到的空气隙内蒸汽冷凝程度也和实验观察符合,说明其传热传质模型是正确的。5、本文开展了太阳能膜蒸馏用于淡化水的预研工作。为使膜蒸馏逐步从实验室走向实际应用,并主要针对解决我国西部无电地区淡水缺乏问题,提出综合利用低品位能源作为膜蒸馏的驱动力,设计了太阳能膜蒸馏集成系统,将太阳能光伏发电系统、太阳能热利用系统和太阳能制冷系统应用到膜蒸馏过程中,使其与膜蒸馏构成一集成系统,并建立该集成系统各个部分的数学模型和相应的仿真模型。运用LabVIEW开发平台,编制了太阳能膜蒸馏集成仿真系统。模拟仿真膜通量分析比较,结果表明,模拟仿真结果与实验结果的相对误差小于10%,说明该仿真系统具有较好的预测性和通用性。通过搭建“太阳能膜蒸馏仿真系统”,基本完善了该系统的实际运行装置的设计思路及设计方法,为下一步工作进行了探索性研究。更多还原

【Abstract】 Air gap membrane distillation (AGMD) is an innovative membrane distillation technique. AGMD separation process not only has the advantages common in membrane distillation system, such as using low grade energy, operating under low temperature and pressure, yielding highly purified permeate and no chemical action in distillation solution, but also has its own advantages that is distillation solution can be collected alone and its thermal efficiency is high because its permeate vapor is not direct contact with cooling liquid. Consequently its application is more widespread than other membrane distillation and separation technique, especially in corroding solution extraction, radiate wastewater treatment, sea water desalination, subterranean water treatment and drinking water production. The main disadvantage of AGMD is low membrane permeate. If we can develop a new high flux air gap membrane distillation module in which membrane flux is close to or exceeds the flux of direct contact membrane distillation, it will be more valuable to commercial application of AGMD.There are two methods to improve the flux, one is to develop new membrane material, the other is to design new membrane module which can provide high heat and mass transfer efficiency. In this paper, a new high flux air gap membrane distillation module is developed. Its characteristics are adopting a rotation and tangential inlet pipe in the module to improve the temperature and concentration polarization, and lessening the air gap width to decrease the resistance of mass transfer in the air gap and improve the efficiency of heat transfer. The mechanism of heat and mass transfer of the high flux membrane distillation module is studied in this paper and the mathematic model and optimum design methods for this new membrane distillation module are also researched with experiment demonstration.1.Improve and perfect the high flux membrane distillation experiment system. Based on the former experiment system, the flow regulation range is enlarged in this new experiment system. At the same time, the refrigeration cycle and control system for experiment system is developed to solve the problem of unstable temperature in cooling side. The adjustable multipoint temperature test devices that install the intelligent measure instrument and computer system to collect and manage data are adopted to improve the temperature test and the whole experiment test precision.2.Develop a new style high flux membrane distillation module. The rotation and tangential inlet flow membrane module is designed and manufactured. The temperature polarization and concentration polarization in this module are reduced thus the heat and mass transfer efficiency and flux are increased. The V grooves are machined in the surface of cooling plate to make vapor condense rapidly and condensed water flow out alone grooves more rapidly. Lessen air gap width to make membrane contact partly with cooling plate so the mass transfer resistance is reduced and flux is improved distinctly.3.Experiments proved that the ideal experiment result will be obtained when 70%-80% membrane surface contact with cooling plate under some rotation and tangential inlet conditions. The permeate flux of the new module was about 120kg/m2.h with water as feed solution, 1mm air gap width and temperature difference up to 65℃. However the maximum flux of conventional air gap membrane distillation system is 28 kg/m2.h with air gap width 4mm. In this paper the same results are obtained when using 15 wt% salt solutions. The ultrasonic technique is also adopted to enhance the membrane distillation process and improve membrane permeate flux. The experiment results showed that ultrasonic technique is of research and application value to membrane distillation. The flow field in hot solution cavity is simulated by software of Fluent. The influence of tangential inlet pipe and position of inlet pipe on flow field near the membrane are compared. It indicated that tangential inlet flow increased the scour for membrane surface therefore the temperature and concentration boundary layer were destroyed and membrane flux was increased.4.A new heat and mass transfer model for high flux membrane is proposed in this paper. The characteristic of this model is to taking the effect of vapor condenses in air gap and membrane contact with cooling plate on heat and mass transfer into consideration. The error between flux predicted by this model and experiment results is less than 10% under six different air gap width and membrane and cooling plate contact degree. The prediction of condensate in air gap agrees with the measurement data. That indicates the heat and mass transfer model is correct. 5.The solar driven membrane distillation system for desalination is also prepared beforehand in this paper. In order to make membrane distillation technique enter the commercial market from laboratory and to solve the problem of freshwater shortage in western area where there is no electricity, the solar driven membrane distillation system is proposed which can use low grade energy as driven power. The assemble system applied solar photovoltaic system, solar heating system and solar refrigeration system to membrane distillation system. The mathematic model and simulation model of every system are also proposed in this paper.The simulation system of solar driven membrane distillation is studied by software Labview. The comparison result showed that the error between simulation and experiment data is less than 10%. It is proved that the simulation system has good prediction and generality. The design idea and design method for the real assemble system are perfected through building the simulation software for solar driven membrane distillation system. So the exploratory research was done for the future work.更多还原