基于流体力学响应的膜污染控制方法研究

发布时间：2019-03-16 16:23

【摘要】：为了减轻膜污染,本文基于流体力学原理设计了一种泄压式脉冲过滤工艺。实验以高污染性酱油作为模拟料液,以聚偏氟乙烯(PVDF)中空纤维内压式超滤膜作为过滤介质,考察了泄压式脉冲过滤工艺对减轻膜污染,提高膜通量的效果。然后借鉴前期科研成果,向料液中投加适量硅藻土助滤剂以强化对膜污染的控制。最后,提出临界运行通量概念,考察不同工艺在较高压力时的膜污染情况,以分析所提工艺对减轻膜污染,提高膜通量的效果。论文所设计的泄压式脉冲工艺,实现了对膜表面滤饼层冲刷的目的。结果表明该泄压式脉冲在压力损失22.5%的不利情况下,通过减薄滤饼层,获得膜通量比传统无脉冲过滤方式提高了14.9%。说明该种工艺对膜污染的控制发挥了积极作用,弥补了因压力损失造成的膜通量下降,是一种可行的膜污染控制方法。并且,该工艺简单实用,有利于工业化应用。为强化对膜污染的控制效果,基于微粒子辅助过滤原理,首次提出通过向料液中投加硅藻土助滤剂强化脉冲工艺控制膜污染。利用硅藻土在膜表面微孔处的架桥作用,形成相对疏松的滤饼层,避免污染物直接在膜表面形成致密滤饼层而导致膜通量迅速衰减,然后再通过脉冲产生的强剪切力,对滤饼层进行有效冲刷,从而降低滤饼层阻力,达到提高膜通量的目的。结果表明,通过硅藻土与脉冲工艺耦合,滤饼层阻力相对于无脉冲工艺降低了24.5%,其所占总过滤阻力百分比由原来无脉冲工艺的72.7%,降低到67.9%,膜通量提高了33.3%。与仅投加硅藻土助滤剂膜通量提高8%和脉冲工艺下膜通量提高14.9%相比,硅藻土与脉冲组合工艺下,膜通量实现了大幅度提高。为反映所提工艺对膜污染控制情况,提出了临界运行通量概念：在过滤过程中,膜通量随着压力的增大而增加,当到达某点后,膜通量不再增加,只是随着压力继续增大而维持稳定甚至下降,此膜通量最大点即为临界运行通量,其对应操作压力定义为临界运行压力。结果表明,滤饼层阻力由滤饼层致密性和滤饼层厚度两个因素构成,料液性状(有无助滤剂)和过滤压力决定滤饼层致密程度,工况条件(有无脉冲、过滤时长等)决定滤饼层厚度。硅藻土与脉冲组合工艺,既可有效改善滤饼层致密程度,又能减薄滤饼层厚度,因此可以提升操作压力,获得更高膜通量,提高膜工效：临界运行通量达到65.7 kg·m-2·h-1。与无脉冲工艺临界运行通量相比,提高了38.9%；与投加硅藻土条件相比,提高了16.9%；与脉冲工艺相比,膜通量提高了17.3%。与临界通量比较,临界运行通量可以更真实的反映膜过滤过程中膜污染(特别是滤饼层阻力)对膜通量的影响,与临界通量相比,更具实际意义。
[Abstract]:In order to reduce membrane fouling, a pressure-relief pulse filtration process was designed based on the principle of fluid dynamics. In this experiment, soy sauce with high pollution and polyvinylidene fluoride (PVDF) hollow fiber inner pressure ultrafiltration membrane was used as filter medium. The effect of pressure relief pulse filtration process on reducing membrane fouling and increasing membrane flux was investigated. In order to strengthen the control of membrane fouling, some diatomite filter aids were added to the feed solution for reference to the previous research results. Finally, the concept of critical operating flux is put forward, and the fouling of different processes at higher pressure is investigated to analyze the effect of the proposed process on reducing membrane fouling and increasing membrane flux. The pressure-relief pulse process designed in this paper realizes the purpose of scouring the cake layer on the surface of the membrane. The results show that under the unfavorable condition of pressure loss 22.5%, the membrane flux is increased 14.9% compared with the traditional pulse-free filter by reducing the filter cake layer. The results show that this process plays an active role in the control of membrane fouling and makes up for the decrease of membrane flux caused by pressure loss. It is a feasible method for membrane fouling control. Moreover, the process is simple and practical, and is beneficial to industrial application. In order to enhance the control effect of membrane fouling, based on the principle of particle-assisted filtration, it is proposed for the first time to control membrane fouling by adding diatomite filter aid to the feed solution. By using the bridging effect of diatomite on the micropores of the membrane surface, a relatively loose cake layer is formed, which prevents pollutants from forming a dense cake layer directly on the surface of the membrane, which leads to the rapid decay of membrane flux, and then the strong shear force generated by pulse. The filter cake layer is effectively scoured to reduce the cake layer resistance and to improve the membrane flux. The results show that, by coupling diatomite and pulse process, the resistance of cake layer is reduced by 24.5%, and the percentage of total filtration resistance is reduced from 72.7% to 67.9% of the original pulse-free process, and the resistance of cake layer is reduced by 24.5% to 67.9% from 72.7% of the original pulse-free process. The membrane flux increased by 33.3%. Compared with the addition of diatomite only, the flux of the membrane increased by 8% and 14.9% respectively, and the flux of the membrane was greatly increased by the combination of diatomite and pulse process, and the flux of the membrane was increased by 14.9% in the combination of diatomite and pulse process. In order to reflect the control of membrane fouling by the proposed process, the concept of critical operational flux is put forward: in the filtration process, the membrane flux increases with the increase of pressure, and when the membrane flux reaches a certain point, the membrane flux no longer increases. The maximum flux point of the membrane is the critical operating flux, and the corresponding operating pressure is defined as the critical operating pressure. The results show that the resistance of cake layer consists of two factors: the compactness of cake layer and the thickness of cake layer. The properties of feed liquid (with or without filter aids) and filtration pressure determine the density of cake layer and the operating conditions (whether there is pulse or not). The length of filter time, etc.) determines the thickness of the filter cake. The combined process of diatomite and pulse can not only improve the compactness of cake layer, but also reduce the thickness of cake layer. Therefore, the operating pressure can be increased and the membrane flux can be higher. Improvement of membrane efficiency: critical operating flux of 65.7 kg 路m-2 路h-1. Compared with the pulse-free process, the critical flux increased by 38.9%, 16.9% and 17.3%, respectively, compared with the addition of diatomite. Compared with the critical flux, the critical flux can more truly reflect the effect of membrane fouling (especially the cake resistance) on the membrane flux, which is more practical than the critical flux.
【学位授予单位】：天津工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ051.893

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