【摘要】：為了減輕膜污染,本文基于流體力學(xué)原理設(shè)計了一種泄壓式脈沖過濾工藝。實(shí)驗(yàn)以高污染性醬油作為模擬料液,以聚偏氟乙烯(PVDF)中空纖維內(nèi)壓式超濾膜作為過濾介質(zhì),考察了泄壓式脈沖過濾工藝對減輕膜污染,提高膜通量的效果。然后借鑒前期科研成果,向料液中投加適量硅藻土助濾劑以強(qiáng)化對膜污染的控制。最后,提出臨界運(yùn)行通量概念,考察不同工藝在較高壓力時的膜污染情況,以分析所提工藝對減輕膜污染,提高膜通量的效果。論文所設(shè)計的泄壓式脈沖工藝,實(shí)現(xiàn)了對膜表面濾餅層沖刷的目的。結(jié)果表明該泄壓式脈沖在壓力損失22.5%的不利情況下,通過減薄濾餅層,獲得膜通量比傳統(tǒng)無脈沖過濾方式提高了14.9%。說明該種工藝對膜污染的控制發(fā)揮了積極作用,彌補(bǔ)了因壓力損失造成的膜通量下降,是一種可行的膜污染控制方法。并且,該工藝簡單實(shí)用,有利于工業(yè)化應(yīng)用。為強(qiáng)化對膜污染的控制效果,基于微粒子輔助過濾原理,首次提出通過向料液中投加硅藻土助濾劑強(qiáng)化脈沖工藝控制膜污染。利用硅藻土在膜表面微孔處的架橋作用,形成相對疏松的濾餅層,避免污染物直接在膜表面形成致密濾餅層而導(dǎo)致膜通量迅速衰減,然后再通過脈沖產(chǎn)生的強(qiáng)剪切力,對濾餅層進(jìn)行有效沖刷,從而降低濾餅層阻力,達(dá)到提高膜通量的目的。結(jié)果表明,通過硅藻土與脈沖工藝耦合,濾餅層阻力相對于無脈沖工藝降低了24.5%,其所占總過濾阻力百分比由原來無脈沖工藝的72.7%,降低到67.9%,膜通量提高了33.3%。與僅投加硅藻土助濾劑膜通量提高8%和脈沖工藝下膜通量提高14.9%相比,硅藻土與脈沖組合工藝下,膜通量實(shí)現(xiàn)了大幅度提高。為反映所提工藝對膜污染控制情況,提出了臨界運(yùn)行通量概念：在過濾過程中,膜通量隨著壓力的增大而增加,當(dāng)?shù)竭_(dá)某點(diǎn)后,膜通量不再增加,只是隨著壓力繼續(xù)增大而維持穩(wěn)定甚至下降,此膜通量最大點(diǎn)即為臨界運(yùn)行通量,其對應(yīng)操作壓力定義為臨界運(yùn)行壓力。結(jié)果表明,濾餅層阻力由濾餅層致密性和濾餅層厚度兩個因素構(gòu)成,料液性狀(有無助濾劑)和過濾壓力決定濾餅層致密程度,工況條件(有無脈沖、過濾時長等)決定濾餅層厚度。硅藻土與脈沖組合工藝,既可有效改善濾餅層致密程度,又能減薄濾餅層厚度,因此可以提升操作壓力,獲得更高膜通量,提高膜工效：臨界運(yùn)行通量達(dá)到65.7 kg·m-2·h-1。與無脈沖工藝臨界運(yùn)行通量相比,提高了38.9%；與投加硅藻土條件相比,提高了16.9%；與脈沖工藝相比,膜通量提高了17.3%。與臨界通量比較,臨界運(yùn)行通量可以更真實(shí)的反映膜過濾過程中膜污染(特別是濾餅層阻力)對膜通量的影響,與臨界通量相比,更具實(shí)際意義。
[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.
【學(xué)位授予單位】：天津工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TQ051.893

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