海水淡化前處理中之無機微粒去除與濾速提升之研究

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Title:	海水淡化前處理中之無機微粒去除與濾速提升之研究
Other Titles:	Inorganic particle removal and filtration flux enhancement in seawater desalination pretreatment
Authors:	汪書伃;Wang, Shu-Yu
Contributors:	淡江大學化學工程與材料工程學系碩士班黃國楨;Hwang, Kuo-Jen
Keywords:	海水淡化前處理;無機微粒;濾速提升;掃流微過濾;迴轉盤微過濾;desalination pretreatment;inorganic particles;filtration flux enhancement;dynamic microfiltration;cross-flow microfiltration
Date:	2014
Issue Date:	2015-05-04 09:57:47 (UTC+8)
Abstract:	本研究利用純水與無機鹽類配置成模擬海水，再加入二氧化矽粉體模擬海水中之無機微粒。第一個部分使用微過濾裝置分析其過濾機制與濾液水質。實驗結果證實增加透膜壓差與掃流速度皆可有效的提升濾速，但是透膜壓差對濾速提升的效果較明顯，且低壓差下的掃流速度對濾速提升之效果較高壓差下好。高壓差壓下，掃流速度0.5 m/s之濾速比0.1 m/s高約34.4 %，低壓差則能提高72.3%，而透膜壓差100 kPa下之濾速皆比20 kPa時高約130 %以上。利用微過濾可將濾液濁度降至0.5NTU以下，SDI15降至2以下，符合RO入水要求。而利用力平衡方程式與阻力串聯模式解聯立即可預估濾速，其誤差範圍在35 %以內。第二個部分則是使用不同的過濾薄膜、過濾模組或操作方式，試圖得到最佳之濾速提升效果。實驗結果顯示：在微粒濃度高的情況下，可使用孔徑較接近微粒粒徑之濾膜，而疏水膜的過濾通量較親水膜低。在掃流微過濾系統中，改變模組之擺設方向並無法明顯提升濾速。而放置沙網在過濾渠道中做為紊流促進器，其造成的剪切力變化可使擬穩態濾速提升2.8~10 %。間歇式進料法每20分鐘關掉幫浦5秒造成的擾流則可提升0.7~6 %之濾速，但通入氣泡的兩相流動所造成的剪切力並無法有效提升濾速，因為濾餅的平均過濾比阻會因為粒子排列緊密而增加。加入絮凝劑可以有效的提升濾速，但分散劑反而會使濾速下降。在迴轉盤式過濾模組中，葉片距離膜面1.5 mm時，葉片的旋轉會使流體在膜面上形成剪切力， 500 rpm時可提升69 %之濾速。但葉片距離膜面為0.8 mm時，葉片可以直接把濾餅刮除，在500 rpm時能提高143.3%之濾速。利用掃流過濾之經驗式推估迴轉盤之剪切力，並建立經驗式得到葉片半徑對剪切力與濾速的關係，再配合功率的計算，得到使用兩個半徑為0.01m之迴轉盤並配合高轉速與低葉片距離0.8 mm，其單位功率能得到的濾速效益最大。 Using purified Water and inorganic salts to simulate seawater in this study, then add silica powder to simulate inorganic particles in seawater. The first part of this study used microfiltration apparatus analyzing filtration mechanism and quality of filtrate. The experimental results confirm that the enhancement of transmembrane pressure and cross-flow velocity could improve the filtration rate, but the effect of the transmembrane pressure was more obvious than cross-flow velocity.Using high cross-flow velocities to enhance filtration rate under lower pressure was more effectively then higher pressure. Under low pressure, the filtration rate of cross-flow velocity 0.5 m/s to 0.1 m/s was enhanced about 72.3%, but high pressure just increase 34.4%, while the filtration rate under 100 kPa was higher than 20 kPa about more than 130%. The turbidity of filtrate could be reduced to below 0.5 NTU, and SDI15 less than 2, conform to the requirements of the water into the RO. Using of force balance model associated with basic filtration equation could estimate the filtration rate, the relative deviation of filtration rates between estimated results and experimental data is less than 35%. The second part used different filtration membrane, filtration modules or operating mode, trying to get the best method to improve the filtration rate. The experimental results showed that: At high particle concentrations, the membrane pore size could be close to particles size. The filtration flux of hydrophobic membrane was lower than the hydrophilic membrane. In the cross-flow microfiltration system, changing the orientation of module could not improved filtration rate. Putting spacer in the filter channels as turbulence promoters, the increasing shear stress could improve the filtration rate about 2.8 ~ 10%. Intermittent feeding method that every 20 minutes stopping the pump 5 seconds could enhance the filtration rate about 2.8 ~ 10%, but the two-phase flow unable to enhance the filtration rate effectively, because the particle packing becomes more regular and more compact under two-phase flow cause the higher average specific cake filtration resistance. Adding flocculants could effectively improve the filtration rate, but dispersing agent will make filtration rate decrease.In dynamic filtration module, when the distance between vanes and membrane surface equal to 1.5 mm, the shear stress acting on membrane surface caused by vanes rotation could improve the filtration rate 69% while rotational speed was 500 rpm, but when the distance was equal to 0.8 mm, the vanes could scrape the cake to improve the filtration rate 143.3 % while rotational speed was 500 rpm. Using cross-flow filtration empirical formula to estimate the shear stress of dynamic filtration, and establishing the relationship between the radius of vanes, shear sress and filtration rate, moreover, coupled with the power of calculation, could get the results that use two dynamic filtration modules which with the vanes of radius was 0.01m, and with high speed, low vanes distance 0.8 mm, the filtration rate per unit power efficiency can be maximized.
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