||Inorganic particle removal and filtration flux enhancement in seawater desalination pretreatment
||Department of Chemical and Materials Engineering
filtration flux enhancement
||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。
||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.
第一章 緒論 1
1-1 薄膜分離 1
1-2 海水淡化程序 4
1-3 研究動機與目的 6
第二章 文獻回顧 7
2-1 海水中之無機微粒 7
2-2 海水淡化之薄膜結垢因素 8
2-3 海水淡化前處理 10
2-3-1 前處理水質目標 10
2-3-2 傳統前處理 12
2-3-3 薄膜前處理 16
2-4 薄膜過濾之濾速提升 19
第三章 理論 23
3-1 阻力串聯模式 23
3-2 濾餅平均過濾比阻與孔隙度 24
3-3 粒子力平衡方程式 25
3-4 單相流之剪切力理論計算 27
3-5 通入氣體之影響特性 27
3-6 兩相流之剪切力理論計算 28
3-7 迴轉盤力矩與功率 31
第四章 實驗裝置與步驟 32
4-1 濾餅恆壓過濾實驗裝置 32
4-2 掃流過濾實驗裝置 33
4-3 迴轉盤微過濾實驗裝置 34
4-4 瓶杯試驗裝置 35
4-5 實驗設備與分析儀器 36
4-5-1 實驗設備 36
4-5-2 分析儀器 37
4-6 實驗物料 38
4-6-1 實驗藥品 38
4-6-2 實驗濾膜 42
4-7 實驗流程 43
4-7-1 模擬海水之配置 43
4-7-2 瓶杯試驗 46
4-7-3 微過濾實驗 46
第五章 結果與討論 49
5-1 模擬海水微過濾特性 49
5-1-1 透膜壓差對濾速的影響 49
5-1-2 濾餅恆壓過濾操作條件對濾餅性質的影響 52
5-1-3 掃流速度對濾速的影響 56
5-1-4 掃流過濾操作條件對濾餅性質的影響 59
5-1-5 濾液之水質 65
5-1-6 掃流微過濾理論計算 68
5-2 模擬海水之濾速提升方式 73
5-2-1 薄膜孔徑與性質對濾速之影響 73
5-2-2 模組擺設對濾速之影響 77
5-2-3 渠道障礙物對濾速之影響 81
5-2-4 進料方式對濾速之影響 83
5-2-4.1 間歇式進料 83
5-2-4.2 兩相流式進料 84
5-2-5 粒徑對濾速之影響 90
5-2-6 機械葉片對濾速之影響 97
第六章 結論 107
6-1 模擬海水之微過濾特性 107
6-2 模擬海水之濾速提升 107
Fig. 1-1 Fundamentals of membrane and membrane processes. (Fane, 2011) 1
Fig. 1-2 Range of molecular weights and particle or droplet sizes of common materials, how they are measured, and the methods employed for their removal from fluids. (Osmonics Inc.) (Walas, 1988). 2
Fig. 1-3 Schematics of dead-end filtration and cross-flow filtrations. 3
Fig. 1-4 General process for production of fresh water by desalination processes. (Chen, 2010) 5
Fig. 2-1 Schematic diagram showing the interaction of aluminium species with initially negatively charged particles in water. (Duan,Jinming and Gregory, 2003) 13
Fig.2-2 The bridging mode of polymer flocculant. (O’ Melia, 1972) 14
Fig.4-1 A schematic diagram of cross-flow filtration system. 33
Fig.4-2 A schematic diagram of cross-flow filtration system. 34
Fig.4-3 A schematic diagram of rotating-disk dynamic filtration system. 35
Fig.4-4 A schematic diagram of Jar Test system 36
Fig.4-5 SiO2 particle size distribution in artificial seawater. 44
Fig.4-6 The microphotograph of SiO2 particles with 3600 times. 45
Fig.4-7 The TEM images of SiO2 particle in artificial seawater with 30k times. 45
Fig. 5-1 Time courses of filtration flux during dead-end microfiltration of artificial seawater under various transmembrane pressures. 50
Fig. 5-2 Time courses of filtration volume during dead-end microfiltration of artificial seawater under various transmembrane pressures. 51
Fig. 5-3 Comparison of dt/dv vs. v data during dead-end microfiltration of artificial seawater under various transmembrane pressures. 53
Fig. 5-4 The relationships between average specific cake filtration resistance and transmembrane pressure during dead-end microfiltration 54
Fig. 5-5 The relationships between average cake porosity and transmembrane pressure during dead-end microfiltration. 55
Fig. 5-6 Time courses of filtration flux during cross-flow microfiltration of artificial seawater under different cross-flow velocities. 57
Fig. 5-7 The pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under various operation conditions. 58
Fig. 5-8 Filtration resistances in cross-flow microfiltration of artificial seawater under various operation conditions. 59
Fig. 5-9 Effects of cross-flow velocity on the cake weight at transmembrane pressure from 20 to 100 kPa. 60
Fig. 5-10 Effects of cross-flow velocity on the cake height at transmembrane pressure from 20 to 100 kPa. 62
Fig. 5-11 The relationships between average specific cake filtration resistance and transmembrane pressure under different cross-flow velocities. 63
Fig. 5-12 The relationships between average cake porosity and transmembrane pressure under different cross-flow velocities. 64
Fig. 5-13 The relationships between and . 68
Fig. 5-14 Comparisons of cake height between calculated results and 69
Fig. 5-15 Comparisons of filtration flux between calculated results and experimental data. 70
Fig. 5-16 The cake height calculated results under different cross-flow velocities and channel spacing. 71
Fig. 5-17 The filtration flux calculated results under different cross-flow velocities and channel spacing. 72
Fig. 5-18 The pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under different membranes. 74
Fig. 5-19The cake weight in cross-flow microfiltration of artificial seawater under different membranes. 75
Fig. 5-20Filtration resistances in cross-flow microfiltration of artificial seawater under different membrane. 76
Fig. 5-21The pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under different module orientation. 78
Fig. 5-22 FV/FH in cross-flow microfiltration of artificial seawater under different module orientation. 79
Fig. 5-23 The relationships between cake weights and FV/FH in cross-flow microfiltration of artificial seawater under different module orientation. 80
Fig. 5-24 A schematic diagram of Gauze structure 81
Fig. 5-25 The pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater with and without turbulence promoter. 82
Fig. 5-26 The pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under different feeding ways. 83
Fig. 5-27 Comparison of pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under various aeration conditions. 85
Fig. 5-28 Comparison of cake weight in cross-flow microfiltration of artificial seawater under various aeration conditions. 86
Fig. 5-29 Effect of wall shear stress on the average specific filtration resistance of cake under different feeding method. 87
Fig. 5-30 Effect of wall shear stress on the pseudo-steady filtration flux under different feeding method. 88
Fig. 5-31 Effect of wall shear stress on the cake weights under different feeding method. 89
Fig. 5-32 Floc sizes distribution of artificial seawater under different chitosan dose. 91
Fig. 5-33 Mean floc diameter and supernatant turbidity under various dose of chitosan. 92
Fig. 5-34 Comparison of pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under various conditions. 93
Fig. 5-35 Comparison of cake weight in cross-flow microfiltration of artificial seawater under various conditions 94
Fig. 5-36 Particle sizes in artificial seawater under different condition. 95
Fig. 5-37 Pseudo-steady filtration flux in cross-flow microfiltration of artificial seawater under different particle size. 96
Fig. 5-38 The pseudo-steady filtration flux in dynamic microfiltration of artificial seawater under different disk rotation speeds. 98
Fig. 5-39The cake weight in dynamic microfiltration of artificial seawater under different disk rotation speeds. 99
Fig. 5-40 The membrane surface after filtered under different distance between vanes and membrane. (P=20kPa, Q=5×10-6, ω=350rpm)(a)1.5 mm (b) 0.8mm. 99
Fig. 5-41 The relationships between shear stress and disk rotation speeds in dynamic microfiltration of artificial seawater. 101
Fig. 5-42 The relationships between pseudo-steady filtration flux and shear stress in dynamic microfiltration of artificial seawater. 102
Fig. 5-43 The relationships between cake weight and shear stress in dynamic microfiltration of artificial seawater. 103
Fig. 5-44 The power of dynamic filtration under different distances between vanes and membrane. 104
Fig. 5-45 The power and filtration flux calculated results of dynamic filtration under different radius. 105
Fig. 5-46 The ratio of filtration flux calculated results and power of dynamic filtration under different radius. 106
Table 2-1 Seawater quality characterization for preatment. (Nikolay, 2010) 11
Table 3-1 The average specific filtration resistance and filterability. 24
Table 4-1 Constituents of artificial seawater. 43
Table 4-2 The operating conditions used in this study. 48
Table 5-1 Turbidity of permeate. 65
Table 5-2 Quality requirements for RO feed water and Filtrate of this study 67
Table 5-3 The parameters calculated in this study.(SI system) 69
Table 5-4 Permeate turbidity of 0.45 μm MCE membrane. 76
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