臺灣博碩士論文加值系統

薄膜蒸餾至今已經發展了四十餘年，在水資源缺乏及能源成本增加的時代，薄膜蒸餾受到廣泛注意。本研究首先以管膜模組來進行模擬預估，模擬一開始就針對不同進料溫度、進料濃度及進料流速進行模擬，並與文獻上之實驗數據作比較，其預估之誤差值都約小於11%，表示此程式所預估之通量都能與實驗數據值符合，接著分析不同管膜之管長對於通量及效率之影響，當管膜長度增加，其通量會隨之下降，而效率值也是會隨管模膜長增加而減少。
另外，在模擬方面也作了平板膜面上濃度極化之模擬，在高溫70℃，進料溶液為高濃度24wt% NaCl，其膜面濃度高達27.3 wt%，接近NaCl的飽和濃度，因此進料在高溫高濃度的情形下，操作時不僅要注意濃度極化現象，也要考慮膜面積垢之問題。
在膜積垢方面，針對進料端不同溫度及濃度做了SEM-EDS的分析探討，首先從進料端不同溫度的結果顯示，經24小時實驗測試，在高溫70℃下通量衰退了約51%，表示膜面上已有大量積垢，而且此積垢大概都是碳酸鈣之結晶，另外吾人也使用飽和指數(saturation index, SI)及濃度極化來分析膜面上結垢之情形，在高溫70℃時，其碳酸鈣的飽和指數約在144.75，表示膜面已形成碳酸鈣之積垢層，使通量嚴重衰退。
在進料端不同濃度之情形下，在進料端高溫70℃，仿海水淡化之高濃縮液15wt%下(NaCl:14.5wt.%, MgSO4:0.185wt.%, MgCl2:0.115 wt.%, CaCl2:0.08 wt.%, NaHCO3: 0.12 wt.%)，經24小時實驗測試通量衰退了約58%，經SEM-EDS的分析後，其大部分之積垢有氯化鈉、碳酸鈣及硫酸鈣等結晶，而且多為細小且緻密之型態，容易阻塞膜孔，因此通量才會嚴重衰退。
添加抗結垢劑的結果分為兩部分，一是直接添加抗結垢劑，另一是20個小時後再添加清洗，前者添加的劑量為0.1、0.5及1 wt%的檸檬酸，經24小時實驗後，通量都能保持在80~90 kg/m2.hr之間，但在較高劑量的情況下，其鹽阻擋率會下降，表示說檸檬酸特性可能會降低膜面之疏水性，造成膜孔潤濕現象。而後者添加劑量為0.1及0.5 wt%的檸檬酸，在20小時實驗後加入進料桶，其結果顯示通量會回復提升，但鹽阻擋率會大幅下降，這表示說先前膜面之積垢物可能有些已結晶在膜孔裡，經檸檬酸清洗過後而使膜孔潤濕，導致鹽阻擋率下降，因此在添加檸檬酸清洗的過程中，要注意檸檬酸添加之劑量。

Membrane distillation (MD) has been studied over 40 years, however, there is still very few applications in industries due to the concern of high energy consumption and lack of knowledge in scaling effect of the process. It is important to get a better understanding of the mechanism of membrane scaling and how to limit scaling for MD desalination. In the study, DCMD of tubular membrane module was simulated first and compared with the experimental data from literatures under different feed temperature, feed concentration and feed flow. The differences between both are less than about 11%, which means that the simulation program is feasible to estimate DCMD flux in tubular modules. Then the effect of hollow fiber length on permeate flux and thermal efficiency was also simulated and the results showed that the average flux and thermal efficiency decrease with the increase of hollow fiber length.
In addition, the concentration polarization of flat-sheet DCMD was also concerned in the simulation to predict the solute concentration near membrane surface. The results based on PTFE membrane showed that when the feed solution of imitation seawater has a high salinity as 24wt.% NaCl and a temperature of 70oC, the concentration near membrane surface will accumulated up to 27.3 wt.%NaCl, which is very close to the saturation concentration of NaCl. Therefore, when the feed solution is of high temperature and high salinity concentration, the concentration polarization will cause the problem of membrane scaling.
Experimental results of synthesized seawater solution(NaCl:3.0wt.%, MgSO4:0.185wt.%, MgCl2:0.115 wt.%, CaCl2:0.08 wt.%, NaHCO3: 0.12 wt.%) at 70 oC with PTFE membrane showed that the initial permeate flux reaches 101.3 kg/m2.hr, but after 24 hours operation the flux has a 51% decline due to a scaling layer formed on the membranes surface. The condition of membrane surface scaling was then evaluated by saturation index based on the concentration polarization analysis. At high temperature 70℃, the saturation index of calcium carbonate is about 144.75, which means that scaling layer formed on membrane surface was dominated by calcium carbonate.
Experimental results of feeding 15 wt % synthesized seawater solution at 70 oC showed that the flux has a 58% decline after 24 hours operation. By SEM-EDS analysis, it was found that the scaling layer containing sodium chloride, calcium carbonate and calcium sulfate crystals, and the crystals morphology are in small size and compact structure, which may block pore and results in a significant flux decline.
In order to investigate the effect of adding antiscalant on the DCMD performance, antiscalants were added with two different ways, one is adding antiscalant into the feed before entering the MD cell and , and the other is adding antiscalant into feed after 20 hours MD operation. The former are with the addition of a dose of 0.1, 0.5 and 1 wt% citric acid, and the flux can be maintained at between 80 ~ 90 kg/m2.hr after 24 hours operation. But in the case of higher doses, the salt rejection will decrease, which means that under the higher dosage may cause some membrane pore wetting. The latter with the addition of a dose of 0.1and 0.5 wt % citric acid after 20 hours continuous operation showed the declined flux will be recovered to close to or higher than the initial stage values, but the salt rejection will be substantially reduced. It is indicated that adding antiscalant to remove the preformed scaling layer will cause wetting of membrane pore.

目錄
摘要 I
Abstract III
誌謝 VI
目錄 VII
圖表索引 IX
圖目錄 IX
表目錄 XIV
第一章 緒論 1
第二章 文獻回顧 5
2-1 薄膜蒸餾概述 5
2-1-1 蒸餾的操作種類 6
2-1-2 薄膜蒸餾之優點 11
2-1-3 薄膜蒸餾的其他應用 12
2-2 薄膜蒸餾之影響因素 15
2-2-1 薄膜性質 15
2-2-2 操作條件 19
2-2-3 模組設計 22
2-3 薄膜蒸餾之積垢問題 29
2-3-1 薄膜積垢之探討 29
2-3-2 積垢預防及處理 32
第三章 理論背景 37
3-1 直接接觸薄膜蒸餾傳輸機制 37
3-2 質量傳輸 40
3-3 熱量傳輸 49
3-3-1 平板模組之熱量傳輸 49
3-3-2 管狀模組之熱量傳輸 53
3-3-3 系統耗能及效率的模擬計算 61
3-3-4 通量與溫度及濃度極化現象之關係 64
3-4 薄膜蒸餾通量模擬預估 65
3-4-1 薄膜蒸餾通量計算流程 65
3-4-2 薄膜蒸餾模擬計算流程圖 71
3-5 薄膜蒸餾之膜面上的積垢 72
3-5-1 薄膜蒸餾之膜面上的飽和濃度 72
3-5-2 膜面上的積垢之成長過程 74
第四章 實驗設備與步驟 77
4-1 實驗材料 77
4-2 實驗裝置 80
4-2-1 直接接觸薄膜蒸餾系統 80
4-2-2 直接接觸薄膜蒸餾模組模組裝置 82
4-2-3 太陽能加熱系統 83
4-3 實驗儀器 84
4-4 分析儀器 85
4-5 實驗步驟 86
4-6 實驗注意事項 88
第五章 結果與討論 91
5-1 管狀膜組之通量模擬預估 91
5-1-1 不同進料端溫度之比較 91
5-1-2 不同進料端濃度之比較 97
5-1-3 不同進料端流速之比較 98
5-1-4 管膜之管長對於通量及效率之影響 99
5-2 模擬濃度極化對通量之影響 103
5-3 進料溫度對於膜積垢之分析 107
5-4 進料濃度對於膜積垢之分析 112
5-5 抗結垢劑對於膜積垢之抑制效果 117
5-5-1 直接添加抗結垢劑之探討 117
5-5-2 抗結垢劑清洗膜積垢效能之探討 121
第六章 結論 125
符號說明 128
參考文獻 132

 
圖表索引
圖目錄
第二章
Fig. 2- 1 Heat and mass transfer in DCMD【Ibrahim等,2012】 6
Fig. 2- 2 Direct contact membrane distillation，DCMD 7
Fig. 2- 3 Air-gap Membrane Distillation ( AGMD ) 8
Fig. 2- 4 Sweeping-gas Membrane Distillation ( SGMD ) 9
Fig. 2- 5 Thermostatic Sweeping-gas Membrane Distillation【Khayet,2011】 9
Fig. 2- 6 Vacuum Membrane Distillation ( VMD ) 10
Fig. 2- 7 Three different types of pore number distribution with an average pore size of 0.2μm (a) Narrow distribution (b) Normal distribution (c) Beta distribution【陳2011】 19
Fig. 2- 8 Feed concentration distribution【Yun等,2006】 22
Fig. 2- 9 Spacer-filled membrane distillation channels【Shakaib等2012】 23
Fig. 2- 10 Schematic diagram of hollow fiber module.【Gabelman和Hwang 1999】 24
Fig. 2- 11 Schematic of (a) air gap membrane module (b) air gap membrane process. 【Singh和Sirkar,2012】 25
Fig. 2- 12 (a) DCMD hollow fiber membranes module; 26
Fig. 2- 13 Schematic of the spiral wound module concept: (1) condenser inlet, (2) condenser outlet, (3) evaporator inlet, (4) evaporator outlet, (5) distillate outlet, (6)condenser channel, (7) evaporator channel, (8) condenser foil, (9) distillate channel and (10) hydrophobic membrane. 【Winter等,2011】 28
Fig. 2- 14 Module channelarrangementforPGMD. 【Winter等,2011】 28
Fig. 2- 15 a. Air inlet connected to the membrane module; b. Air nozzle. 33
第三章
Fig. 3- 1 Temperature profile, solute concentration profile and transport resistances in DCMD.【Martìnez , 2008】 39
Fig. 3- 2 Transport mechanism through a pore of a membrane used in DCMD: (a) Knudsen type of flow and(b) molecular diffusion type of flow【Khatet等 , 2001】 42
Fig. 3- 3 Regions and mechanisms of mass transport the membrane with pore size distribution.【Phattaranawik et al., 2003b】 45
Fig. 3- 4 Heat resistance of DCMD for single membrane 49
Fig. 3- 5 DCMD heat and mass fluxes through boundary layers in hollow fibres (a) and total heat exchanged between feed and permeate (b). 【Bui等 , 2010】 53
Fig. 3- 6 Energy balance on a tubular module. 61
Fig. 3- 7 Schematic representations of the DCMD general concept cells 65
Fig. 3- 8 Flow diagram of the algorithm for the prediction of the permeate flux. 71
Fig. 3- 9 Six main physical aspects to understand membrane scaling. 74
第四章
Fig.4- 1 Process flow diagram of the DCMD system. 81
Fig.4- 2 Schematic diagram of DCMD flat-sheet module. 82
第五章
Fig.5- 1 Effect of inlet feed temperature on permeate flux with pure PVDF membrane. 94
Fig.5- 2 Effect of inlet feed temperature on permeate flux with 30wt%PTFE additive membrane. 94
Fig.5- 3 Effect of inlet feed temperature on permeate flux with 50wt%PTFE additive membrane. 95
Fig.5- 4 Effect of inlet feed temperature on permeate flux with 50wt%PTFE additive membrane fabricated using 0.5-cm air gap. 95
Fig.5- 5 Effect of inlet feed temperature on permeate flux with 50wt%PTFE additive membrane fabricated using 2-cm air gap. 96
Fig.5- 6 Effect of inlet feed temperature on permeate flux with 50wt%PTFE additive membrane fabricated using 4-cm air gap. 96
Fig.5- 7 Effect of salt concentration on permeate flux. 98
Fig.5- 8 Effect of inlet feed flow rate on permeate flux. 99
Fig.5- 9 Effect of hollow fiber length on permeate flux. 102
Fig.5- 10 Effect of hollow fiber length on thermal efficiency. 102
Fig.5- 11 Solubility curves with temperature. 104
Fig.5- 12 Effect of with or without concentration polarization of 3.5wt.% NaCl aqueous solution on DCMD flux. 105
Fig.5- 13 Effect of with or without concentration polarization of 15wt.% NaCl aqueous solution on DCMD flux. 105
Fig.5- 14 Effect of with or without concentration polarization of 20wt.% NaCl aqueous solution on DCMD flux. 106
Fig.5- 15 Effect of with or without concentration polarization of 24wt.% NaCl aqueous solution on DCMD flux. 106
Fig.5- 16 Effect of feed temperature of 3.5wt.% NaCl aqueous solution 109
Fig.5- 17 (a)SEM (b)EDS and (c) mapping micrographs of scaled membrane after 24hr 50℃ DCMD. 110
Fig.5- 18 (a)SEM (b)EDS and (c) mapping micrographs of scaled membrane after 24hr 70℃ DCMD. 111
Fig.5- 19 Effect of feed temperature of 15wt.% NaCl aqueous solution 114
Fig.5- 20 Effect of feed temperature of 15wt.% NaCl aqueous solution 114
Fig.5- 21 (a)SEM (b)EDS and (c) mapping micrographs of scaled membrane after 24hr 50℃ DCMD. 115
Fig.5- 22 (a)SEM (b)EDS and (c) mapping micrographs of scaled membrane after 24hr 70℃ DCMD. 116
Fig.5- 23 Effect of adding citric acid into 3.5wt.% NaCl aqueous solution on DCMD flux decline (CMT ePTFE) 119
Fig.5- 24 Effect of adding citric acid into 3.5wt.% NaCl aqueous solution on DCMD salt rejection(CMT ePTFE) 119
Fig.5- 25 SEM of membrane after 24hrs DCMD with 3.5wt.% NaCl solutions.((a)free membrane.(b)1.0wt% citric acid.(c) 0.5wt% citric acid. (d)0.1 wt% citric acid. 120
Fig.5- 26 Effect of adding Citric acid into 3.5wt.% NaCl aqueous solution after 20 hr on DCMD flux decline. 122
Fig.5- 27 Effect of adding Citric acid into 3.5wt.% NaCl aqueous solution after 20 hr on DCMD salt rejection. 123
Fig.5- 28 (a)SEM and (b)EDS micrographs of fouled membrane from adding 0.1wt% Citric acid into 3.5wt.% NaCl aqueous solution after 20 hr. ….123
Fig.5- 29 (a)SEM and (b)EDS micrographs of fouled membrane from adding 0.5wt% Citric acid into 3.5wt.% NaCl aqueous solution after 20 hr. …124
 
表目錄
第二章
Table 2- 1 Amounts of coagulate found for 100 mg/L humic acid at various conditions.【Surapit, 2005】 31
第三章
Table 3- 1 Heat transfer correlations for 『laminar flow』 57
Table 3- 2 Heat transfer correlations for 『turbulent flow』 57
第四章
Table.4- 1 Specification of solar power collector 83
第五章
Table. 5- 1 Experimental conditions for feeding solution 92
Table. 5- 2 Effect of hollow fiber length on permeate flux and thermal efficiency. 101
Table. 5- 3 Simulation of concentration of the membrane surface. 104
Table. 5- 4 The simulated concentration and saturation index of CaCO3 on the membrane surface and bulk solution. 108
Table. 5- 5 The simulated concentration and saturation index of CaSO4 on the membrane surface and bulk solution. 108

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