薄膜蒸餾於溶液氨氮移除之模擬與實驗探討

Simulation and experimental study on ammonia removal from solution by membrane distillation

陳銘豪(Ming-Hao Chen)

指導教授 ： 莊清榮

中原大學/工學院/化學工程研究所/碩士(2020年)

https://doi.org/10.6840/cycu202000310

摘要

水體中氨氮濃度過高，會造成環境優氧化，致使水中生物大量死亡，為防止此問題發生，現今已發展出許多技術來去除水中氨氮，其中薄膜蒸餾技術(Membrane Distillation)因操作不受限於廢水中氨氮濃度高低，且在單位體積下能提供較大接觸面積等特性，應用於氨氮移除甚有發展潛力。
本研究建立直接接觸式薄膜蒸餾(DCMD)及真空式薄膜蒸餾(VMD)之氨氮移除模擬程式，探討不同操作條件下，對通量、質傳係數及進料槽內氨氮濃度之影響，並與文獻實驗數據進行比較。並建置一VMD實驗系統，於改變進料溫度及pH值下進行實驗，分析進料槽內氨氮濃度及總質傳係數(Overall mass transfer coefficient)之變化，並與模擬結果相比較，也同時估算其選擇率以及產出之氨水濃度。
於DCMD及VMD模擬中，當進料pH值增加時，模擬之總質傳係數會隨之上升，但pH大於11後總質傳係數變化便趨於平緩，模擬結果與文獻實驗數據之差距介於1~7 ％間。增加進料溫度時，模擬之通量及總質傳係數會隨之增加，且與文獻實驗數據之差距小於10 ％，在相同操作時間下，進料槽內氨氮濃度下降程度(或氨氮移除率)會隨溫度上升而增加。增加進料濃度時，雖模擬之氨氣通量會增加，但總質傳係數並無明顯變化，而此現象也曾在相關文獻中提及。在VMD模擬中，滲透端壓力上升時，模擬之通量會隨之下降，此現象與文獻實驗結果頗為相符，於相同的操作時間，氨氮移除率會隨滲透端壓力上升而下降。當進料流速增加時，模擬之通量也會增加，與文獻實驗數據相差1~4 ％間，而操作時間相同時，氨氮移除率會隨進料流速增加而上升。
根據VMD之實驗結果顯示，在進料氨氮濃度為1000 ppm、溫度為45 ℃，及有效膜面積與進料體積之比值 (A/V)為0.012 m-1，而進料pH值由9上升至11時，總質傳係數從0.9×10^-5 上升至"2.2×10^-5 m/s，而在相同操作時間下(3 hr)，氨氮移除率由60增加至99 ％。藉由模擬程式推估選擇率由2.5增至4.2，而滲透端之氨水濃度從2300上升至3700 ppm。當進料溫度由45下降至35 ℃，並將pH值控制於11時，總質傳係數從2.2×0^-5 下降至1×10^-5 m/s，在相同操作時間下(3 hr)，其氨氮移除率由99下降至72 ％。藉由模擬程式，推估選擇率會從4.2上升至10.5，而滲透端之氨水濃度從3700上升至9600 ppm。

關鍵字

薄膜蒸餾 ； 氨氮移除 ； 模擬預估

並列摘要

Ammonia removal from wastewater is a topic of continuous concern around the world because it causes eutrophication. Many technologies so far have been developed to remove ammonia nitrogen from wastewater. Among them, membrane distillation (MD) technology is less restricted in the concentration of ammonia nitrogen in wastewater. Despite many experimentally studies in ammonia removal from aqueous streams by MD, little attentions has been given to theoretical analyses for the effects of membrane properties and operation conditions on the flux and selectivity for ammonia removal. The objective of this study is to analyze the effects of membrane characteristics and operating conditions on the performances of ammonia removal from aqueous streams by membrane distillation.
In this study, simulation programs for ammonia removal by direct contact membrane distillation (DCMD) and vacuum membrane distillation (VMD) were established to simulate the flux, overall mass transfer coefficient and ammonia removal (%) etc., and also compared with the experimental data from literature. In addition, a flat-sheet VMD experimental system was set up to analyze the time-dependent removal fraction in batchwise operation and overall mass transfer coefficient under different feed temperatures and pH values. The separation selectivity of ammonia was also estimated by simulation.
Simulation results showed that the overall mass transfer coefficient increases obviously at the range of pH 9~11, and then its value tends to be gentle when the pH is greater than 11. The relative difference between the simulation results and the experimental data from literature is ranging from 1 to 7%. With regard to the influences of feed concentration and feed temperature on flux and ammonia removal (%), the relative differences between the simulation results and the literature data is also less than 10 %. Therefore, the feasibility of the simulation program established by this study can be verified.
The experimental results of VMD using flat-PTFE membrane with feed of 1000 ppm ammonia and temperature 45 ℃ showed that the overall mass transfer coefficient increases from 0.9 to 2.2× 10^-5 m / s when the pH was increased from 9 to 11. The increased pH will also lead the ammonia removal (%) increasing from 60 to 99% for three hours batchwise operation under the ratio of effective membrane area to feed volume (A/V) of 0.012 m-1. Simulation based on the experimental conditions showed that the separation selectivity at pH 11 increases from 2.5 to 4.2 and the ammonia concentration of permeated stream increases from 2300 to 3700 ppm for three hours operation. If the feed temperature was reduced to 35 ℃，the selectivity increases from 4.2 to 10.5 and the ammonia concentration in the permeate stream increases from 3700 to 9600 ppm for three hours of batchwise operation.

並列關鍵字

Membrane distillation ； Ammonia removal ； Simulation

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