利用活性碳捕捉模擬脫硫廢水中之氧化態汞研究

濕式煙氣脫硫系統(WFGD)，可去除煙氣中95%以上的Hg2+，但在某些條件下，最初被WFGD系統所捕捉的Hg2+會再再還原以元素汞的型態再釋放進入大氣中，造成二次汙染，導至WFGD脫汞效率的降低。本文以濕式煙氣脫硫漿液中Hg2+易被還原並再釋放進入大氣，造成二次汙染為出發點，並針對活性碳捕捉模擬脫硫漿液中之汞，觀察其捕捉效率及是否會再釋放進行探討。本文亦同時介紹燃煤過程中汞的遷移轉化特性及汞汙染控制技術，並著重描述現有空氣污染控制裝置之脫汞特性。本研究利用批次式實驗，經由配置模擬石灰石FGD廢水於100 ml之PE瓶中加入10 mg商業含硫粉狀活性碳進行實驗，再經由過濾固體沉澱物，測量液相中殘留之總汞量及固相所吸附之總汞含量，並搭配控制溫度、pH、SO32-、SO42-來觀察其活性碳之吸附效果及同步探討等溫吸附、吸附動力模式，及熱力學分析。研究結果顯示，粉狀活性碳比表面積為940 m2 g-1，含硫量為4.6%，其活性碳內微孔隙結構之比表面積較多，有利於活性碳吸附效率。且經由熱力學分析，判斷其主要為物理吸附為主。不同pH值下，含Cl-溶液中，活性碳之吸附量隨pH上升而下降。而在三種等溫吸附模擬中，在45℃、60℃時較符合Temkin等溫吸附模式R2皆為0.99，而在30℃時則較符合Langmuir等溫吸附模式其R2值亦為0.99。動力吸附模式結果指出以擬二階之R2值較高，但比較SSE值及將理論吸附量與實際吸附量進行探討，發現擬一階吸附模式較符合實驗結果。而在不同SO32-濃度中的試驗，活性碳的汞吸附量隨SO32-濃度升高而上升，與SO32-在不同濃度下其主要產物型態不同有關。而在不同SO42-濃度下，對活性碳之吸附量僅些微上升，推估可能為SO42-濃度之提高使HgSO4之沉澱增加造成總汞吸附量微幅上升。

關鍵字

濕式脫硫程序；含硫粉狀活性碳；二價汞；亞硫酸鹽；吸附動力模式

並列摘要

Wet Flue Gas Desulfurization (WFGD) can remove over 95% of Hg2+ from flue gases; but under some circumstances, the Hg2+ captured by the WFGD system might be reemitted to the atmosphere in the form of Hg0 that causes secondary pollution and results in the lower efficiency of mercury removal by the WFGD. This study evaluates the Hg2+ removal with WFGD liquid by adding activated carbon and observes both the capture efficiency and the reemission of aqueous mercury. This study also introduces the general characteristics of mercury during the coal-burning process and the techniques of controlling mercury pollution using coventioanl air pollution control devices (APCD). Batch experiments were conducted by preparing simulated limestone FGD wastewater in a 100 ml PE bottle. Powder sulfur-containing activated carbon of 10 mg was subsequently added. After filtering out the sediments, the residual amount of mercury in the liquid phase and the adsorbed amount of mercury in the solid phase were measured. The test varibles included temperature, pH value, SO32- and SO42- concentrations. The adsorption isotherm, kinetics, and thermodynamic parameters were subsequently obtained. Results indicated that the total surface area powder activated carbon was 940 m2 g-1, with 4.6% of sulfur. The high microporosity of activated carbon made it suitable for the adsorption of mercury. Thermodynamic results suggested that physical adsorption is the dominant Hg adsorption mechanism. In a solution containing Cl- with different pH, the Hg adsorption of active carbon decreased with increasing pH values. Simulation results showed that mercury adsorption was better fitted with the Tenkim isotherm (R2 = 0.99) at 45oC and 60oC. In contrast, the mercury adsorption was better fitted with the Langmuir isotherm (R2 = 0.99) at 30oC. Kinetic simulation showed that the pseudo-second order equation can cause a higher R2; however, comparing the value of sum of squares for error and the equilibrium capacities between theoretical and actual amounts of adsorption, the pseudo-first order adsorption model provided better explanation on the experimental data. The adsorption of mercury ascended with an increase of the SO32- concentration, which may be caused from the products generated SO32- concentrations. In contrast, the mercury adsorption with activated carbon only slightly ascended with increasing SO42- concentrations. The increase in SO42- concentration may cause the increase of HgSO4 precipitate, which resulted in the minor increase of total adsorption of mercury.

並列關鍵字

WFGD ； Sulfur-containing activated carbon ； Hg2+ ； Sulfite ； Adsorption Kinetic Model

參考文獻

朱國偉，濕式排煙脫硫最佳成本函數之探討，碩士論文，環境工程學研究所，國立臺灣大學，台北，2008。

凃信祈，銅鹽含浸改質活性碳纖維氈去除燃煤煙道氣中氣相汞之可行性探討，碩士論文，環境工程與管理研究所，國立台北科技大學，台北，2011。

陳銘宗，海水煙氣脫硫吸收效率研究，碩士論文，環境工程與科學系，國立屏東科技大學，屏東，2008。

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Boehm, H. P., “Some Aspects of the Surface Chemistry of Carbon Blacks and Other Carbons,” Carbon, vol. 32, no. 5, 1994, pp.759-769.

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利用活性碳捕捉模擬脫硫廢水中之氧化態汞研究

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