過渡金屬改質椰殼活性碳同步控制燃煤煙氣中多重污染物(Hg0、SOx、NOx)之研究

隨著世界能源需求持續成長，火力發電需求隨之提高，而火力發電已被認知是主要固定空氣污染源之一，其排放污染物中包含重金屬(如汞)和酸性氣體(如氮氧化物與硫氧化物)等。鑒於其對環境的影響，2011年美國通過Mercury and Air Toxics Standards (MATS)，此法對燃煤電廠排放之重金屬汞、酸性氣體和其他有毒物種增加額外的排放限制。吸附法早已被視為控制電廠汞排放之最佳可行控制技術之一，吸附劑之吸附容量、反應動力及成本均為吸附法成功與否之關鍵。本研究使用商用椰殼活性碳搭配不同過渡金屬(5 wt% 錳或5 wt% 銅) 摻雜程序，探討其改質前後椰殼活性碳物化特性與污染物吸附容量之間相關性。結果顯示，經過渡金屬改質後椰殼活性碳之BET底表面積皆呈現下降之趨勢，推測其原因為活性碳表面微孔被過渡金屬鹽覆蓋所致。SEM、XRD結果顯示椰殼活性碳經過渡金屬改質後其外觀分布平整且晶相結構並無重大變化，推測原因為改質方法屬於溫和且無巨大能量介入之含浸方法，以致活性碳表面之過渡金屬並無明顯晶相結構，此觀察結果亦可推斷其改質金屬能均勻分布於椰殼活性碳表面。氮氣與模擬煙氣條件實驗結果指出，金屬改質椰殼活性碳對於汞去除率皆有明顯提升之效果，煙氣環境下反應溫度上升至350 oC仍能維持34.8-87.5%汞去除率，且煙氣環境下汞去除率高於氮氣環境，此結果指出煙氣組成對活性碳去除汞有正面之效益。其中值得注意的是，銅改質活性碳於150 oC及350 oC下具有最高之汞去除率，分別為87.5%及98.9%。由Hg0氧化實驗結果發現環境中存在氨氣(NH3)，會抑制活性碳催化氧化Hg0反應發生。此外銅改質椰殼活性碳具有較高之NO還原效率(3.7%)及導致較低的SO2去除率(14.7%)，同時保有最佳的Hg0去除效益，因此整體而言銅改質活性碳具有最佳之污染物控制潛勢。

關鍵字

汞；含浸；椰殼活性碳；過渡金屬；吸附劑

並列摘要

With the increasing needs for energy sources all over the world, the demand for thermal power is keeping rising. Thermal power is one of the main causes of air pollution since its emissions contain metal contaminants such mercury, as well as acidic gases such as nitrogen oxide and sulfur oxide. In light of such effects on the environment, the US Environmental Protection Agency passed the Mercury and Air Toxics Standards (MATS) in 2011, which is a law that additionally limits the heavy metal and acidic gas emissions along with other toxic pollutants from coal-fired power plants. Absorption has been considered as one of the best techniques to control the pollutants emitted from power plants. The capacity and kinetics of the absorbents, the chemical reactions in gas streams, and overall cost are the key factors to whether or not that absorption can be successful. This research utilizes a commercially available coconut-shell activated carbon paired with various transition metals (5 wt% Mn or 5wt % Cu) in a mixed sequence to investigate its characteristics before and after modification and its capacity to adsorb contaminants. Results showed that after the transition metal modification, the BET surface area of the activated carbon decreased due to the blockage of micropores of the activated carbon by the doped transition metal salt. SEM and XRD results showed that the surface of modified activated carbon was smooth, and the crystal phase of metal oxides were not observed. It is speculated that the modification method was mild and done without using invasive energy; therefore, significant changes in the surface structure of the activated carbon were not occurred. The doped metal oxides can thus be homogenously distributed onto the surface of the activated carbon. The doped metal oxides had marked effects in enhancing the Hg0 removal under both nitrogen and simulated flue gas conditions. At 350 oC, flue gas condition the Hg0 removal efficiency was 34.8-87.5%. Furthermore, Hg0 removal was further increased under simulated flue gas condition as compared to that under nitrogen condition. These results indicate that flue gas components had a positive effect on enhancing the activated carbon's Hg0 removal efficiency. It is worth noting that the activated carbon modified with copper possessed the greatest Hg0 removal of 87.5% and 98.9% at 150 oC and 350 oC, respectively. The presence of NH3 inhibited the oxidation of Hg0. Cu-modified activated carbon also had greater NO reduction of 3.7% and a lower SO2 removal of 14.7%. Consequently, activated carbon modified with copper salt is considered having the greatest potential in simultaneously removing multipollutants from coal-combustion flue gease.

並列關鍵字

Mercury ； Impregnated ； coconut shell activated carbon ； Transition metal ； Adsorbent

參考文獻

李淑莉，台灣地區燃煤發電廠含汞物質流布與管理之研究，碩士論文，國立台北科技大學環境工程與管理研究所，台北，2008。

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過渡金屬改質椰殼活性碳同步控制燃煤煙氣中多重污染物(Hg0、SOx、NOx)之研究

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