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Title: | 使用含硫活性碳去除海水煙氣脫硫廢水中液相汞之研究 Removal of Liquid-Phase Hg from Actual Seawater Flue Gas Desulfurization (SFGD) Wastewater by Using Sulfurized Activated Carbon (SAC) |
Authors: | Yun-Hsin Chen 陳韻心 |
Advisor: | 席行正(Hsing-Cheng Hsi) |
Keyword: | 汞,燃煤電廠,海水煙氣脫硫,含硫活性碳, mercury,coal-fired power plant,seawater flue gas desulfurization,sulfurized activated carbon, |
Publication Year : | 2018 |
Degree: | 碩士 |
Abstract: | 燃煤電廠的汞排放一直是備受關注的議題,因汞具有高毒性以及生物累積性,必須進行適當的處理,以免造成環境污染以及人體危害。近年燃煤電廠中的海水煙氣脫硫(SFGD)系統逐漸被廣泛使用,因其利用海水的天然鹼基脫除煙氣中的二氧化硫,並以協同效應捕捉氧化汞,不但可減少石膏的生成,更能降低成本;然而,被捕捉的汞會與硫酸根結合為硫酸汞(HgSO4),與海水一併排入海洋中,或因海水中還原物質的存在,再次被還原為氣態汞逸散至大氣中,導致SFGD除汞效率降低。
本研究使用改質過的含硫活性碳,探討在不同吸附條件下的除汞效率,經由批次試驗得到最佳吸附參數,並討論其中的反應機制。經由物化特性分析可得含硫活性碳比表面積約為765 m2 g-1,含硫量為5.8 wt%;台北林口發電廠近海海域取得之海水汞濃度與氯離子濃度分別為8.4 ng L-1以及18190 mg L-1。研究結果顯示,在初始汞濃度較高的條件下,含硫活性碳除汞效率較佳,反之,在初始汞濃度低於大約5000 ng L-1時,則與原始活性碳沒有太大的差異。pH值測試中發現在pH 7和pH 8時,除汞效率有些微的提升,相對在酸性海水的條件下,pH值的改變對去除率並沒有太大的影響。等溫吸附模擬可得知實驗結果較符合Henry’s模式,且熱力學參數計算得到∆H°= 53.3 kJ/mole, ∆S°= 0.221 kJ/mole, and ∆G≒ -17.1 kJ/mole,證實含硫活性碳吸附海水中氧化態汞為吸熱且自發性反應。而動力吸附模式結果指出,實驗結果較為符合擬二階模式。此外,次氯酸鈉常被用來當作消毒劑添加至海水中,因此將次氯酸鈉加入海水中,探討其對汞去除效率之影響,實驗結果得知次氯酸納會導致含硫活性碳對氧化汞的去除效率大幅下降,另外,從氣相汞測試發現,次氯酸鈉能抑制汞的逸散,表示次氯酸鈉的出現會導致汞與氯離子在海水中形成穩定的錯合物而不易被含硫活性碳所吸附。 Preventing the release of Mercury (Hg) from coal-fired power plants (CFPPs) has been a challenge worldwide. Among the up-to-date air pollution control devices, seawater flue gas desulfurization (SFGD) system has raised great awareness with the privilege of utilizing the natural alkalinity of seawater to neutralize SO2, as well as co-benefit control of dissolved Hg. A great concern thus aroused if the Hg-containing wastewater is directly discharged into the ocean environment without proper treatment. In view of this, sulfurized activated carbon (SAC) was applied in this study and a series of batch experiments were conducted to obtain the optimum adsorption conditions. The variables of aqueous Hg removal efficiency test included SAC dosage, initial Hg2+ concentration, pH value, temperature, and contact time. Besides, the effect of sodium hypochlorite (NaClO) as a disinfectant added in seawater was also evaluated. The specific surface area and sulfur content of SAC were 765 m2 g-1 and 5.8 wt% respectively. The Hg2+ and Cl- concentrations in the seawater obtained from the territorial sea of Taipei Linkou Thermal Power Plant were around 8.4 ng L-1 and 18190 mg L-1, respectively. The experimental results indicated that SAC has better performance for Hg2+ adsorption than raw AC at initial Hg2+ concentration over about 5000 ng L-1 whereas significant difference between SAC and AC at lower initial Hg2+ concentration in seawater was not observed. The pH test reported that Hg2+ removal efficiency was slightly higher at pH 7 and 8 than that in an acid seawater condition. Equilibrium isotherm studies showed that Hg2+ adsorption on SAC was favorable at higher temperature in seawater. In addition, the Langmuir, Freundlich, and Henry’s adsorption models have been applied and the data correlate well with Henry’s model. Moreover, thermodynamic analysis concluded that ∆H°= 53.3 kJ/mole, ∆S°= 0.221 kJ/mole, and ∆G≒ -17.1 kJ/mole, further confirming the endothermic and spontaneous process of Hg2+ adsorption on SAC in the seawater in this study. Kinetic results indicated that pseudo-second order with higher correlation coefficient is the rate-limiting reaction. Last but not least, the addition of NaClO was found to significantly reduce the Hg2+ removal efficiency by SAC yet it also inhibits the reduction reaction of Hg2+ by forming Hg-Cl complex. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/70698 |
DOI: | 10.6342/NTU201802587 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 環境工程學研究所 |
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