廢棄物衍生Thermite熔融劑處理焚化飛灰-反應機制及重金屬移行之研究

楊敏鑫(Min-Hsin Yang)

指導教授 ： 王鯤生

國立中央大學/工學院/環境工程研究所/碩士(2006年)

摘要

本研究利用工業下腳料鋁屑和電弧爐集塵灰當作Thermite衍生熔融劑處理都市垃圾焚化飛灰，探討在不同反應氣氛下鋁屑與電弧爐集塵灰之反應最佳配比，並利用最佳配比熔融處理焚化飛灰，探討不同氣氛下及飛灰添加量對重金屬移行之影響。
為了更進一步瞭解Thermite衍生熔融劑之反應路徑，本研究首先利用熱力學軟體計算反應自由能，並推估產物中可能存在之物種。研究結果顯示，添加都市垃圾焚化飛灰後，Thermite產物的反應路徑受氯的影響有些不同，各金屬形成氯化物之潛能遠大於形成氧化物，而大部分氯化物的揮發特性較大，因此飛灰的添加使重金屬在氣相中的移行會增加。當反應溫度在1500～2000℃之間時，熔渣中以NiO、Cr2O3、ZnO、CuO、Cu2O、PbO、CdO為較穩定的物種，在氣相的部分則PbCl2(g)、PbO(g)、Cd(g)、ZnCl2(g)、CdCl2(g)為較穩定之氣相物種。
電弧爐集塵灰添加不同鋁屑劑量進行最佳配比試驗，實驗結果顯示，ψ＝0.47為為本研究中鋁屑和電弧爐集塵灰之最佳配比。此配比在氮氣和空氣下反應均有最高的反應溫度，氮氣下為1873℃，空氣下為2082℃。空氣下金屬錠之重量回收率為30％，氮氣下之回收率為15％，氣氛並不會影響金屬錠中鐵的純度，空氣下與氮氣下鐵純度分別為80.44％和83.43％；鐵在金屬錠中的移行率分別為91.15%和65.94％。
鋁屑與電弧爐集塵灰之最佳配比ψ=0.47（60克電弧爐集塵灰和27.73克鋁屑）添加不同劑量之飛灰後，反應溫度隨飛灰添加量而降低，空氣下與氮氣下最大的飛灰添加量均為40克。反應後熔渣毒性特性試驗均符合法規標準，鋅在氮氣下的溶出較低，可能為鋅在氮氣下的揮發量增高所致。各重金屬在空氣下和氮氣下均以添加20克飛灰時溶出量最低，且熔渣之比重及含水率也最低，顯示在此配比下熔渣孔隙率較小，緻密度較佳且包覆重金屬的能力較佳。比較重金屬移行特性，主要移行金屬錠中的金屬為鉻、銅和鐵，鉛和鎳為中度揮發性金屬，移行至氣相和熔渣中各半，鋅和鎘則屬易揮發性金屬，容易逸散至氣相中。在添加少量飛灰，反應溫度較高時，鉛、銅、鎘、鋅、鎳較易揮發並吸附在二次飛灰上。矽、鈣、錳、鉀、鈦、鋁等元素移行率均不高，主要會分佈在熔渣中；空氣和氮氣下，部分的矽、鈦和鋁會移行至金屬錠中，部分的錳在氮氣下會移行至金屬錠中。

關鍵字

Thermite ； 電弧爐集塵灰 ； 飛灰 ； 氣氛 ； 重金屬移行

並列摘要

This study investigated the feasibility of municipal solid waste incinerator (MSWI) fly ash melting by industrial waste Al dross and electric arc furnace (EAF) dust as a waste-derived-Thermite (WDT) reaction. The best ratio of Al dross and EAF dust are examined under different atmospheres. The fate of heavy metals is discussed by varying fly ash content and atmospheric compositions.
The Gibbs energy was calculated to confirm between experimental results and prediction by a thermodynamic model. The results indicated that speciation and partitioning of heavy metals are affected by the presence of chlorides. As the reacting temperature varies from 1500℃ to 2000℃, the most stable species in the slag are NiO, Cr2O3, ZnO, CuO, Cu2O, PbO and CdO, and the most stable species in the flue gas are PbCl2(g), PbO(g), Cd(g), ZnCl2(g), and CdCl2(g).
The best ratio of Al dross/EAF dust yielding the maximum of heat is 0.47 by weight. The maximum temperature of the WDTs reaction is 2082℃ under air, and 1873℃ under N2. Ingots presented 30% of the reaction output in air, and 15% in N2. The purity of iron in the ingot are 80.44% and 83.43% under air and N2, respectively. Partitioning of Fe in the ingot are 91.15% under air and 65.94% under N2, respectively.
The self-propagating characteristics of the Thermite treating MSWI fly ash was evaluated by varying the fly ash content in the starting mixture (27.73g Al dross/ 60g EAF dust) from 10g to 40g. The results indicate that the content maximum of fly ash less than 40g at this ratio. The reaction temperature decreased with increasing fly ash content. The slag recovered showed stable vitrified structure with lowest TCLP leaching concentrations of heavy metals complies with current regulatory thresholds at 20g fly ash added. The partitioning of heavy metals was determined in this study. Cr, Cu and Fe mainly transferred to the ingot. Pb and Ni mainly transferred to flue gas and slag. Zn and Cd evaporate to flue gas easily. Pb, Cu, Cd, Zn and Ni evaporate easily and adsorbed by secondary fly ash at higher reaction temperature.

並列關鍵字

Thermite ； EAF ； fly ash ； atmosphere ； partition of heavy metal

參考文獻

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