| 摘要: | 環保署之統計資料顯示都市垃圾焚化廠飛灰產量有逐年上升的趨勢，因此，如何妥善處理飛灰中戴奧辛，成為亟需解決的問題。本研究先前已建立飛灰批次熱裂解系統，並根據其成果與經驗，建置連續飛灰熱裂解處理系統。測試結果得知當高溫爐溫度控制於500oC時，飛灰熱解區之平均溫度可穩定控制於350oC。當反應器傾斜角度控制為1o、3o及5o時，飛灰於反應器中之停留時間分別為40、25及20分鐘，經熱裂解處理後飛灰中PCDD/Fs之毒性去除效率分別為99.84%、99.76%及99.44%，PCBs部分則分別為99.43%、98.25%及97.26%。研究結果指出隨著飛灰停留時間增加（傾斜角度減小），PCDD/Fs、PCBs之去除效率亦隨之提升。PCDD/Fs毒性去除效率部份，相較於高氯數物種(6-8氯)，低氯數物種(4-5氯)之毒性去除效率較低，顯示脫氯反應亦發生於連續熱裂解反應器中。處理後之飛灰中PCDD/Fs毒性濃度均低於有害事業廢棄物之認定標準(1.0 ng I-TEQ/g)，尾氣中PCDD/Fs濃度亦符合排放標準(0.1 ng I-TEQ/Nm3)。實驗結果顯示飛灰經熱裂解後PCDD/Fs之氣固相分佈主要殘留於固相中，只有少量(< 0.2%)揮發至氣相中。PCBs氣固相分佈部分，未受破壞之PCBs主要揮發至氣相中。添加5%氫氧化鈣於飛灰中，和未含添加劑相同操作條件相比，飛灰中PCDD/Fs、PCBs毒性去除效率皆有顯著提升。 Based on the Taiwan EPA statistics, the amount of fly ash generated by municipal solid waste incinerators (MSWIs) has increased year after year. Therefore, how to properly treat dioxin in fly ash has become an emerging issue. Batch pyrolysis tests for removing PCDD/Fs in fly ash had been conducted. Based on the experiences and results of batch pyrolysis tests, a continuous pyrolysis system is designed and constructed. Preliminary tests indicate that temperature in reactor can be stably controlled at 350oC as working temperature of electric furnace is set at 500oC, and the retention time can be controlled at 20, 25 and 40 minutes, respectively, with the corresponding inclination angle of 5o, 3o and 1o. Results indicate that total TEQ removal efficiencies of PCDD/Fs are 99.84%, 99.76% and 99.44% with 40, 25 and 20 minutes of retention time, respectively. The PCB destruction efficiencies are 99.43%, 98.25% and 97.26%, respectively. Total TEQ removal efficiencies increase with increasing retention time. Furthermore, removal efficiencies of lowly Cl-substituted congeners (4-5Cl) are lower than that of highly Cl-sbustituted congeners (6-8Cl). It may be attributed to the significant dechlorination of PCDD/Fs taking place in the system. Besides, the PCDD/F concentrations of fly ash after treatment with this continuous system are lower than 1.0 ng I-TEQ/g of dioxin-containing standard for hazardous waste and the PCDD/F concentrations of flue gas are lower than 0.1 ng I-TEQ/Nm3. Regarding the distribution of gas- and solid- phase PCDD/Fs, the results indicate the PCDD/F congeners remain in the fly ash are significantly higher than that vaporize into the gas phase after pyrolysis. However, the trend of PCB distribution is opposite. Based on the same operating condition, TEQ removal efficiencies of PCDD/Fs increase as 5% Ca(OH)2 is added into the fly ash for pyrolysis. |
