以微波穩定焚化飛灰及其重金屬揮發控制之探討

Abstract

台灣每年約產生23萬噸焚化飛灰，垃圾中之重金屬於焚化處理過程中不會被破壞分解，以致於大多數重金屬均殘留其中，經過毒性特性溶出程序後其鉛溶出濃度高於法規標準，因此仍有危害環境之風險存在，須經過適當穩定化、安定化處理後始能進行再利用或最終處置。焚化飛灰之安定穩定化技術主要可分為固化及熔融兩大類，水泥固化法雖為最常用之處理方法，但由於處理後之固化體積增大，且仍須進入掩埋場做最終處置。而熔融法則需耗費大量之能源而造成成本上升。因此本研究利用微波特性作為飛灰安定化之處理程序，且收集逸散之重金屬燻煙，探討其金屬逸散性，即利用固相及氣相兩相之分析求取質量平衡，並配合毒性溶出試驗，以期達到飛灰安定穩定化之目標。 微波穩定化技術係藉由微波功率、反應時間之控制參數來增加焚化飛灰之穩定化效果並求得其最佳操作條件。另外，並在微波氣體出口端進行排放管道中重金屬檢測，以探討其重金屬逸散性；再配合毒性溶出試驗、總量消化及化學序列萃取等，探討及證明其安定穩定化。最後再比較傳統高溫爐與微波加熱處理飛灰所消耗之能量多寡，以求得降低能源之目的。 結果顯示，於微波功率500瓦，隨著照射時間增加，可有效降低鎘、銅及鉛之溶出濃度；鉻溶出濃度雖隨時間有上升趨勢，但仍低於法定溶出標準(5 mg/L)。於照射時間30分鐘，隨著微波功率之上升，可有效降低鎘、銅及鉛之溶出濃度；鉻溶出濃度雖無明顯趨勢，但仍低於法定溶出標準。進行微波穩定化技術過程中，僅有4~5%之鉛逸散至空氣中；以符合TCLP溶出標準為基準，飛灰進行微波穩定化技術之最佳操作參數為微波功率500瓦、照射時間10分鐘，鉛之溶出濃度為3.5 mg/L；亦是鉛逸散量最低之操作條件，氣相逸散量為4.3%，固相穩定量為101.5%。若在TCLP中鉛溶出濃度均為2.16 mg/L左右時，微波穩定化技術相較於高溫爐熱處理可節省較多能源，所需時間減少為1/6，且安定穩定化效果較佳。綜合以上所述，微波穩定化技術過程中，於氣相端無明顯逸散，固相端亦有穩定化效果存在，效率上也提升許多，故可證實微波穩定化技術之可行性。

Municipal Solid Waste Incinerators (MSWI) in Taiwan generates 230,000 tons of fly ash annually. Many heavy metals in the waste will not be degraded or oxidized and they may end up in ashes. The ashes may need to be stabilized before reuse or disposal because heavy metal concentrations in the leading solution of Toxicity Characteristic Leaching Procedure (TCLP) may exceed the regulatory limits. Stabilization of MSWI fly ash can be divided into two common methods: solidification and thermal treatment. Solidification has a disadvantage of increasing waste volume, which would shorten the service life of landfills. On the other hand, thermal treatment consumes a lot of energy. In this study, microwave was used to stabilize MSWI fly ash. Gas samples were collected and analyzed during microwave radiation to determine the extent of fugitive the emission of heavy metals. Experiments were conducted to determine the optimal operating parameter conditions in terms of microwave power and reaction time. The decision was made based on the extent of stabilization as well as the amount of all emission. The energy consumption of the microwave irradiation was compared with that of conventional heating. The results showed at a power setting of 500 watts, microwave irradiation, can effectively reduce the leaching concentrations of cadmium, copper and lead, and the performance improved with reaction time. Chromium leaching concentration increased with reaction time, but still below the regulatory limit of 5 mg/L. Time of 30 minutes, the leaching concentrations of cadmium, copper and lead decreased with microwave power, but there was no obvious trend for chromium. For all the conditions tested, the optimum operating parameters were found to be microwave power of 500 watts and reaction time of 10 minutes. The lead leaching concentration was 3.5 mg/L, gaseous emission of 4.3%, and solid-phase stability of 101.5%. When compared to conventional heating, microwave irradiation consumed less energy and required 1/6 of the reaction time.