政府近年來積極推動大型都市垃圾焚化爐的興建計劃，至民國93年全國垃圾焚化處理率預估將達90％，然而焚化為戴奧辛之主要來源，焚化廠興建所增加之戴奧辛排放不可忽視，因此發展有效的戴奧辛控制技術提供未來興建焚化爐設計時之參考，實為當務之急。本研究以國內二座運轉中的都市垃圾焚化爐為對象，針對兩座國內都市垃圾焚化爐的APCD（空氣污染控制設備）之前及煙囪排放在典型操作下之煙道氣進行戴奧辛採樣，分析其中17種2,3,7,8鍵結之急毒性戴奧辛，以初步評估既有空氣污染防制設備（APCD）對氣流中戴奧辛之去除效率。A廠配有靜電集塵器與濕式洗煙塔，B廠則為旋風集塵器、乾式洗煙塔及袋濾集塵器。研究結果顯示，在經過APCD之後，各物種的分佈特性並沒有太大的改變，兩廠煙囪排氣中總PCDD/PCDF濃度相距不大，但在APCD前B廠高於A廠2.75倍，顯示A廠在氣流通過APCD之過程中生成了較多的戴奧辛。B廠排放之戴奧辛經過APCD之後其濃度減少，但是A廠卻不減反增，APCD對戴奧辛的去除率為負值，推測可能是由於廢氣通過靜電集塵器（ESP）時的溫度正好處於200~350℃戴奧辛生成的溫度窗口，使得爐外低溫再合成現象嚴重，造成戴奧辛濃度上升，導致戴奧辛去除率成為負值。B廠第一年在分別噴入35.0及37.7 mg/Nm3之活性碳後，戴奧辛排放濃度明顯下降，去除效率由原來之5.88％提升至87.63％及91.28％，但去除效率仍未達應有之水準，可能是由於記憶效應（memory effect）所造成，使得排放管道所殘留之戴奧辛或戴奧辛之前驅物質緩慢釋出，因而增加戴奧辛的出口濃度，造成改良之初的APCD無法達成原先設計之戴奧辛去除效率。而第二年在噴入量43.4 mg/Nm3時去除效率提升至98.6％，活性碳注入量相似而去除效率卻有明顯差距，即為記憶效應逐漸被克服所致。 Due to the rapid increase of municipal solid waste in Taiwan, the government has enacted the policy of building large-scale municipal solid waste incinerators (MWIs) since 1984. The percentage of municipal waste to be incinerated will be greater than 90% after 2004. Because of the incineration of municipal solid waste (MSW) is the most important source of dioxin, the dioxin emission from the MWIs has caused much public concerns. Development of effective dioxin control technology is essential for the successful waste management plan. In this study evaluation of the dioxin removal efficiency of the air pollution control device (APCD) at two existing MWIs in Taiwan is conducted via stack sampling and analysis. MWI-A is equipped with electrostatic precipitators followed by wet scrubbers while MWI-B is equipped with cyclones, dry lime scrubbing systems and fabric filters as APCDs. Results indicate that the patterns of dioxin isomers at APCD inlet and stack are similar for both MWIs. The dioxin concentration at APCD inlet of MWI-B is 2.75 times higher than that of MWI-A, but it’s similar at stack. This indicate that the concentration of dioxins generated at MWI-A is higher than that of MWI-B as the gas stream flows through APCD. Dioxin removal efficiency at MWI-A is negative because the operating temperature of the APCD falls in the de novo reaction window (200~350°C). During the first year of carbon injection, the concentrations of emitted dioxin decrease greatly at MWI-B. The dioxin removal efficiency increases from 5.88% to 87.63 and 91.28 %, respectively compared to the condition without activated carbon injection. At the second year, the dioxin removal efficiency reaches 98.6% after injecting 43.4 mg/Nm3 of activated carbon. The lower efficiency at the first year can be attributed to the memory effect, i.e. the dioxin or precursor desorbs slowly to the flue gas and increases the dioxin concentration at stack, resulting in lower dioxin removal efficiency than expected.
