| 摘要: | 戴奧辛自污染源排放後係以氣相及固相之方式分布於大氣環境，因此系統性地對污染源煙道排氣及大氣環境中戴奧辛的氣固相分布特性進行深入之研究確有其必要性。就污染物控制的角度審視這個問題，若無法實際釐清氣固相戴奧辛之生成途徑以及控制機制，現場之操作單位或政策主管機關將無法有效控制污染排放並擬定適當之管制策略。本論文嘗試探討煙道氣中戴奧辛之氣固相分布，以釐清戴奧辛各物種於污染源中之去除機制，並瞭解污染源周界大氣中戴奧辛污染物之氣固相分布特性，以釐清大氣環境中戴奧辛之傳輸行為及氣固相轉換特性，藉以評估國內現行之空氣污染控制技術對氣固相戴奧辛物種去除效率之差異，並藉由實廠採樣數據初步建立戴奧辛各物種於煙道氣中之氣固分布推估模式。本篇論文針對國內六座戴奧辛排放源包括二座都市垃圾焚化廠(MWI-1及MWI-2)、二座事業廢棄物焚化廠(IWI-1及IWI-2)、電弧爐煉鋼廠(EAF)以及電弧爐集塵灰資源回收廠(Waelz plant)進行氣固相戴奧辛煙道採樣及分析工作，研究結果指出，各污染源煙道氣中氣固相戴奧辛之去除效率亦隨其使用之APCDs不同產生變化，進而影響戴奧辛於煙道氣中之氣固相分布。當煙道氣分別經過旋風集塵器(CY)及袋濾式集塵器(BF)後，煙道氣中70%以上之戴奧辛分布於氣相，而活性碳注入技術(ACI)搭配BF其對煙道氣中固相戴奧辛之去除效率高於氣相，使得煙道氣中之氣相戴奧辛由70％上升至90%以上，另外使用選擇性還原觸媒反應器(SCR)則可有效將煙道氣中之氣相戴奧辛予以破壞去除。由於污染源控制設備對戴奧辛去除機制之不同，將改變煙道氣流中戴奧辛之氣固分布特性進而對整廠之戴奧辛排放量造成影響，使用SCR作為戴奧辛控制設備之MWI-2其整廠戴奧辛排放量僅為使用ACI之MWI-1的三分之二，而都市垃圾焚化廠之戴奧辛排放量95％以上皆分布於飛灰及反應灰中，這些含有戴奧辛污染物固體廢棄物可能成為未來環境污染問題的隱憂。此外使用傳統空氣污染控制設備(CY及BF)的戴奧辛排放源，由於其無法有效控制氣相戴奧辛之排放，其戴奧辛排放量將近47%至66％由煙囪排出，其對鄰近地區環境生態的影響值得重視。污染源煙道排氣及周界大氣中之氣固相戴奧辛樣品採樣結果亦指出MWI-1周界大氣中其戴奧辛物種將近80%以上分布於固相，而EAF周界大氣中戴奧辛物種有35%至55%分布於氣相。造成上述差異的原因除了受污染源與大氣測站的距離遠近、大氣中懸浮微粒濃度高低影響之外，污染源所排放出之氣固相戴奧辛濃度分布亦造成相當程度的影響，由於EAF並未配置可有效控制氣相戴奧辛排放之控制設備，進而造成鄰近地區大氣中戴奧辛物種分布於氣相之比率較MWI-1周界地區高。此外研究結果亦指出大氣溫度下降100C時大氣中戴奧辛物種分布於固相之比率將會增加20％，顯示環境溫度之變化對戴奧辛氣固相分布特性之影響值得注意。MWI-1實廠煙道氣採樣結果指出煙道氣溫度之改變將影響氣固相戴奧辛之去除效率，兩者之間雖不具線性相關，但以ACI+BF技術控制氣固相戴奧辛亦存在一最佳操作溫度（1600C）。而本研究所建立之氣相戴奧辛吸附載體測試系統(PAS)分析結果指出當氣流溫度為1500C時，約50％之氣相戴奧辛轉移至固相，當氣流溫度上升至2000C時戴奧辛由氣相轉移至固相之比率則下降至20％，此外該測試結果亦顯示當煙道氣流溫度介於de novo再合成之溫度窗時(2500C)，吸附載體上將會有戴奧辛再生成的現象發生，並揮發至氣流中。 綜觀來說，戴奧辛於煙道氣中之氣固分特性受粒狀物濃度、環境溫度以及空氣污染控制設備形式影響甚巨，故整合實廠採樣結果以及參考相關文獻本論文初步建立戴奧辛污染排放源煙道氣中戴奧辛氣固相之推估模式log (Cv/Cs) =m logP0L+log (c/PM)。該模式可推估煙道氣於高溫爐體出口以及氣流通過旋風集塵器、袋濾式集塵器、乾/濕式靜電集塵器、固定式活性碳吸附塔、活性碳注入以及觸媒反應器後戴奧辛於氣固相之分布係數。經由模式推估結果與實廠採樣分析數據之比對，亦發現其推估結果尚稱理想，但若是煙道氣中粒狀物濃度過高時，其氣固相之分布係數推估結果將明顯高估，此外若煙道氣溫度介於de novo再合成之溫度窗(2500C?4500C)時其氣固相之分布係數推估結果將明顯低估。綜觀來說，此推估模式可初步作為國內探討污染源煙道排氣中氣固相戴奧辛分布特性之參考。 Around 60 to 80% of the seventeen 2,3,7,8-substituted PCDD/F concentrations in the atmosphere are bounded to particles. Partitioning of PCDD/F congeners between vapor and solid phases in flue gas of the PCDD/F emission sources and ambient air in Taiwan are evaluated via stack sampling and analysis in this study. This dissertation emphasizes the understanding of the partitioning and removal efficiency of PCDD/Fs of flue gas at two municipal wastes incinerator (MWI-1 and MWI-2), two industrial wastes incinerators (IWI-1 and IWI-2), one electric arc furnace (EAF) and one Waelz plant equipped with different types air pollution control devices (APCDs). The results indicate that the vapor-phase PCDD/Fs can be emitted from the stack by penetrating through cyclone (CY), bag filter (BF) and electrostatic precipitator (EP) if no effective control device is applied. Vapor-phase PCDD/Fs can be removed by various means including adsorption with carbon-based adsorbents, and catalytic destruction. Compared to the activated carbon injection technology which only transfers vapor-phase PCDD/Fs to the fly ash and would make ash disposal even more complicated, selective catalytic reduction (SCR) system can destroy PCDD/Fs and serves as a better control technology for removing PCDD/Fs from gas streams. The results of the emission from several facilities demonstrate that 99.7% and 0.3% of PCDD/F output in MWI-2 is discharged with EP ash (98.3 µg-TEQ/ ton waste) and stack gas, respectively. SCR system removes and destroys most of the PCDD/F congeners. The emission rate of MWI-1 is much higher than that of MWI-2 caused by the PCDD/F removal efficiencies achieved with different APCDs adopted, resulting in different PCDD/F removal mechanisms. It is noted that total PCDD/F discharge in Waelz plant is 840.3 µg-TEQ/ton EAF-dust, among which 33.3% is discharged with fly ash and needs to effectively reduce PCDD/F formation and install better PCDD/F control devices for the perspective of total environmental management. The results obtained from the ambient air sampling indicate that the mean PCDD/F concentration measured in the vicinity area of the MWI (56~348 fg-I-TEQ/m3) and EAF (61~312 fg-I-TEQ/m3) investigated are lower than the ambient air standard proposed in Japan (600 fg-I-TEQ/m3). The results obtained on vapor/solid partitioning of PCDD/Fs in ambient air indicate that the solid-phase portion accounts for more than 80% of the total concentration in the vicinity area of MWI investigated. Besides, the vapor-phase PCDD/Fs account for 35% to 55% in the vicinity area of EAF investigated. In addition, the temperature and the distance between emission source and sampling site would also affect the partitioning of PCDD/Fs between vapor and solid phases. The results of MWI-1 flue gas sampling indicate that there is optimal operating temperature for PCDD/F removal with ACI. In addition, the results of pilot-scale adsorption system (PAS) experimentation indicate that about 50% and 20% vapor-phase PCDD/Fs transferred to solid phase at Group 1 (1500C) and Group 2 (2000C), respectively. As the temperature is increased to 2500C, de novo synthesis significantly affects the partitioning of PCDD/Fs between vapor/solid phases. Based on results of the partition of vapor/solid-phase PCDD/F achieved with the APCDs applied upstream and the particulate matter concentration in flue gas, this dissertation applies the equation log(Cv/Cs) =m logP0L+log(c/PM) for predicting vapor/solid-phase PCDD/F partition in flue gases downstream various APCDs including CY, EP, BF, wet electrostatic precipitator (WEP), fixed activated carbon bed (FCB), ACI and SCR. As the PM concentration is over 20,000 mg/Nm3 or temperature in flue gas is within the temperature window of de novo synthesis, the log(Cv/Cs) of observed data is significantly higher or lower than the result predicted, respectively. Accordingly, the equation can be used to predict the partitioning of PCDD/Fs between vapor and solid phases in flue gas if de novo synthesis is not significant. |
