| 摘要: | 於PCDD/F控制技術當中，觸媒處理技術屬於管末控制中唯一對PCDD/F有破壞分解效果，利用觸媒控制煙道氣中PCDD/Fs，戴奧辛會氧化分解達到排放減量的目的，控制戴奧辛的觸媒主要為五氧化二釩觸媒，一般俗稱selective reduction catalystic (SCR) catalyst，戴奧辛物種經過觸媒催化後會以CO2、H2O及HCl的形式排放。本研究將嘗試利用SCR觸媒技術，控制焚化過程中氣相戴奧辛污染物。探討在不同的操作條件下，煙道排放氣體中戴奧辛物種的破壞分解效率與觸媒操作之控制因子，同時也對物種間催化分解的反應作初步研究，期掌握SCR觸媒在操作上之反應特性。 研究結果顯示溫度條件影響1,2,3,4-TCDD與OCDD物種於觸媒表面吸附與脫附之速率；於系統中，較低氯數物種其轉化速率比高氯數物種率為大；操作溫度與副產物之關係，當反應溫度較低時，反應產物較具多樣性，偵測到其他同源物種的機率增加，隨溫度提升偵測到其他同源物之機率也隨之降低，系統對戴奧辛之減毒效果亦與溫度成正相關。反應過程中，氧氣含量對影響物種吸附於觸媒之比例，OCDD物種在氧氣含量0%時吸附比例與供氧10%時相差七倍。影響較為顯著為水氣含量，水氣含量增加提升物種OCDF的去除效率，對去除OCDD則無顯著影響，同時改變OCDD與OCDF物種吸附於觸媒表面之比例，出流氣體中所含物種種類亦受水氣含量影響，反應過程中經由OCDD脫氯生成其他物種之機率增加，水氣含量為10%時，氣體中出現六氯與五氯物種。以戴奧辛物種的毒性當量來看，水氣的添加使觸媒系統對戴奧辛毒性的去除率減低，系統中水氣的存在提高了出流氣體毒性風險。比較OCDD與OCDF兩物種經，OCDD經觸媒反應器反應後，生成其他17種同源物種的機率低於OCDF物種，且於相同條件下OCDF經觸媒催化分解之效率低於OCDD，兩物種在反應器中生成其他PCDD/F同源物之機率以OCDF較為顯著。以戴奧辛物種的毒性當量來看，OCDD與OCDF兩物種經反應後，毒性當量的去除率分別為99.8% 與-51.9%，OCDF經反應後造成毒性當量增加的現象，顯示deDioxin觸媒催化OCDF物種分解之效果較OCDD分解為低。 Selective catalytic reduction (SCR) units are commonly used in coal-fired power plants for controlling NOx emissions. In some municipal waste incinerators (MSWIs), SCR units have also been installed. In the late 1980s, it was incidentally found that SCR also decomposes polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Oxidation of representative congeners of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated debenzofruans (PCDFs), was investigated on commercial V2O5-WO3/TiO2-based catalysts by passing the gas streams containing specific concentrations of PCDD/Fs at controlled temperature and space velocity in this study. A decrease in the amount of PCDD/Fs adsorbed on catalyst with increasing reaction temperature was found for species 1,2,3,4-TCDD and OCDD. The conversion rate of 1,2,3,4-TCDD was faster than that of OCDD. At 200℃, one derivate of seventeen 2,3,7,8-substituted dioxin homologues was detected in downstream flow, but no derivates were found at 250℃. Adding oxygen into the gas stream would lower the quantity of OCDD adsorbed on catalyst. Experiment conducted in the presence of water vapor exhibits a higher removal efficiency of species OCDF than that without water vapor. Three derivates of seventeen 2,3,7,8-substituted dioxin homologues are generated from reactant OCDD, and the concentration of toxic equivalent quantity was higher than that without water vapor. |
