歷經多年的深入研究，學術界對戴奧辛之特性、生成來源及控制技術，已有相當程度之了解。台灣自今年起已開始管制飛灰中戴奧辛之濃度，對於會增加飛灰戴奧辛濃度的活性碳噴入技術已不適合作為最佳可行控制技術。介電質放電技術(dielectric barrier discharge, DBD)已廣泛應用於臭氧之生成及VOCs、PFC等氣體之破壞分解。本研究將DBD應用於高溫(150oC)下，了解該系統之熱穩定性外，並導入含有特定PCDD/Fs濃度之氣流，以了解PCDD/Fs於DBD系統中之分解特性。透過模擬工具(BOLSIG)了解反應器中主要之自由基物種，並推測可能之反應途徑。本研究之介電材料為硼矽玻璃，內徑26.8 mm，內電極直徑3.2 mm及放電長度105 mm。實驗之固定參數包括溫度150oC，空間流速2000 hr-1，施加電壓12 kV及頻率100 Hz，操作參數則改變進流氣體之含氧量(0 % ~ 21 %)及水氣含量(0 % ~ 20 %)。 在放電系統與溫度變化之關係上，隨著溫度由室溫(300K)提高至473K，崩潰電壓由12 kV降至8.4 kV；室溫下的最大施加電壓可大於18 kV，423K下施加電壓為13.5 kV即會產生電弧現象。系統經測試後，於150oC下證實戴奧辛之管線殘留量低於2 %，且施加電壓為12 kV時，可穩定操作達90分鐘。在戴奧辛去除效率與氧含量改變之關係上，無氧狀態之質量與毒性當量去除效率分別為61.3 %及49.9 %；有氧狀態下，改變氧含量對PCDD/Fs之去除無顯著影響，當氧含量由5 %增加到21 %時，質量去除效率由44.9 %降至43.1 %，且毒性當量去除效率介於40.2 %至36.6 %之間。改變水氣含量對戴奧辛去除的影響，當水氣含量20 %時(16.8 %O2)有最佳之去除效率，質量效率與毒性當量效率分別為78.1 %與71.4 %；水氣含量5 %時(20.0 %O2)之質量去除效率最低為37.3 %；水氣含量1 %時(20.8 %O2)之毒性當量去除效率最低為32.1 %。在反應途徑方面，透過BOLSIG模擬於DBD反應器中可能生成之自由基物種，結果顯示由氧氣生成的自由基物種對戴奧辛之去除並不顯著，並推測在無水氣存在下，戴奧辛之去除主要由電子碰撞所貢獻。由氫氧自由基之模擬結果發現其生成速率提高，效率亦隨之提高，顯示氫氧自由基對PCDD/Fs之分解能力顯著。 The characteristics, formation mechanisms and control technologies of dioxin have been studied for many years. In Taiwan, dioxin content in the ash has been regulated by Taiwan EPA since May 2007. Since activated carbon injection causes the increase of dioxin concentration in the fly ash, it is not regarded as the best available control technology. Dielectric barrier discharge (DBD) has been applied for generating O3 and degrading VOCs and PFCs in flue gas, but has not been investigated for its effectiveness in dioxin removal. This study aims to evaluate the characteristics of PCDD/F removal via DBD at elevated temperature (150oC). DBD reactor is made of the borosilicate glass tube with the inner diameter of 26.8 mm. A stainless steel rod with the diameter of 3.2 mm is used as the inner electrode and the length of discharge region is 105 mm. Experimental tests are conducted at fixed temperature (150oC), space velocity (2000 hr-1), applied voltage (12 kV) and frequency (100 Hz), while the concentrations of oxygen (O2) vary from 0 % to 21% and water vapor [H2O(g)] contents vary from 0 % to 20 %, respectively. The breakdown voltage of the DBD reactor investigated decreases from 12 kV to 8.4 kV as the temperature is increased from 300K to 473K. The maximum applied voltage is greater than 18 kV at 300K and decreases to 8.7 kV as the temperature is increased to 453K. Residual dioxin is less than 2 % of the total injected dioxin at 150oC and system can be operated over 90 minutes with the applied voltage of 12 kV. The mass and TEQ removal efficiencies of dioxin are 61.3 % and 49.9 %, respectively, with pure nitrogen as the carrier gas. As the oxygen content is increased from 5 % to 21 %, the mass removal efficiency is reduced from 44.9 % to 43.1 % and the TEQ removal efficiency decreases from 40.2 % to 36.6 %. The PCDD/Fs removal efficiency does not change significantly with the oxygen content in the gas stream. As the water vapor content is increased from 0 % to 20 %, the highest PCDD/Fs removal efficiency is achieved at 20 % (16.8 % O2) and the mass and TEQ removal efficiencies are 78.1 % and 71.4 %, respectively. On the other hand, the lowest mass removal efficiency (37.3 %) is achieved with the water vapor content of 5 % (20.0 % O2) and the lowest TEQ removal efficiency (32.1 %) is achieved with the water vapor content of 1 % (20.8 % O2). Free radicals including OH can be effectively generated in the DBD reactor if the gas stream contains H2O(g) and O2 as predicted by BOLSIG. On the other hand, free radicals generated from O2 are not effective for PCDD/F removal. Removal of dioxin is mainly achieved by electron collision in the absence of water vapor while OH radical is essential for PCDD/F removal for the gas stream containing H2O(g).
