以釩鈦SCR觸媒轉換元素汞及去除NO與Dioxin之效率探討;Conversion and reduction of multipollutant (Hg0/NO/dioxin) by V2O5-WO3/TiO2 catalysts from simulated flue gas streams of coal-fired power plant

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Title:	以釩鈦SCR觸媒轉換元素汞及去除NO與Dioxin之效率探討;Conversion and reduction of multipollutant (Hg0/NO/dioxin) by V2O5-WO3/TiO2 catalysts from simulated flue gas streams of coal-fired power plant
Authors:	徐瑋廷;Hsu,Wei-Ting
Contributors:	環境工程研究所
Keywords:	元素汞;SCR;多重污染物;戴奧辛;氮氧化物;elemental mercury;SCR;multiple pollutants;dioxins;nitrogen oxides
Date:	2015-08-27
Issue Date:	2015-09-23 15:30:31 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究旨在建立含汞氣流產生系統，以測試不同氣流條件下傳統SCR觸媒針對元素態汞之轉化效率，並進一步掌握NO轉化率及戴奧辛之去除效率。實驗室測試結果指出氣流中添加NH3/NO會降低V2O5/WO3/TiO2觸媒對汞的轉化能力，而隨V2O5/WO3之含量增加汞之轉化效率明顯上升。此外，本研究進一步模擬實廠煙道氣之條件，於氣流中添加水氣、HCl、CO2、SO2等，結果指出三種板狀觸媒中，以V0.26W3.05TiO2觸媒對汞與NO轉化率較差，V1.52W5.11TiO2觸媒具有最佳的汞轉化效率。測試結果顯示元素態汞濃度降低時其轉化效率亦隨之下降，當入口汞濃度為6 g/m3時，V0.26W3.05TiO2觸媒之轉化率最低，僅有6%，推測該觸媒較容易受到水氣及質傳限制影響而抑制其汞轉化效率。為了探討實廠添加HCl與否之影響，本研究亦測試未添加HCl時之元素汞轉化率，結果顯示元素汞之轉化效率明顯下降，主因是無氯源之情況下，元素汞不易吸附於觸媒表面進行轉化；此外，隨著HCl濃度提升觸媒汞轉化活性明顯上升，當HCl添加濃度超過25 ppm時，三種觸媒的汞轉化活性僅些微提升。比較V1.52W5.11TiO2與V0.26W3.05TiO2觸媒，V1.52W5.11TiO2觸媒在汞轉化效率、De-NOx及De-dioxin皆優於V0.26W3.05TiO2，未來須審慎評估不同觸媒之適用性及組成成分的影響。戴奧辛去除效率測試結果顯示，V0.26W3.05TiO2觸媒、V0.66W5.86TiO2及V1.52W5.11TiO2觸媒對戴奧辛之去除效率分別達50%、57%及65%。值得注意的是高氯數戴奧辛物種去除效率普遍高於低氯數戴奧辛物種，初步推測係觸媒在較高之空間流速（34000 hr-1），對於高氯數物種的脫氯不完全導致低氯數物種有生成之情形。本研究亦測試擔載V2O5/WO3/TiO2觸媒之濾布，在添加水氣之條件下，其元素汞、NO轉化率為53%、47%。此外，利用積分型反應器結合Eley-Rideal mechanism求取釩鈦板狀觸媒應用於元素汞轉化的活化能(Ea)和碰撞因子(A)，經由實驗數據計算結果顯示，此類觸媒的活化能為10.7-14.2 kJ/mole，而碰撞因子為25.2-39.0 sec-1。;This study aims to investigate the effectiveness of selective catalytic reduction (SCR) V2O5-WO3/TiO2 catalysts for the conversion or removal of multi-pollutant (i.e., Hg0/dioxin/NO) from simulated flue gas streams of coal-fired power plant. A continuous mercury-containing gas stream generation system is established for evaluating the conversion efficiency of elemental mercury by various catalyst. The variation of inlet Hg0 concentrations is within two standard deviations. Experimental results indicate that the conversion efficiency of elemental mercury is reduced by adding NH3 into the stream. In addition, water vapor, HCl, CO2 and SO2 are also added to simulate the flue gas composition of the coal-fired power plant. The results indicate that plate-type V0.26W3.05TiO2 catalyst has the lowest efficiency for mercury and NO conversion. On the other hand, V1.52W5.11TiO2 catalyst has the highest Hg0/NO conversion efficiency of these catalysts. When the inlet elemental mercury concentration is decreased to 6 μg/m3, the conversion efficiency of mercury achieved with V0.26W3.05TiO2 is only 6%. It may be attributed to the competition for active sites available to Hg0. It also indicated that the mass transfer plays an important role in convering elemental mercury. Furthermore, this study also investigates the influence of HCl in the stream for mercury conversion. The results show that the conversion efficiency of elemental mercury is significantly increased after adding HCl into the stream. It indicates that the presence of chlorine species is beneficial for elemental mercury conversion. However, when HCl concentration exceeds 25 ppm only slight improvement of mercury conversion activity is observed. This study also compares the effectiveness of V1.52W5.11TiO2 and V0.26W3.05TiO2 catalysts, and it shows that V1.52W5.11TiO2 catalyst has higher efficiencies for multi-pulltant control. Moreover, the dioxin removal efficiencies achieved with V0.26W3.05TiO2, V0.66W5.86TiO2 and V1.52W5.11TiO2 are 50%, 57% and 65%, respectively. It is worth noting that the removal efficiency of highly chlorinated PCDD/Fs is slightly higher than that of low chlorinated PCDD/Fs. It may be attributed to the incomplete dechlorination of highly chlorinated PCDD/Fs with a high gas hourly velocity space (34,000 hr-1). The activation energies and frequency factors of elemental mercury conversion are calculated as 10.7-14.2 kJ/mole and 25.2-39.0 sec-1, respectively. This study also evaluates the effectiveness of catalytic filter in converting elemental mercury (with V2O5/WO3/TiO2 catalyst). Results indicate that elemental mercury and NO conversions achieved with catalyst filtration are 53% and 47%, respectively, as NH3/NO is controlled at 0.6.
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