水蒸气对甲烷在金属铁表面还原NO行为的影响

采用程序控温电加热水平陶瓷管反应器,在N2气氛和模拟烟气气氛中、300~1100℃下,研究了水蒸气对甲烷在金属铁表面还原NO行为的影响,并对反应前、后铁样品进行了X光衍射(XRD)、扫描电子显微镜(SEM)及X光电子能谱(XPS)等表征。结果表明,水蒸气对甲烷在金属铁表面还原NO行为的影响较小。在N2气氛中,水蒸气参与了金属铁的氧化;与无水蒸气时相比,水蒸气存在时NO还原效率有所下降。当水蒸气含量从2.5%增加到7%时,由于水蒸气对金属铁的氧化导致其表面形成疏松的微观孔隙,使得NO的还原效率随水蒸气含量的增加而提高。甲烷则参与了铁氧化物的还原,使铁样品表面形成相对致密的Fe3O4和FeO氧化层,不利于NO与金属铁的接触,使得NO的还原效率低于无甲烷时的结果。在模拟烟气条件下,水蒸气使得甲烷在金属铁表面还原NO的效率增加;在1050℃下,反应段过量空气系数SR1=0.7和燃尽段过量空气系数SR2=1.2时,含7%的H2O和无H2O条件下脱硝效率分别为96.7%和90.6%。而在湿烟气中SO2使NO还原效率略有下降。持久性脱硝实验结果表明,当反应温度为1050℃时,在含7%的H2O、0.02%的SO2的模拟烟气中,1.14%的甲烷在金属铁表面持续50h都能保持90%以上的脱硝效率。

Effect of water vapor on NO reduction by methane over iron

The effect of water vapor on NO reduction by methane over iron was investigated at 300~1 100 ℃ in an electrically heated ceramic tubular flow reactor in both N₂ and simulated flue gas atmospheres. The iron samples before and after reaction were characterized by XRD, SEM and XPS. The results demonstrated that water vapor has a small effect on NO reduction by methane over iron. In N₂ atmosphere, water vapor is involved in the oxidation of iron; compared with that in the absence of water vapor, the NO reduction efficiency is decreased slightly when 2.5%~7% water vapor is added into the reaction stream. However, the NO reduction efficiency increases with the increase of water content from 2.5% to 7%, as water vapor may promote the oxidation of iron, forming porous iron surface. Methane is involved in the reduction of the iron oxides, leading to the formation of a dense layer of Fe₃O₄ and FeO, which may inhabit the interaction of NO with metallic iron and then decrease the NO reduction efficiency, as compared with that without methane. In the simulated flue gas atmosphere, water vapor promotes the NO reduction by methane over iron. When the excess air ratio is 0.7 in reaction zone (SR₁) and 1.2 in burnout zone (SR₂), the NO reduction efficiency at 1 050 ℃ is 96.7% in the presence of 7% water vapor, compared with the value of 90.6% in the absence of water vapor. SO₂ causes a slight decrease of NO reduction. Long term test results showed that over iron at 1 050 ℃ in the simulated flue gas atmosphere containing 7% H₂O and 0.02% SO₂, NO reduction efficiency remains higher than 90% after reaction for 50 h in the presence of 1.14% methane.