活性焦超低温催化脱硝及原位热再生实验研究

Experimental study on ultra-low temperature catalytic denitrification and in-situ thermal regeneration of activated coke under different atmospheres

超低温催化脱硝是具有烟气成分简单、能耗低、阻力小等优点的新型脱硝工艺,而活性焦在超低温催化脱硝方面发挥重要作用,因而针对活性焦在不同气氛下的超低温催化脱硝及原位热再生实验研究,可为提升超低温催化脱硝性能提供技术支撑。利用微型固定床实验装置研究超低温(≤130℃)下不同气氛(氧化和还原)对活性焦脱除NO性能及热再生中NO_(x)气体的影响规律与原位热再生机理。结果表明:活性焦在实验条件下脱除NO过程中,出口NO体积分数曲线随时间延长呈逐渐上升趋势,表明活性焦样品中的活性位不断被占据。其他条件不变,还原气氛下NO吸收量是氧化气氛的数倍,说明还原气氛更有利于活性焦对NO的脱除;温度越低,还原气氛与氧化气氛的NO脱除量差距越大,活性焦对NO的脱除性能越强。超低温氧化气氛下,活性焦对NO的脱除过程除存在吸附作用外,还存在催化氧化作用,可将NO氧化为NO_(2),并将NO_(2)吸附于活性焦孔隙表面,吸附态NO_(2)发生歧化反应,生成NO_(3)。催化氧化脱硝后的活性焦在原位热再生过程中,氧化生成的高阶NO_(x)受热又分解为NO。超低温氨气还原气氛下,除了发生NO催化氧化反应外,在还原剂NH_(3)的作用下,活性焦表面还发生NO催化还原反应,推测有部分NO的氧化产物与NH_(3)进一步反应生成硝酸铵,该3种反应是相互影响促进的关系。催化还原脱硝后的活性焦经原位热再生,催化氧化产物以NO形式释放,同时硝酸铵盐产物部分分解为N_(2)和H_(2)O。因此,还原气氛脱硝后热再生气中NO释放量与吸收量的比值比氧化气氛脱硝后的要小。随脱硝温度升高,数值随之增大,说明在实验条件下温度越高,催化还原占比越大。

Ultra low temperature catalytic denitrification is a new type of denitrification process with the advantages of simple flue gas composition,low energy consumption and low resistance.Activated coke plays an important role in ultra-low temperature catalytic denitrification.Therefore,experimental research on ultra-low temperature catalytic denitrification and in-situ thermal regeneration of activated coke under different atmospheres can provide technical support for improving the performance of ultra-low temperature catalytic denitrification.Using a micro fixed bed experimental device,the influence of different atmospheres(oxidation and reduction)at ultra-low temperature(≤130℃)on the NO removal performance of activated coke and the NO_(x)gas in thermal regeneration,as well as the in-situ thermal regeneration mechanism,were studied.The results show that during the NO removal process of activated coke under experimental conditions,the outlet NO concentration curve shows a gradual upward trend with time,indicating that the active sites in the activated coke sample are continuously occupied.Other conditions remain unchanged,and the absorption of NO in a reducing atmosphere is several times that of an oxidizing atmosphere,indicating that the reducing atmosphere is more conducive to the removal of NO by activated coke;the lower the temperature,the greater the difference in NO removal between the reducing atmosphere and the oxidizing atmosphere,and the stronger the NO removal performance of activated coke.Under ultra-low temperature oxidation atmosphere,the removal process of NO by activated coke not only involves adsorption,but also catalytic oxidation,which can oxidize NO to NO_(2)and adsorb NO_(2)on the pore surface of the activated coke.The adsorbed NO_(2)undergoes a disproportionation reaction,generating NO_(3).During the in-situ thermal regeneration process of the activated coke after catalytic oxidation and denitrification,the high-order NO_(x)generated by oxidation is heated and decomposed into NO.Under the ultra-low temperature ammonia reduction atmosphere,in addition to NO catalytic oxidation reaction,under the action of reducing agent NH_(3),NO catalytic reduction reaction also occurs on the surface of the activated coke.It is speculated that some NO oxidation products further react with NH_(3)to generate ammonium nitrate,and these three reactions are mutually influencing and promoting.After catalytic reduction and denitrification,the activated coke undergoes in-situ thermal regeneration,and the catalytic oxidation product is released in the form of NO,while the ammonium nitrate product is partially decomposed into N_(2)and H_(2)O.Therefore,the ratio of NO release to absorption in the hot regeneration gas after denitrification in a reducing atmosphere is smaller than that after denitrification in an oxidizing atmosphere.As the denitrification temperature increases,the numerical value increases,indicating that under experimental conditions,the higher the temperature,the greater the proportion of catalytic reduction.