超低排放改造情景下燃煤电厂脱硝催化剂表征、活性及其影响因素

Characterization,activity and its affecting factors of denitrification catalyst V2O5-WO3/TiO2 under ultra-low pollutant emission transformation

脱硝催化剂活性变化是影响燃煤电厂NO x去除效率的关键因素。为实现稳定NO x超低排放目标,燃煤电厂增加喷氨量,改变了催化剂运行工况条件,可能会缩短其使用寿命。目前燃煤电厂催化剂活性研究主要集中在超低排放改造前,而超低排放改造后,催化剂失活的影响因素及其机制鲜有报道。以超低排放改造情景下不同运行时间(分别约25200 h、29520 h和33480 h)的脱硝催化剂为研究对象,使用多种表征方法系统研究了催化剂表征和活性的变化,探讨了超低排放改造情景下催化剂失活的因素及机制。结果表明:催化剂的活性和主要组分含量(TiO 2、W和V)随运行时间的延长而降低,最低活性仅为0.56,显著低于新催化剂;同时催化剂中有毒元素S、K、Na和As等含量显著增加。相对于新催化剂,运行后的催化剂表面颗粒聚集,比表面积及表面V 4+占比和化学吸附氧浓度下降。燃煤电厂超低排放改造后,过量氨逸出,会加剧硫酸盐在催化剂表面的形成和沉积,相比较超低排放改造前,可能导致催化剂失活加快。总体上催化剂表面K、Na、As沉积、硫酸盐的形成和沉积、V价态改变和化学吸附氧含量降低等,是超低排放改造后催化剂失活的主要因素和机制。

The changes of reaction conditions of selective catalytic reduction(SCR)catalysts might accelerate the deactivation of denitrification catalysts due to the increase of ammonia injection in the inlet of SCR denitrification reactor after the ultra-low emission transformation in coal-fired power plants.The research on catalyst activity of coal-fired power plants is mainly concentrated before the ultra-low emission transformation,and the factors affecting the deactivation of catalysts and their mechanisms have rarely been reported after the ultra-low emission transformation.The denitrification activity and physiochemical characterization of the catalysts,which had been used for about 25200 h,29520 h,33480 h in a coal-fired power plant,were investigated to show their deactivation mechanisms based upon the analyses of XRF,ICP-OES,AFS,XRD,BET,FT-IR,SEM and XPS.Results showed that the catalytic activity and the contents of main components(TiO2,W and V)for the used catalysts decreased with the operating time with the lowest activity of only 0.56,whereas the S,K,Na and As concentrations were significantly higher in the used catalysts than in the control.The used catalysts displayed coarse surface with particle agglomeration,and relatively lower surface areas.Compared to the control catalyst,the V^4+and surface chemisorbed oxygen concentrations in the used catalysts decreased with the operation time.After the ultra-low emission transformation,excessive ammonia escape will aggravate the formation and deposition of sulfate on the catalyst surface,which may lead to accelerated catalyst deactivation.The formation of sulfate,surface deposition of K,As and the valence change of V atoms were the main causes of the deactivation of catalyst after the ultra-low emission transformation.