焦化厂SCR脱硝催化剂积碳失活研究

Study on coking deactivation of SCR denitration catalyst in a coke-oven plant

以焦化厂烟气脱硫前脱硝中失活的板式选择性催化还原(selective catalytic reduction,SCR)催化剂为研究对象,采用比表面及孔径分布分析仪、元素分析仪、热重/差示扫描量热分析(TG/DSC)、X射线光电子能谱(XPS)对失活催化剂进行表征,并对未经焙烧和经焙烧处理的失活催化剂的脱硝性能进行测试。结果表明:相较新鲜催化剂,失活催化剂比表面积和孔容大幅下降;失活催化剂表层吸附了大量的硫酸氢铵(NH4HSO4)/硫酸铵〔(NH4)2SO4〕和积碳,其中积碳以单质碳(C)形式存在,C浓度达0.87%;350℃焙烧可清除失活催化剂表面附着的NH4HSO4,使催化剂活性得到小幅度的恢复,400~500℃焙烧使积碳氧化生成二氧化碳从催化剂表面脱离,从而使催化剂活性得到大幅度的恢复;积碳是导致SCR脱硝催化剂失活的主要原因,可在脱硝前设置布袋除尘器,捕集烟气中的焦油积碳等有害物质,以降低积碳对SCR脱硝催化剂的有害作用。

The plate type SCR catalyst which was deactivated in flue gas denitration before desulfurization in a coke-oven plant was studied.Specific surface and pore size distribution analyzer,elemental analyzer,TG-DSC analysis,and X-ray photoelectron spectroscopy(XPS)were used to characterize the deactivation catalyst,and the denitration activity test of the untreated catalyst with that of the calcined catalyst was compared.The results showed that compared with fresh catalyst,the specific surface area and pore volume of deactivation catalyst were greatly reduced.The surface of catalyst was seriously polluted,and a large amount of ammonium bisulfate/ammonium sulfate and coke deposit was adsorbed on the surface of catalyst.The coke deposit existed as element carbon with the content of 0.87%.The calcination temperature of 350℃could remove the ammonium bisulfate on the surface of the deactivated catalyst,resulting in the recovery of a small part of the catalyst activity;however,after the treatment of 400-500℃,the appearance and activity of the catalyst were greatly restored.This was because the deposited coke was oxidized to carbon dioxide at 400-500℃and was separated from the catalyst surface,resulting in the recovery of catalytic activity.The results of denitration activity test further proved that the coke deposition was the main cause of catalyst deactivation.A bag filter could be set before denitration to catch the tar,coke and other harmful substances in the flue gas,so as to effectively reduce the harmful effect of coke deposition on the SCR denitration catalyst.