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

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.