Effect of flue gas components on Hg 0 oxidation and adsorption by modified walnut shell coke in O 2 /CO 2 atmosphere

Walnut shell was pyrolyzed and then impregnated with NH 4 Br to make sorbent for Hg 0 removal. The effect of flue gas components on Hg 0 removal performance was studied in O 2 /CO 2 atmosphere, and the results were compared with those in O 2 /N 2 atmosphere. The mercury valence distribution during adsorption was obtained. NH 4 Br‐modified walnut shell coke promoted Hg 0 removal, the Br‐containing chemisorption site was a crucial factor. Although addition of CO 2 did not introduce new oxygen‐containing functional groups or change the mercury species, Hg 0 removal efficiency increased significantly. This may be because CO 2 can increase the active sites on the carbon surface. In O 2 /N 2 atmosphere, O 2 promoted formation of active center on the sorbent surface, which made Hg 0 more easily adsorbed and then reacted with Br‐functional group to form more HgBr 2 . In O 2 /CO 2 atmosphere, O 2 promoted formation of some reactive carbon–oxygen complexes which acted as catalyst to facilitate Hg 0 oxidation and formation of HgO. NO improved removal of Hg 0 , because the C─O functional group on the sorbent surface could catalyze the conversion of NO to NO 2 in the adsorbed state and then formed Hg 2 (NO 3 ) 2 . SO 2 consumed oxygen on the sorbent surface and inhibited the Hg 0 removal.