Abstract: In order to study the effects of flue gas pollutants purification facilities on mercury emission and migration characteristics， content and form distribution of mercury discharged from four ultra-low emission coal-fired units were measured. Experimental results show that selective catalytic reduction （SCR） devices only remove an insignificant amount of mercury directly， but the denitration catalyst can facilitate the mercury removal in rear devices by catalytic oxidizing Hg0.ESP would remove the majority of Hg0 ，and WFGD could effectively eliminate Hg2+ .Mercury in fire coal would transport into fly ash， by-product of WFDG and flue gas，while mercury discharged in flue gas is mainly in form of Hg0 .Mercury emission factor （EFe） was between 15.20～30.00 μg/（kW·h）.The results show that the ultra-low emission transformation has a certain effect on mercury emission reduction， and the reduction is affected by technical routes of the transformation.

Key words: ultra-low emission, mercury in flue gas, removal rate, distribution of forms, migration patterns, emission characteristics, emissions factor, denitration catalyst