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The mechanical–chemical-modified fly ash (FA-MC) and mechanical–chemical-brominated fly ash (FA-MC-Br) were prepared by omnidirectional planetary ball mill, and impregnated–brominated fly ash (FA-I-Br) was also prepared using the same mass ratio of fly ash/NH4Br as a comparison. The mercury-removal efficiency of raw fly ash (FA), FA-MC, FA-MC-Br, and FA-I-Br was evaluated in a fixed-bed reactor. The physical and chemical properties of the four samples were investigated by the Brunauer–Emmet–Teller, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and mercury temperature-programmed desorption analysis. The results showed that the mercury-removal efficiency of the four samples followed the order of FA-MC-Br > FA-I-Br > FA-MC > FA, the value of which was 67, 30.98, 26.12, and 17.96%, respectively. The mercury-removal performance of the four samples was mainly reflected in the oxidation (>90%), while the adsorption only accounted for a small proportion (<10%). The mechanical–chemical activation improved the content of the surface-adsorbed oxygen and amorphous phase of FA, which promoted the oxidation efficiency of the samples. Due to the generation of Br-containing complexes and further increase in the content of surface-adsorbed oxygen on FA-MC-Br, the mechanical–chemical activation coupled with the addition of NH4Br significantly improved the mercury-oxidation and -adsorption efficiency. The mercury-adsorbed species of fresh FA-MC-Br is HgBr2, and that of used FA-MC-Br is HgBr2 and HgO. The reaction between elemental mercury and FA-MC-Br was followed Eley–Rideal reaction. As a comparison, the mercury-removal efficiency of FA-I-Br was far less than that of FA-MC-Br, demonstrating that FA-MC-Br was a cost-effective alternative material to activated carbon for potential industrial applications.

The synergistic removal of mercury by injecting activated carbon between the selective catalytic reduction (SCR) and fabric filter (FF) as well as some influencing factors were investigated in a pilot-scale 0.3 MWth circulating fluidized bed (CFB) combustion system. The Ontario Hydro Method (OHM) was used to sample mercury in the coal-fired flue gas. The gaseous elemental mercury (Hg 0 ), gaseous oxidized mercury (Hg 2+ ), particle-bound mercury (Hg p ) in the flue gas after the boiler, SCR, activated carbon injection (ACI) device, FF, and wet flue gas desulfurization (WFGD) were sampled simultaneously, and the flue gas components were monitored online. The results showed that the mercury removal efficiency of the SCR+ACI+FF system (SAFs) and the proportion of Hg P after ACI increased with the increase of the flue gas temperature. The mercury removal efficiency decreased with incremental SO 2 concentration probably due to its suppressive effect on the combination of mercury and halogen and its competitive adsorption with mercury. The higher NO concentration can improve the mercury removal efficiency resulting from Hg 0 oxidation by NO 2 , which could counteract its adverse effect on mercury oxidation in SCR. The FF device not only could capture all Hg P but also had a considerable effect on gaseous mercury. The synergistic mercury removal efficiency of the ACI and air pollution control devices (APCDs) system was more than 97.4%. The presented work could provide useful information and guidance for the optimization of the operational parameters of the ACI+APCDs mercury removal technology.

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