Preparation and evaluation of coal-derived activated carbons for removal of mercury vapor from simulated coal combustion flue gases

Coal-derived activated carbons (CDACs) were tested for their suitability in removing trace amounts of vapor-phase mercury from simulated flue gases generated by coal combustion. CDACs were prepared in bench-scale and pilot-scale fluidized-bed reactors with a three-step process, including coal preoxidation, carbonization, and then;steam activation. CDACs from high-organic-sulfur illinois coals had a greater equilibrium Hg-0 adsorption capacity than activated carbons prepared from a low-organic-sulfur Illinois coal. When a low-organic-sulfur CDAC was impregnated with elemental sulfur at 600 degrees C, its equilibrium Hg-0 adsorption-capacity was comparable to the adsorption capacity of the activated carbon prepared from the high-organic-sulfur coal. X-ray diffraction and sulfur K-edge X-ray absorption near-edge structure examinations showed that the sulfur in the CDACs was mainly in organic forms. These results suggested that a portion of the inherent organic sulfur in the starting coal, which remained in the CDACs, played an important role in adsorption of Hg-0. Besides organic,sulfur, the BET surface area and micropore area of the CDACs also influenced Hg-0 adsorption capacity. The HgCl2 adsorption capacity was not as dependent on the surface area and concentration of sulfur in the CDACs as was adsorption of Hg-0. The properties and mercury adsorption capacities of the CDACs were compared with those obtained for commercial Darco FGD carbon.