Effects of modified fly ash on mercury adsorption ability in an entrained-flow reactor

This study investigated the effectiveness of fly ash modified with halogenated material in absorbing mercury in an entrained-flow reactor. Two different types of fly ash from coal-fired power plants were treated with varying amounts of CaCl2, CaBr2 and HBr. The first derivative of the Hg removal concentration was explored to help quantify the effectiveness of adsorbents. Characterization studies of the fly ash using SEM and BET indicate that the surface structure of the modified fly ash was altered, and the specific surface area, average pore size and pore volume were all slightly increased. Compared to the unmodified fly ash, both the mercury adsorption efficiency and the mercury concentration change rate in the flue gas improved significantly. The fly ash oxidized by HBr showed the greatest adsorption ability among the three additives. The improvement in the characteristics of the modified fly ash was due to both physical and chemical adsorption. The study also showed that particle size of the fly ash is a significant factor in the removal of mercury from the flue gas. Under experimental conditions, the adsorption efficiencies for the two HBr-modified fly ash (A and B) were 2.4 and 6.7 times greater for >200 mesh than for 80–200 mesh.