(589d) Factors Affecting Mercury Adsorption On Fly Ash

In coal combustion process, mercury in coal is vaporized to elemental mercury (Hg⁰) and a portion of Hg⁰ is adsorbed on fly ash. Since fly ash is a source of mercury emissions in the cement industry, the purpose of this study is to clarify the factors affecting mercury adsorption on fly ash. Different fly ash samples collected from an electrostatic precipitator (ESP) hopper of a pilot-scale coal combustion facility were exposed to a simulated coal combustion flue gas for a brief time (5 ? 10 min). The effects of unburned carbon, SO₂, HCl, H₂O, NO concentrations, and gas temperature on adsorption of elemental mercury were investigated. As a result, the content of unburned carbon was the dominant factor of mercury adsorption on the fly ash. The gas temperature (90 ? 200 °C) and HCl (5 ? 100 ppm) had a small effect, however, SO₂ (0 ? 2000 ppm), NO (0 ? 100 ppm), and H₂O (4 ? 12%) had little effect. To verify the effects of the above-mentioned factors on mercury adsorption, two different bituminous coals, which had the almost similar mercury content, and blend of the coals were burned in a pilot-scale coal combustion facility. Fly ash samples were collected from different temperatures positions to analyze the diameter, the amount of unburned carbon, and the amount of mercury in the fly ash samples. It was found that the amount of mercury in the fly ash did not depend on the fly ash diameter but on the amount of the unburned carbon. The ESP operation temperature in the range of 90 to 130 °C and the chlorine contents in the range of 67 to 600 mg/kg did not show affect mercury adsorption.