Behavior of mercury emitted from the combustion of coal and dried sewage sludge: The effect of unburned carbon, Cl, Cu and Fe

As the behavior of mercury generated from the combustion of mercury-containing fuels is highly dependent upon mercury speciation, many studies have investigated mercury speciation following combustion of various fuels. Unburned carbon and the content of chlorine (Cl), copper (Cu), and iron (Fe) compounds in ash are reported to affect the behavior of mercury. This study was conducted to understand the important factors impacting behavior of mercury from single coal combustion and co-combustion of dried sewage sludge with coal. Factors reported in previous studies were selected as potential factors affecting mercury oxidation and retention. Six coal and six dried sewage sludge samples were used to conduct single coal combustion and co-combustion tests. Each fuel sample was combusted in a lab-scale drop tube combustion system. Concentrations of elemental and oxidized mercury were determined using the Ontario Hydro Method. Ash samples collected on the bottom of the combustion system were analyzed to determine unburned carbon and mercury retention percentages. Unburned carbon and Cl were found to be important in both oxidation and retention of mercury for single coal combustion. Cl, Cu, and Fe content increased the oxidation of elemental mercury generated from co-combustion of dried sewage sludge with coal.