Investigation on the behavior of mercury across the flue gas treatment of coal combustion power plants using a lab-scale firing system

The behavior of mercury across the flue gas path was investigated in order to obtain a comprehensive understanding of the reactions regarding mercury. An improved high-dust honeycomb selective catalytic reduction (SCR) catalyst was compared with a conventional one regarding its mercury oxidation at different gas hydrogen chloride concentrations and ammonia dosing levels. The measurements were taken in a lab-scale firing system using coal derived flue gas to check the influence of other gas components and competing reactions. The diminishing effect of ammonia presence due to the compatible reactions could be shown in the measurements of both catalysts. On the other hand presence of ammonia increases mercury removal with fly ash. The correlation of mercury adsorption with the unburned carbon of fly ash was shown. Mercury inventory in the slurry of flue gas desulfurization (FGD) was higher when more oxidized mercury was present in the flue gas, which is shown through the mercury content of the gypsum and filtrate in each measurement. Ammonia containing flue gas resulted in higher Hg re-emission from slurry. It was observed that the mercury oxidation was higher by using the improved catalyst, which enhances the total mercury removal efficiency in FGD downstream of the catalyst.