EMISSIONS OF MERCURY AND OTHER TRACE ELEMENTS FROM A COAL-FIRED POWER PLANT

This paper provides details concerning emissions of mercury and other trace elements conducted at a coal-fired power plant with SCR and wet FGD. Mercury emission concentration and its speciation were measured with Ontario Hydro Method (OHM) and Semi-continuous emission monitor (SCEM). The emission of trace elements was determined by EPA method 29. Mercury mass balance and partitioning of trace elements were analyzed based on the analyses of solid samples (such as: coal, bottom ash, fly ash, and flue gas desulphurization (FGD) slurry) and concentration of trace elements in the flue gas. The results indicated that total mercury (Hg-T, sum of Hg-0, Hg2+, and Hg-P) remained relatively constant along the flue gas path before passing through FGD. The ratio of Hg2+ to Hg-VT increased from 45.7% to 83.3% after flue gas passed through SCR. Hg monitoring methods of OHM and SCEM agreed that over 95% of Hg in flue gas was in oxidized form before FGD. The mercury removal efficiency of FGD was more than 96%. A better ratio of Hg output to Hg input (within the range of 0.8 to 1.2) was obtained while Hg content in ashes reached a dateable level. The emission concentration of each element was very low, and the change of the gaseous phase compositions of the selected trace elements was found insignificantly throughout the flue gas path. Mercury and Selenium are almost fully released in the gaseous phase. The main proportion of other trace elements is bound with the fly ash and collected in the electrostatic precipitator (ESP).