DIFFERENTIAL PARTITIONING AND SPECIATION OF Hg IN WET FGD FACILITES OF PCC POWER PLANTS

The speciation and partitioning of mercury from two Spanish pulverized coal (co) combustion (PCC) power plants equipped with wet limestone-based flue gas desulphurization facilities (FGD) have been evaluated in this work. The results were obtained by simultaneously sampling the solid, liquid and gaseous streams in the power plants and by determining the mercury content in the representative samples in two laboratories. The behavior, partitioning and speciation of Hg were found to be similar during the combustion processes but different in the FGD system of the power plants. A high proportion (86-88 %) of Hg escapes the ESP in gaseous form, Hg being the predominant mercury species (75-86 %) entering the FGD. A similar and relatively high potential for total Hg retention (64-74 %) was achieved in both FGD facilities, Hg being the prevalent Hg species retained by the desulphurization process (72-90 %). A low abatement capacity was observed for Hg (close to 25 %). The prevalent Hg species after FGD, depends on the input of mercury, 71 % Hg at low mercury inputs and 66 % Hg at high mercury inputs. Furthermore, the partitioning of mercury is different in each FGD system. In the low mercury input power plant, 38% of the total Hg input escaped in gas phase. In the FGD byproducts, more than half of the mercury (52 %) was retained by the gypsum whereas only low amount (9 %) was captured in the aqueous fraction of the slurry. Conversely, a very high fraction (80 %) of the incoming mercury was found to be water soluble while only 6 % was captured by gypsum in the power plant with a high mercury input. In this plant only 14 % of the mercury was emitted into the atmosphere. Most probably this is not only because the different input and/or mode of occurrence of Hg but also because the different operational conditions, which modifies the partitioning of this pollutant in wet FGD systems. 2009 World of Coal Ash (WOCA) Conference May 4-7, 2009 in Lexington, KY, USA http://www.flyash.info/