Mercury is a leading concern among the air toxic metals addressed in the 1990 CleanAir Act Amendments (CAAA) because of its volatility, persistence, and bioaccumulationas methylmercury in the environment and its neurological health impacts. TheEnvironmental Protection Agency (EPA) reports for 2001 shows that total mercuryemissions from all sources in USA is about 145 tons per annum, of which coal firedpower plants contribute around 33% of it, about 48 tons per annum. Unlike other tracemetals that are emitted in particulate form, mercury is released in vapor phase inelemental (Hg0) or oxidized (Hg2+, mainly HgCl2) form. To date, there is no postcombustion treatment which can effectively capture elemental mercury vapor, but theoxidized form of mercury can be captured in traditional emission control devices such aswet flue gas defulrization (WFGD) units, since oxidized mercury (HgCl2) is soluble inwater.The chlorine concentration present during coal combustion plays a major role inmercury oxidation, which is evident from the fact that plants burning coal having highchlorine content have less elemental mercury emissions. A novel method of co-firingblends of low chlorine content coal with high chlorine content cattle manure/biomass was used in order to study its effect on mercury oxidation. For Texas Lignite and Wyomingcoal the concentrations of chlorine are 139 ppm and 309 ppm on dry ash free basis, whilefor Low Ash Partially Composted Dairy Biomass it is 2,691 ppm.Co-firing experiments were performed in a 100,000 BTU/hr (29.3 kWt) Boiler Burnerfacility located in the Coal and Biomass Energy laboratory (CBEL); coal and biomassblends in proportions of 80:20, 90:10, 95:5 and 100:0 were investigated as fuels. Thepercentage reduction of Hg with 95:5, 90:10 and 80:20 blends were measured to be 28-50%, 42-62% and 71-75% respectively. Though cattle biomass serves as an additive tocoal, to increase the chlorine concentration, it leads to higher ash loading. Low Ash andHigh Ash Partially Composted Dairy Biomass have 164% and 962% more ash thanWyoming coal respectively. As the fraction of cattle biomass in blend increases inproportion, ash loading problems increase simultaneously. An optimum blend ratio isarrived and suggested as 90:10 blend with good reduction in mercury emissions withoutany compromise on ash loading.
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