Mercury is a leading concern among the air toxic metals addressed in the 1990 Clean
Air Act Amendments (CAAA) because of its volatility, persistence, and bioaccumulation
as methylmercury in the environment and its neurological health impacts. The
Environmental Protection Agency (EPA) reports for 2001 shows that total mercury
emissions from all sources in USA is about 145 tons per annum, of which coal fired
power plants contribute around 33% of it, about 48 tons per annum. Unlike other trace
metals that are emitted in particulate form, mercury is released in vapor phase in
elemental (Hg0) or oxidized (Hg2+, mainly HgCl2) form. To date, there is no post
combustion treatment which can effectively capture elemental mercury vapor, but the
oxidized form of mercury can be captured in traditional emission control devices such as
wet flue gas defulrization (WFGD) units, since oxidized mercury (HgCl2) is soluble in
water.
The chlorine concentration present during coal combustion plays a major role in
mercury oxidation, which is evident from the fact that plants burning coal having high
chlorine content have less elemental mercury emissions. A novel method of co-firing
blends 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 Wyoming
coal the concentrations of chlorine are 139 ppm and 309 ppm on dry ash free basis, while
for 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 Burner
facility located in the Coal and Biomass Energy laboratory (CBEL); coal and biomass
blends in proportions of 80:20, 90:10, 95:5 and 100:0 were investigated as fuels. The
percentage 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 to
coal, to increase the chlorine concentration, it leads to higher ash loading. Low Ash and
High Ash Partially Composted Dairy Biomass have 164% and 962% more ash than
Wyoming coal respectively. As the fraction of cattle biomass in blend increases in
proportion, ash loading problems increase simultaneously. An optimum blend ratio is
arrived and suggested as 90:10 blend with good reduction in mercury emissions without
any compromise on ash loading.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2535 |
| Date | 15 May 2009 |
| Creators | Arcot Vijayasarathy, Udayasarathy |
| Contributors | Annamalai, Kalyan |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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