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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.

Dairy biomass (DB) is evaluated as a possible co-firing fuel with coal. Cofiring of DB offers a technique of utilizing dairy manure for power/steam generation, reducing greenhouse gas concerns, and increasing financial returns to dairy operators. The effects of cofiring coal and DB have been studied in a 30 kW (100,000 BTU/hr) burner boiler facility. Experiments were performed with Texas Lignite coal (TXL) as a base line fuel. The combustion efficiency from co-firing is also addressed in the present work. Two forms of partially composted DB fuels were investigated: low ash separated solids and high ash soil surface. Two types of coal were investigated: TXL and Wyoming Powder River Basin coal (WYO). Proximate and ultimate analyses were performed on coal and DB. DB fuels have much higher nitrogen (kg/GJ) and ash content (kg/GJ) than coal. The HHV of TXL and WYO coal as received were 14,000 and 18,000 kJ/kg, while the HHV of the LA-PC-DBSepS and the HA-PC-DB-SoilS were 13,000 and 4,000 kJ/kg. The HHV based on stoichiometric air were 3,000 kJ/kg for both coals and LA-PC-DB-SepS and 2,900 kJ/kg for HA-PC-DB-SoilS. The nitrogen and sulfur loading for TXL and WYO ranged from 0.15 to 0.48 kg/GJ and from 0.33 to 2.67 for the DB fuels. TXL began pyrolysis at 640 K and the WYO at 660 K. The HA-PC-DB-SoilSs began pyrolysis at 530 K and the LA-PC-DB-SepS at 510 K. The maximum rate of volatile release occurred at 700 K for both coals and HA-PC-DB-SoilS and 750K for LA-PC-DB-SepS. The NOx emissions for equivalence ratio (φ) varying from 0.9 to 1.2 ranged from 0.34 to 0.90 kg/GJ (0.79 to 0.16 lb/mmBTU) for pure TXL. They ranged from 0.35 to 0.7 kg/GJ (0.82 to 0.16 lb/mmBTU) for a 90:10 TXL:LA-PC-DB-SepS blend and from 0.32 to 0.5 kg/GJ (0.74 to 0.12 lb/mmBTU) for a 80:20 TXL:LA-PC-DB-SepS blend over the same range of φ. In a rich environment, DB:coal cofiring produced less NOx and CO than pure coal. This result is probably due to the fuel bound nitrogen in DB is mostly in the form of urea which reduces NOx to non-polluting gases such as nitrogen (N2).

Coal fired power plants will face many challenges in the near future as new regulations, such as the Clear Sky Act, are being implemented. These regulations impose much stricter limits on NOx emissions and plan to impose limits on mercury emissions from coal fired boilers. At this time no technologies are currently being implemented for control of Hg and this explains the strong interest in this area by the Department of Energy (DOE). Reburn technology is a very promising technology to reduce NOx emissions. Previous experimental research at TAMU reported that Feedlot Biomass (FB) can be a very effective reburn fuel, for reduction of NOx up to 90%-95%; however, little work has been done to model such a process with Feedlot Biomass as reburn fuel. The present work addresses the development of a reburn model to predict NOx and Hg emissions. The model accounts for finite rate of heating of solid fuel particles, mixing with NOx laden hot gases, size distribution, finite gas phase and heterogeneous chemistry, and oxidation and reduction reactions for NOx and Hg. To reduce the computational effort all the reactions, except those involved in mercury oxidation, are modeled using global reactions. Once the model was validated by comparison with experimental findings, extensive parametric studies were performed to evaluate the parameters controlling NOx reduction. From DOE research programs some experimental data regarding the capture of mercury from power plant is available, but currently no experimental data are available for Hg emission with reburn process. This model has shown a very large mercury reduction using biomass as a reburn fuel. The model recommends the following correlations for optimum reduction of NOx: Equivalence Ratio should be above 1.05; mixing time should be below 100ms (especially for biomass); pure air can be used as the carrier gas; the thermal power fraction of the reburner should be between 15% and 25%; residence time should be at least 0.5s and the Surface Mean Diameter (SMD) of the size distribution should be as small as possible, at least below 100 µm.

Thesis (Ph. D.)--University of Sydney, 1987. / Includes tables. Bibliography: leaves 191-199. Also available in print form.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xi, 106 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 96-98).

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xvi, 135 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 107-109).

Thesis (MEngSc.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xxiii, 271 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 268-271).

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