| Systematic measurements on Hg concentrations in the feed coal and the CCPs produced from two different power plants burning Illinois coal were carried out. Not only were there substantial variations in the total Hg concentration in the parent coal from week to week from a single mine, but there were also significant variations in the weekly Hg content of the CCPs. Surprisingly, there was no linear dependence between Hg content of coal and its CCPs. No correlation was observed between Hg content of fly ash and its loss-on-ignition (LOI) values.;In order to control and further understand the fate of Hg in FGD scrubber material, the following was systematically examined: (a) whether there is a strong correlation between the parent coal and the Hg captured in FGD scrubber materials, (b) the thermal behavior of Hg in parent coal, FGD gypsum, and sulfite-rich FGD material, (c) whether there is a potential of Hg re-emission during gypsum-to-hemihydrate-to-gypsum transition, and (d) how Hg behaves in sulfite-rich scrubber material at higher temperatures and pressures. Ultimately, no direct correlation between the total Hg concentration of the parent coal and its associated FGD scrubber materials was found. Mercury desorbed from FGD gypsum at relatively low temperatures (90°C < T < 250°oC), compared to the sulfite-rich scrubber materials which released Hg continuously at ambient pressures up to 600°C. However, it was found that mildly-elevated pressures immobilized Hg, even at temperatures as high as 250°oC.;In most coal preparation processes, significant amounts of fines (< 850 mum) and ultrafines (< 105 mum) are generated. Because these particles are difficult to dewater, they are often discarded in waste ponds. This translates into a major economic loss for the coal industry, not only because of the fuel value lost but also the substantial economic resources required to manage coal waste ponds in an environmentally-sound manner. A new approach developed using a high intensity sonication process in recovering, cleaning, and dewatering fine/ultrafine coal particles from the waste ponds, while concurrently reducing the Hg concentration in the fine and ultrafine particles was successful. Combining sonication with vegetable oil agglomeration significantly reduced the moisture, ash, and Hg content of the cleaned, recovered coal.;Differential scanning calorimetry (DSC) measurements on the recovered coal were used to understand the interaction between the coal particles, water, and oil. The results suggested that vegetable oil was effective in displacing water from the coal-water interface, with the enthalpy of the water-vapor transition of oil-agglomerated coal particles decreasing on sonication of the particles. In fact, combining sonication treatment with oil agglomeration reduced the moisture content of run-of-mine (ROM) coal and waste coal, to 6 wt% and 12 wt% respectively, and increased their loss-on-ignition (LOI) content to 91 wt% and 76 wt%, respectively.;Massive quantities of synthetic gypsum are produced when the flue gases from coal burning power plants are wet scrubbed with limestone. The sulfate-rich FGD scrubber material is largely construction-quality gypsum. Because of the large production of FGD gypsum every year, the economic and environmental impetus dictates that strategies be developed to effectively utilize FGD gypsum rather than just landfill it. Beneficial uses have been found in wallboard construction and agriculture. An important aspect of this research was to evaluate whether there was potential of Hg re-emission from scrubber materials during their utilization phase. Mercury emission occurs not only with elevated temperatures but with increased time. While external pressure retards these emissions, they are not the only concern associated with CCPs. The more global, urgent problems of greenhouse gases must be resolved.;To evaluate the risk of carbon dioxide sequestration under non-equilibrium conditions, dynamic mechanical properties of pressurized Illinois coals were measured. The results suggest that Illinois bituminous coal in its unperturbed state, i.e., when not pressurized with CO2, showed large variations in its mechanical properties. The Young's modulus varied from 0.7 GPa to 3.4 GPa even though samples were extracted from a single chunk. No glass transition was observed for any Illinois bituminous coal under ambient conditions. Upon pressurizing the Illinois bituminous coals with CO2, the DMA results showed a transition at temperatures as low as ambient. This could be a potential risk for the structural integrity of a mine if any man-made or seismic activity were present. (Abstract shortened by UMI.)... |
