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Show 7 Conclusions Iron evolution from coal/char particles in combustion environments representative of practical systems has been observed. The extent of iron release typically is between 40 and 70 percent of the original amount of pyritic iron in the coal. It occurs most dominately over a 25 ms period immediately following coal devolatilization and volatiles combustion. Iron comprises over 80 percent of all mineral matter evolved from these chars (excluding sulfur) on an elemental basis. The experimental data are shown to be statistically significant at high levels of confidence. The temperatures, residence times, and particle sizes involved in this study preclude vaporization as a satisfactory explanation of the data. Potential vaporizing species are eliminated based on chemical kinetic, thermodynamic, and mass balance considerations. The data indicate that the chemical reactivity of the decomposition products of pyrite are responsible for the release of the submicron sized iron fume. Experiments have shown that the release is sensitive to the presence of both pyrites and oxygen. The data also indicate a greater release when the degree of oxygen penetration in the particle increases. A detailed mechanism for the formation of the submicron sized fume is postulated. The release is related to the porous structure of the pyrrhotite and its disintegration when exposed to oxygen. In more general terms, this study indicates the need to consider the chemical reactivity of inorganic species as a mode of mineral matter release during coal combustion. This mechanism dominated the evolution of mineral matter from coal in this study. References Canavos, G.C., Applied Probability and Statistical Methods, Little, Brown and Company, Boston, 1984. Groves , S.J., J. Williamson, and A. Sanyal, "Decomposition of pyrite during pulverized coal combustion," Fuel} 66, 461 , (1987). Harvey, R.D ., and R.R. Ruch, "Mineral Matter in Illinois and Other U.S. Coals," in Mineral Matter and Ash in Coal, K.S. Vorres , ed., American Chemical Society, Washington, 1986. Mims, C.A., M. Neville, R.J. Quann, and A.F . Sarofim, "Laboratory Studies of Trace Element Transformations During Coal Combustion," paper no. 3070, presented at the National 87th AIChE Meeting, Boston, Massachusetts, August 19-22, 1979. 17 |