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Show lampblack requires a higher temperature than the laboratory char to achieve equal reaction rate. Comparison of the ambiguous data for the U T and C K top and bottom fractions, however, indicates that the soot and char reactivities m a y also be affected by surface area and mineral ash content. Hyde reported that under the conditions used for this study the assumption of insignificant diffusional resistance was not completely valid [22]. The observed range of char reactivity m a y also indicate the importance of catalytic metals in the ash mineral inclusions, {cite} and are consistent with reports of reduced T G A reactivity of char collected from full-scale boilers compared to char prepared under laboratory conditions from the same coal. [25] Conclusions Soot has been detected in laboratory-generated pulverized coal fly ash and in power plant fly ash from several sites, but additional studies are needed to determine the conditions under which the amount of soot is of practical significance for particulate emissions and for ash disposal. The presence of both soot and char in the unburned carbon from pulverized coal combustion needs to be considered in fundamental studies of heterogeneous combustion, carbon particle formation mechanisms, and of final fuel burnout. A method to quantify the soot and char in the fly ash from pulverized coal combustion has been developed and preliminary data has been obtained for a limited range of fuels and combustion conditions. The laboratory furnace used in this study has a Reynolds number, based on furnace diameter, of 1000-2000 and experiments in a larger laboratory furnace with fully-turbulent flow are planned. Future work is needed to improve the separation method to reduce both systematic bias and material balance closure errors so that trends in soot formation with changes in combustion conditions can be quantified. Differences in the morphology of the separated particle fractions indicate that these are different carbon-rich species and not simply a continuum of large and small particles generated by a single process. The Char and Soot 13 September 4, 1998 |