Fly ash was collected from eight mechanical and 10 baghouse hoppers at each of the twin
150-MW wall-fired units in a western Kentucky power station. The fuel burned at that time was
a blend of many low-sulfur, high-volatile bituminous Central Appalachian coals. The baghouse
ash showed less variation between units than the mechanical hoppers. The mechanical fly ash,
coarser than the baghouse ash, showed significant differences in the amount of total carbon and
in the ratio of isotropic coke to both total carbon and total cokethe latter excluding inertinite
and other unburned, uncoked coal. There was no significant variation in proportions of inorganic
fly ash constituents. The inter-unit differences in the amount and forms of mechanical fly ash
carbon appear to be related to differences in pulverizer efficiency, leading to greater amounts of
coarse coal, therefore unburned carbon, in one of the units. Mercury capture is a function of both
the total carbon content and the gas temperature at the point of fly ash separation, mercury
content increasing with an increase in carbon for a specific collection system. Mercury adsorption
on fly ash carbon increases at lower flue-gas temperatures. Baghouse fly ash, collected at a lower
temperature than the higher-carbon mechanically separated fly ash, contains a significantly
greater amount of Hg.
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