ABSTRACT
The degrees of fouling and slagging vary throughout the steam generator depending on local gas temperatures, tube temperatures, temperature differentials, gas velocities, tube orientation, and local heat flux. Since economics dictate that steam generators must be designed to minimum capital, operating, and maintenance costs, with maximum efficiency and fuel flexibility, the philosophy used to characterize fuels must change from one predicting its slagging or fouling potential based on the fluid temperature of its ash, to one permitting the selection of a matrix of engineering parameters that will allow proper location and orientation of the heat-transfer surface in the combustion and heat recovery process. The mineral grains and organically associated inorganic elements undergo several physical changes during combustion of the coal char which alters their size and composition by partitioning attributed to ash shedding, char fragmentation, mineral fragmentation, decomposition and volatilization, and coalescence, as illustrated by the mineral transformations.
