The effect of combustion temperature on coal ash fine-fragmentation mode formation mechanisms

Pulverized Illinois #6 bituminous coal was combusted at three different peak combustion temperatures in a self-sustaining downflow combustor operated at 15 kW to generate ash, resulting in incremental temperature/residence time profiles following the same general trend. The size segregated ash samples were collected from the post-combustion zone in a Dekati low pressure inertial impactor. The mass of each fraction was measured and the ash was analyzed using scanning electron microscopy and X-ray microanalysis. The fine fragment mode ash types were classified into char, coarse, agglomerates, fragments, multi-spheres, and odd/unidentifiable classes. The abundance of these particle types were used to evaluate the significant fine fragment ash formation mechanisms and determine potential impacts of heating rate/temperature on fine-fragment particle formation. The results revealed that the mass fraction of multi-sphere, fragments, char, and agglomerates all increase with decreasing temperature. Further, there appears to be multiple formation mechanisms responsible for the generation of fine fragment sized multi-sphere and fragment type particles.