A microscopic study of the combustion residues of subbituminous and bituminous coals from Alberta, Canada

Chars produced by the combustion of a set of three coals from Alberta, Canada, were classified morphologically using reflected light microscopy. Produced chars are different in morphological features, pore thickness, anisotropy and degree of reactivity, because of differences in the vitrinite and inertinite contents.The subbituminous A coal produced the highest percentage of unreactive or slightly reactive components due to its high inertinite content (20.0%), followed by isotropic cenospheres. Isotropic cenospheres, both thin- and thick-walled, and exploded cenospheres are the characteristic chars produced by the high-voltile bituminous B coal, whereas the low-volatile bituminous coking coal produced cenospheres with granular anisotropy (mosaic) on the walls and abundant coke fragmentsOptical microscopy is useful in differentiating the performance of a series of coals during combustion based on petrographic composition and rank and can aid in understanding the relationship between ‘reactive’ and ‘non-reactive’ coal macerals to burnout performance.