Combustion char morphology related to combustion temperature and coal petrography

The morphology of chars sampled from various laboratory-scale reactors operating at temperatures from 800 to > 1400°C, together with chars collected directly in the flame zone in a full-scale pulverized fuel combustion experiment, was examined. A coal and coal blend dominated by vitrinite-rich microlithotypes together with four coals dominated by inertinite-rich microlithotypes were used to produce the combustion chars. Char samples produced at temperatures above ∼1300°C have a morphotype composition very similar to the composition of the full-scale char samples, whereas the morphotype compositions of those produced at ∼1150°C or lower are significantly different. Correlation between coal petrography and char morphology and determination of char reactivity should thus be attempted only using chars produced at temperatures comparable with those for the intended use of the coal. A clear distinction between the high-temperature char samples (burnout 50-60 wt% daf) emerges which is related mainly to the parent coal petrography and probably secondarily to the rank. Vitrite, clarite and vitrinertite V may be correlated with the porous tenuisphere and crassisphere morphotypes, whereas inertite, durite, vitrinertite I, duroclarite and clarodurite may be correlated with the crassinetwork - mixed-network - mixed morphotype group.