Ash liberation from included minerals during combustion of pulverized coal: The relationship with char structure and burnout

In this study, the float fraction (<specific gravity of 2.0) of a size cut (63-90 mu m) bituminous coal was combusted in a drop tube furnace (DTF) at a gas temperature of 1300 degrees C under an atmosphere of air, to investigate the ash Liberation at five coal burnoff levels (35.5%, 54.3%, 70.1%, 87.1%, and 95.6%). The data indicated that char structure determines the ash liberation at different burnoff levels. Fragmentation of porous char was found to be the determinative mechanism for formation of fine ash during the early and middle stages of char combustion, while coalescence of included mineral matter determines the coarse ash formed in the later stages of combustion. The investigation confirmed that the char morphology and structure play a key role in determining char fragmentation, char burnout history, and the ash liberation during combustion.