A bituminous coal with a size faction of 63-90 mu m was combusted under oxi
dizing atmosphere (air) in a drop tube furnace (DTF) and a pressurized drop
tube furnace (PDTF) at a gas temperature of 1573 K and pressures of 0.1, 0
.5, 1.0, and 1.5 MPa. Ash generated at high pressure was found to be much f
iner than ash generated at low pressure due to the differences in char stru
cture. Pressure influences ash formation by its effect on the structure of
char particles after devolatilisation. Char samples produced at high pressu
re have higher proportions of porous char particles which fragment to form
finer ash particles. This study confirms and elaborates upon previous studi
es relating the structure and morphologies of char to ash formation.