Sv. Pisupati et Aw. Scaroni, EFFECTS OF NATURAL WEATHERING AND LOW-TEMPERATURE OXIDATION ON SOME ASPECTS OF THE COMBUSTION BEHAVIOR OF BITUMINOUS COALS, Fuel, 72(6), 1993, pp. 779-785
The influence of natural weathering (in situ) and low-temperature labo
ratory oxidation on the combustion behaviour of bituminous coals was i
nvestigated. Five sets of coals, each comprising a fresh and crop coal
from the same seam, were used. One selected fresh coal sample was oxi
dized in the laboratory at 200-degrees-C for 2 and 72 h to elucidate t
he effect of low-temperature oxidation (simulated weathering) on the s
ubsequent combustion behaviour. The combustion behaviour of the coals
was evaluated using char reactivity and burning profiles obtained in a
thermogravimetric analyser (TGA) and combustion efficiency determined
in a drop-tube reactor (DTR). The reactivities of the chars produced
from the crop and laboratory-oxidized coals were higher than those for
the chars from the corresponding fresh coals. The reactivities of the
crop coal chars were higher than those of the laboratory-oxidized coa
ls due to the presence of inorganic species (cations) in the former wh
ich could be removed by acid washing. Reactivity changes due to such i
norganic species changes did not occur upon laboratory oxidation. The
combustion efficiencies of the weathered coals were higher than those
of the corresponding fresh coals. A correlation was obtained between t
he difference in combustion efficiency between a crop coal and its fre
sh counterpart and oxygen uptake during natural weathering. There was
an inverse relationship between the combustion efficiencies determined
in the DTR and the 'initial temperature' in the TGA burning profiles.