COMBUSTION PROPERTIES OF MACERALS FROM 4 ALBERTA COALS

The combustibility of handpicked vitrinite and inertinite concentrates from four Alberta coals ranging in rank from subbituminous C to low-v olatile (LV) bituminous was measured and compared with the parent coal . The combustion properties of the concentrates were studied by routin e analysis of the maceral concentrates, examination of low-temperature reactivity on a thermogravimetric analyzer examination of high-temper ature burnout profiles on the entrained flow reactor, and measurement of char combustion reactivity on a single-particle combustor. The stru cture of partially combusted chars from two of the coals and their mac erals concentrates were examined using scanning electron microscopy. L ow-temperature oxidation of pyrolysis chan formed from the coals and m acerals indicated that all of the samples had similar activation energ ies of between 29,900 and 35,600 cal / mol. For three of the coals, th e inertinite chat had lower reaction rates under these conditions. Und er entrained flow combustion conditions at 1000 degrees C, the subbitu minous and high-volatile (HV) bituminous coals were very reactive, wit h 90% burnout in air in less than 0.2 s. The initial weight loss of th e inertinite maceral during devolatilization was significantly less th an the vitrinite maceral or parent coal for the three reactive coals. However; the chars formed from inertinite burned at similar rates to v itrinite char. The similarity in maceral char combustion rates was con firmed on a single-particle combustor; however, the three reactive coa ls and their macerals burned at the diffusion limit. Although char com bustion rates were similar the low initial weight loss of the inertini te fraction would result in longer combustion times for complete combu stion of the inertinite char. Scanning electron microscopy revealed th at inertinite chars from the HV bituminous and the LV bituminous coals generally retained their original morphology during deuolatilization, while the vitrinite macerals went through a plastic phase. The ''reac tive'' HV bituminous coal formed porous, spongelike chars, while the ' 'unreactive'' LV bituminous coal developed vesicular chars with low su rface area.