AN EXPERIMENTAL INVESTIGATION OF THE INITIAL STAGES OF PULVERIZED BITUMINOUS COAL COMBUSTION (PYROLYSIS, MACERAL, IGNITION, MODEL, CHAR STRUCTURE)

The effect of maceral composition and particle size on the weight loss and structural changes of pulverized coal particles during combustion has been investigated. A comparison of the results between pyrolysis and combustion was used to examine the physical and chemical changes of the coal particles in the initial stages of a pulverized coal flame. A numerical investigation of the time-temperature history of coal particles was also conducted to elucidate their thermal behavior. The pyrolysis and combustion experiments were conducted in an entrained-flow reactor at temperatures from 1000 K to 1200 K in N(,2) and air atmospheres. Variations in maceral composition were achieved by size and gravity separations of a pulverized bituminous coal.; The order of decreasing weight loss by pyrolysis of samples with various maceral compositions was the same as that of the proximate volatile matter; that is, liptinite rich > vitrinite rich > inertinite rich. However, for combustion this trend did not always apply. Heterogeneous char combustion occurred and contributed to a substantial portion of the observed weight loss during the preignition and volatiles combustion stages. The extent of heterogeneous reaction was greater in the case of the combustion of large particles and inertinite rich fractions. Consequently, the effect of maceral composition on weight loss is less pronounced for large particles than for smaller ones.; Examination of the coal/char structural transformations suggested that the vitrinite in the bituminous coal softened earlier and developed larger cenospheres than the other macerals. The development of microporosity occurred predominately after the resolidification of the swelled char particles and was dominated by the extent of secondary volatiles evolution. The type of macerals originally in the coal did not significantly affect the final microporosity developed. Conversely, the presence of liptinite tended to enhance the thermoplasticity and formation of thin-walled cenospheres with a high extent of anisotropy; a high concentration of inertinite led to the formation of isotropic lacy or thick-walled cenospheres.