CHAR FRAGMENTATION AND FLY-ASH FORMATION DURING PULVERIZED-COAL COMBUSTION

Experimental measurements of char and fly ash size distributions are reported in the size range from approximately 0.5 to 100-mu-m for three coals, ranging in rank from high-volatile bituminous coal to lignite. These measurements are coupled with a theoretical model of fly ash formation to determine the extent of char fragmentation as a function of initial char particle size. These data reveal several mechanistic aspects of fragmentation. The extent of fragmentation is strongly dependent or size and coal rank. Bituminous coals may form over 100 fragments per char particle at large initial char particle sizes (above 80-mu-m) and less than 10 at small initial char particle sizes (less than 20-mu-m). Lignites fragment less extensively, with the number of fragments per original char particle being less than 5 at all particle sizes. These results partially resolve some apparent discrepancies in published studies of fragmentation.