Combustion and Emission Characteristics of Sawdust-Coal Fine Pellets

Pellets made from wood and coal residues at various ratios (0, 25, 50, 75, and 100% wood, and 50% wood-plus-limestone) were burned at different underfire/overfire air mixtures (20, 40, 60, and 80%) in a laboratory stationary bed burner to determine the effects of wood/coal ratio and underfire/overfire air mixture on the combustion and emission characteristics of wood-coal pellets. The results indicated: 1) the oxygen depletion periods appeared to increase with increasing percentages of wood in the pellets and also to increase with increasing underfire air (UFA); 2) increasing wood percentages in pellets decreased flame temperature and total run time, and, thus increased the firing rate; 3) increasing percentages of wood in pellets reduced sulfur dioxide (SO 2 emissions but increased carbon monoxide (CO) and methane (CH 4 ) emissions; 4) increasing UFA increased the CO, CH 4 , and SO 2 emissions; and 5) adding a small quantity of limestone to wood-coal pellets greatly increased the capture of sulfur in the bottom solids and thus reduced the SO 2 emission substantially.