Swelling and plastic behavior of coal devolatilized at elevated pressures of air in the absence and presence of calcium oxide

Swelling and plastic properties of an lv bituminous coal (PSOC 1197) devolatilized at elevated air pressures (at 60 or 150 K/min) were monitored using a high-pressure microdilatometer. It was observed that the maximum swelling parameter (V₈) of the coal was markedly reduced when devolatilized at elevated air pressures, provided that the heating rate of the coal was sufficiently low (60 K/min to 923 K). In marked contrast, at a relatively higher heating rate (e.g., 150 K/min), the swelling of coal at elevated air pressures was closer to V_s obtained in N₂ pressures. An implication of this finding is that coal swelling can be very high at actual utilization conditions (rapid heating of coal in air). The reduction in coal V_s at a relatively slow heating rate is attributable, at least in part, to the preoxidation (chemisorption of oxygen to form oxygen crosslinks) of coal during initial heat-treatment in air (before there is significant devolatilization). Devolatilization of coal in the presence of CaO, however, markedly reduced the swelling of coal at various air pressures and heating rates. This reduction in coal swelling is attributed to crosslinking reactions of pyrolyzing coal that have been catalyzed by CaO.