Rapid pyrolysis and combustion of pulverized montana rosebud subbituminous coal

Abstract

The pyrolysis and combustion of narrowly size-graded pulverized Montana Rosebud subbituminous coal has been studied in an entrained-flow reactor which allows independent control of the gas temperature (1150 K–1750 K) and oxygen concentration (0–15%), with a dilute particle loading to eliminate inter-particle interactions. The use of both gas and solids sampling provides independent characterizations of the extent of pyrolysis and combustion. At high gas temperatures (1750 K) rapid pyrolysis is observed, with ultimate pyrolysis yields reached within 11 msec. Physical analysis of the partly reacted chars quantitatively confirm the pyrolysis yields based on gas sampling, with a rapid formation of voids within the particles and ejection of mass (before 11 msec), and relatively little change thereafter. Gas sampling indicates carbon conversion during pyrolysis of 29% at 1540 K and 40% at 1750 K. Carbon-containing pyrolysis products include CO, CO 2 , light hydrocarbons and tar; nitrogen is detected primarily as HCN, with smaller amounts of NH 3 . Under oxidizing conditions, even at oxygen concentrations as low as 2.0%, these pyrolysis products are oxidized at early residence times, and virtually no hydrocarbons, tar, HCN or NH 3 are detected. Following pyrolysis, diffusion-limited char combustion is observed at 2.0% O 2 , with a transition from zone III to zone II kinetics as the oxygen concentration increases from 2.0% to 15%.