Variation of char reactivity during simultaneous devolatilization and combustion of coals in a drop-tube reactor

Intrinsic reactivities and activation energies are presented as a function of reaction conditions and carbon conversion for five coal chars produced in situ in the devolatilization zone of a simulated one-dimensional pulverized coal flame environment in an electrically heated drop-tube reactor. Oxygen partial pressures varied from 0.01 to 0.09 atm and gas temperatures from 1123 to 1573 K. Carbon conversion rates were determined by elemental analysis of solid material collected along the axis of propagation. The intrinsic activation energies obtained varied from around 135 kJ mol −1 in the initial char combustion stage to 220 kJ mol −1 towards the end of reactor, where the remaining solid burned with little volatiles evolution. Results are presented indicating that a transition from regime II to regime I conditions takes place over the experimental conditions investigated. The intrinsic reactivities were further compared with the rate of elemental hydrogen release from the particles.