The influence of oxygen and total pressure on the surface oxidation rate of bituminous coal

The intrinsic reaction rates of several bituminous coals and a carbon black have been studied over a range of particle temperatures (1700–2200 K), total gas pressures (5.5–10 atm) and oxygen mole fractions (0.1–0.5) in a conventional shock tube. The surface reaction rates (based on external surface area) of the coals were observed to vary inversely with total pressure while no such dependence was noted for the carbon black. In conjunction with observations of reducing diameter burnout mode and large surface reaction rate Arrhenius activation energies, these results suggest the existence of a roughsphere kinetics regime. The true reaction order with respect to oxygen partial pressure measured at constant gas temperature is observed to be nearly 1/2; however, correction for the accompanying increase in particle temperature reduces the overall order to about 1/5. The true activation energies for both coals are about 34 kcal/mole over the temperature range studied. When corrected for pore penetration, the intrinsic reaction rates of the coals are observed to be greater than those measured for the carbon black and those predicted by a recent correlation in the temperature range of 1500 to 2100 K.