Numerical studies of the flash pyrolysis of cellulose

Abstract

Numerical simulations reveal that the time required for rapid pyrolysis of cellulosic biopolymer particles (diameter ⩽ 0.5 mm) is composed of a heatup time t h and a devolatilization time t d . Approximations of t h and t d are given by the time required for radiative and convective heat transfer to raise the particle's temperature to a pyrolysis temperature T p (‘sensible’ heat requirement) and to provide the endothermic heat of reaction ΔH (‘latent’ heat requirement). The value of T p is specified by the chemical rate law governing pyrolysis. Recently reported rate laws place a practical upper limit on T p of ≈ 500 °C and provide for the complete vaporization of cellulose at high heating rates. Strong analogies exist between the time required for a given power input to provide both the sensible and latent heat requirements of a solid undergoing a phase change and the time required for heat transfer to effect cellulose pyrolysis. Correction factors reported here permit an accurate estimate of the time required for cellulose pyrolysis, based on the times required for the rate of heat transfer (power input) to provide the ‘sensible’ and ‘latent’ heats of pyrolysis at the (‘melting point’) temperature T p .