Kinetic and Heat Transfer Control in the Slow and Flash Pyrolysis of Solids

The coupled effects of particle size and external heating conditions (reactor heating rate and final temperature) on cellulose pyrolysis are investigated by means of a computer model accounting for all main transport phenomena, variable thermophysical properties and primary, and secondary reaction processes. The dynamics of particle conversion are predicted, and final product distributions are favorably compared with experimental measurements. A map is constructed, in terms of particle size as a function of the reactor temperature, to identify the transition from a kinetically controlled conversion to a heat transfer controlled conversion (thermally thin and thermally thick regimes) and from flash to slow-conventional pyrolysis. Conditions for maximizing oil, gas, or char yields are also discussed.