Modeling intra- and extra-particle processes of wood fast pyrolysis

A detailed single-particle model, including a description of transport phenomena and a global reaction mechanism, is coupled with a plug-flow assumption for extraparticle processes of tar cracking, in order to predict the fast pyrolysis of wood in fluid-bed reactors for liquid-fuel production. Good agreement is obtained between predictions and measurements of product yields (liquids, char, and gases) as functions of temperature. Particle dynamics are very affected by the convective transport of volatile products. The average heating rates are on the order of 450 - 455 K/s, whereas reaction temperatures vary between 770 and 640 K (particle sizes of 0.1 - 6 mm and a reactor temperature of 800 K). The effects of several factors, such as size, shape, and shrink-age of wood particles, and external heat-transfer conditions are also examined.