Prediction of Sawdust Pyrolysis Yields from a Flat-Flame Burner Using the CPD Model

High heating rate pyrolysis experiments were performed on a softwood sawdust in a flat-flame burner reactor at temperatures from 1163 to 1433 K with particle residence times ranging from 23 to 102 ms at atmospheric pressure. Volatile yields of the 45-75 mu m sawdust were measured and are believed to be similar to those that would occur in an industrial entrained-flow combustor or gasifier. A refractory tar yield near 1.5 wt % (dry, ash-free) was measured. A high percentage of the fully pyrolyzed sawdust char was spherical, having lost the original sawdust structure. It is suggested that the morphology of sawdust char may continue to change after complete mass release from pyrolysis. Sawdust pyrolysis was modeled using the chemical percolation devolatilization (CPD) model assuming that biomass pyrolysis occurs as a weighted average of its individual components (cellulose, hemicellulose, and lignin). Thermal cracking of tar into light gas was included using a first-order kinetic model from the literature. The devolatilization yields of three kinds of sawdust from three different reactors (flat-flame burner, drop-tube, and thermogravimetric analyzer) were accurately predicted.