Effects of thermal conditions on char yield and char reactivity of woody biomass in stepwise pyrolysis

Stepwise pyrolysis with one low-temperature thermal pretreatment (torrefaction or carbonization) and one high-temperature pyrolysis is an important utilization of biomass. This study aims to investigate the effects of thermal conditions on char yield and char reactivity in the stepwise pyrolysis with woody biomass used as feedstock. The accumulated char yield (on original mass basis) and char reactivity were determined. Pyrolysis products were analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectrum. The results show that thermal pretreatment increases the aromaticity of feedstock as well as char yield, and reduces the char reactivity and degree of order, which indicate probable intrinsic correlation among them. The effect of thermal pretreatment on char yield is more pronounced at elevated pyrolysis temperature, but indiscernible at low heating rate. The influences of particle size and residence time of thermal pretreatment are relatively small.