Thermal Decomposition of Biochar from Oxidative Spruce Torrefaction - A Kinetic Study

In this work, biochar produced via torrefaction of Norwegian spruce at different temperatures (250, 275, or 300oC) in a simulated oxy-fuel combustion flue gas (CO2/H2O=1:0.7 mole/mole, O2/CO2=10 % v/v) for 30 minutes was examined by means of a thermogravimetric analyser (TGA) operated non-isothermally in an N2 environment. A distributed activation energy model (DAEM) was applied for a kinetic analysis of the TGA data,assuming three pseudo-components. The results showed that the model closely described the pyrolysis of the biochar obtained from spruce torrefied at 250 or 275oC, but not 300oC. The effect of the torrefaction temperature on pyrolysis kinetics of the Norway spruce is stronger than that of the carrier gas composition. Oxidative torrefaction increases the activation energy of hemicellulose and lignin, but decreases the activation energy of cellulose.