Torrefaction Kinetics of Norwegian Biomass Fuels

Torrefaction kinetics of Norwegian biomass fuels, including spruce (softwood) and birch (hardwood) was studied using a thermogravimetric analyser. Small samples of approximately 10 mg and particle size of 63−125 μm were heated at a constant heating rate of 5 °C/min and kept afterwards for 4 hours in isothermal conditions at different temperatures (230, 240, 250, 260, 270 and 280 °C). A two-step kinetic model was employed to simulate the recorded mass loss curves. The results showed that the decomposition of the initial biomass in the first step, to form an intermediate solid and volatiles, exhibited a higher conversion rate compared with the second step. The rate constants (in s) for two steps are: = 21.2 × exp . , = 4.74 × 10 exp . for spruce and = 106.6 × exp . , = 2.80 × 10 exp . for birch. Moreover, the final solid yield, which decreased gradually with increasing torrefaction temperature, reproduced the experimental results well.