Investigation into torrefaction kinetics of biomass and combustion behaviors of raw, torrefied and char samples

Thermal decomposition of sugarcane bagasse (SCB), yellow poplar (YP), and biomass polymers (xylan, cellulose and lignin) were studied under isothermal conditions using a specially designed thermogravimetric analyzer (Quartz Wool Matrix, QWM) in the temperature range 240-300 degrees C. Reactivity of biomass was predicted using the measured reactivity of three individual polymers and a simple arithmetic superposition principle. The superposition model was modified to increase the prediction accuracies of torrefaction behavior. To evaluate the impact of torrefaction on combustion, the combustion kinetics were also studied for the torrefied SCB and YP, and for the pyrolyzed YP. Activation energies for combustion reaction using the Flynn-Wall-Ozawa (FWO) method for the non-isothermal events were estimated as a function of the degree of conversion. Reactivity indexes were also determined for each sample when 50% of decomposition was reached. Different stages of thermal degradation of each polymer in the material were identified in the combustion process, which was significant only at the low heating rate. The results confirm that the reaction rate decreases with torrefaction, thereby increasing the reaction index. The char from the torrefied biomass has more thermal stability than the char from raw biomass, which can be confirmed by the increased reaction index.