Combustion kinetics and mechanism of biomass pellet

The effect mechanism of biomass pelletization on the property of bio-char, combustion kinetics and mechanism of pellet remain unclear. Therefore, in this work combustion behavior and kinetics of typical biomass pellets were investigated using TGA and Distributed Activation Energy Model. The bio-chars, from the pellets and raw biomasses, were also characterized in detail, to deeply understand the combustion mechanism of biomass pellet. The results showed that the activation energies of devolatilization stage of the pellet combustion were 118.1–230.2 kJ/mol, higher than that of raw biomasses, however, the activation energy decreased to 201.4–222.4 kJ/mol, for char combustion stage of pellet combustion, lower than the raw biomass. The compact physical structure of the biomass pellet caused by pelletization suppressed the mass and heat diffusion and thus enhanced the activation energy of devolatilization stage. The pelletization also suppressed the deoxygention, polymerization and aromatization reactions during the devolatilization stage, which caused higher reactivity of the pellet char than raw biomass char. This was the main reason for the lower activation energy of the pellet char combustion stage. Thus, the controlling factor of biomass pellet combustion is mass and heat diffusion for devolatilization stage, on the contrary, it was chemical reactions for char combustion stage.