Kinetics investigation on the combustion of biochar in O₂/CO₂ atmosphere

Oxy-biomass combustion produces negative CO₂ emissions. This study investigated the combustion kinetics of biochar in O₂/CO₂ atmosphere using a thermo-gravimetric analyzer. The effects of atmosphere, O₂ concentration, and fuel type were considered in this investigation. Results show that the reaction order of biochar combustion ranges from 0.5 to 1. Furthermore, the kinetic compensation effect can be observed between the apparent activation energy E and the frequency factor A. This relation is given by lnA = 0.181E - 14.618. Compared with O₂/N₂ atmosphere, O₂/CO₂ atmosphere delays biochar ignition and reduces activation energy. The ignition temperature of straw char is significantly lower than that of wood and coal char. The apparent activation energy of char combustion follows the inequality wood char > straw char > coal char. This result indicates that biochar combustion is more sensitive to temperature than coal char combustion. The reactivity of char combustion improves with increasing O₂ concentration, but biochar has a lower degree of improvement than coal char. The change from air combustion to oxy-fuel combustion and the increase in O₂ concentration exert minimal effects on biochar combustion than on coal char combustion.