Investigation into the kinetic behavior of biomass combustion under N2/O2 and CO2/O2 atmospheres

Isoconversional kinetic method (model-free kinetics) was used in this study to determine the activation energies (E (a)) of the combustion process of five different biomass samples, namely pine sawdust, sugarcane bagasse, coffee husk, rice husk and tucum seeds, widely available in Brazil. Two different atmospheres with 20 % O-2:N-2/O-2 (conventional combustion) and CO2/O-2 (typical oxy-fuel combustion) were studied. Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves were used to obtain experimental data on the thermal degradation behavior of the biomasses, and the activation energy values were obtained for hemicellulose, cellulose and residual lignin separately. The results show that the E (a) obtained for N-2/O-2 ranged from 68 to 236 kJ mol(-1) for hemicellulose, 119 to 209 kJ mol(-1) for cellulose and 87 to 205 kJ mol(-1) for residual lignin, depending on the type of biomass. Under CO2/O-2 atmosphere, E (a) showed decreases, in average, 35 % for hemicellulose and 26 % for cellulose, in comparison with N-2/O-2 atmosphere. However, a 6 % increase was observed for the residual lignin. These changes can be understood by differences between CO2 and N-2 gas properties. However, the results show that the variation in the E (a) is more dependent on the type of biomass than on the atmosphere at which the combustion takes place.