In-depth investigation on the pyrolysis kinetics of raw biomass. Part I: Kinetic analysis for the drying and devolatilization stages

► Two different stages were shown in the pyrolysis process of biomass. ► Nonisothermal Page model is the best model for describing the drying kinetics. ► DAEM is not adequate for kinetics analysis in the first stage of biomass pyrolysis. ► Three ranges of activation energy are identified for the whole pyrolysis process. An in-depth investigation was conducted on the kinetic analysis of raw biomass using thermogravimetric analysis (TGA), from which the activation energy distribution of the whole pyrolysis process was obtained. Two different stages, namely, drying stage (Stage I) and devolatilization stage (Stage II), were shown in the pyrolysis process in which the activation energy values changed with conversion. The activation energy at low conversions (below 0.15) in the drying stage ranged from 10 to 30kJ/mol. Such energy was calculated using the nonisothermal Page model, known as the best model to describe the drying kinetics. Kinetic analysis was performed using the distributed activation energy model in a wide range of conversions (0.15–0.95) in the devolatilization stage. The activation energy first ranged from 178.23 to 245.58kJ/mol and from 159.66 to 210.76kJ/mol for corn straw and wheat straw, respectively, then increasing remarkably with an irregular trend.