Kinetics analysis and numerical simulation of eucalyptus sawdust pyrolysis

In this study, thermogravimetric analysis (TGA) was employed to investigate the thermal decomposition characteristics and kinetic parameters of eucalyptus sawdust at heating rates of 5, 10, 15, 20, and 30 ℃/min (20–900℃) under a nitrogen atmosphere (99.99 %, 30 mL/min). The pyrolysis process of eucalyptus sawdust was divided into three stages: drying and preheating (DH), fast weight-losing pyrolysis (FP) and carbon growing (CG). Mechanism function fitting determined that the DH and FP stages followed follow n-order reaction and Jander-type 3D diffusion, respectively. The activation energy ( E ), pre-exponential factor logarithm (lg A ) and reaction order ( n ) of the DH and FP stages are 82.42 and 143.40 kJ/mol, 10.77 and 9.00 s −1 , and 2.58 and 2.00, respectively. The results are highly consistent with the E and lg A values estimated by FWO and Friedman methods in the conversion rate ( α ) range of 0.2–0.8. For the CG stage, a new reaction process fitting equation ( α = 0.8695 β 0.1319 ln T − 5.0275 β 0.1442 ) was developed by numerical simulation of fitting α , temperature ( T ) and heating rate (β ). The high coefficient of determination (R 2 >0.9700) confirms the equation's reliability. This study provides crucial theoretical support for optimizing the pyrolysis process of eucalyptus sawdust and guiding the reactor design. • The unexplained pyrolysis behavior of eucalyptus was studied in three stages. • The models of the first two stages of eucalyptus pyrolysis are Fn and D3. • Numerical simulation reveal final stage that cannot be explained by current models. • New fitting equation was established and its reliability was verified.