Comparison between two-step and single-step kinetic models for non-isothermal CO2 gasification of biomass char generated by fast pyrolysis

Abstract

Kinetic analysis plays a critical role in the gasification process. The kinetics of CO2 gasification for various wood chars, which were prepared in a single particle reactor (SPR), were studied using a non-isothermal method in a thermogravimetric analyzer. To statistically derive significant conclusions, the data obtained from the gasification of fast pyrolyzed chars are used to compare the performance of the volumetric model (VM), grain model (GM), random pore model (RPM), integrated core model (ICM), and two-step (first step: VM; second step: ICM) parallel model. The obtained results show that most |DDTG| curves show one local minimum, representing at least one reaction step. When combined with the TG curves, the gasification process exhibits a distinct devolatilization and char gasification component. ICM has a better performance compared to the other single-step models. The two-step model significantly improves over the single-step model due to the additional equation. The two-step model's average deviation DEV(X) is 0.95 %, which shows an 80 % improvement compared to ICM (DEV(X) = 4.64 %). The predicted activation energy (devolatilization: 54.8–76.2 kJ/mol; gasification: 185.7–247.5 kJ/mol) falls within a reasonable range, which is consistent with the findings reported in the literature.