Study of the kinetics of thermal decomposition of sunflower hull pellets by thermogravimetric analysis under air atmosphere

Abstract

Sunflower husk pellets are considered a promising renewable biofuel due to their high carbon content, considerable calorific value, and low concentrations of sulfur, chlorine, and ash. In this study, thermogravimetric analysis was performed to investigate the thermal decomposition behavior of sunflower husk pellets in an air atmosphere at heating rates of 5 30 °C/min. The decomposition process was divided into three main stages: drying, devolati lization and combustion of volatiles, and oxidation of the coke-ash residue. Increasing the heating rate shifted the decomposition temperature range and the peak of the pyrolysis rate toward higher temperatures, while reducing the amount of residual carbon due to more inten sive oxidation. The presence of oxygen causes additional oxidation of intermediate products and promotes a more thorough degradation of wood compared to an inert atmosphere. The kinetic parameters were determined using three isoconversional (model-free) methods: Kissin ger-Akahira-Sunose, Ozawa-Flynn-Wall, and Starink. The Ozawa-Flynn-Wall and Starink methods showed the highest linear correlation (R2=0.91–0.98), yielding average activation energies of 47.86 ± 1.33 kJ/mol and 41.43 ± 1.31 kJ/mol, respectively. The most probable reaction mechanism, evaluated by the Avrami theory and the Coats-Redfern method, corre sponds to a first-order reaction model typical for the thermal degradation of lignocellulosic materials. The pre-exponential factor lnA was found to vary between 22.98 and 27.19 as the conversion degree increased, demonstrating a compensation effect between the kinetic parame ters. The obtained kinetic data can be effectively applied for computational fluid dynamics simulations of sunflower husk pellet pyrolysis and for modeling mass and energy balances in biomass combustion systems. Bibl. 80, Fig. 5, Tab. 3.