Kinetic analysis on low-temperature oxidation of wood pellets by isothermal microcalorimetry

Abstract

Low-temperature chemical oxidation is the major driver of self-heating during storage of wood pellets and its kinetics is essential to describe the heat evolution. In the present work, isothermal microcalorimetry was used to characterize heat generation behavior of three types of wood pellets (pine, fir, and redwood pellets) at 30–70°C. The obtained data were employed to derive the kinetics of low-temperature oxidation by the peak power, iso-conversional method, and non-steady analysis. The consistency and applicability of the kinetics derived by the three methods were evaluated. Kinetic parameters determined by the peak power method were observed to match those from the iso-conversional method at lower conversions of the oxidation for heat generation. The kinetics derived by the iso-conversional method indicated the oxidation reactivity generally decreasing and activation energy increasing with the conversion because of O₂ consumption and reaction mechanism changing. With the impact of O₂ consumption considered separately, the kinetics from the non-steady analysis is capable of describing the evolution of heat power with the conversion and also consistent with that from the peak power method in describing intrinsic reactivity of pellet materials. The kinetics from the peak power and iso-conversional methods lump the impact of O₂ concentration with the reaction reactivity, suggesting their applications requiring additional models for connecting with O₂ consumption.