An innovative kinetic model dedicated to mild degradation (torrefaction) of biomasses

Abstract

This study proposes an innovative approach to investigate the thermal degradation kinetic of biomasses when submitted to torrefaction. This process is expected to have a relevant impact in exploiting the potentialities of biomasses in many major end energy uses. The main motivation of this work moves from the observation that the adoption of the “model-free” isoconversional approach is applied, conventionally, limited to the activation energy (E) determination. This work extends the potentialities of these methods and demonstrates their feasibility in setting up a complete kinetic model.Moving from the fundamentals of the isoconversional analysis, this study identifies a specific constrain linking together the Arrhenius pre-exponential factor (A) and the reaction model function f(α). This achievement is exploited to derive a new kinetic parameter (φα) which replaces the two terms A and f(α) that, jointly with E, constitute the conventional kinetic triplet.The introduced parameters E and φα found the new two parameters kinetic equation whose solution is achieved by defining an innovative computational approach based on a finite difference scheme.As main result this study introduces an original exploitation of the “model-free” methods that avoids, contrarily to conventional solutions, any assumption for the f(α) function. Besides, the introduced equation solver scheme can be generalized to any heating program, isothermal or not.Three biomasses, belonging to the same hardwood family, have been specifically investigated. The performances of the model reach, in terms of Absolute Average Deviation, a predictive accuracy level within 1–5%.Considering the encouraging achieved results, the proposed model can be directly applied to support the design procedures specifically pertaining to biomass torrefaction plants.