Lignocellulosic biomass torrefaction is an important step for diesel production through the BTL (Biomass To Liquid) chain. Torrefaction is a non-oxidative thermal treatment in the temperature range from 200 to 300°C. The aim of this process is to modify biomass structure in order to facilitate pneumatic transportation after grinding. However, some exothermic reactions are triggered in this temperature range which can lead to a lack of temperature control inside the reactor with detrimental effects on the product quality or even destructive effects on the facility. The purpose of this study is to contribute to the development of a multi-scale model for simulating these thermal runaway phenomena. Starting with the smallest scale, anhydrous weight loss combined with heat flux measurement from powders have been performed in a TGA-DSC. A data base was developed from three types of woody biomass, namely locust, spruce and an eucalyptus and from the main lignocellulsic components which are cellulose, xylan, glucomannan and lignin. A thermo-kinetic model able to reproduce the measured mass loss and heat flux during torrefaction has been developed by using the Distributed Activation Energy Method. Kinetic parameters and reaction enthalpies have been identified by inverse method taking into account the comprehensive set of data over several isothermal conditions with residence times of up to ten hours. Proceeding to larger scales, temperature measurements under torrefaction conditions have been performed separately in individual macro-particles and in a large scale packed bed of wood chips in order to test models at these scales. Thermal excursions were observed both within the particles and the bed due to the exothermic reactions. In the fixed bed an actual amplifying thermal wave was observed to propagate along the axial direction have been performed. A macroscopic heat and mass transfer model coupled with the kinetic model developed in this work allowed to simulate the temperature field at the macro-particle scale. Further model developmental work is needed to simulate the bed scale, Experimental observations and modelling carried out in this work represent an important improvement for the prediction of the heat released by torrefaction reactions in order to make this thermal pre-treatment safer and economically valuable.
