Biomass torrefaction: Modeling of reaction thermochemistry

Abstract

Based on the evolution of volatile and solid products predicted by a previous model for willow torrefaction (Bates and Ghoniem, 2012) a thermochemical model has been developed to describe their thermal, chemical, and physical properties as well as the rates of heat release. The first stage of torrefaction, associated with hemicellulose decomposition, is exothermic releasing between 40 and 280 kJ/kginitial. The second stage is associated with the decomposition of the remaining lignocellulosic components, completes over a longer period, and is predicted to be either endothermic or exothermic depending on the temperature and assumed solid properties. Cumulative heat release increases with the degree of torrefaction quantified by the mass loss. The rate of mass loss and rate of heat release increase with higher temperatures. The higher heating value of volatiles produced during torrefaction was estimated to be between 4.4 and 16 MJ/kg increasing with the level of mass loss.