Modeling of biofuel pellets torrefaction in a realistic geometry

Abstract

Low temperature pyrolysis also known as torrefaction is considered as a promising pretreatment technology for conversion of biomass into a solid biofuel with enhanced properties in terms of lower moisture and volatile matter content, hydrophobicity and increased heating value. A thermal treatment leads to a non-uniform temperature field and chemical reactions proceeding unevenly within the pellets. However the temperature is assumed to be uniform in the pellets in the majority of models. Here we report on the model of single pellet biomass torrefaction, taking into account the heat transfer and chemical kinetics in the realistic geometry. The evolution of temperature and material density in the non-stationary thermo-chemical process is described by the system of non-linear partial differential equations. The model describing the high-temperature drying of biomass pellet was also introduced. The importance of boundary effects in realistic simulations of biomass pellets torrefaction is underlined in this work.