Kinetic Models of Wood Biomass Drying in Hot Airflow Systems

Abstract

In the field of convective drying, several models have been proposed by different research groups, both theoretical and empirical. However, research on theoretical mathematical models has been superficial and needs to be extended. Empirical models present difficulties in their implementation in other research. It is suggested that further research should focus on obtaining models adaptable to different species and environmental conditions. The aim of this work was to analyse the current state of research on the drying process and mass transfer. It is concluded that drying is a mathematically complex process that must be modelled with differentiated equations in two stages: constant drying rate stage and decreasing drying rate stage. The modelling of the constant drying phase can be based on the convective mass transfer equation, although the prediction of the coefficient with analogies to heat transfer has deviations in biomass. Modelling of the variable rate drying phase should focus on the variation of water diffusivity in porous materials or vapour permeability as a function of material moisture and temperature. A database of homogenised equations particularised for each material needs to be generated to predict drying rates and times under predetermined convection conditions. This represents a scientific challenge and suggests that research in drying kinetics still needs development.