A Comparative Study of Diffusion Coefficients from Convective and IR Drying of Woodchip

Convective and infared (IR) Halogen Drying processes are used in the woodchip biomass industry to test the moisture content of woodchip. Woodchip drying, though energy intensive, is necessary to increase the calorific content of woodchip, in turn increasing combustibility. The bulk process within the production of woodchip uses convective drying with agitation. Analysis of the diffusion in wood can be used to estimate the time to dry lumber to a specified moisture content value. Relationships between the effect of temperature and moisture content allow more accurate predictions and operational evaluations of driers. The aim of this study was to investigate constant heat source convective and IR drying by comparing the drying curves when batch drying a sample of woodchip biomass whilst controlling the heat source temperature at 328K, 338K, 348K and 358K. This was achieved through comparison of preexponential diffusion coefficients and activation energy, determining the temperature dependency of these terms in convective and IR drying of wetted wood. Lower temperatures increased drying time for both convective and IR drying, with convective drying taking up to 5 times longer than IR. The preexponential diffusion coefficient and activation energy found for IR drying were 3.555 ×10±0.824 ×10 m2.s-1 and 3.405 ×10±0.065 ×10 J.mol-1. The convective drying preexponential diffusion coefficient and activation energy calculated was 2.948 ×10±0.376 ×10 m2.s-1 and 1.619 ×10±0.037 ×10 J.mol-1 respectively.