Abstract
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 pre-exponential 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 pre-exponential diffusion coefficient and activation energy found for IR drying were m2.s-1 and J.mol-1. The convective drying pre-exponential diffusion coefficient and activation energy calculated was m2.s-1 and J.mol-1 respectively.
Highlights
Woodchip production consists of processing wood through three main stages (i) sourcing timber, (ii) chipping of logs, and (iii) drying the chipped wood
To identify the goodness of the fit commonly used statistical criteria were used; these include the sum of the square estimate errors (SSE), Equation 12, residual squared (R2), Equation 13, and root mean squared error (RMSE), Equation 14
RMSE = [0.5 ∑ni=1(MRi − MRi)2]0.5. These results show the goodness of fit to the models within Table 1
Summary
Woodchip production consists of processing wood through three main stages (i) sourcing timber, (ii) chipping of logs, and (iii) drying the chipped wood. With the calorific (MJ/kg) value of woodchip being linearly proportional to its moisture content [1], drying wet chip. Biomass boilers are rated to a defined moisture content of wood feed. Other benefits of drying include quality, characterisation of wood allowing comparison between various origins, reduced energy consumption for transport and storage, driven by a reduction in mass and fungal build up. The fuel sourced from woodchip is generally in higher demand over the winter period when the supply faces a higher moisture content due to both the colder and wetter weather. In winter months drying is required to improve the fuels quality and preserve and keep a consistent supply
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