Accessible Unlicensed Requires Authentication Published by De Gruyter June 4, 2008

Water absorption thermodynamics in single wood pellets modelled by multivariate near-infrared spectroscopy

Torbjörn A. Lestander
From the journal

Abstract

Samples of wood pellets were adjusted into six water content classes from 0% to 12%. The water content in single pellets varied between 0.1% and 14.2%. Three equations were constructed to estimate the differential heat of sorption (-ΔH) values from (1) fractal-geometry, (2) isosteric, and (3) calorimetric data. The ranges in calculated -ΔH of single pellets were (1) 133–1475, (2) 315–881, and (3) 195–1188 J g-1 water, respectively, across the studied moisture content range. Partial least squares regression was used to model near-infrared (NIR) spectra from single pellets and to predict -ΔH values and water content. The explained variation in test sets for the different models ranged from 97.1% to 99.9%. The shifts in peak absorbance for two water bands indicated that frequency in overtone vibration of O-H stretching and bending decreased, when water content was raised. Simulations of mixes between pellets of differential heat values showed that released heat was up to 0.03% of the gross calorific value of wood pellets. This heat may be a major contributor to initial temperature increases in pellet stacks during storage. The results indicate that on-line NIR based predictions of differential heat in wood pellets is possible to apply in the pellet industry.


Corresponding author. Unit of Biomass Technology and Chemistry, Swedish University of Agricultural Sciences, P.O. Box 4097, SE-904 03 Umeå, Sweden Phone: +46-90-7868795 Fax: +46-90-7868799

Received: 2007-7-6
Accepted: 2008-2-8
Published Online: 2008-06-04
Published in Print: 2008-07-01

©2008 by Walter de Gruyter Berlin New York