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Research article2008Peer reviewed

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

Lestander, Torbjorn A.


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 (-Delta H) values from (1) fractal-geometry, (2) isosteric, and (3) calorimetric data. The ranges in calculated -Delta H 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 -Delta H 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 online NIR based predictions of differential heat in wood pellets is possible to apply in the pellet industry.


bioenergy; biofuel; initial heat; moisture sorption; multivariate calibration; near-infrared (NIR) spectroscopy; pellet storage

Published in

2008, Volume: 62, number: 4, pages: 429-434