Estimation of moisture in wood chips by near infrared spectroscopy

In order to assess the moisture content of wood chips on an industrial scale, readily applicable techniques are required. Thus, near infrared (NIR) spectroscopy was used to estimate moisture in wood chips by means of partial least squares regressions. NIR spectra were obtained in spectrometer with an integrating sphere and optical fiber probe, on the longitudinal and transverse surface of Eucalyptus wood chips. The specimens had their masses and NIR spectra measured in 10 steps during drying from saturated to anhydrous condition. Principal Component Analysis was performed to explore the effect of moisture of wood chip on NIR signatures. The values of moisture content of chips were associated with the respective NIR spectra by Partial Least Squares Regression (PLS-R) and Partial Least Squares Discriminant Analysis (PLS-DA) to estimate the moisture content of wood chips and its moisture classes, respectively. Model developed from spectra recorded on the longitudinal face by the integrating sphere method presented statistics slightly better (R²cv = 0,96; RMSEcv = 7,15 %) than model based on optical fiber probe (R²cv = 0,90; RMSEcv = 11,86 %). This study suggests that for calibration of robust predictive model for estimating moisture content in chips the spectra should be recorded on the longitudinal surface of wood using the integrating sphere acquisition method

Structural and compositional changes in eucalyptus wood chips subjected to dry torrefaction

The aim of this study was to evaluate the structural and compositional changes in eucalyptus wood chips subjected to dry torrefaction. The experiment was conducted in a semi-continuous screw reactor with indirect heating system. Wood chips samples of three initial moisture contents (0, 15 and 30% dry basis) were torrefied up to three final temperatures (220, 260 and 300 °C) and at three heating times (10, 15 and 20 min). The effect of these variables was evaluated through the analysis of chemical composition, thermogravimetry and mechanical durability of the torrefied wood chips. The increase at temperature and time of torrefaction, as well as the drop in the initial moisture content, promoted significant structural and compositional changes in the wood chips. The torrefied samples present a higher resistance to thermal degradation, more friable structure, higher lignin and lower polysaccharides contents than the untreated samples. These changes made it possible to increase the quality of the eucalyptus wood chips to be use as a solid fuel