Estimating hardness and density of wood and charcoal by near-infrared spectroscopy
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Estimating hardness and density of wood and charcoal by near‑infrared spectroscopy Raul de Abreu Neto1 · Fernanda Maria Guedes Ramalho1 · Lívia Ribeiro Costa1 · Paulo Ricardo Gherardi Hein1 Received: 9 March 2020 / Accepted: 5 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Hardness has been considered an important indicator of wood quality and presents a high correlation with density, and, as far as the authors know, there is no specific methodology to evaluate the hardness of charcoal. In this context, it is necessary to develop a reliable and efficient methodology to classify charcoal mechanical properties. Therefore, the aim of this study was to establish multivariate models to estimate dynamic hardness and density of wood and charcoal based on near-infrared spectra. For this, nine wood specimens were examined and pyrolyzed at 300, 450, 600 and 750 °C. The density of wood and charcoal was determined according to standard NBR 11941 (2003) and hydrostatic method, respectively. Dynamic hardness of wood and charcoal was determined by an automated portable hardness tester. Materials submitted to thermal treatment have different spectral signatures compared to those obtained by the wood. Charcoals produced at temperatures of 450, 600 and 750 °C exhibit similar behaviour, with low absorbance compared to wood and thermally treated material at 300 °C, indicating homogenization of charcoal caused by pyrolysis temperature. NIR spectroscopy was able to estimate density and dynamic hardness of wood and charcoal. Charcoal produced at 450 °C obtained a model with highest coefficient of determination and smaller errors. The results show the potential of NIR technology for fast and reliable estimation of physical and mechanical properties of charcoal based on spectra recorded on charcoal and even from wood before pyrolysis.
* Raul de Abreu Neto [email protected] 1
Department of Forestry Sciences (DCF), Federal University of Lavras (UFLA), Campus Universitario, Lavras, Minas Gerais 37200‑900, Brazil
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Wood Science and Technology
Introduction Brazil produced over 6.4 million tons of charcoal in 2018 (Faostat 2019) and is known to be the largest producer in the world. Steel industries are the main charcoal consumers (IBA 2019) and require charcoal with a quality compatible for metal production, such as charcoal with high density (Santos et al. 2011; Nones et al. 2015) and hardness (Zickler et al. 2006). Two main factors control charcoal quality: raw material properties (wood density, lignin content, etc.) and process variables (temperature, pressure, etc.). Wood properties used to produce charcoal are known to directly influence its quality (Dufourny et al. 2018), and pyrolysis temperature can change the mechanical characteristics of charcoal (Abreu Neto et al. 2018). Within blast furnaces, charcoal is used as a source of energy for the process and as a reducing agent for iron ore (Gupta 2003; Suopajarvi et al. 2013). Moreover, charcoal layers must mech
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