Moisture is the most important variable in biomass supply chain. It increases costs and emissions in transportation and reduces the heating value in combustion. During storage, moisture promotes the biological degradation of the fuel. Torrefaction has been presented as a solution for the moisture-related problems, as it significantly reduces the hygroscopic character of biomass. In order to investigate the interaction of torrefied wood and moisture, thorough measurements were conducted. The dynamic vapour sorption apparatus (DVS) was used to quantify the adsorption and desorption properties, sorption hysteresis, and hydroxyl group accessibility. In addition the particle size, BET surface area, and clustering behaviour of water molecules were analysed. As a result adsorption, sorption hysteresis, accessibility, particle size distribution, and the BET surface area were reduced from original. The clustering of water molecules shifted towards the high end of the hygroscopic range. In practice the most important results are the overall reduction of hygroscopicity, the smaller particle size, and the changes in the internal volume of the material, as they have both positive and negative effects on the logistics of the material.
Keywords: accessibility, dvs, hysteresis, sorption, torrefied wood
Authors
Kymäläinen M.
Department of Forest Sciences, University of Helsinki
Rautkari L.
Department of Forest Products Technology, School of Chemical Technology, Aalto University
Hill C.A.S.
Norwegian Forest and Landscape Institute, Ås, Norway
Department of Architecture and Civil Engineering, University of Bath, Claverton Down, Bath, UK
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