The pre-treatment of biomass intended as fuel through the process of torrefaction has provoked much interest during the last few years because the resulting material has improved features compared to those of untreated biomass and might even allow outside storage. In order to assess the effect of sorption on storage properties, the adsorption of water vapour into torrefied wood and charcoal was studied by measuring the influence of different pyrolysis temperatures on the equilibrium moisture contents of the samples in constant temperature of 20°C and relative humidities ranging from 30 to 95%. The absorption of water into sample pieces was studied by an immersion experiment. The amount of hydroxyl groups free for binding water molecules is to be determined with P³¹ Nuclear Magnetic Resonance (NMR) measurements.
The preliminary results from the adsorption experiment show a decrease in the equilibrium moisture content following increasing severity of treatment, as higher treatment temperatures result in lower water binding ability. This is mainly due to less available hydroxyl groups, a result of degradation of the wood constituents, namely hemicellulose and amorphous cellulose. In contrast to this, the moisture contents of the samples increased with increasing treatment temperatures.
Keywords: Adsorption, absorption, water, torrefaction
Authors
Kymäläinen M.
Department of Forest Sciences, University of Helsinki
Havimo M.
Department of Forest Sciences, University of Helsinki
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