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This work continues our assessment of wet torrefaction for energy applications, looking at effects of the process parameters (temperature, holding time and pressure) on the reactivity and intrinsic kinetics of wood under air combustion conditions. Woody materials, Norway spruce and birch, were wet torrefied in various conditions (temperature: 175, 200, 225 degrees C; holding time: 10, 30, 60 min; and pressure: 15.54, 70, 160 bar). The reactivity of the treated and untreated woods was thermogravimetrically examined under a synthetic air environment (21% O-2 and 79% N-2 in volume). A four-pseudo-component model with different reaction orders was adopted for kinetic modelling and extracting the kinetic parameters. The results showed that when increasing either torrefaction temperature or holding time, the torrefied woods behaved more char-like than the raw fuels. However, pressure did not show significant effect on the reactivity. Relatively longer char combustion stages and higher conversion rates (up to 0.5 x 10 (3) s (1)) were observed for the woods after torrefaction. The activation energy was decreased for hemicellulose and char, but increased for cellulose after torrefaction, whereas the trend for lignin is not clear. In addition, the hemicellulose mass fraction decreased after torrefaction (from 0.15 to 0.05 for spruce and from 0.23 to 0.06 for birch). The amount of char in the torrefied woods increased gradually with increasing torrefaction temperature or holding time (from 0.24 to 0.40 for spruce, and from 0.18 to 0.34 for birch). (C) 2014 Elsevier Ltd. All rights reserved.
Author(s): Bach QV, Tran KQ, Skreiberg O, Khalil RA, Phan AN
Publication type: Article
Publication status: Published
Journal: Fuel
Year: 2014
Volume: 137
Pages: 375-383
Print publication date: 01/12/2014
Online publication date: 19/08/2014
Acceptance date: 05/08/2014
ISSN (print): 0016-2361
ISSN (electronic): 1873-7153
Publisher: Elsevier
URL: http://dx.doi.org/10.1016/j.fuel.2014.08.011
DOI: 10.1016/j.fuel.2014.08.011
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