Effect of a mild torrefaction for production of eucalypt wood briquettes under different compression pressures

The heat treatment of wood (i.e. torrefaction) followed by densification of wood particles (e.g. by briquetting) may be used as a process to improve homogeneity and energy properties of wood for use as a solid fuel. The wood of Eucalyptus grandis and Eucalyptus spp. were treated at 180, 200 and 220 degrees C for 60 min under a nitrogen atmosphere. Briquettes were produced with untreated and heat-treated wood particles using 120 degrees C, for 7 min pressing and 6 min cooling time, under pressures of 6.9, 10.3 and 13.8 MPa. The briquetting compacting pressure showed no significant influence on the briquettes properties. Briquettes density was similar for all cases presenting 1.14 g cm(-3) for Eucalyptus spp. and 1.06 g cm(-3) for Eucalyptus grandis wood. A mild torrefaction of the wood at 200-220 degrees C increased the potential energy of the particles and briquettes, showing an improvement in their density, dimensional stability and hygroscopicity. Briquettes produced from heat-treated Eucalyptus spp. wood presented higher energy density (24.79 GJ m(-3)) at 200 degrees C-treatment when compared with untreated wood (20.76 GJ m(-3)). Regarding E. grandis, briquettes produced with heat-treated (200 degrees C) particles showed only a marginal higher energy content than with untreated wood, 21.70 GJ m(-3) and 21.38 GJ m(-3), respectively. The two eucalypt woods showed differences regarding the heat treatment and briquetting, pointing out that the optimization of these processes should be specific for each species. However, a mild torrefaction of the wood particles decreased the differences between materials which might be useful as a process to increase feedstock homogeneity when using mixed raw-materials. (C) 2016 Elsevier Ltd. All rights reserved.