Características termogravimétricas e combustão da madeira de Tachigali vulgaris proveniente de plantios com diferentes espaçamentos

Abstract

Tachigali vulgaris (tachi-branco) is a woody species of Amazonia commonly used for energetic purposes by local populations. The knowledge of kinetics of the thermal degradation of its wood is essential to adequate the thermos-chemical conversion processes aiming at the direct production of energy or charcoal. Therefore, the aim of this study is to evaluate the thermal behavior of tachi-branco wood from different crop spacings during combustion and pyrolysis. 7-years old trees were harvested from an experimental trial, located at Monte Dourado, Pará, Brasil, planted at different spacings of 3.0 x 1.5 m, 3.0 x 2.0 m, 3.0 x 2.5 m, 3.0 x 3.0 m, 3.0 x 3.5 m and 3.0 x 4.0 m. For wood pyrolysis under inert nitrogen atmosphere, the TG (thermos-gravimetric) and DTG (first derivative of the thermos-gravimetric) curves exhibited three different stages of mass loss that correspond to thermal degradation of hemicelluloses, cellulose and lignin. The temperature range for hemicelluloses decomposition varied from 280°C to 320°C, with mass loss of 17%. For cellulose, the range was from 340°C to 380°C with mass loss of about 50%. From the temperatures near 400°C on, the wood thermal degradation decreased, with mass loss of 5%. The wood from 3.0 x 2.0 m, 3.0 x 2.5 m and 3.0 x 3.0 m spacings showed higher residual mass, which suggests higher charcoal yield. For the combustion, two main decomposition reactions were observed, corresponding to the volatilization of hemi-celluloses, cellulose, and a fraction of lignin. At the second stage, the decomposition of the remaining lignin and fixed carbon occurred. Regardless of the tree spacing, the low ignition temperature (233.7°C), the high final combustion temperature (451.6°C) and the high ignition (4 x 103%/min3) index showed that the species show adequate characteristics for the direct production of thermal energy.