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A utilização dos pellets de madeira para a geração de energia térmica está se difundindo no Brasil e a análise termogravimétrica tem sido amplamente aplicada para o estudo da decomposição da madeira e seus principais componentes como a celulose, as hemiceluloses e a lignina. O objetivo deste trabalho foi investigar o comportamento térmico de quatro diferentes amostras de pellets de madeira, em condições não isotérmicas, por meio das análises termogravimétricas TGA. Os ensaios foram conduzidos desde a temperatura ambiente até 500C, com taxa de aquecimento de 20C/min, em atmosfera inerte de gás nitrogênio, com fluxo de 100 mL/min. Os termogramas mostraram três estágios de decomposição: o primeiro, atribuído à evaporação da água e dos materiais voláteis; o segundo, refere-se à decomposição da holocelulose na pirólise ativa; e o terceiro, atribuído a decomposição da lignina na pirólise passiva. Além disso, conclui-se que a maior decomposição térmica ocorreu na faixa de temperatura compreendida entre 250C e 400C, com perdas superiores a 60,8% da massa inicial do biocombustível. PALAVRAS-CHAVE:Pellets de Madeira, Biomassa, Pirólise da Madeira, Termogravimetria por TGA. THERMAL DECOMPOSITION OF WOOD PELLETS BY TGA ABSTRACTThe use of wood pellets for generating thermal energy is spreading in Brazil and thermogravimetric analysis has been widely applied to study the decomposition of wood and its main components such as cellulose, hemicellulose and lignin. The objective of this study was to investigate the thermal behavior of four different samples of wood pellets in non-isothermal conditions by means of thermogravimetric analysis TGA. Assays were performed from room temperature to 500°C with a heating rate of 20°C/min in an inert atmosphere of nitrogen gas with a flow of 100 mL/min. The thermograms showed three decomposition stages: first, assigned to the evaporation of water and volatile materials; the second, refers to the decomposition of the active holocellulose pyrolysis; and third, attributed to the decomposition of lignin pyrolysis passive. Furthermore, it is concluded that most decomposed in the temperature range between 250°C and 400°C, with greater than 60.8 % of the initial mass of the biofuels losses.

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Wood pellets are biofuels produced from agroforestry waste such as sugarcane bagasse, wood sawdust and shavings. They are compressed biofuels that have low moisture, allowing high combustion efficiency, especially because they are natural products of easily handling with high energy density. To explore pellets opportunities in Brazil (production and marketing), it is necessary to provide information about the chemical and energy characteristics, technologies, prices and prospects of this market. Thus, this article aims to organize and make this information available, enabling general knowledge on the subject and subsidize more investment in the biofuels sector; mostly by adding value to agroforestry waste, available in large volumes in this country. The results showed a young industry, with sixteen plants and production of 49.39 ktonnes of pellets in 2014, but using only 25.5% of its annual production capacity.

Torrefaction is a thermal process that improves the energy properties of plant biomass pellets, providing greater biofuel efficiency for gasification technologies, as well as replacing coal in thermoelectric plants. In Brazil, many agroforestry residues can be improved in value through this technological process, transforming them into modern solid biofuels. There are few studies comparing torrefied wood and elephant grass pellets, especially in relation to their energetic characteristics. This study analyzed the high heat value, energy density, ash content, fixed carbon, volatile materials, lignin, holocellulose, extractives, bulk density, and mechanical durability of these pellets. Due to the absence of Brazilian normative standards for these pellets, the international standard ISO 17225 (2014) was used for comparisons. The results revealed substantial differences among the samples, mainly regarding their moisture content, higher heating value, and energy density in torrefied pellets. It was concluded that these torrefied pellets are biofuels having lower water adsorption, higher heating value, and higher energy density than the pine and elephant grass pellets.