Características dos resíduos da colheita de madeira de eucalipto e pinus, submetidos ao tratamento térmico, com foco na aplicação energética

Abstract

In the current worldwide context, the search for renewable energy sources and less polluting fuels than petroleum has become unavoidable. The use of biomass energy as source of energy is extremely important, especially due to its renewable character and abundance. The forest residues have been increasingly recommended as an important source of biomass. This is due to its abundance, facility of provision and low cost. We can cite examples such as the residues generated during the forest harvest (bark, leaves, branches, stem tips, among others) and during the mechanical processing of wood (slabs, chips, sawdust, among others). The use of this kind of material for energetic purposes has been increasing, however, there is room for benefits to be implemented in this field, involving a deeper knowledge on its characteristics and the potential for the application of processes to its conversion into more optimized products in relation to its energy values. In this scenario, and considering the wood, there comes the opportunity to the adoption of thermal treatment processes, to which there are already references that indicate the occurrence of changes in the characteristics of this material, which leads to the prediction of the possibility to obtain positive results in relation to what is demanded for energetic uses. Besides the traditional and widely used process of drying, it is observed, in the field of thermal treatment, the increase in the interest for the application of the so-called torrefaction and thermal rectification, comprising zones of temperature between 150 and 300 ° C. In this context, residues of eucalyptus and pine forest harvest were submitted to a thermal treatment conducted in an electric laboratory oven, at temperatures between 140 and 300 ° C. The goal was to study the alterations that the treatment might provide to the characteristics of the material, aiming at empowering its use to energetic purposes, through the density evaluation of a sample of the material, the size of residue particles, gross calorific value, combustion index, immediate analysis, resistance to grinding (particle size reduction) and the evaluation of microscopic images. The results indicated, for both species, that the heating caused a significant influence on the gravimetric yields and on the characteristics of the experiments cited above with changes in the values with the increase of the temperature, except for the ash content of eucalyptus. The effect of the thermal treatment was more evident from 220 ° C, which is more strongly observed at the temperature of 300 ° C, with a larger fragmentation of the treated materials in comparison to the control material. Besides the increase in the friability of the studied materials, found in the experiment of resistance to grinding, in which there was a relevant increase in the amount of low granulometry material (smaller than 4 mm), they presented a higher energetic gain (more calorific value) considering the witness, mainly at 300 ° C, with high combustion indexes for the eucalyptus and pine residues.