Potencial energético de pellets produzidos a partir de resíduos lignocelulósicos e finos de carvão vegetal

Abstract

Brazil has great potential for the production of renewable fuels due to the vast biodiversity and the existence of arable land, as well as favorable technology and climate. Of the abundant residues of the lignocellulosic biomass that exist in Brazil, due to the good characteristics for pelletizing and heat generation, the sugarcane bagasse and the residues generated in the processing of coffee stand out. The objective of this work was to characterize and evaluate the physical, chemical, energetic and mechanical properties of pellets produced from the mixture of: 1) sugarcane bagasse (BC) with charcoal fines and 2) residues from coffee processing (RC) with charcoal fines (FN) in different proportions (treatments). In addition, find out which mixtures (treatments) will produce pellets which have characteristics that meet the requirements of one of the European marketing standards for biomass pellets, DIN EN 14961-6. The amount of ash of the charcoal fines (FN) is high (20,95%), which caused an increase in the percentage of ash in sugarcane bagasse (BC) and coffee residue (RC) pellets with increasing the amount of FN used in the preparation of the same (from 0,55 to 2,62% for BC and from 6,10 to 9,60% for RC). The calorific values of the pellets presented significant differences between the treatments with the addition of charcoal fines. The useful calorific value of sugarcane bagasse pellets ranged from 19,58 MJ kg-1 (100% BC) to 17,85 MJ kg-1 (80% BC and 20% FN), and the coffee residue pellets presented values that were 15,3 MJ kg-1 (100% RC) at 16,96 MJ kg-1 (70% RC e 30% FN). All sugarcane bagasse pellets and charcoal fines met the parameters for commercialization in accordance with DIN EN 14961-1, except for the treatment BC85 (85% of BC and 15% of FN) that presented value of mechanical durability below that required. None of the pellets produced with coffee residues conformed to the parameters established by the standard because they did not present the minimum mechanical durability required. Even so, parameters such as bulk density, ash, useful calorific power and production of fines met the norm. Among the pellets produced, the BC80 treatment was noted for having the highest useful calorific value compared to all other treatments performed, and met all the parameters of the European standard for biomass pellets. Even with high amount of ash presented by the residue of charcoal fines, there was a positive contribution that can be observed mainly in the increase of the useful calorific value of the pellets as coal fines were added to the treatments. In order to avoid problems with the high amount of ash, it is recommended to use low percentages of charcoal fines in the mixtures or to use fines with less ash.