Energy evaluation of biochar obtained from the pyrolysis of pine pellets

Abstract

The wood pellets are mainly used in heating environments, commercial and residential, as well as fuel for production of thermal and electric energy in industrial plants. Furthermore, the heterogeneity and variable moisture content, combined with the high cost of transport, are limiting challenges that must be overcome with new technologies and new products. In this context, torrefaction and pyrolysis are attractive alternatives for increasing energy density and decreasing the moisture content of the samples, based on thermochemical conversion in a non-oxidizing atmosphere. Samples were produced to perform the energetic characterization of biochar from pine pellet using different heating rates 5–30 °C min−1, different residence temperatures 200, 280 and 570 °C and different residence time (1 and 0.5 h). The high heating value (HHV) of each variable was measured and allowed to observe that the heating rate did not influence of a significant way the results, in other words, a 5 % variation between the lowest and highest heating rate. Notwithstanding, the HHV was expressive compared to the pellet in nature, when it has been found an energetic gain over 80 %. In general, the biochar from pine pellets obtained by torrefaction or pyrolysis has appropriated characteristics compared to pellets in nature, showing a greater amount of energy per unit, high stability, reduced moisture content and reduced ash content. The kinetic of combustion to biochar in oxygen-rich atmosphere showed the dependence between the activation energy and conversion degree, with a continuous decrease in the activation energy, characteristic of complex processes comprised by initial reversible reaction followed by an irreversible one.