Pyrolysis of burnt maritime pine biomass from forest fires

Abstract

Forest fires in Portugal give rise to a large amount of burnt wood, a waste, and as such with few applications. Its energy recovery can be seen to manage these residues with advantages for the environment and as a source of income for the populations that depend on the primary sector of the economy. Burnt pine wood was evaluated as raw material for pyrolysis. The collected biomass samples, from the maritime pine trunk, were cut to separate the burnt part (external layer) from the part not affected by the fire, giving rise to the two distinct biomass samples, raw and burnt. The lignocellulosic composition was assessed by thermogravimetry and the differences in composition arise from the fact that the raw sample is sapwood, whereas the burnt sample is mainly cambium. Biomass pyrolysis kinetics evaluated by the KAS method led to an activation energy of 192 kJ/mol for raw and 169 kJ/mol for burnt biomasses. Biomass was pyrolyzed in a fixed bed pyrex reactor for temperatures in the 673–773 K range corresponding to the maximum thermal degradation rate assessed by thermogravimetry. The burnt biomass showed lower bio-oil yields (maximum 31%), which increase with the pyrolysis temperature. Besides, burnt biomass bio-char yield was always greater than the analog produced from raw biomass over the entire temperature range. The catalyzed pyrolysis tests using carbonate catalysts (limestone, CaCO3, Na2CO3, and Li2CO3) showed improved pyrogas which are compatible with the gasification role of alkali carbonate catalysts reported in the literature.