The Thermochemical Conversion of Forestry Residues from Silver Fir (Abies alba Mill.) by Torrefaction and Pyrolysis

Forestry residue is a renewable energy biomass whose valorization has increased due to the interest in replacing exhaustible and environmentally unfriendly fossil resources. Needles, cones and bark from silver fir were thermally processed by separated and combined torrefaction (250 degrees C) and pyrolysis (550 degrees C). The torrefaction removed the humidity and extractives and degraded the hemicelluloses, significantly decreasing the oxygen content to similar to 11 wt% and increasing the carbon content to --80 wt%, while enhancing the calorific value of the solids (similar to 32 MJ/kg). The pyrolysis produced solid materials with high amounts of fixed carbon (similar to 60-70 wt%) and high heating values, of similar to 29 MJ/kg. The combined torrefaction + pyrolysis increased the energy yield of the process and decreased the O/C and H/C atomic ratios to about 0.1 and 0.5, respectively, which is close to those of coals. It also led to condensable products with more homogeneously distributed compounds, regardless of the initial biomass type. More than 110 chemical compounds were confirmed in the condensable products, in amounts that depended on the type of starting material and on the thermal treatment. These included the following: terpenes, from extractives; furans, acids and linear ketones, from hemicelluloses; cyclic ketones and saccharides, from cellulose; and aromatic hydrocarbons and phenol derivatives, from lignin. Clear distinctions between the thermal procedures and the sample origins were evidenced by an exploratory data analysis (PCA), which suggested the presence of different types of lignin in the three starting materials.

Automated summary

Forestry residues, such as needles, cones, and bark from silver fir, can be thermally processed through torrefaction and pyrolysis. These processes result in high energy yield and condensable products with uniformly distributed compounds.