The impact of dry torrefaction on the fast pyrolysis behavior of ash wood and commercial Dutch mixed wood in a pyroprobe

In this study torrefied feedstocks, consisting of mixed wood and wood residues torrefied at 300 °C and ash wood torrefied at 250 and 265 °C, were pyrolyzed in a pyroprobe at five pyrolysis temperatures (600-1000 °C) and a fast heating rate (600 °C·s−1) to investigate the effect of torrefaction on the formation of volatiles and their evolution in a 100 kW circulating fluidized bed gasifier. Results showed that torrefaction converted mostly the hemicellulose content of feedstocks. Furthermore, torrefaction resulted in decreasing the bio-oil and gas yields, increasing the char and phenol yields and not affecting the polyaromatic hydrocarbons yield. Phenol and naphthalene showed the largest yield at 600-700 °C and 800-1000 °C, respectively. At such high temperatures, the rest polyaromatic hydrocarbons showed yields similar to phenol's. At 900 °C torrefaction affected mainly the phenolic species, with 4-propyl-phenol being the dominant species of its group for mixed wood and wood residues feedstock. In the gasifier, H2 and CO2 yields increased, CH4 yield remained constant, and CO yield depended on tar conversion and oxidation and steam reactions. The phenol and naphthalene yields further decreased and increased, respectively, whereas, polyaromatic hydrocarbons did not change in the gasifier.