Torrefaction of heavy metals contaminated biomasses

Biomass for energy production has been extensively studied in the recent years. In order to overcome some constraints imposed by the chemico-physical properties of the biomass, several pre-treatments were proposed. Torrefaction is one of the most interesting as torrefied biomass holds a wide range of advantages over raw biomass suche as the increase of the calorific value, both on mass and volumetric basis. The process raises some concerns when biomass from phytoremediation and wood from demolition and construction activities are used as feedstock, since they could contain potential toxic elements (PTEs). During the torrefaction treatment, the fate of PTEs should be controlled in order to avoid their release in the gas phase and evaluate the extent of their concentration in the torrefied biomass. Herein, torrefaction tests on Populus nigra L. branches from phytoremediation, and demolition wood were conducted at three temperatures. For each temperature, biomasses have been holding at the final temperature for different residence time, namely 15 min for 250 °C, 10 for 270 °C and 5 min for 300 °C. The energetic content of the torrefied biomasses was evaluated; the fate of PTEs (Cd, Pb and Zn) as a function of the temperature was studied and their mobility in the torrefied biomasses was investigated and compared to the mobility in the in the raw biomass.