Investigation of the Combustion of Biochar Obtained by Hydrothermal Carbonisation and Torrefaction of Sawdust

The effect of the temperature regimes of hardwood sawdust thermochemical treatment (hydrothermal carbonization and torrefaction) on biochar properties and combustion characteristics are investigated. The mass yields of biochars were considered from the viewpoint of the processes that take place during thermochemical treatment, along with the changes in the elemental composition resulting from these processes. The optimal method and temperature regime of thermochemical treatment were determined. The effect of the method and temperature of sawdust thermochemical treatment on the composition of gaseous products from biochar combustion was assessed by FTIR spectroscopy combined with thermogravimetric analysis. Two main stages of biochar combustion were detected: the phase of removal and combustion of volatile substances (up to 400 C-degrees) and the phase of semi-coke combustion (above 400 C-degrees). The analysis carried out by means of FTIR spectroscopy during combustion allowed us to determine the released components of the gaseous mixture and to observe thermochemical decomposition of biochar components in the real time mode. Investigation of biochar combustion showed that an increase in sawdust processing temperature reduces the formation of gaseous products at the first stage of combustion and promotes an increase in the amount of carbon dioxide at the second stage.