Influence of oxygen concentration on torrefaction of Leucaena: gas formation rates and chemical properties analysis

This research investigated the oxidative torrefaction behavior of Leucaena over a temperature range of 220 to 260 °C and varying O₂ concentrations from 0 to 22 vol%. Mass yield decreased with increased temperatures and O₂ concentration, and H₂O was the main gaseous product during oxidative torrefaction. The yields of H₂O, CO₂, and CO increased continuously with the increase in O₂ concentration. The carbon content in Leucaena increased with the increase in temperatures. At 220 °C and 240 °C, the carbon content increased with O₂ concentration and had a peak at O₂ concentration of 10%. On the other hand, the carbon content at 260 °C had a peak at an O₂ concentration of 5%. At 240 °C, the HHV of torrefied biomass increased to 20.5 MJ/kg at an O₂ concentration of 10%, while at 260 °C, the HHV of torrefied biomass increased to 21.4 MJ/kg at an O₂ concentration of 5%. The combustion characteristics of oxidative torrefied Leucaena clearly demonstrated a decrease in the combustion rate of the volatile components and an increase in the combustion rate of the char as the concentration of oxygen increased. From the analysis of gas formation rates and chemical properties of the torrefied Leucaena, it was suggested that O₂ played an important role in two ways: At low temperatures, the O₂ accelerated the dehydration and decarboxylation reactions resulted in low O/C ratios, while at high temperature, the O₂ participated in partial combustion of biomass and resulted in higher O/C ratios.