VALORIZATION OF SUGAR BEET PULP RESIDUE AS A SOLID FUEL VIA TORREFACTION

The potential of torrefaction treatment for upgrading sugar beet pulp residue (SBP) into a high-quality solid bio-fuel was investigated in this work by using a new bench-scale experimental apparatus. In particular, the influence of the main process variable, namely the temperature, on both the torrefaction performance parameters (i.e., mass yield, energy yield and energy densification index of torrefied solids) and the main properties of torrefied SBP (i.e., low heating value, the ratio of fixed carbon to volatile matter, H/C and O/C ratios) was studied. Torrefaction tests were performed at three different temperatures (i.e., 200, 250, and 300 °C) and 30 min reaction time. The torrefaction treatment of SBP resulted in a significant improvements of its fuel properties. It was observed that higher temperatures led to an increase in the calorific value of the torrefied SBP with respect to the parent one. More specifically, the calorific value increased by a factor of 1.4 for the biomass treated at 300 °C and 30 min, changing from 17.2 to 24.5 MJ/kg on a dry basis. Under the same experimental conditions, a 59 % reduction in the O/C elemental ratio was also observed. These positive effects of the torrefaction treatment, however, occurred while returning a mass yield (45 %, daf) and an energy yield of the solid product (61 %, daf) rather low compared to that typically arising from the torrefaction treatment of woody-biomass to get the same energy densification factor. This was mostly a consequence of the low lignin content of SBP compared to woody biomass.