Effect of torrefaction on pellet quality parameters

Abstract

Torrefied biomass is characterized as a high-quality renewable energy commodity that can substitute fossil fuels. Combined torrefaction and pelletization are used to increase the value of biomass by improving its handling and fuel properties. The aim of this study is to present the influence of pelletization process on torrefaction in a pilot-scale unit. Above that, two process modes were assessed, and the properties of the torrefied and pelletized biomass and vice versa were studied. Mode I involved torrefaction prior pelletization. In mode II, on the contrary, the waste biomass was first pelletized and then torrefied. Analysis of mechanical parameters and chemical composition was therefore used to determine which of the modes was more advantageous. The results showed that within both modes it is evident that a higher torrefaction temperature caused wettability index decrease with a simultaneous higher heating value increase. Pellets produced in mode I showed better calorific values, however worse mechanical properties particularly durability.