Biomass pellets with organic binders - before and after torrefaction

Given the current energy situation in the world, torrefaction offers a promising technique to produce fuel that can be used as a substitute for coal in combustion. The pelletization process can be simplified by the addition of a binder. The aim of this study was to determine the influence of the binders on the mechanical and energetic properties of the pellets before and after torrefaction. The initial material was meadow hay. The hay was crushed and three binders (lignosulfonate, wheat flour, starch) were added – 2 and 15 wt% The basic powder characterisation (compressibility, internal friction, and angle of repose) were performed on all binders. Lignosulfonate had the best flowability and therefore appeared to be the most suitable from a process point of view. Testing were also carried out on non-torrefied and torrefied pellets. The mechanical-physical properties (hardness, mechanical resistance, wettability) were also determined. Hardness and mechanical resistance for non-torrefied pellets was increased by adding lignosulfonate (15 wt%) and flour (2 wt%). After torrefaction, hardness and pellet durability index of the pellets decreased significantly, but still the best pellets were those with lignosulfonate (15 wt%) and flour (2 wt%). Non-torrefied pellets do not have a good resistance to water absorption, but lignosulfonate in ratio of 15 wt% and as well as flour in ratio of 2 wt% have a positive effect on this feature. Moreover, torrefaction has a positive effect on the pellet's resistance to water absorption. The results were supported by FTIR analysis. Last but not least, a simple calculation of the consumption of pellets for heating and hot water heating for a family home is given.