The present study has evaluated the impact of pellet length, die
temperature, biomass moisture content and particle size on the
pelletizing pressure during fuel pellet production from biomass.
It has been shown that the pelletizing pressure increases exponen-
tially with the pellet length. A mathematical model, predicting the
increasing pelletizing pressure was in good accordance with exper-
imental data. The pelletizing pressure was shown to be dependent
on biomass species, temperature, moisture content and particle
size. An increasing temperature of the die during pelletization de-
creased the pelletizing pressure, and infrared spectra of the pellet
surface indicated hydrophobic extractives for pellets produced at
higher temperatures that might have acted as a lubricant reducing
the friction between biomass and steel surface. The influence of the
biomass moisture content was ambiguous and depending on the
biomass type. For woody samples, the pelletizing pressure dropped
with increasing moisture content while it increased for wheat
straw. The effect of particle size on the pelletizing pressure was
more defined, showing that the pelletizing pressure increases with
a decreasing particle size. An increasing pelletizing pressure is
resulting in an increasing pellet density and it was shown that
pressures above 250 MPa resulted only in minor increase in pellet
density