This article has presented tools and methods
that separate the pelletizing process into compression,
flow, and friction components to measure
the importance of raw materials properties
for the energy requirements of pelletizing and
pellet strength. The study showed that in all
components, European beech sawdust required
more energy to process than Scots pine and that
increasing temperature and MC decreased the
energy requirements for both species. It was
shown that a significant part of the energy for
the pelletizing process is allocated to the process
of forcing the compressed sawdust from
the surface of the die into the press channels. It
was also shown that beech produced the strongest
pellets, and it is suggested that the sawdust’s
bonding properties are an important
factor for the energy required in the pelletizing
process. The high bonding strength of beech
was reflected in the energy required to force
the compressed sawdust into the channels and
to high friction in the press channels. The magnitude
of these may be correlated with a greater
number of high-energy bonding sites (e.g., hydroxyl
groups) for bonding in beech than pine
because of the lower extractives content in
beech. Also, a method to measure the energy
requirement in the continuous pelletizing process
was shown to provide data comparable to
an industrial pellet