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studies conducted on pellet quality. Furthermore, this approach Eucalyptus and poplar pellets showed excessive shortcomings,
is not only limited to pellets, but to all those cases in which making them less preferable as suitable raw materials for small-
there is the need of comparing the obtained value with a scale pellet production. These facts confirm that producing
constant threshold, as is the case for wood chips quality or high-quality pellet from short and medium rotation forestry is

wood-based panels mechanical performance. particularly challenging.
Regarding broadleaved pellet quality, we confirmed that Our results showed the significant influence on pellet quality
bulk density, ash content, and heating value are the most generated by not only the species but also of the stem age,
troublesome parameters to produce high-quality pellet from which is a direct consequence of the forest management
broadleaves species. systems applied, as highlighted in Latterini et al.
The previous literature largely confirmed that the thresholds Surprisingly, we did not find a significant influence on
indicated by the standard for these variables can be particularly pellet bulk density, but only on ash content.
challenging to be achieved. In particular, the increasing age of the raw material led to
None of the investigated pellet typologies showed fully an improvement in ash content. This is probably related to an

satisfactory results for all the variables. For instance, beech increase in the wood/bark ratio which is generally observed
pellets showed proper bulk density and satisfactory ash with increasing diameter of the stem.
content, but the resulting heating value to be significantly Increased ash content is often observed with an increase
lower than the standard’s threshold. in the amount of bark. The influence of bark on heating value
However, oak pellets showed satisfactory heating values, is instead less straightforward and depends on the species
whereas bulk density was low and ash content was too high intrinsic features; in beech, for instance, bark has a lower
to be classified as an A1 pellet. heating value than wood.

These results are related to the intrinsic characteristics of In summary, we applied an innovative statistical approach
the raw materials. Broadleaved wood has lower lignin content to evaluate the quality of pellets in relation to the official
than coniferous wood and, considering that lignin is the major standards. The applied approach was revealed to be effective
binding component for pellet production, this can obviously and easy to interpret.
affect the quality of the pellets. We recommend that this approach be applied in the
Furthermore, the presence of material other than sawdust, sector of biomass quality evaluation. We further confirmed
as it happens when producing pellet from the whole tree, is
another critical aspect that can decrease pellet quality.
However, based on the results obtained a possible solution Collections - GetArchive

could be blending raw materials from different species. Additional
dedicated studies are needed to confirm this.
Based on our findings, it could be interesting to blend
beech (high bulk density and low ash content) with turkey
oak (high heating value). These species are widely distributed
along the Italian Apennine.
Often, they are located in stands very close to each other

and with a certain degree of admixture, so this kind of blend
could represent an interesting solution.