How Are Wood Residues Pelletised?

In Europe, wood pellets are mostly produced from sawdust, wood shavings and other woody byproducts. Traditionally, production units are located on or nearby sawmills and other wood processing sites, representing complementary outlet for these plants. In this context, a first crucial step for producers consists of grinding and drying the moist wood residues. The energy needed for this is mainly made available by the burning of bark or any low quality wood, which likewise accumulates on site. In many cases, not only is heat produced by burning the bark, but also electricity that can be optimally used to run unit.



After the residue is dried, it is fed into a pellet mill. Within the mill, dry woody materials are squeezed through a die with holes of the required size (normally 6 mm diameter, sometimes 8 mm or larger) called a matrix. The high pressure of the press causes the temperature of the wood to increase greatly, causing the surface to plasticise slightly to form a natural “glue” that binds the pellet together as it cools. To facilitate the pressing process and improve quality parameters, small quantities (max. 2%) of natural binder such as starch can be added, but no glues enter the composition of wood pellets.

Newly compressed pellets are now ready to be cooled and sieved to remove any residual particles. Finally, wood pellets can be stored and/or bagged prior being delivered to end consumers.

A complete wood pellet line is shown on the below animated graphic²:

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