Wood pellets as climate-neutral fuel

Wood and fibres

Wood pellets are a climate-neutral fuel derived from biomass. Ideally, pellets do not contain chemical binders and have a high energy density. Two kilograms of wood pellets are roughly equivalent to the efficiency of one litre of heating oil. The combustion of wood releases only as much carbon dioxide as the tree absorbed while growing. Pelletising makes the wood more practical for use in private and industrial incinerators; wood pellets are like a bulk material and have good flow properties. The material is also compacted and the pellets have a higher bulk weight than loose wood, which reduces transport volumes. Tietjen’s hammer mills optimally crush wood for the pellet mill.

From tree to pellet

Depending on the pellet quality requirements, the wood must be smaller than 3 to 4 mm before it enters the pellet mill. Of course, it is impossible to obtain this particle size from the entire log in a single step. First, the trunk is debarked and crushed into wood chips by a woodchipper. Because these wood chips are made of fresh wood, they can have humidity levels of 30 to 60%, depending on storage and environmental conditions. However, finished pellets may only have a maximum humidity of 10%, so the material must be dried in any case.

Processing of wet wood

The plant we want to look at more closely produces wood pellets from beech and other hardwoods in Croatia. Here, a belt dryer is used to efficiently dry further crushed material measuring approximately 30 x 10 x 5 mm. Furthermore, the fines content must be very low, as fine particles obstruct the fabric belt of the dryer and lead to dust problems in the exhaust air.

In the Croatian plant, a Tietjen wet wood mill W 1000 performs this task at a capacity of 12 t/h and a humidity of 30-40%. This mill is specially designed for wet and damp wood. The special design of the grinding chamber and housing guarantees the removal of the damp grinding material leading to adhesion.

Fine grinding with the GD 20 large chamber mill

The wood leaves the belt dryer with the final moisture content before finally being ground to the pelletising fineness in a Tietjen GD 20 large chamber mill with a throughput of up to 8 t/h. The GD series is characterised by its generously dimensioned grinding chamber, robust construction and quick change of beaters by a frame system – advantages that also come into play in wood grinding. Moreover, the grinding plant is completely explosion-proof according to the proven Tietjen concept, which is of particular importance for a highly flammable material such as wood.

More sustainability by recycling waste wood

The life cycle assessment of wood pellets can be further improved if residual and waste wood from sawmills, wood-based material production or similar materials are used. Here, too, Tietjen offers a wide range of solutions, such as for crushing wood shavings and sawdust.

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