The color of wood pellets is first indicator of quality. Clients know that white color pellets are free of bark. Most of producers are therefore using the coniferous timber sawdust not only for good acquisition price and burning value, but for the color as well. Although pellets of Ash or other hardwood sawdust are equally calorific, the very color with dark tendencies is an obstacle to many
buyers, because they fear there’s too much bark there. However, most important factor is raw material quality and the debarking procedure. Usually, mechanical diesel (rarely – electric) engines are equipped for this stage of preparation. If performed well, the sawdust can further be transported to the drying drum. The drying drum is fed by the remains after log debarking and other excess timber. Sawdust need to be about 12 % dry to be fit for the cyclone and matrix.
In some markets, the traditional standard is the 8 mm pellets – typically Sweden or Denmark. The rest of Europe – Belgium, Germany, France, Austria, Italy are using the 6 mm diameter.
The production lines vary in size and number in different pellet plants. However, it is common to install a capacity of some 1.5 – 3 tons an hour power.
Once pressed through the matrix, the pellets travel to the cooling unit – a type of tower – to evaporate excess heat. These bulks pellets later are distributed via various conveyor belts and reach their final point of storage. Basically, pellets for home use are packed into packages that are not to heave for a human being to lift by hand – 15 or 20 kg. Other pellets, that are destined to be shipped out and later packaged in marketing bags, would be filled into 1000 kg big bags. in case the plant is located near the coast, a special feed line is mounted to spill the pellets directly into a vessel.
Last stage of production is qualification to an industrial standard. Wood pellets are mainly evaluated by the remaining ash level. Very low, highly industrial pellets shall not have more than 1.5 %. Hence, each 1 ton of pellets shall not leave more than 15 kg of ashes. Next step is the premium quality domestic pellets. These shall have no more than 0.7 %. Among European countries there is quite a few standards for quality, most commonly used are the DIN plus and the EN Plus A1 for the premium grade and DIN51731 or EN Plus A2 for the industrial grade. Both are German origin an equal in principal technical values, but differ in certification process and cost of this procedure.