Pellet production

From chestnut biomass to the high quality pellets

The pellet production process has different preparation stages of the raw materials in order to allow the system to operate efficiently. The main operations performed are the following:

• Drying the chestnut wood chippings and debarking

• Drying of the biomass to a moisture level between 10 and 12%

• Milling of chips to a dimension of 25 and 60 mm

• Storage of the dried material

• Conversion of the material to sawdust

• Loading the sawdust into the pelletiser

• Pellet production

• Sieving and cooling of the pellets

• Dust extraction and packaging in bags, bulk and tanks

It is essentially an extrusion process, carried out by rotating elements such as a press or roller within a cylindrical element called a compression drawplate. This process compresses the wood chips through perforated plates found all along the drawplate walls. During the compression, a progressive densification of the material is carried out permitting the formation of small cylindrical shapes. Knives placed outside the drawplate cut the pellets into the desired size. During the extrusion process, temperatures higher than 90°C are reached and high pressures generate the plasticisation of the constituents of the woody matrix, more specifically the lignin. This converts to a thermoplastic polymer which acts as a natural adhesive and provides cohesion to the finished product. Cooling is the final stage, then later drying of the pellets and the sieving of the finest particles, indispensable to the stabilisation and formation of the small cylinders.

Bruciabene^® pellets are manufactured using biomass derived from the production of the debarked chestnut wood, previously dried in order to take the raw material to the optimal moisture for pelletisation. Such a pellet is therefore preferable as a natural fuel, compared to the chestnut wood as it can be used immediately. In fact, the wood has to be seasoned for a few years, in order to naturally wash out the tannins that otherwise would incrust the boilers and chimney flues. The debarking process also allows the ash content of the pellets to be lower in relation to the wood fuel. The ash is used as fertiliser.