Pellet wood is a fuel obtained from virgin wood, sometimes starting from processing waste (such as planing, sawdust, chips, cuttings) other times from the entire trunk. It can be defined as “solid biofuel, generally in cylindrical form, of random length typically between 5 mm and 30 mm and with interrupted ends, produced from pulverized biomass with or without pressing additives”. The UNI EN 17225-2 standard determines the specifications and classification of wood pellets for industrial, commercial and private use. The standard refers only to wood pellets obtained from the following raw materials:
1) Forest, plantation and other virgin wood;
2) Products and residues from the woodworking industry;
3) Reclaimed wood.
It does not include wood resulting from the demolition of buildings or civil engineering plants, nor that heat treated using the roasting system.
The binding capacity of the lignin, contained in the wood, allows to obtain a compact product without adding additives and chemical substances extraneous to the wood, obtaining a high-yield fuel. When the raw material enters the pellet press, the moisture content must be approximately 12-13%, an essential condition for the pellet extrusion process. The combustion of wood pellets produces carbon dioxide and pollutants typical of the combustion of solid biomass such as PM10. Typical residue are the unburnt materials, and in particular the ashes, the quantity of which is strictly dependent on the type of biomass: generally the pellets produced starting from soft woods such as the conifer family (fir, larch, pine, etc.) is characterized by a lower ash residue, while hard woods such as many broad-leaved trees (beech, oak, oak, hornbeam, ash, etc.) a higher value. However, this is not a rule in fact the percentage of ash also depends on which part of the tree is used: in the case of the bark the residual ash will be higher, in the case of the lower pulp.
Thanks to pressing, the calorific value of the pellets, with the same volume but not weight, is approximately double that of wood. The percentage of hardwoods of origin also minimally affects the calorific yield. The universally recognized standard for calculating calorific value is ISO 18125: 2017 Solid biofuels – Determination of calorific value. The pellet is used as fuel for the latest generation stoves, replacing the wood logs. This involves a series of ecological, energy and management improvements compared to traditional stoves. Among the environmental advantages it should be noted that the production of pellets is not strictly linked to the felling of whole trees: in fact the pellets can be produced from numerous waste materials such as sawdust and carpentry processing waste, which in this way are revalued as consumer fuel.
Italy is the leading European market for the consumption of wood pellets, with over 3 million tons per year.
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