Wood pellets are a type of solid fuel in the form of small cylindrical granules, made from wood waste. Pellet heating has several advantages, such as automatic fuel feeding to the burner and relatively low residue produced as a result of combustion.
Production
Pellet manufacturers are usually large woodworking companies, for which the raw material is a by-product of their production processes. During pellet production, no additional chemical binders are required for the biomass used. Besides wood residues, sawdust, and other by-products, pellets can also be made from raw wood material. The actual pellet production process includes the following stages:
- Coarse grinding of the wood;
- Drying;
- Fine grinding;
- Pelletizing;
- Cooling;
- Packaging or storage, and when using dry wood, it may be necessary to include a wood moisture treatment step in the production process;
Pellets are formed in a pellet press under high pressure and temperature. The pressure generates heat, which allows the lignin naturally present in the wood to melt at temperatures above 100 °C, enabling the compressed wood to take the desired shape. The hot lignin acts as a natural binding agent. In the production of pellets from wood with low lignin content, the use of additives is sometimes necessary.
Quality and Standardization
Wood pellets have the following qualities:
- Calorific value of approximately 4.8 kWh/kg (17,000 kJ/kg); 2 tons of pellets produce as much energy as about 1,000 liters of liquid fuel (fuel oil);
- Bulk density of 650 kg/m³;
- Moisture content of 10%;
- Ash content below 0.5% for high-quality pellets;
Standards: ÖNORM / DINplus / SWISSPELLET
Data according to ÖNORM M 7135. Requirements and regulations according to DINplus:
- 5–6 mm diameter, 8–30 mm length;
- Calorific value greater than 18 MJ/kg ≈ 5 kWh/kg ≈ 3.25 kWh/l;
- Bulk density: 650 kg/m³;
- Moisture content: less than 10%;
- Ash content: less than 0.5%;
- Produced 100% from wood;
Before the adoption of the European standard, the German standard DIN 51761 and the Austrian standard ÖNorm 7135 were in effect. In the new European standard, the certification requirements have been updated and expanded. The certification process monitors and controls both the production process and the quality of the produced pellets. Such certification is carried out worldwide.
Since 2002, Switzerland has had the Swisspellet trademark, whose requirements comply not only with Swiss standards but also with the German and Austrian norms. Pellets produced in Switzerland carry this trademark.
European Standard EN 14961-2
Since 2010, the European standard (EN 14961-2) has established uniform rules across Europe for wood pellets. It also introduces new requirements for pellets, including length, diameter, ash content, moisture content, and more. With the adoption of this EU standard for wood pellets (EN 14961-2) in 2010, new certifications were introduced: ENplus for pellets used in domestic boilers and EN-B for industrial pellets used in industrial boilers. The main difference between standards and certifications is that standards are not enforced—they are general guidelines. Certifications, on the other hand, are mandatory throughout the entire production-to-consumption chain. ENplus has two quality classes: A1 and A2. Class A1 imposes the strictest limits on ash content in the pellets, while Class A2 allows ash content up to 1.5%. For industrial pellets, the EN-B certification has significantly relaxed limits. Introducing a unified quality standard for domestic and industrial pellets allows for clear tracking of consumption and product quality.
