Fuel pellets: properties, standards and applications

Fuel pellets (wood pellets) are compressed cylindrical granules produced from shredded wood biomass without added chemical binders. They are one of the most in-demand types of solid biofuel in the world, used for heating residential buildings, municipal facilities and in industrial energy. Due to their high bulk density, low moisture content and stable granulometric composition, pellets ensure automated dosing, efficient combustion and minimal emissions, making them a key element in the decarbonization of heat supply.

Chemical Nature and Physical-Mechanical Properties

Pellets are produced mainly from softwood and hardwood, as well as from woodworking waste (sawdust, shavings, chips) and untreated used wood. During pressing under high pressure, the cell walls of the wood are destroyed, and natural lignin is released, acting as a natural binder. This is why quality wood pellets do not require the addition of glues or chemicals.

Key pellet quality indicators are defined by standards and directly affect combustion efficiency and boiler equipment life:

• Diameter: 6 ± 1 mm or 8 ± 1 mm. 6 mm is most common for residential and municipal boilers; 8 mm is used for industrial installations.

• Length: 3.15–40 mm. Too long granules can disrupt dosing; too short ones reduce combustion uniformity.

• Moisture content: not more than 10% as received. High moisture reduces calorific value and increases losses.

• Ash content: from ≤0.7% for the highest class to ≤2.0% for industrial. Low ash means less slag and lower maintenance costs.

• Mechanical durability: not less than 97.5–98.0%. Durable pellets crumble less during transport and pneumatic loading.

• Bulk density: 600–750 kg/m³. High bulk density reduces logistics costs per unit of energy.

• Calorific value: not less than 17.0 GJ/t (about 4.7–5.0 kcal/kg) as received.

• Fines content: standardized separately; for quality pellets — not more than 1% at the point of shipment.

Classification, Standards and Grades

In Russia and CIS countries, requirements for wood pellets are established by GOST 33103.2-2017 (ISO 17225-2:2014) "Solid biofuel. Fuel specifications and classes. Part 2. Graded wood pellets". The standard applies to pellets produced from forest trees, woodworking by-products and chemically untreated used wood, and establishes quality classes.

In international trade and certification, the European ENplus system is the most widespread, distinguishing three quality classes:

• ENplus A1 — the highest class for residential and municipal heating. Ash ≤0.7%, mechanical durability ≥98.0%, moisture ≤10%. Raw material — clean wood stems and untreated waste.

• ENplus A2 — an intermediate class. Ash ≤1.2%, durability ≥97.5%. Allows a wider range of raw materials.

• ENplus B — industrial class. Ash ≤2.0%, durability ≥97.5%. Used in large energy installations.

The standard also limits additive content (not more than 1.8% by mass) and requires mandatory indication of diameter, length, moisture, ash and durability in the accompanying documentation.

Production Technology

Fuel pellet production includes several successive stages:

1. Raw material preparation. Wood waste is sorted and cleaned of impurities (stones, metal, sand). Large fractions are ground to 1–4 mm.

2. Drying. The ground mass is dried with hot air to a moisture content of 8–12%, optimal for pressing. Drying is one of the most energy-intensive stages.

3. Pressing (pelletizing). The prepared mass is fed into a pellet press with a flat or ring die. Under pressure (up to 30 MPa) and elevated temperature, the wood softens, lignin is released and binds the particles into a durable pellet. The die hole diameter determines the pellet diameter.

4. Cooling. Hot pellets are cooled in a counter-flow cooler to stabilize shape and strength.

5. Screening and packaging. Pellets are screened to remove fines and packaged in bags (15–25 kg), big bags, or shipped in bulk in specialized railcars and vessels.

Modern production facilities are equipped with automatic control systems for moisture, temperature and pressure, ensuring product quality stability.

Applications

Residential and municipal heating. Pellets of classes A1 and A2 are used in automatic pellet boilers for heating private houses, cottages, schools, hospitals and administrative buildings. Automatic fuel feed from the hopper provides comfort comparable to gas heating, with a significantly lower carbon footprint.

Industrial energy. Class B and industrial pellets are used at biomass-fired CHPs and large boiler houses, including within programs to convert coal plants to renewable fuel. They are used for co-firing with coal and for the production of heat and electricity.

Export and exchange trading. Pellets are an exchange-traded commodity. The largest exporters are North America, Vietnam, the EU and Russia. Export contracts for pellet supply are registered on exchanges, making pricing more transparent.

Other applications. Pellets are also used for heating greenhouses, as animal bedding (after appropriate treatment) and as a raw material for activated carbon production.

Safety and Storage

Fuel pellets are a combustible material, so fire safety rules must be observed during storage. The main risks are associated with self-heating and spontaneous combustion when storing large volumes of wet or freshly produced pellets. Pellets should be stored in dry, ventilated rooms or silos protected from atmospheric precipitation. When storing in bulk, the temperature in the pile must be monitored and moisture ingress avoided, as it leads to swelling and destruction of the pellets. When working with pellet dust, a respirator is recommended.

Market and Trends

The global wood pellet market is showing recovery growth. According to Bioenergy Europe, global pellet production reached 53.5 million tonnes, a 10% increase compared to the previous year, and consumption also reached an all-time high. The largest producer remains the USA, followed by Canada, Vietnam, the EU and Russia. Europe remains the largest consumer of industrial pellets but is actively diversifying supplies.

The Russian pellet market has undergone a serious transformation. While before 2022 up to 85–90% of products were exported, mainly to Europe, after the closure of the European market the industry reoriented towards domestic demand and Asian destinations (China, South Korea, Turkey, EAEU countries). Production has recovered to 1.31 million tonnes, although it has not yet reached previous maximums. Key drivers for further growth are the development of the domestic biofuel market, the modernization of boiler houses in non-gasified regions and the expansion of exports to the Asia-Pacific region.

Conclusion

Fuel pellets remain a key type of solid biofuel, combining environmental friendliness, processability and high energy efficiency. Understanding the quality classes according to GOST 33103.2-2017 and ENplus, the indicators of ash, durability and moisture, as well as production technologies, is the basis for competent selection of pellets for specific boiler equipment and the organization of stable supplies.