The quality standards for biomass pellet fuel cover multiple aspects, including physical, chemical, and combustion properties. While there is no unified national standard in China, there are relevant industry standards and authoritative certification standards in Europe and the United States. The details are as follows:
1.Physical Indicators
Particle Size and Length: Generally, the diameter is 6-12mm and the length is 10-50mm. EU standards require a pellet diameter of 6-8mm, while the ENplus A1 standard specifies a diameter of 6-8mm and a length of 3.15-40mm.
Density: Generally, it should be greater than 350kg/m³, but this varies depending on the grade. Grade 1 biomass fuel has a density greater than 650kg/m³, grade 2 greater than 500kg/m³, and grade 3 greater than 350kg/m³. The ENplus A1 standard requires a density of 1.12kg/dm³ or higher.
Moisture Content: It should be kept below 15%, with the lower the better. The moisture content of first-grade biomass fuel is less than 8%, second-grade biomass fuel less than 10%, and third-grade biomass fuel less than 15%. Some European and American standards recommend a moisture content between 10% and 12%.
2.Chemical Indicators
Ash Content: Ash content should be kept as low as possible, generally below 3%. The lower the ash content, the higher the calorific value of the pellets and the easier they burn. The ENplus A1 standard requires an ash content ≤ 0.7%. The US PFI standard categorizes pellets into three grades: Premium grade biomass fuel has an ash content ≤ 1%, Standard grade biomass fuel has an ash content ≤ 3%, and Utility grade biomass fuel has an ash content ≤ 6%.
Sulfur Content: Sulfur content is a key environmental indicator and should generally be controlled below 0.05%. The US PFI standard requires a sulfur content of ≤ 0.05%.
Volatile and Fixed Carbon Content: Volatile matter content is generally required to be between 75% and 85%. First-grade biomass fuel has a volatile content below 75%, second-grade biomass fuel has a volatile content below 80%, and third-grade biomass fuel has a volatile content below 85%. Fixed carbon content is generally between 15% and 25%, which is crucial for ensuring continuous heating during combustion.
3.Combustion Performance Indicators
Heating Value: This is a key quality indicator and should generally be above 16MJ/kg. The higher the calorific value, the higher the combustion efficiency. EU standards require that the calorific value of biomass pellets must be no less than 4.6 kWh/kg (approximately 16.56 MJ/kg), while the ENplus A1 standard requires a calorific value of 16.5 MJ/kg or higher.
Combustion Efficiency: The higher the combustion efficiency, the higher the energy utilization rate. The combustion efficiency is generally required to be no less than a certain value, which varies by standard.
Combustion Stability: The combustion process must remain stable, without flameout or deflagration, to ensure safety.
4.Other Indicators
Mechanical Durability: The US PFI standard requires a breakage rate of ≤1% to accommodate long-distance transportation and storage.
Feedstock Sustainability: The ENplus A1 standard requires that raw materials be sourced from sustainably managed forests or agricultural waste, and prohibits the use of preservatives or chemical additives.