Key indicaters of wood pellet quality
Even though wood pellets standards varies with different areas or markets, they share the core indicators. According to the requirements of their terms of different standards, about the wood pellets quality standards we should consider the following crucial indicators:
We clearly understand wood pellets are generally for heating. Compared with fossil fuels, wood pellets release much less ash. Then what’s the standard of ash content?
According to Pellet Fuels Institute (PFI), the new standard about ash content requirements of wood pellets is as follows:
Super-Premium - <0.5% Ash
Premium - <1% Ash
Standard - <2% Ash
Utility - <6% Ash
While the important quality criteria of wood pellets ash content of ENplus which is the benchmark for wood pellets is that at 550 °C for ENplus -A1(the premium quality used in private household boilers or stoves) is≤0.7%/mass, and for ENplus -A2 (used in larger installations) is≤1.5%/mass.
Ash content is one of the indicators of quality standards for wood pellets, from the above description, ash content of qualified wood pellets should be below three percent.
One of the reasons that wood pellets are popular all over the world is that its moisture content is ralatively reasonable for heating compared to some raw materials. Now that the primary purpose of wood pellets is for heating, so the lower the moisture content is, the higher utiliztion rate it is. In accordance with European Pellet Quality Certification (DIN51731 or Ö-Norm which refers to Austrian Standards Institute- Österreichisches Normungsinstitut M-7135), no matter for household or industrial, the requirement of moisture content is less than or equal to 10 w-%, otherwise the wood pellets will not be burned completely.
This is another standard which can determine the quality of wood pellets. It mainly refers to the wood pellet mass per cubic foot. The bulk density of wood pellets is much higher than that of wood chips which can improve the cumbustion rate. You can detect the bulk density by this way: Use a kitchen scale to weigh a vessel larger than 1 litre, fill the vessel with wood pellets until it is full and weigh again, then fill the vessel with water and weigh. At last, deduct the weight of the vessel and the weight full of wood pellets, in accordance with the standard of Enplus, the result should be between 0.6-0.7kg/litre due to the bulk density requirement which ranges from 600 to 750kg /m³. However accroding to the Pellet Fuels Institute, it is from 38.0 to 46.0 lb/cubic foot.
Diameter and length
Wood pellets are produced uniformly, generally they are cylinder-shaped. In this case, the diameter and length must be regular, otherwise the wrong size wood pellets may alter combustion conditions which will result in an increase in emissions and a loss of efficiency. To comply with ENPlus standards the diameter must between 6mm and 8mm and the length ranges from 3.15mm to 40mm.
Durability is also a good representative parameter of wood pellets quality standards. Comply with EN Quality Class Specification, the wood pellets quality standard is greater than 97.5%, while in accordance with the PFI, it is more than or equal to 95%.
In addition, there are still some other indicators which determine the wood pellets quality standards, such as fines, ash melting temperature, etc., which will be simplify presented in diagrams in the next section.
Wood pellets quality classification
According to different wood pellet standards, the quality classification of wood pellets are differentiated with each other. EN quality class specification and PFI classification standards are presented in the following diagram for your reference:
EN Quality Class Specification