Wood Pellet Specification
Wood pellets are porous solid, with high or low moisture content. The moisture content has great effect on the thermo-chemical conversion of the wood pellets. Therefore, moisture content is one of the basic indicators to identify the wood pellet quality. Over-high moisture content will influence the calorific value and heat efficiency. According to ENplus standard, the moisture content of qualified wood pellets should be lower than 10%.
Ash refers to residues after full combustion of wood pellets, generated by the complex reactions such as decomposition and combination of all combustible matters and minerals in wood pellets. Ash content and impurities in the wood pellets have great effect on the coking of boilers. According to ENplus standard, wood pellets fall into 3 grades according to the ash content. The grade A1 has the ash content lower than 0.7%, A2 lower than 1.5%, and grade B lower than 3%.
Volatiles are the decomposed and precipitated organic matters generated under high heat, when the wood pellets burn in isolation from the air. Usually, the higher the volatiles content, the better the combustion effect.
The fixed carbon is the residues of wood pellets with the moisture, ash and volatiles removed. The same as ash, fixed carbon is a thermal decomposition product, not a inherent content in biomass pellets. Fixed carbon contains not only carbon, but also hydrogen, oxygen, nitrogen, sulfur, etc. The lower the fixed carbon content, the easier the wood pellets burns, and the less carbon emission.
Wood pellet calorific value includes net calorific value and gross calorific value. The units are Mg/kg.
Gross calorific value (Qgr) refer to all heat generated by the full combustion of 1kg wood pellets, including the latent heat of vaporization when the water vapor in smoke condenses into water. Net calorific value(Qnet) equals the gross calorific value deducts the latent heat of vaporization. In the transaction and use of wood pellets, people usually adopt net calorific value as the measure of calorific value.
Wood pellet standard
Wood pellet inspection is important for sellers and buyers to confirm the quality of wood pellets. Besides, The wood pellets used in industrial boilers should meet the following standard:
The diameters are 6-10mm
The length is 4-5 times that of the diameter.
The bulk density is more than 600kg/m3.
The wood pellet density is 1.1-1.4kg/m3, but 0.8-1.1kg/m3 is more economical in industrial boilers.
The crushing rate is less than 1.5%-2.0%.
The moisture content of dry base is less than 10%-15%.
The ash content is less than 1.5%.
The sulfur content and chlorine content are both less than 0.07%.
The nitrogen content is less than 0.5%.
EU doesn’t have specific requirement on the calorific value, but according to the Swedish standard, the calorific value of wood pellets should be higher than 16MJ/kg.