Pellets are currently one of the most used biomass fuels for space heating and sanitary water.
It is obtained by compressing, through a mechanical process, the sawdust of the wood from which small cylinders are obtained with a diameter of 6-8 mm. Thanks to the production of this compound, it is possible to reuse wood waste in the past 100%, which in the past were only partially used or thrown away.
Advantages of pellets compared to other fuels:
- Greater caloric yield
- Easy to find in pre-packaged bags
- lower costs
The cost of pellets is much lower than that of other fuels: using a pellet boiler you get a saving that goes from 15% compared to methane, up to over 70% compared to LPG.
In addition, facilities such as the Thermal Account and the Ecobonus incentive the purchase of modern pellet stoves and boilers, making them even more attractive.
Nevertheless, to obtain the economic, performance and environmental benefits, it is necessary to use certified quality pellets.
Pellet fuel quality
The quality of the pellets is defined by technical specifications developed at various levels.
At international level the reference standard is the ISO 17225: 2014, implemented in Italy by the UNI EN ISO 17225-2: 2014 "Solid biofuels - Fuel specifications and classification -
Part 2: Definition of wood pellet classes "and which replaced the previous one UNI EN 14961-2: 2011.
This classification is also important for the purpose of obtaining government incentives, being conformity to the standard one of the specific technical requirements for obtaining the deduction of 50% in the case of installation of biomass boilers.
UNI EN ISO 17225-2 determines the specifications and classification of wood pellets for commercial, residential and industrial use. As for pellets for commercial and residential use, the reference classes are the A1, A2 and B. For pellets for industrial use, the classes are I1, I2 and I3.
When the pellet is defined as "good quality"?
For the selection of a good pellet it is necessary to pay attention to some parameters.
1) Aspects related to the energetic function:
The chemical composition of the pellet determines its calorific value, ie its ability to release thermal energy during combustion.
The legislation refers to the lower calorific value (PCI) of the pellet, which defines the useful heat actually obtainable from combustion and is given by the difference between the heat made available by the fuel minus the amount of heat supplied to the water to become steam in the fumes .
In fact, during the combustion, part of the heat developed serves to transform the water contained in the fuel into steam inside the fumes.
If the latent heat of the water vapor contained in the combustion fumes is used for energy purposes, it is called higher calorific value (PCS).
To classify a pellet in the A1 class, the PCI must be greater than / equal to 4,6 kWh (or 16,5 MJ) per kg of pellets.
2) Physico-mechanical aspects
Ashes are the residue of combustion: the content depends on the type of wood from which the pellet is derived.
Ashes tend to settle on the combustion grate or in the appropriate collection drawer and therefore must be removed periodically.
They can contribute to the increase of dust emissions in the atmosphere and, more evidently in boilers of higher power classes, also to the formation of solid aggregates difficult to remove (incrustations) and to the appearance of corrosion phenomena of the components inside the boiler.
It follows that a high ash content can cause inefficiency in the combustion phase, higher emissions in the environment and risk of damaging the boiler.
The ash content is one of the key parameters in determining the quality of a wood pellet.
The limit set for the A1 class is equal to 0,7% by weight on dry matter. For the A2 class the limit is 1,2% and for the B of 2%. If the ash content of a wood pellet intended for commercial and residential use exceeds this last limit, it can no longer be considered compliant with the UNI EN ISO 17225-2 standard.
The quantity of powder present in the pellet packaging is an indication of its mechanical durability, ie the ability of the product to keep its structure stable as a result of the impact it has undergone during its handling and during transport.
Pellets that tend to crumble easily can produce more fouling of the boiler, increase in emissions and decrease in efficiency.
The moisture content is a parameter to pay attention to both when choosing pellets and during storage: an increase in humidity increases the volume of the capsules and favors their disintegration. As a result, yield losses are produced up to malfunctions.
3) Environmental characteristics
In addition to ensuring energy performance and having the right physical-mechanical requirements, the pellet must also preserve certain environmental characteristics and must not contain elements unrelated to those characteristic of wood.
The content of chlorine, nitrogen, sulfur and heavy metals (eg lead, mercury, cadmium and chromium) may indicate the presence of contaminants derived from the use of waste products from the wood industry and containing glues or chemically treated.
According to the legislation, for example, the amount of sulfur (normally present at low concentrations in the wood) must not exceed 0,04% by weight on dry matter for the A1 class, 0,05% for the A2 class and 0,05% for the class B.
Always choose certified pellets
At national level there is no obligation to certify the quality of the pellets. Despite this, however, many manufacturers are voluntarily joining international certifications such as Pellet Gold or ENplus.
It is advisable to always use certified quality pellets for which all the parameters listed above are classified and guaranteed.
To ensure excellent returns and high comfort,
choose the Rossato pellet boilers