Chapter 2
INSTALLATION AND USE MANUAL
page
8
Theoretical notions for installation
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2.
Theoretical notions for installation
2.1.
Pellets
Wood pellets are manufactured by hot-extruding compressed sawdust which
is produced during the working of natural dried wood. The compactness of
the material comes from the lignin which is contained in the wood itself, and
allows the production of pellets without the use of glues or binders.
The market offers different types of pellet with characteristics which
vary depending on what mixture of woods is used. The diameter varies
between 6 mm and 8 mm, with a standard length in the range 5 mm to
30 mm. Good quality pellets have a density which varies between 600
kg/m3 and 750 kg/m3, with a moisture content which varies from 5%
to 8% by weight.
Besides being an ecological fuel (exploiting timber residues to the
maximum and achieving cleaner combustion than is possible with fossil
fuels), pellets also have technical advantages. While good-quality
timber has a calorific power of 4.4 kW/kg (with 15% moisture,
therefore after about 18 months' seasoning), the equivalent figure for
pellets is 5.3 kW/kg.
To ensure good combustion, the pellets must be stored in an area that
is free of humidity and protected from dirt. The pellets are usually
supplied in 15 kg. sacks, so storing them is very convenient.
Good quality pellets ensure good combustion, thus lowering the
emission of harmful agents into the atmosphere.
The poorer the quality of the fuel, the more
frequently will intervention be necessary for cleaning
the internal parts, such as the grate and the
combustion chamber.
The pellets must be produced from pure wood which has not been
treated chemically.
The standards
DIN 51731
and
ONORM M 7135
certify a high-quality
pellet with the following characteristics:
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Calorific power: 5.3 kW/kg
9
Density: 700 kg/m3
9
Water content: max 8% of weight
9
Percentage of ashes: max 1% of weight
9
Diameter: 6 – 6.5mm
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Length: max 30mm
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Contents: 100% untreated wood, with no added bonding
substances (bark percentage 5% max)
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Packaging: in sacks made from ecologically compatible or
biologically decomposing material
Fuel pellets
15 Kg sack of fuel
