Environmental Engineering Reference
In-Depth Information
Figure 12.5
Different processed forms of wood. From top left to bottom right: round wood, fi rewood,
wood briquettes, wood pellets.
■
Diameter: 5 - 6 mm; length: 8 - 30 mm
■
Minimum calorifi c value:
H
i
: 18 MJ/kg or 5 kWh/kg
■
Bulk stacked density: 650 kg/m
3
; raw density: larger 1.12 kg/
l
■
Water content: less than 10%; ash content: less than 0.5%
■
Limit values for sulphur, nitrogen, chlorine and abrasion
The standards applied in the USA are generally less strict than those in Europe. The
new standard CEN/TS 14961 applies to all future production of wood pellets. A
pile of pellets weighing one ton takes up 1.54 cubic metres of space and has a calo-
rifi c value of 5000 kilowatt hours. This equates to a calorifi c value of approximately
500 litres of heating oil. Therefore, two kilos of wood pellets can replace one litre
of heating oil.
A Tree - the World Record Holder
An 80-year-old beech tree reaches a height of 25 m (82 ft). The crown of the
tree has a diameter of 15 m (49 ft) and contains about 800 000 leaves. If the
leaves were spread out lying next to one other on the ground, they would cover an area
of about 1600 square metres (0.4 acres). This beech tree supplies the oxygen needs of
