Environmental Engineering Reference
In-Depth Information
to a big vacuum cleaner the pellets are also sucked up from below. The suction
hoses are very fl exible and even enable the bridging of large distances between the
store and the burner. As the suctioning of the pellets can be noisy, modern pellet
boilers have a small hopper from which the pellets are conveyed to the burner
through gravity or a small feeding screw. The hopper is then fi lled from the store
via an automatic timer switch so that the pellet feeding system does not disturb
anyone at night.
Optimally, the store would be in the cellar. It should be big enough to cover fuel
requirements for one year. If a cellar is not available, the pellets can also be
stored in special silos in a large utility room or in an adjoining shed. Waterproof
tanks in the ground are also suitable for stocking pellets. Normally, the store will
have two openings (Figure 12.9). The pellets are blown in directly through
one opening from the tanker truck that delivers them. The displaced air from
the blowing process escapes through the other opening. As the blowing-in of the
pellets creates a great deal of dust, a fi lter traps the wood dust before the air is let
out again.
Figure 12.9
Wood pellet heating with pellet store.
Source: BBT Thermotechnik GmbH.
The controls of pellet boilers always ensure that an adequate supply of pellets is
available, thereby guaranteeing that the operation of the system is fully automated.
The fl ame is also lit automatically by an electric hot-air blower. When the required
heating level has been reached, the heating system switches off again independently.
Another feeding screw transports the accumulated ashes to a special ash pan. Wood
pellet heating therefore does not require any manual intervention for its daily opera-
tion. As with fi rewood boilers, buffer storage should be installed to reduce the
frequency with which a fi re has to be lit.
