Environmental Engineering Reference
In-Depth Information
Figure 12.8
Solid fuel
boiler for heating with
fi rewood.
Source: BBT
Thermotechnik GmbH.
Compared to the top burn-up of fi replaces where the fl ame rises upwards, many
boilers work with the burn-up at the bottom or on the side. Air is fed into the boiler
so that the fl ame is shown pointed either downwards or to the side. This increases
burning time and cuts down on emissions. The controls, which mainly regulate air
supply, ensure that a boiler is burning at an optimal level and adapt it to the heating
requirement. Firewood boilers are available in different performance classes and
reach maximum effi ciencies of more than 90%. The effi ciency of smaller boilers is
usually somewhat less.
As fi rewood boilers cannot be regulated downward to any specifi c temperature
desired, the installation of buffer storage is recommended. This will enable a boiler
to work under optimal operating conditions at all times. The storage absorbs the
excess heat and then continues to supply the heating needed after the fi rewood has
burnt down. The combination of a fi rewood boiler with a solar thermal system is a
good idea because the boiler can be switched off completely in summer when there
is very little need for heating.
12.2.4 Wood Pellet Heating
Wood pellet heating systems offer by far the greatest ease of operation. The fuel is
kept in a special pellet store, and an automated feed mechanism using either a feed-
ing screw or a suction device transports the pellets directly to the burner. A screw
conveys the pellets from the bottom part of the store. With a suction device similar
