Fuel store
Tilted floor
67
Maximum fill height
The maximum fill height for wood chips is 5 m (approx.
200 kg/ m³). Due to the greater weight (approx 650
kg/m³) with a floor agitator, pellets can only be filled up
to a maximum height of 2 m.
If the fill height is more than twice the diameter of the
agitator (e.g. higher than 4 m for an agitator with 2 m
diameter), there is a risk of cavitation (also called
bridging). This is especially the case with wood chips
with a high water content, a lot of fine content or
shredded wood chips.
Cavity formation means that the wood chips wedge
into each other and no longer slip into the agitator. This
creates a cavity above the agitator over time, which is
not visible from the outside. This is often only noticed
when the boiler outputs an error message because no
more wood chips reach the boiler. The remedy here is
to poke in the wood chips with, e.g. rods, so that the
hollow space collapses.
For this reason it is forbidden to enter the wood
chip store, especially the area above the agitator,
because there is a danger of collapse due to the
formation of cavities and thus an increased risk of
injury.
11.3
Tilted floor
Slanted floor for the fuel
With a slanted floor in the storeroom, the fuel cannot
get under the floor agitator so no unused space results.
Without the slanted floor, the space under the flat
spring arms is filled first when filling the fuel store. This
volume is not accessible to the flat spring arms and
remains unused and over time the material there will
decay.
Fig. 11-2: Slanted floor
Benefits of the slanted floor:
•
The flat spring arms move along the floor and
cannot "float" over the fuel.
•
The fuel is not compacted in the outer area of the
floor.
However, some points have to be considered when
building a slanted floor:
•
The static load upon the substructure must be
considered.
•
A slanted floor is required for operation with
pellets.
•
For the cavity below the slanted floor, sufficient
ventilation must be provided so that moisture can
escape. Country-specific regulations are to be
observed.
•
The cavity under the slanted floor forms a
resonating body. As a result, sound transmissions
can be generated throughout the residential
building or adjacent structures.
If the fuel storage is located in a residential
building or adjacent to one, a slanted floor is
not recommended.
If no slanted floor is installed, the first filling of the
storeroom must be performed with dry wood
chips. Because these remain on the floor and later
form the support for other fillings. In contrast, moist
wood chips would slowly rot, thus reducing the heating
value of later fills.
Chamfer for size 2 floor agitator
For size 2 floor agitators, a 45° chamfer needs to
be built into the slanted floor at the open trough.
Otherwise, the conveyor screw will become clogged,
triggering a malfunction.
Fig. 11-3: Size 2 floor agitator
Fig. 11-4: 45° chamfer in slanted floor