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Dimensioning
Fuel store
Dimensioning of the storeroom
To dimension the storeroom, the expected fuel
consumption must first be determined. This can either
be estimated from the boiler output, or from the
running hours of the boiler.
Estimation based on boiler output
The formula for this is as follows:
Example:
For a boiler with an output of 50 kW and average fuel
quality, an annual consumption of approximately 125
cubic metres is expected.
For higher fuel qualities (low contamination, low
bark, low water content), this is reduced by a
factor of "2". For the above example, the annual
consumption is reduced to approx. 100 cubic metres.
Estimation based on running hours
The formula for this is as follows:
Example:
For a boiler with an output of 50 kW and spruce wood
chips of size "P16S" with 30% water content, the
resulting annual consumption is about 128 cubic
metres.
You can find the heating values of different fuels
in chapter
Determining the number of refills
With an agitator with a diameter of 4 m and a
maximum filling height of 5 m, a storage volume of
about 62.8 m³ (= ((d² x π)/4) x filling height) is
achieved.
With an annual consumption of 128 m³, the storeroom
must be filled twice per year (128 / 62.8 = 2).
However, if a 6 m diameter agitator is used
instead of the 4 m agitator, a storage volume of
approx. 141 m³ is obtained at a maximum fill height of
5 m. With a consumption of 128 m³, the storeroom
must therefore only be filled once per year.
Floor agitator dimensioning
The rotation of the floor agitator clears a circular area
in the storeroom. In a storeroom with corners, a portion
of the fuel will always remain unused in the corners. To
use all of the fuel, a round storeroom (maximum
diameter 6 m) would be preferable.
For a storeroom with, for example, interior dimensions
of 4 x 4 m a floor agitator with a diameter of 4 m would
usually be used. However, a slightly larger floor
agitator with 4.5 m diameter can also be used. With it,
the flat spring arms are able to reach the otherwise in-
accessible corners of the fuel store and can also clear
out the fuel there. This requires planning, because the
open trough must be located entirely in the storeroom
and should not protrude through the wall.
When there is little fuel in the storeroom, the flat spring
arms are relaxed and extend to the inner walls. To
avoid damaging the walls, boards should be attached
to them at the height of the flat spring arms.
To prevent bridging in the fuel store, the size of
the floor agitator should never be smaller than the
diameter of the storeroom.
If the storeroom is square, a larger floor agitator
can be installed. It is acceptable for the flat spring
arms to strike the edge of the storeroom and also
convey the fuel there. In order to protect the masonry,
wooden panels can be fitted all around, against which
the flat spring arms can strike. This also minimizes the
risk of bridging. However, it must be noted that the
open trough must not be located in the wall. Therefore,
the floor agitator is to be offset from the centre. Plans
for this are available from ETA.
V
srm
... Volume in loose cubic metres in [m³].
A loose cubic metre (srm) corre-
sponds to 1 m³ of loosely filled wood
chips.
P
k
... Boiler output in [kW]
V
srm
... Volume in loose cubic metres in [m³]
P
k
... Boiler output in [kW]
t
VLH
... Maximum permissible full load hours of the
boiler per year in [h].
This is stated in the guarantee conditions
of the respective boiler.
Hw
... Calorific value of the fuel in [kWh/srm]
