Unical ALLBIOMIX, Инструкции по установке, использованию и обслуживанию

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18
2.7 - WOOD CHARACTERISTICS
Wood is formed mainly by cellulose and lignite. It
also contains other substances, such as resin (fir -
pine), tannin (oak - chestnut) and, obviously, a large
quantity of water.
Good quality woods are oak, ash, beech, maple and
fruit trees, except cherry; medium quality wood is:
chestnut and birch; sufficient quality wood: lime tree,
poplar and willow. Resinous trees are, normally,
second-rate quality fuels.
Wood is therefore an extremely heterogeneous
fuel, due to different essences (beech, oak, fruit,
resinous), different moisture content, and due to
different shapes and dimensions.
Boiler operation will inevitably be effected by all
these factors. Especially by the log dimensions, the
moisture content and the way wood is loaded in the
boiler.
WOOD MOISTURE
The calorific value of the different types of wood
depends on their moisture content, as illustrated in
the table. Boiler output and autonomy will diminish as
the moisture increases. The table provides the power
reduction factor based on the moisture of the wood
being used. The heat output of the ALLBIOMIX boiler
is calculated for wood with a 17% moisture content.
As an example, wood which has been dried for
2 years in a sheltered area has a 25% moisture
content.
Example:
moisture of the wood being used = 30%
output = nominal output x 0.79
Correction factors for wood moisture
% OF
HUMIDITY
CALORIFIC
VALUE
kWh/kg
CORRECTION
FACTOR
15
20
25
30
35
40
45
50 4.50
4.18
3.87
3.60
3.24
2.92
2.65
2.34 1
0.93
0.86
0.79
0.72
0.65
0.59
0.52
DIMENSIONS
The dimensions, together with the moisture content,
contribute to determine the boiler’s output. Small
pieces (with a length, however, conforming to indi-
cations indicated hereby) are more easily flammable
and therefore have the tendency to increase the
boiler’s output and therefore to reduce its auton-
omy. Moreover, they fall with greater facility, in the
lower chamber, reducing the risk of the formation of
“bridges”. The so-called “bridge” is an empty space
in the firewood storage compartment, where unburnt
wood logs remain. In this case the bed of embers
is not fed with continuity and the refractory burner’s
slot is uncovered. In these conditions, preferential
air ducts are created with a very small flame due
to an excess of air.
USEFUL TIPS AND WHAT TO AVOID
- Logs which are too long do not fall down properly and can
cause "bridges".
- Logs which are too short cause irregular air ducts, with con-
sequent reduction in output and efficiency.
- If the quality of the wood causes "bridges", it could become
necessary to load logs cut in half so that the total length “L”
is as indicated in the previous paragraph.
To avoid the formation of "bridges", it is unadvisable to place
logs against the side walls of the wood storage compartment.
(see fig. 3).
- Always open the upper door slowly, in order to avoid blow-
backs and smoke formation.
- During normal boiler operation, it is absolutely forbidden to
open the lower combustion chamber door.
tagliare
=
=
L
L
CALORIFIC
VALUE
MJ/kg
16.20
15.05
13.93
12.96
11.66
10.51
9.54
8.42
cut