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1.4 Fuel
features
The main feature of this heater is that it burns a natural fuel (the pellet) obtained
in an environmentally-friendly way from scraps of the timber industry (wood
chippings, sawdust, etc.).
Wood chippings and sawdust from wood products, after having been duly
recleaned and dried, are compacted in state-of-the-art very high-pressure
plants, into pure rounded wood pieces: the pellet. Each rounded piece can
have variable lengths and thicknesses, respectively between 1÷3 cm in length
and 6÷8 mm in diameter. The pellet’s main features are low moisture content
(below 12%), its high density (=600 kg/m
3
0 as well as its regularity and
compactness that give this type of fuel characteristics of high calorific power
(I.C.P. 4000÷5000 kcal/kg).
Figure 1.1: Wood in pellet form.
The pellet to be used to feed the heater must have high quality characteristics
such as, those defined by standards DIN 51731 and ÖNORM M 7135, some basic
details of which we set out below.
Quality standard for
wood in pellet form
Unit of
measurement
Onorm M7135
DIN 51731
DIN plus
Diameter
Mm
from 4 to 10
from 4 to 10
from 4 to 10
Length
Mm
5 x D1
< 50
5 x D1
Density
Kg/dm3
>1,12
1,0 /1,4
> 1,12
Moisture Content
%
< 10
< 12
< 10
Ashes
%
< 0,50
< 1,50
< 0,50
Calorific Power
Kwh/kg
> 5
4.86 / 5.42
>5
Sulphur
%
< 0,04
< 0,08
< 0,04
Nitrogen %
<
0,3
<0,3
<0,3
Chlorine %
<
0,02
<0,03
<0,02
Powders %
weight <2,3
-
<2,3
Binding agents
% of pressed mass
<2
2
<2
1
Not more than 20% of the pellet may have a length greater than 7.5 times its diameter D.
2
The DIN prohibits the use of any added substance. However, this prohibition is not valid for small
heating systems.
DIN plus proposes the combination of the qualitative parameters proposed by
standard DIN 51731 and by Austrian standard Önorm M 7135.
