Minimum Wood Fuel Requirements; Content; Non-Wood Biomass Fuels; Wood Fuel Regulations And Standards - Viessmann KOB PYROTEC Technical Manual

Principles of wood combustion
Poor woodchips:
■ Frayed surface
■ More than 5 % outliers
1

1.3 Minimum wood fuel requirements

Content

When procuring wood for combustion, it is important to ensure that
foreign matter (e.g. stones, metal parts, brick fragments, plastics, etc.)
is avoided. These change the composition of the charge and therefore
the critical parameters of the combustion process.
Chlorine Cl
Sulphur S
Total Cl, S
Ash content total
Alkali oxides in the ash (K
2
SB starting of ash sintering
A consequence of exceeding the above limits is a shortened combus-
tion chamber and wood boiler service life. This also means that the
maintenance work is increased and the servicing intervals are short-
ened.

Non-wood biomass fuels

Non-wood biomass fuels, such as needles, leaves, grain, straw, husks,
fruit kernels, etc., are generally unsuitable as a fuel for trouble-free
operation and therefore not permissible.

Wood fuel regulations and standards

Germany 1.BImSchV in the revised version dated 22.03.2010
Austria FAV dated 18.11.1997 "Ordinance for Combustion Systems" § 3.(1) 3. Solid fuels
Switzerland Clean air regulations LRV dated 16.12.1985 (as at 28.03.2000)
ÖNORM M 7133 Woodchips for energy purposes (1998)
EN 303-5 Boilers for solid fuels, table 8 "Test fuels"
CEN/TS 14961 Solid biofuels
6
(cont.)
mg/kg
mg/kg
mg/kg
g/kg
O and Na O) g/kg
2
°C
■ Coarse percentage higher than 20 %
■ Greater than G50
The values must not exceed or fall below the following limits (per kg of
dry fuel) for the non-combustible contents (ash at an analysis temper-
ature of 815 °C):
Limit Comparison with natural wood from forest
max. 300
max. 1000
max. 1000
max. 15.0
max. 1.0
min. 1000
The proportion of dust-like and fine-grain materials should also be
minimised (in accordance with ÖNORM M 7133).
In some cases, the fuel properties (essential composition, ash sinter-
ing point, etc.) differ considerably from those of wood. Combustion in
a PYROTEC can lead to impairment of the combustion characteristics
and to greater stress on the fireclay lining and the heat exchanger sur-
faces. Warranty claims can therefore only be asserted when using
permissible fuels.
thinnings
10
120
130
5.0
0.35
approx. 1200
PYROTEC