Bulk density of woodchips
Bulk densities of woodchips as defined by water content, according to EN ISO 17225-4
Water content based on
moisture mass
% of the mass
8 to 18
18 to 25
25 to 35
35 to 45
Bulk density for conifer-
ous species
kg/m
3
160 to 180
180 to 200
200 to 225
225 to 270
Property class
BD150
BD150
BD200
BD200
Bulk density for decidu-
ous species
kg/m
3
225 to 250
250 to 280
280 to 320
320 to 380
Property class
BD200
BD250
BD250
BD300
Woodchip quality characteristics
Good woodchips:
■ Low, homogeneous water content, no moisture pockets or mould
■ Low proportion of needles, leaves, fine branches and bark
■ Low proportion of fine wood material (hardly any particles < 3 mm)
■ No contamination from mineral soil and foreign matter or impurities
■ Uniform particle size (no excess length)
■ Smooth edges, no fraying
Low quality woodchips:
■ High proportion of fraying surfaces or edges
■ High proportion of needles, leaves, fine branches and bark
■ Contamination from mineral soil and foreign matter or impurities
■ Heterogeneous particle size
■ High fine fraction and water content
Substances
When buying wood for combustion, it is important to ensure that the
following foreign matter is avoided:
■ Stones
■ Metal particles
■ Masonry remnants
■ Plastics
Foreign matter changes the composition of the fuel and therefore the
critical parameters of the combustion process.
Observe the following limits per kg of dry fuel or dry matter content
of non-combustible constituents. The limits for ash were determined
at an analysis temperature of 815 °C. If the specifications are
observed, the minimum temperature at which ash sintering starts is
1000 °C.
Limit
Comparison with natural wood from forests
Chlorine Cl
mg/kg
Max. 300
10
Sulphur S
mg/kg
Max. 1000
120
Total Cl, S
mg/kg
Max. 1000
130
Ash content, total
g/kg
Max. 15.0
5.0
Sum of alkali oxides in the ash (K
2
O and Na
2
O)
g/kg
Max. 1.0
0.35
Start of ash sintering (SB)
°C
min. 1000
approx. 1200
Note
Avoid foreign matter, such as nails and iron particles, as such foreign
bodies increase the wear of system parts.
It is imperative that light metals are avoided, as these will melt in the
combustion chamber and lead to faults in the grate area.
Exceeding the above limits will shorten the service life of the com-
bustion chamber and the solid fuel boiler. This also means a greater
amount of maintenance work and shorter service intervals.
Non-wood biomass fuels
Non-wood biomass fuels such as needles, leaves, cereals, straw,
husks, fruit stones, etc. are unsuitable as fuels for trouble-free oper-
ation, and are therefore not permitted.
In some cases, the fuel properties (elemental composition, ash sin-
tering point, etc.) differ considerably from those of wood. Combus-
tion of such fuels in a solid fuel boiler can lead to an impairment of
the combustion characteristics. The fireclay lining and the heat
exchanger surfaces will be subject to increased stress. Warranty
claims can therefore only be asserted when using approved fuels.
1.4 German Immissions Ordinance (1st BlmSchV)
Contents of the 1st BImSchV
The German Immissions Order (1st BImSchV) regulates the follow-
ing for small and medium-scale biomass combustion systems which
do not require approval:
■ The conditions under which small and medium-scale biomass
combustion systems may be installed and operated.
■ Establishing the emission limits of small and medium-scale sys-
tems
■ How often and to what extent a system must be monitored in order
to protect the environment from emissions.
Update of the 1st BImSchV – Tightening of the emission limits
The update of the 1st BImSchV, which contains the following essen-
tial new points, came into force from 22 March 2010 onwards:
Principles of wood combustion
(cont.)
10
Viesmann
VITOFLEX 300-UF
1
5682428
