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Section 5 – Various types of fuel
Section 5- Various types of fuel
5.1 Wood pellets
Wood pellets are made by pressing fine grinded wood through a matrices under high
pressure adding steam. Pellets are produced in diameters between 3 and 25 mm. If
they are over 25 mm, they are called briquettes. The pellets are cooled down and put
through sieves to remove dust.
According to (
Danish
) notice no 638 regarding biomass you can only use clean wood
such as sawdust, chips and grinding dust. Any added binding material may not change
the character of the wood pellets from being biomass combustible. The basic material
may contain maximum 1 % glue of approved types, but neither paint, plastic, metal,
impregnating material or the like. Pellets containing such material are defined as waste
and should NOT be used in any furnaces
How do I get good wood pellets?
The supplier must be able to issue a declaration, stating that the pellets are made of
clean wood without any prohibited additives. Further the following should be checked.
The pellets must smell as fresh wood.
The smell coming through the combustion must be as from clean wood.
The colour must be as wood without any traces of paint or the like.
The specific weight must be OK.
There should not be any kind of additives in the pellets.
The amount of saw dust and the like should be very low.
How to control these preconditions?
Smell
Put a few handfuls of pellets into a plastic bag and smell the content. If the pellets
smells from wood, they are OK. But remember, that some pellets are made of beech
or oak which smells different than pine. The smell alone cannot define a good pellet.
Smell during combustion.
The smell from the flues must be as from wood combustion. If the flues smells
differently, you should carefully check the pellets.
The colour
The pellets must be homogeneous and have a wood like colour. The colour can vary
depending on the kind of wood used or if smaller amounts of finely grinded bark is
mixed into the pellets (this is permissible). The exterior must be dark brown (caused by
the heat during production). No particles, not looking like wood, should be visible, as
this indicates pollution from paint, plastic, carpet or similar items.
The specific weight
The specific weight for wood pellets depends partly on how hard they were pressed,
partly on moisture content (typically round 6 – 8 %) Due to the amount of air between
pellets the specific weight is round 0,6 to 0,7 kg pr litre. But if you put a good pellet into
a glass of water it should sink like a stone (due to the compression of the material.
