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Section 5 – Various types of fuel
Additives
If the pellets are produced without any binding materials, they will easily dissolve in
water, when immersed. Try to put a few pellets into a glass of water. If they dissolve
within a few minutes, the risk of unwanted binding material and the like is very low.
Dust
The content of dust between the pellets should be very low, as dust can be a real
problem. It prevents the pellets from moving freely and ads to the risk of building
bridges in the fuel store or in the auger. Good, clean pellets easily runs down into the
auger, where as dust often remains in the lower part of a silo or the fuel store.
The dust originates from the production process, from the transport or from being
blown into a silo. The pellets are considered to be OK, if the amount of dust is below
8 % at delivery. As dust is not homogeneous distributed between the pellets, it may be
hard to check this figure, but you should use your best judgement to distinguish
between “good pellets” and “not good pellets”.
5.2 Wood chips
In general Wood chips is a good fuel, but the size of the chips and the water content is
of immense importance. The best wood chip is made from hardwood, which has been
dried for 2 – 3 years
The chips should be maximum 2 x 2 x 1 cm, but some few parts may be larger. If the
chips in general is too rough (too many large parts) you will increase the rubbing off on
the auger and auger channel considerable, as the auger has to squeeze the material
through the channel.
In other words: relatively rough chips increases the wear and reduces the life
expectation of the equipment.
If you compare wood pellets with app. 6 % water content against wood chips of fresh
hardwood (with app 50 % water content) you half the heating value - only due to the
increased water content. Therefore always aim at so low a water content as possible –
and always below 30 %
Wood chips from coniferous tree has app. the same heating value as hardwood, but
has typically a higher bark content and often also contains sand, which burns into slag.
At the same time you will often see more long, thin pieces of branches in such chips,
which further complicates the handling of such chips –
and once again always below
30 % water content
Wood chips has a tendency to building bridges in the fuel store, hence it is
recommendable to connect the stirrer.
Should the water content in the chips used be above 30 – 35 %, you might have to set
the controller to “Manual operation” (see section 1.5, O2 regulation ore manual
operation)
