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Preparation
What ash is suitable for ash recycling?
Ash to be spread on the forest land will mainly come from
forest fuels, as the idea of the spread is that the
ecological cycle will be completed. From this perspective,
clean ash from the incineration of exclusively forest fuel
is the
most appropriate.
It is obviously a
pity to deposit the ash of good quality if only, for example,
minor amounts of peat are included in the fuel mixture. It
can therefore also use mixed ash from combustion of wood
fuel with a certain admixture of peat and oil, provided that
the ash pass the limits of the Forest Board's
recommendations.
In addition to the requirements on the fuel ash source, it must also
meet a number of requirements with regard to the chemical
content to be suitable for ash recycling.
Fly ash is the best from fluid beds,
bottom ash is best from
the grate boiler.
The quality of fly- and bottom ash varies between different
boiler types. Bottom ash from the CFB and BFB boilers do not
normally spread in woodland because it largely consists of
the bed material.
Fly ash, however, has many good characteristics, it is well
torrid and uniform. In rosterpannor, it is normally the
bottom ash which are the best because it is better usage and
have lower levels of metals than fly ash. In smaller
establishments often mixed bottom ash and fly ash.
Sandvik plant, VEAB. They produce ash,
which we then spreads in the forest.
Source:
www.veab.se
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Hardening of ash
The ash is taken from the thermal plant or
sawmill to one of our storages. The ashes need to be stored
for at least 3 months in order to harden. During this
process the ash becomes less alkaline.
When the ashes are hardened, they are crushed and sieved to
a grain fraction that does not harm the trees at spreading
and were the dissolution rate of the grains in the forest
soil is optimal.
Ash for spreading in the forest
should be treated so that acute damage to soils and
vegetation as well as mechanical damage to trees is avoided.
It is important that it becomes an even distribution and
that the ash is dissolved slowly. The ash can be hardened by
the addition of water and mechanical processing to the
appropriate particle size and hardness (granulation or
pelleting).
The ash can also be
hardened by the addition of water by self-curing, with
subsequent decomposition and/ or sieving if its needed. The recommendation is that the ash will be
dissolved over a period of 5-25 years in the field.
Furthermore, the initial resolution rate be so slow that no
acute adverse effects occur after the distribution. Poorly
hardened ash can damage the flora and fauna and increasing
the risk of leaching of nutrients in the ash.
For requirements on the
ashes solubility will be met has The National Board of
Forestry developed a method to test if an ash product is
sufficiently hardened that the most sensitive of our common
mosses should not be harmed if the ashes spread with
acceptable spreading evenness in a forest. Ash that is not
sufficiently hardened by the method should only be
disseminated in woodland where it can be shown that it can
safely be done without burns on Spagnum.
The risk of leaf damage will be less if the ashes have
coarse grains. Itīs because the distance between the
particles become larger and itīs easier for the grains to
fall to the ground under leaf surfaces.
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