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Suitable fuels
Information on fuel
9
Information on fuel
9.1
Suitable fuels
The amount of ash depends on the fuel
Ash is the non-flammable residue from the wood. It
consists of minerals such as calcium and potassium
without which life cannot exist, but also soil, sand and
stones, i.e. impurities in the fuel.
Wood chip, with its very low bark content, has an ash
content of approximately 0.5 %. The bark itself has an
ash content of nearly 4 %. In practice, there is always
soil and sand stuck to the bark.
Fuel from crops has a very high potassium content.
The ash content is in the range 3 to 6%.
Wood residues with a high proportion of fine branches
and needles is extremely dense in storage, is poorly
ventilated and does not dry. Frequently, this material
already begins to rot at the timber storage site. With
this process of decomposition, the heating value
diminishes and the ash content rises.
How often ash waste containers have to be emptied
depends on the heat capacity of the boiler and the
quality of the fuel (ash content, heating value, etc..).
The preferred fuel is coarse wood chips with a low
fine content
The length of the individual wood chips should be
between 30 and 50 mm, to ensure that air can circulate
well among the stored chips, water can escape from
the pile and the tendency to rot and turn mouldy is
minimal.
If the fine content (sawdust, bark, needles, soil, sand)
is too high, it can obstruct the airways. Water
evaporates inside the warm wood chip pile. If the
vapour cannot escape, it will condense in the upper
part of the heap. Some of the wood chips will then rot
and turn to compost with no heating value.
Avoid green, moist wood chips
Only wood chips that are sufficiently dry (water content
below 25%) can be stored in a concrete bunker without
problems. Moist, coarsely chopped chips stored in an
open hall exposed to the wind quickly reach a water
content under 35%.
Be especially careful with waste wood
When waste wood is on offer, it may be rotten with no
heating value; only buy waste wood by weight and with
limited water content (25% maximum). Also ensure
that the wood contains no contaminants. The
applicable laws only allow the use of untreated wood
without foreign substances for heating purposes.
Wood-processing facilities may burn chipboard if
it contains no halogens or wood preservatives.
Binding agents containing chlorine used to frequently
be used in wood products. if these are burned in a
boiler without appropriate cleaning of the flue gas, con-
taminants detrimental to health will be emitted. Apart
from this, a very high chlorine content will have a
severe negative effect on the life of the boiler.
Only burn wood products or painted, coated or
varnished wood if you are sure these contain no wood
preservatives, organohalogen compounds or heavy
metals.
Nails and stones
Nails and stones will hardly bring the boiler to a halt,
but they cause increased wear on the screws and the
blades in the rotary valve.
Impurities in the fuel
Impurities in the fuel result in a higher ash content and
are frequently responsible for a lower ash melting
point. If the ash melting point is exceeded, the ash
fuses (slag formation). It is therefore in the plant
operator's interests to keep impurities to a minimum.
Types of wood chips
The best quality wood chips are finely chopped
hardwood, without bark, with low dust content and a
water content below 20%. With the highest heating
value and the lowest storage volume requirement, this
would be the optimum fuel for any boiler.
Fine wood chips can be made from dry wood, enabling
a higher storage density.
Even if wood is stored dry, the energy content wanes,
and the heating value of dry wood decreases by 10%
over 10 years.
Wood chips from dry branches and shrubbery cuttings
have higher bark content and usually also large
amounts of dirt and decayed material. Resulting in
more ash.
If they were chopped from dry wood, there will be no
storage problems and the reduction in boiler output is
low.
Forest-
chopped wood chips from fresh branches are not fit f
or storage and reduce the achievable boiler output si
gnificantly.
Summary of Contents for HACK 20
Page 1: ...2017 01 30 EN 0000000294 V 003 2 38 0 3005 3106 93526 001 Wood chip boiler 20 90 kW Operation ...
Page 15: ...Changing the fuel Settings 15 4 2 Settings ...
Page 35: ...ETAtouch controller Boiler function block HACK 35 ...
Page 45: ...ETAtouch controller Buffer function block 45 ...
Page 49: ...ETAtouch controller Hot water tank function block 49 ...
Page 53: ...ETAtouch controller Fresh water module function block 53 ...
Page 67: ...ETAtouch controller Solar function block 67 ...
Page 73: ...ETAtouch controller Heating pipeline function block 73 ...
Page 92: ...www eta co at www eta co at downloads DOWNLOAD ...