13
2009-03
RVR
Energy Technology Experts
Lighting the pellets
Wooden pellets are an environmentally friendly fuel, which give
low discharge of materials that are harmful to the environment.
Due to the fact that each pellet is small in size, the fl ow of fuel
can be controlled to achieve the desired output setting. This
gives good combustion and high boiler effi ciency levels.
Viking Bio is designed for an
∅
8 mm wooden pellet. The ash
content for this wooden pellet is approx. 1 %. A bark pellet
gives more ash than a wooden pellet.
Combustion
The wooden pellet's energy content is approx. 4,7 kWh/kg.
Pellet burning produces a certain amount of ash, which needs
to be accommodated. The removal of ash from the boiler
should also be relatively easy. This means that it is important to
clean the boiler of soot on a regular basis, so that the cooling
of fl ue-gases is not adversely affected by the presence of ob-
structions on the heat absorbing surfaces.
If the combustion temperature is very high, ash particles will
fuse. If this happens, either the combustion temperature is too
high, or the pellets are of substandard quality with high ash
content. Please check the air settings. Please do not mix up
fused ash clumps with the easily removed ash cakes, which
may be present in the boiler.
Effi ciency level
The aim is to achieve a high effi ciency level, which means
extracting as much heat as possible from each pellet. In real-
ity, we are talking about reducing heat loss. Below we have a
description of the various loss factors which need to be mini-
mised:
Flue-gas losses:
The heat contained in fl ue-gases which
escape via the the fl ue.
Losses when in
When the burner is in idle mode,
idle mode.:
the fl ue airfl ow sucks cold air through the
boiler so that it begins to cool.
Insulation losses:
Heat loss via the boiler insulation. A small
part of this is retrieved by the fact that
combustion air is heated. Another part
may also be of overall benefi t to the build-
ing.
With a lower output on the burner, fl ue-gases are cooled more
effectively, which gives a higher boiler effi ciency level, longer
running time, and reduces losses in down time.
Hot water application in the summer-time
In the six coldest months of the year, approx 80% of annual
energy requirements are consumed. In this period, heating re-
quirements should be covered by pellet burning.
In that part of the year when heating requirements are low, and
mainly consist of hot water requirements, pellet burning is often
not advisable. In this period, the burner has short operational
periods, which leads to losses when in idle mode, effi ciency
levels can be <30%.
The burner can be set for different outputs. A good rule of
thumb, is not to use the higher output option more than is nec-
essary for the prevailing heating requirements.
When heating requirements are low, it is advisable to use an
electrical element with the boiler, or alternatively, a separate
electrical hot water application. In the latter case, the boiler's
fl ue gas damper should be closed when burning with pellets is
not undertaken.
Be careful when closing your pellet unit as spring arrives and
do not start it up again until it is absolutely necessary.
Effi ciency savings
Proper care of the unit, and regular adjustments, will ensure re-
duced fuel consumption for all those who make the effort.
Where the heating requirements on a cold winter's day go up to
145 kWh, 35 kg of pellets will be used with an boiler effi ciency
level of 85- 90%. If the burner is not correctly set, this can go up
to 45 kg. This can make a difference of several tons per year.
Please check regularly that:
•
the fl ame is light yellow.
•
the smoke is invisible.
•
the fl ue gas temperature has been adjusted.
•
the boiler contains no ash or soot.
•
the burner is running on the lowest output possible
.
Pellet class
Some requirements regarding the pellets, as per SS 18 71 20
group 1:
Length:
max 4 ggr
∅
(max 32 mm for
∅
8 mm pellet)
Volume:
≥ 600 kg/m
3
Fine parts < 3 mm:
≤ 0,8 weight %
Heat value:
≥ 4,7 kWh/kg
Ash content:
≤
0,7%
Total moisture content:
≤ 10 weight %
Changing to a different pellet means that settings for the
burner must be rechecked and may also cause operational
problems.
Handling and storage of pellets
Pellet storage can be solved in different ways. The key point
is the storage area that is available and the work and cost in-
volved in setting this up.
The wooden pellet must be kept in covered storage but does
not require a heated environment, as long as the room is dry.
Installing a silo is one practical storage solution. There are
a range of options where silo design and placement is con-
cerned, or these can be bought "off the shelf".
Another alternative is to build a silo, bag silo, sheet metal silo,
plywood silo etc; a converted oil tank is also an option.
Pellets will run easily from a silo set at an angle of 40±5°.
However a problem can arise if the fuel contains a large
amount of fi ne particles, which can cause a damming problem
and promotes bridging at the bottom of the cone, thus pre-
venting free fuel fl ow.
Transportation of the pellet from the the supply unit to the
burner burner chamber is carried out using normal feeder
screws of various types, both fi xed and fl exible. The feeder
screw should not have too large a lift angle, nor be dimen-
sioned too narrowly.
Checking the screw feeder's capacity
1. Release the quick release device on the downpipe and
keep hold of the device, which is attached to tube.
2. Start the screw and let it run for 3. 5 – 4 revolutions.
3. The quick release device on the tube is fi lled with pellets.
If this does not happen, check the slope on the the screw
and the gap in the pellet supply unit.
Operation and Maintenance
Caution when handling ashes as these can be red hot.
In the event of fi re or other danger, switch off the current to
the burner and carry out the necessary actions.
Clean the boiler and clear it of soot when fl ue gas tempera-
ture rises to approx. 50°C against a newly soot free boiler.
The unit should always have an alternative energy source in
order to reduce dependency.
Use only wooden pellets, which satisfy the requirements found
in industry standard SS 18 71 20, group 1.
