As a result clean, low-emission combustion is
achieved. The horizontal combustion results
in a flame shape smiliar to that of an oil or gas
burner. This combustion system achieves a
high pellet burnout rate. Mainly due to the large,
mostly refractory lined combustion chamber, it is
possible to acheive a large residence time of the
hot gases as well as sufficiently high combustion
temperatures.
Hot water is subsequently generated by heat
exchange between the hot gases and boiler
water by means of a thermolytic secondary heat
exchange surface. The secondary heat exchange
surface is automatically cleaned by means of a
motor driven mechanical cleaning device. This
improves the efficiency, lowers maintenance
requirements and ensures a constant low fuel
usage.
Boiler Cleaning Regime
Automatic ash removal with integrated ash box
– Empting of the ash box will need to be carried
out periodically by the operator. In addition, there
is a requirement for the operator (or maintenance
engineer) to routinely take the boiler off line, to
clean out the combustion chamber, retort, and ID
fan chamber. This will involve a partial strip down
at the front and top of the boiler. Please refer to
the BioLyt Operating and Technical Manual pages
for further information. These can be accessed
via the Downloads page of our website www.
hoval.co.uk. The frequency of the cleaning and
de-ashing intervals will vary with the quality fo the
pellets used (see above) and heat load profile/
operating time.
Flues and chimneys
General Guidelines
- Individual boiler chimneys and flues should be
used.
- The chimney/flue must be gastight, impervious
to moisture, non corrosive and acid proof.
- The chimney/flue design should encompass the
minimum number of bends - any bends should
be swept - avoid excessively long horizontal
runs and if possible have the flue enter the main
chimney riser at an angle of 45o to minimise the
flue duct resistance.
- The flue should be fitted with the combined
draught stabiliser and pressure relief damper
that is supplied loose with all BioLyt boilers (see
included accessories). This damper should be
installed within 1 metre of the boiler flue outlet
connection. Please note that fitting of this item
is excluded by Hoval.
- We recommend flues should be at least
200mm I/Dia after the above damper.
Engineering
Thermal flow safeguard
The heat exchanger must be connected to the cold
water supply at a minimum required flow pressure
of 2 bar and minimum water flow rate, as follows:
BioLyt (50)
2000 l/h
BioLyt (70)
2000 l/h
BioLyt (110- 160) 2000 l/h
Fuel Pellet Storage Room, Silo or Bunker
The design of the intended fuel pellet storage room,
silo or bunker must be approved by Hoval prior to
confirm ation of an order being given.
Pellet Fuel Specification
The pellets should be formed from CLEAN or
VIRGIN TIMBER and to the specification outlined in
wood pellet specification CEN/TS 14961.
The fuel MUST NOT contain halogenated organic
compounds or heavy metals as a result of treatment
with wood preservatives or coatings.
Typically the wood pellet fuel would have the
following As Received properties,
Calorific Value (min) nCV
basis (CV)
17,000 kJ/kg, or
4.72 kWh/kg
Mechanical Durability (DU) > 97.5%
Ash Content (A)
< 1.0%
Moisture Content (M)
< 10 %
Size Diameter (D)
Length
D 06, Diameter 6mm
20 – 30mm
Sulphur Content (S)
<0.05%
Fines (- 3.15mm into
vehicle) (F)
< 1.0%
Bulk Density
650 kg/m
3
Hoval do not endorse any particular wood pellet
manufacturer, however it is recommended that
fuel is supplied against the specification indicated,
and the supplier operates well maintained vehicles
and fully trained delivery drivers to ensure that the
boiler and fuel transfer system are presented with
well sized wood pellets, which are free from any
contamination.
Boiler operation
Hot water for heating is generated by the controlled
combustion of quality wood pellets through a
thermolytic heat exchanger. The wood pellets are
conveyed by a dosing screw from the pellet hopper
over a drop tube to the boiler feed screw. The speed
of this dosing screw modulates in line with the heat
demand.
Degassing of the pellets takes place in the rear
part of the burner tube into which primary air is
supplied by a high pressure fan. In this way the
combustion gases generated are thoroughly mixed
with secondary air, which is supplied by an induced
draught fan within the front section of the burner
tube.
- Fuel Quality Requirement. The design of the
combustion system is dependant on using the
correct quality wood pellet fuel, as previously
outlined.
- Note: Flue gas temperature at high fire may
approach 200
o
C and the flue system should be
able to safely operate under such conditions
(further advice can be found at www.hetas.
co.uk).
D
D
2xD
< 2D
1D
Flue Gas
test point
Drain line to
tundish
Thermostatically
operated valve
Cold water supply
Chimney sizes and height will need to take into
account the following:
1) Clean Air Act.
2) Local Regulations.
3) Considerations to adjacent buildings.
4) The discharge to atmosphere of the
products of combustion that may
contribute to health dangers and be
such to minimise the impact of the
same. When used with the correct
quality fuel, the BioLyt meets the
requirements of Class 3 of EN 303-5 in
this respect.
IMPORTANT
Condensation from the flue system should not
be allowed to run back into the BioLyt boiler. A
suitable trap arrangement must be provided to
ensure this requirement is met.
Guidance for sizing flues and chimneys is
given in CIBSE and HVCA guides and also
Hoval Technical Data Sheets. Flues should
conform to the relevant British Standards,
Codes of Practice and current legislation.
- The flue design will be such that the chimney
height should provide sufficient buoyancy to give a
negative pressure condition of between 5 and
20 Pa at the boiler flue outlet
. The chimney and
flue should, under normal firing conditions, provide
a draught at the boiler outlet.
- With a cold chimney some external draught
assistance may be required e.g. flue fan.
- Common flue headers must be avoided.
- Steps should be taken to prevent or minimise
condensation forming within the flue by using twin
walled insulated systems.
- Adequate doors should be provided in flues and
chimneys for cleaning and inspection purposes. This
is particularly important on any horizontal section.
- Flues should be supported independently to prevent
any undue weight and forces due to expansion being
transmitted to the boiler outlet connection.
- A flue gas sampling point, with a circular internal
diameter of 10-21mm, must be fitted in the flue pipe
adjacent to the boiler. Please see the diagram below
(damper not shown).
7
Hoval BioLyt (50-160)