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6.8
Start-up the flue gases recirculation system
The flue gases recirculation function has the task of reducing the
quantity of NOx contained in the combustion gases. To this end,
a part of the combustion gases is put back into the combustion
chamber, creating a drop in temperature.
The amount of recirculated flue gases is fixed using FGR servo-
motor (channel 3).
When adjusting you should keep in mind that the
excessive amount of recirculated flue gases can
cause the flame to rise above the burner head
WARNING
WARNING
(flame stability limit).
NOTE:
Reduction of the burner's maximum output
The use of the flue gases recirculation function (FGR) or the input
of the mass of flue gases into the feeding air pipe could reduce
the maximum output of the burner.
This means that the maximum amount of combustion air that can
be put in will be reduced.
Therefore it is necessary to reduce the amount of fuel for the high
range operation to ensure the correct combustion values.
The control box supports the flue gases recirculation function
(FGR) without temperature compensation.
With these operating principles, the positions of FGR servomotor
can vary only between CLOSED (ignition position) and the posi-
tions on the combustion curves.
First configuration
Start-up of the system without influence of the flue gases recircu-
lation.
Adjust the air/fuel ratio control system as if operating without flue
gases recirculation.
6.9
Steady state operation
Once the start-up cycle is completed, the servomotor command
moves on to the thermostat/pressure switch TR that controls the
pressure or the temperature in the boiler.
If the temperature or the pressure is low the burner gradually
increases the output up to the MAX.
If the temperature or the pressure increases, the burner
gradually lowers the output up to the MIN and so on.
6.10
Ignition failure
If the burner does not switch on, there is a lockout within 3s of
the electrical supply reaching the gas valve. It may be that the
gas does not arrive at the combustion head within the safety
time of 3s. In this case increase gas ignition delivery. The arrival
of gas to the pipe coupling is shown by the pressure gauge in
Fig. 48.
In the event the burner stops, in order to prevent
any damage to the installation, do not unblock the
burner more than twice in a row.
WARNING
WARNING
If the burner locks out for a third time, contact the
customer service.
Start-up, calibration and operation of the burner
Once the settings of the fuel/air ratio of the curves without flue
gases recirculation, it is possible to pass to the settings of the
FGR servomotor.
From the moment that this could influence the combustion set-
tings, it might be necessary to adjust the servomotors position
again.
FGR first configuration
The FGR position servomotor is kept in lighting position until an
adjustable time and temperature is reached.
During operation, check the temperature of the flue gases recir-
culation (FGR). It should be 100-130°C to reduce the condensa-
tion in the burner or in the suction pipe.
FGR operation configuration
The FGR position servomotor is kept in lighting position until an
delay time and an adjustable temperature is reached.
During the initial start-up of the flue gases recirculation (FGR), we
recommend to verify the control box FGR delay time. Use a value
between 5 and 15 minutes.
Check the FGR temperature sensor and make sure that the tem-
perature of the flue gases reaches the value within the time set.
If necessary, it is possible to adjust the FGR temperature of the
control box with a different value.
–
Factory setting time (default): 300s.
–
Factory setting FGR temperature: 50°C
Check the air temperature when the flame sensor
is fitted. If the temperature exceeds 50-60°, the
flame sensor could get damaged.
WARNING
WARNING
When the burner is operating with flue gases re-
circulation it is possible that a high temperature is
reached.
The burner stops when the heat request is less than the heat
supplied by the burner at MIN output.
The thermostat/pressure switch TL opens, the control box
carries out the switching off phase.
The air damper closes completely to reduce heat losses to a
minimum.
In the event there are further lockouts or faults
with the burner, the maintenance interventions
must only be carried out by qualified, authorised
personnel, in accordance with the contents of this
DANGER
manual and in compliance with the standards and
regulations of current laws.
35
GB
20168262
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