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4.6
Firing rate
The burner delivery must be selected within the range of the
Fig. 2. This area is known as the firing rate and provides the max-
imum delivery of the burner according to the combustion cham-
ber pressure.
This area is delimited by:
–
the 15 - 30 kg/h delivery line
–
the 0 + 2.5 mbar combustion chamber pressure line
–
the combustion chamber maximum pressure curve
The work point may be found by plotting a vertical line from the
desired delivery and a horizontal line from the pressure in the
combustion chamber. The intersection of these two lines is the
work point which must lie within the firing rate area.
4.6.1
Burner firing rate according to air density
The firing rate of the burner shown in the manual is valid for a
room temperature of 20°C and an altitude of 0m above sea level
(barometric pressure around 1013 mbar).
It may be that a burner has to operate with combustive air at a
higher temperature and/or higher altitudes.
The heating of the air and the increase in altitude produce the
same effect: the expansion of the air volume (i.e. the reduction of
its density).
The delivery of the burner fan remains essentially the same, but
3
the oxygen per m
of air, and the thrust (discharge head) of the
fan are reduced.
It is therefore important to know if the maximum output requested
from the burner at a determinate combustion chamber pressure
remains within the firing rate of the burner even with the changed
temperature and altitude conditions.
To check it, proceed as follows:
1
find the corrective factor F (relating to the air temperature
and altitude of the system) in the Tab. E.
2
Divide the output Q required from the burner by F to obtain
the equivalent output Qe:
Qe = Q : F (kW)
3
In the firing rate of the burner, mark the work point identified
by:
Technical description of the burner
Thermal power
9
GB
The firing rate value (Fig. 2) has been obtained
considering an ambient temperature of 20°C, an
atmospheric pressure of 1013 mbar (approx. 0m
above sea level), and with the combustion head
WARNING
adjusted as shown on page 16.
Consult paragraph "Burner firing rate according to air density", for
operation at different surrounding temperatures and/or altitudes.
The burner can also operate in depression combustion cham-
bers.
Qe = equivalent output
H1 = pressure in combustion chamber
point A that must remain within the firing rate.
4
Trace a vertical line from point A)(Fig. 3), and find the maxi-
mum pressure H2 of the firing rate.
5
Multiply H2 by F to obtain the maximum lowered pressure
H3 of the firing rate:
H3 = H2 x F (mbar)
If H3 is greater than H1)(Fig. 3), the burner can produce the de-
livery requested.
If H3 is less than H1, it is necessary to reduce the output of the
burner. The reduction in output is accompanied by a reduction in
the combustion chamber pressure:
Qr = reduced output
H1r = reduced pressure
Qr
2
( )
H1r = H1 x
Q
S9270
Fig. 2
20098582
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