Riello 2916463 Manuel D'entretien page 38

Appendix - Firing rate on basis of air density
D
The firing rate of the burner shown in the manual is valid for an
ambient temperature of 20°C and an altitude of 0 m above sea
level (barometric pressure around 1013 mbar).
It may be that a burner has to operate with combustion 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,
3
but 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 re-
quested 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 table alongside.
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:
Qe = equivalent output
H1 = pressure in combustion chamber
point A that must remain within the firing rate (Fig. 40).
4 -Trace a vertical line from point A, Fig. 40, and find the max-
imum 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)
Average
Altitude barometric
pressure
m. above sea level mbar
0 1013
100 1000
200 989
300 978
400 966
500 955
600 944
700 932
800 921
900 910
1000 898
1200 878
1400 856
1600 836
1800 815
2000 794
2400 755
2800 714
3200 675
3600 635
4000 616
6463
0 5 10
1.087 1.068 1.049
1.073 1.054 1.035
1.061 1.042 1.024
1.050 1.031 1.013
1.037 1.018 1.000
1.025 1.007 0.989
1.013 0.995 0.977
1.000 0.982 0.965
0.971 0.954
0.988
0.977 0.959 0.942
0.964 0.946 0.930
0.942 0.925 0.909
0.919 0.902 0.886
0.897 0.881 0.866
0.875 0.859 0.844
0.852 0.837 0.822
0.810 0.796 0.782
0.766 0.753 0.739
0.724 0.711 0.699
0.682 0.669 0.657
0.661 0.649 0.638
If H3 is greater than H1, as in Fig. 40, the burner can produce
the delivery 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
H r = H x
1 1
Q
Example, 5% reduction in output:
Qr = Q x 0.95
2
H1r = H1 x (0.95)
With the new values - Qr and H1r - repeat steps 2 - 5.
Warning:
the combustion head should be adjusted in relation to the
equivalent output Qe.
mbar
mbar
H2
H3
H1
D388
F
Air temperature °C
15 20
1.031 1.013
1.017 1.000
1.006 0.989
0.995 0.978
0.983 0.966
0.972 0.955
0.960 0.944
0.948 0.932
0.937 0.921
0.926 0.910
0.914 0.898
0.893 0.878
0.871 0.856
0.851 0.836
0.829 0.815
0.808 0.794
0.768 0.755
0.726 0.714
0.687 0.675
0.646 0.635
0.627 0.616
36
GB
A
Qe
Qe
25 30 40
0.996 0.980 0.948
0.983 0.967 0.936
0.972 0.956 0.926
0.962 0.946 0.916
0.950 0.934 0.904
0.939 0.923 0.894
0.928 0.913 0.884
0.916 0.901 0.872
0.906 0.891 0.862
0.895 0.880 0.852
0.883 0.868 0.841
0.863 0.849 0.822
0.842 0.828 0.801
0.822 0.808 0.783
0.801 0.788 0.763
0.781 0.768 0.743
0.742 0.730 0.707
0.702 0.690 0.668
0.664 0.653 0.632
0.624 0.614 0.594
0.606 0.596 0.577
kW
kg/h
Fig. 40