33
Appendix
Content
•
Combustion analysis
•
Notes
Combustion analysis
For safe, economic and environmentally friendly operation
of the plant, flue gas measurements are essential when
commissioning.
Example of a simplified calculation for determining the
CO
2
setting value
Given: CO
2 max.
= 15·4 %
At smoke limit measured (smoke number
≈
1):
CO
2 meas.
= 14·9 %
CO
2 max.
15·4
Gives excess air :
λ
≈
=
= 1·03
CO
2 meas.
14·9
To provide for a safe amount of excess air, increase by:
1·03 + 0·15 = 1·18
CO
2
value to be set with excess air
λ
= 1·18 and
15·4 % CO
2 max.
:
CO
2 max.
15·4
CO
2
≈
=
= 13·0 %
λ
1·18
The CO content must not be more than 50 ppm.
Be aware of the flue gas temperature
Flue gas temperature for full load is the result of the burner
setting to the maximum required combustion heat input to
the heat exchanger.
The flue gas installation should also be set out to protect
against damage through condensation (excluding acid-
proof chimneys).
Determination of flue gas losses
The oxygen content of the undiluted flue gas and the
difference between the flue gas and the combustion air
temperature must be determined. The oxygen content and
the flue gas temperature must be measured at the same
time at one point. Instead of oxygen content, the carbon
dioxide content of the flue gas can also be measured. The
combustion air temperature is measured in the proximity of
the burner air intake.
The flue gas losses are calculated when measuring the
oxygen content according to the equation:
A
2
q
A
= (t
A
- t
L
) • (
+B)
21 – O
2
If the carbon dioxide content is measured instead of the
oxygen content, the calculation is carried out according to
the equation:
A
1
q
A
= (t
A
- t
L
) • (
+B)
CO
2
whereby:
q
A
= flue gas losses in %
t
A
= flue gas temperature in °C
t
L
= combustion air temperature in °C
CO
2
= % carbon dioxide content in dry flue gas
O
2
= % oxygen content in dry flue gas
Fuel oil
A
1
= 0·50
A
2
= 0·68
B = 0·007
