Testo 350 Field Guide - Actoolsupply.com

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2.4 Combustion air; excess air value
The oxygen required for a combustion process is supplied as part of the combustion
air which consists of (see table 3) nitrogen (N 2 ), oxygen (O 2 ), a small amount
of carbon dioxide and rare gases, and a variable content of water vapor. In some
processes pure oxygen or a air/oxygen mixture is used for the combustion.
The combustion air components, except oxygen, are all contained in the resulting
raw flue gas.
Component Content [%]
Nitrogen 78,07
Oxygen 20,95
Carbon dioxide 0,03
Hydrogen 0,01
Argon 0,93
Neon 0,0018
Table 3: Composition of clean and dry air
2.4.1 Stoichiometric and excess-air combustion; material balance
The minimal amount of oxygen required to burn all combustible components
completely depends on the fuel composition. 1 kg of carbon e.g. requires 2,67 kg
oxygen to be burnt completely, 1 kg of hydrogen requires 8 kg oxygen, 1 kg of
sulfur however only 1 kg oxygen! Combustion occuring at these exact gas
quantity ratios is called ideal combustion or stoichiometric combustion.
The relevant equations are
Carbon: C + O 2 CO 2
Hydrogen: 2H 2 + O 2 2H 2 O
Sulfur: S + O 2 SO 2
The ideal combustion procedure is shown schematically in figure 1. The amount
of oxygen supplied to the combustion is just sufficient to burn all fuel combustibles
completely. No oxygen nor combustibles are left. The excess air value
(ex.air) is 1 in this case.
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