The excess air is determined from the oxygen concentration in the flue gas using stoichiometric relationships. The calculation accounts for the fact that excess oxygen in flue gas indicates incomplete combustion air utilization. The formula uses empirical factors derived from combustion stoichiometry for typical fuels.

This calculation is a fundamental component used throughout process heat calculations, including:

O2 enrichment analysis (O2 Enrichment Calculator)
Solid/liquid flue gas material calculations (Solid/Liquid Flue Gas Material Calculator)

The formula provides a quick estimate of excess air based on measured flue gas oxygen content. For more complex fuel compositions, iterative refinement may be applied (as in solid_liquid_flue_gas_material::calculateExcessAirFromFlueGasO2).

\begin{equation}\label{eq:process-heat-excess-air} EA = \frac{k_1 \cdot O_{2,flue}}{2 - k_2 \cdot O_{2,flue}}\end{equation}

Symbols

\(EA\)	Excess air \([\unit{ \unitless}]\)
\(O_{2,flue}\)	Oxygen in flue gas \([\unit{ \unitless}]\)
\(k_1\)	Stoichiometric air factor (8.52381) \([\unit{ \unitless}]\)
\(k_2\)	Oxygen flue gas factor (9.52381) \([\unit{ \unitless}]\)

Note: Input oxygen should be provided as a fraction (not percentage). For example, 3% O2 should be passed as 0.03.