The flue gas mass flow rate is calculated using the heat input, stoichiometric air requirement, excess air, and fuel heating value. The empirical coefficient 0.0763 represents the density relationship, and 0.6 is a base flow factor. The result is converted from MMBtu/hr to Btu/hr by multiplying by 1,000,000.

\begin{equation}\label{eq:air-water-cooling-flue-gas-flow} \dot{m}_{flue} = \frac{Q_{in} \cdot 0.0763 \cdot (0.6 + SA_{req} \cdot (1 + EA)) \cdot 10^{6}}{HHV_{fuel}}\end{equation}

Symbols

\(\dot{m}_{flue}\)	Flue gas mass flow rate \([\unit{ \pound\per\hour}]\)
\(Q_{in}\)	Heat input \([\unit{ \mega\btu\per\hour}]\)
\(SA_{req}\)	Stoichiometric air required \([\unit{ \standardCubicFeet\per\standardCubicFeet}]\)
\(EA\)	Excess air fraction \([\unit{ \unitless}]\)
\(HHV_{fuel}\)	Higher heating value of fuel \([\unit{ \btu\per\standardCubicFeet}]\)