The heat input is estimated from the flue gas temperature using an empirical linear relationship. Higher flue gas temperatures indicate greater heat losses, resulting in lower available heat for the process. The relationship is based on typical industrial furnace operating conditions.

\begin{equation}\label{eq:o2-enrichment-heat-input} Q_{in} = 95 - 0.025 \cdot T_{flue}\end{equation}

Symbols

\(Q_{in}\)	Heat input \([\unit{ \percent}]\)
\(T_{flue}\)	Flue gas temperature \([\unit{ \degreeFahrenheit}]\)
\(95\)	Heat input intercept constant \([\unit{ \percent}]\)
\(0.025\)	Heat input slope constant \([\unit{ \percent\per\degreeFahrenheit}]\)