Flare gas is considered a global environmental concern. Flaring contributes to wasting limited material and energy resources, economic loss, and greenhouse gas emissions. Utilizing flared gas as a fuel feed to industrial cracking furnaces grants advantages in terms of fuel economy and emissions reduction. This work presents the results obtained by ansysfluent simulation of a flare hydrocarbon gas utilized in a steam-cracking furnace of ethylene process when combusting hydrocarbons flare gas in a low-NOx burner. In addition, the study determined the suitability of different hydrocarbon fuel mixtures in satisfying the required adiabatic flame temperature. The flared stream is assumed to be inlet from both primary and secondary staged fuel burners. The simulation results illustrated the detailed temperature profiles along the furnace flue gas side. They also presented the influence of flare stream compositions and Wobbe Index (WI) on the temperature profile. It was found that having an alternative fuel with a heating value or WI similar to that of methane would not result in the same temperature profile of methane, as the current fuel source. In addition, using different excess air percentages has no linear effect on the burner’s temperature profile. However, the results showed that the best replacement of methane, as the main fuel source, is a flare mixture with the same WI of methane as well as a certain H2 content needs to be added to every flare mixture composition to reach the same temperature profile of methane.