This investigation develops a three-dimensional Computational Fluid Dynamics (CFD) model to simulate the turbulent diffusion flame on the fire-side of the radiation section of a thermal cracking test furnace coupled with a non-premixed low NOx floor burner. When this type of burners which uses the internal Flue Gas Recirculation (FGR) technique is coupled with large scale furnaces, both the turbulent mixing and chemical reaction rates are comparable and hence this should be considered in the model. Different combustion models are used to simulate the turbulence-chemistry interactions for this flame. The CFD model, based on the Eddy Dissipation Concept (EDC) combustion model coupled with the detailed GRI2.11 reaction mechanism, gives the most reasonable predictions compared with the available experimental data or empirical correlations for the diffusion flame in the thermal cracking test furnace, especially for the flame length and the CO and NOx emissions. (C) 2013 Elsevier Ltd. All rights reserved.