Non premixed burners are widely installed in many industrial applications. To model non premixed flames a CFD (computational fluid dynamics) software is used. The Flamelet combustion model was choosen to predict the concentration and temperature fields accurately in an adequate computation time. For that the model has to be set up carefully. Many parameters have an effect on the results and also the computation time. To compare the simulation results the measured flame Sandia flame D from the Sandia National Laboratories was chooen to verification. This thesis starts with studies on the turbulence models and the discretization schemes. In the next step the grid was optimized. Because of the high temperatures in flames radiation models has to be used. Therefore, the DTRM and the DO radiation model, including the WSGGM model for the gas absorption coefficients, are analyzed. To describe the formation of NOX, the Unsteady Flamelet post processing and the NOX post processing are compared. For some industrial applications the replacement of methane with coke oven gas has economical advantages. Therefore, a reaction mechanism for coke oven gas was set up and a comparison of a methane flame and a coke oven gas flame was done. The Flamelet model is basically applicable for the calculation of flames and also industrial kilns for the flow-, temperature- and the main concentration field. However, an accurate prediction on NOX, using the San Diego or the GRI 3.0 reaction mechanism, is hardly possible. Therefore, the reaction mechanisms has to adapted. The comparison of the methane and the coke oven gas flames shows, that the coke oven gas flame is 20% shorter and thinner than the methane flame. This is a consequence of the higher calorific value of methane and the concentration oxygen in the coke oven gas.