Kinetic study of combustion behavior in a gas turbine - Influence from varying natural gas composition

Abstract: The purpose of the numerical study was to investigate the influence of three different natural gas compositions on the combustion behaviour of an Advanced Environmental Vortex (AEV) burner. The flow conditions apply to the AEV burners installed in the Siemens gas turbine SGT-800. Numerical simulations were carried out using the software Chemkin 4. Ignition temperatures, adiabatic flame temperatures, NOX emissions and laminar flame speeds were determined using models included in the software. To find suitable reaction mechanisms for the simulations a mechanism study was made. The behaviour of the mechanisms was studied burning methane and ethane. The two reaction mechanisms chosen for the simulations represent combustion of hydrocarbons with up to two carbon atoms and seven carbon atoms. The reaction mechanisms are developed by Danmarks tekniske universitet and Lawrence Livermore National Laboratory respectively. The simulations gave the following results. The ignition temperature differed up to 80 K and the adiabatic flame temperature up to 30 K between the gases. The highest NOX emissions were obtained at =0.95 and increased with the residence time. The largest difference in laminar flame speed was 10 cm/s. The conclusion from the results when applied to the conditions in the AEV burner is that the difference in gas composition does not influence the performance of the burner noticeably. However some differences in NOX emissions are noticed but since NOX emissions are difficult to predict the levels of the emissions are to be treated with caution.