Investigation of NOx and CO Formation in a Premixed Swirl-Stabilized Flame at Ultra Wet Conditions

摘要

Humidified Gas Turbines promise a significant increase in efficiency compared to the dry gas turbine cycle. In single cycle application, efficiencies up to 60% seem possible with humidified turbines. Additionally, the steam effectively inhibits the formation of NO_x emissions, and also allows operating the. gas turbine on hydrogen-rich fuels.The current study is conducted within the European Advanced Grant Research Project GREENEST. The premixed combustion of natural gas at atmospheric pressure is investigated over a wide range of equivalence ratios, steam content in the air between 0% and 30%, and different degrees of nitrogen dilution. Emission formation, local temperature distribution, and flame shape and position were m,easured in the gas-fired tests. A UV probe was used to determine local OH radical concentrations in the flame.A reactor network was designed to model the combustion process and to investigate the influence of steam dilution on important species concentrations and on CO and NO_x formation. The simulations were conducted with GRI-Mech 3.0 and with the Konnov mechanism, rev. 05.The measurement results confirm that steam effectively inhibits the formation of NO_x emissions, even at constant flame temperature. Both NO_x and CO emissions of below 10 ppm were measured up to near-stoichiometric gas composition at wet conditions. The numerical analysis shows, that the influence of steam dilution on radical concentrations and emission formation pathways depend strongly on the degree of humidity and on the equivalence ratio. The concentration of OH is increased at low steam content, but can decrease for higher dilution levels at high equivalence ratios. The H radical is reduced at low degrees of humidity, but noticeably increased at ultra-wet conditions. Both reaction mechanisms seem to over-predict the formation of CH and, therewith, the prompt NO_x formation pathway.