Effect of Exhaust Gas Recirculation on NOx Formation in Premixed Combustion System

Abstract

*† ‡ Exhaust gas recirculation (EGR) is an enabling technology to reduce CO2 capture cost for gas-turbine-based power plants. Experiments performed in fully premixed mode using Dry Low NOx single nozzle combustor at General Electric Global Research Center also revealed NOx reduction at same flame temperature by EGR. This paper presents systematic chemical kinetics analysis to study the effect of EGR on NOx formation in lean premixed combustion system under gas turbine representative temperatures and pressures. Simulation results are first presented for perfectly premixed combustion system to study the effect of EGR at different pressures (1-30 atm), oxidizer compositions, and EGR ratios. Based on detailed analysis, dominant mechanisms responsible for NOx formation are identified for different pressures. The effect of fuel-air unmixedness is then introduced to model the industrial gas turbine combustors. It is found that NOx formation is much less sensitive to the unmixedness with EGR than the baseline case. For typical gas turbine combustors, EGR introduces large benefits (up to 50%) for raw NOx reduction at same flame temperature, and even larger reduction if NOx concentration is corrected to 15% O2.