Development of a dual-stage lean premixed (DLPM) burner of ultra-low emissions for gas turbine combustion applications

The technology of lean premixed combustion (LPM) has been proposed and developed by gas turbine manufacturers to abide by the stricter regulations of emissions control for the sake of reducing the rate of global warming. This technology reduces the flame temperature by premixing fuel with oxidizer in fuel-lean proportions prior to combustion to control mainly the resulting NOx emissions; however, lean fuel burning results in flame instabilities especially under start-up and part-load conditions. The proposed dual lean premixed (DLPM) combustion technique is considered as an extension of the LPM one to improve the combustor adaptability to different operating conditions, especially at low-load, while keeping the same environmental performance. In DLPM, two premixed reactants streams of two different equivalence ratios enter the flame. The central stream is richer to act as pilot for sustaining flame stability, while the outer stream is leaner to keep the overall equivalence ratio low and thus sustain the environmental performance of the combustor. Diffusion of active radicals and heat transfer from the central stable flame help stabilize the outer leaner flame. This stabilization mechanism, based on charge stratification, enables the DLPM burner to sustain a stable flame under low-load conditions and even outside the fuel flammability limits. Integrating the oxy-fuel combustion technology with the DLPM one can result in zero NOx emissions while facilitating low-cost CO2 capture for zero emissions power plants (ZEPP) applications. This integration of oxy-fuel combustion and DLPM technologies has never been addressed in research as per the open literature, and that is exactly what the present investigators will examine experimentally and numerically in this proposed study. Oxy-fuel combustion has its own challenges in terms of controlling the combustion temperature within the stable operability window of a gas turbine, as well as flame stability under lower oxygen concentrations in the oxidizer mixture. A DLPM burner will be designed to sustain oxy-methane flames in a swirl-stabilized gas turbine model combustor. The combustor will be tested over wide ranges of operating conditions, and the stability maps defining the upper and lower operability limits will be generated. The stability maps of the stratified DLPM flames will be compared to those of homogeneous (non-stratified) oxy-methane and oxygen-enriched-air-methane flames under the same overall operating conditions to show the effect of flame stratification on combustor stability. The combustion and emissions characteristics of the stratified DLPM flames will be investigated. A numerical model based on three-dimensional (3-D) large eddy simulations (LES) will be developed to solve for the DLPM stratified oxy-flame, and the results will be compared with the available experimental data.