LOW NO_x EMISSION FROM AN AMBIENT PRESSURE DIFFUSION FLAME FIRED GAS TURBINE CYCLE (APGC)

摘要

The prospects of reduced NO_x emission, improved efficiency, stable and oscillation-free combustion, and reduced construction costs achieved by an "Inverted Brayton Cycle" applied to mid-size (0.5 to 5.0 MWe ) power plants are discussed. In this cycle, the combustion products of an atmospheric pressure combustor are expanded in the gas turbine to sub-atmospheric pressure and following heat extraction are compressed back to slightly above the atmospheric, sufficient to enable a controlled fraction of the exhaust gas to be recirculated to the combustor. Due to the larger volume flow rate of the gas, the polytropic efficiency of both the turbine and compressor of this small machine is increased. Because of the low operating pressure and flue gas recirculation, both of which are instrumental to low NO_x formation, the combustor can be operated in the diffusion flame mode; this, on the other hand, assures good flame stability and oscillation-free combustion over wide ranges of the operating variables. For the task of obtaining very low NO_x formation, the well-tested Multi Annular Swirl Burner (MASB) is chosen. Recent computational and experimental development of the MASB by Siemens-Westinghouse as a Topping Combustor is reviewed. It is shown that the MASB operated in the Rich-Quench-Lean mode is capable of single digit No_x emission. These emissions are further lowered in the APGC by ambient pressure combustion and flue gas recirculation. Results of a computational optimization study of the APGC are presented.