Numerical Studies Of The Pilot Burner Design And Emissions Characteristics In A Natural Gas Lean Premixed Gas Turbine Combustor

At present,lean premixed combustion technology is commonly used in commercial heavy gas turbine combustors to achieve low NOx emissions.Due to the relatively narrow stable range of lean premixed combustion,pilot nozzles are usually set to achieve stable combustion under ignition and wide load conditions.The pilot nozzle usually adopts the diffusion combustion method.Its outlet burns near stoichiometric and promotes the return of high-temperature flue gas through swirling and other structures to achieve flame stabilization.However,the central high-temperature area formed becomes one of the sources of NOx generation in the combustion chamber.Nozzle optimization design has become an important way to further reduce NOx emissions in gas turbine combustion chambers.For a self-developed natural gas lean premixed combustor,the characteristics of the flow field,composition field and temperature field inside the combustion chamber and the emission characteristics of outlet pollutants were studied using numerical simulation research methods,based on the single cylinder combustor The test results carried out a structural parameter influence study on the fuel injection structure of the pilot diffusion nozzle,and formed an optimal plan,and combined with the steam dilution and micropremix combustion method to carry out the pilot nozzle scheme design and study,in order to further reduce the NOx emissions of this type of gas turbine combustion chamber Provide theoretical support and basic data.The main work of this thesis is as follows:(1)For a certain type of lean natural gas premixed combustion chamber structure,modeling and numerical simulation of the combustion chamber performance of the combustion field flow field,component field and outlet temperature field,pollutant emissions,etc.,and the effect of pilot load ratio on emissions was studied,Combined with the test results,it is determined to carry out the research with a pilot load ratio of 7% to 8%;(2)The effect of the structure parameters of the pilot diffusion nozzle on NO/CO emissions was simulated.The effects of changes in the ratio of fuel and air equivalence ratio on the temperature field of the combustion chamber,the concentration distribution of OH groups and NO/CO emissions caused by the changes in the diameter and number of fuel injection nozzle holes are analyzed;(3)The steam dilution characteristics of the pilot diffusion nozzle were studied.The effects of different fuel-air momentum ratios on combustion characteristics and NO/CO emission characteristics under steam dilution conditions are analyzed.The results show that changing the fuel-air momentum ratio has little effect on the addition of steam to the pilot diffusion nozzles studied in this study.The internal mechanism of the effect of steam dilution on NO/CO emissions is analyzed.The results of the study show that steam dilution can significantly reduce the range of the high temperature zone of the pilot flame and achieve low NOx emissions without basically affecting the combustion efficiency;(4)The design and combustion characteristics of the pilot micromix nozzle were carried out.The flow fields of different micromix nozzle swirl structures were simulated,and the results showed that for a certain type of gas turbine combustor in this study,the pilot micromix nozzle could form a central recirculation zone for flame stabilization under a small swirl number.The research results show that for a gas turbine combustor independently developed by the research group,the feasibility of using pilot micromixing nozzles on the premise of ensuring the ignition characteristics and effectively reducing the emissions from the combustor is initially verified.