Session: 04-43 Combustion dynamics - modeling I

Paper Number: 124313

124313 - Predicting Exhaust Gas Recirculation Impacts on Instability and Emissions of an Industrial Gas Turbine Combustor Using Large Eddy Simulations 

Carbon capture at engine exhaust is a promising technology to reduce carbon footprint for industrial gas turbines. The cost associated with carbon capture reduces exponentially as the concentration of CO2 in the exhaust increases. Exhaust gas recirculation (EGR) has been proposed as a potential solution to increase the exhaust CO2 concentration. A key challenge of applying EGR to production gas turbines is the increased combustion instability as the level of EGR increases. Hence, identifying the upper limit of EGR that maximizes the exhaust CO2 concentration while still allowing for stable combustion is critical to demonstrating the technology feasibility and reducing the number of expensive experimental tests. In this study, a large eddy simulations (LES) based computational fluid dynamics (CFD) model is developed for accurately predicting the combustion instability and emissions in an industrial gas turbine combustor under EGR conditions. Adaptive mesh refinement (AMR) is used to better capture complex local flow and flame structures. Finite rate chemistry based combustion model is used to predict the highly transient combustion and emissions behaviors. To accelerate the finite rate chemistry calculation, a 39-species reduced chemical reaction mechanism accounting for NOx chemistry is developed for methane/air mixture under a wide range of temperature, pressure, equivalence ratio, and EGR conditions. The model is validated against the measured exit temperature profile and good agreement is achieved between LES and experiments. The LES model is then employed to conduct a parametric study comprising of various levels of EGR and piloting. As EGR level increases, pressure fluctuation inside the combustor is shown to increase monotonically attributed to the decreased flame speed. The NOx emissions are found to first decrease until EGR reaches a level that is sufficiently large to trigger unstable combustion. On the other hand, piloting is shown to promote or inhibit pressure fluctuation depending on the level of EGR. Detailed analyses of the pilot flame mixture properties suggest that increasing piloting may deteriorate combustion stability when the corresponding pilot flame temperature is lower than the main flame temperature. Finally, combustion stability and emissions maps are developed that can be used to inform experimental design matrix.

Presenting Author: Chao Xu Argonne National Laboratory

Presenting Author Biography: Dr. Chao Xu is currently a Research Scientist at Argonne National Laboratory. Dr. Xu's research focuses on developing accurate and efficient numerical methods for DNS and LES of chemically reacting flows. Dr. Xu has extensive expertise on turbulent combustion modeling with detailed chemical kinetics and on CFD based design optimization for reciprocating engine and gas turbine applications.

Authors:

Chao Xu Argonne National Laboratory
Yonduck Sung Solar Turbines Incorporated
Daniel Johnson Solar Turbines Incorporated
Chris Steele Solar Turbines Incorporated