Abstract
This work contributes to the understanding of mechanisms that lead to increased carbon monoxide (CO) concentrations in gas turbine combustion systems. Large-eddy simulations (LES) of a full scale high pressure prototype Siemens gas turbine combustor at three staged part load operating conditions are presented, demonstrating the ability to predict carbon monoxide pollutants from a complex technical system by investigating sources of incomplete CO oxidation. Analytically reduced chemistry is applied for the accurate pollutant prediction together with the dynamic thickened flame model. LES results show that carbon monoxide emissions at the probe location are predicted in good agreement with the available test data, indicating two operating points with moderate pollutant levels and one operating point with CO concentrations below 10 ppm. Large mixture inhomogeneities are identified in the combustion chamber for all operating points. The investigation of mixture formation indicates that fuel-rich mixtures mainly emerge from the pilot stage resulting in high equivalence ratio streaks that lead to large CO levels at the combustor outlet. Flame quenching due to flame-wall-interaction are found to be of no relevance for CO in the investigated combustion chamber. Post-processing with Lagrangian tracer particles shows that cold air—from effusion cooling or stages that are not being supplied with fuel—lead to significant flame quenching, as mixtures are shifted to leaner equivalence ratios and the oxidation of CO is inhibited.
Highlights
The operating hours of gas turbines at part load are becoming increasingly important in the energy turnaround
Post-processing with Lagrangian tracer particles shows that cold air—from effusion cooling or stages that are not being supplied with fuel—lead to significant flame quenching, as mixtures are shifted to leaner equivalence ratios and the oxidation of carbon monoxide (CO) is inhibited
Large-eddy simulations of a high pressure full scale Siemens prototype combustor at three staged part load conditions have been performed, demonstrating the ability to predict CO from a complex technical combustion system and mechanisms leading to incomplete carbon monoxide burnout in either cases were investigated
Summary
The operating hours of gas turbines at part load are becoming increasingly important in the energy turnaround. Part load operation of gas turbines is limited by incomplete carbon monoxide (CO) burnout at the lowest power settings [1]. A validated LES combustion modeling approach [20] is applied for a predictive study of a high pressure full scale technology prototype Siemens combustion system at part load to reveal sources leading to incomplete CO burnout observed at two of the tested operating conditions, with the focus on the following goals: (i) to demonstrate the ability to predict CO from a very complex full scale combustor and, (ii) to investigate the impact of mixture formation in the different fuel stages on CO and, (iii) to analyze the effect of local flame quenching due to secondary air on CO
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