Numerical investigations of pollutant emissions from novel heavy duty gas turbine burners operated with natural gas

A numerical investigation of pollutant emissions of a novel dry low-emissions burner for heavy-duty gas turbine applications is presented. The objective of the work is to develop a robust and cost-efficient numerical setup for the prediction of NOx and CO emissions in industrial gas turbines and to investigate the pollutant formation mechanisms, thus supporting the design process of the novel burner. In the first part of this work, a RANS approach is adopted to characterize the global flame behavior. Then, unsteady simulations exploiting the Scale Adaptive Simulation (SAS) approach have been performed to assess the prediction improvements that can be obtained with the unsteady modelling. For all simulations, the Flamelet Generated Manifold (FGM) model has been used. However, FGM typically faces issues predicting flame emissions, such as NOx and CO, due to the wide range of time scales involved. Specific models are typically used to predict NOx emissions, introducing additional transport equations. Also CO prediction, especially at part-load operating conditions could be an issue: as the load decreases and the extinction limit approaches, a super-equilibrium CO concentration appears in the exhaust gases. To overcome this issue, a specific CO burn-out model, following the original idea proposed by Klarmann, has been implemented. In order to support the design process, an in-depth CFD investigation has been carried out, evaluating the impact of an alternative burner geometrical configuration on stability and emissions and providing detailed information about the main regions and mechanisms of pollutants production.