Abstract
In the context of fuel-flexible operation of gas turbines, providing on-demand large-scale electric power without incurring in emissions of carbon dioxide, a convenient feature of Ansaldo Energia’s Constant Pressure Sequential Combustion (CPSC) system is the possibility of controlling the amount of fuel independently fed to the two combustion stages depending on the reactivity and combustion characteristics of the fuel itself. Crucially, in the case of ammonia-based fuels, this includes the capability of switching the CPSC operating mode from a conventional Lean Pre-Mixed (LPM) combustion to a Rich-Quench-Lean (RQL) staging strategy that mitigates undesired emissions of atmospheric pollutants (NOx) and greenhouse gases (N2O) emerging from the oxidation of fuel-bound nitrogen. Building upon an earlier numerical-modelling assessment of the CPSC system capability to operate in RQL mode (GT2023-103835) [1], the present work extends the scope of the initial preliminary study with a comprehensive set of additional calculations, based on massively parallel Large Eddy Simulation (LES) performed in conjunction with detailed chemical kinetics. Firstly, it is reported that, according to the numerical modelling predictions, a transition to stable, low-emission combustion of pure (non-decomposed) ammonia in the Multi-Burner First Stage (MBFS) can be achieved following an initial ignition and flame stabilization of a more reactive, partially decomposed ammonia blend. Secondly, it is shown that, at the equivalence ratio investigated, the unburnt fuel fractions emerging from the fuel-rich MBFS flames are completely oxidated by secondary air injected within the Dilution-Air Mixer (DAM) section of the CPSC. Furthermore, it is found that this burnout process occurring in the DAM section of the CPSC does not lead to significant increase of NOx and N2O emissions, thereby confirming the excellent potential of the CPSC to operate cleanly and efficiently with ammonia-based fuels.