Session: 04-07 Ammonia Combustion I

Paper Number: 153561

Numerical Concept Study for Part-Load Operation of the Ansaldo Constant Pressure Sequential Combustion System Operated in Rich-Dilute-Lean Mode Using Ammonia-Based Gaseous Fuels 

The ongoing energy-system transition that aims to reduce its dependency on non-renewable fossil fuels has resulted in significant uncertainty about future availability, preferably both geographically widespread and uninterrupted, of various carbon-free alternative energy carriers as hydrogen and ammonia. The significant uncertainty about which fuels will be available where, when and at what price implies that fuel flexibility and fuel-switch capability are emerging as crucial features that future-proof gas turbines must implement while conserving high efficiency and low emissions. In this context, sequential combustion systems, like Ansaldo Energia’s Constant Pressure Sequential Combustor (CPSC), are intrinsically well-suited to switch between fuels characterized by very different combustion properties. This is due to the CPSC’s ability in controlling the amount of fuel independently fed to the two combustion stages and adapting to the fuel’s reactivity and combustion characteristics. An increasing amount of experimental evidence and numerical simulations suggest that, in the case of premixed combustion of ammonia-based fuels, a Rich-Dilute-Lean (RDL) staging strategy is recommended to mitigate undesired emissions of atmospheric pollutants (NO_x) and greenhouse gases (N₂O) resulting from the oxidation of fuel-bound nitrogen. Two earlier concept studies (GT2023-103835 & GT2024-128946), exploiting state-of-the-art high-resolution numerical simulations, have shown that Ansaldo’s CPSC, specifically its Multi-Burner First Stage (MBFS) jointly with the Dilution-Air Mixer (DAM) placed between the two combustion stages, is theoretically capable of switching from conventional Lean Pre-Mixed (LPM) combustion to a RDL-type staging strategy at full-load operating conditions and still ensure low-emissions performance and high combustion efficiency. However, an intrinsic challenge related to operational design of RDL combustion systems is the implementation of a fuel-rich primary combustion stage during part-load operation when significantly less fuel is required because of the lower target flame temperature.

The present work extends the scope of the two earlier numerical studies with a comprehensive set of additional calculations. Massively parallel Large-Eddy Simulation (LES), performed in conjunction with detailed chemical kinetics, are carried out to assess the impact of part-load operating conditions on the emissions performance of the MBFS fired in RDL mode with ammonia-based fuels. The numerical investigation compares alternative implementations at 40% and 50% part-load operating conditions. These two part-load operating conditions of the MBFS combustion system, composed by a bundle of four identical conical burners, are numerically investigated considering different combinations of switch-off burners. Part-load performance of the MBFS for several switch-off burners scenarios is assessed in terms of predicted flame stability, NO_x and N₂O emissions. It is shown that low-emissions operation of the CPSC with ammonia-based fuels is achievable even at the globally fuel-lean conditions required by part-load operating conditions as long as a RDL staging strategy is implemented at the level of the single burner. The present research is supported by the NCCS Centre, performed under the Norwegian research program Centres for Environment-friendly Energy Research of the Research Council of Norway (257579/E20)

Presenting Author: Andrea Ciani Ansaldo Energia Switzerland

Presenting Author Biography: Hydrogen Combustion Technology Manager of Ansaldo Energia and combustion technologies developer

Authors:

Ole H. H. Meyer SINTEF
Andrea Gruber SINTEF
Luis Tay-Wo-Chong Ansaldo Energia Switzerland
Andrea Ciani Ansaldo Energia Switzerland