Combustion and Emission Characteristics of Ammonia under Conditions Relevant to Modern Gas Turbines

ABSTRACT

Ammonia (NH₃) is considered a promising alternative fuel, capable of producing energy with zero CO₂ emissions. Its combustion, however, poses a series of challenges due to the low reactivity of NH₃ and the formation of very high quantities of NO_x. This work numerically investigates the combustion and emission characteristics of ammonia in three modern stationary gas turbine concepts, namely (a) lean-burn dry-low emissions (DLE); (b) rich-burn, quick-quench and lean-burn (RQL); and (c) moderate or intense low oxygen dilution (MILD), under operating conditions typical of commercial gas turbines (inlet temperatures of 500 K and pressure of 20 bar). Numerical simulations employing detailed chemical kinetic mechanisms are carried out to study the propagation speed of ammonia, the combustor temperatures, and the emissions of NO_x and NH₃. The simulations are first validated against literature NO_x data and then the most accurate mechanism is selected. The performance of the different gas turbine engine concepts is subsequently compared based on the results from the selected mechanism. The results show that the lowest emissions are achieved with the RQL and MILD combustion concepts, while the DLE combustion concept only presents acceptable emission values under conditions deemed unstable, where the laminar flame speeds are below 3 cm/s.

KEYWORDS:

• Ammonia/air flames
• chemical kinetic modeling
• lean-burn dry-low emissions
• rich-burn
• quick-quench and lean-burn
• moderate or intense low oxygen dilution

Acknowledgments

The authors would like to acknowledge Prof. Christian Brackmann and Dr. Vladimir Alekseev for sharing information from their article. This work was carried out in the framework of the Short-Term Scientific Mission Program of SMARTCATs COST Action (CM1404, www.smartcats.eu), supported by COST (European Cooperation in Science and Technology, www.cost.eu). The authors would also like to acknowledge the financial support from the Fundação para a Ciência e a Tecnologia (FCT), through IDMEC, under LAETA, project UID/EMS/50022/2019.

Additional information

Funding

This work was supported by the Fundação para a Ciência e a Tecnologia and COST (www.cost.eu).