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Continuously-staged NH3 oxidation in a stagnation-point reverse-flow combustor for low NOx emissions

par Giuntini, Lorenzo ;Novelli, Chiara ;Mustafa Kamal, Mustafa;Cafiero, Marianna ;Galletti, Chiara;Coussement, Axel ;Parente, Alessandro
Référence Proceedings of the Combustion Institute, 40, 1-4, 105674
Publication Publié, 2024-08-01

Article révisé par les pairs

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Résumé :

Employing ammonia as an alternative fuel to defossilize hard-to-abate processes is promising but poses challenges. Ammonia's unique combustion properties require the optimization of existing and future burners and the adoption of ad-hoc fuelling strategies to enhance flame stability and mitigate NOx emissions. Previous studies involving staged combustion concepts paved the way to achieve high efficiency and low-NOx ammonia oxidation. However, the majority of the works focused on swirled burners and none of them could guarantee both pollutants and unburned emissions within regulatory limits. In this work, we present a stagnation-point reverse-flow (SPRF) combustor originally designed for natural gas fuelling and here converted to burn ammonia in a staged configuration. Experiments were carried out by varying the equivalence ratio, and data collected on the exhaust gas composition and temperature were used to calibrate a Computational Fluid Dynamics (CFD) model of the system. Hence, the numerical model was used to optimize the combustor's operation and geometry. Results showed that the present SPRF system allows for achieving very low NOx and unburned emissions, below environmental limits. Nonetheless, conventional two stage rich-lean setups exhibit extremely narrow operating windows, which can make their use impractical for real applications. To solve this issue, a continuously-staged configuration was proposed demonstrating to be a viable solution to further improve the performance of NH3-fired combustors.