Session: 04-01: Fuel flex

Paper Number: 78304

78304 - Lean Stability Limits and Exhaust Emissions of Ammonia-Methane-Air Swirl Flames at Micro Gas Turbine Relevant Pressure 

Ammonia is a carbon-free fuel that is gaining traction as a hydrogen carrier. It is a promising fuel for heat and power generation because it can be produced from abundant hydrocarbons and renewable energy sources. Nevertheless, ammonia-air combustion faces challenges such as turbulent flame stabilization and high NOx emissions, which are very high at the current lean equivalence ratios at what micro gas turbines for power generation operate. This study reports the lean stability limits and exhaust emissions of ammonia-methane-air swirl flames for several ammonia fractions in the fuel blend. A reduced-scale burner was manufactured, inspired by Ansaldo’s micro gas turbine AE-T100 burner, and it was installed inside a high-pressure combustion duct to operate at 4.5 bar. This pressure corresponds to that found at full-load in the actual micro gas turbine’s combustion chamber. The burner comprises a non-premixed pilot flame and a technically premixed main flame. The lean stability limits were measured by igniting the flame at an equivalence ratio of ϕ = 0.85 and then progressively decreasing the equivalence ratio until lean blowout. NO, N₂O, and CO₂ emissions were also recorded for different equivalence ratios and ammonia fractions. In addition to lean cases, rich flames at an equivalence ratio of ϕ = 1.2 were considered. Results show that the equivalence ratio at lean blowout increases when the ammonia fraction increases, and all the ammonia fractions tested lead to flames more prone to lean blowout than the pure methane reference flame. On the other hand, the CO₂ emissions are monotonically reduced by increasing the ammonia fraction, both for lean or rich flames. Moreover, NO emissions would be higher than many regulations limit regardless of the ammonia fraction for all lean equivalence ratios. N₂O emissions are almost negligible, except for very lean equivalence ratios where the N₂O mole fraction in the exhaust reaches unacceptably high values. Only rich ammonia-methane-air flames show good NO and N₂O performance. Therefore, FTIR analysis was carried out to quantify the amount of the unburnt NH₃ in the exhaust for these flames. Results show that unburnt NH₃ concentration is invariant, around 200 ppm, between 0.7 ≤ X_NH3 ≤ 0.95. Data reported in this study provide insights for future work on combustors and after-treatment systems towards zero-emissions micro gas turbines.

Presenting Author: Cristian Avila KAUST

Presenting Author Biography: B.Sc and M.Sc in Mechanical Engineering from Universidad de Antioquia, Colombia. I am currently doing my Ph.D. in the Clean Combustion Research Center (CCRC) at the King University of Science and Technology. My research is towards integrating ammonia combustion into real-scale micro gas turbines for electrical power generation to reduce CO2 emissions.

Authors:

Cristian Avila KAUST
Guoqing Wang King Abdullah University of Science and Technology
Xuren Zhu King Abdullah University of Science and Technology
Et-Touhami Es-Sebbar King Abdullah University of Science and Technology
Marwan Abdullah Saudi Aramco
Mourad Younes Saudi Aramco
Aqil Jamal Saudi Aramco
Thibault Guiberti King Abdullah University of Science and Technology
William L. Roberts King Abdullah University of Science and Technology