Kinetic modeling and emission characteristics of multi-staged partially cracked ammonia/ammonia-fueled gas turbine combustors

Abstract

Ammonia (NH${}_3$), as a zero-carbon fuel, plays a pivotal role in achieving carbon neutrality. However, the challenges of its low reactivity and high ignition energy have driven the development of partial ammonia cracking in gas turbines. The gaps exist regarding the emission characteristics of single- and dual-fuel staged gas turbine combustors fueled by partially cracked ammonia (PCA) and NH${}_3$. Effects of the ammonia cracking ratio, combustor inlet temperature and pressure, and water injection ratio on emission characteristics are analyzed in the typical two-staged single-fuel PCA combustor. With the ammonia cracking ratio increasing from 0 to 0.6, the optimal equivalence ratio of the rich fuel zone rises from 1.25 to 1.45, although the adjustment range remains limited. In contrast, the dual-fuel configurations fueled by PCA/NH${}_3$ are proposed for the reduced cracker cost and flexible control range over combustion parameters. The multi-staged configuration has demonstrated the capability to balance both combustion stability and emission control through parameter studies of the NH${}_3$ substitution rate, local equivalence ratio, and ammonia cracking ratio. Except for postmix configuration and high global equivalence ratio, the rich nitrogen oxides (NO${}_x$) account for 55% to 77% of total emissions with the overall NO${}_x$ emissions below 50 ppm, indicating the low-NO${}_x$ potential of the dual-fuel configuration design. Also, the nitrous oxide formation can be controlled through operating parameters in a multi-staged configuration, avoiding simultaneously high global and second rich fuel zone equivalence ratios. Furthermore, the dominating NO${}_x$ formation and reduction mechanisms in the rich and lean fuel zones are identified with high and low nitrogen-hydrogen intermediates (NH${}_i$) levels. The high NH${}_i$ radicals in the lean fuel zone promote nitrous and nitric oxides formation, which should be minimized.