Premixed ammonia/hydrogen swirl combustion under rich fuel conditions for gas turbines operation

Abstract

Energy storage is one of the highest priority challenges in transitioning to a low-carbon economy.Fluctuating, intermittent primary renewable sources such as wind and solar require low-carbon storage options to enable effective load matching, ensuring security of supply. Chemical storage is one such option, with low or zero carbon fuels such as hydrogen, alcohols and ammonia having been proposed.Ammonia provides zero-carbon hydrogen storage whilst offering liquefaction at relatively low pressures and atmospheric temperatures, enabling ease of transportation in a pre-existing infrastructure. Ammonia can also be used directly as a fuel in power plants such as gas turbines to avoid complete conversion back to hydrogen. It is a relatively unreactive fuel, and so it is of interest to explore the potential utilisation of ammonia/hydrogen mixtures. Hence, the goal of this paper is to provide a first assessment of the suitability of a chosen 70%NH3-30%H2 (%vol) blend for utilisation within a gas turbine environment, based on primary combustion diagnostics including combustion stabilityvia OH chemiluminescence -and emissions (NOx and NH3). An established optical generic swirl-burner enabled studies of the influence of equivalence ratio (φ >1), ambient temperature (<484±10 K) and bypass air, with a focus on NOx reduction, one of the main challenges for ammonia combustion. A numerical GT cycle model is developed alongside the experimental investigation. The results demonstrate that the blend has considerable potential as a fuel substitute with reasonable combustion stability and significant reduction of emissions for the cases without bypass air, due to increased chemical reactivity of unburned ammonia. However, emissions are still above those recommended for gas turbine cycles, with a theoretical cycle that still produces low efficiencies compared to DLN methane, highlighting the requirement for new injection techniques to reduce NOx/unburned NH3 in the flue gases whilst ensuring increased power outputs.

Experimental and modeling study on ignition delay of ammonia/methane fuels

“…In terms of utilizing ammonia in combustion equipment, pertinent studies have tested and applied ammonia in internal combustion engines, 10‐12 gas turbines, 13‐15 etc. Meanwhile, in order to support the application and have better understanding of ammonia combustion, fundamental studies also have been performed using ammonia fuels 16‐19 .…”

Numerical Predictions of a Swirl Combustor Using Complex Chemistry Fueled with Ammonia/Hydrogen Blends

“…Initial results were conducted to validate the CFD model against previous experimental data [34,39,50]. The results in Figures 3 and 4 show good correlations.…”

“…A numerical study was conducted to determine the exhaust gases obtained from the combustion of a 70-30 (mol%) ammonia-hydrogen blend under rich conditions (equivalence ratio of 1.2) and medium swirl (0.8), thus providing details for further thermodynamic analyses of a combustor previously evaluated using these settings [34,39]. Validation of the model was performed using the results from Valera-Medina et al [39] and Pugh et al [34]. Correlations were established between experimental and numerical concentrations of NOx, NH 3 , and H 2 emissions.…”

“…Different to the Eddy dissipation concept (EDC), which integrates chemistry for a time scale close to Kolmogorov's timescale, thus delivering slower reaction rates, LFC integrates the chemistry with respect to the residence time in the cell. The selection was based on results from previous campaigns and findings that denoted the high reactivity of this ammonia-hydrogen blend, with high NH 2 , OH, and H/O pools close to the flame front that increase the reactivity of the former [34,39]. Finally, the LFC model is appropriate for premixed, partially premixed, and unsteady flames [48].…”

“…Unfortunately, one of the markers that scored the lowest for ammonia was the specific energy of the fuel (MJ/kg), whilst in comparison, hydrogen showed the highest. The approach applied by the group only briefly raised the potential of ammonia-hydrogen blends, which are well-known to be more efficient for combustion purposes whilst having higher specific energies and the potential of the production of hot, unburned hydrogen [34,39]. Simultaneously, hydrogen, a well-known substitute for many power applications, has the potential to generate clean power whilst ensuring the distribution and storage of large renewable energy sources.…”