Performance of cracked ammonia combustion in a gas turbine engine - Evaluation through CFD and chemical reactor network modeling

Abstract

The issue of global warming and the increasing global energy demand requires introduction of new, renewable fuels for energy- and electricity production. If generated from green hydrogen, ammonia could be of particular importance in future sustainable energy systems as an energy carrier and a carbon free gas turbine fuel. Opposed to hydrogen, transportation and storage of ammonia is already widely established and easily facilitated; however, the combustion properties of pure ammonia are not feasible with a turbulent gas turbine environment due to low reactivity. By partially cracking ammonia into its elementary components, suitable combustion properties can be obtained. Ammonia combustion is also prone to substantial levels of NOX and N2O emissions. However, adoption of rich-lean staging has previously been shown to mitigate NOX emissions from the combustion process. In this thesis, the combustion performance of cracked ammonia in the SGT-750 gas turbine combustor, provided by Siemens Energy AB, is evaluated in terms of emissions and ame stability. Numerical CFD and chemical reactor network (CRN) models are used to investigate the feasibility of di erent fuel compositions, originating from cracked ammonia, as gas turbine fuels. Equivalence ratios ranging from approximately 0.4 to 1.5 are investigated, in single stage and air-staged combustion. The results revealed that ame stability was achievable for ammonia cracking degrees of at least 40% at lean conditions, and NOX emissions below 100 ppmvd were emitted for rich-lean staged combustion. Global warming potentials, as CO2-equivalents, far below those of conventional natural gas combustion were found for several fuel compositions and equivalence ratios. However, great discrepancies were apparent among the resulting N2O emissions from the di erent models. Thus, further experimental validation of the applied computational models and chemical mechanism is required, to establish the environmental performance of cracked ammonia as a gas turbine fuel.