EXPERIMENTAL STUDY ON STABILITY ENHANCEMENT OF A NATURAL GAS GT BURNER WITH HYDROGEN FLAME PILOTING OPERATED WITH SIMULATED EXHAUST GAS RECIRCULATION

Efficient coupling between gas turbine power plants fuelled with natural gas and Carbon Capture and Storage (CCS) units can be achieved by taking advantage of turbine Exhaust Gas Recirculation (EGR), since CCS efficiency increases with the CO2 content of the incoming flow. On the other hand, the combustion process has to endure the reduction of overall flame reactivity caused by EGR, with a potential increase of CO and UHC emissions, and modifications in the flame dynamic behaviour. In order to extend the combustor operability window, non-conventional pilot flames can be exploited to improve overall flame stabilization: in the current study the use of local hydrogen pilots was investigated. A lean-premixed burner for heavy-duty Gas Turbines was studied at ambient pressure in a reactive single-cup test rig at the THT Lab of the University of Florence, replicating EGR with the addition of CO2 to the combustion air. Reactive PIV measurements revealed a jet flame flowfield, not significantly affected by simulated EGR, which instead alters substantially the flame structure. Hydrogen addition has been found beneficial in widening the burner operating window, allowing higher premix splits to be achieved and reducing pressure oscillations also in EGR conditions. A modest decrease in CO emissions with high EGR levels was observed, and the flame structure detected with OH* chemiluminescence suggests that an optimization of the pilot injection geometry for dual fuel configuration could remarkably improve burner performance with EGR by enhancing the interaction between hydrogen pilot jets and natural gas flame.