Hydrogen is a clean and carbon-free fuel and is considered a key element for the energy transition. Renewable power generation by solar and wind is increasing, requiring flexible operation to balance the load on the energy grid with the ability to rapidly adjust the output. Gas turbines with a combustion system for hydrogen operation offers a low carbon solution to support the stability of the energy grid. This provides a solution capturing the needs for energy storage, in the form of hydrogen, and flexible power generation. High flame temperatures in the primary zone facilitates the production of NOx which can be reduced by using premixed combustors. But this introduces the risk of flame flashback. Several combustor concepts have been proposed and studied in the past few years to tackle the problem of flame flashback in premixed high hydrogen fuel combustors. This study looks at one of the concepts which uses Aerodynamically Trapped Vortex to stabilize the flame.  

Burner concepts based on trapped vortex flame stabilization have a higher resistance towards flame blowout than conventional swirl stabilized burners. This work looks at the flow and flame behavior in the proposed Aerodynamically Trapped Vortex Combustor (ATV) for 100% premixed hydrogen operation. Numerical simulations for the analysis were performed with commercial Computational Fluid Dynamics (CFD) simulation package AVL Fire^TM^.   

The flow field characterization was focused on the investigation of the influence of the inlet velocity and inlet turbulence intensity (u’) on the mean velocity, wall velocity gradient and turbulence intensity in the combustor. The turbulence field can be separated into two distinct parts - grid generated turbulence and turbulence generated in the two shear layers formed inside the combustor. To study the flame stabilization mechanism, reactive simulations were performed at two fuel equivalence ratios. The combustion regime of the flame, turbulent flame speed (S~T~) and temperature distribution in the combustor were quantified from the simulation results. 

A validation study was performed prior to the analysis of the ATV combustor to validate both the turbulence and the reactive models for premixed hydrogen combustion. The models were validated against the experiments performed in a dump stabilized cylindrical combustor at Combustion Research Laboratory, Paul Scherrer Institute (PSI), Switzerland. The k-ε and k-ζ-f turbulence models were selected for modelling the turbulence. Simulations of non-reacting flow with k-ε model resulted in a more accurate prediction of the flow field, turbulence levels and recirculation zone than the k-ζ-f model. 

Combustion is modelled using the FIRE^TM^ detailed chemistry solver with the k-ε turbulence model to resolve turbulence. No additional turbulence-chemistry interaction model is used in the current research. To reduce chemistry computational time, the multi-zone method is employed. To capture the effect of preferential diffusion, two approaches were used to quantify the diffusion coefficient of each species. The diffusion coefficients were calculated using both mixture averaged approach and the multi component diffusion approach. 

A detailed chemistry approach with sufficient mesh resolution for modelling the reaction in 100% premixed hydrogen combustion predicted the flame behavior with acceptable accuracy. The two approaches used for quantifying diffusion coefficients showed no significant difference. The flow analysis in the Aerodynamically Trapped Vortex (ATV) combustor revealed that the inlet velocity or inlet turbulence had no significant effect on the relative turbulence properties in the flame stabilization zone. The proposed design for the Aerodynamically Trapped Vortex (ATV) combustor was able to stabilize a 100% premixed hydrogen flames without flashback for the simulated conditions.


Numerical Investigation of 100% Premixed Hydrogen Combustor at Gas Turbines Conditions Using Detailed Chemistry

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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