CFD simulations for the development of gas turbine low NOx hydrogen combustors

In the frame of Enel's Hydrogen Project, a hydrogen-fed mid-size gas turbine will be installed at Fusina power station (Venice, Italy). One of the main items to address is the development of a specific combustor able to burn hydrogen efficiently and safely keeping NOx emission down to very low values. The paper describes development and validation of a CFD model that will be used to design the hydrogen-fed burner. The commercial GE MS-5001 combustor has been used for the purpose, since experimental data on temperature distribution and NOx emissions were available under different operating conditions, using both natural gas and hydrogen as fuel. The burner has been modeled using FLUENT 6.1 software. Fluid dynamic experimental data collected under cold operating conditions have been used to validate the CFD results related to air mass flow distribution inside the burner, which has been simulated using a porosity model for the burner walls. Hydrogen combustion simulations have been carried out at three different thermal loads, namely 50%, 75% and 100% of full load, while oxygen excess in the flue gases has been kept constant, equal to 16%. Hydrogen combustion has been firstly simulated by means of a one-step reaction scheme, but this approach did not allow to predict NOx emissions effectively. Therefore, a 5-step kinetic scheme dealing with radical species and a 'third body' has been implemented using the Eddy Dissipation Concept Model (EDC): in this way the model has been able to predict NOx emissions accurately under all the investigated conditions (i.e. around 25% discrepancy with respect experimental data). In addition, simulation results related to temperature distribution, velocity fields, reaction rate for each of the chemical species and NOx emissions are available for the three cases. The CFD model coupled with a 5-step kinetic scheme is going to be used to analyze the effects of geometrical modifications, air staging and vapour injection on natural gas-designed burners in order to reduce NOx emissions to very low values when they use hydrogen as fuel. (authors)