EFFECT OF NATURAL GAS COMPOSITION ON THE OPERATION OF LOW NOX BURNERS IN COMBUSTION CHAMBER FOR HEAVY-DUTY GAS TURBINE

Modern heavy-duty gas turbines employ lean-premixed combustion system to meet more and more strict emission regulations. The development of such combustion technology with low emissions and stable operation in an increasingly wide range of operating conditions requires a deep understanding of the mechanisms that affect the combustion performance or even the operability of the entire gas turbine. Furthermore, gas turbine manufacturers are tasked increasingly with expanding operational fuel flexibility, due to the relative wide range of natural gas composition supplies, the increased demand from Oil&Gas customers to burn gas with notable higher hydrocarbons (C2+) content and considering the potential addition of hydrogen to the natural gas infrastructure in the next future; therefore the impact of gas composition on gas turbine operability and combustion related aspects it is a matter of several studies. This work aims to address the impact of natural gas composition, observed during an experimental test campaign of a lean premixed annular combustor for heavy-duty gas turbine, on both emissions and flame stability with focus on natural gas blends containing a certain level of ethane and hydrogen. For this purpose, Large Eddy Simulations (LES) of an annular combustor sector equipped with a partially-premixed burner are carried out at relevant pressure and temperature for three different natural gas compositions. An extended approach of the Zimont TCF model that includes the combined effects of strain rate and heat loss on the flame brush modelling has been implemented resulting in a more adequate description of flame shape, thermal field and extinction phenomena with respect to standard model, thus improving the predictive accuracy of CFD analysis that can be used since the preliminary design phase of combustion systems. Indeed, an accurate tool capable to predict fuel composition effects would reduce expensive tests on prototypes. Such novel approach has been used to investigate NOX emission and lean blow off (LBO) showing promising results and good accuracy compared against available experimental data.