Fuel Flexibility Test Campaign on a GE10 Gas Turbine: Experimental and Numerical Results

Medium- and low-LHV fuels are receiving a continuously growing interest in stationary power applications. Besides that, since in many applications the fuels available at a site can be time by time of significantly different composition, fuel flexibility has become one of the most important requirements to be taken into account in developing power systems. A test campaign, aimed to provide a preliminary assessment of a small power gas turbine’s fuel flexibility, was carried over a full-scale GE10 prototypical unit, located at the Nuovo-Pignone manufacturing site, in Florence. The engine is a single shaft, simple cycle gas turbine designed for power generation applications, rated at 11 MW electrical power and equipped with a silos-type combustor. A variable composition gas fuel was obtained by mixing natural gas with CO₂ to about 40% by vol. at engine base-load condition. Tests involved two different diffusive combustion systems: the standard version, designed for operation with natural gas, and a specific system designed for low-LHV fuels. Tests performed aimed to investigate both ignition limits and combustors’ performances, focusing on hot parts’ temperatures and pollutant emissions. Regarding NO_x emissions, data collected during standard combustor’s tests were matched a simple scaling law (as a function of cycle parameters and CO₂ concentration in the fuel mixture), which can be used in similar applications as a NO_x predictive tool. In a following step, a CFD study was performed in order to verify in detail the effects of LHV reduction on flame structure and to compare measured and calculated NO_x. STAR-CD™ code was employed as main CFD solver while turbulent combustion and NO_x models were specifically developed and implemented using STAR’s user-subroutine features. Both models are based on classical laminar-flamelet approach. Three different operating points were considered at base-load conditions, varying CO₂ concentration (0%, 20% and 30% vol. simulated). Numerical simulations point out the flexibility of the GE10 standard combustor to assure flame stabilization even against large variation of fuel characteristics. Calculated NO_x emissions are in fairly good agreement with measured data confirming the validity of the adopted models.