Analysis of water-fuel ratio variation in a gas turbine with a wet-compressor system by change in fuel composition

Yonatan Cadavid, Andres A. Amell, Juan Alzate, Gerjan Bermejo and Gustavo Alfonso Ebratt Herazo

The wet compressor (WC) has become a reliable way to reduce gas emissions and increase gas turbine efficiency. However, fuel source diversification in the short and medium terms presents a challenge for gas turbine operators to know how the wet compressor will respond to changes in fuel composition. For this study, we assessed the operational data of two thermal power generators, with outputs of 610 MW and 300 MW, in Colombia. The purpose was to determine the maximum amount of water that can be added into a gas turbine with a WC system, as well as how the NOx/CO emissions vary due to changes in fuel composition. The combustion properties of different gaseous hydrocarbon mixtures at wet conditions did not vary significantly from each other - except for the laminar burning velocity. It was found that the fuel/air equivalence ratio in the turbine reduced with lower CH4 content in the fuel. Less water can be added to the turbine with leaner combustion; the water/fuel ratio was decreased over the range of 1.4 to 0.4 for the studied case. The limit is mainly due to a reduction in flame temperature and major risk of lean blowout (LBO) or dynamic instabilities. A hybrid reaction mechanism was created from GRI MECH 3.0 and NGIII to model hydrocarbons up to C5 with NOx formation. The model was validated with experimental results published previously in literature. Finally, the effect of atmospheric water in the premixed combustion was analyzed and explained.