Impact of inlet fogging and fuels on power and efficiency of gas turbine plants

A computational study to assess the performance of different gas turbine power plant configurations is presented in this paper. The work includes the effect of humidity, ambient inlet air temperature and types of fuels on gas turbine plant configurations with and without fogger unit. Investigation also covers economic analysis and effect of fuels on emissions. Gas turbine frames of various sizes/ratings are being used in gas turbine power plants in Saudi Arabia. 20MW_e GE 5271RA, 40MW_e GE-6561B, and 70 MW_e GE-6101FA frames are selected for the present study. Fogger units with maximum mass flow rate of 2 kg/s are considered for the present analysis. Reverse osmosis unit of capacity 4 kg/s supplies required water to the fogger units. The relative humidity and temperature have been varied from 30 to 45% and from 80 to 100 °F, respectively. Fuels considered in the study are natural gas, diesel and heavy bunker oil. Simulated gas turbine plant output from Gas turbine PRO has been validated against an existing gas turbine plant output. It has been observed that the simulated plant output is less than the existing gas turbine plant output by 5%. Variation of humidity does not affect the gas turbine performance appreciably for all types of fuels. For a decrease of inlet air temperature by 10 °F, net plant output and efficiency have been found to increase by 5 and 2%, respectively, for all fuels, for gas turbine only situation. However, for gas turbine with fogger scenario, for a decrease of inlet air temperature by 10 °F, net plant output and efficiency have been found to further increase by 3.2 and 1.2%, respectively for all fuels. For all Gas turbine frames with fogger, the net plant output and efficiency are relatively higher as compared to gas turbine only case for all fuels. Net plant output and efficiency for natural gas are higher as compare to other fuels for all gas turbine scenarios. For a given 70MWe frame with and without fogger, break even fuel price and electricity price have been found to vary from 2.2 to 2.5 USD/MMBTU and from 0.020 to 0.0239 USD/kWh, respectively. Turbines operating on natural gas emit less carbon relatively as compared to other fuels.