Modelling and Analysis of Gas Turbine Fog Cooling System

Fog cooling is one of the most efficient and economical methods to cool the inlet air of the gas turbine to improve the performance. In this paper, firstly a model has been developed to estimate the cooling of ambient air by fog cooling method. The model is based on basic thermodynamics and psychometry process and analyses the effect of ambient condition (temperature and relative humidity) on inlet air cooling. Secondly, power and heat rate models are developed which is based on characteristics curve of heavy-duty and aero-derivative gas turbine. In order to comprehensively understand the effects of fogging, a sensitivity study, by varying the ambient condition, was conducted. For each gas turbine, five values of ambient inlet air temperature (25, 30, 35, 40, and 45 °C) and relative humidity (20, 30, 40, 50, and 60%), were examined. For all 25 cases analysed, the maximum cooling and power augmentation is achieved for high ambient temperature and low relative humidity at 45 °C and 20% relative humidity. The aero-derivative gas turbine is more sensitive to ambient condition and for the same ambient condition (45 °C and 20% relative humidity) achieves up to 21.417% power augmentation, as compared to heavy-duty gas turbine (18.807%). The paper is intended to provide a simple method to evaluate the potential of power augmentation by using air cooling potential of the fog cooling technique and that can be useful for the gas turbine users and manufacturers.