1029 Effects of a fogging system on a combined cycle performance M Z Yilmazoˇ glu Department of Mechanical Engineering, Faculty of Engineering and Architecture, Gazi University, Maltepe, Ankara 06570, Turkey. email: zekiyilmazoglu@gazi.edu.tr The manuscript was received on 17 October 2009 and was accepted after revision for publication on 14 June 2010. DOI: 10.1243/09576509JPE909 Abstract: Combined cycle power plants consist of a gas cycle, which uses gas turbines to generate electricity, and a water–steam cycle, which uses steam turbines to generate electricity. In gas tur- bine power plants, operation performance is the function of ambient air temperature, pressure, and humidity. Electricity consumption increases in summer seasons due to increasing cooling demand to satisfy thermal comfort conditions. Ambient air temperature affects gas turbine power output and peaking problem occurs at higher temperatures in the electricity grid. Inlet air cooling is a method to increase the power output of a gas cycle by decreasing the temperature of inlet air to the cycle. Inlet air cooling in gas turbine power plants can be obtained by the evaporative cooling method, fogging, absorption, and mechanical compression chillers mainly. Evaporative media or fogging system increases the relative humidity up to 95 per cent and as a result inlet air temperature decreases and mass flowrate to the compressor increases. In this study, a combined cycle power plant is considered with a fogging system and a parametric study is performed to analyse the effects of the ambient temperature and the humidity on the combined cycle perfor- mance. When a fogging system is applied to the cycle, the net power generation and the net fuel input of the combined cycle are increased by 8.3 per cent. Besides, plant auxiliaries and water consumption is also increased by 0.55 per cent and 4.2 per cent, respectively. However, energy and exergy efficiencies are decreased by 0.2 per cent in the case of applying a fogging system. Keywords: inlet air cooling, fogging, power augmentation, exergy analysis 1 INTRODUCTION Gas turbines (GTs) that operate in hot climates, like Mediterranean countries, are affected by ambient air temperature especially in summer time and the net electricity generation decreases. The electricity demand is more than the winter season due to the cooling demand to satisfy thermal comfort conditions in living spaces [1]. The net power production of GT power cycles decreases as cooling demand increases, while the ambient air temperature rises. Therefore, obtaining more power output from the GT is possi- ble by decreasing the inlet air temperature. There are different ways for inlet air cooling such as fogging, evaporative cooling, absorption cooling, and mechan- ical compression chillers. In a liquefied natural gas (LNG)-fuelled power plant, the evaporation heat of LNG can also be used to decrease inlet air temper- ature [2]. Inlet air cooling systems have advantages and disadvantages when compared to each other. The first investment cost of the evaporative cooling and fogging systems is lower than others. However, water consumption of these systems is higher and in hot climates water is not abundant. The wet bulb tem- perature is the minimum temperature limit of these systems and shows better results in hot and dry cli- mates. The specific investment cost of absorption and mechanical compression chillers are higher than evaporative and fogging systems. However, electricity consumption is very high for mechanical compression chillers, and it increases auxiliary power consump- tion of the power plant. Absorption chillers consume heat instead of electricity to supply cooling demand. However, in the decision step of installing an inlet air cooling system, it has to be kept in mind that heat also has an economic value. The wet bulb temper- ature is not a limit for absorption and mechanical compression systems. JPE909 Proc. IMechE Vol. 224 Part A: J. Power and Energy