Numerical Analysis of a Fogging System in a Gas Turbine

Abstract

Air cooling via evaporation of water droplets injected at the compressor intake duct is the process known as Fogging System, which is among the most used technologies for increasing output power of gas turbines nowadays. The optimal design of this system must consider numerous variables, such as: air temperature (Ta), air relative humidity (RH), duct geometry, amount of water injected (mw), droplets size (Dd), and nozzles location. Since there are so many variables the flow under study is very complicated. In consequence the analytical determination of an optimal Fogging System design is not feasible. In this paper, a numerical model was developed in order to characterize the injection of water at the air intake duct of a Gas Turbine. First, the expressions characterizing the model were included in the CFD software ANSYS CFX v-11 and simulated in a simple geometry (rectangular duct). Validation of CFD results was carried out by comparison with experimental data. Good agreement between numerical results of a control case and experimental data was achieved (deviation < 2%). Then, the influence of key parameters such as: Ta, RH, Dd, mw over the performance of the air cooling system was investigated. Finally, the model was used to design a Fogging System for an existing 120 MW Gas Turbine. For this gas turbine operating under real conditions, the model predicts a net power increment of 2% [7].