The effects of third substances at the particle/surface interface in compressor fouling

Since the beginning of the 1950s, manufacturers and operators have struggled to understand, reduce and eliminate compressor fouling and its effects on gas turbine operation. Several devices (inertial separators, barriers, filters, etc.) and strategies (on-line and off-line washing, manual cleaning, etc.) have been adopted in order to limit and/or eliminate the foulants which stick to the compressor blade and vane surfaces. The state of the power plant design and installation and environmental conditions determine the rate of fouling and, in turn, gas turbine performance losses. The types of contaminant (organic or inorganic), their concentration and their ability to stick are variable depending on the weather conditions. Desert, tropical, rural, and off-shore conditions are characterized by different foulants with different characteristics which determine compressor fouling. In this paper, an analysis of the influence of third substances at the particle/surface interface is presented. The analysis is carried out on two different compressor rotors, transonic and subsonic. Firstly, a sensitivity analysis is proposed related to the particle diameter and foulant mixture in order to highlight the influence of air humidity due to environmental conditions or the pressure drop after the filtration stages. The effects of a water electrolytic solution (generated by the presence of inorganic matter) and a water surfactant solution (used in the case of washing) are also considered. In this case, the properties of the mixture substance (solid particles bound by a liquid film) are considered. Secondly, using previous numerical analyses (particle-laden flow with a Eulerian-Lagrangian approach) as a starting point, the variation in particle sticking ability is evaluated against the presence of third substances (water solutions and oily substances) and the particle kinematic characteristics using a sticking model based on an energy balance equation. The results show the influence of the third substance on particle sticking capability using a susceptibility-to-fouling criterion. Particularly in the presence of humid conditions, sticking capability increases with respect to dry conditions, even though the major effects are due to the mixture viscosity and not only to the presence of liquid water. The sticking capability of the mixture varies according to particle diameter as a function of the particle normal velocity. The results are presented in order to easily quantify the effects of the presence of a third substance at the particle/surface interface according to the type of liquid phase involved in the sticking process.