As gas turbine technology continues to advance and fuel quality varies along with growing expectations of longer life, higher efficiency and reduced maintenance requirements, intake filter selection has become increasingly important.
Below are excerpts from the paper "Strategy for selecting optimized technologies for gas turbine air inlet filtration systems" presented by Stephen D. Hiner of GE Energy at the ASME/IGTI expo in Vancouver in 201.
Gas turbines are used throughout the world in an ever increasing diversity of application and environment. This presents a number of challenges to the air filtration system, that require unique solutions for each subset of environment specific challenge, gas turbine platform technology and fuel quality being burnt.
With the widespread availability of fuel gas and their economic attractiveness, GT’s have become standard for many applications including; propulsion, power generation (power gen), mechanical drive (pumping and compression) and steam generation. Today a GT is a high precision, highly optimized machine and as such is sensitive to contaminants in the air or fuel that may pass through it. The massive amount of air passing through a GT means that even with a very efficient filter system, appreciable amounts of contamination will still reach the GT. For example, a GE Frame 9 GT will consume all the air within Wembley Stadium in 2 hours. As a result of this, it is essential that an appropriate and effective filtration system is installed on the GT intake. However the selection of this can depend upon a considerable number of factors.
The use of an incorrect filtration system can lead to the following four main types of issue, which may result in reduced performance or costly repairs due to failure:-
Relatively large (typically >10 µm) particles or droplets impact the blades within a GT, over time this can change their aerodynamic shape, or create high stress points via pitting, which can lead to crack formation and catastrophic failure.
Corrosive substances, even in small quantities, when entering a GT can cause substantial damage. In the “hot sections” of the GT this is particularly true of sodium which combines with sulfur in the fuel at high temperature and in the “cold sections”, chlorides and sulphates which combine with water to form acids. Both cause blade pitting with similar failure modes to erosion.
Small particles adhere to the blade surfaces, changing the aerodynamic shape and affecting it’s performance. Primarily this affects the compressor section of the GT and may be caused by sticky particles, or by the coating of a sticky substance such as a hydrocarbon vapour, which then promotes the adherence of non-sticky particulate. This is typically not permanent and most often alleviated by performing a compressor wash, which to be most effective requires the GT to be shutdown.
Particle fusion and Plugging
Particles such as sodium chloride or potassium chloride melt in the hot stages of the GT forming molten contaminants which then adhere to the internal surfaces of the GT and change the profiles of blades affecting their performance, or block critical cooling passages causing thermal fatigue and eventually catastrophic failure.