ALTHOUGH the air filter “element” determines the quality of the ingested air, the filtration “system” is paramount in allowing that to happen.

Effective air filtration means that the filtration system is designed to remove the various contaminants that exist at a particular installation. This is not the easiest thing to do and can be perplexing to many of the owners and operators of turbo machinery.
Air filtration takes many forms and has evolved over the years since first introduced. Considering the singular application of nothing more than coarse trash screens, today’s air filters and air filtration systems have come a long way in protecting turbo machinery. Combustion turbines when first applied as the drivers for pumps and generators required minimum protection. These were simply aircraft engines that were modified for use as “fixed” mechanical drives. As such, the engines were capable of ingesting moderate amounts of contaminant without interrupted service. However, as the range of service conditions increased, the need for continuous protection increased. The technologies applied to all rotating equipment have changed dramatically, again making the need for improved filtration capability absolutely essential.
Functionally, most of those used in the protection of sophisticated rotating equipment work in the same manner. However, selecting the wrong system can negatively affect equipment performance resulting in internal wear or shortened overhaul cycles. The result in many cases is lost output combined with increased maintenance cost as a result of frequent replacement of the air filters. Additionally, selecting the wrong filter can reduce the protection afforded to the rotating equipment.

FILTER SYSTEMS
Virtually every turbo machinery installation has unique needs when it comes to the operating environment. Unfortunately no one “standard” exists that is all encompassing. Those factors most typically encountered are: Moisture, both free and ultra high humidity; Icing, which includes hoar frost and ice fog; Chemicals, including hydrocarbons; Corrosive materials, including marine salt; Seasonal activity, ranging from insect swarms to pollens to farming practices and sandstorms.
Critical to operational success is an “understanding” of the design features available. The two most common filter systems are described as follows:
Typical Static Filter System: Static filtration systems include all filter systems that utilise “impingement”, “interception”, and “straining” type filters.
Pre-filters: Pre-filtration infers that multiple stages of media filtration are utilised. The “pre-filter” is of lesser efficiency and lower replacement cost. These filters are typically manufactured of fibreglass and of varying efficiencies. These filters are normally classified as pads, pleats, socks/wraps, or panels.
Final filters: Final filters offer maximum protection to the combustion turbine parts and ultimately determine success in the design of the inlet system. These filters are generally rated at 90 per cent or greater efficiency, although higher efficiency ratings are becoming increasingly cost effective. These filters are generally referred to as panel, mini-pleat, cartridge, or bags.
“Pulse type” self-cleaning filtration systems incorporate the same filter processes, but utilise a “reverse-pulse” of compressed air as a means of removing accumulated dust on the media surface. The term “pulse-jet” is also seen, with both terms having universal acceptance and interchangeability. The filters perform functionally the same as “static” filters in that dust is prevented from entering into the clean air stream. The fundamental difference being that the media is formulated to ensure “surface” loading, verses “depth” loading for static filtration.