Understanding the impacts of poor air filtration on gas turbine performance
In the world of turbomachinery air filtration engine performance should be considered as a function of the total mass of contaminant ingested which is directly influenced by the type of atmospheric and industrial environment i.e. the ambient air quality of a given installation. Any ingested contaminant decreases the airflow performance of the inlet compressor due to degradation in blade shape and surface finish. Ultimately, the overall performance of the gas turbine can be significantly affected.
The air quality in any given location is completely unique and an in depth understanding of the challenge criteria is critical to understand the issues. Evaluating the quality of intake air often reveals a mixture of challenge criteria in any given location e.g. a coastal site with a nearby woodland may have high levels of salt and moisture all year round, but seasonal pollen could be an intense challenge for a few weeks of the year. This very localised example is not uncommon across gas turbine installations, and is why it is important to speak to AAF before considering which products are right for your installation.
Typical environmental challenges
Industrial & Urban
In the industrial and urban environment, air quality can be particularly low with a high concentration of particles from energy production, vehicle traffic, industrial process, building construction and demolition projects. These particles are invisible to the naked eye and typically fall between 0.01 and 10 microns (for reference a human air is approximately 50-70 microns in diameter).
In the offshore and marine environment, the air is laden with high levels of salt and moisture. Salt is prevalent as both a dry particulate and as a wet aerosol, it is typically found in high concentrations due to the prevailing wind picking up sea spray from the waves. Mists and fogs can also intensify the amount of free moisture that enters the air filtration system, while dusts and other man-made particles from the platform processes will lower compressor efficiency.
In desert, arid, and dry environments high concentrations of dust particles are the greatest air quality challenge, especially in areas susceptible to sandstorms and where particles can stay suspended in the air for many hours. Moisture can also be a surprising challenge in some of these environments, caused by morning and evening fogs and/or locations near to the coast.
Free moisture removal is the greatest challenge in tropical locations or environments with sustained high humidity. This can be exacerbated through torrential rains, fogs and mists. Removing all free moisture is essential to provide an optimum level of protection and to reduce the risk of particles absorbing the moisture. Prolonged free moisture results in particles swelling, blocking the filter media, leading to an increase in pressure drop.
In rural and agricultural environments air quality filtration challenges are often seasonal. Airborne contamination that occurs naturally includes pollen, seeds, and insects. A pollen season is determined by the surrounding trees and plants and may result in a very high volume of airborne particulate. Farming also creates many air filtration challenges, including high concentrations of dust in the ploughing season.
In coastal environments sustained high humidity and the removal of salt are the greatest filtration challenges, however, this is often combined with local man-made contaminant from industrial processes. Salt is prevalent as both a dry particulate and as an aerosol, it is typically found in high concentrations due to the prevailing wind picking up sea spray from the waves. Removing all free moisture is essential to provide an optimum level of protection and to reduce the risk of particles swelling in the presence of water and blocking the pores within the filter media.
Extreme heat is not necessarily a filtration challenge but as gas turbine output is affected by the temperature of the air entering the compressor it can be a big challenge for operators. In general gas turbines are rated at ISO conditions with an ambient temperature of 15 °C (59 °F). Therefore, when the temperature increases above this point there is a loss of power due to the lower air density. To optimize the gas turbine power output the intake air must be suitably cooled.
Snow & Ice
In sub-zero climates snow and ice are the biggest filtration hazards, often covering the outer surface of the filter elements and significantly reducing the airflow. This in turn causes high pressure drop, resulting in gas turbine power output deterioration or a unit trip. Worse still, ice formed in the gas turbine inlet can be ingested into the engine, this may result in foreign object damage and can ultimately result in the subsequent failure of the gas turbine.
AAF uses air quality data to understand the filtration challenge of any given site, this is combined with years of experience and a detailed understanding of air quality to recommend the right products and solutions for your environment. There is no ‘one size fits all’ approach to gas turbine filtration but the impacts of poor filtration can be very costly, inefficient and lead to increased emissions and environmental impact.
To understand more contact us and we will happily demonstrate this approach through our total cost of ownership evaluation tool. AAF Optimize is an industry-leading support service that provides gas turbine users the capability to optimize all aspects of their air inlet systems, to improve plant efficiency, availability and reliability as well as helping to extend the asset operational life.