Q&A: What constitutes the ideal inlet air filter?

Published on: 
Turbomachinery Magazine, March/April 2020,

Stuart Blackburn, Product Management Director at AAF International, discusses his company, evolving market trends and what constitutes a good filter for gas turbines.

Tell our readers about AAF

AAF International was founded in 1921 and specializes in air filtration across residential, industrial and commercial applications. Founded in Louisville, Kentucky, it now has office and manufacturing locations around the world.

Since the 1960s, AAF has focused on the gas turbine (GT) air inlet filtration market, suitable for all GT technologies across a wide range of applications and environments. The focus of the business is to ensure GT owners and operators can extract the maximum plant performance, availability and reliability by using optimized air inlet filtration systems.

As well as upgrading existing installations, AAF supplies OEMs with new equipment, including air inlet filtration systems, inlet heating and cooling, acoustic enclosures and exhaust systems.

What trends have you noticed with regard to filtration?

There is a growing need for inlet filter system optimization. GT air inlet systems present far higher levels of complexity and individuality than previously appreciated. Owners and operators have begun to understand the benefits available from optimizing these systems to improve performance, availability and reliability, while reducing operating costs and CO2 emissions.

Solutions need to be individual, and based on operational requirements and environmental conditions. A tailored approach increases inlet air quality, reduces offline water washing frequency and reduces GT maintenance spend.

What changes have you observed in the GT marketplace?

Customers are moving away from traditional F-grade filters and upgrading to high performance(H)EPA filters. Their positive impacts outweigh initial filter supply costs.

The higher the operating hours, the more likely you are to see the greatest benefit. But it is dependent on the plant’s contractual arrangements. Overall, high-efficiency filters have grown in popularity and low cost, low-performance filters are viewed as a false economy.

What advice would you pass on to GT users?

Air inlet filters represent the largest consumable spend on a GT power plant outside of the hot section. This makes them a high priority for spend reduction initiatives.

The benefits derived from optimizing filter systems can be many multiples of the filter cost. Therefore, don’t be fixated on filter cost. Instead, focus on total cost of ownership (TCO), by taking into account performance, longevity, GT maintenance and other factors.


Also, be sure to understand environmental operating conditions: do you have periods of high dust concentration or high humidity, extreme temperature or driving rain, seasonal pollen or insect swarms, high levels of industrial pollution or a high concentration of hydrocarbons? For example, regular early morning fog requires a filtration system that can remove moisture without spikes in differential pressure.

What constitutes a good filter for GTs?

The filter efficiency grade and the filter media are significant features, as well as how the filter deals with varying environmental conditions, and how the construction of the filter affects performance. GTs consume large volumes of air every second. Therefore, a well-designed filter frame and faceguard (or protective screen) add much more than just strength.

Shutdowns, restarts and changing operating conditions lead to large variations in the airflow through the filter system. These turbulent conditions can result in distortion and weakening of the filter over time. A high-strength GT filter supports both the media pack and the filter frame, eliminating the risk of distortion of the filter and deflection of the media pack. This results in extended stable filter life, for optimum performance and protection.

Tell our readers about one of your products

AAF’s HydroGT V450+ has a larger media area for higher dust holding capacity. It is designed to maximize protection for GT turbine performance and power output. Its (H)EPA efficiency reduces compressor fouling and the need for offline water washing, resulting in increased machine availability and reduced operational costs.

The frame and protection screen prevent distortion of the media pack over its lifespan. The media repels water, oil, hydrocarbons and salt. Efficient drainage ensures performance is maintained and the GT remains protected, even during moist and humid conditions.

What other products and services do you offer?

AAF Optimize is a new web-based platform to help operators understand TCO. It contains details on over 33,000 GTs around the world. Based on site location, it can understand environmental challenges and weather data. An operator enters operating data to establish existing TCO and to evaluate how this figure could be improved with better filtration.

What changes have you noticed in the oil & gas market?

In the oil and gas industry, there remains a limited amount of capex spend so operators are keen to find filtration solutions without a major overhaul. Ambient air offshore is heavily contaminated with sea salt aerosols, salt in solution, fog and mist.

Industrial processes such as drilling, grit blast, and mud burn, as well as GT and supply-vessel exhaust fumes further contaminate the air. High velocity (smaller) air inlet filtration systems that use low efficiency bag filters are the norm offshore.

However, these bag filters provide inadequate protection against highly contaminated ambient air. The result is air compressor blade fouling, corrosion, erosion and frequent offline water washing. The AAF N-hance filter provides EPA E12 efficiency and can be retrofitted internally within the existing filter housing with no increase in differential pressure.