Gas Turbine Inlet Filter – True Cost Investigation


Speeches: None are directly applicable although Mitchell Krasnopoler of Kiewit will be speaking about air emissions and can address the fact that with HEPA filter gas turbine inlets the outlets are reduced below requirements in California where ambient air levels exceed emission limits.

Stands: The only stand displaying gas turbine inlet filters is DHA stand 1331. An open meeting at their stand is scheduled for 10:AM Wednesday but check updates for changes.

Issues to be Discussed:  DHA will be displaying a rugged cleanable HEPA filter. The debate has centered on whether the theoretical value of lower maintenance with the HEPA filter is worth the higher cost. The argument against the HEPA filter has been fragility.  (see separate analysis)


Company Name

Last Name

First Name






571 259 5840




904 614 7226

DHA  is a  supplier of high efficiency cleanable gas turbine intake filters






As the costs and complexity of gas turbine generators increase, end users seek ways to both protect and maximize their investment. Many gas turbine operators have explored high efficiency options for their inlet filters. Switching to HEPA grade intake filtration greatly reduces the presence of contaminates in the turbine compressor. This helps extend turbine life and efficiency while reducing the costs in fuel and maintenance. There have been a few drawbacks to making the move to HEPA filters. One issue is that with a more restrictive filter media comes increased initial pressure drop. There have also been questions surrounding the long-term durability and lifespan of the HEPA filters.


The true cost of a gas turbine inlet filter can be affected by a large number of factors. These factors are not constants but are changing. The filter purchaser is challenged to not only identify these factors but to keep up with the changes.


Large gas turbines are used to generate electricity by utilities. Smaller gas turbines, drive pumps and compressors in locations with extreme conditions such as desert dust, artic snow or sea spray on an oil rig. As turbines have become more efficient, they have become more susceptible to damage from contaminants in the combustion air. This ambient air from the surrounding environment can contain high dust loads. In California, with very tight emission standards, the particulate in the inlet air to the turbine can exceed emission limits. Thus, the gas turbine has to act as an air cleaning device.


The challenge for  gas turbine inlet fiber, media, and filter suppliers is to increase gas turbine availability in all environments with newer and more sensitive gas turbines. The newer turbine designs are negatively impacted by small particles. This has led to the use of HEPA filters with efficiencies classed as H10/E10 and higher. Studies show that turbine maintenance can be reduced with even higher efficiency E12-U17. One study showed that even if the cost of higher efficiency filtration were four times higher than lower efficiency filters, the true cost would be lower.


One can choose a system with non-cleanable filters. They are relatively inexpensive but require continuous filter replacement. By using a sequence of inefficient but inexpensive pre filters and a final high efficiency filter, the replacement cost can be minimized.


An alternative is to use a cleanable filter. Periodic air pulsing knocks off accumulated dust. These systems are available from many suppliers if the F-9 efficiency is all that is desired.  Cleanable filters with H12 efficiency are available from only a few suppliers. On the other hand, there are many new developments which will expand the number of choices.


In terms of high efficiency dust capture mechanisms there is a choice between wet laid glass and synthetic nanofiber non-woven laminates or membranes. The traditional glass media for HEPA filtration has been used primarily in non-cleanable filters.


Quantifying the benefit is a balance between reduced fouling and increased pressure drop. The increased pressure drop can be estimated to restrict performance by approximately 0.4%, while cutting fouling provides a 1.2% improvement in output (empirical average). Therefore, the overall result is a potential efficiency improvement of 0.8%.


Alliance Pipeline believes that the E12 filters from Gore may allow Alliance to extend the interval between overhauls of its aero engines from 25,000 to as many as 50,000 hours (from three to six years).


The many factors and media choices impacting gas turbine inlet filter selection  have been discussed in a background document on display at


In the past the most efficient filters that were used on gas turbine inlets were rated F-9 with efficiency of more than 95% on particles 0.4 um diameter. The most penetrating particle size is about 0.2 um where the efficiency is much lower. Higher efficiency filters are rated based on the most penetrating particle size as follows:



HEPA Class

Retention (total)


> 85%


> 95%


> 99.5%


> 99.95%


> 99.995%


> 99.9995%


> 99.99995%


> 99.999995%


Membrane laminates such as used for dust collection can meet efficiencies up to E12.  The question is whether this is sufficient?


There are a number of new filter and media designs, which need to be evaluated. Mann & Hummel Vokes introduced the Aircube Pro Power S, which utilizes a new synthetic base media with much higher resistance to mechanical stress than glass fiber media and a stable high efficiency during operation. It is water and salt repellent while being extremely robust.



DHA Filter has developed a new line of intake filters that address many of these

concerns. DHA’s Duraweb™ Elite line features a new 3-layer media that combines high efficiency filtration with durability and breathability. The base layer is a 100% synthetic material that gives the media pack its strength and enable the filter to be pulse cleanable. The 2nd layer is a thin “relaxed” ePTFE membrane. The membrane is what gives the filter its high E11 efficiency while maintaining a low initial pressure drop. The physical properties of this membrane repel water and dust ensuring maximum filter life. Finally, a synthetic top layer adds dust holding capacity while protecting the membrane. The media is hydro- and oleophobic which helps it to perform in environments where hydrocarbons and/or high humidity are present. 



DuraWeb_Filter_Revised_Numbers (2)DHA’ Duraweb™ Elite line features a new filter media that uses 3 layers to prove HEPA grade inlet filtration:

1.      The fully synthetic top layer adds dust holding capacity and protects the membrane.  This layer is treated to be oleophobic and hydrophobic to repel hydrocarbons and moisture.

2.      A very thin “relaxed” ePTFE membrane gives the filter an E12 efficiency while maintaining a low initial pressure drop.  This membrane is applied with a proprietary process that ensures durability and maximum filter life.

3.      The synthetic base layer is made from a robust material that provides strength for the media pack.  This allows the filter to hold up over time even after going through numerous pulse cleaning cycles.


Boldrocchi is offering complete systems including gas intake filters.


Boldrocchi's integrated approach for gas turbine power plants


Background Information In Gas Turbine Decisions  (Free To Operators)


Gas Turbine Intake Filters Webinar - Hot Topic Hour May 21, 2015

The session covered four route maps in the Gas Turbine Combined Cycle Air Treatment Guide Revision Date:  5/21/2015

Nonwovens in Gas Turbine Air Filtration

Clarcor offers a full range of air inlet filters for gas turbine applications including panel, pocket V-cell and cartridge filters. This presentation addresses ways to improve inlet filtration to avoid fouling and corrosion of turbine equipment.Revision Date:  4/24/20

Gas Turbine Air Filter System Optimization

Proper air filtration is critical to the overall performance and reliability of gas turbines. This article discusses various aspects of the air filtration and conditioning process including inlet cooling, filters and water wash cycles.

Addressing Moisture Issues by McLeod Stephens, Nederman - Hot Topic Hour May 15, 2014

McLeod explained that the filter is part of a train of treatment elements with the screen, weather hood coalescers, filters, evaporative cooler and droplet eliminator. Revision Date:  5/15/2014

Gas Intake Filters: HEPA or Medium Efficiency Webinar - Hot Topic Hour May 15, 2014

A high level discussion attended by knowledgeable end users, consultants, fiber makers, media suppliers and filter manufacturers. Revision Date:  5/15/2014

EMW recommends HEPA filters for air intakes to reduce compressor cleaning

A new trend is emerging in the sector of gas turbine inlet air filtration. Frequently, highest-efficiency (H)EPA filters are selected as the solution of choice for optimum protection of gas turbines. A leader in (H)EPA technologies for many years, EMW offers comprehensive product solutions to keep your gas turbine plant at the cutting edge.Revision Date:  4/2/2014

HEPA Air Filtration Technology Keeps Compressor Blades Clean

Combustion turbine operators generally experience turbine fouling from airborne particles passing through existing inlet air filters. Fouling can be caused by the particle capture limitations of conventional F-class (EN779:1998) or MERV-class (ASHRAE 52.2) filters. The consequence is reduced performance of the turbine operation. Revision Date:  3/20/2014