AAF International Ltd.

The economic benefits of HEPA-grade filtration for gas turbine operation in the power generation industry

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Courtesy of AAF International Ltd.

Everywhere we look these days, one message stands above all the rest: energy must be used with greater efficiency
Global energy demand is estimated to rise between 25 and 30 percent between now and 2040, fueled by growth in economic output and by a growing population in which billions of people —despite working hard to advance their standards of living — subsequently and inevitably end up consuming ever greater amounts of energy.

The DOE Energy Information Administration predicts that total electricity consumption, including both purchases from electric power producers and on-site generation, will grow from 3,879 billion kilowatt-hours in 2010 to 4,775 billion kilowatt-hours in 2035, increasing at an average annual rate of 0.8%.

In the countries belonging to the Organization for Economic Cooperation and Development (OECD), including those in North America and Europe, energy use is predicted to remain flat— even as economic growth progresses. One underlying factor is the assumption that increased investment in new technology will create efficiency gains in production and distribution that will in turn converge with a reduced consumption profile resulting from a more energy-conscious industrial and commercial customer base.

The electricity generation sector is witnessing the arrival of new, advanced-class, highly efficient natural gas plants and continuing to invest in the use of renewable sources of production.

This backdrop places even greater pressure on the present installed base, consisting of many thousands of gas turbines, to help the electric utilities develop more competitive business models capable of meeting demand with clean, efficient and reliable modes of generation.

If operators hope to achieve peak business performance, finding new ways to extract a greater number of megawatt hours at reduced fuel usage rates and with lower overall operational costs has never been more important. The question is: can maintaining a gas turbine (GT) engine in an as-new state of cleanliness help electric utility companies meet this challenge?

Overview

In order to combust fuel, GTs consume vast amounts of atmospheric air heavily contaminated by natural pollutants such as wind-blown dust, agricultural pollution and salt and seawater spray in coastal locations, plus pollutants created by chemical refining, along with hydrocarbon emissions from industry and traffic. As an accumulated mass in fluctuating humidity, these pollutants seriously impact the performance and operating efficiency of precision GT engines.

To protect the turbine from these pollutants, most GT original equipment manufacturer (OEM) specifications—both past and present—call for air inlet filtration using a final 'fine' filter with a classification of MERV 15/F9 (98 grade efficiency) or less. These are filters that deliver initial particle removal efficiencies of 60% or less at 0.5 microns.

HEPA (high-efficiency particulate air) filtration, now also known as EPA, was originally developed for clean room and pharmaceutical applications. HEPA H12 (EPA E12) filters, with efficiency levels thousands of times greater than the MERV 15/F9 classification and capable of removing 99.5% of particles as small as 0.07 microns, are increasingly being used to protect gas turbines. The initial demand for H-class filters came from oil companies seeking to maintain a very high level of cleanliness for turbine compressor blades, which eliminates the requirement for offline water wash and, consequently, production downtime.

Since introducing HEPA filters onto gas turbines over ten years ago, AAF has carried out long-term studies on a large sample of GTs —both with and without HEPA (EPA) filtration—totaling hundreds of thousands of operating hours. This work has led to the counterintuitive conclusion that more power is obtained with HEPA (EPA) filters than with only fine filters. The consistent finding: initial power lost due to increased differential pressure is more than offset by the maintenance of a clean condition within the first four weeks of operation. In other words, the energy payback period of HEPA (EPA) filtration can be measured in days.

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