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Tech Topics

GTS-5127/03

7 Things to Know When Purchasing Air Filter ElementsHigh Performance Inlet Air Filters Can Aid Turbine Performance

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For further discussion oneach point, see next pages.

The price of replacement filters is, of course,of primary consideration, but the total cost and,

conversely, the value of the filters go deeper than that.More efficient air filters can actually help reduceoperating costs.

Large particles (>10-20 in size) cause blade erosionwhen present in sufficient quantities, while smallerparticles (

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4 In order to compareASHRAE (or any) testresults for two differentfilters, the tests must beperformed at comparable

airflow rates.

Air filter elements used in turbineair inlet systems have been sized fora design airflow rate. Filter testresults performed at a significantlydifferent airflow will be of littlevalue in predicting how well thatair filter element will perform atthat design airflow rate. Forexample, comparing results of an

ASHRAE test for a filter tested at a500 cfm airflow to results of anASHRAE test for a similar filtertested at a 900 cfm airflow wouldprovide very little meaningfulinformation.

Donaldson has ASHRAE test resultsavailable for all of the filterelements used in Donaldson first-fitequipment. Those filter tests were

performed by AFTL, an indepen-dent testing lab, at airflowsappropriate for turbineinstallations. Donaldson also hasASHRAE test results for somecompetitive air filters that wereperformed (by AFTL) for directcomparison purposes.

Any filter manufacturer claiming tohave equivalent or comparablereplacement filter elements shouldbe able to provide ASHRAE testresults performed at appropriateairflows to support those claims.

1 Why shouldnt filterperformance be evalu-ated on mass efficiency(that is, efficiency byweight).

Because mass efficiency doesntmeasure the effect of the smaller,atmospheric dust particles thatcause compressor blade fouling.

Filter mass efficiency is based onthe filters ability to capture thedust used during testing, whichtypically has an average particle sizeof approxi-mately 5. There is

widespread disagreement as to whatthe typical particle size make-upis for atmospheric dust; however,there is a general agreement that inNorth America the averageatmospheric particulate concen-tration is 50-100 micrograms percubic meter, with most of thatparticulate not being visible to thehuman eye (i.e., < 25 in size).There is also agreement that 70-

80% of that mass concentration ismade up of particles

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5 Filter pressure dropcan impact your annualoperating costs.

The pressure drop of an inlet air

system can have a significant effecton turbine performance. In fact,turbine manufacturers say that 4.0"w.g. of inlet loss will reduce aturbines output by 1.0-1.4%.The effect of inlet pressure drop is astraight-line function, which meansthat each 0.10" w.g. increase in(average) inlet pressure drop willdecrease a turbines output by0.025%, or more.

In more specific terms:

The cost of operating a turbinewith 0.10" w.g. of added inletpressure drop over an 8000 houroperating year is equivalent tooperating a turbine for two hoursat full load without getting any ofthe revenue from the powergenerated. This is one of thehidden costs of using less efficient

filters.

Lower P filters yield increaseturbine output!

6 Despite generic filtermedia descriptions(blended or synthetic),filters from one filtermanufacter may not have

the same operating charac-tistics as filters from anotherfilter manufacturer.

It is easy to assume that blendedand synthetic media are the samefrom different filter manufacturersbecause the media comes from the

same mills. But its NOT true, atleast with regard to the filtersmanufactured by Donaldson.

Donaldson Company, Inc. is the

leading manufacturer of air filtersystems and replacement air filtersfor gas turbines and is one of only afew filter manufacturers that hasits own media developmentcapabilities. All of the air filterelements that Donaldson manufac-tures use proprietary mediaformulations that were developedin Donaldson labs. Each media hasa specific formulation and

engineering specification thatdifferentiate it from media thatother manufacturers try to claim asbeing equivalent or compar-able. By comparison, other filtermanufacturers typically use one ofseveral standard, non-proprietarymedia options available from themedia mills.

7Some 100% Synthetic

media filter elementshave performancecharactistics that arecomparable -- but are notequivalent -- to filters madewith Donaldson Duratek

Spider-Web.

Donaldson Spider-Web is one ofthe proprietary filter products thatwas developed in the Donaldsoncorporate media developmentlaboratory. It is not available toany other filter manufacturer or toany of the filter media mills.Donaldson originally developed

the nanofiber technology forSpider-Web in the early 1980s foruse in Donaldsons industrial dustcollection products for capturingsub-micron particulate on the

surface of the media, whichallowed the particulate to be easilypulsed off of the filters during pulsecleaning.

High Performance Filter Media:

Synthetic & Duratek Spider-Web

ASHRAE test results of Donaldsonfilters with Duratek Spider-Web

media are comparable (but notequivalent) to ASHRAE test results

for Donaldson 100% syntheticmedia filters. The average pressuredrop characteristics of the twomedia are similar; however, theDuratek Spider-Web media hasslightly higher efficiencies and hassignificantly better self-cleaningperformance charactistics.

ASHRAE tests suggest similarperformance characteristics for

other filters with 100% syntheticmedia; however, NO filtermanufacturer offering standardcellulose or blended media filter asbeing similar or equivalent toDonaldson Duratek Spider-Web hasprovided appropriate ASHRAE testreports to substantiate those claims.

Considerations When Replacing Air Filter Elements on Gas Turbine Air Inlet Systems -- page 3

Copyright by Donaldson Company, Inc. 2003 All rights reserved.

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DuratekDuratekDuratekDuratekDuratek (Donaldsons proprietary blend ofnatural & synthetic fibers) -- Synthetic fibers mixed in

add strength and moisture resistance.

In these photos taken with our scanning electronmicroscope (SEM), youre seeing filter media magnified200, 500, or 1000 times! Note the pore size (spacesbetween the fibers) and the construction of the fibers(smooth, rough, large, small.)

DuratekDuratekDuratekDuratekDuratek with Spider-Webwith Spider-Webwith Spider-Webwith Spider-Webwith Spider-Web -- You can seehow adding the layer of nanofibers (Spider-Web) over

the Duratek

substrate creates very small poresizes, enabling entrapment of sub-micron dust.

SyntheticSyntheticSyntheticSyntheticSynthetic (Donaldsons man-made filter media) --By controlling the fiber diameter and the pore size, wecan design filter media to be effective in variousenvironments (desert, arctic/frost, urban, industrial,marine, etc.) The smooth fibers provide verylow impedance to airflow -- helping to maintainlow P for the entire life of the filter.

Synthetic with Spider-WebSynthetic with Spider-WebSynthetic with Spider-WebSynthetic with Spider-WebSynthetic with Spider-Web -- Note theweb of nanofibers bonded over the syntheticsubstrate. This media formulation has proven to bethe most effective filter solution for gas turbineprotection -- best filtering efficiency, best pulsingcharacteristics, best P over the life of the filter,and longest filter service life.

Up Close and Personal!...The heart of the filtersystem: the filter media.

And Now Its DirtyAnd Now Its DirtyAnd Now Its DirtyAnd Now Its DirtyAnd Now Its Dirty -- The webcatches most of the very fine particulate,

allowing two major benefits: (a) very fine (