Best Practice Compressed Air

1 Introduction 3

GeneralRecommendations 4

2 Overview 5

3 CompressedAirSystem 6

4 Energysavingmeasures 7

4.1 Avoidleakage 7

4.2 Reducethesetpressure 7

4.3 Reducepressuredrop 8

4.4 ReduceIntakeairtemperature 8

4.5 CheckAirquantity 8

4.6 CheckAirquality 9

4.7 Donotusecompressedairwhenitisnotnecessary 9

4.8 Isolateareasorequipment 9

4.9 Maintainthecompressedairsystem 9

4.10Selectefficientcompressor 10

4.11ReviewtheCompressorControlSystem 10

4.12PeakShaving 11

4.13Usemulti-stagecompressors 11

4.14Combinecompressedairsystems 11

Contents

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1 | Introduction

Compressedairisaveryusefulandvaluableutility.Althoughitisbeingusedformostofthe

plants,compressedairisoftenignoreduntilsomethinggoeswrongwithit,orthecompressors

failtokeepupwithrisingairdemand.Compressedairsystemsgenerallyincludecompressor(s),

filters,dryers,piping,valvesandconnectedprocessequipment.ThisBestPracticesisdeveloped

toprovideyouenergysavingmeasurestoreducetheoperatingcostsassociatedwiththeuseof

compressedairandimprovethereliabilityoftheentiresystem.Theenergyefficiencyofatypical

compressedairsystemcanbeimproved20%ormore.

Introduction

Source: AkzoNobel

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1 | Chemie voor duurzame ontwikkeling 4

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General Recommendations

Savingcanbeachievedinthecompressedairsystemby

applyingenergysavingmeasureslistedbelow;

• Avoidleakage

• Reducesetpressure

• Reducepressuredrop

• Reduceintakeairtemperature

• CheckAirquantity

• CheckAirquality

• Donotusecompressedairwhenitisnotnecessary

• Isolateareasorequipment

• Maintainthecompressedairsystem

• Selectefficientcompressor

• Reviewthecompressorcontrolsystems

• Peakshaving

• Usemulti-stagecompressors

• Combinecompressedairsystems

Foraplantwithanaverageairconsumptionof1000m3/

hrthroughouttheyear,energycostsisapproximately

120000Euro/year.Forinstance,

24000Eurocanbesavedwhen20%savingisachievedin

theenergyusagewhenabovelistedmethodsareapplied.

Note:Calculationsinthisdocumentarebasedon

compressedaircost0.02Euro/m3or0.09Euro/kWh

(approximatevalueforEurope).Annualoperatingtimeis

takenas6000hrtocalculatethesavings.

1 | Introduction

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EnergySavingMeasure SavingOpportunity Applicabilityofthemeasuretothecompressedairsystem

Existing Revamp New

Avoidleakage High

Reducesetpressure High

Reducepressuredrop Low

Reduceintakeairtemperature Medium

CheckAirquantity Low

CheckAirquantity Medium

Donotusecompressedairwhenitisnotnecessary Medium

Isolateareasorequipment Medium

Maintainthecompressedairsystems Medium

Selectefficientcompressor High

Reviewthecompressorcontrolsystems High

Peakshaving Low

Usemulti-stagecompressors Medium

Combinecompressedairsystems Low

2 | Overview

Overviewoftheenergysavingmeasureswithrespecttosavingopportunity,andtheir

applicabilitytothecompressedairsystem(new,revamporexistinginstallations)is

indicatedinTable1.Savingopportunityispercentageenergyreductioninthecompressed

airsystem.Potentialsavingcanvaryfromsitetosite,approximatesavingpotentialis

giveninthetable.EnergysavingopportunityisrankedasLow<Medium<High.For

example,10%reductionisconsideredashigh.

Tabel 1: Overview of the saving measures

Overview

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Typicalcompressedairsystemblockdiagramis

giveninFigure1.

Compressedairsystemsconsistgenerallyofthe

followingmainparts.

• Compressor

- Compressesairtoasmallvolumeby

increasingthepressure.Maincompressor

typesarereciprocatingcompressors,screw

(rotary)compressors,vanecompressorsand

centrifugalcompressors.

• Filter

- Removessolidsandliquidsfromthe

compressedair.Filtercanbeplacedthroughout

thesystem.

• Dryer

- Condensesandextractswatervaporfrom

thecompressedair.Threetypesofdryers

areavailable:membrane,refrigerant,and

desiccant.

• Receiver

- Storescompressedairinordertomeet

rapidincreasesindemand.Inthisway,air

compressorscanbeturnedoffforcertain

periodsorrunatalowerload.

• Distributionpiping:

- Linksthecomponents.Itdistributestheair

fromamainheadertobranchlinesandsub

headerstodroppointsconnectedtoindividual

tools.

Abriefdescriptionofothercomponentsisgiven

below;

• Inletfilter:removesparticlesfromtheair

enteringthecompressor.Itisusuallypartofthe

compressorpackage.

• Motor:drivesthecompressor–alsoknownas

primemover.

• Compressorcontroller:directsthe

compressor’soutput.Itmaybemicroprocessor,

electromechanicalorpneumaticallybased.

• Aftercooler:lowersthetemperatureoftheair

leavingthecompressorandremoveswaterthat

condensesastheaircools.

• Separator:removesliquidsfromthecompressed

air.

• Condensatetrap:collectsanddischargesliquid

thatcondensesoutoftheairstream.Itisan

integralpartofaftercoolers,dryersand

separators.

• Pressureregulator:controlsairpressureandflow

atindividualpointsofuse.

3 | Compressed Air System

Figure 1: Compressed air system block diagram

Air Compressor(s)

Filter

Dryer

Reciever

End User

End User

End User

Compressed Air System

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becheckedandmaintained.Minimizingcompressed

airleakscanalsocontributetoproblemswithsystem

operationse.g.fluctuatingsystempressuredueto

partlyremovalofthebaseload,excesscompressor

capacityduetolessairconsumption.

4.2 Reduce the set pressure

Atmostplants,severalairpressuresrequiredfor

differentprocesses.Oftenthepressureset-pointof

thecompressor(s)issethigherthannecessaryfor

practicalreasons.Bydeterminingtheactualrequired

pressure(oftencontrol/safetyvalves)thesetpoint

canbereduced.Notethattherequiredsetpoint

canbedifferentduringdayandnight.Alsoduring

weekendsandholidaysareducedsetpointmight

bepossible.Figure3illustratestheeffectoftheset

pressurereductionontheenergysaving.

systempressures.Leakageratesidentifiedinm3/hr

arealsoproportionaltothesquareofthehole

diameter.Indicationofairleakagebasedonthe

holediameterisgiveninFigure2.

Forinstance,4mmleakagecostsapprox.11500Euro/

year.

Makingstaffawareofthecosttothebusinessfrom

leaksandencouragingthemtoactivelyreportleaks

isanimportantstep,astheyarealwayspresent

ontheshopfloorandarebestplacedtonoticeany

changes.

Fixingleaksofteninvolvestighteningorreplacing

connections,fixingholesinpipesorrepairing

damagedequipmentsuchaspressureregulators.

Often,simplycleaningandapplyingthreadsealant

tofittingswillhelp.Replacingequipmentwill

benecessaryinsomesituations.Onceleaksare

regularlybeingrepaired,thesystemisregularlyto

4.1 Avoid leakage

Leaksareasignificantsourceofenergywasteina

compressedairsystem.Leakscanwasteupto50%

ofthecompressedairproducedbythecompressor.

Reducingleakageisakeymeasurethatcanbeused

toimproveenergyefficiency.

Althoughleakscanoccurinanypartofthesystem,

themostcommonproblemareasarepipejoints,

pressureregulators,filters,lubricator,valvesleft

open,flanges,equipmentleftrunningornotisolated

hoses,condensatetraps,couplings,andthreaded

fittings.Therearethreekeywaystofindcompressed

airleaks.

• Thesimplestwayistolistentotheleakages.

However,itmustbenotedthatlisteningforleaks

isunreliableespeciallyinanoisyenvironment,

• Anothermethodistobrushsoapywaterover

areassuspectedofleakingandlookforbubbling.

Thismethodischeapandsimple,butitisavery

time-consumingprocess.

• Thethirdisultrasonicleakdetection.Ultrasonic

detectorscanpinpointleaksveryaccuratelyand

quicklybydetectingthesignatureultrasound

signalsofhighpressureleaks.

Somecompressedairserviceproviderscanperform

ultrasonicleakdetectionprogramsiftheresources

fromthesitearenotavailable.

Leakageratesarefunctionofthesupplypressure

inanuncontrolledsystemandincreasewithhigher

4 | Energy saving measures

Figure 2: Indication of air leakage based on the hole diameter (at 6barg)

Figure 3: Effect of the set pressure reduction on the energy saving

0

10

20

30

40

50

60

70

80

90

100

110

Air

lost

(m3/

hr)

Hole Diameter (mm)

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 5,5

0

2

4

6

8

10

12

14

16

18

20

22

24

26

Savi

ng (%

)

Compressor New Set Pressure (barg)

8 7 6 5 4

Energy saving measures

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4 | Energy saving measures

Anotherimportantconsiderationiswherethewaste

heatfromthecompressorisdischargedto.Isit

exhaustedintothecompressorhouseorintothe

atmosphere?Figure5showsenergysavingsin

theaircompressorbytheairinlettemperature.

Especiallywithair-cooledcompressors,thecooling

airwithinthatcompressorroomcanget15°Chigher

thantheoutsidetemperature.Forexample2550

Euroenergysavingcanbeachievedannuallyfrom

100kWcapacityaircompressorwhentheinletair

temperatureisreducedby15°C.

4.5 Check Air quantity

Therequiredcompressedairsystemvolumecan

bedeterminedbysummingaplant’scompressed

airrequirementsandthedurationofsuchvolumes

(systemloadprofile).Totalairrequirementisnotthe

sumofthemaximumrequirementsforeachtooland

Pipe diameter has a large impact on the pressure

drop of the system. The smaller the pipe, the more

energy is lost by the system (see Figure 4 for power

loss for a given diameter pipe). It should be kept in

mind that while the pipe diameter may have been

large enough for the capacity required at the time

of installation, if demand has since increased; the

pipe diameter may now be too small for the system’s

requirements.

4.4 Reduce Intake air temperature

Theaircompressoroftensucksairfromthe

ompressorroomitself.Theefficiencyofthe

compressorcanbegreatlyimprovedbyproviding

coolerairatitsintake.Thiscanbeassimpleas

suckingairfromoutsidethecompressorhouseor

anotherlocationon-site.

Forexample,energyconsumptioncanbereducedby

9%,whenairsetpressureisreducedfrom7bargto

5.5barg.Itmeans5000Eurocanbesavedannually

for100kWpowercompressor.

4.3 Reduce pressure drop

Pressuredropisanothermajorcauseofinefficiency

incompressedairsystems.Pressuredropisthe

decreaseinpressurebetweenthecompressorand

theuser.Excessivepressuredropwillresultina

poorsystemperformanceandexcessiveenergy

consumption.Acertainamountoflossisinevitable

fromsomecomponentssuchasfilters,dryersand

separators.

However,therearewaystoensureaminimal

pressuredropinthesystem.

Agoodperformedcompressedairsystemshould

haveapressuredropoflessthan10%betweenthe

compressoroutletandtheuser.

Pressuredrop(therebytheenergyconsumption)

canbereducedbyfocusingonthefollowingunits;

• Filters,dryersandseparators

• Regulators

• Valves

• Pipinglayout,Themorebends,elbowsetc.

inpipingnetwork,thehigherthepressure

dropwillbe.

• Pipediameter

Figure 4: Power loss for a given diameter pipe (for air flow 50 m3/hr and 100m pipeline at 7 barg)

Figure 5: Energy saving in the air compressor by the air inlet temperature reduction

Pow

er (w

)

Pipe Diameter (mm)

20 30 40 50 60 70 800

4000

8000

12000

16000

Ener

gy S

avin

g (%

)

Temperature Reduction (°C)

00 3 6 9 12 15 18 21

1

2

3

4

5

6

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4 | Energy saving measures

considermovingthatequipmentontoapointofuse

systemwithamuchsmallercompressoranddryer.

Thiswillsaveonenergycosts,asitwilluseless

energyintreatingtheairfortheentiresystem.

4.8 Isolate areas or equipment

Sometimesareasorequipmentareusedonlyshort

periodsoftime(batchorcampaignproduction).

Duringnon-productionhourscompressedairisstill

usedandleakagesarestillpresent.Byisolatingand

shuttingdownthecompressedairsystem,allair

consumptioniseliminatedinthispartoftheplant.

4.9 Maintain the compressed air system

4.9.1 Maintain the compressorEnsuringregularmaintenanceiscarriedoutonthe

compressorwillalsoreduceenergycosts.Ensure

theinletfilterisnotblockedandkeepcoolersclean

andproperlylubricated.

4.9.2 Maintain separators, filters, dryers and valves

Filters

Regularlycheckandreplacefilters.Blockedfilters

cancauseasignificantpressuredropandwaste

energy.Gaugescanbeinstalledthatmeasurethe

pressuredropacrossthefilterandindicatewhen

anewfilterisrequired.Becausesomeendusers

mayrequireahigherlevelofairqualitythanothers,

4.7 Do not use compressed air when it is not necessary

Becauseofitsavailabilityandanotheralternative

wouldrequirehighercapitalcost,compressedairis

oftenpreferred.However,itsrunningcostsisoften

moreexpensivethanthealternatives.Toreduce

compressedairenergycosts,alternativemethodsof

supplyinglow-pressureusersshouldbeconsidered

beforeusingcompressedairinsuchapplications

(seelistbelowforthealternativemethods).

• Airmotorsandairpumps

- Mechanical(electricaldriven)pumpsaremore

efficientthanairdrivendiaphragmpumps.

• Openblowing,mixing

- Open-blowingapplicationswastecompressed

air.Forexistingopen-blowingapplications,

ablowerorafanorhighefficiencynozzles

canbeconsidered.

• Partscleaning,sparging,aspirating,atomizing

Low-pressureblowers,electricfans,brooms,

andhigh-efficiencynozzlesaremoreefficient

thancompressedair.

• Idle,andnotusedequipment

- Putanair-stopvalveatthecompressedair

inlet.Disconnectairsupplytoequipment.

Beforedecidingtoreplacealow-pressureend

userwithanalternativesource,itisimportantto

determinetheminimumpracticalpressurelevel

requiredfortheapplication.

Ifmostofyourequipmentuseslow-qualityairwhile

afewpiecesofequipmentrequirehighquality,

process,butthesumoftheaverageairconsumption

ofeach.Trytoavoidpeakconsumptioncoincide.

Oversizingleadstoadditionalenergylossdue

toloweryieldsatpartialload.Plantswithwide

variationsinairdemandneedasystemthatoperates

efficientlyunderpartload.Insuchacase,multiple

compressorswithequencingcontrolsmayprovide

moreeconomicaloperation.Plantswithaflatter

loadprofilecanusesimplercontrolstrategies.

4.6 Check Air quality

Highqualityairismoreexpensivetoproduce.

Knowingtheproperairqualitylevelrequiredfor

successfulproductionisanimportantfactorin

containingcompressedairenergyandother

operatingcosts.Airqualityisdeterminedbythe

airdrynessandcontaminantlevelrequiredbyend

users.Separators,filters,dryersandcondensate

drainsareusedtoimprovecompressedairquality.

Overtreatingairbeyondtherequireddrynessand

allowablecontaminantlevelwastesmoneyand

energy.

Equipmentmaintenanceisalsoimportantfor

sustainingthedesiredairqualitylevels.Poorair

qualitycanhaveanegativeeffectonproduction

equipmentandcanincreaseenergyconsumption

andmaintenanceneeds.

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4 | Energy saving measures

4.11 Review the Compressor Control System

Therearedifferenttypesofcontrolsystemsavailable

forcompressors.Theexistingcontrolmaynotbethe

mostefficientmethod,orthecompressormayhave

nocontrolsystematall.

Start/Stop

Thismethodofcontrolwillstartthecompressor

oncethepressuredropsbelowacertainleveland

stopitoncethedesiredpressurehasbeenreached.

Thismethodisnotpreferredwhenthereisafrequent

increaseindemand.

4.9.3 Leakage SurveyLeakscanbecheckedandmaintainedbyconduction

aleakagesurveyregularly.

4.10 Select efficient compressor

Optimizingandupgradingthecompressorshould

alsobeconsideredwhenlookingatimprovingthe

efficiencyofthecompressedairsystem.InTable2

comparisonofcompressortypeswithrespectto

energysavingisrepresented.

itmaynotbenecessarytohavetheentireairflow

filteredtothehighestlevelofairquality.

Dryers

Dryersshouldbesizedforthemaximumanticipated

rateofflowandmustbematchedtotheairquality

requirements.Overdryingwastesenergy.

Drainvalves

Thelongerdrainsremainopen,evenpartlyopen,

themorecompressedairislostfromthesystem.

Replacemanual,discandtimeddrainswithnew

electroniclevelsensingdrainstoreducetheamount

ofwaste.

CondensateTraps

Trapsshouldallowremovalofcondensate,butnot

compressedair,andshouldnotbeleftopen.Regular

checkoncondensatetrapsisadvisedtoseethey

functionsgoodornot.

Receiver

Whenareceiveristoosmall(e.gduetothecapacity

expansion)forairdemandneeds,thecompressor

willstartandstopmorefrequently.Eachstart/stop

givesadditionallosses.Byimprovingtheabilityof

storagetomeetdemand,start/stopfrequencycan

beminimized.Inanexistingsystem,therearetwo

thingsthatcanbedonetoimproveairstorage:

• Installalargermainreceiverfortheentire

system.

• Installsecondaryreceiversnearequipmentthat

willrapidlyincreaseitsdemandforcompressedair.

Compressor Reciprocating Screw Vane Centrifugal

Efficiency(kW/m3/min)

7.8-8.5 6.4-7.8 5.8-7

Advantage • Alsosuitablefohighpressures(>13bar)

• Canberelativelysmallsizeandweight

• Smallerinitialcost• Simplemaintenance

procedures• Efficientmulti-stage

compressionavailable

• Simpleoperation• Lowertemperatures• Lowmaintenance7

investmentcosts• Quietandcompact• Vibrationfree• Commerciallyavailable• Variablespeedunitswith

relativelygoodturndown

• SimpleoperationLowertemperatures

• Quiet• Lowmaintenance

• Energyefficient• LargeCapacity• QuietHighair

quality

Disadvantage • Highnoiselevels• Highmaintenancecost• Suitableforsmaller

systems• Requiresstrong

foundation• Highoilcarryoverwhen

won

• Highenergyuse• Lowairquality• Loseefficiencyrapidlyat

partialload

• Onlysuitableforlowpressure

• Lowairquality

• Highinitialcost• Inefficientat

lowcapacitySpecializemaintenance

• Onlywater-cooledmodelsavailable

Tabel 2: Overview of the saving measures

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arenowofferingfactory-fitted,variable-speed

units.Theseallowthemotortoberunattherate

requiredinordertofulfilldemandatthattime.

However,variablespeeddrivesshouldonlybefitted

incaseswhereairdemandvaries.Usingavariable-

speeddriveforacompressorthatrunsatfullload

constantlywillconsumemoreenergy.Alternativeis

toinstallonevariablespeedunit,withtwoormore

baseloadunitstosaveoncapitalcost.

4.12 Peak Shaving

Peakshavinghastobeconsideredtogetherwiththe

compressorcontrolstrategyandcompressorsizes.

Whenacompressorisrunningatno-loadoperation

itstillconsumes20-35%oftheenergy.Oneofthe

possibilitiestopreventno-loadoperationispeak-

shaving.Thiscanbedonebyschedulingproduction

orinstallingabuffer.

4.13 Use multi-stage compressors

Multiplestagescanbeusedtoimprovetheefficiency

ofscrewandcentrifugalcompressors.Additional

coolingcanbeplacedbetweenthestagestofurther

increasetheefficiencyofthesecondstage.

4.14 Combine compressed air systems

Sometimemultiplecompressedairsystemsexist

onsite.Combiningsystemscanhavevarious

benefitssuchaspeakshaving,moreoptimaluseof

compressors,bettercontroletc.

Howeveritalsocanturnouttobeunfavorablefor

examplewhenmultiplepressurelevelsareusedand

afterthechangealltheairhastobeproducedatthe

highest.

4 | Energy saving measures

Load/Noload

Usingthismethod,thecompressorwillchargethe

systemtothedesiredpressure,thenthecompressor

motorwillcontinuetorunatconstantspeedwhile

thecompressoractionisdisengaged.Atconstant

speedthemotorcanusebetween20and35%offull

loadpower.

Throttling

Thismethodisonlyenergyeffectivewithscrewor

vanecompressorsthatrunat70%loadorabove.

Variable-speedscrewcompressors

Variable-speedscrewcompressorscontrolthe

motorspeedwhilstkeepingtheslidevalvetothe

compressorfullyopentomeetfluctuatingair

demand.

Otherenergyefficientcontrolwaysare;slide

vale(internalaircirculation),pistoncylindersfor

reciprocatingcompressors,andinletguidevanes

forcentrifugalcompressors.Dependingontheload

profile,theadditionofvariablespeeddrivesand/

oranother(differentlysized)compressorcanbe

consideredtosaveconsiderableamountsofenergy.

Variablespeeddrivescanbefittedtothemotorsof

screwandvanecompressors,andmostsuppliers

www.vnci.nlSource: AkzoNobel