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