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PRODUCTIONOPERATIONSCOMPETENCYLEARNINGMODULE
Module7:
GasMeasurement
No. #:
Category: Operations Production
Version: 01
Date: February 2009
Initial Writing by: Sardjono
Review by: Kodeco Operations Team
Copyright to: KODECOENERGYCO.,LTD.
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GASMEASUREMENT
ORIFICEMETERMEASUREMENT
Tomeasure volume of vapor/gas or liquid commonly use differentialmeasurement device, orifice
meter.
Definitions:
DifferentialTaps:Formeterusingflangetapsthecenteroftheupstreampressuretapisplacedoneinchfromtheupstreamfaceoftheorificeplate.Thecenterofthedownstreampressuretap isplacedone inch from the downstream face of the orifice plate. Formeters using pipe tap the upstream
pressuretapisplacedtwoandonehalftimestheactualinsidepipediameterfromtheupstreamfaceof
theorificeplateandthedownstreampressuretapisplacedeighttimestheactualinsidepipediameter
fromthedownstreamfaceoftheorificeplate.
DifferentialPressure :Differentialpressure is thedifferencebetween twopressures.Thedifferentialpressureacrossandorificeinametertubeisthedifferencebetweenthepressureattheupstreamtap
before thegaspasses through theorificeand thepressureat thedownstream tapafter ithaspasses
throughtheorifice.
StaticorLinePressure :StaticPressure isusuallymeasuredbyacoiledmetal tubewitha flattenedcrosssection(apressurespring).Thepressureofthegasinthelineisadmittedtoandactsontheinside
of the tubeand theatmosphericpressureactsupon theoutsideof the tube.Therefore thepressure
springmeasures thedifferencebetween thepressure in the line and the atmosphericpressure.The
pressure inthe linemaybegreateror lessthantheatmosphericpressure.Thestaticpressuremaybe
takenfromeithertheupstreamorthedownstreampressuretap.
AbsolutePressure :AbsolutePressure is thepressure above the absolute zero,or aboveaperfectvacuum.Theatmosphericpressure isalwaysexpressedasanabsolutepressure. Ifthepressureofthe
gasinalineisgreaterthantheatmosphericpressure,theatmosphericpressureinpsiaisaddedtothe
gagepressureinpsigtoobtaintheabsolutepressureofthegasintheline.Ifthegagepressureis40psig
(aboveatmosphericpressure)and theatmosphericpressure is14.4psia, theabsolutepressurePf, is
54.4psia.
Tomeasurepressurebelowatmosphericpressurewithgagescalibratedininchesofmercuryvacuum.
Insuchcases it isnecessary toconvert thevacuum from inchesofmercury intopoundspersquare
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inchbymultiplyingbytheconversionfactor0.491;forexample,10inchesofmercuryvacuum=4.91
psig(10x0.491)belowtheabsolutepressureoftheatmosphere.
PressureBase:Thepressurebaseisthepressureatwhichthecubicfootistheunitofmeasurementaccordingtothecontract.Thebasicorificeflowfactorsinthispublicationwerecalculatedforapressure
baseof14.73psia.
AbsoluteTemperature :On theFahrenheit thermometerscale the temperature isexpressed in thedegreesaboveorbelowanarbitraryzero,which is32degreesbelowthefreezingpointofwater.The
absolute zero is 460 degrees below the zero of the Fahrenheit thermometer scale. The absolute
temperatureisthetemperatureabovetheabsolutezeroandisobtainedbyadding460degreestothe
readingof the thermometer. If the readingof theFahrenheit thermometer is60, thecorresponding
absolute temperature is60 added to460 or520 Fabsolute. If the reading is 20 F, theabsolute
temperatureis 20 F+460 For440 Fabsolute.
TemperatureBase :The temperaturebase is the temperatureatwhich thecubic foot is theunitofmeasurementaccordingtothecontact.Theorificeflowfactorsinthispublicationwerecalculatedfora
temperaturebaseconditionof520 Fabsolute(60 F).
SpecificGravity:Therealspecificgravityofagasistheweightofacubicfootofgascomparedtotheweightofa cubic footofdryairunder the samepressureand temperature condition. If the specific
gravityof gasis2.0,itistwiceas heavyasair,orifthespecificgravityofagasis0.6,itissixtenthsas
heavyasair.
Acorrectlyinstalledorificecanprovideanoverallaccuracywithinplusorminus2%.
Theorificemeterconsistsof staticpressureanddifferentialpressure recording gauges connected to
anorificeflangeororificefitting.
Theorificemetertube(meterrun)consistsofupstreamanddownstreamsectionofpipe.
Theorificeplateisheldperpendiculartoflowbyflangesorfitting.Borecircumference,edgesharpness.
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ORIFICEFITTING
(3TypesofOrificeFitting)
StandardOrificeFlange. Requirethatthelineneedtobeshut down and depressurized inordertoinspectorchangetheorificeplate.
Single Chamber Orifice Fitting. This fitting also requires that the line be shut down anddepressurizedinordertoinspectorchangethe orificeplate.
SeniorOrificeFitting.Thisfittingallowstheremovalandinspectionofanorificeplatewhilethelineremainsunderpressure.
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ORIFICEPLATE
Thethicknessoftheorificeplatefor2 inchthrough10 inchnominaldiameterpipeshallbeat
least0.115in.,for12inpipeshallbeatleast0.175in.
Theupstreamfaceoftheorificeplateshallbeflatandperpendiculartotheaxisofthemeter
tube,wheninposition betweentheorificeflangesorintheorificefitting,squareand sharp,
shallnothaveaburredorfeatherededgeandshallbe maintainedinthisconditionatalltimes.
Thethicknessoftheorificeplateattheorificeedgeshallnot exceedthesmallerof:
a.1/50ofthepipediameterD
b.1/8oftheorificediameterd
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BETARATIO (d/D).
Theorificetometertubediameterratio, ,beta=d/D,shouldbelimitedasfollows:
a.Withmetersusingflangetaps,betashallbebetween0.15and0.70
b.Withmetersusingpipetaps,betashallbebetween0.20and0.67
Whenusingtheabovebetaratio,thetoleranceoftheorificecoefficient(Fbfactors)isplusor
minus0.5%forflangetapsandplusorminus0.75%forpipetaps.Betaratiosdownto0.10andupto0.75maybeusedforflangetapsbutthecoefficienttoleranceincreases.Betaratiosdown
to0.10andupto0.70maybeusedforpipetapsbutthecoefficienttoleranceincreases.
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METERTUBE
TheMeterTubemean thestraightupstreampipeof thesamediameter (of lengthAandA)
betweentheorificeflangesorfittings,andthesimilardownstreampipe( lengthBbeyondthe
orifice).
Thesectionofpipetowhichtheorificeflangesareattachedshallcomplywiththefollowing:
a. Seamless pipe , the pipewallsmay be honed,machined, or ground. Thewall finish
shouldsimulatethatofnewsmoothpipe.
b. Grooves,scoring,pits,raisedridgesresultingfromseams,distortioncausedbywelding
whichaffecttheinsidediametershallnotbepermitted.
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STRAIGHTENINGVANES
Thepurposeofstraighteningvanes istoeliminateswirlsandcrosscurrentssetupbythepipe
fittingsandvalvesupstreamofthemetertube.
Theconstructionofvanesthemaximumtransversedimensionaofanypassagethroughthe
vanesshallnotexceedthe insidediameter,Dof thepipe.ThecrosssectionalareaAof
anypassagewithintheassembledvanesshallnotexceed1/16 of the crosssectional area of
thecontainingpipe.ThelengthLofthevanesshallbeatleast10timesthelargesinsideadimension.Allthe vanespassagesisnotnecessarythesame sizebutshouldbesymmetrical.
Thevanestubeshouldbesecurelyweldedtogetherateachtangentpoint.Allweldmetalshould
begroundoffsmoothtopreventdisturbancestotheflowandshouldbesecurelyanchored in
themetertubebyuseof aflangeringorsetscrews.
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GASMEASUREMENT.
Inthemeasurementofgasbyorificemeter,thechartcontainsrecordsofthedifferentialandthestatic
pressure.Fromtheserecordsthequantityofgasmeasuredisdeterminedbytheuseoftheformula:
Qh = C ,inwhich
Qh = rateofflowatbaseconditionincu.Ft.perhr.
C = orificeflowconstant.Itistherateofflowincu.Ft.perhr.atbaseconditionwhenthe
Pressureextension =1.000
hw = differentialininchesofwater.
Pf = staticpressureinpsia.
= pressureextension
C=FbxFrxYxFpbxFtbxFtfxFgxFpvxFmxFaxF
Fb : basicorificeflowfactor
Fr : Reynoldsnumberfactor
Y : expansionfactor
Fpb : pressurebasefactor
Ftf : flowingtemperaturefactor
Fg : specificgravityfactor
Fpv : supercompressibilityfactor
Fm :manometerfactor(formercurytypemetersonly)
Fa : orificethermalexpansionfactor
F : gagelocationfactor
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Note :Fororificeconstantfactor,pleaseseetableonpage1through62oforificeconstant
factor.
BasicOrificeFlowfactor,Fb :Theorifice factor isbasedupon theconditions :pressurebase,Pb=14.73 psia; temperature base, Tb = 60F (520 F absolute); specific gravity, G = 1.000; flowing
temperature,Tf=60F.(520Fabsolute);andunderconditionswheretheReynoldsnumberisinfinite
andexpansionfactorisunity.Thevalueofthisfactordependsonupon:thelocationofdifferentialtaps;
thediameteroftheorifice,d;andupontheinternaldiameterofthepipe,D.
TableofFbareshownonpage2through4forflangetaps.
ReynoldsNumberfactor,Fr:TheReynoldsnumberfactortakes intoaccountthevariationsofthedischarge coefficient of an orifice with Reynolds number. The discharge coefficient of the orifice
decreasesas theReynoldsnumber increasesuntil theReynoldsnumber infinite,when thedischarge
coefficientwillhavethe leastpossiblevalueforthatparticular installation.Dischargecoefficientsvary
considerablywithReynoldsnumber inthemeasurementofviscousliquids;theytendtobecomemore
constant as the viscosity of the liquid decreases, and as the Reynolds number correspondingly
increases.Withinthelimitsofcommercialmeasurementofgases,thedischargecoefficientispractically
constant, varying only slightly with Reynolds number. The variation is sufficiently slight, and the
viscositiesofcommercialgasesaresufficientlyconstant towarrantarbitrarilyusing theaveragevalue
forthegasviscosity incomputingReynoldsnumberfactors.Forallpracticalpurposes,this leavesthe
Reynoldsnumber factorasa functionof theorificeandmeter tubedimensions, the locationof the
differentialpressuretaps,andtherateofflow afunctionofthepressureextension, .
When gaseswith other characteristics are to bemeasured, the ReynoldsNumber factor should be
adjustedasfollows:
(Fc), Fc=5124 ,whereistheabsolutevicosityinlb/ftsec
TablesofbvaluesfromwhichtheReynoldsnumberfactorcanbereadilyobtainedareshownonpage
10through15forflangetaps,andpages32through37forpipetaps.
ExpansionFactor,Y:Whenagasflowsthroughanorifice,thechangeinvelocityandpresureisaccompaniedbyachangein
specificweightandafactormustbeappliedtothecoefficienttoallowforthischange.Theexpansion
factordependsupon the locationof thedifferentialpressure taps, the locationof thestaticpressure
tap,andtheratiooftheorificediametertothediameterofthemetertube.Itisalsodependentupon
theratioofdifferentialpressuretostaticpressureanduponofspecificheatsfortheflowinggas.The
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variationofthefactorisslightandtheratioofspecificheatsforcommercialgasesissufficientlyconstant
towarrantusinganassumedconstantratioofspecificheats.Anassumedratioofspecificheatsofk=1.3wasused incalculating theexpansionfactors inA.G.AReportno.3andthispublication (SingerOrifice
MeterConstantHandbook).Thispermits tabulationof the factorsaccording to thediameter ratio,,
andtheratioofdifferentialpressuretostaticpressure,hw/pf.Inthetablespfisindicatedaspforpf
dependinguponwhetherthestaticpressureisobtainedfromtheupstreamtaporfromthedownstream
tap.
Whengasesbeingmeasuredhaveasignificantlydifferentratioofspecificheats thanthevalueof1.3
assumed inReportNo.31969, thedesirabilityofusingadjustedYvaluescanbedetermined from the
following:
AdjustedvalueofY = )
AdjustedvalueofY =Y )
Tablesofexpansionfactorsareshownonpages17through20forflangetaps.
Pressure Base Factor, Fpb : The orifice factorswere calculated to give gas volumes at a basepressure,pb,of14.73psia. Ifthemeasurementatanyotherbasepressure isdesired,thenapressure
basefactormustbeapplied. Thesefactors,andtheequationrepresentingthefactors,areindicatedon
page16.(Fpb=14.73basepressure,psia.).
TemperatureBaseFactor,F tb :Theorifice factorswere calculated togivegasvolumesatabasetemperature,Tb,of60F.(520F.absolute). Ifmeasurementatanyothertemperaturebaseisdesired,
then a temperature base factormust be applied. These factors, and the equation representing the
factors,areindicatedonpage16.(Ftb= )
Flowing Temperature Factor, Ftf : The orifice factorswere calculated, assuming that the gas isflowingthroughthemetertubeatatemperature,Tf,of60F.(520F.absolute).Ifmeasurementistobe
made at any other flowing temperature, then a flowing temperature factormust be applied. These
factors,andtheequationrepresentingthefactor,areindicatedonpage21.
Ftf =
SpecificGravityfactor,Fg: Theorificefactorswerecalculatedtogivegasvolumesbasedupontheflowinggashavingaspecificgravity,G,of1.000.Forgaseshavingaspecificgravityotherthan1.000a
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specificgravity factormustbeapplied.These factors,and theequation representing the factors,are
indicatedonpage16.Fg =
SupercompressibilityFactor,Fpv:Thesupercompressibilityfactoraccountsfordeviationfromidealgaslaw.Inthebasicflowequations,gasvolumesareassumedtovarywithpressureandtemperature
in accordancewith Boyles andCharles laws ( the ideal gas laws).Actually the volume occupiedby
individualgasesdeviate,byaslightdegree,fromthevolumeswhichtheidealgas laws indicate.The
amountofdeviationisafunctionofthecompositionofthegasandvariesprimarilywithstaticpressure
andtemperature.Theactualdeviationmaybeobtainedbyalaboratorytestconductedonasampleof
thegas,carefullytakenatlineconditionsofpressureandtemperature.
Practicalrelationshipshavebeenestablishedbywhichthisdeviationcanbecalculatedandtabulatedfor
natural gases containing normalmixtures of hydrocarbon components, considering the presence of
smallquantitiedofcarbondioxideandnitrogenandalsorelatingthedeviationtotheheatingvalueof
thegas.
TheA.G.AmanualfortheDeterminationofSupercompressibilityFactorsforNaturalGasshouldbeused
fordeterminationofthefactorFpv.ThevalueofthesupercompressibilityfactorFpvcanbedetermined
fromtablesonpages44through58. Illustrativeexamplesare includedwiththesetablestoclarifythe
methodbywhichthesefactorsareobtained.
ManometerFactor,Fm : Themanometerfactor isusedwith themercurytypedifferentialgagetocorrecttheslighterror inmeasurementcausedbytheweightoftheunbalancedcolumnofdensegas
above the mercury. This factor is not applicable where measurement is made with bellowstype
differentialgagessincethereisnounbalancedcolumnofdensegasinamanometerofthattype.Atable
ofmanometerfactorsisshownonpage21.
Orifice Thermal Expansion Fator, F a : The thermal expansion factor is used to adjust for thedeviationoforificediameter,fromthatofitsmanufacture,withextremetemperaturechange.Withina
temperature rangeof0Fto120F, thisdeviationordinarily isnogreater than tolerancesassigned to
orifice platemanufacture. Therefore, it is recommended that thisfactor be ignored in natural gas
measurement. The thermal expansionfactor is usually appied to steam and high temperature liquid
measurement.A tableof thermalexpansion factors forstainlesssteelandmonelorifices isshownon
page22.
GageLocationFactor,F l: Thegagelocationfactoris included inordertoadjustforlocationotherthan45latitudeandsealevel.Atableoflocationfactorsisshownonpage22.
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EXAMPLES
DETERMINATIONOFTHEORIFICEFACTOR,FbThevalueoftheorificefactor,Fb,isexpressedbytheformula:
Fb=338.17Kod,inwhich
338.17 = constant formeasurementwhen the pressure base is 14.73 psia, the temperature
basis60F,theflowingtemperatureis60F,andthespecificgravityis1.000.
Ko =dischargecoefficientwhentheReynoldsnumberisinfinite.
d =diameteroforificeininches.
When theorifice factor is tobe determined for ameter tube of standard internal diameter and an
orificeofevensizethevalueofthebasicfactorcanbefoundfromtablescontainedonpages2through
4forflangetaps,andonpage24through26forpipetaps.
Example:Ifa2.375inchorificeisusedwithflangetapsina9.564inchI.D.line,theorificefactor,Fbis
foundfromthetableonpage3 tobe1140.1.
Intheformula,Fb=338.17Kod,thedischargecoefficientKoforanygivenvaluefor,variesslightly
withthesizeoftheline.Theorificefactorforvarioussizesoforificesandforthelinesizesnotgivenin
thetablescanbecomputedbytheuseofthetablesonpages5through9forflangetaps,andonpages27through31forpipetaps.
Thebasic empirical equations fromwhich valuesof Ko are calculated arequite complex. Itwas felt
desirable todevelopamethodbywhichorifice factorscouldbedeterminedwithout resorting to the
basicequations.
Inordertodothis,theformulafortheorificefactorisconvertedto:
Fb=FFddinwhich
F =338.17Kofor4.026inchline.
Fd =factorforconvertingKofor4.026inchlineforacertainvalueof,intoKofor the
samevalueof,forothersizeoflines.
d =diameteroftheorificeininches.
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Fb=FxFdDinwhich
Fx =338.17Ko fora4.026inchlineorFx= F
Fd =factorforconvertingKofor4.026inchlineforacertainvalueof,intoKofor the
samevalueof,forothersizeoflines.
D =internaldiameterofthepipeininches.
Example : Ifa3.800inchorifice isusedwithpipe taps ina line7.981 inches indiameter,=3.800
7.981=0.47613.Refferingtopage31,
For=0.477, Fx=54.994
For=0.476, Fx=54.713
Byinterpolation,for=0.47613;Fx=54.749
Seepage29,for =0.476andD=7.981;Fd=0.9999
ThenFb=54.749x0.9999x7.981=3487.0
DETERMINATIONOFPRESSUREBASEFACTOR,FpbUsing the table on page 16 for apressurebase of 14.65psia thepressure base factor, Fpb,willbe
1.0055.Tocomputeapressurebasefactor,Fpb,foranyvalueofpressurebasenotshown,thefollowing
relationshipcanbeused:
Fpb= ,where: Pb=therequiredcontractpressurebaseinpsia.
Ifthecontractpressurebaseis14.65psiathenthepressurebasefactorequal
Fpb= =1.0055
DETERMINATIONOFTEMPERATUREBASEFACTOR,FtbTochangetoanybasetemperatureotherthan60 F,thetableonpage16maybeused.Iftherequired
contracttemperaturebaseis70 F,thenfromthetablethetemperaturebasefactorFtb=1.0192.Ifthe
contracttemperaturebaseisnotshowninthetablethefactorcanbedeterminedfromtheexpression:
Ftb= ,where: Tb=theabsolutetemperaturebasespecifiedbythecontract,(460+ F).
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Using70Fasrequiredcontracttemperaturebase,thetemperature basefactor,
Ftb= ,=1.0192
DETERMINATIONOFSPECIFICGRAVITYFACTOR,FgThespecificgravityfactor,Fg,canbedeterminedfromthetableonpage16.Ifthespecificgravityisnot
foundinthistablethenthefactorcanbedeterminedfromtheexpression:
Fg = ,where:G=specificgravityoftheflowinggas,air=1.000
Example: Ifthespecificgravityoftheflowinggasis0.450,thenthespecificgravityfactor,
Fg = =1.4907
DETERMINATIONOFFLOWINGTEMPERATUREFACTOR,FtfWhen the flowing temperature of the gas beingmeasured is something other than 60 F a flowing
temperaturefactor,Ftf,mustbeapplied.Foraflowingtemperatureof146 Fafactorof0.9263canbeobtainedfromthetableonpage21.Ifthetemperatureoftheflowingfluidisnotshowninthetablethe
factorcanbedeterminedfromtheexpression:
Ftf = ,where: Tf=actualflowingtemperatureindegreesFabsolute,(460+ F).
Iftheactualflowingtemperatureis146 FthenFtf = =0.9263
DETERMINATIONOFREYNOLDSNUMBER FACTOR,FrWhentheReynoldsnumberfactor,Fr, isrequiredusingastandardsizepipeandanevensizeorifice,
thisfactorcanbedeterminedusingthebfactorsonpages10through12forflangetaps,andpage32
through34forpipetaps.
Example : If an 8.000inch orifice is used in a 19.000inchmeter tube, and the average extension,
, is 115, using flange taps, the Reynolds number factor, = =
1.0001.
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DETERMINATIONOFEXPANSION FACTOR,YValuesofexpansionfactor,Y,arecontainedinthetablesonpages17through20forflangetapsandon
pages38through41forpipetaps.Sincetheexpansionfactordependsuponthepointwherethestatic
pressuretapsislocated,twotablesofexpansionfactorsforflangetapsarerequired:Y,forupstream
static pressure and Y, for downstream static pressure. For expansion factor using pipe taps, two
additionaltablesareprovided:Y,forupstreamstaticpressure,andY,fordownstreamstaticpressure.
Example:Usingflangetaps,withadifferentialof53inchesandwithastaticpressureof264.4psia(250
psig)observedatthedownstreamtap;= = =0.20.Ifthevalueof is0.40,thepropervalueof
theexpansionfactorcanbeobtainedfromthetableonpage19.Y=1.0013
DETERMINATIONOFSUPERCOMPRESSIBILITY FACTOR,FpvThevalueofthisfactorcanbeevaluatedfromthetableslistedanddescribedonpages44through58.
It is recommended that theappropriatealternatemethoddeterminingadjusting factorFpandFT,be
usedforgasmixturesexceedingaspecific gravityof0.75.Forgasmixturesexceedingaspecificgravity
of1.00,itisrecommendedthatcompressibilitytestsberuntodeterminethesuitabilityofapplyingthe
standardoranalternatemethod.Thediluentcontentofanygasmixturetowhichthemethodistobe
appliedshouldbe limitedto15mol.percentcarbondioxideand15mol.percentnitrogen,andactual
testsarerecommendedfordiluentcontentexceedingthesequantities.
Thespecificgravity,carbondioxideandnitrogencontents,inconjunctionwiththeflowingpressureand
temperature,areusedtodeterminetheadjustingpressureandtemperaturenecessaryforrelatingany
gas to the supercompressibility data of the 0.600 specific gravity, hydrocarbon gas. The adjusted
pressureisobtainedbymultiplyingthegagepressureoftheflowinggasbythepressureadjustingfactor
Fp,and theadjusted temperature isobtainedbymultiplying theabsolute temperatureof the flowing
gasbythetemperatureadjustingfactorFTandsubtracting460fromthisproduct.AdjustingfactorFp
andFTarecalculatedasfollows:
WhereKpisthediluentpressureconstant,Kp=Mc0.392Mnand
WhereKTisthediluenttemperatureconstant,KT=Mc+1.681Mnand
G=specificgravity;Mc=Mol.Percentcarbondioxide;Mn=Mol.Percentnitrogen.
Adjustedpressure=PfFppsig;adjustedtemperature=TfFT 460 F
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After the adjusted pressure and the adjusted temperature are determined, the supercompressibility
factorFpvcanbefoundintableA(page44through58)usingtheadjustedvalues.
TablesB (page59 through 60) andC (page 61 through62) give the valuesof Fpand FT for specific
gravities between 0.550 and 1.000 and appropriate ranges of the diluent constants. In the ranges
coveredbythesetables,conditionsmaybeindicatedwhichwouldneverexist;however,incommercial
measurementtheuseoftheseareaswillseldomoccur.
ThefollowingexampleillustratestheAGAspecificgravitymethodofcalculatingthesupercompressibility
factorFpv.
Example :Assumeagashavinga specificgravityof0.570, zeropercent carbondioxideand1.1mol.
Percentnitrogen,atapressureof370psigand65 F.
Pressureconstant:Kp=00.392(1.1)= 0.431
Referring to Table B, the pressure adjusting factor, Fp, for G = 0.570 and Kp = 0.431 is found by
interpolationas:Fp=1.0014.
Temperatureconstant:KT=0+1.681(1.1)=1.849
ReferringtoTableC,thetemperaturearenowcalculatedfrom:
Adjustedpressure=PfFp=370(1.0014)=370.5psig
Adjustedtemperature=TfFT460=525(1.0376)460=84.7 F
ReferringtoTableAandusingtheadjustedpressure (370.5psig)andadjustedtemperature (84.7 F),
thesupercompressibilityfactor,Fpvisfoundbyinterpolationas:Fpv=1.0254
DETERMINATIONOFTHEMANOMETER FACTOR,FmThis factor isusedwithmercurytypemeterswhere thegas comes in contactwithmercury surfaces.
Thisfactorcanbeobtainedfromthetableonpage21.
DETERMINATIONOFTHETHERMALEXPANSION FACTOR,FaThisfactormaybeusedwhenflowingtemperatureareoutsidethelimitsof0 Fto120 Fandcanbe
obtainedfromthetableonpage22.
DETERMINATIONOFTHEGAGELOCATION FACTOR,FlThisfactor isspecificallyapplicabletothemanometer.Thisfactor isrepresentedbythetableonpage
22.
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CALCULATIONOFORIFICECONSTANT,CThevalueoftheorificeconstant,C,correspondstotheexpression:
C=FbxFrxYxFpbxFtbxFtfxFgxFpvxFmxFaxFl
In the following examples the conditions ofmeasurement and some of the calculations are
givenontheleft.Thefactorsrequiredtoobtaintheorificeconstant,withcorrespondingpage
references,aregivenontheright.
Example1.
ConditionAtMeter ValueOffactor
MeterequippedwithPipeTaps AndReferencePage
d=diameteroforifice=3.000inches
D=internaldiameterofmetertube=7.981inches.. Fb=2012.7 24
Staticpressureobtainedatupstreampipetap
Averagedifferential=64.5inches
Averagestaticpressure=539.4psia(525psig)
=3.0007.981=0.38
=pressureextension(average)=187.
Seepage36.For =0.38 andD=7.981;b=0.0214
Fr=1+(0.0214187)Fr=1.0001 36
Differentialratio,hwPf=64.5539.4=0.12
Seepage38.For=0.38andhwPf=0.12.. Y =0.9983 38
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Pb=pressurebase,4oz,above14.4=14.65psia. Fpb=1.0055 16
Tb=temperaturebase=60 F. Ftb=1.0000 16
Tf=flowingtemperature=60 F Ftf=1.0000 21
G=specificgravity=0.64. Fg=1.2500 16
Itisassumedinthisexamplethatthesupercompressibility factor
isnotused,bytermsofcontract.
Manometerfactor. Fm=0.9989 21
ThenC=2012.7x1.0001x0.9983x1.0055x1.0000x1.0000x1.2500x0.9989=2522.9
Foranaveragepressureextension, = =186.52,theflowratewouldbe
Qh=C =2522.9x186.52=470,570cu.Ft.perhr.
Example2.
ConditionAtMeter
ValueOffactor
MeterequippedwithFlangeTaps AndReferencePage
d=diameteroforifice=4.200inches
D=internaldiameterofmetertube=9.800inches
=4.2009.800=0.42857;interpolatingforFfromthetable,
page5,F=206.87
Interpolatingfromthetable,page7,Fd=0.9992
Fb=FxFdxd=206.87x0.9992x4.200. Fb=3646.3
Staticpressureobtainedatdownstreamflangetap
Averagedifferential,hw=55.0inches
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Averagestaticpressure,Pf=1523psia(1510psig)
=pressureextension(average)=290.
Seepage14,interpolatingfor =0.43andD=9.800,b=0.0227
=1+0.0227290 Fr=1.0001 14
Differentialratio,hwPf=0.04
Seepage19,interpolatingforhwPf=0.04and=0.43.. Y =1.0002 19
Pb=pressurebase,10oz,above13.0=13.625psia
Fpb=14.7313.625 . Fpb=1.0811 16
Tb=temperaturebase=50 F. Ftb=0.9808 16
Tf=flowingtemperature=70 F Ftf=0.9905 21
G=specificgravity=0.68.. Fg=1.2127 16
Supercompressibility,asdeterminedbyanactualtestfactor
Onasampleofgas .. Fpv=1.1130
Manometerfactor... Fm=0.9957 21
ThenC=3646.3x1.0001x1.0002x1.0811x0.9808x0.9905x1.2127x1.1130x0.9957=5148.3
Foranaveragepressureextension, = =289.42,theflowratewouldbe
Qh=C =5148.3x289.42=1,490,000cu.Ft.perhr.
Example3.
ConditionAtMeter ValueOffactor
MeterequippedwithFlangeTaps AndReferencePage
d=diameteroforifice=3.500inches
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D=internaldiameterofmetertube=6.065inches.. Fb=2654.9 2
Staticpressureobtainedatdownstreamflangetap
Averagedifferential=52.5inches
Averagestaticpressure=562.7psia(548psig)
=3.5006.065=0.577
=pressureextension(average)=171.877
Seepage10.For =0.577 andD=6.065;b=0.0426
Fr=1+(0.0426171.877) Fr=1.0002 10
Differentialratio,hwPf=52.5562.7=0.093
Seepage19.For=0.577andhwPf=0.093. Y =1.0006 19
Pb=pressurebase,14.7psia.. Fpb=1.0020 16
Tb=temperaturebase=60 F. Ftb=1.0000 16
Tf=flowingtemperature=120 F Ftf=0.9469 21
G=specificgravity=0.74. Fg=1.1625 16
Supercompressibilityfactor,N2=0.0856Mol.%,CO2=0.6087Mol.%
Thisfactorwouldbecalculatedinaccordancewiththeformulabelow:
Kp=Mc0.392Mn=0.60870.392(0.0856)=0.60870.03355=0.57515
=1.0102
KT=Mc+1.681Mn=0.6087+1.681x0.0856=0.7526
=0.8867
Adjustedpressure=PfFp=562.7x1.0102=568.43psig.
AdjustedTemperature=TfFT460=580(0.8867)460=514.286460=54.286 F
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ReferringtoTableAandusingtheadjustedpressure(568.43psig)andadjustedtemperature(54.286
F),thesupercompressibilityfactor byinterpolationas:. Fpv=1.04948 44
ManometerfactorFmandFl isneglected(notmercurytypemeter)
Areafactor,Fa(flowingtemperature120 F):.. Fa =1.0010 22
ThenC=2654.9x1.0002x1.0006x1.0020x1.0000x0.9469x1.1625x1.04948x1.0010=3078.7084
Foranaveragepressureextension, = =171.877,theflowratewouldbe
Qh=C =3078.7084x171.877=529,159.1636cu.Ft.perhr.(12,699,819.9280cu.Ft.perday).
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ExampleofGasAnalyzeReport:
INSTITUT TEKNOLOGI SEPULUH NOPEMBER SURABAYALEMBAGA PENELITAN DAN PENGABDIAN PADAMASYARAKAT
GAS COMPOSITION ANALYSIS
SPESIFIC GRAVITY AND CALORIFIC VALUE CALCULATIONS
Sample : BW
Date of Sampling : July 28, 2008 at 17.00 Opening Condition :
Pressure : 548 Psig - Opening Press : 548 psig
Temperatur : - Opening Temp : 120oF
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