1. Muhammad Usman Saeed
E-III Visbreaking& Gas Concentration Unit
Email:ing.usmansaeed@gmail.com
Pak ArabRefineryLtd| QasbaGujrat MehmoodKot DistrictMuzaffarGarh
DRAFT GAUGES AND ARCH PRESSURE
INSTRUMENTATION SENSING LINE
PLUGGING PROBLUM

2. PAK ARAB REFINERY LTD Department: Process
Visbreaking& Gas ConcentrationUnit Area: 200 (U – 130 & 411)
Muhammad Usman Saeed – 5509
TABLE OF CONTENTS
1 Introduction....................................................................................................................... 1
2 Draft Instruments as per Standard....................................................................................... 1
2.1 Firebox Pressure Control.............................................................................................. 1
2.2 Low/High Draft............................................................................................................ 2
2.3 High Firebox Pressure..................................................................................................2
2.4 Low Firebox Pressure...................................................................................................2
2.5 SootBlowers................................................................................................................ 2
3 Draft Gauge 130-PI227ABC Specifications ............................................................................ 2
4 Possible Causes .................................................................................................................. 3
4.1 Steam......................................................................................................................... 3
4.2 Particulates................................................................................................................. 3
4.3 Water Contents...........................................................................................................3
4.4 Improper Impulse Piping Size....................................................................................... 3
5 Special Purging System .......................................................................................................3
5.1 Case I.......................................................................................................................... 3
5.2 Case II......................................................................................................................... 3
5.3 CASE III(Air Purging)....................................................................................................4
5.4 Chemical Seal for PT & PSHH switch ............................................................................. 5
6 Conclusions........................................................................................................................ 5
7 PARCO’s Forced Draft Fired Heater Draft Comparision.......................................................... 6
8 UOP Recommendation Regarding Heater Operations ........................................................... 6
9 Referneces......................................................................................................................... 6

3. PAK ARAB REFINERY LTD Department: Process – A200
Draft Gauge & Arch Pressure InstrumentationSensingLine PluggingProblem
Muhammad Usman Saeed – 5509 Page 1 of 7
1 INTRODUCTION
Furnace draft isdefinedasthe pressure inside of the heaterminusthe pressure outside of the heater
measuredatthe same elevation. Stackdampersandsecondaryairregistersaffectthe draftandbothadjustments
are related.The hotgas pushessothat the pressure isalwaysgreatestatthe firewall.The stackdraftpullsand
whencorrectlybalancedthe pressure atthe bridgewallshould be close tozeroorveryslightlynegative.A process
heateroperatingproperlywill alsohave azero,orslightlynegativedraft,atthe shieldsection.The fireboxwill be
slightlypositive(+0.5to +2.0 “water column(wc)) andthe stack will have arange of -0.5 to -1.0” wc.Excessive
draft,eitherpositivepressureornegative pressure,canleadtosevere problemsinthe convectionsection.
2 DRAFT INSTRUMENTS AS PER STANDARD
Draft isan importantmeasurementonall firedequipment.This
measurementisusedasa guide toproperheateroperation.Pressure
measurementsshouldbe made atthe outletof a forced-draftfan,across
the air preheater,inthe preheaterairductbefore the burners,inthe
firebox (nearthe burnersandatthe topof the radiant section),andacross
the damper.The pressure tapsusedfor control andheatershutdown
shouldbe separate anddedicated.Diaphragmtype gaugesare usedforlow
pressures.Drafttransmitterrange shouldbe sufficienttocoverunusual
conditionsandsensing linesdesignedtoresponse small changed.Purge
systemmaybe usedto preventplugging.
2.1 FIREBOX PRESSURE CONTROL
The fired-heaterpressure control systemshall control the fireboxpressuretomaintainitsdesired
setpointandtoavoidfirebox implosionsorexcessive pressures.Whenthe heaterhasaninduced-draftfan,itis
recommendedthatthe fireboxpressurebe maintainedbyautomaticallyadjustingthe induced-draftcontrol
damper,or inducedfanspeedutilizingafirebox pressure controller.
If an airpreheaterisused,fireboxpressurecontrol requiresfurtherconsiderationsrelatingtothe control
of fuel andcombustionairtomaintainthe heaterina stable operatingcondition.Shouldapreheaterorinduced-
draft fanmalfunctionoccur,orshoulda preheaterbe takenoutof service,the pressure control shouldbe
switched,eitherautomaticallyormanually,tothe stackdamper.Firebox pressure onheaterswithforced-draft

4. PAK ARAB REFINERY LTD Department: Process – A200
Draft Gauge & Arch Pressure InstrumentationSensingLine PluggingProblem
Muhammad Usman Saeed – 5509 Page 2 of 7
fansor natural-draftburner(s) maybe controlledbyautomatingthe stackdamper. Automaticoxygentrimcontrol
alsousesthe stack damperon natural-draftheaters;therefore,care mustbe exercisedtoavoidclosingthe
damperto the pointwhere the firebox pressure exceedssafe designlimits.
2.2 LOW/HIGH DRAFT
In natural-draftinstallationswhere lossof draft,inotherwords,positivepressure,mayoccur,a low-draft
alarm shouldbe provided.Low-draftconditionsmaycause backfiringthroughinletairregisters.A high-draft
alarm shouldbe providedif thisconditioncancause impropercombustion.
2.3 HIGH FIREBOX PRESSURE
A pressure alarmandtrip shouldbe consideredtoguardagainsthighfirebox pressure.
2.4 LOW FIREBOX PRESSURE
Whenthe possibilityexiststodamage the firebox asaresultof low firebox pressure(vacuum),suitable
alarmsshouldbe provided.
2.5 SOOTBLOWERS
Operationof sootblowerscanbe manual or automatic.Sootblowers,if requiredbythe qualityof the
fuel,are normallyprovidedinthe convectiontube banksof firedheaterstoprolongonstreamtime andmaintain
thermal efficiencybypreventingbuild-upof sootorotherforeigndeposits.Theymaybe fixed,rotary,or
retractable.Sootbloweroperationshouldbe automaticallysequencedtoreduce operatorinvolvement,to
preventfurnace overpressure,torestrictparticulate emissions,andtopreventsuddenlarge demandsonthe
steamsystem.Itmay be necessarytomanuallycontrol the firingof the heaterwhenusingthe sootblower.Soot
blowersshall be operatedonlywhenheatinputtothe furnace isat a rate highenoughtopreventa flameout
duringthe soot bloweroperation.
3 DRAFT GAUGE 130-PI227ABC SPECIFICATIONS

5. PAK ARAB REFINERY LTD Department: Process – A200
Draft Gauge & Arch Pressure InstrumentationSensingLine PluggingProblem
Muhammad Usman Saeed – 5509 Page 3 of 7
4 POSSIBLE CAUSES
4.1 STEAM
Atomizingsteam(mostlyused whengunburnerislightupwhichprevent
carbonizationof burnertip),sootblowersteamandpurgingsteam(usingwhile
cleaningof burnersgun) couldbe cause of pluggingof sensinglinesof instruments.
Steamdidn’tparticipate individuallybutmix withsoot/ashinfuel oil,burnerassembly
tiles&refectorymaterial andforma stickymixture whichhasabilitytoplugsensing
lines.
4.2 PARTICULATES
All fuelswillcontainorproduce particulates.Particulateswillbe formedingreaterquantitiesinfuel oils
(especiallyinheavyfuel oils) thaninfuel gases.Ashinthe fuel will be carriedoutthe stackas particulates.
Pyrolysisandpolymerizationreactionsmayproduce highlyviscousorsolidparticlesthatremainunburnedwhen
firingheavyfuel oils.These reactionscontributetothe quantityof the particulates.The asphaltene contentand
Conradson carbonnumberof a fuel oil canbe an indicationof the particulate formingtendencies.All particulates
do notcome fromthe fuel.Some maycome fromtube or fuel line scale aswell aserodedrefractory.Particulate
mattermay be entrainedwithinthe combustionairinsome locations.
4.3 WATER CONTENTS
Water contentsincombustionair(expressedashighhumidityinsummerseason) andincombustion
products(Highwhenthere ishighH2 contentsinfuel gas) alsomixedwithsolidparticlesinside furnace cause
pluggingof sensinglines. Duringheavyrainwaterentersfromstackside orany air leakentrance become cause of
plugging.
4.4 IMPROPER IMPULSE PIPING SIZE
Too small diameterandflatpipingarrangementalsocause of pluggingatdesignstages,if your
instrumentshasdustyorsmokyservice,thenpipingdiametershouldbe increaseandarrangementshouldbe
slopedtoletwaterplusparticlesfall undergravitytoblockvalve arrangement.
5 SPECIAL PURGING SYSTEM
5.1 CASE I
FollowCase Iispurposedpurgingscheme forfull of dustparticle service infurnace withCoal andFuel Oil
burning.Infollowingscheme purgingthe impulse tube constantlywithlow-pressure nitrogenandalsonitrogenat
regularintervalsusingsolenoidvalves. Purge the impulselinewithlow-pressure nitrogenconstantlysoasto
avoidchokingof the impulse lines.Alsoprovision made atregularintervalsusingasolenoidvalve that isoperated
by our PLCsystem.
5.2 CASE II
FollowCase IIisalsopurposedpurgingscheme forfull of dustparticle service infurnace withCoal and
Fuel Oil burning.Thisscheme ismanuallycontrolledunlikeCASEI.Pressure transmittersensorlocationis
adjustedsuchthat it make the furnace nozzle largerandinstall itwitha 45° slope. Italsouse a seal diaphragmon
the pressure transmitterandmake itan indicatingone,sothatthe operatorcan see the pressure withoutgoing
to the control room.
A "purge"rotometerwithinletendneedle valve iscommonlyused.Unlessthe impulse line issosmall
enoughthatthisflowwill create apressure drop.Somethingaround250 cm3/minisa commonrange.Adjustthe

6. PAK ARAB REFINERY LTD Department: Process – A200
Draft Gauge & Arch Pressure InstrumentationSensingLine PluggingProblem
Muhammad Usman Saeed – 5509 Page 4 of 7
flowto50% withthe needle valve.Because the purge pressure dropisall acrossthe needle valve the flowis
nearlyconstantdespite pressure changes.Itdependsonthe actual pressures.
Airis commonlyusedunlessthere issome requirementforaninertgaslike nitrogen.Inrare problem
situationswe have usedasecondsmall liquidsolventpurge towashthe diptube,thisof course must be added
close to the processconnectionandfromthat pointon,the impulse linemustslope downwardstothe process.
5.3 CASE III (AIR PURGING)
A typical targetis –0.1 in WC, measuredatthe top of
the radiantsection,whichisa verysmall number.Draft
meterscompare the pressure insidethe furnace toambient
pressure.Therefore,draftmeasurementerroris
compoundedbysmall changesinambient pressure (suchas
by the wind) thatcan make the draft pressure signal erratic
and difficulttocontrol.
Mitigatinganerratic draftsignal can be achieved
througha combinationof hardware designanddistributed
control system(DCS) controllerdesign.First,the draft
instrumentitself shouldbe designedandinstalledproperly.
The ambientlegof the draft instrumentshouldbe equipped
witha winddampeningdevice.Then,the nozzle connection
to the furnace shouldhave anair purge back intothe
furnace, adjustedappropriatelytodiscourage water
condensationinthe draftinstrumentwithoutaffectingthe
pressure measurementdue tofrictional losses.
The draft meterinstallationshouldalsomitigate potential condensationinthe instrumenttubing.Flue
gas istypically15% to 20% waterby volume,andcollectedcondensationmayaffectthe meteraccuracyor
damage the tubingconnectionif frozen.The meterinstallationshouldthereforebe physicallylocatedabove the
furnace connection.The stainlesssteel tubingconnectiontothe furnace shouldbe self-drainingbackintothe
furnace. Self-drainingisaccomplishedbyusingthe shortestfeasiblerunof tubing(atleast½-in.diameter)
withoutanylowpoints.Tubingjointsshouldbe minimizedtoreduce the possibilityof leakage.

7. PAK ARAB REFINERY LTD Department: Process – A200
Draft Gauge & Arch Pressure InstrumentationSensingLine PluggingProblem
Muhammad Usman Saeed – 5509 Page 5 of 7
5.4 CHEMICAL SEAL FOR PT & PSHH SWITCH
To avoidpluggingof impulse piping,Chemical sealedpressure transmitterwhichisfilledwithglycol or
any temperature resistance liquidcouldbe used.Forexamplepressuredifferential transmitter like 130-PDI027AB
and 130-PDI194ABC sensorlinesare filledwithglycolliquid.
6 CONCLUSIONS
I. Revise PMschedule of Draftinstrumentations(longterm).
II. Checkand Isolate DraftGauge from Sensinglinesandkeepdrainof sensingline headeropenedso
that if there isany condensate leftovercanbe removed. Alsokeepopendrainof draftgauge itself to
remainat atmosphericpressure whicheventuallyhelptoincrease life of draftgauge.Commission
gauge onlywhenreadingistobe takenfromgauge otherwise remainisolated.
III. Make arrangementfordraftgauge purgingusingplantair or N2 weekly.One operatorcheckand
confirmflowof PA or N2 fromsensingpointinheatersandotheropenthatfromdraft gauge sensing
line headerwhile keepinggauge itself isolatedanddrainedopen.Thisactivityreducemechanical
maintenance man-hourswhichisusedinbreakingflangefromimpulse line andmakingconnectionof
steamhose.
IV. Mostlyconvectionlinesof gauge isbeingblockeddue tosootblowingactivity.Openingimpulselines
drainwill helptoreduce pluggingissue.
V. Increase size of impulse pipingtoavoidplugging.
VI. Minimize numberof bendsincase of draftgauge.
VII. Introduce slope inpipingof draftgauge towardsheaterside,sothatcondensate draintowards
heater.
VIII. Try to avoidopeningatomizingsteaminBurner# 3/4 on Fuel Gas for preventingcarbonizationof
burnertipat hightemperature becauseheaterdraftgauge andPSHHswitchsensinglinesare almost
above Burner# 3/4. Adjusttiptemperature usingsecondaryairregister.
IX. Checkburnerpatternif it require cleaningeitherchange burnertofuel gasand lightotherburneron
fuel oil orcleanit as soonas possible.
X. Remove coke weatheritisonFuel Gas or Fuel Oil,sometimesFOcockvalve passesasburneronfuel
gas isignited.
XI. Optimize RefineryFuel Oil viscosityandCCRcontents.
XII. Seal all air leakage intoheaterespeciallywhenhumidityin airishigh.
XIII. Optimize gasburnersincase of highDiesel Max bleedgasesandLPG infuel gas systembecause
Hydrogencontentsof FG will varywhichliberate more heat.

8. PAK ARAB REFINERY LTD Department: Process – A200
Draft Gauge & Arch Pressure InstrumentationSensingLine PluggingProblem
Muhammad Usman Saeed – 5509 Page 6 of 7
7 PARCO’S FORCED DRAFT FIRED HEATER DRAFT COMPARISION
Tag No. Load SV of Draft PT Draft (Design)
% mmH2O Radiation Convection Breaching Stack
100H1 105% -3.0
Design -20 -10 -5 -20
Actual -18 -12 -8 -24
110H1 77% -3.0
Design -20 -10 -10 -20
Actual -19 -10 -8 -17
130
H1B/C
100% -9.0
Design -20 -10 -5 -20
Actual -18 -11 -9 -22
284H50A
70%
Based on
Thermal
-6.5
Design -20 -10 -5 -20
Actual -18 -11 -7 -19
8 UOP RECOMMENDATION REGARDING HEATER OPERATIONS
I. Min. of 3mmH2O to avoidblowout
II. If openingthe stackdamperdoesn’tincrease draughtthe firingratesshall be reducedand capacityof
furnace shall be reduced.
III. There shouldbe single fuelmode of firingata time.
IV. Dual firingleadstohighflame length,vendorsaidthat,flame lengthshallnotincrease more than
1/3rd of the fire box.
V. Under anycircumstance flame impingement isstrictlyavoided.
VI. Cock valvesof Fuel gasor fuel oil shall be 100% openedwhileburnerisinoperation.
VII. Heatershall be operatedaccordinglywithfollowingairregisters
a. Fuel Gas: PrimaryAir:25% (min) SecondaryAir:AsperexcessO2 requirementTertiary
Air:25% (max)
b. Fuel Oil:PrimaryAir:100% (min) SecondaryAir:25% (min) TertiaryAir:25% (min) Excess
O2: 5 - 5.5 %
VIII. The carbon residue flowingwithfluegasesaccumulatedinthe finnedconvectiontubeswhich
reducesoverall efficiencyof heattransferinheater.UOPpersonadvicedtocarry out soot
blowingtwice in24hrsoperationwhenmaximumburnersfiringmode is“Fuel Oil”. (Twicein24hr
SootBlowingoperationalsoone of reasonof draftgauge sensingline plugging frequency.)
9 REFERNECES
I. Emerson,Eliminate ImpulsePiping,HeatTrace & Purge Lines,
http://www2.emersonprocess.com/siteadmincenter/pm%20rosemount%20documents/eliminate%20im
pulse%20piping%20heat%20trace%20and%20purge%20lines%20on%20dp%20measurements.pdf
II. EJX Series,Overviewof ImpulseLine Blockage DetectionFunction,
https://www.yokogawa.com/fld/pdf/ejx/TI01C25A31-01E.pdf
III. http://www.controlglobal.com/articles/2012/protecting-blast-furnace-pressure-transmitters/
IV. http://coking.com/eliminating-plugged-impulse-lines-tapping-points/
V. FOSTER WHEELER HeaterOperatingManual
VI. HydrocarbonProcessing Magazine June 2014 Issue,EnergyEfficiencyD.MICKITY,Phillips66,Linden,New
Jersey