ethylene unit pyrolysis furnace opportunity & strategic...
TRANSCRIPT
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Ethylene Unit Pyrolysis FurnaceOpportunity& Strategic Improvements
Sharipah Jalil - Presenter
Karl Kolmetz
Charles D. Nolidin
Cyron Anthony Soyza
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Pyrolysis Furnace Opportunity &Strategic Improvements
• Furnace layout
• Radiant Coil Elongation
• Convection tube bowing
• Shadow box hot-spots
• U-bend erosion
• Radiant Coil Thermal shock
• Conclusion
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Unit 2 Furnace Layout
• 6 furnaces (12 Zones)
• 10 Naphtha Zones & 2 Recycle Zones
• Common Convection Heat Recovery Bankfor two zones with Induced draft fan
• Radiant products cooled by quench coolersproducing SHP (105 bar) steam
• Effluent sent to Quench Section
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Furnace Layout
NAPHTHA
STEAM
QUENCH COOLER
BURNERS
FUEL GAS
NAPHTHA
STEAM
QUENCHCOOLER
BURNERS
EFFLUENTEFFLUENT
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1st Opportunity :Coil Elongation - scenario
• Creep rate is between 60 - 78 mm per yearin one zone example
• Coil needs shortening approx. every 5 years
• Recycle zones are fired harder to achieveoptimum yield causing higher Tube MetalTemperature (TMT)
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• Flame impingement- burner tip blockage
• Heat maldistribution- uneven firing- mixture of old & newburner tips
• ASWT- average sound wallthickness- thicker walls more prone tocreep
Coil Elongation- theory
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Coil Elongation-a glance
Creep amount
0
50
100
150
200
250
300
350
400
450
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Tube no.
Cre
ep
, m
m
Creep amt
Maximum limit when shortening
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• Burner tip cleaning andmaintenance
• Coil elongation monitoring
• Future:-
Kubota MERT tubes -lowers TMT’s byincreasing heat transfer
Auto Excess O2 control -lowers firing needs
Coil Elongation-current & future mitigation
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2nd Opportunity :Convection Coil Bowing - scenario
• Bottom section of convectionbank bowed approx. 30cm
• Cracks at weldment from mixingheader to inlet manifold
Mixing header
Inlet manifold
Radiant Section
Convection Section
XOTConvection coil
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• Zone mainly recycle feed
• Recycle cracking requires higher CoilOutlet Temperature for conversion
• Excess heat recovered in convection
Convection Coil Bowing- theory
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• Too much excess heat raises XOTtemperature which initiates prematurecracking
• Metallurgy limits promotes creep andexpansion
Convection Coil Bowing- theory
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Convection Coil Bowing- a glance
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Convection Coil Bowing-current & future mitigation
Current
• Stress analysis required on piping andfull understanding of metallurgy limits
• Spring hanger adjusted to relief pipingstress
• Bowed convection coils replaced
• Secondary steam injection optimized
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Convection Coil Bowing-current & future mitigation
Future
• Upgrading of crossover and convectionmaterial
• protect convection coils by insulativematerial
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3rd Opportunity- Shadow Box Hotspots- scenario
• Insulation around radiant outlet replacedand shadow box plates upgraded to SS304after turnaround
• Hotspots detected on shadow box duringthermograph survey
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- Shadow Box Hotspots- scenario
• Plates deteriorated and warped
• Some insulation cladding melted
• Insulation material noticed on firebox floor
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Shadow Box Hotspots- theory
• Heat escaping shadow box due toimproperly installed insulation
• Gaps existed which allowed heat to escapethe radiant box
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Shadow Box Hotspots- a glance
The Past
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Shadow Box Hotspots- a glanceThe Present
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Shadow Box Hotspots- current & future mitigation
• Insulation stuffed from outside andinside
• Reengineer installation procedureand shadow box plate
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Shadow Box Hotspots- current & future mitigation
• Final assessment ofinsulation integrity mustbe carried out each timefurnace insulationreplaced
New Old
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SLE U-Bend Erosion - scenario
• Thinning 1mm per year at the inlet sweepbend
• Change U-bend if thickness drops below
3.5 mm from initial of 8.8mm
• Replacement every 3 years
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SLE U-Bend Erosion - theory
• Erosion main contributing factors includesolid presence, material specification andflow path geometry
• Initially, gradual transition in flow sectionand shallow-angle intersections was enoughto mitigate erosion
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SLE U-Bend Erosion - theory
Area badly eroded
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SLE U-Bend Erosion - theory
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SLE U-Bend Erosion - a glance
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SLE U-Bend Erosion - current &future mitigation
• Inlet and outlet sweeps alternated to evenout erosion effect
• Ultrasonic Thickness Scanning (UTS) todetect thinning and make replacements
• Modify U-bend to increase integrity of pipeinline with increasing flow turbulence
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5th OpportunityRadiant Coil Thermal Shock -theory
• Coke formation is an undesirable feature ofthe cracking process
• The carbon coats the inside surface of thetubes, increasing in thickness
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Radiant Coil Thermal Shock-theory
• The coke layer canreach > 10 mmthicknessdepending on thetype of feedstockand severity
12 mm8 mm
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Radiant Coil Thermal Shock-theory
• The thickness ofthe coke is afunction of theTMT
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Radiant Coil Thermal Shock-theory
• Coke layer is hard, relatively brittle, and has a lowercoefficient of thermal expansion than the tube metal
• With coke presence during sudden shutdown twothings can happen:-
~ coke falls off - spalling that leads to tube blockage
~ coke remains - coil splitting due to it’s faster rateof contraction
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Radiant Coil Thermal Shock-scenario
• 1st Dec 01 power supply interruption due tonational power grid
• Steam from utilities lost during poweroutage
• Furnace damper goes to minimum openingto avoid heat loss
• Bottom air register dampers manuallyclosed
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Radiant Coil Thermal Shock-scenario
• Coil temperaturedrops 100 ~200oC in 1st hourafter trip
• Allowable temp.drop is <80 oC
COT trend
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0
12-1-
01 9:
36 AM
12-1-
01 2:
24 PM
12-1-
01 7:
12 PM
12-2-
01 12
:00 AM
12-2-
01 4:
48 AM
12-2-
01 9:
36 AM
12-2-
01 2:
24 PM
12-2-
01 7:
12 PM
12-3-
01 12
:00 AM
12-3-
01 4:
48 AM
Tem
p. (o
C)
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Radiant Coil Thermal Shock-scenario
• Difference in cooling rate depends onamount of coke and insulation condition
• Coils inspected after temperature almostambient : ~ 70 coils needed replacement
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Radiant Coil Thermal Shock-scenario
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Radiant Coil Thermal Shock-scenario
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Radiant Coil Thermal Shock-mitigation
• Decoke End Of Run tubes as soon aspossible before shutting down furnaces
• Avoid unnecessarily furnace emergencyshutdowns
• Ensure reliability of Uninterrupted PowerSupply (UPS)
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Pyrolysis Furnace Opportunity &Strategic Improvements
• Reviewed Furnace layout
• Reviewed Furnace opportunities
• Reviewed current and future improvement strategies
Conclusion
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Pyrolysis Furnace Opportunity &Strategic Improvements
• Implemented improvements to reduce EquipmentOpportunity Losses
• Prolonged life and operability of equipment, thusreducing downtime and maintenance cost
• Further opportunities to improve are being evaluated
Conclusion
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Thank You