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Transcript of Furnace Design
Advances in Advances in CrackingCracking Furnace Technology Furnace Technology
Karl [email protected]
John [email protected]
Jeff [email protected]
Cheah Phaik [email protected]
Cyron Anthony [email protected]
Refining Technology ConferenceDubai Crown Plaza Hotel
14-18 December 2002
Advances in Cracking FurnaceAdvances in Cracking FurnaceTechnologyTechnology
Outline
1. Introduction2. Historical Development3. Design Constraints4. Comparison of Current Designs5. Furnace Run lengths6. Anti Coking7. Future Opportunities8. Conclusions
IntroductionIntroduction
• Furnace technology is an area of activeresearch. The high-energy consumption,capital and maintenance cost of thecurrent cracking furnace are a drivingforce to develop improved conversionroutes.
IntroductionIntroduction
• The pyrolysis ofhydrocarbons for theproduction ofpetrochemicals isalmost exclusivelycarried out intubular coils locatedin fired heaters.
IntroductionIntroduction
• Steam is added tothe feedstock toreduce the partialpressure of thehydrocarbon in thecoil.
IntroductionIntroduction
• The reactions that result in thetransformation of saturatedhydrocarbons to olefins are highlyendothermic and require temperaturesin the range of 750 to 900 degrees Cdepending on the feedstock and designof the pyrolysis coil.
HistoryHistory
• The first commercial unit for pyrolysiscracking of hydrocarbons wascommissioned at Esso’s facility in BatonRouge, Louisiana during 1943.
• The feedstock was Gas Oil and theButadiene extracted from the crackedproducts was used to make Butylrubber.
HistoryHistory
• Ethylene, propylene and other productswere flared.
• Shortly thereafter, two morecommercial pyrolysis-cracking unitswere constructed along with ethanoland ethylene glycol plants to utilize theethylene.
HistoryHistory
• All pyrolysis cracking furnacesconstructed during the 40’s and 50’shad horizontal radiant tubes andresidence times in excess of 0.5 seconds.
• Radiant tube materials were 310stainless (wrought 25 Chrome 20 Nickel)or incoloy. Cast tubes were not yetinvented.
HistoryHistory• Prior to the mid
60’s all furnaceswere fired with avery large numberof wall burnersspaced on aboutsix foot centers inthe horizontalwalls and facingthe row of radianttubes.
HistoryHistory
• Thereafter most designers working withburner manufacturers developed thecapability of firing cracking furnacesmainly or exclusively with a muchsmaller number of floor burners.
HistoryHistory
• Some Technologies still utilizes wallburners for a small portion of the heatfired. This change made possiblebecause of much better control of theexcess air within the firebox.
HistoryHistory
• During 1960 the first vertical radianttube pyrolysis cracking furnace wascommissioned at Esso’s plant in Koln,Germany.
• Shortly thereafter essentially all newcracking furnaces were designed withvertical tubes.
HistoryHistory
• The driving force was the much lowerinvestment cost required for verticaltube furnaces.
• The residence time for these furnaceswas about 0.3 seconds. Typical tube IDwas about 4 to 5 inches.
HistoryHistory
• By 1965 manufacturers (initiallyDuraloy in the US) started to producecast tubes.
• A number of plants tried them withlittle success.
HistoryHistory
• Finally it was realized that the dross atthe tube ID was causing very rapidcoking and very poor tube life.
• Then the manufacturers found a way tomachine the tube ID to a smooth,imperfection free, surface and theirperformance greatly improved.
HistoryHistory
• During the late 70’s and 80’s the radianttube diameters used in crackingfurnaces decreased.
• The smaller diameter tubes had ahigher surface to volume ratio, whichallowed the heat necessary for crackingto enter the tubes in a much shortertube length.
HistoryHistory
• This allowed the cracking to take placein a much shorter residence time whichgave much better yields of the desiredproducts (mainly ethylene, propyleneand butadiene).
HistoryHistory
• Ultimately, about 1979 both Kellogg andEsso (Exxon) developed furnaces withmultiple parallel radiant tubes eachabout 40 feet long and 1 to 1.5 inches ID.
Design ConstraintsDesign Constraints
• The typical modern pyrolysis furnacesconsist of a rectangular (important)firebox with a single or double row ofvertical tubes located in the center planebetween two radiating refractory walls.
Design ConstraintsDesign Constraints
• The heat transfer to the tube is effectedlargely by radiation and only to a smalldegree by convection.
• The firebox temperature is typically inthe range of 1200 degrees Centigrade.
Design ConstraintsDesign Constraints
1. Process Chemistry
2. Heat of Reaction
3. Metallurgy
4. Flame pattern / Fire Box
Design ConstraintsDesign Constraints
Process Chemistry
• To fully understand the furnace designconstraints a review of processchemistry is required.
Design ConstraintsDesign Constraints
• When a hydrocarbon feedstock isundergoing pyrolysis a multitude ofreactions are happening simultaneously,but for practical purposes a simplifiedoutlook will explain many of the endresults in which are of primary interest.
Design ConstraintsDesign Constraints
• Hydrocracking - Decomposition byfree radical chain mechanisms intothe primary products: hydrogen,methane, ethylene, propylene andlarger olefins.
Design ConstraintsDesign Constraints
• Hydrogenation anddehydrogenation – reactions whereparaffins, di-olefins, and acetylenesare produced from olefins.
Design ConstraintsDesign Constraints
• Condensation – reactions wheretwo or more small fragmentscombine to produce larger stablestructures such as cyclo-di-olefinsand aromatics.
Design ConstraintsDesign Constraints
Hydrocracking of Ethane
C2H6 = CH3* + CH3* (1)
CH3* + C2H6 = CH4 + C2H5* (2)
C2H5* = C2H4 + H* (3)
H* + C2H4 = H2 + C2H5* (4)
C2H6 = C2H4 + H2 (5)
Design ConstraintsDesign Constraints
The process chemistry review revealsat least three design requirements:
1. Low Pressure
2. Low Hydrogen Partial Pressures
3. Short Residence Time
Design ConstraintsDesign Constraints
1. Low Pressure
• The predominately desired reactionis: C2H6 = C2H4 + H2
• Any time the moles of products arelarger than the moles of reactantsthe equilibrium favors lowpressures.
Design ConstraintsDesign Constraints
2. Low Hydrogen Partial Pressure
• To reduce the unwantedhydrogenation reaction, lowerhydrogen partial pressures wouldproduce more of the desiredproducts.
Design ConstraintsDesign Constraints
3. Short Residence Time
• To reduce the unwantedcondensation reaction, shorterresidence times would producemore of the desired products.
Design ConstraintsDesign Constraints
Heat of Reaction
• The reaction is endothermic andrequires high temperatures.
• Couple the heat of reaction with thelow pressure requirement - size andlength of coils are dictated.
Design ConstraintsDesign ConstraintsDiameter To Length Ratio
Q = U A DT
1. If the pressure drop is fixed Q is set by thediameter of the coil.
2. U and DT are fixed.
3. A determines the length of the coil.
Design ConstraintsDesign Constraints
Diameter To Length Ratio
1. 1 inch diameter is approximately 40 feet.
2. 2 inch diameter is approximately 80 feet.
3. 3 inch diameter is approximately 120 feet.
4. 4 inch diameter is approximately 160 feet.
Design ConstraintsDesign Constraints
Typical Metallurgy Constraints
Trade Name Composition Temperaturelimits
Developed Carbon PickUp
HK 40 25/20 : Cr/Ni 1830 F1000 C
Late1960’s
1% at1055 C
HP Modified 25/35 : Cr/Ni 2,060 F1125 C
Early1970’s
1% at1125 C
35/45 35/45 : Cr/Ni 2100 F1150 C
Mid1980’s
1% at1155 C
Design ConstraintsDesign Constraints
Flame Pattern Constraints
Design ConstraintsDesign Constraints
Flame Pattern Constraints
• The pyrolysis reaction are endothermic andtime dependant reactions.
• The flame pattern and the resulting heat fluxcan have the net effect of changing theeffective length of the coil.
Design ConstraintsDesign Constraints
Flame Pattern Constraints
• If the heat flux is not uniform the coileffective length can be reduced.
• If heat flux is not uniform hot areas can causeover-cracking and shorting coil life.
Design ConstraintsDesign ConstraintsFlame Pattern Constraints
HEAT FLUX DISTRIBUTION
0
1
2
3
4
5
6
7
8
9
20 40 60 80 100
RELATIVE HEAT FLUX (% OF MAX)
RA
DIA
NT
SE
CTI
ON
HE
IGH
T (M
ETR
ES
)
Existing
Improved
Design ConstraintsDesign Constraints
Flame Pattern Constraints
The shape of the flameis determined byburner designersaccording to heatinput requirements bythe technologyprovider.
Design ConstraintsDesign Constraints
Flame Pattern Constraints
• The shape of the fire box will effect the flamepattern and heat flux.
• Deviation from rectangular have not provedto be successful.
Design ConstraintsDesign ConstraintsFlame Pattern ConstraintsFire Box Shape CONVECTION
SECTION
SHP STEAMDRUM
CROSSOVERLINES
PRIMARYQUENCH
EXCHANGERS
DOUBLEIN-LINE
TUBEROWS
BOTTOMFIREDEACHSIDEINLET
MANIFOLD
Design ConstraintsDesign Constraints
Flame Pattern Constraints
• Steam may be added to the fuel gas to reducethe NOx emissions.
• This steam has been shown to even the heatflux distribution resulting in higher yields andrun lengths.
Com parison of Current DesignsCom parison of Current Designs
• It is the diameter and length of thetubes and the manner in which they areinterconnected to and from thepyrolysis coil which determine to whatextent a particular design will becharacterized by an optimumcombination of pyrolysis parameters.
Com parison of Current DesignsCom parison of Current Designs
• The design calculations applied topyrolysis coils are necessarily complexsince heat transfer and chemicalreaction are involved.
Com parison of Current DesignsCom parison of Current Designs
• Various options exist for the specificdesign of a pyrolysis coil, and thisaccounts for the variety of industrialpyrolysis furnaces presently inoperation.
Com parison of Current DesignsCom parison of Current Designs
Types of Furnace Coils
SINGLEPASS
“U”- COIL orTWO PASS
“W”- COIL or“M” - COIL
HYBRID COIL
Com parison of Current DesignsCom parison of Current Designs
• If short residence time is considered thesingle most important objective, then ashort coil with tubes of small diameterwill be considered.
Com parison of Current DesignsCom parison of Current Designs
• If a combination of high capacity,medium resident time and lowhydrocarbon partial pressure is judgedto be most beneficial, then a relativelylarger tube will result.
Com parison of Current DesignsCom parison of Current Designs
• For this presentation the comparisonwill be limited to four designs:
1. Short Residence Time - One pass of uniform size- Fire box floor to roof orientation
Com parison of Current DesignsCom parison of Current Designs
Typical End ViewSingle Pass
CONVECTIONSECTION
SHP STEAMDRUM
CROSSOVERLINES
PRIMARYQUENCH
EXCHANGERS
DOUBLE IN-LINE TUBE
ROWS
BOTTOMFIRED
EACH SIDE
INLETMANIFOLD
Com parison of Current DesignsCom parison of Current Designs
2. U Sweep Bends - one or more passes of uniform size - U configuration - fire box roof to roof orientation
Com parison of Current DesignsCom parison of Current Designs
Typical End ViewTwo Pass CONVECTION
SECTION
SHP STEAMDRUM
PRIMARYQUENCH
EXCHANGERS
DOUBLEIN-LINE
TUBEROWS
BOTTOMFIRED
EACH SIDE
INLETMANIFOLD
Com parison of Current DesignsCom parison of Current Designs
3. W Sweep Bends - one or more pass of increasing size - W configuration -fire box roof to roof orientation
Com parison of Current DesignsCom parison of Current Designs
Coil Configuration
Com parison of Current DesignsCom parison of Current Designs
4. Hybrids - one or more passes of increasing size - fire box roof to roof orientation -
Com parison of Current DesignsCom parison of Current Designs
FEEDDISTRIBUTORS
MANIFOLDS
INLET TUBES
OUTLETTUBES
QUENCHERS
Coil Configuration
Hybrid Coil
Com parison of Current DesignsCom parison of Current Designs
Size ResidenceTime
(seconds)
Design runLength onNaphtha
DesignDecokeTime
(hours)Coil One 1 inch by
forty feet0.08 - 0.12 30-35 Days 18-24
Coil Two 2 inch byeighty feet
0.20 – 0.25 35-45 Days 24-30
Coil Three 4 inch by120 feet
0.35 – 0.45 45-60 Days 30-36
Coil Four 2 inch to 6 inch by
80 feet
0.20 - 0.25 35-45 Days 24-30
Com parison of Current DesignsCom parison of Current DesignsTypical Residence Times Yields for Light Naphtha
ResidenceTime
(seconds)0.10 0.20 0.50
Methane 15.48 15.78 16.16
Ethylene 34.16 32.16 29.37
Propylene 17.02 17.35 17.78
Butadiene 5.2 5.1 5Benzene 5.89 6 5.75Toluene 2.59 2.65 2.52Fuel Oil 3.12 3.35 3.61
Com parison of Current DesignsCom parison of Current Designs
Advantages of Coil 1
1. Highest Olefin Conversion due to short residence time
2. Down Stream Separation Section can be smaller.
Comparison of Current DesignsComparison of Current Designs
Advantages Of Coil 2
1. Moderate Olefin Conversion
2. Operations Friendly
3. Dilution Steam and Feed tolerant
4. Moderate coil life
4. Moderate Thermal shock
Radiant Coil Therm al ShockRadiant Coil Therm al Shock-theory-theory
• The coke layercan reach > 10mm thicknessdepending on thetype of feedstockand severity
12 mm8 mm
Radiant Coil Therm al ShockRadiant Coil Therm al Shock-theory-theory
• The thickness ofthe coke is afunction of theTMT andconversion
Com parison of Current DesignsCom parison of Current Designs Thermal Shock
Com parison of Current DesignsCom parison of Current Designs Thermal Shock
Com parison of Current DesignsCom parison of Current Designs
Advantages Of Coil 3
1. Good run length between decokes
2. Good coil life
3. Moderate Thermal shock
Com parison of Current DesignsCom parison of Current Designs
Advantages Of Coil 4
1. Good run length between decokes
3. Good coil life
4. Good Thermal shock
5. Dilution Steam and Feed tolerant
Com parison of Current DesignsCom parison of Current Designs
Coil 1 Quench Exchanger
1. Established reliable system
2. Many units in operation
3. Metallurgy of Quench Exchanger is very important - Should be sodium stress corrosion resistant
Comparison of Current DesignsComparison of Current Designs
Typical ElevationSingle Pass
ID FAN
PRIMARYQUENCHERS
RADIANTTUBE
BANKS
CONVECTIONSECTION
STACK
STEAMDRUM
OUTLETMANIFOLDS
CROSSOVERLINES
RADIANTBOX
INLET MANIFOLDS
Com parison of Current DesignsCom parison of Current Designs
Coil 2 Quench Exchanger
1. Established reliable system
2. Many units in operation
3. Metallurgy of Quench Exchanger is very important - Should be sodium stress corrosion resistant
Com parison of Current DesignsCom parison of Current Designs
Coil 3 Quench Exchanger
1. Established reliable system
2. Many units in operation
3. Metallurgy of Quench Exchanger is very important - Should be sodium stress corrosion resistant
Com parison of Current DesignsCom parison of Current Designs
Coil 4 Quench Exchanger
1. Recently changed system to reduce residence time
2. Metallurgy of Quench Exchanger is very important - Should be sodium stress corrosion resistant
3. Previous design required hydro blasting every 6 months
Com parison of Current DesignsCom parison of Current Designs
Quencher
Furnace Run LengthsFurnace Run Lengths
• Many factors influence furnace run lengths.A partial list includes
1. Decoke Procedure
2. Sulfiding Procedure
3. Tube size and metallurgy
4. Feed and Steam impurities
5. The ability to utilize steam only decokes
6. Use of coke mitigating additives
Furnace Run LengthsFurnace Run Lengths
Design runLength onNaphtha
Actual runlength onEthane
Actual runlength onNaphtha
Cause of Deviation
Coil One 30-35 Days 10-20 30 1. Feed Impurities2. Dilution Steam Impurities3. Flame / Fire Box Issues
Coil Two 35-45 Days 20-25 30-35 1. Over sulfiding2. Low air during decokes
Coil Three 45-60 Days 35-40 40
Coil Four 35-45 Days 30-40 45-50 1. Sulfiding impurities
Furnace Run LengthsFurnace Run Lengths
Mixing Element Radiant Tube (MERT)
• Developed by KUBOTA
• Aims to create additional turbulence resulting inefficient and homogeneous heating of gas
• Efficient heating allows lower Tube Skin Temperatures and Higher yield
Furnace Run LengthsFurnace Run Lengths
• Properties include:-1. Heat transfer Co-efficient increased by 20-50%
compared to bare metal
2. 2% larger surface area
3. 3% weight gain
4. 2.0-3.5 times higher pressure drop
Mixing Element Radiant Tube (MERT)
Furnace Run LengthsFurnace Run Lengths
PEP Cast Finned tubes
Anti-Coking TechnologiesAnti-Coking Technologies
1. GE Betz - Pycoat
2. Nalco - Cokeless
3. Chevron / Phillips
- CCA 500
4. Westaim
5. Nova / Kubota
Coking in Ethylene Furnace
Reduce product yields
Restrain cracking severity Increase
Loss of production capacity
Increase energy consumption
Shorten coil service life
Increase maintenance cost
Add operator load
Furnace Utilization, 90~95%
Worldwide Production Loss 5% Improvement = $1 Billion/yr
10% Improvement = $2 Billion/yr
Coking Im pact in EthyleneCoking Im pact in Ethylene
Metal catalysisMetal catalyze dehydrogenation -->Carburized / metal boosted
Radical reaction
-->Filamentous coke growth
Acetylene / Butadiene etc. , growth on radical active site
C
Alloy tube
Linear growth
Lateral growth
Blocked metal cluster
Still active metal cluster
M echanism of Coke Form ationM echanism of Coke Form ation
Types of CokeTypes of Coke
Anti-Coking TechnologiesAnti-Coking Technologies
1. GE Betz - Pycoat
Advantages
• Treated off line - no unit contamination
• Silicon Based
• Diffusion barrier
- Adherent film : enhance binding film with m etal surface
- Barrier film : prevent carbon & oxygen from penetrating
Tube material
Coke Precursor
Diffusion Barrier
No Diffusion No Catalytic
Coke+ Minimize Pyrolytic Coke
H2, CO, CO2
+ No Pyrolytic Coke
Decoking Film
•Decoking Film : Gasify the remained coke (In Development)
GE Betz PY-COAT ConceptGE Betz PY-COAT Concept
Coated Film
Tube Metal
Coating CharacteristicsCoating Characteristics
Ethane Furnace Designed by KBR
DescriptionLocated in North AmericaMillisecond Furnace27 T/Hr and 70 % Conversion160 1.3” tubesMain Criteria for Decoking : CoilInlet PressureOriginal R/L : 13-15 days
Com m ercial ReferenceCom m ercial Reference
PY-COAT Perform ancePY-COAT Perform ance
PY-COAT Performance Vs. Baseline
0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10
Run #
Ru
n le
ng
th (
day
s)
Baseline Treated
Plant Upset
Gas Furnace Designed by KBRGas Furnace Designed by KBR
Test started Mid OctoberTest started Mid October
PY-COAT PERFORMANCE @ NORTH AMERICACOIL PRESSURE DROP_MAX
0
5
10
15
20
25
30
35
40
45
50
55
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
R un days
PY-COAT RUN 1
PY-COAT RUN 2
BASE 1
BASE 2
BASE 3
Still operating
Anti-Coking TechnologiesAnti-Coking Technologies
2. Nalco - Cokeless
Advantages
• First to develop on line coating - Severalgenerations of development
• Present generation has shown some success
• Applied on line - high furnace utilization
• Phosphorus based
TMT Profile ComparisonTMT Profile ComparisonTube Metal Temperature Coil 3
1010
1020
1030
1040
1050
1060
1070
1080
1090
1100
1110
1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86
Day of Run
De
gre
es
, C
Lummus
Naphtha cracker
Lummus
Naphtha cracker
4 Coke-Lessruns average
4 Coke-Lessruns average
3basecaserunsaverage
3basecaserunsaverage
Anti-Coking TechnologiesAnti-Coking Technologies
3. Chevron Phillips CCA 500
Advantages
• Treated off line
• Tin / Silicon Based
50
55
60
65
70
75
80
85
90
0 2.5 6 11 16 21 26 31 36 41 46
Time of Stream (days)
% M
ax
imu
m C
oil
Pre
ss
ure
Dro
p
Hydrogen Sulfide
CCA 500
Coil Pressure Drop (S-Coil, Ethane Feed)
Anti-Coking TechnologiesAnti-Coking Technologies
3. Westaim COATALLOY™
Advantages
1. Coating applied on new tubes - Furnace Utilization
2. Carbonization Resistant
M ICROGRAPH OF COATALLOY™ ENGINEEREDM ICROGRAPH OF COATALLOY™ ENGINEEREDCOATING SYSTEM - BEFORE SERVICECOATING SYSTEM - BEFORE SERVICE
EngineeredSurface
EnrichmentPool
DiffusionBarriers
Bulk HighTemperatureAlloy
50 microns
COATALLOY™-1100 CASE HISTORY - FORMOSACOATALLOY™-1100 CASE HISTORY - FORMOSA
0.0
0.5
1.0
1.5
2.0
2.5
Typical Runs forUncoated Furnaces
Runs 3-9 forCoatAlloy™-1100
coated Coil
Days on Line
Max
imu
m P
ress
ure
Dro
p R
atio
96
HIGHLIGHTS OF OTHER CASE HISTORIESHIGHLIGHTS OF OTHER CASE HISTORIES
•Short Residence Time• 2% increase in ethylene yield• 3 x run length• 5% increase in conversion
•Long Residence Time• 4% increase in ethylene yield• Min. Feed rate increase ofapprox.. 8%
• 9% increase in conversion
•Medium Residence Time• 4.5% increase in ethylene
yield• 2 x run length• 8% increase in conversion
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Uncoated-BaseConversion
Coated-BaseConversion
Coated-10%Conversion Increase
ShortResidence
MediumResidence
LongResidence
Co
kin
g r
ate
(psi
ris
e/d
ay)
Anti-Coking TechnologiesAnti-Coking Technologies
4. Nova / Kubota - ANK 400
Advantages
• Coating applied on new tubes -Furnace Utilization
• 400 + Run lengths
Future OpportunitiesFuture Opportunities
1. Better Coil Metallurgy
• Coil manufactures will continue todevelop new designs with highertemperature limits
Future OpportunitiesFuture Opportunities
2. Better Coil Coatings
• Research is presently ongoing inceramics and other coke resistancematerials.
• Betz / SK is developing a coke filmingagent that will keep the coke in gasphase reducing accumulation on thetube.
Future OpportunitiesFuture Opportunities
3. Catalyst Development
• Research is presently ongoing foroxidative coupling of methane toethane and ethylene by Li/MgOcatalyst at 700 degrees C.
ConclusionsConclusions
1. Introduction
2. Historical Development
3. Design Constraints
4. Comparison of Current Designs
5. Furnace Run lengths
6. Anti Coking
7. Future Opportunities
8. Conclusions
ConclusionsConclusions
• Thanks for your time
• Our goal was to give an overview of thecurrent advancements pyrolysiscracking furnaces
• Please contact us for additionalinformation or questions