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CrackingintheAbsenceofSteamIntensifyingtheCrackingfurnace
MohamedEllob1,ArthurGough2,JonathanLee2
1.LibyanPetroleumResearchCentre
2.SchoolofChemicalEngineeringandAdvancedMaterials,NewcastleUniversity
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TalkOutline
Mo.va.onforsteamlesscrackingExperimentalworkSimula.onIntegra.onofsteamlesscrackingreactorwiththeplant
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WhatisThermalCracking?
Oneofthemostimportantprocessesinthepetrochemicalindustry
Co-productsincludehydrogen,fuelgas,gasoline,butadiene Endothermicreac.oncarriedout800-900C Homogeneousgasphasereac.onintheabsenceofcatalyst Cokeislaiddownonthewallsofthereac.ontubes
productscopropeneethenesteamnshydrocarbo
mixed heat+++
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TypicalSteamCrackingFurnaces
TotalNumberofcrackingtubesabout600
ProcessVolumeabout45m.Fireboxvolumeabout4500m
Totalvolume:processvolume=100ResidenceTime0.25to0.75s
FireboxEfficiencyabout65%
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TheUseofSteaminThermalCracking
Advantages Enhancesheattransfer Reducescokeforma.onanddeposi.on Improvesselec.vitytowardsolefinsbyreducingpar.alpressure
Disdavantages Energyisrequiredtogenerateit Noten.relyinert:
- ReactswithhydrocarbonsandcarbonattubesurfacetoformCO- Sulphurinthefeedisrequiredtomoderatethisreac.on- Formscarboxylicacids,aldehydes,ketonesandphenols
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Intensifica.onoftheCrackingProcessReducingthesizeoftheFurnace
InacrackingfurnaceLHisoftheorderofmetres LargeTbetweenflameandreac.ontubes Cokeformsdueto:
hightubesurfacetemperatures(TS) cataly.ceffectoftheNiinthetubewalls
ReduceLHtoreducetheTSandfurnacevolume IfTSisloweredmaybewedontneedsteam Beware!surfaceareatovolumera.oishighinamicro
channeluseanon-cataly.cmaterial
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propane
air fuel gas
heattransfer
distanceLH
micro channelreactor
fuelgas+air
hydrocarbonLH mm
combus.on
catalys
t
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Laboratorywork
Propane,ethaneandn-heptanewerecracked Temperatures810-860C Pressure1117bar Residence.mes0410sec
Tubeinsidediameters 2mm,3mm,4mm
Tubematerials Silica,Alumina,Type316stainlesssteel,coatedsteels
Markergas
Propane
Preheat
furnace
Insula.on Reac.on
furnace
Quenchgas
Cooledproduct
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Thepreheatandreac.onsec.onswereeach450mmlong
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Analysisofproducts
Thequenchedproductsweresenttotwoon-lineGCs: Hydrogen,methane,nitrogenandargonononeGC C2toC3onsecondGC
Yieldsandconversiondeterminedbyra.otomarkergasorquenchgas
Cokewasdeterminedbyburningoffinnitrogencontaining2%O
2Thegaswaspassedthroughheatedcopperoxideto
convertanyCOtoCO2andanalysedbyanon-lineIRanalyser
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Coke
Decokeswerenormallyperformedimmediatelyaertherunwithoutcoolingthefurnace
Occasionallythetubewasremovedanddecokedusingamicroburnermovingalongthetube
Usingthismethodthecokewasfoundtobeevenlydistributedalongthelength
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Air
Nitrogen
Preheat
furnace
Insula.on Reac.on
furnace
SampletoCO2
analyser
Excessdecoke
gas
Decokeflows
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Coke
Standardrunslasted2hours Duringthis.me6-8productanalysesweredoneThey
showedhighrepeatabilityandnotrendwith.me
Afewlongerrunsupto8hoursshowedthatcokedeposi.onincreasedlinearlywith.me
Cokedensityassumedsimilartographitewhencalcula.ngreduc.onintubediameter
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Parameterschosentogivehighestconversionssimilartotypicalcommercialvalues
P
P
T
F
F
T
DesignofExperiments
P = pressureT = temperature
F = flow
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Effectofpressureonproductsandcoke4mmSilicatube:
Flowrateadjustedtomaintain90%conversionat855C
Pressure
bar
PropaneFlow
g/h
Yields %w/w coke
H2 CH4 C2H4 C2H6 C3H6 C4+ ppm mg/h
17 329 131 2276 3547 423 1598 782 218 72
14 246 145 2300 3676 370 1386 1097 187 46
11 211 139 2167 3639 303 1463 1117 212 45
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YieldsandConversionasafunc.onofTemperature4mmSilicaTube:PropaneFlow15Nl/h:Pressure16bar
Yields%w/w Coke
ppm
Temperature
C
Conversion
%
H2 CH4 C2H4 C2H6 C3H6 C4+
810 675 103 1457 2356 280 1907 538 31
820 715 116 1614 2635 301 1919 625 47
830 759 127 1787 2915 325 1871 712 70
840 809 135 1980 3195 353 1763 799 105
850 866 138 2192 3475 386 1597 886 160
860 932 138 2428 3755 427 1371 974 241
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YieldsandConversionfordifferenttubediametersand
materialsat850Cand135bar
Yields%w/w
Coke
ppm
TubeFlow
Nl/h
Conversion
%H2 CH4 C2H4 C2H6 C3H6 C4+
2mmSilica 37 8937 146 2192 3666 339 1403 1267 407
3mmSilica 77 878 168 2366 3898 356 1558 524 231
4mmSilica 105 8820 146 2229 3603 357 1447 1086 170
AlsintAlumina 105 885 147 2278 3575 421 1374 567 217
PythagorusAlumina
105 895 158 2441 3854 356 397 670 313
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Ethane
Temp
oC
Pressure
bar
Flow
Nl/h
Conversion
%
Cokeppm Yield(weight%)
H2 CH4 C2H4
850 135 1616 5671 91 354 305 4649
850 135 1206 6519 137 397 449 5232
870 135 1801 6510 122 395 411 5287
900 135 3051 6607 107 420 371 5022
900 201 3453 6536 125 373 476 4919
4mmsilicatube
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N-Heptanecracking4mmSilica:1hrunlength
TempoC
Pressure
bar
Flow
g/h
Coke
ppm
Passyield(weight%)
H2 CH4 C3H6 C2H4 C2H6 C4+
810 135 202 303 076 154 1411 4261 823 185850 135 407 306 081 144 1409 4371 719 191
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KeyExperimentalresults
Stainlesssteelcokesextremelyrapidly Cokingratesinsilicaandaluminaaresimilar
Ratesextrapolatetoon-line.meof15daysbetweendecokesforpropaneat90%conversionand30daysforethaneat65%conversion
Cokelay-downoccursalmostevenlyalongthewholelengthofthereactor
Thecoatedtubesperformancedeterioratedsignificantlyaeronly4react/decokecycles
Addingsteam(inaluminatube)gavecokingratesimilartothesteamlessrateatthesameHCpar.alpressure
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CFDModelling
Fluentused Modelincludedcrackingreac.onsand
combus.on
Simplemolecularreac.onschemeschosen
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Froment - Propane cracking reaction scheme
No. Reaction Reaction
order
Frequency factor
S-1, l mol-1 s-1
Activation
Energy kJ/ mol
1C3H8 C2H4 + CH4
first 4.692 1010 211.71
2C3H8 C3H6 +H2
first 5.888 1010 214.59
3C
3H
8+ C
2H
4 C
2H
6+ C
3H
6 second 2.536 1013 247.10
42C3H6 3C2H4
first 1.514 1011 233.47
52 C3H6 0.5 C6 + 3CH4
first 1.423 109 190.37
6C3H6 C2H2 + CH4
first 3.794 1011 248.48
7C3H6 + C2H6 C4H8 + CH4
second 5.553 1014 251.08
8C2H6 C2H4 + H2
first 4.652 1013 272.79
9C2H4 + C2H2 C4H6
second 1.026 1012 172.63
10C4H8 C6
first 6.960 107 143.59
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Predictedtemperatureprofilesinthe
4mmAlsintreactor
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Conversionalong4mmreactor
Massfraction of
C3H8
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ModellingCokeDeposi.on
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Fromentssimpletwocomponentmodelofcokedeposi.onwasused
C2H42C+2H2
C3H83C+4H2
Deposi.onrat
ekgm-2s
-1
Thepredictedrateofcokedeposi.onwassimilartothatobservedexperimentally
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Modellingtheeffectofcoke
Theworkdidnotextendtosimula.ngcokedeposi.on Simulatedbyauniformlayerofcoke04mmthickonthewall
ofa4mmtube
Comparingthiswithacleantubeatthesameflowrateandfurnacetemperature:
Pressuredropincreasedfrom11Pato25Pa
Conversiondroppedfrom92%to86%
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Integra.ngSteamlessIntensifiedReactors
intoanolefinsprocess
Capitalsavings Environmentalsavings Energysavings
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Capitalsavings
Totalvolumeoffireboxreducedto2-300m3 Dilu.onsteamraisingsystemnotrequired Caus.cscrubbertoremoveCO2andH2Snotrequired MethanatortoremoveCOnotrequired Furnacescanbefactorybuiltanddeliveredtosite Lessstructuralsteelandcivilworkrequired
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Environmentalsavings
Nodisposalofspentcaus.ccontainingNa2CO3,Na2Sandaldehydicpolymers
Nodisposalofcontaminatedprocesswatercontainingorganicacidsandphenols
Cataly.ccombus.onatlowertemperaturesreducestheproduc.onofNOx
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Energysavings
Crackersareenergyintegratedunits Heatinputtothefurnacesisrecoveredashighpressuresteamand
hotwater
Thesestreamsprovideenergyandpowerforthegassepara.onsec.onoftheplant Itisnotsimpletodeterminetheeffectofremovingthesteam Energysavingcalculatedbycomparingapropanecrackerusing
conven.onalfurnaceswithoneusingsteamlessintensifiedreactors
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BasisForComparison
750,000tpaethyleneunitbasedonpropane
PlantFeedpropane269t/h Steam:propanera.o04 Ex-furnaceyields:
H2CH4C3H8C3H6C2H4C2H6C4+
15%24%94%136%368%345%112%
Coilexittemperature850C TemperatureaerQuench340C HPsteampressure90bar
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Process Water 80C
108 t/h
Methane
31.4 t/h
Saturator
P-76
Steam 4.5 bar
Propane/steam
7 bar 120C
600C
850C
90 bar SH steam
130C
60C
35C
100MW
60C
30C
56.7C
Cooling water
22.5 MW
C3 Splitter
reboiler 51.6MW
46 MW
Cooling water
340C
277 t/h
80C
21.6 MW
Propane
269 t/h
AConven.onalPropanePlantFrontEnd
quench
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Summaryofconven.onalplant
Methaneconsump.on 314t/h Shapower
Condensingturbine 46MW Pass-outturbine 216MW Total 676MW
HotWaterforpropanetower 100MW Propanetowerreboil 516MW
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35 C
15.2 MW
60C
30C
56.7C
C3 Splitter
reboiler 51.6MW
Cooling water
Methane 18.2 t/h
850C
Propane 269 t/h
P-91
68 C
76C
9.3 MW
30C
73 C
54 MW
10.3 MW
25.7 MW
16 MW
Methane 7 t/h
650 C
600C
106C
Methane 3.6 t/h
340C
210 t/h
540C
90 bar
BFW
Cooling
Water
ASteamlessPropanePlantFrontEnd
To stackCombustion gas
Combustion gas
pre-heater
Reactor
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SummaryofIntensifiedUnit
Methaneconsump.on: Turbine 70t/h Reactor 182t/h Superheater 36t/h
Total 288t/h (314t/h)
ShaPower GasTurbine 16MW CondensingTurbine 54MW 73CcondensingTurbine 103MW Total 803MW(676MW)
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Credi.ngtheextraPower
1 Creditaselectricitygeneratedonamodernpowersta.on(60%efficiency):127MW=14t/hmethane
2 Extrapowerisneededontheplant:Producing127MWonconven.onalboiler/turbine=29t/hmethane
Thereforesavingfromomingsteamis4to55t/hmethane
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Conclusions
Demonstratedthefeasibilityofanintensifiedsteamlesscracker
Olefinsproduc.onnotaffectedbyremovingthesteam Rateofcokinginsilica,aluminaandcoatedstainlesssteel
tubesallow15daysopera.onbetweendecoking
Lackofsteampreventsoxygenatedbyproductsfromforming Fuelgassavingsof12-18%
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Questions?
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