Newcastle University Autumn Session PINNL 2011

7/28/2019 Newcastle University Autumn Session PINNL 2011

1/36

CrackingintheAbsenceofSteamIntensifyingtheCrackingfurnace

MohamedEllob1,ArthurGough2,JonathanLee2

1.LibyanPetroleumResearchCentre

2.SchoolofChemicalEngineeringandAdvancedMaterials,NewcastleUniversity

02/11/2011 Autumn Session 2011 PIN-NL


2/36

TalkOutline

Mo.va.onforsteamlesscrackingExperimentalworkSimula.onIntegra.onofsteamlesscrackingreactorwiththeplant



3/36

WhatisThermalCracking?

Oneofthemostimportantprocessesinthepetrochemicalindustry

Co-productsincludehydrogen,fuelgas,gasoline,butadiene Endothermicreac.oncarriedout800-900C Homogeneousgasphasereac.onintheabsenceofcatalyst Cokeislaiddownonthewallsofthereac.ontubes

productscopropeneethenesteamnshydrocarbo

mixed heat+++



4/36

TypicalSteamCrackingFurnaces

TotalNumberofcrackingtubesabout600

ProcessVolumeabout45m.Fireboxvolumeabout4500m

Totalvolume:processvolume=100ResidenceTime0.25to0.75s

FireboxEfficiencyabout65%



5/36

TheUseofSteaminThermalCracking

Advantages Enhancesheattransfer Reducescokeforma.onanddeposi.on Improvesselec.vitytowardsolefinsbyreducingpar.alpressure

Disdavantages Energyisrequiredtogenerateit Noten.relyinert:

- ReactswithhydrocarbonsandcarbonattubesurfacetoformCO- Sulphurinthefeedisrequiredtomoderatethisreac.on- Formscarboxylicacids,aldehydes,ketonesandphenols



6/36

Intensifica.onoftheCrackingProcessReducingthesizeoftheFurnace

InacrackingfurnaceLHisoftheorderofmetres LargeTbetweenflameandreac.ontubes Cokeformsdueto:

hightubesurfacetemperatures(TS) cataly.ceffectoftheNiinthetubewalls

ReduceLHtoreducetheTSandfurnacevolume IfTSisloweredmaybewedontneedsteam Beware!surfaceareatovolumera.oishighinamicro

channeluseanon-cataly.cmaterial


propane

air fuel gas

heattransfer

distanceLH

micro channelreactor

fuelgas+air

hydrocarbonLH mm

combus.on

catalys

t


7/36

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


Thepreheatandreac.onsec.onswereeach450mmlong


8/36

Analysisofproducts

Thequenchedproductsweresenttotwoon-lineGCs: Hydrogen,methane,nitrogenandargonononeGC C2toC3onsecondGC

Yieldsandconversiondeterminedbyra.otomarkergasorquenchgas

Cokewasdeterminedbyburningoffinnitrogencontaining2%O

2Thegaswaspassedthroughheatedcopperoxideto

convertanyCOtoCO2andanalysedbyanon-lineIRanalyser



9/36

Coke

Decokeswerenormallyperformedimmediatelyaertherunwithoutcoolingthefurnace

Occasionallythetubewasremovedanddecokedusingamicroburnermovingalongthetube

Usingthismethodthecokewasfoundtobeevenlydistributedalongthelength


Air

Nitrogen

Preheat

furnace

Insula.on Reac.on

furnace

SampletoCO2

analyser

Excessdecoke

gas

Decokeflows


10/36

Coke

Standardrunslasted2hours Duringthis.me6-8productanalysesweredoneThey

showedhighrepeatabilityandnotrendwith.me

Afewlongerrunsupto8hoursshowedthatcokedeposi.onincreasedlinearlywith.me

Cokedensityassumedsimilartographitewhencalcula.ngreduc.onintubediameter



11/36

Parameterschosentogivehighestconversionssimilartotypicalcommercialvalues

P

P

T

F

F

T

DesignofExperiments

P = pressureT = temperature

F = flow



12/36

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



13/36

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



14/36

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



15/36

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



16/36

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



17/36

KeyExperimentalresults

Stainlesssteelcokesextremelyrapidly Cokingratesinsilicaandaluminaaresimilar

Ratesextrapolatetoon-line.meof15daysbetweendecokesforpropaneat90%conversionand30daysforethaneat65%conversion

Cokelay-downoccursalmostevenlyalongthewholelengthofthereactor

Thecoatedtubesperformancedeterioratedsignificantlyaeronly4react/decokecycles

Addingsteam(inaluminatube)gavecokingratesimilartothesteamlessrateatthesameHCpar.alpressure



18/36

CFDModelling

Fluentused Modelincludedcrackingreac.onsand

combus.on

Simplemolecularreac.onschemeschosen



19/36

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



20/36

Predictedtemperatureprofilesinthe

4mmAlsintreactor



21/36

Conversionalong4mmreactor

Massfraction of

C3H8



22/36

ModellingCokeDeposi.on


Fromentssimpletwocomponentmodelofcokedeposi.onwasused

C2H42C+2H2

C3H83C+4H2

Deposi.onrat

ekgm-2s

-1

Thepredictedrateofcokedeposi.onwassimilartothatobservedexperimentally


23/36

Modellingtheeffectofcoke

Theworkdidnotextendtosimula.ngcokedeposi.on Simulatedbyauniformlayerofcoke04mmthickonthewall

ofa4mmtube

Comparingthiswithacleantubeatthesameflowrateandfurnacetemperature:

Pressuredropincreasedfrom11Pato25Pa

Conversiondroppedfrom92%to86%



24/36

Integra.ngSteamlessIntensifiedReactors

intoanolefinsprocess

Capitalsavings Environmentalsavings Energysavings



25/36

Capitalsavings

Totalvolumeoffireboxreducedto2-300m3 Dilu.onsteamraisingsystemnotrequired Caus.cscrubbertoremoveCO2andH2Snotrequired MethanatortoremoveCOnotrequired Furnacescanbefactorybuiltanddeliveredtosite Lessstructuralsteelandcivilworkrequired



26/36

Environmentalsavings

Nodisposalofspentcaus.ccontainingNa2CO3,Na2Sandaldehydicpolymers

Nodisposalofcontaminatedprocesswatercontainingorganicacidsandphenols

Cataly.ccombus.onatlowertemperaturesreducestheproduc.onofNOx



27/36

Energysavings

Crackersareenergyintegratedunits Heatinputtothefurnacesisrecoveredashighpressuresteamand

hotwater

Thesestreamsprovideenergyandpowerforthegassepara.onsec.onoftheplant Itisnotsimpletodeterminetheeffectofremovingthesteam Energysavingcalculatedbycomparingapropanecrackerusing

conven.onalfurnaceswithoneusingsteamlessintensifiedreactors



28/36

BasisForComparison

750,000tpaethyleneunitbasedonpropane

PlantFeedpropane269t/h Steam:propanera.o04 Ex-furnaceyields:

H2CH4C3H8C3H6C2H4C2H6C4+

15%24%94%136%368%345%112%

Coilexittemperature850C TemperatureaerQuench340C HPsteampressure90bar



29/36

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



30/36

Summaryofconven.onalplant

Methaneconsump.on 314t/h Shapower

Condensingturbine 46MW Pass-outturbine 216MW Total 676MW

HotWaterforpropanetower 100MW Propanetowerreboil 516MW



31/36

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



32/36

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)



33/36

Credi.ngtheextraPower

1 Creditaselectricitygeneratedonamodernpowersta.on(60%efficiency):127MW=14t/hmethane

2 Extrapowerisneededontheplant:Producing127MWonconven.onalboiler/turbine=29t/hmethane

Thereforesavingfromomingsteamis4to55t/hmethane



34/36

Conclusions

Demonstratedthefeasibilityofanintensifiedsteamlesscracker

Olefinsproduc.onnotaffectedbyremovingthesteam Rateofcokinginsilica,aluminaandcoatedstainlesssteel

tubesallow15daysopera.onbetweendecoking

Lackofsteampreventsoxygenatedbyproductsfromforming Fuelgassavingsof12-18%



35/36


Questions?


36/36


Documents

Newcastle University Autumn Session PINNL 2011