Simulation of Bitumen Upgrading Processes

8/19/2019 Simulation of Bitumen Upgrading Processes

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2 PTQ Q2 2013 www.digitalrefining.com/article/1000796

The atmospheric-topped bitu-

men (ATB) is fed to a vacuumdistillation unit (VDU) toobtain naphtha, light gas oil(LGO), heavy gas oil (HGO)and vacuum-topped bitumen(VTB). The VTB is processedeither in a coker unit or in anebullated-bed hydroconversionreactor, or even in both. Thetotal liquid product (TLP) fromthe coking and/or hydrocon-

version stage is fractionated,and the resulting streams arecombined with the correspond-ing fractions coming from theVDU and routed separately tohydrotreating (HDT) units.After hydrotreating, thesestreams are blended to formSCO, which is transported bypipeline to reneries in Canadaand the US.

needs. It is important to identify

the possible avenues for betterupgrading technology forcurrent and future projects.10 While some new primaryupgrading technologies are

being developed and imple-mented, such as slurry-phasehydrocracking and supercriticalsolvent extraction/deasphalt-ing, the existing commercialprocesses and technologies —

namely, coking, ebullated-bedhydroconversion, hydrotreatingand hydrocracking — will stilldominate for the foreseeablefuture.4 Therefore, modelling,simulation and optimisation ofthese integrated processes willprovide valuable and helpfulknowledge towards innovativeprocess design and operation.

The objective of this study is

to evaluate commercial bitu-

men upgrading schemes byperforming process modellingand simulation, which willhelp the industry to improveprocess efciency, reduceGHGs emissions and otherrelated environmental impacts(for instance, optimised H

2 and

water use) in future bitumenupgrading and reningschemes.

Bitumen upgrading processFigure 1 presents a genericow diagram of the bitumenupgrading process. The diluted

bitumen from extraction andfroth treatment plant rstpasses through the diluentrecovery unit (DRU), where thediluent is recovered and recy-cled to the extraction plant.

Coke

Dilutedbitumen

Atmospherictopped

bitumen

Unconvertedresidue

Diluent

Naphtha hydrotreating

Sourgas

Gasoline

H2

LGO hydrotreating

Sourgas

Diesel

H2

HGO hydrotreating

Sourgas

FCC feed

H2

Syntheticcrude oil

Coking/hydroconversion

Feed+H

2

Products

Cat.

Cat.

Feed

Products

Sourgas

Diluent

recovery

Vacuum

distillation

Naphtha (IBP–204ºC)

LGO (204–343ºC)

HGO (343–524ºC)

Figure 1 Generic diagram of bitumen upgrading process

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Modelling and simulationapproachThe simulation was conductedin the Aspen Hysys environ-ment. Two typical bitumenupgrading schemes wereanalysed: coking and hydro-

conversion based. Oilproperties of interest (APIgravity, sulphur, nitrogen andmetals, among others) andproduct yield shifts at everyconversion step were handled

by the Petroleum Rening toolin Hysys. Since Hysys does nothave modules for certain unitsof the bitumen upgradingscheme —namely, coker, ebul-lated-bed hydroconverter andnaphtha hydrotreater — kineticmodels were developed andimplemented into Hysys topredict the performance ofthose processes, as will bediscussed below. Other units,such as distillation columnsand gas oil hydrotreaters, weresimulated with built-in Hysysmodules. All of the units werecarefully calibrated based on

in-house experimental data andpublished data.6-18

Coking and hydroconversionkinetics were formulated basedon simple reaction networksinvolving the following lumps:gas (C

1-C

4 , H

2S and NH

3),

naphtha (IBP-204°C), LGO(204-343°C), HGO (343-524°C),vacuum residue (524C°+) andcoke (for the coker unit

only). The hydroconversionmodel also included hydro-desulphurisation (HDS),hydrodenitrogenation (HDN),hydrodemetallisation (HDM)and hydrogen consumption.The rate equations accountedfor the effect of temperatureand pressure in the case ofhydroconversion, whereas theywere only temperature

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dependent in the case ofcoking. The models were prop-erly tuned and implemented ina Hysys spreadsheet. Thisfeature enables user-denedcalculations to be performedusing any variable from the

simulation owsheet and thenthe results exported to anystream or unit. In this case, thespreadsheet imported the oper-ating conditions from the feedstream to calculate the productdistribution. The yield shiftwas then performed by thePetroleum Shift Reactor toolusing the product yield esti-mates as input. The effect ofhydrotreating on the chemicalcomposition and physicalproperties of the feed washandled by the AssayManipulator. This tool adjuststhe distribution of assay prop-erties (such as sulphur content)along the entire boiling range

by specifying a target bulkvalue, which is determined byhydrotreating kinetics.

Naphtha HDT was modelled

according to a kinetic modelfor coker naphtha hydrotreat-ing reported in the literature.19 The model accounts for HDS,HDN and aromatics saturation.Simulation of LGO and HGO

hydrotreating was performedusing the gas oil hydrocrack-ing-hydrotreating module. Rateconstants were properly cali-

brated in order to producetypical operational parameterssuch as reactor temperature

proles, hydrogen consump-tion and product quality.20

Results and discussionSimulation owsheets wereconstructed for the twoupgrading schemes by assum-ing a processing capacity of100 000 b/d diluted bitumen.The bitumen-to-diluent ratiowas assumed to be 75/25 vol/vol. The properties of the bitu-men feed and its products afterdiluent recovery (atmosphericdistillation) and vacuum distil-lation are shown in Table 1.The ATB, which is equivalentto the raw bitumen, is mainlycomprised of VTB and HGO,with a small amount of LGOand almost no naphtha. It ischaracterised by having a lowAPI gravity (10.7°API) and

high contents of undesiredcontaminants such as sulphur,nitrogen, metals andConradson carbon residue(CCR), all of which make bitu-men upgrading operations

Diluent recovery Vacuum distillationa

Property Diluted bitumen Diluent ATB Naphtha LGO HGO VTBYield, wt% 100.0 20.4 79.6 0.8 12.1 30.7 56.4SG 60/60°F 0.9381 0.7659 0.9953 0.7730 0.8691 0.9565 1.0556API gravity 19.3 53.2 10.7 51.6 31.3 16.4 2.5Sulphur, wt% 3.72 0.81 4.46 0.89 1.63 3.20 5.80Nitrogen, wppm 3299 10 4139 11 114 1301 6602Aromatics, wt% 61.7 14.7 73.8 15.8 35.2 57.6 91.6Nickel, wppm 59.1 - 74.1 - - 0.1 131.3Vanadium, wppm 196.8 - 247.1 - - 0.2 437.8CCR, wt% 10.5 - 13.2 - - - 23.4

a) Yield values are based on total ATB feed.

Properties of the bitumen feedstock and its distillation products

Table 1





very difcult, costly and envi-ronmentally detrimental.Practically all metals andcarbonaceous material areconcentrated in the VTB frac-

tion, which constitutes thecoker/hydroconverter feed.The naphtha and gas oil frac-tions also require furtherprocessing due to their highconcentrations of sulphur andnitrogen.

The details of coker andhydroconversion reactor perfor-mance are shown in Table 2. Itis clear from the product distri-

bution that hydroconversion ismore selective towards valuableliquid products, without gener-ating solids. This is the mainadvantage of hydrogen addition

technologies over carbon rejec-tion (thermal cracking) ones.The residue conversion usingH

2 addition upgrading is about

78%, and there is a substantialcatalytic removal of sulphur,nitrogen and metals.Hydroconversion also generatesfewer C

1-C

4 compounds, but

more H2S and NH

3 due

to sulphur and nitrogen

conversion. Conversely, cokingoffers almost complete residueconversion but with signicantcoke formation (about 31 wt%

based on coking feed). There isalso nearly 100% rejection ofmetals and partial sulphur and

nitrogen elimination, all ofwhich are concentrated in thecoke. Table 3 shows the proper-ties of the liquid streams afterfractionation of the total liquidproduct for the two schemes.

Generally and relativeto coking-based schemes,hydroconversion produces

better-quality distillates due tothe catalytic hydrogenationeffect. Also noted is that for thehydroconversion-based schemethere is a portion of uncon-verted vacuum residue withmuch lower quality than theoriginal VTB feed. Usually, thisstream is recycled to the ebul-lated-bed reactor or fed to acoker unit. For this study, itwas considered that this streamis recycled back to the hydro-conversion reactor, meaning

that there is complete overallresidue conversion even whenthe once-through conversionreported in Table 2 is 78%.

The fractionated productsfrom the VTB conversion step,along with the correspondingVDU distillates, require furtherhydrotreating to reducesulphur, nitrogen and aromaticcontents for producing suitable

blending components for SCO.The properties of the hydro-treated products and nal SCOare provided in Table 4. TheSCO has no residue and verylow sulphur and nitrogencontents. The coking-derivedSCO is slightly more aromaticthan that derived fromthe hydroconversion-basedscheme. Table 5 summarises


Coker Hydroconverter

Product yields, wt%

H2S 1.5 4.3

NH3 0.1 0.5

Gas (C1-C

4) 6.1 4.0

Naphtha 15.5 12.6

LGO 20.8 34.0HGO 23.5 27.2Vacuum residue 1.5 19.2Coke 31.0 -Total 100.0 101.7H

2 consumption, scf/bbl - 1218

Conversion ,wt%

Sulphur 39.1 67.3Nitrogen 68.4 55.2Metals (Ni+V) 98.5 76.6Vacuum residue 98.5 78.0

a) Product yield values are based on total VTB feed.

Coker and hydroconverter performancea

Table 2

Coker Hydroconverter Property Naphtha LGO HGO Naphtha LGO HGO Vacuum residueYield, wt% 26.8 34.1 39.1 14.0 37.9 27.8 20.4SG 60/60°F 0.7363 0.8715 0.9736 0.7365 0.8710 0.9715 1.1240API gravity 60.7 30.9 13.8 60.6 31.0 14.2 -5.6Sulphur, wt% 1.79 3.67 4.43 0.25 0.71 1.37 6.90Nitrogen, wppm 316 1694 3973 393 1582 3063 8905Aromatics, wt% 27.1 58.0 66.0 20.5 42.5 53.0 99.8Nickel, wppm - - 8.2 - - 3.0 262.9

Vanadium, wppm - - 27.4 - - 6.2 458.3CCR, wt% - - 1.5 - - 0.2 14.3

a) Yield values are based on total liquid product.

Properties of coker and hydroconverter liquid productsa

Table 3





the details of the HDT units. Itis observed that the hydrotreat-ing of coker products requireshigher average reactor temper-atures than those ofhydroconverter products(naphtha HDT: 285°C vs 275°C;

LGO HDT: 340°C vs 335°C;HGO HDT: 370°C vs 363°C) inorder to achieve similarconversion levels. This alsoexplains why hydrogenconsumption is higher forcoker products. In the case ofHGO hydrotreating, the prod-uct distribution shows thatthere is mild hydrocracking ofHGO into LGO and naphtha.Total conversion of aromaticsis relatively low during LGOand HGO hydrotreating, sincemost of the aromatics hydro-genation is partial saturation ofpolyaromatics to form di- andmono-aromatics.

Finally, an overall compari-son of the two process schemesis presented in Table 6.The hydroconversion-basedupgrading scheme exhibits a

substantially higher yield ofSCO than the coker-basedscheme (94 wt% vs 76 wt%SCO). The difference in theSCO yield between the twoschemes is due to the fact thatthe ebullated-bed hydroconver-sion unit completely convertsthe vacuum bottoms into gase-ous and liquid productswithout forming any solid

byproducts. However, thiscomes with the cost of almostthree times more hydrogenconsumption (1269 scf H

2/bbl

bitumen vs 426 scf H2/bbl bitu-

men), which in return makesthis scheme more energyintensive.

SummaryThis article presents a detailed

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for every major unit wereconstructed and calibrated

based on representative data.

simulation of two typical bitu-men upgrading schemes usingAspen Hysys. Process models

Coker-based scheme Hydroconverter-based schemeProperty Naphtha LGO HGO SCO Naphtha LGO HGO SCOSG 60/60°F 0.7375 0.8597 0.9131 0.8680 0.7375 0.8573 0.9115 0.8665API gravity 60.4 33.1 23.5 31.5 60.4 33.6 23.7 31.8Sulphur, wt% 0.018 0.112 0.16 0.13 0.014 0.044 0.15 0.10Nitrogen, wppm 12 204 740 482 21 264 455 336Aromatics, wt% 19.9 41.8 54.2 45.9 15.8 36.5 50.9 41.7

Properties of hydrotreated products and SCO

Table 4

Coker-based scheme Hydroconverter-based scheme Naphtha LGO HGO Naphtha LGO HGOOperating conditions Liquid hourly space velocity (LHSV), h-1 2.5 2 1 2.5 2 1Average temperature, °C 285 340 370 275 335 363Pressure, MPa 4 5 9 4 5 9H

2/oil, scf/bbl 1680 1680 3370 1680 1680 3370

Product yields, wt%H

2S 1.8 2.7 3.6 0.3 1.0 2.5

NH3 0.03 0.1 0.2 0.04 0.1 0.2

Gas (C1-C

4) 0.0 0.2 0.1 0.0 0.1 0.1

Naphtha 91.7 1.5 1.6 92.8 1.4 2.3LGO 6.8 95.9 15.2 7.1 97.8 12.7HGO - - 80.4 - - 83.2Total 100.3 100.4 101.1 100.2 100.4 101.1H

2 consumption, scf/bbl 142 262 736 100 259 690

Conversion, wt%

Sulphur 99.0 95.9 95.6 95.4 95.7 94.0Nitrogen 95.8 77.7 66.0 94.3 76.0 77.1Aromatics 25.7 12.2 12.4 21.9 9.7 10.5

a) Product yield values are based on total hydrotreater feed.

Hydrotreater performancea

Table 5

Coker-based scheme Hydroconverter-based scheme

Products, wt%

Gases 7.0 8.0Naphtha 10.3 11.0LGO 30.3 42.5HGO 35.5 40.4Coke 17.6 -Total 100.6 101.9

SCO, wt% 76.1 93.9SCO, vol% 87.1 107.3H

2 consumption, scf/bbl 427 1269

a ) Product yield and H2 consumption values are based on total ATB feed.

Overall performance of the two schemesa

Table 6





The simulations predicted typi-cal upgrader performance andallowed tracking of the trans-formation of the feedstock atevery stage of the process. Itwas concluded that the hydro-conversion-based scheme is

more selective towards valuable products such as LGO andHGO and therefore exhibits ahigher SCO yield (about 94wt%) when compared withthat obtained in the coking-

based scheme (76 wt%).However, hydrogen

consumption in hydroconver-sion-based upgrading is muchhigher than that in the coker-

based scheme (1269 scf H2/bbl

bitumen vs 426 scf H2/bbl bitu-men), which makes the formeroption more energy intensive.In general, the simulation ow-sheet is versatile and can beused for exploring differentoperating scenarios. Therefore,it can be considered as animportant and useful tool toguide bitumen upgradingprocess design, operation and

optimisation.

Acknowledgments

Partial funding for this study was provided

by the Canadian Interdepartmental

Program of Energy Research and

Development (PERD 1.1.3). Comments

and suggestions from Dr Edward Little

and Dr Mustafa Al-Sabawi on revising the

manuscript are greatly appreciated. The

authors are grateful for the support and

help from IT staff at CanmetENERGY.

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Anton Alvarez-Majmutov is an NSERC

Visiting Fellow at CanmetENERGY

working on bitumen upgrading process

modelling and simulation. He holds a PhD

from Mexican Institute of Petroleum.

Jinwen Chen is a Senior Research Scientist

and Group Leader at CanmetENERGY. Heholds a PhD in chemical engineering from

Tianjin University.Mugurel Munteanu is a Lead Process

Engineer at CoSyn Technology, a division

of WorleyParsons, in Edmonton, Canada.

He holds a PhD in chemical engineering

from Laval University, Canada.


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