kbr-to vacuum or not to vacuum

7/29/2019 KBR-To Vacuum or Not to Vacuum

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Vacuum distillation units (VDU) have been the workhorse in the rening industry or recovering distillable products

contained in crude oil. The eed to the VDU is the atmospheric tower bottoms (ATB) let behind when the lighter portions

o the crude are distilled o in a column operating near atmospheric pressure. The vacuum gas oil (VGO) distilled in

the VDU is converted to lighter more valuable products, typically in a fuidised catalytic cracker (FCC) or a hydrocracker.

The vacuum tower bottoms (VTB) is the least valuable portion o the crude oil and its characteristics require cost intensive

processing, typically delayed coking, or recovery o more usable products. For a given crude mix, the renery protability will

be higher i more eed or conversion units such as FCC or hydrocracker is recovered rom ATB, while maintaining or improving

its quality.While vacuum distillation allows a decent recovery o gas oils, another commercially utilised process, solvent deasphalting

(SDA) allows urther recovery o oils rom VTB by extracting with a solvent. An ecient implementation o the SDA technology

utilises supercritical process conditions to dramatically reduce energy consumption. This technology, oered by KBR, is

Vasant Patel, Rashid Iqbal and Odette Eng, KBR, USA,

discuss residue upgrading options involving solventextraction, with and without using a vacuum column.

To vacuumor not to vacuum

www.hydrocarbonengineering.com ReprintedfromJune2007HydrocarbonEnginEEring


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called Residuum Oil Supercritical Extraction (ROSE) and

includes design eatures that allow sharper separation

between deasphalted oil (DAO) and asphaltenes. In this

process, a paranic solvent such as butane is contacted

with VTB. The asphaltenic components o VTB, which

contain much o the undesirable contaminants, are

insoluble in the solvent and rejected as a separate phase.

The soluble oil, DAO, is separated rom the solvent and isgenerally processed along with VGO thereby enhancing the

yield o more valuable products.

The eed to a ROSE unit can be either the VTB or ATB.

With ATB eed, the recovered DAO includes the part o

crude oil that could have been recovered as VGO (i the

ATB was processed in a VDU) plus additional material

that is soluble in the solvent. Thus a single ROSE unit

processing ATB will have VGO+DAO yield and quality

similar to that obtained with a conguration that includes

two units: the VDU and a ROSE processing VTB. Having

one unit instead o two is economically attractive in many

situations.

This article will provide a brie overview o the ROSE

technology and a discussion o the results o a case

study that examines the relative economics o renery

congurations that dier in the way VDU and ROSE units

are used or processing residues.

Value the bottom baelThe vacuum residue is among the least valuable

intermediate products in a renery. Renery protability is

greatly impacted by how much value is recovered rom thisstream by either processing it urther, as in a delayed coker,

by minimising its yield by deeper vacuum distillation or by

solvent extraction to recover DAO.

The steady increase in rened product demand has

lead to an increased dependency on heavier crudes to

meet the incremental demand. The heavy crudes, available

at a signicant discount to light sweet crudes, yield

signicantly more processable residue than light crudes.

Today, more than ever, there is a need to extract the

most value rom residues to realise the maximise renery

protability. Figure 1 shows how solvent extraction allows

increased recovery o oils suitable or FCC eed compared

to the traditional method o vacuum distillation.

rOSE techoloyROSE is a proven solvent extraction technology that

can be used or recovering high value eed or FCC or

hydrocracker rom atmospheric and vacuum residues. A

simplied fow sketch is shown in Figure 2. Vacuum or

atmospheric residue mixed with circulating solvent enters

the asphaltene separator. The asphaltenes are insoluble in

the solvent and are drawn rom the bottom o the separator.

A small amount o solvent carried with the asphaltenes is

stripped in a reboiled trayed asphaltene stripper.

The light phase in the asphaltene separator, containing

most o the solvent and the DAO, is heated slightly so that

the solvent and DAO separation occurs under supercriticalcondition in the DAO separator. A key eature o ROSE

is that this supercritical separation does not require ull

vaporisation o the solvent thus ar less energy is required

than in conventional SDA processed. The solvent separated

in the DAO separator leaves rom the top o the separator

and cools by giving up heat to the incoming DAO/solvent

mixture in the ROSE cross exchanger. The cooled solvent

is recirculated back to the asphaltene separator. The DAO

rom the DAO separator is heated and stripped to remove

any solvent contained in it. The solvents rom both product

strippers are mixed with the circulating solvent entering the

asphaltene separator.

The process conditions and the type o solventdetermine the DAO yield. The solvents are typically one

o the light parans: propane, isobutene, normal butane,

isopentane or pentane. The quality o DAO depends on

the yield. The higher the DAO yield, the higher the metals,

sulur and other contaminants in DAO. Typical DAO

contaminant levels are shown in Figure 3. These curves

are typical and the actual contaminant levels vary with the

nature o the eed.

The parans present in the eed are soluble in the

paranic solvents and as a result the DAO, even at high

yields, is more paranic than VGOs obtained in a VDU. For

conversion units such as FCC, this is desirable because

parans crack to desirable products easier than othertypes o molecules.

The ROSE process described above has two products,

DAO and asphaltenes. With the addition o one more

Figure 2. ROSE process scheme.

Figure 3. DAO quality versus yield.

Figure 1. Value in the bottom barrel.


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separator vessel and a product stripper, a ROSE

unit can make three products: a light DAO

(LDAO), a heavy DAO (HDAO) and asphaltenes.

Compared to the DAO rom a two product ROSE,

the LDAO can have much lower metals and other

contaminants and density. When processing ATB,

this ROSE option would provide LDAO o quality

better than LVGO rom a VDU that would make anexcellent eed to a hydrocracker. The HDAO could

be processed in an FCC.

A vast database o commercial and pilot plant

perormance is maintained by KBR to help predict

the perormance with any specic eedstock

source. The yield and solvent are determined

based on the quality targets or downstream

processing o DAO and asphaltenes.

ROSE unit eed can be either vacuum or

atmospheric residue. The eeds or two o the

grassroots ROSE units currently under design are

atmospheric residues. Two o the operating units have run

on atmospheric residue eeds when the vacuum residues

were not available.

ROSE units can be designed or large capacities

with single train ROSE units having capacities o up to

100 000 bpd.

Vacuum ut ad rOSEcompasoThe atmospheric bottoms can be processed in a vacuum

distillation unit or in a ROSE unit. The dierences between

the two are highlighted in Table 1. While ROSE can be an

alternate to a VDU, it can also economically supplement an

existing VDU by processing the vacuum tower bottoms or a

portion o the VDU eed (ATB).

Case studyHow a renery processes the residues has a very signicant

impact on the protability especially when processing

heavier crudes. In the case study presented here, three

dierent renery congurations have been considered,

each with two heavy representative crudes so as to

compare the relative economics o each conguration. The

study basis and methodology are listed below.

Grassroots reinery.

Conigurations with and without VDU and ROSE.

One set o cases with Arab heavy crude, the other set

with Maya crude.

Reinery wide balances incorporating yield and quality

estimates or each unit.

Capital and operating costs account or eed quality.

Compare capital cost and operating margin to identiy

the most economical cases.

Case definitionFigures 4 - 6 show the renery congurations. All

congurations include the atmospheric column, delayed

coker, FCC eed hydrotreater and FCC. The crude oils

processed in the renery are Arab heavy (API 28.2, sulur

2.8 wt%) and Maya (API 21.5, sulur 3.4 wt%). The renery

crude throughput or all cases is 200 000 bpd.Cases 1A and 1M (Figure 4): This is the base reinery

coniguration with a VDU. Crude or Case 1A is Arab

Heavy and or Case 1M Maya.

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Figure 4. Base refinery configuration (cases 1A and 1M).

Figure 5. Refinery configuration with VDU and ROSE (cases 2A and 2M).

Figure 6. Refinery configuration with ROSE, No VDU (cases 3A and 3M).

Table 1. Vacuum distillation and ROSE comparison

Vacuum distillation ROSE

Commercial

applications

Extensive, several hundred

commercial units

Wide, several dozen

commercial units

Feed type Atmospheric tower bottoms Atmospheric or vacuum tower

bottoms

Oil recovery

limitations

VGO recovery limited by

maximum permissible tem-perature and vacuum levels

achievable

DAO recovery not limited by

process considerations butonly by the quality of DAO and

asphaltenes products

Nominal b.p. of

heaviest recovered

components

1050 F (566 C). Design

enhancements allow some-

what deeper cut.

1200 F (649 C) or higher,

limited only by product quality

Metallurgy High TAN crudes require

upgraded metallurgy

Due to low temperature in the

key process steps, higher TAN

crudes do not require upgraded

metallurgy


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Cases 2A and 2M (Figure 5): Similar coniguration as

base with a ROSE unit added to process VTB.

Cases 3A and 3M (Figure 6): Similar as base except

that VDU is replaced with a ROSE. The ROSE eed is

ATB.

Feed and product pricing

Prices or the eedstocks and primary products are listed inTable 2.

ROSE yieldsFor this study, the ROSE yields were limited so that the

asphaltenes to be processed in the downstream coker were

limited to 38% Conradson Carbon. This resulted in DAO

quality acceptable or processing in FCC eed hydrotreater

(CFHT). Operating and capital costs or CFHT were

adjusted or eed quality. Table 3 summarises the ROSE

unit yields, eed and product qualities.

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Refinery balance and product yieldsThe yields and product quality rom each unit were

estimated considering the quality o the eed. For each

case a renery wide balance was prepared using a renery

simulation sotware package that also allowed estimates

o the utilities and blending o the nished products to

specied quality. The simulation results were used to

compare the economic merits o each case.The renery product yields or the Arab heavy cases

are listed in Table 4 (this inormation is not shown or the

Maya cases but the pattern is similar). The main dierences

in the overall yields are related to the amount o FCC eed

variations that result because o extra DAO recovered by

ROSE. The incremental liquid yield or ROSE cases is at

the cost o petroleum coke and the act that incremental

DAO when processed through FCC results in over 100%

liquid yields. For Arab heavy, the ROSE units provide more

incremental FCC eed than or Maya and the net renery

product slate improvement is more with Arab

heavy.

Economics

Arab heavyTable 5 shows the renery operating prots or

each case as well as the incremental investments

required over the base case 1A. Case 2A has

US$ 52 million/yr higher margin than base

primarily due to increased yield o liquid

products. The incremental capital or case 2A is

US$ 147 million; primarily due to the addition

o ROSE and added investments due to larger

downstream units. For FCC eed hydrotreater,

the quality o the eed was an additional reason

or higher investment. The incremental prot orCase 2A over Case 1A pays out or investment in

2.8 years.

The economics are even better or Case

3A as the incremental investment over Case

1A is smaller (US$ 66 million); the savings

rom elimination o the vacuum unit more than

osetting the investment in a larger ROSE unit.

The 1.2 year payout over Case 1A is better or

this ATB ROSE option than or Case 2A. The

yields and operating margins or Case 3A are

similar to that o Case 2A.

MayaTable 6 shows the economics when processing

Maya crude. The ATB ROSE (Case 3M) with

a payout o 2.4 years over Case 1M is more

attractive than VTB ROSE (Case 2M). Compared

to the corresponding Arab heavy ROSE cases,

Maya economics are less attractive primarily

due to the act that ROSE did not increase the

FCC eed amount as much (limited by ROSE

asphaltenes concarbon) and thus the renery

liquid product yields were less improved than or

Arab heavy.

revamp/expasocosdeatosOptions or a grassroots acility were considered

in the case study presented here in order to

Table 4. Product rates, Arab Heavy

Case 1A

No ROSE

Cases 2A

VTB ROSE

Cases 3A

ATB ROSE

LPG ('000 bpd) 17 18 18

Gasoline ('000 bpd) 95 101 101

Diesel ('000 bpd) 73 69 69

# 6 fuel oil ('000 bpd) 6 7 7

Total Liq. ('000 bpd) 190 195 195

V% crd. 95.0 97.5 97.5

Coke (million tpd) 2702 2136 2136

Sulfur (million tpd) 517 544 544

Table 2. Prices for feedstocks and primary products (US$/bbl)

Benchmark WTI crude 60.00

Arab heavy crude 50.50

Maya crude 46.75

Natural gas (for utilities) 7 (US$/million btu)

Gasoline (RBOB) 68.34

Diesel 66.70

Table 3. ROSE yield and quality

Case 2A

AH VTB

Cases 3A

AH ATB

Case 2M

Maya VTB

Cases 3M

Maya ATB

FEED

Rate ('000 bpd) 49.7 103.3 63.6 116.9

API 3.2 11.5 -0.2 7.6

CCR (%) 23.8 12.4 31.2 18.3

Metals (ppmw) 251 129 816 477

DAO PROD.

Rate ('000 bpd) 23.3 76.8 14.5 67.7

API 13.4 18.1 17.9 18.0

CCR (%) 6.0 2.2 4.4 1.5

Metals (ppmw) 9 3 8 6

PITCH PROD.

Rate ('000 bpd) 26.5 26.5 49.1 49.1

API -4.7 -4.7 -4.7 -4.7

CCR (%) 38 38 38 38


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make clear comparisons o the yields, operating margins,

investment and economics. However, the benets o

recovering more FCC (or other conversion process) eed

rom residues could be signicant in existing acilities

or the same reasons discussed in the case study. Each

renery has dierent sets o constraints and economic

drivers; it is dicult, thereore, to discuss in this

article the best way to utilise the ROSE unit toprovide incremental yield or the conversion units.

However, there are many possible ways a ROSE

unit would t in the existing renery with or without

the addition o new conversion units while still

meeting the constraints o the existing units.

CoclusoSolvent extraction o VTBs oers an economical

route to recovering more value rom heavy crude

oils by recovering more FCC eed while maintaining

the quality o eeds to other units (such as CFHT,

FCC and coker) in the renery. The overall renery

product yields and operating margin o a VDU and

ROSE combination can be achieved with a lower

capital when ROSE, without the vacuum tower,

is used to process ATBs. The margin contributed

by the addition o ROSE is the highest or crudes

or which the DAO yield can be maximised while

staying within the limits o eed qualities or

downstream units. While in this case study the

gas oil conversion unit was an FCC, economic

advantage could also be realised when the DAO is

the eed to a hydrocracker.

The results presented in this article or a grassroots

acility are also applicable or many revamp situations

where the addition o residue processing capacity may

open up opportunities or a heavier but cheaper renery

crude slate.

Table 5. Profitability, Arab heavy

Case 1A

No ROSE

Cases 2A

VTB ROSE

Case 3A

ATB ROSE

Product - Feed -

Utilities

US$/bbl crd. 10.32 11.06 11.11

US$ million/yr 722 774 778

Incremental margin over case 1A - 52 56

Incremental capital over case 1A

(US$ million/yr)

- 147 66

Payout over case 1A (years) - 2.8 1.2

Table 6. Profitability, Maya

Case 1M

No ROSE

Cases 2M

VTB ROSE

Cases 3M

ATB ROSE

Product - Feed -

Utilities

US$/bbl crd. 11.83 12.28 12.34

(US$ million/yr) 828 860 864

Incremental margin over case 1M

(US$ million/yr)

- 31 35

Incremental capital over case 1M

(US$ million/yr)

- 161 86

Payout over case 1M (years) - 5.1 2.4

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