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
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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