Hydrocracking_HP2009

Refining Developments
Originally appeared in:
November 2009, pgs 79-87.
Used with permission.
Hydrocracking solutions squeeze
more ULSD from heavy ends
New processing alternatives enable upgrading vacuum residuals
into higher-value products
F. Morel, J. Bonnardot and E. Benazzi, Axens, Rueil-Malmaison, France
D
espite the present economic crisis, demand for diesel fuels
is forecast to increase through 2020, albeit at a slower rate.
Various forecasts indicate that world demand for diesel
fuels should reach about 28.2 million bpd (MMbpd) by 2020
as compared to the present demand of 24.3 MMbpd. It is foreseen that the gap between demand for diesel and gasoline, which
during 2008 was 2.6 MMbpd, will double to approximately
5 MMbpd by 2020.
Diesel market. There are two elements within the diesel market: off-road, and on-road sales. Off-road sales relate to diesel for
marine inland waterways, for heating, and for locomotives and
tractors. This market is expected to experience an annual 0.4%
growth rate. On-road use of diesel fuel for light-duty vehicles
(LDVs), heavy-goods vehicles (HGVs) and buses is anticipated
to increase 1.8% annually through 2020.
Off-road diesel consumption will decline as a proportion of
total sales. By 2020, off-road diesel usage will represent only
40% of the global market, compared to 58% in 1990. This
change is mainly due to reduced gasoil consumption for domestic heating (Fig. 1).
Worldwide on-road diesel consumption is essentially due to
freight movement via trucks. In 2008, HGVs accounted for 74%
of diesel purchases, with buses and LDVs each consuming 13%
Worldwide diesel/consumption, %
100
On-road diesel
• Light duty vehicles (LDVs)*
• Heavy goods vehicles (HGVs)
• Buses
80
60
AAGR 08–20
+1.8 %/y
58%
40
20
0
1990
44%
Off-road diesel
• Marine
• Railways
• Heating oil
• Others
1995
AAGR 08–20
+0.4 %/y
2000
2005
2010
Asia-Pacific and EU-25 regions’ fuel demand. The
highest demand growth for diesel is expected in Asia-Pacific and
EU-25 regions, expanding by 0.7 MMbpd and 1.04 MMbpd,
respectively, over a 12-year period (see Fig. 3). Consequently, the
worldwide ratio of gasoline to on-road diesel will decrease from
1.9 in 2000, to about 1.3 by 2020. Europe will continue its established trend, falling to a very low ratio of 0.4. Conversely, North
America will remain a gasoline-oriented marketplace.
Specifications will continue to be tightened, with an on-road
ultra-low-sulfur diesel (ULSD) with less than 10 parts per million (ppm), low polyaromatics content and high cetane. These
requirements appear necessary to meet the environmental targets
for nitrous oxide (NOx) and particulate matter (PM) imposed
on engine emissions in regions such as Europe. During the next
15 years, sulfur will virtually disappear from all diesel fuels. To
complete the fuel market picture, jet fuel demand will increase,
while heavy-fuels demand will diminish.
Differential price between diesel and heavy fuel oil will continue to make resid and vacuum gasoil (VGO) hydrocracking processes attractive opportunities. The challenge will be to produce
more quality middle distillates, to convert refractory feeds and to
upgrade lower-quality refinery streams.
2020
Worldwide on-road and off-road diesel consumption.
19%
13%
40%
2015
10%
Heavy goods vehicles (HGVs)
Buses
Light-duty vehicles (LDVs)
13%
*LDVs = Passenger cars (PCs) + sports utility vehicles (SUVs) + light trucks (LTs)
Source: Axens & other sources (2009)
Fig. 1
(Fig. 2). By 2020, demand is projected to expand by 24% and reach
16.8 MMbpd. Within this increase, fuel consumption by LDVs will
have grown by 82%, and will account for 19% of total demand.
+24%
71%
2020: 16.8 MMbpd
74%
2008: 13.5 MMbpd
*LDVs = Passenger cars + Sports utility vehicles + Light trucks
Source: Axens (2009), World Business Council for Sustainable Development (2004)
Fig. 2
Worldwide on-road diesel demand.
HYDROCARBON PROCESSING november 2009
Refining Developments
Technical way forward. Hydrocracking
technology offers an excellent solution to
these issues that can upgrade a variety of feedstocks to be upgraded, including VGO from
conventional and heavy crude, deasphalted
0.10 MMbdoe
oil (DAO) from solvent deasphalting (SDA)
FSU
unit of vacuum residue (VR), coker distil0.7 MMbdoe
lates, light-cycle oil (LCO), and heavy-cycle
0.41 MMbdoe
Europe
oil (HCO) from fluid catalytic cracker (FCC)
North America
units and vacuum distillates from vacuum
0.46 MMbdoe
resid (VR) hydrocracking units (Fig. 4).
1.04 MMbdoe
0.29 Middle East
Depending on the feedstock impuriAsia Pacific
MMbdoe
ties
and conversion level required, several
Africa
0.29 MMbdoe
proven hydrocracking processes can proLatin America
vide upgrading from low to medium conversion through high to full conversion and
Global on-road diesel incremental
yields of high-quality middle distillates.
demand
2008–2020
+
3.3
MMbdoe
Source: Axens
There is no universal solution. So, different
hydrocracking technologies are required to
Fig. 3 On-road diesel incremental demand.
meet various refinery conversion needs.
Mild-hydrocracking. For example, a
mild hydrocracking process integrated with a finishing middledistillate hydrotreater can upgrade VGO and DAO -based feeds,
Crude
Topping
LCO and light and heavy coker gasoil (LCGO and HCGO)
oil
streams. This process increases the refinery’s ULSD production
while minimizing capital expenditure (CAPEX). In addition,
VGO
unconverted VGO is an excellent FCC feedstock, having a lower
CFHT*
FCC
MHC**
sulfur and higher hydrogen content.
High-pressure high-conversion hydrocracking processes. To
Hydrocracking
Vac. dist.
achieve higher conversion levels, a high-pressure (HP) high-converLCO
sion fixed-bed hydrocracking can provide full conversion of VGObased feedstocks, HCGO, or light C3 or C4-DAO, mainly to topquality middle-distillate products. This method can upgrade FCC
Residue
RDS***
effluents such as LCO and HCO. The technology can be engineered
FCC
Ebullated bed
for liquid recycle, one-stage and two-stage processes. HP high-conhydrocracking
VR
version fixed-bed hydrocracking processes have successfully produced
ULSD from VGO when integrated with a VR hydrocracking unit.
DAO
Ebullated bed
SDA
Ebullated-bed technology can be applied for deep conhydrocracking
DAO
version of high refractory feedstocks such as C5-DAO-based
HCGO
feeds—particularly difficult VGOs mainly converting them to
*CFHT = Cat feed hydrotreating; Pitch
**MHC = Mild hydrocracking
middle distillates.
***RDS = Residual desulfrization unit
In addition, new-generation hydrocracking catalysts have been
Fig. 4 VGO and residue conversion processes.
developed for a wide range of feedstock characteristics, product
Conradson Carbon Residue in feed, %
Table 1. Arabian heavy derived feeds
VGO + HCGOLCO
Heavy DAO-based feeds
MHC with
guard bed
Yield on VR, wt%
Mild
hydrocracking
Integrated hydrocracking/
hydrotreating
Low asphaltene VGO/DAO feeds
0
Fig. 5
10
20
30
40 50 60 70
Net conversion, %
VGO and DAO conversion mapping.
80
90
—
—
70
0.943
0.945
0.996
Sulfur, wt%
3.36
0.13
4.45
Nitrogen, ppm
1,550
100
2,600
Conradson carbon residue, wt%
< 1
< 0.1
12
Nickel + vanadium, ppm
< 2
< 0.1
52
< 0.05
< 0.05
< 0.05
Sp. gr.
Ebullated bed
hydrocracking
C7 insolubles, wt%
ASTM distillation, °C
100
C5 DAO
T 5%
366
239
T 50%
459
281
T 95%
555
350
Note: The VGO–HCGO blend is a typical hydrocracking feed containing 24% HCGO.
HYDROCARBON PROCESSING november 2009
529
Refining Developments
Table 2. The refractory nature of diesel from MHC is
due to high nitrogen and aromatics contents
Lights,
naphtha
VGO
Low S
VGO
Diesel
HDT
H2
SR diesel already
hydrotreated
Converted diesel
from MHC
Sulfur, ppm
265
340
4,6-DBT, % of total sulfur
37.4
35.7
Nitrogen, ppm
14
254
Aromatics, wt%
25
56
Table 3. Mild hydrocracking product results
VGO sectionPolishing section
Diesel from
CDU, FCC, VB,
coker, etc.
Fig. 6
10 ppm S
diesel to
stripping
Integrated MHC and diesel hydrotreater process.
Feed Characteristics
Sp. gr.
0.9317
0.889
Sulfur, wt%
2.67
2.0
Nitrogen, ppmw
1,392
TBP cut point, °C
350–570
200–360
Yields vs. feed, vol%
slates and quality targets. These catalysts can maximize diesel
selectivity, improve diesel and jet fuel quality, as well as upgrade
the quality of the unconverted bottoms for lube-oil production.
Guidance for selecting these technologies is listed in Fig. 5. The
X-axis represents the conversion level. The Y-axis defines the refractory level of the feedstock to be converted, expressed as Conradson
Carbon Residue (CCR) content. VR hydrocracking and residue
desulfurization technologies will not be discussed in this article.
Integrated solution for ULSD production. Conven-
tional mild hydrocracking (MHC) has a low to medium conversion rate within typically 20% to 40% of the feedstock being
converted mainly to diesel. Unconverted oil is a high-quality FCC
feedstock producing higher gasoline yields, higher octane retention and low-sulfur products. Although providing remarkable
improvements in FCC operations, MHC is not a panacea.
The low hydrogen partial pressure (typically, 40 bar to 80
bar) do not achieve a ULSD below 10 wt ppm. The diesel
obtained, owing to higher aromatics and organic-nitrogen content, is more refractory to hydrotreating than straight-run (SR)
diesel and requires further hydrotreating. This has resulted in
the integrated MHC development. The integrated MHC process resolves the problem by disassociating the quality of the
diesel cut from the conversion level, thereby achieving ULSD
specifications while avoiding the production of over-quality
FCC feed. Table 2 shows the higher aromatics and organic
nitrogen species between MHC and SR diesel, which inhibit
hydrodesulfurization reactions, making it more suitable for
refractory than for further hydrotreating.1
In the integrated MHC process flow diagram (Fig. 6), VGO
feedstock is fed to the MHC reaction section. The reactor effluent is stripped and fractionated. The hydrotreated VGO cut is
dispatched to the FCC unit or storage, while the MHC diesel
receives the entire hydrogen make-up required for both reaction
sections, after which it is polished with the reactor in a oncethrough mode.
The highest hydrogen partial pressure within the polishing
reactor enables to convert the highly refractory nitrogen and sulfur
compounds remaining in the hydrocracked diesel cut. Regardless of operating variations in the MHC section, diesel quality
is guaranteed to remain constant throughout the entire process
Naphtha
3.4
0.5
Diesel
28.7
99.0
Hydrotreated VGO
70.7
—
H2 consumption, wt%
1.17
1.08
HDT VGO (FCC feed) properties Diesel properties
Sp. gr.
0.897
< 0.845
Sulfur, ppm
< 400
< 10
Cetane number
—
> 51
Hydrogen, wt%
13.0
—
cycle. Disassociating diesel quality from the MHC operation
makes it possible to improve other characteristics such as density
or polyaromatics content.
In engineering terms, the integrated MHC process eliminates two compressors and an air cooler, while providing better
heat integration than would two separate units. Systems can be
designed to co-process other difficult refinery feedstocks, typically
LCO, LCGO and visbroken GO.
Commercial experience. Over 40 MHC units have been
licensed four of which use integrated diesel hydrotreating techniques. CAPEX ranges between $1,700/bbl and $3,200/bbl
depending on capacity, feedstock properties and conversion levels.
Table 3 lists the results of a commercial integrated MHC unit
using a blend of heavy VGO from Arabian/Russian crude, operating at 30% conversion and processing at the same time in the
integrated polishing section a blend of heavy SRGO with LCO.
The diesel cut exiting the VGO section is not inline with
Euro V specifications. This diesel cut is then co-hydrotreated in
the polishing section with a blend of LCO and heavy SRGO.
The final diesel cut achieves Euro-V specification with a specific
gravity lower than 0.845, a cetane number higher than 51 and a
sulfur content under 10 ppm.
The unconverted oil (UCO) is used as an FCC feedstock, with
hydrogen content of 13 wt% providing a gasoline production
boost to the FCC of about 14 wt%. Additional UCO hydrogen
content would only lead to a small increase in gasoline yield. In
that case, the integrated MHC technology can produce at the
same time, optimum feed to FCC and Euro-V specification diesel
stream while minimizing CAPEX and hydrogen consumption.
HYDROCARBON PROCESSING november 2009
Refining Developments
FG/LPG
FG/LPG
Naphtha
CCR/Isom
Naphtha pool/CCR
Feed
Integrated
hydrocracking/
hydrotreating
HDT
Kerosine Jet A1
SEP
Feed
Diesel Euro V
Fixed-bed
hydrocracking
HDT
Frac
Purge
HDT1
SEP1
HDT2
Integrated reaction section
Hydrocracking
Feed
FG/LPG
Fig. 9
Naphtha
pool/CCR
Kerosine
Jet A1
SEP2
Diesel
Euro V
Frac
Fig. 8
UCO
Lube oil
Single-stage high-pressure hydrocracking process using
once-through with intermediate separation.
High-conversion hydrocracking solutions. The HP
high-conversion, fixed-bed hydrocracking technology is appropriate when maximizing middle distillate production from VGO and
light DAO, and it can provide excellent characteristics and high
conversion rates for distillates. Twenty-five HP high-conversion,
fixed-bed hydrocracking units, including all three configurations,
have been licensed. Investment cost per barrel of feedstock is
$4,100 to $6,700. The choice of configuration is determined by
product slate and investment strategy.
85
Case study—three process configurations. The three
85
Full
Full
Base
Naphtha
30–35
Base -2
Base +0.5
Base -8
Middle distillate (kerosine + diesel)
65–70
Base +2
Base +15
Base +24
UCO
H2 consumption, wt%
14–20
Base -3
< 4
<2
2.5–2.9
Base +0.2
Base +0.1
Base +0.1
Middle distillate properties (kerosine + diesel)
Sp. gr.
0.820
0.829
0.823
0.826
Sulfur, ppm
< 10
< 10
< 10
< 10
Cetane number
53
50
54
56
Sp. gr.
0.835
0.835
0.838
Sulfur, ppm
< 50
< 50
< 50
Hydrogen, wt%
14.3
14.3
14.3
BMCI
< 10
< 10
< 10
Viscosity Index after dewaxing
> 120
> 120
> 120
UCO properties
Purge
Single-stage once-through configuration. Feedstock flow
is sent through two reactors in series containing hydrorefining
and hydrocracking catalysts, respectively. Up to 90% feedstock
conversion is attained, as shown in Fig. 7.
When needing to process feedstocks with nitrogen content
of 5,000+ ppm, the refining technology licensor proposed the
addition of a hydrotreatment reactor and separator, to reduce
ammonia pressure in the main process section, can be installed to
maximize hydrocracking activity (Fig. 8).
Single-stage with liquid recycle. By recycling unconverted
residue to the hydrocracking reactor (Fig. 7) a full-conversion level
can be reached. Conversion-per-pass is typically around 60 vol%,
and higher selectivity to middle distillation is achieved compared to
a once-through configuration. A small purge prevents heavy polynuclear-aromatics (PNAs) accumulating in the recycle oil loop.
Two-stage hydrocracking. The first stage operates as a oncethrough process for a mild conversion, and the unconverted fraction is separated for second-stage processing (Fig. 9). The process
offers a maximum yield of middle distillates, along with a good
diesel vs. kerosine ratio.
FeedVGO + HCGOVGO+HCGO+LCOVGO + HCGOVGO + HCGO
Scheme
1-stage 1-stage
1-stage 2-stage
Once-throughOnce-through
Recycle
Yields vs. feed, vol%
Frac
Two-stage high-pressure hydrocracking process.
Table 4. HP high-conversion fixed-bed hydrocracking results
Conversion%
Diesel
Euro V
Fixed-bed
hydrocracking
Single-stage high-pressure hydrocracking process
once-through or with liquid recycle.
H2S + NH3
SEP
2nd stage
Liquid recycle
Fig. 7
Kerosine
Jet A1
HYDROCARBON PROCESSING november 2009
different process configurations were compared using the VGO + HCGO feedstock,
as defined in Table 1. In all instances, the
middle distillate products, including kerosine, jet fuel and a ULSD cut, surpassed the
international specifications. Table 4 lists the
yields and product properties.
Single-stage once-through configuration. This is the lowest-cost configura-
tion and it provides high yields of naphthaplus-middle distillates along with UCO.
With a typical octane of 80, the light naphtha is sent to the gasoline pool, while the
heavy naphtha, with a naphthene content
of over 50%, makes an excellent catalytic
reforming feedstock.
Middle distillates yield typically is
between 65 vol% and 70 vol% and meets
ULSD specifications. The product can be
divided between on-specification kerosine
with a smoke point of 25 mm, and heavy
diesel with a cetane number higher than 60
(Table 4, column 1).
Refining Developments
UCO with a Bureau of Mines Correlation Index number less than 10 is indicative
of a highly hydrogenated product that can
be used as a steam-cracker feedstock.2 After
dewaxing, UCO exceeding 120 on the viscosity index is suitable as a Group III lube
oil base stock.
To meet middle distillates demand, some
refineries maximize LCO production from
the FCC unit, despite needing to upgrade
the LCO before being blended with the
diesel pool. One solution is to co-process
LCO with a VGO-based stream in the same
hydrocracker. LCO content in the feedstock
depends on the capacity of the FCC and HP
high-conversion, fixed-bed hydrocracking
units. Column 2 of Table 4 indicates yields
Fig. 10 Comprehensive reaction progress—3D gas chromatography.
and products obtained when 20% LCO is
blended with VGO+ HCGO, and hydrotion of zeolite-based catalysts (HYK series) as shown in Fig. 10.
cracked in a once-through mode. Most of the LCO remains as
Product quality remains excellent throughout the cycle without
middle distillate, with the rest converted to naphtha. The overall
a noticeable change in cetane number, or kerosine smoke point.
gasoline quantity is reduced, with middle distillate yields increased
Depending on the level of metal and other impurities in the feedas compared to the previous case. The cetane number of the
stock, a demetallization catalyst could be required at the top of
middle distillate is lower, but it remains acceptable. Hydrogen
the first reactor to ensure long cycle length.
consumption is marginally higher, owing to the higher aromatic
Knowledge of inhibiting species, refractory compounds, and
level in the LCO stream.
feedstocks is necessary to determine pretreatment operating conditions and select the most adapted catalysts. An understanding
Single-stage configuration with liquid recycle.
of the relative kinetic reactivity of feedstock molecules is desirSingle-stage recycle and two-stage configurations are both suitable to accurately tune the hydrogenation/acidity balance, which
able for full-feed conversion. Each produce similar volumes
improves middle distillate selectivity and qualities (Fig. 10). These
of C5+, but the two-stage configuration yields a higher diesel/
are key parameters for a successful unit design and catalyst seleckerosine ratio.
tion providing higher operability and profitability.
With the single-stage and liquid recycle scheme, the middle
distillates yield is typically 80 vol% to 85 vol%, and the quality remains high. A small purge is needed to prevent heavy PNA
Integrating high conversion VGO hydrocracking
process with VR hydrocracking technology. Residue
concentration in the recycle loop, and the purge can subsequently
be processed as part of the FCC feedstock, or as feed for a steam
hydrocracking processes use ebullated-bed technology to manage
cracker. Hydrogen consumption is slightly higher than consumpheavy feedstock containing high metal traces, sulfur, nitrogen,
tion for the once-through configuration.
asphaltenes and solids. They can achieve conversion without
producing coke material.
Two-stage hydrocracking configuration. This conThe VR ebullated-bed hydrocrackers reactor converts over
figuration provides an optimum yield of middle distillates that
75% of residue, while producing high-quality distillate VGO, and
can surpass 90 vol% with a maximum share of diesel in middle
unconverted bottoms that can be incorporated to low- or mediumdistillates. Product quality exceeds the fuel specifications. A
sulfur fuel oil storage. Further hydroprocessing units are necessary
limited purge is needed, and hydrogen consumption is similar
to upgrade primary products from residue hydrocracking.
to other configurations.
Integrating HP high-conversion, fixed-bed hydrocracking
methods with ebullated-bed technology is an interesting soluHydrocracking catalyst developments. A typical
tion to convert both VGO resulting from residue hydrocracking
hydrocracker can use three new-generation catalysts developed to
and SR VGO into diesel (Fig. 11). This solution is based on
treat a wide variety of feedstocks for the production of diverse prodan optimized management of the high-pressure pure hydrogen
uct slates, with high quality outcomes.3 Hydrorefining catalysts are
network feeding the two hydrocracking units and including
highly stable and promote hydrodenitrogenation (HDN) reactions
the amine section. The developed solution can reduce CAPEX,
to protect the downstream hydrocracking catalysts. They also ensure
while guaranteeing flexibility and independent operation. The
hydrodesulfurization (HDS) and aromatic saturation reactions.4
VGO and VR hydrocracking units are both equipped with a
Amorphus hydrocracking catalysts (HDK series) offer high
separation and fractionation section, thus maximizing diesel
cracking activity and excellent selectivity, while being very active
production. This is owing to the full recovery of VGO coming
for removing the ultimate organic nitrogen compounds. These
from the VR hydrocracking unit (no loss in the fuel-oil cut), the
catalysts orient selectivity toward middle distillates, and create
absence of ammonia and light hydrocarbons, and no asphaltene
better UCO characteristics in high VI base lube oil production.
carry-over from the ebullated-bed hydrocracking unit to the
Very high activity and selectivity coupled with full conversion,
integrated hydrocracking/hydrotreating unit.
even with refractory feedstocks, are provided by a new generaHYDROCARBON PROCESSING november 2009
Refining Developments
H2
Gas to hydrogen
separation and purification
1st stage
2nd stage
3rd stage
Common HP To FG
and MP amine
PSA and MPU
Common makeup compressor
Catalyst addition
Separator
H2 rich gas
Oil to separation
and fractionation
VGO
VDU
VGO
VR
Fig. 11
VGO full
conversion
fixed-bed
hydrocracking
VGO
separation and
fractionation
Ebullated-bed
hydrocracker
reactor
Separation and
fractionation
Ebullated-bed
hydrocracker
Naphtha
Euro V ULSD
Naphtha and gasoil
LSFO
Catalyst withdrawal
Ebullating pump
Hydrogen
Simplified scheme for ebullated-bed VR hydrocracking with
VGO hydrocracking.
Feed
Fig. 13
Ebullated-bed hydrocracking reactor system.
FG
SRGO
CDU
VGO
AR
HDT
Integrated
Fixed-bed
hydrocracker
VDU
VGO
VR
Ebullated-bed
hydrocracker
HCO
Existing/revamped
New
Middle distillate 52%
Fig. 12
LPG
C3=
FCC
VR
(100)
Naphtha
SDA at 75%
DAO lift
Asphalt (26)
Gasoline
Middle
distillate
LSFO
C3 1% LPG 7%
LSFO 7%
33%
Naphtha
and
gasoline
Refinery configuration selected.
East European case study. The ebullated-bed/hydrocracking
integrated configuration was chosen by an East European refiner.
The objective is to obtain a 70% VR conversion so as to maximize
Euro V diesel production and to produce a heavy fuel oil with less
than 1% sulfur.
The ebullated-bed hydrocracking unit will process 43,000
bpd of VR with a sulfur content of 2.9%, plus nickel and vanadium metal traces of approximately 350 ppm. The integrated
hydrocracking/hydrotreating unit is designed to treat 36,000 bpd
of a blend of SR VGO and VGO produced within the ebullatedbed hydrocracking unit.
Fig. 12 also shows the benefit of upgrading HCO produced by
the existing FCC unit. The investment will allow the refinery to
increase its Euro V diesel and middle distillates production, which
represents 52% of the crude oil, and will reduce low-sulfur fuel oil
(LSFO) production to 7%.
Hydrocracking DAO. Using DAO streams from the SDA
DAO
(89)
Unconverted DAO (15)
Fig. 14
Ebullated-bed
hydrocracker at
85% conversion
Products (74)
Overall conversion on
Ural feed: 74%
SDA plus residual ebullated-bed hydrocracking recycle
scheme.
unit can increase product output. Blended with VGO, C3 to
C5–DAOs can be processed using modified MHC and integrated
hydrocracking/hydrotreating technologies with adapted operating conditions. In case the heavier C5–DAO contains high metal
traces (often above 50 ppm) and a the CCR exceeds 10 wt%, the
ebullated-bed hydroconversion unit is more adapted to produce
light products. The DAO ebullated-bed hydroconversion unit is
the equivalent of the VR ebullated-bed hydrocracker unit.
DAO ebullated-bed hydrocracking requires online catalyst
replacement and is designed for both heavy VGO and DAO
conversion. The typical investment is approximately $4,500 to
$5,500 per barrel of feedstock.
The process uses one or several ebullated-bed reactors in
series with an upward fluid flow (Fig. 13). A circulation pump
maintains the catalyst in optimum mix and suspension, with a
constant low pressure drop. The bed is backward-mixed in terms
of both catalyst movement and reactor liquid composition.
Continuous movement of the catalyst grains and an isothermal
temperature profile inside the reactor mitigate catalyst bed plugging as compared to a fixed bed. Higher reactor temperatures
can be maintained in a moving bed system than in the fixed
type, with the former achieving a higher conversion of feedstock
to light fractions. Conversion levels over 80% can be achieved
by balancing operating temperature, residence time and catalyst
replacement rates, and hydrodesulfurization (HDS) levels of
90% to 98% are obtained.
Controlling conversion and the HDS activity level in the reac-
HYDROCARBON PROCESSING november 2009
Refining Developments
tor is obtained by
continuous catalyst
renewal from the
top of the reactor,
Feed
C5 DAO and a discharge
technology
unit at the bottom.
Yields vs. DAO Feed, vol%
Adding small daily
Naphtha
10.3
quantities of catalyst
Middle distillate (kerosine + diesel)
49.6
to the ebullated-bed
reactor is a key fea
VGO
40.7
ture that promotes
Vacuum residue
–
constant product
H2 consumption vs. DAO feed, wt%
3.03
quality. Unlike a
Yield of asphalt vs. VR feed, wt%
33.5
fixed-bed system,
Middle distillate properties
the unit’s operat
Sp. gr.
0.865
ing period is not a
Sulfur, ppm
< 300 function of catalyst
activity or pressure
Cetane number
45
drop across the bed;
VGO properties
rather, it is is deter
Sp. gr.
0.910
mined by inspection
Sulfur, wt%
< 0.20 and turnaround
Hydrogen, wt%
12.5
schedules set at
CCR, wt%
< 0.5
between 24 and 36
months.
Nickel + vanadium, ppm
< 0.1
Catalysts with
high mechanical properties have been developed to minimize
fines production; achieve high HDS activity, metals removal and
retention capacity; and ensure selective conversion of DAO into
diesel-boiling fractions.
During the processing of C4 and C5–DAO, one option is to
recycle unconverted VR fractions blended with fresh VR in the
SDA unit. This scheme succeeds in the near full conversion of
the DAO to lighter products, such as gasoline, diesel and VGO,
with only a slight increase in asphalt yield (Fig. 14).
Table 5. Hydroconversion of
heavy DAO with ebullated-bed
hydrocracking process
Case study: Combining residual ebullated-bed
hydrocracking and SDA. Table 5 provides performance
details of C5-DAO derived from Arabian Heavy crude processed
through an ebullated-bed hydrocracker. The net conversion levels of 80% can be achieved from a single-stage, once-through
ebullated-bed hydrocracker. However, unconverted DAO, using
VR product, would not be highly upgraded, and could only be
used as low-grade-sulfur fuel oil. A more attractive option is to
recycle the low asphaltene content VR product to the SDA unit
along with fresh VR feed. This will lead to a slight increase in
asphalt production from 30% to 33.5%.
The major benefit of the recycling scheme is the total elimination of heavy DAO and VR through conversion into higher
value products, as shown in Table 5. The small volume of available naphtha is a good reformer feedstock. Although the middle
distillate (50 vol% yield) has an acceptable cetane level, further
treatment in an integrated hydrotreater is required to obtain a
ULSD cut. With its low-sulfur content and a good hydrogen level,
the VGO can be sent to the FCC or VGO hydrocracker to further
increase middle distillate production.
1. Mild hydrocracking with an integrated finishing
hydrotreater can upgrade VGO-based feedstocks, enabling production of low-sulfur FCC feed while producing additional ULSD
and constraining low-sulfur gasoline output.
2. The high-conversion fixed-bed hydrocracker produces near
full conversion of VGO-based feedstocks to top-quality middle
distillate products.
3. Integrated with a residue hydrocracker, the high-conversion
fixed-bed hydrocracker can maximize ULSD throughput and
reduce the refinery’s fuel oil output.
4. Ebullated-bed technology is adaptable for deep conversion
of refractory feedstocks such as C5-DAO-containing feeds. Adding
a SDA unit ensures nearly full conversion of the DAO into lighter
products with only a marginal increase in asphalt yield. HP
LITERATURE CITED
1Sarrazin, P., J. Bonnardot, C. Guéret, F. Morel and S. Wambergue, “Direct
Production of Euro-IV Diesel at 10 ppm Sulfur via HyC-10™ Process,”
ERTC, Prague, Nov. 15–17, 2004.
2Fernandez, M., J. Bonnardot, F. Morel and P. Sarrazin, “Advantageously
Integrating a High Conversion Hydrocracker with Petrochemicals,” ERTC,
London, Nov. 17–19, 2003.
3
Benazzi, E., L. Leite, N. Marchal-George, H. Toulhoat and P. Raybaud,
“New Insights into Parameters Controlling the Selectivity in Hydrocracking
Reactions,” Journal of Catalysis, Vol. 217, No. 2, pp. 376-387, July 25,
2003.
4
Axens website—www.axens.net
Frederic Morel is product line manager for VGO and resid
conversion. Mr. Morel is working at Axens in technology department as a product line manager for VGO and resid conversion. He
was formerly manager of Axens Hydroprocessing and Conversion
Technical Services. He has 30 years of experience in oil refining,
having worked previously with IFP Lyon Development Center as a research engineer,
as a project leader of distillates and residues hydroprocessing and as development
department manager. Mr. Morel holds a degree in chemical engineering from Ecole
Supérieure de Chimie Industrielle de Lyon and a graduate degree from Institut
d’Administration des Entreprises.
Jérôme Bonnardot is deputy product line manager for VGO
hydroconversion. Dr. Bonnardot joined IFP in 1994 as research
engineer at its Lyons Development Center. He moved to Axens
in 2001 where he began as a process design engineer in the field
of distillates hydroprocessing and hydroconversion, and technical
manager for hydrocracking technology, before attaining his current position. Dr. Bonnardot is a graduate of the Ecole Supérieure de Chimie Industrielle de Lyon (ESCIL).
He holds an MS degree in chemistry from the University of Notre Dame (USA) and
received his PhD from the Université de Lyon (France).
Eric Benazzi is Axens’ marketing director. He has over 21
years experience in catalysis applied to fuels and petrochemicals.
Dr. Benazzi joined Axens in 2004 as strategic marketing manager
in charge of market analysis, business planning and acquisition
evaluation. He started his professional career as a research engineer at IFP, where he worked in the field of catalysis, specializing in zeolites and in
hydrocracking processes. Later, he moved to the economic department, where he
was responsible for investment profitability studies for refining and petrochemicals
projects. Dr. Benazzi holds a PhD in chemistry from the University of Paris, and he
graduated as a chemical engineering from the ENCSP.
Squeezing more from the bottom of the barrel. Dif-
ferent process alternatives are available for hydrocracking of VGOs,
HCGOs and DAOs, wherein the options are a function of the
demand for specific finished products and CAPEX constraints;
Article copyright © 2009 by Gulf Publishing Company. All rights reserved.
Printed in U.S.A.
Not to be distributed in electronic or printed form, or posted on a Website, without express written permission of copyright holder.
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