Post on 07-Aug-2018
transcript
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 1/12
Flexible solutions for increaseddiesel production
S
ince 1998, diesel demand in the US has
increased by approximately 40% and is
expected to continue increasing as distillate
margins outperform gasoline in the long term. As a result, reners have been, and will continue
to be, increasingly compelled to evaluate their
processing options to expand diesel production,
while at the same time complying with non-road
ultra-low sulphur diesel (ULSD) regulations and
also competing with diesel imports and the
consequences of the reduction of bunker/fuel oil.
These trends continue as feedstock quality
declines, while governments and consumers
demand increasingly cleaner fuels, and as crude
prices uctuate widely within short periods oftime.
Despite market variations, the higher margin
for diesel over gasoline has remained, although
the gap is decreasing (see
Figure 1). These trends have
forced reners to develop exi-
ble plans in taking advantage
of price uctuations in market
conditions.
Although Table 1 shows the
wider range of issues thatimpact renery diesel produc-
tion, this article will not cover
topics such as hydrocarbon
stream reconguration, hydro-
gen management, advance
process control, best practices
for unit reliability or turn-
around management. Instead,
it will focus on diesel gains via
distillation changes along with
Robert Karlin and Aris Macris Shell Global Solutions (US) Inc Raul Adarme and Kathy Wu Criterion Catalyst & Technologies LP
optimisation of FCC and hydroprocessing units.1
The right solution will depend on the individual
renery’s conguration and marketing position.
The best solution should develop out of deliber-ate evaluation of the application of technologies
and their integration within the renery to
improve return on investment as a result of
improving the rener’s ability to control the
gasoline-to-diesel ratio.
Distillation An easy way to increase diesel production in
reneries is through distillation, since adjusting
product cut points in the crude tower or in
conversion units can favour diesel productionover gasoline. Other opportunities for increasing
diesel through distillation can include:
• Crude towers (atmospheric and vacuum)
www.digitalrefining.com/article/1000610 PTQ Q4 2009 1
Distillation changes and optimised hydroprocessing units represent a broadrange of technical and economic options for increasing production of diesel
2
1
3
4
5
6
7
8
9
0
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
(U)LSD gasoline
N. AmericaULSD
(U)LSD over LSFO value
(U)LSD over HSD/HO value
Three-quarter rolling average
Diesel price vs other fuels – Gulf Coast
B / $ ,
D
S H s v e c i r p
D S L ) U (
B / $ ,
O F S L r o
e n i l o s a g s v e c i r p
D S L ) U (
70
60
50
40
30
20
10
0
–10
–20
Source: CERA data
Figure 1 Historical margins of diesel over gas oil and fuel oil (LSFO)
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 2/12
Maximise diesel while keeping ash point and
90% or 95% boiling point constant or expanding
crude tower capacity.
• Fractionation towers serving: ■ FCCU: include heavy naphtha and increase
light cycle oil (LCO) production without intro-
ducing a tail end ■ Delayed coking unit: revamp to increase
capacity and recovery
■ Hydrocrackers: adjust product cutpoints
(eg, recycle oil 5% boiling point) or revamps to
increase capacity or match changing yield slate
■ Hydrotreaters: Revamps to allow for diesel
production capacity increase.
These distillation-related revamps typically
require feasibility studies to identify and dene
options for increasing diesel production, while
2 PTQ Q4 2009 www.digitalrefining.com/article/1000610
considering the requirements for implementa-
tion and capital expenditure. These studies also
consider how technologies such as Shell GS
tower internals add value, particularly when
more severe operation is required. As reference,
Table 2 provides the advantages of Shell GS’s
several vessel and tower internals that couldcontribute to distillation revamps for increasing
diesel production.
Internal advantages commentsTo illustrate crude unit revamps for increasing
diesel recovery in a generic crude unit (atmos-
pheric tower and vacuum tower), Table 3
summarises the options concerning tower inter-
nals, pumparound location and steam usage,
while maintaining the same product
Enabling technology/ Distillation Hydrocracking FCCU FCCU ULSD Catalyst Reactor Refinery opportunities pretreating hydrotreating technology internals operationsNon-capitalOptimise cutpoints of feedstocksand product mix from alldiesel-producing units •
Optimal disposition of intermediate
streams •
Improve product quality control •
Improve unit reliability & operability •
Crude selection • • • • • • Improve utilisation of process catalysts • • • • •
Small capital Upgrade reactor internals •
Upgrade tower internals •
Evaluate and perform low-costdebottlenecking revamps • • • • • • • • Balance H
2demand with supply • • • • •
Large capital CDU/VDU reconfigurations • • • •
Conversion unit fractionation •
Revamping DHT/HCU/MHCU/CFH • • • • •
Revamping CFH to MHCU • • • •
Grassroots MHCU/HCU/DHT • • • • •
Integrated CDU/HVU/HCU/DHT solutions • • • • • • •
Areas of opportunity for increasing diesel production
Table 1
Internal Advantages CommentsShell calming section trays 10–20% capacity gain vs conventional CDU, DCU, HCU main fractionator Shell HiFi trays 10–30% capacity gain vs conventional Gas plants, light ends, HT, strippers, pumparounds of main fractionator Shell SMS(M) separator internals Up to 100% gain vs conventional Key separators in various unitsSchoepentoeter inlet device Improves separation Broad applicability on many columns and vesselsShell ConSep trays 30–50% capacity gain above high-capacity trays Large capacity with high efficiency & reliable turndown
High-capacity internals
Table 2
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 3/12
specications. The type of crude unit revamp
represented in Table 3 would provide a potential
increase of 3 vol% to 4500 bpd more diesel in a150 000 bpd renery. This additional diesel will
affect the downstream ULSD hydrotreater oper-
ation, which would need to be considered in a
nal economic evaluation.
Similar approaches for increasing distillate
production have been used to debottleneck
conversion unit fractionation sections while
maintaining diesel product specications.
Projects have ranged from small to large Capex,
with small Capex projects using tower internals
and/or changing tower pressure using pump-arounds and steam, which
allows for minimum changes to
the existing fractionation tower,
to handle the increased distil-
lates production. In contrast,
large Capex projects have
involved more signicant
changes, such as the addition of
a tower to handle additional
product fractionation —
discussed here in the context ofhydrocracking and catalytic
feed hydrotreating.
As an alternative to cutpoint
changes, the list of crudes the
renery can run could be
expanded to change the distil-
lates-to-naphtha ratio in the
crude tower and, at the same
time, to increase utilisation of
the diesel-producing units
www.digitalrefining.com/article/1000610 PTQ Q4 2009 3
within the renery. This effort is simplied by a
crude database and the associated tools available
to evaluate the compatibility and protability ofnew crudes. Once the right crude or crude blend
is selected, crude tower operations should be
optimised, which may require small Capex
debottlenecking.
Hydrocracking Most of the conversion capacity of hydrocrackers
operating in North America is geared to the
gasoline market. Nevertheless, many hydroc-
rackers have some exibility for switching from
gasoline to distillate mode by adjusting process
Base Case 1 Case 2 Case 3 Case 4Description of change Baseline unit Increase CDU VGO recycle Reconfigure vac Route HAGO operation internal reflux to CDU tower for top from CDU to VDU
diesel productVol% of total diesel product 33 34 34 35 36Vol% of total diesel in crude recovered 91 93 94 96 98Probable Capex required Zero (base) Zero to low Low Med to high Med to high
Comments Typical operation Shift in heat Case 1 + VDU space dependent. Case 3 + additionalremoval profile additional Additional frac bed piping & controls
could affect piping possible incremental preheat train/ & controls loss of HVGO due
furnace firing to higher VDU dP
The % of total diesel is at constant diesel TBP 90% and flash point. Crude distillation unit (CDU); heavy atmospheric gas oil (HAGO); vacuum distillation unit (VDU);
light vacuum gas oil (LVGO). Special care would be required to avoid introducing a bottoms tail that could affect HDS units.
Increasing diesel recovery in a crude distillation unit
Table 3
10
20
30
40
50
60
70
80
90
100
0Naphtha mode Distillate mode Revamp
% l o v ,
d l e i y e t a l l i t s i D
CAPEX
Catalyst
Internals
Diesel op
Normal op
Figure 2 Example of increasing hydrocracker diesel yield
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 4/12
parameters, such as cracking conversion, liquid
recycle rate and product cut points, without
requiring Capex. Further increases in diesel
production and quality from existing assets can
be achieved through changes in catalyst andinvestment in small or large revamp projects.
Clearly, each hydrocracker is unique and
requires a detailed analysis of feed diet, operat-
ing constraints and desired yield to adjust and
optimise operations. Maintaining exibility to
adjust to market conditions and building in the
capability to handle a variety of feeds will allow
for maximum protability from the
hydrocracker.
The remainder of this section discusses
options for increasing diesel in
existing hydrocracking units and
the development of grassroots
units for current and future
crude sources.
Increasing diesel fromhydrocrackersFigure 2 illustrates the potential
increase in distillate yield based
on a single- or two-stage hydroc-
racker, for which the main
fractionator bottoms are used in
diesel pool blending. Feed qual-
ity, especially the nal boiling
point, needs close monitoring in
these units to meet diesel
specications.
Hydrocracker distillate mode
operation is typically achieved byswitching from a recycle opera-
tion to a once-through operation
while lowering conversion, which
increases diesel (bottoms)
production, as depicted in Figure
3.
Lower conversion may result in
lower distillate quality due to an
increase in aromatics and a resul-
tant drop in American Petroleum
Institute (API) gravity. A drop inproduct quality can be overcome
through the use of a more distil-
late-selective catalyst that will
improve distillate quality via
higher hydrogenation activity
while improving distillate yields.
Hydrocracking catalystsFigure 4 shows the middle distillate selectivity
and cracking activity of exible and naphtha-se-
lective catalysts.In many reneries, an improvement in distil-
late yield and quality has been realised by
switching from a naphtha catalyst to a conven-
tional, exible catalyst. Table 4 illustrates the
advantages of this change in catalysts in a North
American renery.
At this renery, the hydrocracker was
constrained by the gas make from the hydroc-
racker. Since the gas make and hydrogen
consumption were lower for the exible catalyst,
4 PTQ Q4 2009 www.digitalrefining.com/article/1000610
20
0
40
60
80
100
120
80 70 60 50
Overall conversion
f f
% l o v ,
d l e i y n e g o r d y h e v i t a l e R
Relativehydrogen
Naphtha
Distillate
5% loss involume gain
Figure 3 Reducing conversion in HCU to maximise diesel
Z-2723
Z-3723
Z-3733
Z-853
Z-863
Z-723
Z-733
Z-803
Z-753
Flexible
Naphtha
Cracking activity
y t i v i t c e l e s e t a l l i t s i d e l d
d i M
New generation
Z-3xxx: HDA , HDS
State of the art
Conventional
Z-2xxx: HC , ISO
Figure 4 Reducing conversion in HCU to maximise diesel
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 5/12
the feed rate to the unit could be increased to
match the renery’s capacity to handle the gas
generated from the hydrocracker and supply
hydrogen to the hydrocracker. The increase in
the feed rate, combined with the increased selec-
tivity of the catalyst, meant increased barrels of
distillate production. The lower activity of the
exible catalyst compared to the naphtha cata-
lyst did not limit the hydrocracker’s overall
catalyst cycle, since the cracking catalyst’s
temperature window still tted within the
pretreat catalyst’s operating temperature
window.
Although the reactor loop pressure drop was
not an issue in this example, lowering the reac-
tor pressure drop is always benecial to
hydrocracker operation, particularly if it is a
limiting factor for the hydrocracker feed rate
and/or cycle life. The catalyst shape TX has been
designed to reduce pressure drop across thereactor high-pressure loop.2
Hydrocracker revampsFigure 3 shows that an attempt to maximise the
distillate yield by lowering conversion resulted in
reduced hydrogen consumption. Increasing the
feed rate to utilise the available hydrogen can
recover the losses in volume gain across the
hydrocracker.
Thus, the primary modication to gasoline
hydrocrackers to improve distillate yield andthroughput involves a revamp of the fraction-
ation section(s). Hydrocracker revamps for
maximising the distillate range from:
• Small Capex: debottleneck -
ing projects, reactor internals,
tower internals
• Medium Capex: additional
fractionation capacity
• Large Capex: modifying the
reactor section to signicantly
increase throughput.Since, hydrocracker debot-
tlenecking revamps are unique
to each renery, this article
focuses on a higher-level
description of revamps.
Small Capex revamps
Shell GS has maximised distil-
late yield through minor
modications to the fractiona-
tion section of hydrocrackers. In gasoline
hydrocrackers where light and heavy naphtha
are drawn from the main fractionator, the heavy
naphtha draw has been redesigned as a distillate
draw. This modication, for example, increased
the cut point of the fractionator bottoms from
~195°C to ~290°C. It also increases the boiling
range of the recycle oil, thus signicantly mini-mising the cracking of light and middle distillate
products to light naphtha.
Another common hydrocracker revamp
involves replacing existing reactor internals with
Shell GS reactor internals. Some gasoline
hydro-crackers that were designed for an all
vapour phase quench zone have required new
internals based on changes in feed and conver-
sion. It is well documented that this strategy of
minimal capital investment increases liquid
yield. These benets have been seen in over 300hydroprocessing applications, including hydroc-
rackers owned and operated by reners
worldwide.
www.digitalrefining.com/article/1000610 PTQ Q4 2009 5
Table 4
Gas make, scfb -15%Naphtha, vol% ff -1.4Distillate, vol% ff +1.8Unconverted (UCO), vol% ff BaseFeed rate, bpd +15%
Distillate, bpd +20%H2 consumption, MMscfd Base
Commercial results for catalyst changeto increase distillate production
Figure 5 Cross-section of TL Trilobe shape compared to the new TX Trilobe shape
2
4
6
8
10
12
0
10 2 3 4 5 6
TX
2
4
6
8
10
12
0
10 2 3 4 5 6
TL
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 6/12
Replacement of older generation internals with
new internals enabled the catalyst volume in the
reactors to be increased by 11%.2 As a result
of new reactor internals, combined with the
implementation of the new TX catalyst shape,the unit now provides a more protable opera-
tion, indicated by:
• Lower weighted average bed temperature
(WABT), although at higher throughput and
higher conversion (roughly 2–3% higher)
• Signicantly lower liqueed petroleum gas
(LPG) make (previous enhanced oil recovery
(EOR) limiter) and hydrogen consumption from
the hydrocracker
• Increase in total distillate API and yield from
the unit at a constant overallconversion along with improved
yield stability over the catalyst cycle
(Figure 6).
The benets of the modications
to the hydrocracker were approxi-
mately $3 million per year.
Medium Capex revamps
For some reneries, the opportu-
nity to bring heavier feeds into a
hydrocracking unit is desirable, butin cases where the fractionator
bottoms is diesel pool blending
material, adding heavier feed to the
hydrocracker is likely to render the
diesel unsuitable for blending. The
addition of a vacuum asher
(depicted as the red column in Figure 7) to
recover diesel uncouples feed back-end from
diesel cold properties and enables the processing
of heavier/better feeds for maximising the distil-
late yield.Once the means are in place to lift distillate
from the bottoms product, increasing feed heavi-
ness and/or changing catalyst type are the next
steps in maximising distillate yields. The addi-
tion of light vacuum gas oils (LVGO, ~5–20%
depending on the unit) will improve the overall
diesel yield from the feed. Essentially, LVGO will
crack to two diesel molecules, while atmospheric
gas oils tend to crack to diesel and light naphtha.
Changing catalysts to a more diesel-selective
6 PTQ Q4 2009 www.digitalrefining.com/article/1000610
Days on stream
5
10
15
20
25
00 200 400 600 800 1000 1200 1400
Current
Previous
% ,
d e e f
h s e r F
Figure 6 Commercial example of higher distillate yield from Shell GSreactor Internals
Off gases
Naphtha
H2H2
2nd stage feed
1st stage feed
Distillate
Bleed
Figure 7 Illustration of a hydrocracker fractionation section revamp withthe addition of a vacuum flasher
LVGOAdditional LVGO to base feedrate, vol% +13
Catalyst NaphthaGas make, wt% ff -1.1Light naphtha, vol% ff -2.4Heavy naphtha, vol% ff -5.9Distillate draw, vol% ff +6.0UCO (distillate), vol% ff +1.4Distillate production, bpd +30%H
2 consumption, MMscfd Base
WABT, °F +6Total liquid product SFCaromatics, wt% Base
Increase in distillate productionfrom a gasoline hydrocracker through
additional fractionation
Table 5
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 7/12
catalyst will improve distillate yield and quality.
Table 5 illustrates the potential increase in distil-
late production from a base case, described as a
gasoline hydrocracker already operating in distil-
late mode with the additional fractionation of
distillate from the bleed stream. In
the LVGO case in the right-hand column, addi-
tional LVGO is added to the feed to improve
distillate production. The addition of a vacuum
asher has been utilised in at least one North
American hydrocracker to maximise diesel
production.
LVGOLarge Capex revamps
Larger Capex hydrocracker revamps include
paralleling of the stages (conversion to single
stage). These types of revamps will signicantly
increase the feed to the hydrocracker (more than
100%), but they depend on the number of cata-lyst beds available in the rst- and second-stage
reactors. In one North American renery, where
this type of revamp occurred, a portion of the
FCC feed was directed to the revamped hydroc-
racker in return for high-quality bottoms product
from the hydrocracker. A number of other modi-
cations are required for this type of revamp to
succeed, including areas in the fractionation
section.
Grassroots hydrocrackers for difficult feedsFor maximum diesel production, grassroots
hydrocrackers may be hard to justify in the
current economic environment. They are,
however, denitely part of the long-term strategy
of maximising diesel, especially if lower-priced,
heavier, sour feedstocks are used more in
the future.
Making diesel from difficultfeeds and heavy oil fractions
Signicant growth in the produc-tion of renery feeds from
bitumen-based reserves has been
achieved recently and is expected
to continue to grow throughout
the next decade. Canadian and
Venezuelan sweet synthetic
blends, and Canadian sour crudes
are now providing alternative
feedstocks for reners.
In addition to the change in
crude quality they present, difcult streams such
as heavy coker gas oils (HCGO), deasphalted oils
(DAO) and deep-cut heavy vacuum gas oil
(HVGO) have been economically attractive to
upgrade to diesel. Upgrading these crudes and
difcult feeds to clean fuels requires an under-
standing of the feed quality and chemistry
involved, familiarity with operating experience
from processing such feedstocks, and expertise
in combining catalyst technology for heavy gas
oil service and reactor internals, which has
provided reners with the opportunity to process
these feeds economically.
Recent licences An example of a key conversion process unit is a
state-of-the-art DAO hydrocracking unit achiev-
ing 60% conversion, processing DAO feed from
a solvent deasphalting (SDA) unit.3 The combi-
nation of SDA and hydrocracking provides aexible and economical solution to convert
heavy oil to high-quality ultra-clean fuels from
the hydrocracker, such as:
• Kerosene meeting Jet A1 fuel specications,
with sulphur <10 ppmw
• Diesel meeting Euro V specications, with
sulphur <10 ppmw
• Unconverted oil for producing 10 ppmw
sulphur FCC gasoline.
Step changes in middle distillates production
(jet plus diesel) can be achieved from increas-ingly more complex and more expensive residue
upgrading options (see Figure 8). Each technol-
ogy increases net present value (NPV) by
producing higher-value products. When Capex is
not a constraint, applying higher complexity,
high conversion technology, such as delayed
www.digitalrefining.com/article/1000610 PTQ Q4 2009 7
Relative kerosene + diesel, t/d
Residue conversion unit
500
1000
2000
3000
1500
2500
3500
0Shell
deepflashDeep thermal
crackerDelayed
cokerVisbreakerBase
VDU
d / t ,
d l e i y e t a l l i t s i d e l d d i M
Figure 8 Summary of middle distillates comparison for expanded refinery
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 8/12
coking, results in maximum middle distillate
production and highest NPV.
CFH/FCCFCC continues to serve an important role in the
rening industry producing gasoline, with an
estimated 350–400 FCCUs operating world- wide and over 100 in North America. Heavier
and sourer feeds, combined with lower product
sulphur requirements, have required pretreat-
ment of the feed in a catalytic feed hydrotreater
(CFH) or post-treatment of the FCC products in
various hydrotreating units. Continuing
changes in product pricing and quality have
raised questions of how best to utilise CFH/
FCC assets to balance gasoline and diesel
production.
Obtaining maximum distillate yield from theCFH/FCC complex can be achieved via:
• Improving FCC technology and catalysis to
increase conversion of vacuum gas oil feedstocks
into more valuable middle distillates, gasoline
and olen products
• Operating FCCU distillation to optimise the
gasoline-to-diesel ratio in accordance with
downstream hydrotreating capabilities and
market demand
• Recovering diesel from a CFH or converting a
CFH to mild hydrocracking in markets where
diesel is valued higher than gasoline.
FCCUs An FCCU can be operated in different modes to
increase distillate production using:
• Different FCC catalysts
• Lower conversion
• Product cut points (FCC heavy naphtha to
LCO).
Benets and costs from changes in FCC opera-
tion are unit dependent and require thorough
evaluation of each FCCU.
Shell GS introduced the middle distillate and
light olens selective (MILOS) process technol-
ogy as a longer-term, higher Capex opportunity
to increase diesel production and olens from an
FCCU.6 One of the most important features of
the MILOS technology is its exibility to take
advantage of market conditions and seasonaldemands, with capability to operate at:
• Maximum propylene and diesel mode or
• Maximum propylene (maximum conversion)
mode.
MILOS can process a wide variety of feed
components, such as rafnate, FCC naphtha,
coker naphtha, gas-to-liquid (GTL) wax, vegeta-
ble oils and palm oil.
LCO produced from MILOS is higher than that
produced by conventional FCCUs and with
better cetane. Incremental LCO produced fromthe FCC (conventional or MILOS) will have to be
hydrotreated before it goes to the ULSD pool.7,8
Catalytic feed hydrotreating Although the main purpose of a CFH unit is to
improve the quality of the FCC feed, there is an
opportunity to produce diesel from a CFH unit if
it can be fractionated from the hydrotreated
VGO before it goes to the FCCU. Diesel boil-
ing-range material is usually part of the CFH
feed, and more diesel is produced as carbon-sul-phur bonds are broken during the
desulphurisation process. Distillate yield can be
improved by increasing CFH severity and
increasing the VGO conversion through modied
operating strategies or catalyst systems.
Criterion’s Ascent catalysts have enabled reners
to achieve both ULSD (directly from the CFH
unit) and Tier-II gasoline (directly from the
FCCU) production.5 Typically, a CFH unit oper-
ating at moderate to high severity is required to
8 PTQ Q4 2009 www.digitalrefining.com/article/1000610
CFH operating conditionsCatalyst system DN-3551Capacity, bpd 80 000Pressure, psig 2000Gas-to-oil ratio, scfb 4500Feed type SR VGO, coker gas oil,
coker naphthaAPI 22Sulphur, wt% 2.5Nitrogen, ppmw 1050ASTM D2887 10%, °F 516ASTM D2887 90%, °F 1150Metals, ppm <8 ppmCCR, wt% 1.1
Gas oil product API 32Sulphur, ppmw <75
Nitrogen, ppmw 20 Metals, ppmw <0.3
CCR, wt% <0.3 Diesel product sulphur, ppmw <8
Feed and operating conditions
Table 6
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 9/12
produce a ULSD diesel-blending stream.
Reducing the diesel product’s end boiling point
may be necessary, and diesel cetane depends on
the CFH feed. ULSD for the North American
market is easier to make from a CFH, as it does
not have such stringent cetane requirements as
European diesel.
In one renery, the addition of a delayed
coking unit eliminated the need for the
high-pressure residue hydrotreating unit to
process residue. This enabled the high-pressure
hydrotreater to be used as a CFH. Working with
Criterion, the client was able to use this existing
asset at a high level of performance, to provide
both direct production of ULSD from the unit
and low-sulphur gasoline production from
the downstream FCCU. Table 6 summarises the
feed and operating conditions of this unit.
Distillation capabilities are required to produce
ULSD from a CFH unit. The addition of a frac-tionator in series with an existing stripper will
allow for diesel production. Many recent Shell
GS CFH designs include an integrated stripper/
fractionator to recover ULSD.
Producing diesel from a CFH unit will require a
unit-wide feasibility study to ensure the safety
and reliability of the unit is preserved. Hydrogen
consumption, recycle gas requirements and cata-
lyst bed temperature control have to be within the
design margins of the CFH unit. As the severity of
the CFH unit increases, additional light hydrocar- bons and ammonia are produced, which may
cause corrosion issues for the product cooling and
separation equipment in the CFH unit. Possible
solutions can be evaluated through a closer look
at the existing water wash system and amine
treating equipment.
Mild hydrocracking (MHC)Operation of a CFH to produce more middle
distillate can be achieved by increasing conver-
sion. This more severe operation operates in amild hydrocracking mode at higher reactor
temperatures with the existing catalysts and, in
many cases, modifying the catalyst system to
include a more active conversion catalyst such as
an amorphous silica-alumina (ASA) or zeolite.
The difference in operating mode can be seen in
Table 7.
Depending on the conversion and distillate
selectivity required, all alumina, alumina/ASA or
alumina/zeolite stacked systems can be consid-
ered. Higher conversions can be achieved by
alumina/ASA stacks and even higher by
alumina/zeolite stacks compared to a total
alumina system. Figure 9 summarises internal
pilot plant work for cases where a set catalyst
volume is available.
Although operation in the MHC mode using
only the existing reactor volume offers many
potential advantages, it can also have technicaland economic constraints. The relevance of these
constraints varies from renery to renery and a
careful technical and economic evaluation is
needed before converting the unit’s operation.
Several issues need to be considered:
• Product separation capabilities may be a seri-
ous issue, depending on existing conguration;
where a fractionation section is in place, the
tower internals can provide a low-cost solution
for increased diesel production
• The increased conversion will result in more vapour trafc, which needs to be accommodated
for safe operation of the unit
• Additional requirements for water wash, gas
treating and fractionation section equipment
constraints need to be reviewed and addressed
• Conversion of VGO streams may leave the
FCC under-utilised, unless there is additional
FCC feed available, (for instance, from imports),
or there is additional FCC pretreat capacity
(through debottlenecking)
• Additional hydrogen should be available because unit expansion and/or higher conver-
sion will require more hydrogen consumption
• The MHC operation will result in additional
naphtha that may need additional processing
• Seasonal demand factors may lead to opera-
tion with gasoline in the summer and middle
distillate in the winter, so the advantage can only
be realised for a part of the year
• The FCC pretreat unit will have shorter cycles
operating in the MHC mode
www.digitalrefining.com/article/1000610 PTQ Q4 2009 9
Table 7
CFH operation MHC operationCatalyst system options Total alumina Total alumina,
alumina/ASA,alumina/zeolite
Typical WABT, °F 680–750 715–795Conversion to 650°F minus vol% 5–10 10–50
Feed and operating conditions
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 10/12
10 PTQ Q4 2009 www.digitalrefining.com/article/1000610
internals or performing other small
debottlenecking revamps. Depending
on the renery economics, a rener
may also conclude that a new unit is
necessary for maximum diesel
production.
Improved hydrotreating catalysts A strong ULSD catalyst portfolio is a
key enabler for upgrading diesel
quality to meet the sulphur speci-
cation and also to have the ability to
treat more difcult feeds. This is
particularly the case when upgrad-
ing requirements go beyond sulphur
specications and address the
following key elements:
• Maximising activity to reduce the volume of
catalyst to achieve ULSD targets, freeing up
reactor volume for additional feed capacity orother upgrading catalyst system options
• Providing a range of CoMo and NiMo cata-
lysts to control hydrodesulphurisation (HDS),
hydrodenitrogenation (HDN) and hydrodearo-
matics (HDA) in feed preparation for additional
upgrading catalyst system options
• Offering the ability to control hydrogen
consumption to balance the higher hydrogen
requirements associated with additional upgrad-
ing requirements. Criterion has developed CoMo
and NiMo ULSD catalysts that provide very highHDS activity/performance.8
These new catalysts can produce ULSD in a
reactor volume, which is 75% of that required
with rst-generation ULSD catalysts. Therefore,
reners who designed their ULSD units with
rst-generation catalysts can take advantage of
the additional activity to increase run length,
process more barrels, or process tougher feeds
such as LCO and light coker gas oil (LCGO).
As feed capacity increases and feed quality
becomes more difcult, more complex revampsand possibly a new unit design may be required.
Dewaxing catalystsReners who market ULSD in cold climates may
also have the opportunity to increase diesel
production by maintaining a high-diesel
end-point during the winter months or utilising
a more diesel-selective dewaxing catalyst in their
existing distillate HDS/dewaxing units.
Shell GS and Criterion have developed selec-
• Typically, cycles are halved (although this
depends on the feed, operating conditions and
conversion target). A higher Capex solution is to convert the CFH
unit to a mild hydrocracker, with the addition of
catalyst volume (an additional reactor) and the
necessary revamp to take full advantage of the
higher conversion in the unit and increase both
the selectivity of the product and the operating
cycle of the unit. Similar issues need to be
resolved in the revamp to a mild hydrocracker.
In addition to CFH units being converted to
mild hydrocracking, in 2002 Criterion and Shell
GS, working with the Naftan Renery, revampeda distillate hydrotreater (DHT) unit to MHC
operation. The project made maximum use of
existing hardware at the renery in Novopolotsk,
Belarus.7
The mild hydrocracker conversion of VGO to
distillates is typically in the order of 45 wt% with
ultra-low sulphur fuels produced simultaneously.
The unit has experienced more than twice the
expected cycle length due to the excellent stabil-
ity performance of the selected catalyst system
and the use of updated reactor internals.
Diesel hydrotreating/ULSD With the initial wave of ULSD production well
established, attention has turned toward maxim-
ising diesel production in these new assets, as
well as looking forward to future requirements. A
rener has the ability either to increase the feed
rate to these units, or to process more difcult
feeds by utilising improved hydrotreating cata-
lysts, adding dewaxing catalysts, installing reactor
Overall 700°F + conversion, wt%ff
22
24
26
28
30
32
2015 20 25 30
f f
% t w ,
d l e i y e t a l l i t s i d
e l d d i M
Alumina
Alumina/zeolite
· Higher conversion levels
· Lower MD yields
Alumina/ASA
· 4% higher conversion
· 4% higher MD yields
Figure 9 Summary of catalyst systems to achieve varying levels ofconversion
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 11/12
www.digitalrefining.com/article/1000610 PTQ Q4 2009 11
capability to respond to market variation,
particularly when pursuing a targeted gaso-
line-to-diesel ratio.
Depending on a rener’s business goals and
the existing renery conguration, technical
solutions are available that encompass the whole
renery or focus on individual units.
Distillation and hydroprocessing are key tech-
nologies enabling enhanced production of diesel.
Combining unit know-how with best available
technologies and attention to renery-wide inte-
gration will provide optimal, renery-specic
solutions.
The authors wish to thank and acknowledge the contributions
of many colleagues in the preparation and review of this paper:
Sal Torrisi, Larry Kraus and Ward Koester, Criterion Catalysts &
Technologies; Robert Redelmeier, Keith Whitt, Vito Bavaro, Russ
Anderson, John Baric and Dave Dupree, Shell Global Solutions.
References
1 Hu M, Anderson R, Adarme R, Ouwehand C, Smegal J, The era
of ULSD — new challenges and opportunities for hydrocracking
processes, NPRA 2006 Annual Meeting, AM 06-46.
2 Sharpe A, Jones B, Hruska V, Baumgartner G, Anderson
R, Adarme R, Hu M, Ouwehand C, Boer M, A success story:
significant improvement in hydrocracker profitability with ULSD
production through customised catalyst systems, state of the art
reactor internals and outstanding technical cooperation, NPRA
2007 Annual Meeting, AM-07-67.
3 Blew W (Grupo Lotos), Baric J (Shell Global Solutions), Residue
upgrading opportunity with Shell DAO hydrocracking technology,RRTC, Apr 2008, Moscow, Russia.
4 Baric J, Selecting the residue conversion scheme for optimised
diesel production, ARTC, Mar 2009, Kuala Lumpur, Malaysia.
5 Carlson K, De Haan D, Jongkind H, Continued gains in FCC
performance: gains in process capability used effectively in clean
fuels production, ERTC, Nov 2008, Vienna, Austria.
6 Nieskens M, MILOS — Shell’s ultimate flexible FCC technology
in delivering diesel/propylene, NPRA 2008 Annual Meeting, AM-
08-54.
7 Artuch A, Shishov O, Yakubenka U (Naftan Refinery),
Samolienko I, Scheffer B, Kalospiros N, McNamara D (Criterion
Catalyst & Technologies) Kenna C, Snaijer A (Shell Global
Solutions), Increased upgrading at low cost: customised revamp
of a distillate hydrotreater into a mild hydrocracker, BBTC, Apr
2005, Moscow, Russia.
8 Torrisi S, Kraus L, Beyond ULSD, NPRA 2009, AM-09-11.
9 Huve L, Robertson M, Linde B, Pankratov L, Kalospiros N, Gitau
M, Ultra low sulphur diesel with dewaxing: a key technology for
profitable supply of high quality ULSD diesel, RRTC, Apr 2006,
Moscow, Russia.
Robert Karlin is a Senior Hydroprocessing Specialist, Shell
Global Solutions (US) Inc. He is based in Houston, Texas, and
tive cracking (SDD-800) and isomerisation
(SDD-821) dewaxing catalysts.8,9 Selecting the
right hydrotreating catalyst in combination with
SDD-800 allows for a drop-in option for many
existing ULSD units looking for a reduction in
the ULSD cloud point or improvement in cold
ow properties. SDD-800 is formulated to mini-
mise naphtha and light gas production in
selective cracking dewaxing mode and, when no
dewaxing is required, the dewaxing bed can
simply be switched off by quenching. In existing
dewaxing units, the diesel produced for an
equivalent improvement in cloud point is 5–10
wt% higher than with conventional dewaxing
catalysts8 and will allow for higher diesel produc-
tion instead of naphtha.
Small Capex revampsIn addition to catalyst activity and type, reactor
internals, especially for older generation HDSunits, are key to any successful revamp for a
capacity increase to take advantage of the
latest catalysts. Shell GS reactor internals for
gas-liquid distribution (HD Trays) and interbed
quenching (Ultra Flat Quench) have signicantly
enhanced the operation of lower- pressure HDS
units. Their designs utilise “lter trays” installed
in the top of the lead reactor(s) to mitigate pres-
sure drop and make better use of reactor volume
by reducing the volume of catalyst previously
used for pressure drop control.In a particular application, employing these
internals has allowed for ~30% higher catalyst
volume to be used which, with a higher activity
catalyst, resulted in a ~85% capacity increase
based on barrels processed.
To fully achieve the capacity increase provided
by the catalyst and reactor internals, evaluation
of other equipment should be performed to
ensure the successful implementation of any
expansion project. Issues to be evaluated include
hydrogen consumption, treat gas rates, quenchcapacity, recycle loop pressure drop, furnace
capacity, product stripping, water wash, and
corrosion, to mention a few.
ConclusionThe correct solution for increasing diesel
production should develop out of evaluation of
the application of technologies and their integra-
tion within a renery. Flexibility within
an overall renery approach can increase the
8/20/2019 Flexible Solutions for Increased Production
http://slidepdf.com/reader/full/flexible-solutions-for-increased-production 12/12
12 PTQ Q4 2009 www.digitalrefining.com/article/1000610
Kathy Wu is Senior Hydrocracking Tech-Service Engineer, Criterion
Catalyst & Technologies LP. She is based in Houston, Texas, and is
responsible for hydrocracking technical support in the Americas
for Criterion Catalysts and Zeolyst International.
Email: kathy.wu@CRI-Criterion.com
is responsible for Shell Global Solutions’ hydroprocessing
technology and design efforts.
Email: robert.karlin@shell.com
Aris Macris is Licensing Technology Manager, Shell Global
Solutions (US) Inc. He is based in Houston, Texas, and is
responsible for Shell Global Solutions’ licensing technical
hydroprocessing efforts in the Americas.
Email: aristides@shell.com
Raul Adarme is Global Manager, Hydrocracking, Criterion
Catalyst & Technologies LP. He is based in Houston, Texas, and is
responsible for the hydrocracking catalyst business for Criterion
Catalysts and Zeolyst International.
Email: raul.adarme@CRI-Criterion.com
LINKS
More articles from: Shell Global Solutions International
More articles from the following categories:Hydroprocessing