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Licensing Solutions
for Tomorrow
Maximising diesel production
through integrated Hydroprocessing
Well integrated hydroprocessing technology –
for hydrotreating and hydrocracking – can
give refiners an edge over their competition.
John Baric – Licensing Technology Manager, Shell
Global Solutions International B.V. and Justin
Swain – Technical Director, Criterion Catalysts
and Technologies Ltd discuss specific technology
differentiators and case studies which resolve key unit
performance issues and boost margin for refiners.
Hydroprocessing faces significant challenges as
crude feeds get heavier; there will be more sulphur
and nitrogen to extract; more aromatics to saturate;
more metals to remove; and more coke to deal with.
Refiners also have ageing facilities, which may not be
designed and optimised to meet these new challenges.
In an economic environment of constrained capex,
many refiners have successfully revamped their
existing hydroprocessing units with Shell’s reactor
internals technology and the latest generation of
catalysts from Shell’s partner Criterion – the largest
global supplier of hydroprocessing catalysts.
In order to get maximum value from a
revamped unit, the catalyst and the quality of the
reactor internals must both be optimized. The
catalysts have to be protected from particulates
and foulants, and the reaction and catalyst
utilisation must be maximised. In any multi-bed
hydrocracking reactor, for example, particulates
can accumulate even if sophisticated automatic
backwash feed filters are present, affecting top
bed catalyst performance.
Optimum reactor internals design is vital.
Shell installs filters into the top dome of all
vacuum gas oil (VGO) hydrocrackers and residue
hydrodesulphurisation (HDS) units, without
effecting reactor size, cost or affecting active catalyst
volume. The filters have proven to be extremely
effective for coarse removal of particulates that
could cause pressure drop and misdistribution in
the catalyst bed. A liquid-vapour distribution tray
beneath the filters ensures that vapour and liquid
have full radial dispersion across the catalyst bed,
resulting in nearly 100% utilisation of the catalyst.
Effectiveness of the catalytic bed is measured
by up to 36 thermocouples across the top and
bottom of the bed. The High Dispersion (HD) tray
controls temperature radial distribution to within
2-4 o C, confirming optimum catalyst utilisation .
An Ultra-Flat Quench (UFQ) deck at the bottom
of the bed, takes the reactants and mixes them with
cold quench gas, and finally redistributes them
into the next catalyst bed. The compact design
minimizes vertical height, and offers up to 20%
more catalytic volume in a multi-bed reactor.
Over the last decade, improvements in catalyst
formulations have more than doubled the relative
catalytic activity while minimizing the hardware
required. In 2000/2001 Criterion introduced
Centinel Gold, which recently has been upgraded
to the latest Centera® platform. Criterion also offers
in the Ascent platform, a cost-effective catalyst
which balances Type II and Type I active sites.
In addition to major increases in
hydrodesulphurisation activity – producing less
than 10 ppm sulphur diesel regardless of the
feedstock – there has been improvement in winter
diesel quality, with the use of dewaxing catalyst to
improve the cloud point. Shell offers a single-stage,
SDD 800, base metal catalyst to improve the cloud
point by transforming long chain mono-alkyl or
long chain paraffin molecules through isomerisation
to retain a high level of diesel yield. Consequently,
refiners can produce full range heavy diesel product
with a significantly improved cloud point.
Depending on the degree of cloud point
improvement required, an HDS and hydrodenitrogenation
(HDN) catalyst can be applied together
with a dewaxing catalyst. Generally, a discrete small
Licensing Solutions for Tomorrow I 4

Licensing Solutions
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dewaxing bed is used where temperature, dewaxing
and cold flow improvement can be controlled.
Criterion produces a range of hydrocracking
catalysts in partnership with Zeolyst International.
Blends of zeolite differ according to the level of
diesel selectivity required in different markets. The
new 2000 series of zeolite catalysts offers refiners
the flexibility to choose more diesel selectivity at
the same operating temperature, or more activity
for the same selectivity, achieving highest boost in
diesel production within existing unit constraints.
Catalyst shape is also an important performance
variable. Criterion had replaced cylinders with
trilobes to boost hydrocracking performance and
increase diesel production. Over-cracking occurs
if the reactants remain inside the catalyst too long,
reducing diesel yield and creating more undesired
product like naphtha and gas. Criterion’s new
Advanced Trilobe Xtreme (ATX) shape has further
increased diesel yield by 1.5%. A 50,000 bpd
hydrocracker can produce 750 bpd more diesel
product simply by changing catalyst shape.
Let us examine two case studies: a dewaxing
project where Shell was asked to improve the cloud
point of winter diesel by 14 o C and a revamp of a
30-year old hydrocracker with reliability issues.
Many hydroprocessing assets worldwide are
underperforming. A successful revamp project is
low capex with quick payback, ideally within the
subsequent catalyst cycle of the hydroprocessing
unit. Typically, the project is scoped for new reactor
internals and a new catalyst package – and its far
better to do them together than separately.
For upgrading old, low-pressure HDS units,
which do not have enough catalyst volume,adding
a second reactor makes a significant improvement in
performance. A review of the wash-water injection
system is also important. Often feed rate and/or sour
feed rate are increased triggering potential corrosion
problems that can be avoided by additional/optimised
wash water operation. At the back end, the refiner
must ensure that separation, fractionation and workup
sections can recover the additional diesel product.
Depending on the scope, costs of a revamp
hydroprocessing project range from $2-10 million –
with a second reactor at the upper end. A revamp can
typically be carried out in a scheduled turnaround.
Typical payback is within the next cycle and allows
the refiner to process far more difficult feedstocks
and/or produce better quality product.
Case Study 1: An ultra-low sulphur (ULSD)
unit was converted to dewaxing mode, capable of
reducing the diesel cloud point from -5 to -19 o C,
using a high activity nickel-molybdenum catalyst
with SDD 800 dewaxing catalyst and some posttreatment,
implemented within an existing reactor.
Dewaxing requires operating flexibility, as cloud
point improvement is not necessary in the summer.
5 I
Licensing Solutions for Tomorrow
During the summer, dewaxing can be switched off
by quenching, at a small yield penalty. Two-stage
iso-dewaxing offers up to 35 o C cloud point
improvement with minimal diesel yield loss.
Case Study 2: A single-stage, 30-year old
hydrocracker (with recycle) had become less reliable
with age, mainly due to a high catalyst bed pressuredrop
through deposition of solids, corrosion
products upstream of the unit. A top bed skim was
frequently required and the top bed catalyst was
completely replaced during plant turnaround. Shell
implemented new reactor internals technology,
“Over the last decade,
improvements in
catalyst formulations
have more than doubled
the relative catalytic
activity while minimizing
the hardware required.”
including; a filter deck, increasing the cycle length
and eliminating the rapid pressure-drop build up,
and integrated HD/UFQ decks, increasing catalyst
utilisation for higher diesel yields. The total project cost
was about $2 million for hardware, and outstanding
reliability and yield improvement achieved.
Maldistribution of catalyst is a common problem
for reactors, creating local hotspots when liquids
and vapors flow preferentially to one part of a bed,
leaving other parts without proper flow. The resultant
high temperatures and overcracking generates high
gas and LPG yields, consuming hydrogen, at the
expense of diesel product. Ultimately, the operation
is constrained on cycle length, because the reactor
mechanical temperature limit is reached much faster
if radials are 50°C hotter in one part of the bed than
another, so full cycle potential is never achieved.
Installing HD tray and UFQ quench decks resulted
in stable catalyst performance, both temperatures
and yields, in the subsequent cycle.
The reactor internals were complemented by
tailoring a combination of high-activity catalysts with
optimum selectivity resulting in increased conversion
(by 2.5% on feed) and increased diesel yield (diesel
yield actually increased by 10% weight on feed).
Payback was less than a year, given increased
unit performance worth $3.5 million annually.
John Baric – Licensing Technology Manager,
Shell Global Solutions International B.V.
Justin Swain – Technical Director,
Criterion Catalysts and Technologies Ltd