Hydrocarbon Processing - September 2021 - 20

Refining Technology
tionator bottoms pump is routed to the
HPNA stripper, where the target HPNA
separation is achieved using superheated
steam. Stripper overhead is routed to the
main fractionator column to provide the
necessary stripping, while the concentrated
HPNA stream is withdrawn from the
stripper bottoms.
The external HPNA stripper design
FIG. 3. Authors' company's HPNA separation equipment options.
tity. Performance testing results indicate
increased hydrotreating activity in terms
of both hydrodesulfurization (HDS) and
hydrodenitrogenation (HDN) mainly
due to saturation of the least reactive species
like dimethyldibenzothiophenes and
dimethylcarbazoles. Resultant activity
improvements translate to reduced bed
volumes, thereby saving the undesired
capital expenditure associated with new
reactor installation to meet the elevated
severity at low SOR temperatures.
In commercial applications, the novel
unsupported catalystc
is loaded in combination
with conventional, high-performance
catalystsg,h
to debottleneck activity,
and improve reliability and product
quality constraints.
Equipment solutions. While the catalytic
solutions described here can help reduce
the HPNA make, this is not enough
to guarantee a constant low HPNA make
throughout the catalyst cycle. Irrespective
of the unit configuration, fluctuations in
unit feed quality and the gradual fouling
of catalyst hydrogenation function impact
the ability of even the best hydrogenation
catalysts to maintain a UCO HPNA concentration
that is steady and within limits.
The exact timing and concentration at
which HPNAs begin affecting unit performance
may vary, but the associated economic
losses are not trivial to justify living
with them. Including an equipment solution,
therefore, becomes imperative to
overcome HPNA woes and allow the processing
of opportunity feedstocks without
having to bother about product yields and
cycle length.
The authors' company has commercially
proven equipment solutions for HPNA
separation and removal that caters to the
diverse needs of both new and existing unit
designs. These options can be either com20
SEPTEMBER 2021 | HydrocarbonProcessing.com
bined with the catalytic solutions or implemented
alone as part of revamp to cost effectively
mitigate HPNA reliability issues.
Solution 1 of FIG. 3 shows a recycle oil
management systemi that utilizes activated
carbon beds to adsorb HPNAs. It comprises
of two single-bed vessels that operate
as lead and lag beds with the flexibility
to isolate and change the adsorbent bed
as it gets saturated. The lead bed becomes
the lag bed following the change out. The
frequency of change out can vary from
6 mos-1 yr, depending on unit operating
severity and catalyst system. This option
offers a simplistic design that can be conveniently
incorporated into the existing
unit flow scheme with minimum downtime.
This technologyi
was commercialized
in 1990 and has more than 10 units
successfully operating across the globe.
A product fractionator split-shell design
(Solution 2) is considered the best
option for new units where the main fractionator
can be built with a split-shell to
include the HPNA removal section within
the same column. This patented fractionation
scheme utilizes high boiling point of
HPNA species, especially with > 11 rings
to achieve the desired separation. All HPNAs
get concentrated in the UCO with a
purge rate as low as 0.5% of the fresh feed
rate, thereby significantly reducing the
HPNA content in recycle oil to the reactors.
It requires no material handling and
has a minimal footprint. Since its commercialization
in 2008, more than 15 units
with split-shell fractionator design for
both single-stage and two-stage configurations
have been licensed, with multiple in
commercial operation.
The external HPNA stripper design
(Solution 3) utilizes the same fractionation
concept but employs a small external
stripper connected to the main column
instead. A small slip stream from the fracis
a good retrofit option with minimum
changes to product fractionator operating
conditions and design. Only a few pieces
of new equipment, all of which are relatively
small, makes this an ideal option for
a modular offering. This further reduces
the footprint, unit downtime and refiners
work scope. The first unit was sold in
2016 and was commercialized in 2020.
First-hand commissioning experience and
the commercial performance details are
covered in the subsequent case study.
With either solution, the refiner benefits
from being able to maintain very
high conversion throughout the catalyst
cycle, maximizing carbon management.
All equipment options offer significant
economic incentives primarily due to a
boost in middle distillate product yields,
reduced unit conversion and the flexibility
to process VGO with high end point. In
most instances, these revamp options offer
a very high return on investment (ROI),
with a typical payback time of less than 1
yr for an average size HCU (50,000 bpd or
8,000 m3
/d).
COMPREHENSIVE HPNA
MITIGATIONS SOLUTIONS:
A CASE STUDY
In response to the changing refining
landscape, TÜPRAŞ (Türkiye Petrol
Rafinerileri) was one of the few refiners
in the European region that began evaluating
the impact of IMO regulations on
refinery profitability as early as 2009. Turkey
relies heavily on imports for almost all
its energy and fuel needs, as it lacks any
hydrocarbons production facilities. It has
a surplus of gasoline but is heavily dependent
on diesel imports.
TÜPRAŞ could see the silver lining
quite early and acted swiftly to upgrade the
refinery configuration and take advantage
of the declining fuel oil market. The shift
in market dynamics provided a perfect opportunity
to leverage the difference in fuel
oil and diesel prices to justify the Residuum
Upgrade Project (RUP), which aimed
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