Hydrocarbon Processing - September 2021 - 28

Refining Technology
to go online when ready without hampering
the unitk
operation. These tie-in isolations
also provide the flexibility to take
the HPNA stripper offline for any maintenance,
if required. Key HPNA stripper
facts and figures are summarized here:
* Total installed cost: ~ $5.5 MM
* Simple design, no additional unit
downtime required
FIG. 9. (Left) Distillate selectivity cycle comparison; (right) 2nd-stage catalyst activity cycle
comparison.
* Stripper size: 2-m ID × 9.1-m T/T
(designed for enhanced two-stage
processk,l
feed rate of 9,200 m3/d)
* Increased unit conversion by
~1.5 wt%
* Reduced bleed rate by 75%
* Unlocked potential to process
heavy feeds and further increase
profitability.
Following the mechanical compleFIG.
10. (Left) HPNA make vs. feed EP comparison; (right) HPNA make vs. conversion comparison.
tion, the HPNA stripper was taken online
in September 2020 without any product
slopping. Unit commissioning was quick
and easy and involved two key steps:
* Heating the steam lines and stripper
using the existing silencer and
jump over lines. Stripping steam to
the fractionator columnk
was then
slowly diverted through the HPNA
stripper.
FIG. 11. (Left) Typical external HPNA stripper flow scheme; (right) HPNA stripper in operation.
unit conversion to keep recycle oil HPNAs
below 200 ppm, especially at EOR
conditions. This is now a thing of the past.
The plot on the left in FIG. 10 demonstrates
superior hydrogenation performance
of the catalyste
that has kept the
HPNA make consistently below 50 ppm
while processing feeds with an EP > 600°C.
With the reduction in refinery margins
and the advent of IMO regulations, the
new catalyst system has helped boost the
overall revenue by operating the coker
unit at higher capacity and increasing the
feed end point by 20°C-30°C. The plot on
the right in FIG. 10 shows the HPNA generation
as a function of unit conversion. At
SOR conditions, the HPNAs were in the
range of 20 ppm-40 ppm at or above design
conversion, as compared to 100 ppm-
120 ppm HPNAs in the previous cycle.
28 SEPTEMBER 2021 | HydrocarbonProcessing.com
The catalyst systemd
continues to meet
or exceed TÜPRAŞ' goals, consistent
with predicted performance. In addition
to providing excellent catalyst activity and
selectivity, the catalyst system has demonstrated
good temperature stability and
is on target to meet the desired lifecycle.
These process improvements are proof
of the successful application of the proprietary
catalyste
in a second-stage environment
to reduce HPNA make without
compromising middle distillate yields.
HPNA stripper commissioning. The
majority of the equipment and piping
installation work for the HPNA stripper
project was performed with the unitk
online.
All tie-in points were identified during
the project stage and taken during the
turnaround to enable the HPNA stripper
* Introducing the fractionator
bottoms to the HPNA stripper
and increasing the stripping steam
superheat to achieve the desired
stripping efficiency. The overhead
vapor comprising mostly of steam
was routed to the main fractionator
column as stripping steam, while
the HPNA stripper bottom
product can either be routed to the
coker feed tank or coke drums.
The normal and preferred routing is to
the coke drums to destroy the bulk of the
HPNA and reduce any potential recycle to
the unitk
.
Results and takeaway. The authors'
company was able to support the startup
remotely due to ongoing COVID-19
travel restrictions at that time, relying on
its process monitoring software solution
to remotely monitor the startup operation
and provide necessary recommendations.
Despite local labor constraints and
limited vendor support, the startup of the
stripper took just 1.5 d, and the drop-in
recycle oil HPNAs were evident from the
first shift. FIG. 11 provides a high-level flow
scheme of the external HPNA stripper
and a site photo.

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Hydrocarbon Processing - September 2021

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