Hydrocarbon Processing - December 2022 - 23

Catalysts
The luxury of the versatile and flexible
SSREC design and the catalyst system
enabled Preemraff to run economically
during the pandemic, allowing them to
continue running by
adjusting feedrates to
meet decreased market
demand. Additionally,
leveraging the catalyst
system design, Preemraff
operations worked
with the author's company
to fine-tune operations
to maximize
conversion and reduce
fresh feedrate due to
changing market demand. Close cooperation
between ART/CLG technical services
and the Preemraff operations team
was crucial to operate safely within design
limitations and transfer to the new
mode of operation.
The transitions
to different modes
of operation are shown in FIGS. 3 and 4
(note the significant changes in recycle
and fresh feed intake).
Prior to and during the pandemic.
Pre-pandemic (prior to 2020), Preemraff
focused on maximizing fresh feed intake
and conversion while minimizing recycle,
achieving maximum mid-distillate
yields and securing the minimum UCO
amount (130 m3
/hr) to feed the FCCU.
After 2020, minimizing fresh feed intake
and maximizing conversion by maximizing
unconverted oil recycle simultaneously
was required to achieve maximum
mid-distillate yields. Proper heat management
was required to maintain sufficient
heat in the first and second reactors
to keep conversion going during the transition
while changing modes of operation
stayed within design limitations.
Another challenge the client faced
was running low-sulfur North Sea crudes
while maintaining sufficient heat in both
reactors to ensure ongoing conversion.
The challenge was to reduce fresh feed
intake while running these low-sulfur
North Sea crudes and simultaneously increasing
unconverted oil recycle, which
significantly affects the heat of reaction
in the different beds in the first and second
reactors. Consequently, heat management
of the whole unit has changed
significantly, running in this new mode
of operation (e.g., running low-sulfur
North Sea crudes). While reducing feedrate,
special care was taken to keep
conversion going until minimum design
requirements were met, running all
equipment downstream.
Pre-pandemic (2016-2019):
1. 2018: Conversion increased
to utilize surplus activity left
until end of the run
The SSREC design, combined with the designed catalyst
system, has shown to be highly flexible to adapt to
continuously changing market circumstances by allowing
the unit to be run in different modes of operation at
low and high conversion levels for the two cycles.
During and after the COVID-19 pandemic
(FIG. 4), the refinery minimized
fresh feed intake and maximized recycle
conversion to achieve maximum middistillate
yields,
running much more
profitably. During this period, the FCCU
was shut down due to economic reasons,
so no UCO feed was required to feed the
FCCU. Beginning in 2021, the FCCU
was started up again and a minimal UCO
amount was required to meet the FCCU
requirements running at low capacity.
Surplus activity in the 2016-2019 cycle
resulted in further improvement to a more
mid-distillate selective catalyst system.
In FIG. 5, four distinct segmented periods
are selected to demonstrate the operational
requirements through the pandemic.
2. 2019: Reactor 2 catalyst system
with a more mid-distillate
selective system during an
intermediate shutdown
Pandemic (2020-onwards):
3. 2020-2021: FCCU shut down
during pandemic
a. Opportunity to run the
hydrocracker at maximum
conversion running at a
bare minimum fresh feed
intake to continue to meet
contractual obligations
b. Opportunity to convert
maximum UCO required
as no UCO was required
to feed FCCU
c. Opportunity running different
FIG. 5. Four distinct modes of operation visualized vs. the Base Case (filtered data selected).
Hydrocarbon Processing | DECEMBER 2022 23

Hydrocarbon Processing - December 2022

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