Hydrocarbon Processing - September 2021 - 69

Process Optimization
of the offgas compressor also affect LPG product purity.
Corrosion. A copper strip corrosion test (FIG. 4) is a visual
and subjective test. Some results may appear very close to one
another, which may require repeat testing on some occasions.
Corrosion problems in LPG product generally arise from H2
S
content and usually occur due to bad caustic quality or high
caustic spent rate. On rare occasions, the issue stems from the
amine treating section. A problem in the amine system may
bring high H2
the desired zero H2
S load to the caustic system, which may prevent
S in the product.
Actions to be taken for corrosion problems are similar to
those taken for a high-sulfur problem. LPG product with a corrosion
problem is routed to a Merox unit for further treatment, and
the caustic inventory of the unit is investigated and replenished
during this period. Off-spec tanks may be used initially; however,
if the Merox unit is near its design throughput, then the product
with corrosion is treated in the Merox unit to the fullest capacity.
In some units like the new HCU, H2
S analyzers enable observation
of the problem at the beginning. This is important
since, unlike sulfur problems, blending is not a solution when
an LPG tank is subject to corrosion. It cannot be diluted enough
to achieve zero-corrosion product. Also, the risk remains of the
problem spreading to the other LPG tanks.
Evaporation residue. Evaporation residue can easily arise
from a dirty sample bottle or lab equipment, or from a hydrocarbon
leak from the amine system or any of the units. The residue
may change from a dirt particle into a hydrocarbon droplet.
In a complex pool, it may be one of the most difficult problems
to diagnose. A hydrocarbon leak from the process systems to
the amine system may create this issue and cause danger for the
pool, as the amine regeneration section may not be capable of
cleaning the system in a short time. Filters in those units, LPG
sample containers and lab equipment should be checked for
dirt, oil and other potential contaminants.
Another constraint is the test method for residue. The evaporation
residue test is a long process that may take up to 7 hr, and
it is not very sensitive. As time is important for protecting the
LPG pool, product with the residue problem should be routed
to off-spec tanks or a spare product tank. This will create space
and time for detecting the cause of the problem and finding the
best solution while not spoiling the product tank.
Merox units and caustic treatment systems cannot treat
evaporation residue. Blending the off-spec tank or processing
the product in an off-spec tank with low flowrates may be seen
as options, but if the residue amount is high, then it may not be
possible to solve the issue by blending the tanks and processing
the off-spec product, as this will take a very long time.
If the cause of residue is hydrocarbon and the amount is so
high that it is not feasible to blend the tanks or process the product,
then the best way to treat evaporation residue is to route
the off-spec product to the debutanizers for reprocessing. This
may not be an option for many refineries, as extensive lines are
necessary among product tanks and units to enable sending
off-spec LPG to debutanizers. However, this method allows for
eradication of C10
-C40 from the LPG product.5
In the İzmit refinery, a large amount of off-spec LPG product
caused by a process upset was routed to debutanizers from
storage tanks and reprocessed in just two weeks using this
method. Normally, it would take months to process this LPG
FIG. 4. ASTM copper strip corrosion chart.4
in Merox units or blend the tanks, which would create inventory
cost and cause difficulties in production planning due to
blocked LPG tanks.
Takeaway. A complex refinery may have many sources of
problems in its LPG pool, as well as solution alternatives. It is
important to correctly diagnose the problem and the source of
the problem, and then choose the best alternative solution. The
biggest constraint is time, and the biggest concern is the probability
of having an off-spec pool. In 2020, through close observation
and unit cooperation, the on-spec tank ratio was maintained
at approximately 99% in the İzmit refinery. LPG pool
complexity may create problems, but it can also offer solutions.
Propane specification was not elaborated in this article, as
uncertainties exist on the issue. However, according to LPG
product composition, additional needs may help supply the
necessary propane level in the pool. The option of selling C4
to market or importing C3
excess C4 in the fuel gas system or in hydrogen production units
/C4
splitters, evaporators or even storage
tanks that are suitable for propane.
LITERATURE CITED
1
2
BSI, " BS EN 589:2018: Automotive fuels: LPG: Requirements and test methods, "
December 2018.
ESC, " Pengerang energy complex: Environmental impact assessment, " April
2019, Johor, Malaysia, online: https://enviro2.doe.gov.my/ekmc/wp-content/
uploads/2019/05/J18-780_PEC_Chapter-5-Project-Description.pdf
3 " Fuels selective hydrogenation process, " General operating manual.
4
Gao, S., L. Yang, B. Deng and J. Zhang, " Corrosion mechanism for local enrichment
of acids and copper ions in copper-insulating paper contacts leading to the
acceleration of copper sulfide formation induced by dibenzyl disulfide, " RSC
Advances, Vol. 7, Iss. 83, November 2017.
5
Van Raalte, W., " It's all about the residue, " The Analytical Scientist, January 14,
2013, online: https://theanalyticalscientist.com/techniques-tools/its-all-aboutthe-residue
AYLIN
ÖNDER SAKA is a Simulation Supervisor at Tüpraş headquarters in Turkey.
She has previous experience as an Operations Engineer in oil movements, truck
loading/unloading and marine loading/unloading, and as a Refinery Process
Supervisor in LPG, SHU, KTU and ARU. She holds MS and BS degrees in chemical
engineering from Middle East Technical University in Ankara, Turkey.
DANYAL GÖKHAN KUTMAN is a Chemical Management Superintendent at
Tüpraş headquarters in Turkey. He has previous experience as a Process
Supervisor/Superintendent on CDU, LPG units, amine treatment units, SHU, KTU
and SRU. He holds a BS degree in chemical engineering from Hacettepe University
and an MBA degree from Middle East Technical University in Ankara, Turkey.
Hydrocarbon Processing | SEPTEMBER 2021 69
can be analyzed. Additionally, using
may be examined. Most of these options create the need for new
equipment, such as C3

https://enviro2.doe.gov.my/ekmc/wp-content/uploads/2019/05/J18-780_PEC_Chapter-5-Project-Description.pdf https://enviro2.doe.gov.my/ekmc/wp-content/uploads/2019/05/J18-780_PEC_Chapter-5-Project-Description.pdf https://www.theanalyticalscientist.com/techniques-tools/its-all-about-the-residue https://www.theanalyticalscientist.com/techniques-tools/its-all-about-the-residue

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