Hydrocarbon Processing - June 2021 - 32

Process Optimization
A takeaway from this revamp is that
the feed inlet design to the preflash towers
can make or break not only the tower performance,
but also that of the entire crude
unit. Poor design of the inlet can severely
bottleneck the tower and the entire crude
unit. Judicious, low-cost modifications to
the inlet design can largely improve performance,
eliminate bottlenecks and provide
trouble-free operation.
LITERATURE CITED
1
Barber, A. D. and E. F. Wijn, " Foaming in Crude
Distillation Units, " IChemE Symposium, Ser. 56,
1979.
2
Lieberman, N. P. and S. W. Golden, " Foaming is
leading cause of tower flooding, " Oil & Gas Journal,
August 1989.
3
Turner, J., R. J. Asquith and R. Atkinson, " Stop foaming
on hydrotreater 'hot' separator, " Hydrocarbon
Processing, June 1999.
4
FIG. 7. The ribs installed on the impingement
baffle to prevent the horizontal momentum of
the feed mixture issuing from the slots from
pushing the liquid and vapor toward the column
shell: (A) a paper model, used during the
design, to explain the concept to the fabricators;
and (B) the ribs installed on the baffle.
to provide extra protection against vibration
and hammering.
In the laterals, the mixture velocity was
halved to 8.3 m/sec, and the ρM
four times lower (6,660 kg/msec2
VM
2 was
). The
slot velocity was set roughly the same as
the velocity in the laterals, giving the same
ρM
VM
2 (6,660 kg/msec2
). Even though
this is a lot better than in the 10-in. main
feed pipe, it is still about 80% above the
recommended 3,700 kg/msec2
. However,
this is the best that could be done with
the tight space constraints in this 2.1-mdiameter
tower.
Upon turning at the tee, the mixture
momentum becomes horizontal, directed
toward the blanked end of each
lateral. This horizontal momentum will
persist after the mixture exits the slots.
The exiting feed mixture will hit the
baffle with considerable momentum directed
toward the shell ends of the baffle.
The large amount of liquid descending in
a small region at each end of the baffles
near the shell is likely to generate foam
upon impact on the T2 shed deck liquid,
as well as liquid maldistribution on T2,
with high flows near the shell and low
flows in the center. The large amount of
vapor rising near the shell ends of the
baffle can generate entrainment. These
hydraulic issues are likely to reduce the
32 JUNE 2021 | HydrocarbonProcessing.com
FIG. 8. The laterals and the ribbed impingement
baffle. The feed pipe entering the tee is
obscured by an engineering drawing.
effectiveness of the new design and possibly
even defeat its success.
This scenario can be prevented by installing
vertical ribs on the baffle. FIG. 7
shows the ribs. The liquid flowing along
the baffle toward the shell will be directed
downward by the ribs, and the vapor
will be deflected upward. This is a patented
design.5
The installed laterals and baffle are
shown in FIG. 8. As it was expected that
the baffle will receive severe pounding by
the feed mixture, it was fabricated from a
10-mm-thick plate and anchored strongly
to the tower shell.
Takeaway. The tower was restarted on
July 22, 2020. It was in operation until
September 6 of last year, when the unit was
shut down due to falling demand because
of the COVID-19 pandemic. The unit was
then restarted a few months later on November
20. Since that time, no incidents
of dark naphtha have been experienced
during operation. Additionally, the naphtha
production rate was increased by more
than 20% without any adverse effects on
operation. Bazan has not yet pushed the
unit to the maximum but intends to do
so in the future. There was no limit in the
preflash tower, even though naphtha production
was increased by more than 20%.
The entrainment problem has also been
eliminated. The preflash tower is no longer
a bottleneck of the crude unit.
Barletta, T., E. Hartman and D. J. Leake, " Foam control
in crude units, " Petroleum Technology Quarterly,
Autumn 2004.
5
Kister, H. Z. and W. J. Stupin, " Configurations and
Methods for Ribbed Downcomer Wall, " U.S. Patent
7,581,719 B2, September 2009.
BETZALEL BLUM is the Chief
Process Technology Manager for
the Bazan Group (Oil Refineries
Ltd.). During his 35 yr with the
Bazan Group, he has been the lead
process engineer for some major
revamps and debottlenecks of
catalytic and distillation units. Mr. Blum has also
been involved in fractionator process design,
equipment design and optimization, the identification
of flow regime patterns, and field troubleshooting. He
earned a BSC degree in chemical engineering, along
with an MS degree in oil and gas, from Technion-
Israel Institute of Technology.
HENRY KISTER is a Senior Fellow
and Director of Fractionation
Technology for Fluor Corp. He has
more than 35 yr of experience in
design, troubleshooting, revamping,
field consulting, and the control and
startup of fractionation processes
and equipment. He is the author of three books, along
with the distillation equipment chapter in Perry's
Chemical Engineers' Handbook (8th and 9th editions),
the distillation chapter in the Kirk-Othmer
Encyclopedia of Chemical Technology, and more than
120 articles. Mr. Kister has taught the IChemEsponsored
" Practical Distillation Technology " course
over 530 times in 26 countries. He is a Fellow of both
IChemE and AIChE, and is a member of the U.S.
National Academy of Engineering. For more than
25 yr, he has also served on Fractionation Research
Inc.'s (FRI's) Technical Advisory and Design Practices
committees. Mr. Kister earned his BE and ME degrees
from the University of New South Wales in Australia.
RAYMOND TSANG is the Process
Engineering Manager at KochGlitsch,
UK. He has more than
30 yr of experience in the design of
fractionation equipment. Mr. Tsang
earned a BS degree in chemical
engineering from the University
of Newcastle upon Tyne in the UK.
http://www.HydrocarbonProcessing.com
Hydrocarbon Processing - June 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - June 2021
