Chemical Engineering September 2022 - 33

duced, the gamma
scans saw liquid
in the downcomer
and the AGO came
into
specification
for color.
At the next turnFIGURE
2. The diagram shows the first set of modifications
center downcomer, preventing vapor
rise through it. This happened at
about 6,000 bbl/d reflux. Once the
downcomer was sealed, they could
go back down to 1,500 bbl/d.
In the next revamp, the Venturi
valves were replaced by the sharporifice
valves that are resistant to
weeping. Without weeping, there
was no way for liquid to go down, so
even increasing to a reflux of 15,000
bbl/d would not bring the AGO into
specification for color.
After my explanation, the gentleman
asked, " Nice theory, but can
you prove it? "
" Absolutely. We can run a test that
will get your AGO on-color. You will
need to reduce the charge rate to
lower the vapor velocity in the downcomer
and allow liquid to descend.
We will need gamma scans to watch
for liquid in the center downcomer. "
We proceeded with the test in
which we used gamma scans to continuously
watch the center dowcomer.
Initially, the center downcomer
contained vapor, no seal. Then when
the charge rate was sufficiently rearound
we removed
the splash
baffles and installed
inlet weirs. We also
made some modifications
to the AGO
draw. After this, the
tower operated at a
wash rate down to
700-800 bbl/d with the AGO always
on-color.
The takeaway: When the patient's
health suddenly deteriorates for an
obscure reason, always go back to
the last time the patient was well,
and investigate all changes from
then on.
■
Edited by Dorothy Lozowski
FIGURE 3. The second modifications to the atmospheric crude tower wash
section are shown here
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
About the Tower Doctor
" The Tower Doctor " is the honorary
title bestowed upon the author of
this article in 2002 by Richard Darton,
professor of Engineering in Oxford
University and chair of the European
Distillation Network. " When a
tower is not well, " says Darton, " people
call Henry to diagnose the illness
and find a remedy. He arrives with his
doctor's bag, examines the patienttower,
measures its temperature and
pulse, gets radiography to get an inside
look. Then comes his diagnosis
and cure. Towers treated by Henry
mostly get better very quickly. "
Being son to two medical doctors
who were blessed with phenomenal
diagnosis ability, the author
aspired to live
up to this special
honorary title. Like
with medical doctors,
some illnesses
were a struggle
to diagnose, others
were easier.
All were exciting.
This column will
reminisce through
some of the more
entertaining cases.
They may not have
seemed entertainSEPTEMBER
2022
ing at the time, but looking back at
them, they leave unforgettable memories
and raise a smile or two. One
great aspect of being a tower doctor,
one gets to work with and learn from
some of the greatest engineers and
operators that contributed so much
to the chemical industry. We hope
that this column can pass some of
the
fun,
Author
Henry Z. Kister is a senior fellow
and the director of fractionation
technology at Fluor Corp.
(3 Polaris Way, Aliso Viejo, CA;
Phone: 949-349-4679; Email:
henry.kister@fluor.com). He has
over 35 years of experience in
design,
troubleshooting,
revamping,
field consulting, control
and startup of fractionation
processes and equipment. Kister is the author of
three books, the distillation equipment chapter in
Perry's Handbook, and over 130 articles, and has
taught the IChemE-sponsored " Practical Distillation
Technology " course more than 530 times in 26 countries.
A recipient of several awards, Kister obtained
his B.E. and M.E. degrees from the University of New
South Wales in Australia. He is a member of the NAE,
a Fellow of IChemE and AIChE, and serves on the FRI
Technical Advisory and Design Practices.
excitement and lessons
learned to future troubleshooters
and tower doctors.
Where can you find all your
CPI solutions in one spot?
Written for engineers by engineers, Chemical
Engineering delivers solid engineering essentials
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