Hydrocarbon Processing - July 2022 - 67

Process Optimization
* Pump hydraulics, such as net
positive suction head (NPSH)
* Valve erosion problems and
valve packing issues
* Fouling and deposition
of polymers.
Solutions and recommendations include:
* The provision of a permanent
steam facility for steam out
and washing in each section
* Packing open area should not be
blocked by the TSR and support
beam by more than 10%5
* An antifouling/antifoaming
agent should be used
* Temperature must be maintained
within 5°C above dewpoint
to avoid condensation
of hydrocarbon; higher
temperature can lead to caustic
precipitation/salt formation
* The hood plate must be
seal welded rather than bolted
to inhibit leakage
* Venting provision should be
provided for the hood plate,
otherwise the level filled beyond
the hood baffle elevation could
break down the hood plate
* Overfilling the caustic tower with
caustic or water can fill the cracked
gas inlet line up to the compressor
casing, so the inlet line must be
elevated more than 4 m-5 m
to avoid filling of inlet line
* The tower bottom sump's
partition baffle should be
without holes to avoid mixing the
liquids of both compartments
* The yellow oil draw pot
should have no drain hole
* All valves related to column
isolation or working in alkaline
service should be sleeved/coated
with PTFE or any other equivalent
* A valve stem should be installed at
vertical or at a 45° angle to vertical
to avoid any contact of caustic,
and the deposition of caustic
in the gland packing of valves
should be PTFE or equivalent
* Wash oil provision should be
provided for washing of fouling
or polymers during shutdown
and normal operation.6
Takeaway. Applying these recommendations
supports the smooth startup and
operation of the caustic tower. These
Pump
LG
Spent LT
Spent caustic
Draw pot LT
Wedge baffle
Hood baffle
to be seal
welded
FIG. 10. Level transmitter and hood cover plate of the bottom section of the caustic tower.
The hood plate diverts the total liquid into the pump circulation compartment and the caustic
overflow to spent caustic. Both compartments are separated by a partition baffle.
guidelines can be checked either at the
time of design review of a tower drawing
or later-this article can be used as a
checklist for a drawing review; however,
once the tower is operational, it becomes
difficult and expensive to shut down the
plant and modify it. Numerous published
case studies detail the reasons for
various caustic tower flaws and provide
recommendations and solutions. As stated
here, it is better to learn from other's
experiences.
The fundamental guidelines of the article
are: to avoid direct contact with caustic,
all level and flow transmitters should
be capillary type with a water washing
facility; gas impingement on the tower's
shell must be avoided; the open area of
packing should be checked by the process
engineer; all gaskets should be PTFE
or equivalent; and caustic spills must be
avoided for the safety of people, processes,
plants and the environment.
NOTES
These general guidelines are based on the author's
experiences and are not affiliated with any company.
ACKNOWLEDGEMENT
The author is thankful to Shree Krishna and
Upadhyayula Sri Venugopal for supporting and advising
him on this article.
LITERATURE CITED
1
2
Kister, H. Z., Distillation operation, McGraw-Hill
Education, New York, 1990.
Lieberman, N. P. and E. T. Lieberman, A working
guide to process equipment, McGraw-Hill Education,
4th Ed., 2014.
3
4
5
6
Kister, H. Z., Distillation troubleshooting, John Wiley
& Sons Inc., 2006.
Wikipedia, " Aldol condensation and formation of
polymer. "
Lieberman, N. P., Process design for reliable operation,
Gulf Publishing Company (1998).
Sharma, A., " Preferential baffle reboiler-Part 1, "
Hydrocarbon Processing, April 2022.
ABHISHEK SHARMA is a process
engineer at an ethylene plant, and
has more than 4 yr of experience in
the steam cracker unit. He completed
his B.Tech degree in chemical
engineering from the National
Institute of Technology Raipur, India
with honors and completed a process equipment design
course from IIT Roorkee. He is an active professional
member of the American Institute of Chemical
Engineers and an associate member of IChemE. He has
published five articles and participates in the smooth
operation and troubleshooting of the plant.
Hydrocarbon Processing | JULY 2022 67

Hydrocarbon Processing - July 2022

Table of Contents for the Digital Edition of Hydrocarbon Processing - July 2022