Hydrocarbon Processing - February 2021 - 60

Maintenance and Reliability
During the inspection, a uniform contamination deposit was found on the

to compare before-and-after values of
the entire system.

It is important to clean the column and
to maintain steam-out during emergency
shutdown of the unit to guarantee operational
efficiency after maintenance is performed.
trays and on the reboiler exchanger shell
side of the stripper, as shown in FIG. 9.
During the shutdown of the unit, the
atmospheric distillation column was
controlled from top to bottom, the side
strippers were opened and checked for
deposits, and all of the drawing lines
and internals were cleaned both manually and with water. The CDU was then
successfully restarted and closely monitored. After enough data was collected
from the running unit, the next step was

Takeaway. The blockage was de-

As shown in FIG. 10, production draw
temperatures (especially kerosene draw
temperatures) have stopped oscillating
and started to follow a straight line controlled by column dynamics and feed
compositions, as desired. The atmospheric column is producing on-spec product.
The overhead reflux value has also improved since the gas and liquid flows in
the column have become uniform.
As shown in FIG. 11, pressure values
during the oscillation in the column were

FIG. 10. Before and after values of the overhead reflux and draw temperatures.
6,000
5,000

Overhead reflux
∆, top kerosene
∆, kerosene LAD

600

∆, LAD/HAD
∆P, top flash section

500
400
300

∆P, g/cm2

Overhead reflux amount, m3/d

After maintenance
4,000
3,000

200
2,000
1,000
0

FIG. 11. Compared pressure values along the column.

60 FEBRUARY 2021 | HydrocarbonProcessing.com

critically high between the top and flash
sections, but dramatically low between
the light diesel and heavy diesel
parts of the column. After maintenance, differences in pressure values, shown in FIG. 11, indicate that
the pressure was stabilized.

100
0
-100

tected at the downcomer of the kerosene drawing section of the atmospheric distillation column. This
blockage caused an increase in pressure
at the top of column, an increase in temperature (depending on an instant rise in
top load for lighter crude) and an increase
in top reflux due to a high top load. These
problems collectively resulted in temperature oscillation in the column. The unit
did not operate as expected at the maximum unit charge.
When the contamination of the
downcomer at the kerosene drawing section was examined, the content of this
contamination was observed as 17% organic and 77% inorganic material. The
organic part was related to charge content, and the inorganic part resulted from
accumulation in the kerosene downcomer during turnaround blasting operations
in the column.
As learned from this study, it is important to clean the column and to maintain
steam-out during emergency shutdown
of the unit to guarantee operational efficiency after maintenance is performed.
In addition, the control of the column
and its internals is crucial. During column control, the cleaning of the downcomer sections and drawing lines must be
provided, and the drawing lines must be
washed until every line is clean.
GÖZDE ÖZTÜRK is a Process Engineer at Tüpraş'
İzmit refinery, responsible for the crude and vacuum
distillation units. She previously worked as an
Operations Engineer. Ms. Öztürk holds a BSc degree
in chemical engineering from Middle East Technical
University in Ankara, Turkey and an MSc degree
from Boğaziçi University in Istanbul, Turkey.
SEREN KIBAR is an Operations Engineer at
Tüpraş' İzmit refinery, responsible for crude
and vacuum distillation, kerosene treatment,
selective hydrogenation and other units. She holds
BSc and MSc degrees in chemical engineering
from Middle East Technical University.
GIZEM AKYILDIZ is an Operations Engineer at
Tüpraş' İzmit refinery, responsible for crude and
vacuum distillation, kerosene treatment, selective
hydrogenation and other units. She holds a BSc
degree in chemical engineering from Istanbul
Technical University in Turkey.

http://www.HydrocarbonProcessing.com

Hydrocarbon Processing - February 2021

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