Hydrocarbon Processing - May 2021 - 19

Special Focus

Maintenance and Reliability
L. ÖZKAN, İ. AYDIN and G. ÖZTÜRK, Tüpraş, İzmit, Turkey

Cleaning distillation column and heat exchangers
through cutter stock circulation

Operational background. The CDU is the largest, by capacity, and has a more energy efficient design than other CDUs
in the refinery. The CDU has a preflash column upstream of
the crude preheat furnace that removes light fractions of crude
oil to reduce duty required by the furnace and to minimize the
pressure of the main distillation column.
Preflash column pressure drop

0.3
2,000

0.25

1,500

0.2
0.15

1,000

problems three times during the period between two turnarounds in 2014 and 2018, therefore it had to experience two
breakdown maintenances within this time frame. Although
there was a fouling problem followed by a high pressure drop
through the column prior to the 2018 turnaround, it did not
require downtime since maintenance was scheduled to be performed. The unit suffered similar fouling problems in the preflash column before 2014, which was resolved by mechanical
cleaning that took 10 d of downtime.
During the 2018 turnaround, the floating valve trays of preflash column were replaced with fouling-resistant trays, which
are not prone to contamination because they have wider tray
openings that create lower pressure difference. These trays help
avoid downtime from tray contamination in the preflash column. The new trays reduced the ΔP value from 0.15 kg/cm2 to
0.1 kg/cm2, which led to a decrease in pressure drop along the
column. After replacing the column trays, even light crudes with
1,200

0.4

The first point high ∆P observed

0.35

1,000

2,500
Debutanizer feed, m3/d

Preflash column
pressure drop

0.3

800

0.25

600

0.2
0.15

400

0.1

FIG. 1. The debutanizer feed vs. the preflash column ΔP.

11/18/2019

10/18/2019

9/18/2019

0
8/18/2019

7/18/2019

0
6/18/2019

11/18/2019

10/18/2019

9/18/2019

8/18/2019

7/18/2019

6/18/2019

5/18/2019

0
4/18/2019

3/18/2019

0.05

Slop feed flow
5/18/2019

Debutanizer feed flow

200

4/18/2019

0.05

500

3/18/2019

Preflash column ∆P, kg/cm2

0.35

3,000

Problem definition. The CDU had faced tray contamination

Slop feed, m3/g

0.4

However, the CDU's preflash column trays are known to
have poor resistance against fouling problems. The column has
a history of shutdowns-around once every 2 yr, on average-
because of high pressure drop resulting from severe fouling on
the trays. During the refinery's 2018 turnaround, the floating
valve trays in the preflash column were replaced with foulingresistant, fixed-valve trays with wider openings. However the
problem appeared again a few months after startup.

Preflash column ∆P, kg/cm2

The Tüpraş İzmit refinery's largest crude distillation unit
(CDU) is designed with a preflash column prior to the atmospheric distillation column. The preflash column regularly suffers flooding problems, followed by high pressure drop that
results in the discoloration of light straight-run naphtha product. The problem occurs due to organic fouling and choking of
column trays, which causes a shutdown due to off-specification
products. The unit shutdown includes all the required precautions (steam-out phase, blinding, etc.) for the safe entry to the
preflash column. These precautions, along with mechanical
cleaning of the column, extend shutdown time to nearly 10 d,
which significantly impacts refinery margins.
In December 2019, the CDU was again forced to shut down
due to severe fouling of trays. A new method was applied, instead
of mechanical cleaning, to eliminate foulants. The maintenance
of the column lasted nearly 3 d, with promising results. Not only
were shutdown time and production cuts significantly reduced,
but also the fouling-prone heat exchangers and preflash column
heater tubes were cleaned within this time frame. This article
describes the details of the new method for the maintenance of
the preflash distillation column.

FIG. 2. The slop feed amount vs. preflash column pressure drop.
Hydrocarbon Processing | MAY 2021 19

Hydrocarbon Processing - May 2021

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