Chemical Engineering December 2013 - 45

Feature Report
Plant Revamps and
Turnarounds: Some
Lessons Learned
Petr Lenfeld
GTC Technology Europe
Ian Buttridge
GTC Technology US
A
plant turnaround is always
challenging in the chemical
process industries (CPI). But
with proper planning and reliable
procedures in place, last-minute
time crunches and failures can
be prevented. When haste combines
with faulty methods, costly problems
result.
This article presents three examples
of actual plant turnarounds
and the lessons that can be learned
from them.
Case study No. 1:
souR-wateR stRippeR
A sour water stripper (SWS) is a
relatively small unit that treats
wastewater from other process
units of the plant, in this case a petroleum
refinery. After treatment,
the wastewater is directed to the
sewage system, wastewater plant
and ultimately to a nearby river.
The plant
This particular plant has no spare
SWS unit, so in case of failure, the
entire refinery must be shut down
because untreated water is prohibited
from being discharged into
the river.
A sour-water storage tank may be
used in an emergency with a capacity
for five days of normal wastewater
accumulation. In the event that
the SWS is down, it must be repaired
and started within the five days, otherwise
the entire refinery must be
shut down as mentioned before.
In this instance, the SWS column
was packed with metal random
packing. Column performance
was steeply decreasing, because of
packing fouling. The column had to
be cleaned immediately, before the
contaminants concentration in the
treated water reached an unacceptable
limit. A five-day turnaround
was planned, which was long
enough to shut-down the SWS, unload
the metal rings, clean the rings
and repack the column, and finally
to restart the SWS unit. All refinery
units were running at minimum
capacity, directing all sour water to
the five-day storage tank. Under
normal circumstances, this should
be a routine cleaning operation.
Fire
It is well known that pyrophoric
iron is formed or accumulated in
SWS units [1]. When the unit is put
out of operation, the standard safety
precaution is continuous washing
with water to keep all internals
wet and prevent pyrophoric iron
from self-ignition and subsequent
column fire. In this particular unit,
operators had never run across pyrophoric
iron before. Therefore (and
due to the winter conditions), this
" wet procedure " was not applied.
The SWS column was not continuously
washed with water, but
opened after steam-out under dry
conditions. This short-cut caused a
dangerous situation with serious
plant operational consequences.
As one might expect, when air entered
the hot column, pyrophoric iron
self-ignited, resulting in a column
fire. Although the manholes were
Figure 1. After an internal fire, the
column had to be supported to prevent
it from falling onto a pipe-rack
Although time is always precious, taking shortcuts
and skipping standard procedures can be costly
closed immediately and nitrogen
was fed into the column, the fire inside
continued. Temperatures inside
the column reached 2,000°F; the column
shell became warped and bent,
and the tower internals were found
melted into stainless-steel " icicles. "
The fire was extinguished at the last
moment before total shell failure.
Fortunately, the column did not fall
onto the nearby pipe-rack, but it had
to be secured with a mobile crane to
prevent its fall (Figure 1).
Problem
Having no spare SWS unit, the
five-day sour-water-storage tank
slowly filled with water. Only five
days were left to fix the problem or
find another solution, after which
the refinery would have to be shut
down. Plant shutdown in winter
time was a nightmare for plant
management due to the extreme
time and cost involved.
The fire occurred at 8:00 a.m.
By 10:00 a.m., it became clear that
the column could not be used anymore
and had to be replaced or
at least shop-repaired. But there
was no chance to make repairs
within the five days - repairing
the shell in the shop and acquiring
replacements for the damaged internals
were estimated to require
a minimum of two weeks. General
frustration ensued and an emergency
team was set up for express
column-shell repair. By noon, it became
clear to the troubleshooters
that another column was needed to
process sour water.
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Chemical Engineering December 2013

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