Case StoryAn oil tanker (120.000 m3 capacity) needed to be
cleaned before dry-docking. Standard oil tanker cleaning procedure involves the
use of Crude Oil Washing (COW) followed by water cleaning. However, these
operations are not completely effective as tank washing machines have some
shadow areas, where the flow has no direct impact on the sludge. Therefore
after COW some sludge is left in the bottom of the tanks, and has to be removed
manually. ITW
additives have been added both in the COW phase and in the water-washing phase.
In the water-washing phase a patented hydrocarbon solubilizer has been added.
This product is capable of temporarily solubilizing hydrocarbons in water, when
the two phases (additivized water and hydrocarbons) are in direct contact with
each other (e.g. under agitation).The solubilization is temporary and, after
some minutes, the hydrocarbilic and the water phases
separate out. The water phase is very clear and no emulsion is formed. The
additive also facilitates the separation of oil from water. COW was performed
with Bouri crude oil, which is a very severe crude, like the others transported
by the ship. Before performing the additivized COW, some standard COW were
performed: a) one upper cycle 120°/30° and b) two bottom cycles 0°/30°/0°.
At the end of those cycles the slop
tank contained 1300 m3 of Bouri crude and sediments. This is
what the standard COW procedure would have achieved in terms of recovered
sludge. One further bottom cycle with the additive (injected in the suction of
the COW pump) was performed, and stopped after only 12 hours washing (total
time for all the cargo tanks).At the end of this additivized cycle, the slop
tank contained 1500 m3 of Bouri crude and sediments.
Therefore,
the use of ITW stabilizer allowed for a recovery of 200 m3 of sludge
in the COW phase. The
additivized water-washing phase was performed in the same way as the
additivized COW, with water heated at 60 °C. At the end of this phase, further
recovery of 130 m3 of oil was achieved. Therefore,
following injection of ITW additives, the total amount of recovered sludge was 330 m3. All the 1630 m3 of crude oil + recovered
sludge were sent to the refinery for reprocessing. No operational problems were
reported at all. The results achieved are extremely positive in terms of
recovered sludge.
Above results are even more valuable
when taking into account the type of crude oils carried by the ship and hence
the kind of sludge generated by them. The carried crudes are mainly Belayim,
Bouri, Bu Attifel and Es Sider. Belayim and Bouri are particularly well-known
in the petroleum industry as crudes which bear fouling problems. Bouri, in
particular, is a very unstable crude, which causes severe fouling problems in
refinery plants. Its visbroken TAR instability has been well recognized; some
FCCU overhead section restrictions (following coke deposition) have also been
reported when processing Bouri gas-oils. Despite Bouri’s characteristics, the
additivized COW procedure was extremely successful, which confirms the
stabilizing properties of ITW additives.
The payout
of the application has been in the range of 16:1, due to the dramatic reduction
in oil tankers’ cleaning time, and hence recovered freight costs.
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