Chemical tankers operation : How to avoid solidification in cargo tanks ?

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Chemical tankers operation : How to avoid solidification in cargo tanks ?

Why solidification occur ? : Solidification in the cargo tanks can occur when solidifying cargoes are stowed adjacent to “cold cargoes” or cold ballast water in adjacent spaces.
Tank bottoms must therefore always be checked for hard factions especially when carrying vegetable and animal oils, at regular intervals throughout the voyage and always prior to arrival in the discharge port.

To avoid solidification of cargo in adjacent tanks, do not ballast the ballast tanks in contact with the surrounding the cargo tanks. Keep the ballast water in these ballast tanks about 30 cm below the tank top, allowing for trim.

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Special care must be exercised when the vessel is advised that the shore tanks have been “squeezed” (swept) into the vessel, in such cases the “squeezed” (swept) cargo from the shore tank should as far as possible be confined to one tank onboard. The particular tank onboard which received this cargo can then be re-circulated onboard if soundings indicate a “hard bottom” problem. Solidification can also occur when inhibited cargoes or their condensates are exposed to excessive heat. If excessive heat is caused by the sun, spraying the deck area with seawater may prevent this type of solidification (polymerisation).

Because of the risk of solidifying cargo being hard and blocking the venting pipe due to evaporation through the vent pipe, the following precautions are recommended:

During voyage, regular checking of proper functioning of PV valves.
During voyage, regular checking of the vent lines by N2 / air depending on the type of cargo.
During tank cleaning, PV valves, vent lines to be thoroughly washed with hot water and same to be drained to the tank.
After the loading, all cargo lines to be flushed with high pressure N2 / air depending on the type of cargo.

Carrying high melting point cargo - Lack of procedures leading to excessive tank cleaning time & cargo pumps (Framo type) freezing

Discharging high melting point cargoes of various grades of Palm oils including High melting point cargoes such PFAD, Lauric acid and Stearic acid involved some careful considerations. Following are some good practices while handling such grades, however ship specific procedures may vary from vessel to vessel

While monitoring daily temperatures is a must occasional running of cargo pumps during the voyage in a recirculation mode ensures pumps are free and turning.

As far as practical do not introduce ballast into the adjoining ballast tanks of high melting point cargo, should you need to ballast the tank due to stability reasons .Ballast should never come in contact with the bottom of the cargo tanks.

Try to minimize looping at the manifold for cargoes like PFAD, Stearic acid and Palm Stearin.

If for any reasons portable Framo pump is utilized , a proper planning and prior risk assessment to be carried out. When using portable Framo pump for discharging, vessel might have to carry out mandatory pre wash for certain cargoes as instructed by local authorities.

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