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Many of fuels complying with 0.5% sulfur limit are expected to be very paraffinic and also high content of distillate components.
If such fuels are loaded into HSFO fuel tanks that have not been cleaned,
“They could rapidly dissolve and dislodge sediments and asphaltenic sludge in to storage tanks, settling tanks, and pipelines, potential leading to purifier and filter operational issues and in extreme cases fuel starvation resulting in loss of power”.
HSFO sludge and residues that dissolve and enter the fuel system can also potentially increase the sulfur content of the fuel at the engine rail, causing a compliant fuel to become non-compliant.
Some port state inspector may take MGO samples post 2020 and if MGO sulfur is above 0.5%, vessel can be fine.
Operators should ensure the fuel oil tanks and systems are sufficiently clean prior to the first loading and use of compliant fuels to prevent a sudden and severe dislodging of built-up residues.
it can be done in 2 to 4 days per tank. In addition to cleaning tanks, all of the pipework in the fuel oil service system needs to be flushed through. Overall it may take one to two weeks.
(If only the tanks have been cleaned in dry-dock, it could take two to five days to flush through the pipework in the fuel oil service system to ensure full compliance with the 0.5% sulfur cap).
It would likely take a minimum of 4 days per tank. Tanks need to be empty before they can be cleaned, hence the time needed to drain tanks needs to be taken into account when estimating the overall time required.
In addition to cleaning tanks, all of the pipework in the fuel oil service system needs to be flushed. Flushing the remaining pipework and fuel oil service system after all tanks have been cleaned could take another 1 or 2 days.
An alternative to manual cleaning is to gradually clean the sediments and asphaltenic sludge from HSFO tanks and fuel system by dosing additives.
There are successful examples of this approach for ships that needed to reallocate HSFO tanks to fuels complying with the 0.1%
Sulfur limit that took effect in ECAs in 2015
Advantages of using OCTAMAR BT-25
-Maintain long term fuel stability on laid up vessels
-Higher efficiency and better fuel economy
INNOSPEC recommends that a gradual clean-up is conducted over 3 – 5 bunkers prior to the change in tank allocation. This conservative estimate ensures a smooth system clean-up by preventing excessive sludge blockage.
BT-25 would be dosed directly into fuel storage tank, it would clean the whole fuel oil service, systems, including settling and service tanks. The action of dispersant additive will potentially lead to increased levels of sludge and sediments in the fuel which may lead to operational issues. During the clean-up period, it is recommended that the ship’s crew should closely monitor the operation of centrifuges and filters for any issues or deterioration in performance.
Dosage: The recommended regular dosage of OCTAMAR BT-25 is in the range of 1:15,000 or 1:25,000 (1 liter per 15 to 25 tonnes of fuel). Higher dosage rates may be recommended for emergency use.
After using BT-25 to clean out all HSFO residues from a ship’s fuel system, the risk of HSFO residues from the fuel oil tanks and service system causing sulfur non-compliance may be sufficiently reduced from the first bunkering of compliant fuel oil into each tank allocated for either a 0.50% or a 0.10% sulfur limit fuel oil.
To minimize risks of non-compliance, a sulfur fuel analysis should be done to determine if the fuel in the ship’s tank is compliant or whether a second bunkering of compliant fuel is required.