Managing the Change from High Sulfur to Low Sulfur Fuel Oil

Ships entering SOx Emission Control Areas (SECA) that normally operate on high sulfur bunker fuels need to orchestrate the change to the specified low sulfur fuels in advance so that the vessel is burning clean on entry into the area. Operators must also be able to demonstrate to the relevant authorities through appropriate documentation and records that they have complied with the low sulfur limits.

IMO designated SECAs limit the sulfur content of all fuel oils used in those defined areas to a maximum of 1.5 percent or requires equivalent primary or secondary control measures to be applied. The Baltic Sea SECA entered into effect in May 2006 and the North Sea SECA applies from November 2007. Regional controls apply in areas such as Californian waters where, from 1 January

2007 auxiliary diesel engines and diesel-electric engines must use either marine gas oil or marine diesel oil at or below 0.5 percent sulfur. Alternatively, the vessel may use control measures to reduce its emissions to the same level or, in certain situations, the vessel may pay a noncompliance fee. The vessel must also maintain records showing when it entered and departed California waters and when it switched fuels. Records must also be kept regarding fuel purchases and sulfur content. The restriction will be further tightened on 1 January 2010 by restricting usage solely to marine gas oil at or below 0.1 percent sulfur.

Vessels constructed on or after 1 July 1998 are provided with at least two fuel oil service tanks having a capacity of at least eight hours at MCR of the propulsion plant and normal operating load at sea of the generator plant. (Chapter II-l/Reg.26.11 of SOLAS 74 as amended.)

In this case, one service tank is available for low sulfur fuel oil and could be designated as a service tank in which only low sulfur fuel oil is used. To achieve compliant changeover from the high to low sulfur fuels, the following procedure could be considered;

• The high sulfur fuel oil in a settling tank is discharged to the overflow tank through a valve at the tank's bottom by gravity at a loading or unloading port outside the SECA.

• The high sulfur fuel oil in a service tank to be used for the low sulfur fuel oil is shifted to another service tank and/or the overflow tank.

• Upon completion of the fuel oil shifting/transference, a low sulfur fuel oil is transferred to the settling tank from a low sulfur fuel oil bunker tank and then is supplied to the service lank through fuel oil purifiers.

Where the MDO service tank also has a capacity of at least eight hours operation at

MCR of the propulsion plant and normal operating load at sea of the generator plant, the change from high to low sulfur fuels should follow one of the following two procedures:

If using MDO during the change:

• The fuel oil in both a settling tank and a service tank is completely discharged to the overflow lank through a valve at the tank's bottom by gravity after the fuel oil to the main engine and the auxiliary engines has been switched to MDO.

• Low sulfur fuel oil is transferred to the settling tank from a low sulfur fuel oil bunker tank.

• The low sulfur fuel oil is supplied to the service tank through fuel oil purifiers.

• After the service lank level has reached the minimum feasible level for the intended operation, the fuel oil is switched from MDO to the low sulfur fuel oil.

If not using MDO during the change, the following switching procedure should be carried out prior to entering the SECA, taking into account the time needed lor the change to complete:

• The high sulfur fuel oil in the settling tank is completely discharged into an overflow tank under the condition dial the service tank lias been fully filled with a high sulfur fuel.

• The low sulfur fuel oil is transferred to the settling tank from a low sulfur fuel oil bunker tank.

• Once the temperature of the fuel oil in the settling tank has reached the temperature necessary for its purification, the high sulfur fuel oil in the service tank is discharged to an overflow tank up to the minimum feasible level for the intended operation.

• The low sulfur fuel oil in the settling tank is immediately supplied to the service tank through fuel oil purifiers.

Containerships constructed before 1 July 1998, normally have additional settling and service tanks for low sulfur fuel oil, with each tank usually having a capacity of about 100 m. However bulk carriers, product carriers or oil carriers are not provided with such tanks. For owners/operators who decide not to make the necessary structural modifications to install additional settling and/or service tanks on such existing vessels, it is still possible to effect an acceptable changeover from high to low sulfur fuels by considering the following:

Since there was no specific requirement for the capacity of HFO settling and service tanks in SOLAS, their capacity was usually less than is provided on post 1998 vessels. In this case, the fuel oil management procedure for switching from high to low sulfur fuels should be related to the safe operation of the ships. Where an additional service tank and/or settling tank is not provided on vessels entering into a SECA, the switching procedure should be developed taking into account the ship's crews' knowledge and skill level.

If, as a consequence, it is not possible to follow the previously outlined procedures, the changeover can be achieved without discharging the high sulfur fuel oil in both the settling and the service tanks. Taking into account the risks to the safety of the vessel this procedure is performed by switching valves at the suction of the transfer pump.

The low sulfur fuel oil is transferred to the settling tank, mixing with the retained high sulfur fuel oil. The low sulfur fuel oil is then supplied to the service tank with the high sulfur fuel being separated by the purifiers.

Once again, this changeover should be carried out well prior to entering the SECA, taking into account the time required for the transition to low sulfur fuel.

If a shipowner does not intend to modify an existing vessel by adding the required additional settling and service tanks, a fuel oil management plan is to be prepared that takes into account the time required to complete the changeover from a high sulfur oil to a low sulfur oil prior to entering the SECA.

ABS is able to assist owners in developing the fuel management plan for specific ships within a fleet. The specific plans take into account the relative sulfur contents of the fuels, the capacity of each of the fuel oil settling and service tanks, the main and auxiliary engine outputs, the capacity of the fuel oil purifiers, the fuel service system and relevant safety issues.