Image: ExxonMobil

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By John LaRese, Marine Fuels Technical Advisor, ExxonMobil

The International Maritime Organization's (IMO) decision to implement a 0.50 percent cap on sulphur emissions has created uncertainty amongst vessel operators. Questions are already being asked about how to comply with the changing emissions target, what types of fuels will be available and where. However, ensuring compliance isn't just about fuel selection; the actual switchover process from heavy fuel oil (HFO) to new, low-sulphur alternatives needs careful management. There are also implications for the selection of lubricants.

A series of important steps need to be taken before bunkering a low-sulphur fuel; vessel operators will therefore have to work out arrangements that meet the specific requirements of their vessels. Significantly, without careful preparation operators may jeopardise their sulphur compliance, which carries the risk of costly fines. They must also plan around fuel availability, given the possibility that some ports may be unable to meet the demand from the industry.

Tank cleaning

Unless a vessel is fitted with a scrubber, operators will need to ensure that their fuel tanks do not contain high-sulphur HFO by the IMO deadline. Fuel tanks will probably retain sediment from the existing HFO, which is likely to contain those higher levels of sulphur. If this is not removed, there is the risk that the sulphur will contaminate the compliant fuel, pushing its sulphur content above the 0.50 percent limit.

ExxonMobil expects that many compliant fuels entering the market will have a sulphur content very close to the 0.50 percent cap, so even very low levels of residual sulphur left in a fuel tank could tip a vessel over the IMO's compliance limit.

To minimise this risk, ExxonMobil recommends that vessel operators flush fuel tanks with a distillate-based product, which will help remove sludge deposits. This process may need to be repeated, depending on the amount of residue present. In some instances, tank bottoms may have to be manually cleaned.

The fuel used to flush tanks could contain damaging levels of cat fines, which will require on-board treatment. Vessel operators must factor in how long these processes could take and keep in mind that any sludge removed from the tanks will need to be disposed of properly.

Operators should remember that the storage, handling and treatment of 0.50-percent-sulphur fuels will involve bunkering fuels of a wider variety of viscosities, types and formulations than seen today. On-board handling practices have to take into account likely changes in fuel types, including fuel segregation and routine compatibility testing.

Running down cylinder oil stocks

One benefit of the 0.50 percent sulphur cap is that vessels will be able to streamline their lubricant inventory as only one cylinder oil will be required. Vessels with scrubbers will continue to use HFO and high-BN oils, while those who choose to switch to low-sulphur fuels will need correspondingly low-BN formulations. These vessels must deplete their stocks of high-BN cylinder oils prior to the IMO deadline to avoid waste and disposal costs.

To ensure compliance, ExxonMobil recommends that vessel operators work with suppliers who have adopted the latest ISO 8217:2017 fuel standard and have the proven technical expertise to help them navigate the upcoming changes.