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ExxonMobil has issued a list of best practice tips for switching to low-sulphur fuel ahead of the International Maritime Organization's (IMO) upcoming global 0.5 percent cap on fuel sulphur content in 2020.

The guidance is designed to help the marine industry switch to low-sulphur fuels while maintaining a vessel's safe and reliable operation.

John LaRese, Marine Fuels Technical Advisor, ExxonMobil, commented: "With so many different types of fuel potentially set to enter the bunker market, vessel operators are rightly concerned about stability, compatibility and quality issues, such as elevated levels of cat fines. It will therefore be more important than ever for operators to follow best practice when bunkering compliant fuels, including using laboratories to test fuel samples for potential issues."

ExxonMobil has previously warned of the rise in compatibility and stability issues as new 0.5 percent fuels emerge, and recently launched a monitoring service that measures fuel sulphur content in a move designed to give operators "peace of mind that the fuel they have on board is compliant".

In April, ExxonMobil also announced that it would start to supply 0.5% sulphur fuels in Northwest Europe, the Mediterranean and Singapore.

Earlier this month, the American Bureau of Shipping (ABS) issued an advisory on marine fuel oil to help the industry prepare for the 2020 global sulphur cap. It previously issued a guidance on switching from heavy fuel to 0.1 percent sulphur fuel when entering Emission Control Areas (ECAs) back in 2010.

As previously reported, IMO's Marine Environment Protection Committee (MEPC) in April adopted a best practice guidance for fuel oil purchasers/users for assuring the quality of fuel oil used on board ships.

In the same month, the International Bunker Industry Association (IBIA) launched the first edition of its 'Best practice guidance for suppliers for assuring the quality of bunkers delivered to ships', which addresses procedures to safeguard and maintain bunker fuel quality control throughout the entire supply chain - from the production of bunkers all the way through to the delivery to ships.

ExxonMobil's best practice tips have been provided below.

First, establish best practice

Prevention is always better than cure, so it is advisable to:

- Buy fuel that meets the latest ISO 8217:2017 specification;

- Only bunker from reputable fuel suppliers;

- Clean out bunker tank residues when necessary.

Test for cat fines

Some new 0.5 per cent sulphur fuels could contain elevated levels of cat fines which, if not properly treated, could trigger catastrophic engine damage. If laboratory testing shows a high concentration, then: - Maintain storage tank temperatures at least 10C above fuel pour point;

- Keep settling tanks at 85C;

- Operate purifiers at optimum efficiency and minimum throughput;

- Drain water from fuel tanks to aid settling.

Check for compatibility

There is a risk that two compliant fuels will not be compatible, which can trigger sludge formation. It is therefore essential to:

- Test the fuels for compatibility, ideally in a laboratory. If the fuel is already loaded, then test onboard to get immediate results;

- Store fuels separately until testing has been carried out;

- Even when two fuels are compatible, avoid mixing in excess of 80:20.

Monitor for sludge

If sludge does start to form, it is essential to ensure against further fuel blending before any remedial action is taken, as this may exacerbate the problem. Then:

- Operate two or more separators in parallel at their lowest throughput;

- Increase the frequency of purifier discharge;

- Monitor and clean filters frequently.