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Oil major and bunker supplier ExxonMobil has released its latest 'ExxonMobil Insights' video, which covers the issue of fuel switching.

The main topics discussed are: planning and preparation, controlling temperature and viscosity, avoiding thermal shock and ExxonMobil's Emission Control Area (ECA) fuels.

Complex procedure

The new video points out that fuel switching is a complex and very controlled procedure that can differ from one ship to another, depending on a vessel's engine type, machinery and set-up.

There is also the issue of dealing with two potentially incompatible fuel types; when vessels are having to change back and forth from a regular- to a low-sulphur fuel, this increases the chance of compatibility issues between the two fuels.

Planning

The programme notes that all vessels must have a fuel changeover plan in place that is compliant with MARPOL Annex VI; it should identify potential emergency scenarios that could arise if procedures are not strictly followed.

There should also be a design evaluation in place based on the manufacturer's recommendations and covering the entire fuel system and its components.

On the bridge, navigation charts should be marked up indicating the ECA boundary, and an additional position where the fuel-switching operation should commence.

Avoiding thermal shock

When switching from heavy fuel oil (HFO) to marine gas oil (MGO), thermal shock is a key concern which can lead to fuel pump sticking, leaks and even power loss, the video notes.

HFO is injected into the engine at temperatures of between 120 to 140 Celsius. During fuel switching, this should be gradually reduced at the rate of two Celsius per minute to the injection temperature of the MGO, which is around 30 to 40 Celsius.

ExxonMobil products

To help reduce issues related to fuel switching and minimize the danger of thermal shock, ExxonMobil has developed two premium ECA-category products that are designed to make fuel switching safer and easier: ExxonMobil Premium HDME 50 and ExxonMobil Premium AFME 200.

ExxonMobil Premium HDME 50 is a heavy distillate fuel that is compatible with MGO and ECA-compliant.

Commenting on the properties of HDME 50, Krystal Wrigley of the Fuel Products Section of ExxonMobil Research and Engineering, says: "In the example of HDME 50, we have a fuel that has a high viscosity, so it is intrinsically safer than having a fuel like marine gas oil, where you're switching and have the flash concerns, and so it's very similar to HFO in a lot of its bulk properties but then has some optimization and actually exceeds HFO quality in many circumstances as well."

ExxonMobil Premium AFME 200, meanwhile, is said to be fully compatible with ExxonMobil Premium HDME 50 and MGO. It has a higher viscosity, making it comparable to heavy fuel oil, thus enabling similar storage and handling practices for both fuels on board ships.

Both fuels require preheating, therefore reducing the risk of thermal shock to engine components during switchovers. Additionally, they have a higher flashpoint than MGO, which makes them less volatile and safer to use in boilers - as there is reduced risk of boiler furnace explosions.

A link to the video has been provided below.

ExxonMobil Insights: 5. Switching fuels