As shipowners prepare for the International Maritime Organisation (IMO) 0.5pc sulphur cap next year, compatibility concerns have washed over the bunker industry. But could they be overblown?
New low-sulphur fuel oil (LSFO) blends can be mostly aromatic or mostly paraffinic in their compositions, depending on how they are refined and blended. This can lead to compatibility issues between different batches when mixed on ships, a process also known as co-mingling. Co-mingling bunker fuels from different origins could lead to sludge formation, which has the potential to do serious damage to engines.
For example, hydrotreated vacuum gasoil (VGO) and LSFO residue blends tend to be incompatible. Hydrotreating removes sulphur from the VGO, but will also make it less aromatic. LSFO blend components, on the other hand, tend to be paraffinic.
Another problem that could occur when two incompatible fuels are mixed is asphaltene separation, which is when asphaltenes precipitate and form sludge inside engine filters and separators. This can result in a ship losing its propulsion and auxiliary power.
Fuel testing agencies such as VPS and Intertek will be lining up to test compatibility across suppliers and locations. But refiners are only handing out fuel samples for testing under non-disclosure agreements, so that leaves little to public knowledge.
Refiners have been hesitant to address compatibility concerns. Some global refiners — such as Total, Shell, BP and ExxonMobil — have said that their fuels will not necessarily be compatible with other suppliers’ new fuels. ExxonMobil has said its fuels will be compatible with each other, provided storage and handling follows proper procedure.
This is where the appeal of branded products comes in. Producers of branded 0.5pc sulphur bunker fuel ranges, that are said to be compatible with each other across locations, can charge a price premium for their assurances to shipowners.
Aware of the potential issues, shipowners have several options available to limit the risk of incompatibility and consequent engine failure. Most buyers will keep LSFO blends that originate from different suppliers in separate tanks — a practice already common when bunkering high-sulphur fuel oil (HSFO) blends. The International Bunker Industry Association (IBIA) has advised shipowners to avoid co-mingling by segregating tanks to handle a variety of fuel qualities.
“Fuel oil is not supposed to be co-mingled today although some owners have, albeit not more than an 80:20 ratio,” one shipowner said. Shipowner Chembulk Tankers will comply with the cap by burning 0.5pc sulphur fuel, and will try to avoid co-mingling new fuels in its tanks.
Some shipowners have already segregated their fuel tanks in preparation for 2020. For shipowners with the exhaust cleaning equipment known as scrubbers on their vessels, their storage tank ratio of LSFO to marine gasoil (MGO) will likely remain the same after 2020 as their ratio of HSFO to MGO was before.
“Once we obtain the new 2020 grades we will not co-mingle at all, at least not in the initial phase, until we have a better understanding of these fuels,” a shipowner said.
Buyers that intend to co-mingle the new fuels ought to perform compatibility tests first. The best method for doing this is the ASTM D4740 spot test, an analysis tool that can determine possible co-mingling issues between grades. Shipowners can also opt to use several available fuel additives to limit sludge formation.
While there are reasons to be concerned about incompatibility between new LSFO and distillate blends, most shipowners will not co-mingle them any more than they co-mingle HSFO blends today.
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