There has recently been a distinct rise in the average acid number of fuels bunkered in Singapore, along with a number of results above the 2.50 mg KOH/g ISO 8217 limit.
Further analysis on a number of the most recent high acid number fuels has shown that although the chemical constituents vary considerably in composition and concentration, one common factor seen is the presence of high concentrations of various Resorcinol related compounds, specifically various Alkyl-benzenediols. These compounds are associated with Estonian Shale oil which may have been used as a blend component in the fuel.
In the past we have seen a link between Estonian shale oil in fuels and increased problems specifically around excessive sludge production in purifiers and filter blockages.
Shale oil is considered as “Petroleum” under ISO 8217 and therefore not considered a contaminant, however, as with any fuel there is a duty to provide a product that remains stable and homogeneous throughout storage and use.
Any supplier should be able to give some information regarding the acid number of a fuel being sold and some background to the blend products used. Fuels with Estonian Shale oil should not necessarily be avoided, however extra caution should be given to the fuel stability and operational performance when in use.
This is still a situation we are looking into, and as we gain more operational feedback from vessels we may update the advice given.
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