FOBAS Bulletin: High/off-spec Ash due to Calcium, ARA

In recent days FOBAS has tested a number of fuels that have a high tested Ash content, above the 0.100%m/m limit for an RMG380 grade. These fuels were bunkered in the second half of April from ports in the ARA (Antwerp, Rotterdam, Amsterdam) region with tested Ash ranging from 0.102 to 0.127%m/m

These fuels are all high sulphur residual fuels (>0.50% mass) with very similar properties and appear to be from the same source One common factor in all is the high Calcium which is a main contributor to the off-spec Ash in each case. Calcium ranged from 116mg/kg up to 181mg/kg. Sodium was also relatively high ranging from 50 to 86mg/kg., The fuels also had high acid numbers (TAN) ranging from 2.20 to 3.40mgKOH/g.

Often when we see high acid numbers (>2.00mgKOH/g) and high Calcium together this is due to naphthenic acids. These are present in the original crude oil and generally not considered any operational concern. Initial testing on some of these recent fuels show naphthenic acids to be present.

There are some additional points to clarify on the above:

• Firstly, in relation to Calcium, it may be noted that ISO8217 lists a 30mg/kg limit for Calcium. It is important to note the full clarification in the standard however, where the Calcium limit only applies in conjunction with the Phosphorus or Zinc limits of 15mg/kg, used as a measure of ULO (Used Lubricating Oil) presence, rather than to limit the Calcium content on its own.
• Sodium levels, although relatively high are all still below the 100mg/kg RMG380 grade limit.
• On any high acid number fuel, it should also be noted that just because naphthenic acids are present, it does not rule out any other contamination or potential issues with the fuel. Additional attention should be given to the performance of the fuel injection equipment and component conditions during the use of such fuels
• Although Calcium on its own is not a problem, at high levels where it increases the total Ash content as seen here, it can be an issue with increased Ash potentially leading to an increase in post combustion fouling and surging of turbocharger. This should not be allowed to accumulate in particular in the turbocharger, inlet grids, nozzle and blading.

So far we have not had any operation problems reported on the use of these fuels, however caution should be taken in particular to dealing with any increase in post combustion fouling as mentioned, and if further investigation into the nature of the acidic components present is required to confirm they are only naphthenic acids then detailed GCMS forensic testing could be carried out.

Please let us know if you would like further information or if you have concerns over any particular fuel.