3.2 Charter Party and Purchase Contracts
In particular with older vessels in long term charter, fuel specifications referred to in the charter party are often incomplete or obsolete. With the aim to avoid costly misinterpretations shipowners are well advised to update the fuel specification in the charter party whenever this is possible. Otherwise it may happen that charterers aware of the gaps left by older specifications with potentially less stringent limits might draw an advantage out of doing so.
Some ship operators tend to buy one fuel category better than specified. This can be justified in case lower limits for Carbon Residue or Vanadium are seen as beneficial. These being unchanged there is little value in reducing the viscosity alone because some of the problematic properties of a fuel are resulting from the diluent and not from the residual material.
Figure No. 4: Residual Material and Diluents - Refiner
3.3 Production of Residual Material and Diluents
It is a rare exemption that a refinery produces a residual material that matches in its typical data the limits set by ISO 8217: 1996 for any of its categories. Blending to specification without uneconomic quality give away, therefore, is the rule. This can be done at the refinery in case suitable blend components are at hand. In doing this normally two of these are required: one for density and the other for viscosity adjustment. Growing competence in doing this and computer aided blend programmes have resulted in refiners successfully blending nearer and nearer to the limit. The consequence is that a small downwards trend in quality is observed.
Blending marine fuels at the refinery has the advantage that the refiner is aware of the compatibility of his components. In consequence the probability of stability problems with refinery blended fuels is rare these days.
More problematic is the availability of components that are low viscous and cheap because they are not suitable for blending white products .
These are often sold into the bunker market and it is not always sure that resulting blends are meeting the customer' s requests in all aspects, in particular in stability and ignition behavior.
Moreover, such blends may be stable per se, but less in case used in combination with other diluents to blend the low viscosity ISO categories RMA 10 - RMF 25.
Figure No. 5 Residual Material and Diluents - Blender
In some regions it is typical or even promoted to dump used lubricants into diluents for the production of marine fuel oils. This has been controversely discussed in CIMAC, MESJ and other expert bodies [ 7, 8 1. ISO 8217: 1996 does not explicitly prohibit the inclusion of used lubricants in marine fuel oils provided all relevant criteria and limits are met. Some fuel analytical services, however, advise against such and declare fuels blended with used lubricants as "unfit for purpose".
