Cleanliness and stability.
On a practical level, bunker fuel cleanliness and stability are more significant quality indicators, since excess of sludge resulting from poor control of either, will present the operator with enormous difficulties in keeping the fuel treatment plant working at optimal condition. In an era of reduced manned vessels, fuel cleanliness and stability are key features of bunker fuel quality. In practice, bunker fuels supplied by the Majors rarely prove to be problematical - the adoption of a Total Sediment Potential parameter, with limits, at the last revision of the international standards, has all but eliminated concerns from these criteria. Further down the quality ladder however, controls on blending are not necessarily so rigorously administered, either through ignorance of blending procedures (real or convenient), or because of limited flexibility in having access to compatible blend components.
That the Majors appear to have almost eliminated unstable residual fuels from their supply chains suggests use of a very robust control parameter. It may also suggest a degree of quality give-away for the refiner. On-line measuring techniques are being developed and made available to the refiner so as to enable more precise control of residual fuel oil processing and blending, and gives a great step forward in product quality control.
It is also likely that a new generation stability concept will need to be developed, since current concepts do not adequately describe the behaviour of low sulphur residues.
Contaminants.
That residual fuel oil is viewed as a refinery waste stream does not help contribute to a quality image for the product. The term "waste" has many interpretations, but when used in the context of bunker quality, invariably is used to refer to contaminants or undesirable components in the finished fuel. The list of waste streams having the potential to find their way into the fuel pool can be lengthy, and it is a virtually impossible task to implement controls guaranteeing their total exclusion. From an end user perspective the range of contaminants seen as undesirable is much more focussed, and therefore efforts to control their inclusion are potentially more achievable.
Recent contaminations of bunker fuel supplies by polypropylene and acids have hit the headlines, but such large impact incidents are thankfully rare, and usually can be attributable to a single supply source or region, the problem being exacerbated by the vagaries of the bunker market. In International Standards, controls, with limits, are unlikely in the short term to monitor polypropylene. Debate continues as to which test method is best suited for the purpose. Meanwhile, tests to control acid content of residual fuel oil are not sufficiently discreet so as to be meaningful at the lower concentrations seen to date in the market. No doubt if such contaminations become more frequent, pressure will increase for the industry to introduce controls with limits.
Foremost in the mind of the bunker buyer today however is contamination of bunker fuel by deliberate inclusion of used lubricating oil (ULO), or, to be more specific, used automotive engine oil. The rationale behind end-user concern centres on the residual dispersancy of the ULO impairing as it does, the pre-treatment of the bunker fuel in which it is mixed. Once viewed with scepticism by many, there is now irrefutable evidence to show that even a small amount of ULO in bunker fuel can have an adverse effect on the performance of the centrifuge, noticeably reducing solid contaminant and water removal efficiency.
Within the current standards, the only parameter coming close to controlling inclusion of ULO is the ash value. The additive metals contained in ULO will contribute to the total ash level of the fuel, but control by this parameter is vague at best, and very dependent on the other inherent ash-contributing metals (e.g. vanadium, sodium etc.) found in the fuel. On its own therefore, control of the ash level may not be sufficient to exclude influential quantities of ULO.
There is significant pressure from the end user to eliminate ULO from fuel oil as supplied. Current thinking is focussing on control of the common additive metals found in ULO as defined i.e. used engine oils. Since commercial additive chemistry types may vary, and many of the soaps used are based on metals found inherently in residual fuel oil, much statistical data need be examined. The bunker industry is both fortunate and grateful to be availed of the statistical databases of the third party testing services, primarily those of Det Norske Veritas Petroleum Testing Services and Lloyd's FOBAS. Access to these large data sources permits valid interrogation so as to ensure any resultant control levels for additive metals which may evolve are able to take into account base level values for metals inherent in crude oil. Ahead of any formal controls being in place, the responsible supplier will already have policies and guidelines prohibiting such adulteration.
Sulphur and the Environment.
Sulphur occurs naturally in all crude oils, mostly in close association with complex aromatic compounds. Since these compounds have high boiling points, the sulphur content of residual fuel oils will generally be greater than those of the distillate grades.
The marine fuel pool has traditionally been the outlet for higher sulphur residues increasingly prohibited in the inland market, and the continued introduction of secondary processing in the refineries in recent years has resulted in an upward trend in typical levels found in bunker fuel oils. From a practical perspective, these levels have been successfully countered in the modern diesel engine by the use of alkaline lubricants which neutralise the corrosive products of combustion. With the combustion of residual fuel oil however, increased amounts of sulphur oxides are formed in the combustion space, which ultimately exhaust to the atmosphere.
In the medium term, there will be a moderate increase in the global average sulphur level found in bunker fuel oils, currently hovering around the 3%S mark. However, no one engaged in the marine industry can fail to be aware of the intense debate surrounding the reduction of emissions from ships.
It has taken ten years for the current legislative proposals to be agreed at the International Maritime Organisation (IMO) - the governmental body responsible for policing the global maritime industry. At it's September 1997 meeting, the IMO's Marine Environmental Protection Committee (MEPC) finally adopted a proposal to implement a number of measures to reduce such pollution.
