High anxiety in the shipping industry about "Low Sulphur Fuel"

With just several months left before the IMO Marpol 73/78 Annex VI comes into force in 2005, many ship owners and ship operators are still grappling with the technical implications of the fuel sulphur regulations.

The key question is whether commercial vessels with their existing engine and tank configurations are prepared to consume bunkers with lower sulphur content, particularly when they enter the so-called Sulphur Emission Control Areas (SECAs).

Ship owners and ship operators should first be aware of the differences between heavy fuel oils (HFO) and ‘distillates’ such as marine diesel oils (MDO) and marine gas oils (MGO).

Unlike distillate fuels, HFO requires heating before being injected into diesel engines or boilers, due of their high viscosities.

The latest statistics indicate that world average sulphur levels in residual fuels is about 2.6%, but in some areas, fuels with a sulphur content of up to 4.5% are common. Such fuels may be termed high sulphur fuels (HSF). Most engine manufacturers and lube oil suppliers describe low sulphur fuels (LSF) as products containing less than 1% sulphur, although some may include sulphur levels of up to 1.5%.

ISO 8217 specifications currently limit sulphur content to 1.5% for MGO and 2% for MDO as well as blended diesel oils, while  statistics suggest that actual average sulphur content for all distillate fuels is about 0.6%.

The EU directive, however, is proposing that ships at berth in some areas consume LSF with a maximum of 0.2% sulphur. From 2008, this limit may be lowered to 0,1%.

In the absence of an international definition for marine fuels with 0.2% sulphur or less, we will call such fuels Ultra Low Sulphur Fuels (ULSF).

The bunker industry, presently, has little or no knowledge about the characteristics of LSF and ULSF, both of which are not yet readily available in the market place. This could be a major problem for marine fuel refiners as they will soon face mounting pressure to meet the increased demand for low sulphur products, presumably by introducing new production processes.

‘Single-Fuel’ ships, designed to operate all their marine engines on HFO, will also face numerous technical challenges when consuming LSF and ULSF; especially during the change-over from HFO to LSF or ULSF and vice versa.

To begin with, HFO and fuels with low sulphur content may be incompatible in certain blending ratios. During the change-over from HSF to LSF/ULSF, and vice versa, distillate components may disturb the stability of the HFO and cause asphaltenic sludge to precipitate. In the worst cases, the engine hot filters will be choked, causing fuel starvation and other ill consequences for the ship.

LSF and ULSF used in combination with cylinder lubricating oils with high Base Number (BN) may also result in over-lubrication, leading to cylinder liner lacquering and scuffing. On the other hand, some ULSF do not provide sufficient lubricity to high-pressure fuel pumps for problem-free operation. Those high in aromaticity often have poor ignition and combustion properties, possibly due to the de-sulphurising processes in the refineries having a negative impact on the properties of the fuels' blended components.

Last but not least, the existing tank capacity and pipelines designs on many ships make segregation of HSF and LSF difficult or even impossible.

While two-stroke marine diesel engines may be able to consume LSF for short periods, long-term LSF operation can be problematic and thus raise safety concerns, particularly when the vessels are sailing in congested waters or in the SECAs.

To what extent two-stroke main engines will have to consume ULSF remains to be seen, since the regulations are still unclear about the restrictions in SECAs and inland waterways in the EU. Most likely, the consumption of ULSF ‘at berth’ as mentioned in the regulations should imply mainly the use of auxiliary engines to power winches, cargo pumps and cranes.

So how to prepare for the low sulphur regulations ?

The IMO and EU regulations are unfortunately not in line with each other on how SOx emissions can be reduced. As an alternative to burning low sulphur fuels, the IMO permits the use of approved after-treatment exhaust gas cleaning systems or other technologies that can be verified to limit SOx emissions.

The EU directive, in its present edition, is less flexible and only allows fuels with maximum 1.5% sulphur to be used in restricted areas.

Hence, if exhaust gas cleaning is not going to be a viable alternative in the EU, ship operators must equip their vessels with more segregated units of bunker tanks, settling tanks, service tanks and cylinder lubricant tanks. Tank layout and design should ideally be planned during the new building process since modifications on existing installations can be costly. Even so, ships have this option to reconfigure their onboard fuel treatment plants.

For the vessel’s chief engineer, the best way to detect possible problems is to frequently check the condition of the main engine piston crown and to inspect the piston ring pack through the scavenge air ports. Over-lubrication should generally be avoided, but in practice, this may not be a safe practice because engine tolerances are small.

Moreover, when ships according to the proposed EU regulations consume LSF in the SECAs, they could be sailing in narrow straits, channels and passages, where engine failure is potentially disastrous. In this regard, two-stroke engines should preferably use a cylinder lubricant with reduced BN. During prolonged LSF operation or if ULSF consumption is unavoidable, the chief engineer should seek relevant advice from the vessel’s engine builder and the lubricant supplier.

Fuel testing companies(FOBAS) can also help ships cope with low sulphur fuels.

As the Marpol Annex VI regulations will be in force as of May 19th 2005 large ship operators preparing their vessels for low sulphur fuel consumption will have to make many important decisions quickly.

Among the considerations, they will have to assess the necessary modification to current tank arrangements for segregating HSF from LSF.

Ship operators should also know which type of low TBN cylinder oil is most suitable for their vessels’ LSF and ULSF operation. They will need to source for reliable suppliers of low TBN cylinder oils and determine whether adequate amounts of these products can be kept on board to replace high BN cylinder oil when required.

High sulphur content fuels require cylinder oils with a high TBN (Total Base Number). High sulphur fuels generate sulphur oxides during the combustion process which when combined with water, also formed during combustion, can cause corrosive sulphuric acid. The alkaline additives in high TBN cylinder oils neutralize the corrosive acids generated during the combustion process. Accordingly, low sulphur fuels would need a cylinder oil with a lower TBN. Typically your low sulphur fuel oils are gas oils or diesel oils which are "lighter" oils with lower viscosities and consequently lower lubricating qualities when compared to heavy fuel oil (HFO). All slow and most medium speed disel engines are designed to operate on HFO. If running-in an engine on a lighter fuel, more time would be required to wear in the cylinder liner and piston rings.

Finally, ship owners and ship operators must ensure that their chief engineers are comfortable with the change-over procedures for distillate fuel operation, and that the ship crews can monitor cylinder liner condition effectively.

What the regulations say