World Bunkering >Articles > Fuel management > Additives are key to adaptation

Bunker fuel as a product is changing. Driven by developments in refining and bunkering technology, as well as stricter regulations on emissions and the growing emphasis on reduced sulphur content, fuel testing agencies continue to correlate declining sulphur levels with increasing levels of catalyst fines and associated engine damage, as well as declining fuel stability and lack of fuel lubricity.

Worldwide increase in cat fines

There is still a lot of research to be done (Photo: INFINEUM)

Recently released data on marine fuel quality from DNV Petroleum Services (DNVPS) show that the world average aluminium and silicon (Al+Si) content in marine fuel grades has increased. Also known as catalyst fines, DNVPS data show that Al+Si content in heavy fuel oils (HFOs) has gone up from 19.0 mg/kg in 2005 to 23.5 mg/kg in 2008, in line with a drop in average sulphur content. This trend is likely to be exacerbated in July 2010 when the sulphur limit is set to drop to 1.0 mass % in line with the revised MARPOL Annex VI in the Baltic Sea and North Sea Emission Control Areas (ECAs).

The sulphur content in residual fuel is often related to dilution of residual fuel oil refinery product by blending with an appropriate amount of cutter stock, such as catalytic cracking cycle oil. The impending 1% Emissions Control Areas (ECAs) in the North Sea and the Baltic Sea (July 2010) mean that there will be a requirement to introduce additional cutter stock in bunker fuel in order to achieve compliance with sulphur regulations, while also maintaining ISO8217 density and viscosity standards. With increased cutter stock in residual fuels this is expected to exacerbate increasing fragmentation in marine fuel quality, including associated stability issues. Furthermore, as these fuels are known to have an increased level of catalyst fines, increased damage to engine parts such as cylinder liners and other critical components is anticipated.

The lack of distillate fuel lubricity is also becoming increasingly significant for many ship’s engineers and can result in fuel pump and injector “sticking” (metal to metal contact), and ultimately could produce hardware seizures; the natural sulphur-based lubricity agents in fuel are stripped out during the desulphurisation at the refining process. Even when fuel is derived from the most reputable and trusted sources, significant wear to critical equipment and machinery is not uncommon. Indeed a significant number of the vessel problems reported to DNVPS originated from fuels that had met the ISO8217 marine quality specification. The testing of bunker samples is becoming increasingly important, as they identify the need for mitigating engine wear and tackling the effects of reduced lubricity.

Effects of slow steaming

A further recent development in modern shipping has been a reduction of speed. Whether brought about by the need to rationalise the largest costs faced by any shipoperator or in light of impending environmental regulations, the shipping industry has overseen a substantial change in the speed of vessels over the past 18 months. The integration of so-called ‘slow steaming’ into many fleets, particularly container shipping, has shown significant benefits to owners; a 10% slowdown can equate to as much as a 23% reduction fuel burn.

Jean de Kat, Head of Innovation at Maersk Maritime Technology, in a Bunkerworld article entitled ‘Cutting bunker consumption remains a priority’ published on 19 May 2009, was quoted as saying: “Slow steaming is here to stay, at least in terms of operating engines at load levels lower than maximum continuous rating.” The decision to slow steam is not without operational consequences for the ship operators, however. Savings on fuel costs by slow steaming must be balanced with minimising expensive maintenance bills.

This is particularly the case with slow-speed engines, which are designed to steam slowly only for short periods, for example during manoeuvring in port waters. Moreover, vessels are far less suited to prolonged slow steaming, at least without a great deal of extra exhaust tract cleaning and inevitably costly additional maintenance as a consequence of the turbocharger speed being too low to provide adequate scavenge air pressure for design fuel combustion conditions.

Andrew Glynn-Williams, an assistant solicitor in the marine, trade and energy group at Hill Dickinson LLP, wrote in Lloyd’s List in an article entitled ‘Slow steaming can lead to legal hot water’, published on 5 August 2008, that: “… prolonged running of engine machinery below its optimum design could lead to poor combustion. “Where no proper cleaning or maintenance is carried out, this can cause a build-up of soot in the uptake economiser, which increases the risk of an exhaust uptake fire. In severe cases, this could lead to the meltdown of the economiser, or even engine room fire,” he added. Soot can also build up on the turbocharger blades and can result in imbalances and sub-optimum performance – resulting in a spiralling increase in soot build-up.

Some operators have reported incidents where turbochargers require overhaul after as little as 4,000 running hours instead of the recommended 12,000. Also, the auxiliary machinery of a vessel tends to be run as a consequence of slow steaming. Yet, overall plant design is usually such that certain auxiliary machinery – boilers, pumping systems and diesel generators – may not be required to run during a normal full-speed voyage. The necessary increased use of auxiliary machinery as a result of slow steaming, therefore, can also lead to higher expenditure and maintenance needed.

Additives as a solution

At Infineum, a world-class petroleum additives group of companies, we have drawn upon our vast technical expertise in automotive additives where we have addressed fuel issues for many years in order to develop marine additives that can provide solutions to issues associated with marine fuel handling and combustion. For ships burning residual fuel, Infineum F7455 Combustion Improver has been shown to reduce soot and deposit build-up in the exhaust tract – reducing the risk of an exhaust uptake fire.

A reduction in smoke emissions has also been observed – with obvious benefits for shipoperators concerned about visible black soot emissions from the stack and subsequent contamination of decks and cabins, as well as the environment. There are other challenges associated with operating with lower sulphur fuel that can be negated through marine additive use; such as the build-up of liner lacquer, bore polish and associated increased lubricant consumption in four stroke engines, as well as a build-up of deposits on piston rings, injector nozzles and valves. The desulphurisation of fuel during the refining process removes natural lubricity, which can create problems with fuel pumps and injectors leading to hardware seizures – issues that are becoming increasingly significant for many ship engineers.

For ships burning distillates in medium speed engines, Infineum F7451 Marine Distillate Additive is recommended for combustion chamber clean-up in ship main propulsion and auxiliary engines, as well as land-based power generation and railroad applications. Ship trials have shown improvements in combustion chamber fouling, cylinder liner lacquer control, bore polish control, lubricating oil consumption and soot reduction when the fuel is treated with Infineum F7451.

At Infineum we believe that additives can have an impact in the reduction of a number of emissions and – using the wealth of experience the company has in research and development in other transport sectors – we continue to undertake tests to establish the extent to which additives can contribute to reducing shipping emissions through the simple application of robust additives. Environmental legislation and recessionary factors have brought about many challenges for the shipping market and there will be many more difficult challenges ahead.

Dealing with these challenges means ensuring that every detail of shipoperation is optimised and that potentially hazardous consequences of new fuels and operation patterns are mitigated. Fuel additives can contribute towards emissions reductions, optimising fuel combustion and marine engine operations, and improving maintenance efficiencies for ship-operators.