Methanol and Lubrication
A new whitepaper from Chevron describes the development of a lubrication strategy for methanol-fuelled vessels. Since the Annex VI sulphur level regulations and the first ECAs, shipowners, especially those with two-stroke engines, have needed to re-evaluate once established thinking on lubrication.
Now with the 2020 global cap set to reduce permitted levels of sulphur from 3.5% to 0.5% Chevron describes the drivers for alternative bunker fuels; and with the days when the majority of fleets operated with just one fuel and lubrication oil looking to be ending Chevron says that ship engines today witness a far more complex range of operating conditions than ever before.
This is just the beginning of what is set to be the most significant period of industry change in recent memory, as both cost and environmental pressures push owners and operators to explore a diverse new range of alternative bunker fuels.
Understanding the impact for shipping as it heads into a lower sulphur, lower emissions future has been critical for leading lubricants supplier Chevron in their development of new products to meet the challenges of today and tomorrow.
The white paper titled Methanol and Marine Lubricants in a Lower Sulphur, Lower Emissions Future was produced in consultation with Vancouver, Canada-based Methanex Corporation, whose Waterfront Shipping subsidiary and private ship manager and investment group Marinvest Shipping are co-owners of the vessels used for evaluating the fuels and lubricants and MAN Diesel & Turbo designers of the ME-GI methanol dual-fuel two stroke engines for the tankers Mari Jone and Mari Boyle.
With 2020 and more future restriction on emissions in mind, industry innovators are looking beyond oil-based bunkers to a range of new, alternative bunker fuels that includes methanol, LNG, LPG and ethane. Many of the vessels using these alternative fuels are dual-fuelled, meaning the engines can run either on a higher sulphur conventional fuel or on a virtually zero sulphur content alternative fuel, resulting in more extreme operating conditions within the engine.
Chevron believes that this highlights how a “one size fits all” approach to both fuels and lubricants is clearly no longer sufficient, and without proper guidance choosing the right cylinder oil with the correct BN and feed rate can be particularly challenging.
Understanding this has been key to the development of Chevron’s Taro Special cylinder lubricants which range from 25BN to 140BN and cover virtually all fuel options and combinations. Chevron Marine Lubricants is lubricating four of them as well as the world’s only four-stroke methanol dual-fuel vessel, Stena Germanica.
Following their delivery in 2016, Mari Jone and Mari Boyle became two of the world’s first ocean-going methanol dual-fuel ships. The ME-LGI methanol dual-fuel engines aboard the vessels, developed by MAN Diesel & Turbo, allow for operation on methanol, HFO, MDO or MGO. The vessels already have a combined 7,000 hours of operation using methanol bunkers.
Methanol’s attractions as a marine fuel
Using methanol as a marine fuel is a relatively new idea. Its attractiveness as a fuel is due to it being free from sulphur and burning it in a diesel engine only requires the use of a very small amount of pilot fuel — typically around 5% of either HFO or a distillate such as MGO or MDO. The result is that compared to burning traditional bunkers using methanol as a marine fuel reduces the emissions of SOx by 99%, bringing them well within current and future global and ECA standards. At the same time, nitrogen oxides are reduced by up to 60% and particulate matter is reduced by 95%.
Energy density is one area where methanol is outperformed by oil-based fuels with a little more than twice the amount needed to produce the energy equivalent of MGO. While this can lead to considerations over the size of fuel tanks, methanol is a biodegradable liquid and in some vessels it could be stored in the ballast tanks to alleviate some of the issues around space. It also means that if spilled in water, it quickly and completely dilutes to non-toxic levels. On a calorific equivalent basis, methanol bunkers are currently priced at similar levels to MGO.
The MAN ME-GI engines are configured with two injectors each for fuel oil and methanol. It is the injectors that are the limiting factor when it comes to the variety of fuels that can be used by multi-fuelled vessels, rather than the number of different fuels a vessel is able to practically carry.
LNG, for example, is a common rail injection so the pressure build-up is in the supply system. Methanol has a booster injection valve, so the pressure build-up is on the engine. The fact that these injection systems are different for each fuel limits as to what is going on in the engine, and at the moment that limit is two.
Under regular operation for Mari Jone and Mari Boyle, the Methanol is transferred by means of the Framo deep well pump system from a dedicated slop tank which also acts as Methanol Fuel storage tank to the 79m3 methanol day service tank. From there, methanol is transferred via double wall piping to the engine at 10 bar low pressure using a separate fuel supply system. The methanol is used at ambient temperature, and a heat exchanger is available if required.
Loading bunkers in a wide range of ports means that the sulphur content of the HFO they burn alone varies from 1.8% to 3.5%. But by their very nature the dual-fuel methanol engines are subject to an even wider range of sulphur conditions: they could be burning 95% methanol, which has zero sulphur, along with either a low sulphur or high sulphur pilot fuel; they could be burning a 0.10% sulphur distillate fuel for ECA compliance; they could be burning up to a 3.5% maximum sulphur heavy fuel oil; or they could be burning a mix of 70% methanol along with either a high or low sulphur oil product.
Meeting a challenge
According to Fredrik Stubner, Director Ship Management at Marinvest Shipping, this makes it very tricky to know to which level to limit the cylinder oil to the liners, and what the BN of the cylinder lubricant has to be. In fact, one of the biggest concerns when Marinvest ordered the engines early on was the effect that dual-fuel operation has on the liners, and it is something no-one could really answer.
To meet this challenge, Marinvest turned to Chevron Marine Lubricants for not only their range of cylinder lubricants, but also their DOT.FAST service to help with optimising the lubrication of the engines. Chevron has worked closely with Marinvest on creating a lubrication package and attributes the success of the project to the DOT.FAST program, which early on indicated areas for improvement in feed rate settings and engine hardware.
When looking at optimising the feed rates and lubrication of two-stroke engines, the two main parameters are BN and Fe. For onboard analysis, the DOT.FAST Drip Oil Analyzer is unique and innovative, delivering laboratory accurate test results right on the vessel. DOT.FAST onboard analysis delivers immediate feedback on cylinder running conditions, and provides an early indication of elevated levels of both abrasive and corrosive engine wear. At the same time, it helps optimise the cylinder oil feed rate and minimise the build-up of abrasive deposits, cylinder oil consumption, engine fouling, and the risk of scuffing.”
With the onshore analysis component of the DOT.FAST service, samples sent to Chevron’s laboratory are fully analysed for base number, iron, and all other elements. The results are tabulated and reviewed by technical experts, and recommendations are reported back to the ship. Using onshore analysis ensures the testing of drip oil samples to the highest industry standards in a quality certified laboratory and provides comprehensive reporting with to-the-point commentary. Additional benefits include monitoring the effectiveness of onboard (heavy) fuel purification procedure through measurement of Cat Fines.
Lubricants made to measure
As an extra precaution against cylinder wear, and to safeguard against human error with cylinder oil selection, the vessels are also set to employ MAN’s Automated Cylinder Oil Mixing (ACOM) system to ensure the right cylinder oil dosage is used at all times. For new engines being delivered this system is now standard.
“Having the ACOM system will help us a lot as normally when we are talking about zero sulphur fuel you want a low BN cylinder oil, like 25 BN Taro Special HT LF, but in our case we can use methanol along with high sulphur fuel oil where a 140 BN oil might be better. We perform a fuel analysis on all bunkers prior to their use and then input this data into the ACOM system, this then blends the cylinder oils to create the perfect BN mix,” explains Stubner.
“DOT.FAST allows us to see on a daily basis the iron content and the TBN number of the breakdown oil. It tells us immediately whether to adjust the cylinder oil feed rate up or down accordingly. There is no need to wait for shore analysis that would mean you miss the opportunity to act promptly to avoid excessive wear on the piston rings,” said Stubner.
Being among the first to operate with a new fuel will always bring with it unique challenges. “The engines were designed and produced in just ten months. There was testing with one cylinder in Copenhagen at first for a few hours, and it worked, so it was then tested in Japan as well as Korea. Once the engine was built it was tested for a number of hours, but our crew onboard our ships were really the first to do it on a long-term basis.
It’s then you learn things — what has to be improved, what has to be changed, and so on. We feed that back to MAN in Copenhagen, that feeds back to us and we try it out,” says Stubner. “Of course, there is the potential for extra costs and complexities with such a project, such as requiring a dedicated crew, dealing with a prototype engine, and working with a new type of fuel. But was this difficult? I would say no.