VLSFO: Fact Versus Fiction

Unni Einemo is director of IBIA as well as its IMO representative. Image Credit: IBIA

Before the IMO's 0.50% sulphur limit for marine fuels took effect on 1 January, 2020, there was a lot of speculation about the nature of the IMO 2020-compliant very low sulphur fuel oil (VLSFO) blends, and how they would compare to the high sulphur fuel oil (HSFO) blends that were the predominant fuel for the world fleet prior to 2020.

Fear of the unknown is natural and some apprehension was justified, but there was a lot of exaggeration and scaremongering. Already, prior to 2020, IBIA and others had dispelled myths and cleared up misunderstandings about VLSFO many times, and worked hard to help stakeholders prepare for the change and steer clear of anticipated problems. But the same negative misconceptions keep cropping up again and again as inaccurate or incomplete information is recirculated.

Let's look at some of the claims about VLSFO and try to separate fact from fiction.

"There is no specification for VLSFO" is a misconception

A prevailing misunderstanding prior to 2020, and still today, is that there is no specification for the new IMO 2020 compliant blends, or VLSFO. The fact was, and still is, that VLSFOs – just like HSFOs – are blends, and must be blended to meet ISO 8217 specifications in order to be commercially viable.

Fuels with maximum 0.50% sulphur can be classified in accordance with ISO 8217 Table 1 for distillate marine (DM) fuels or Table 2 for residual marine (RM) fuels, which define the maximum, and some minimum, parameters limit for a number of fuel grades (specifications).

ISO 8217:2017 specifies limits for seven categories of distillate fuels (four DM and three with up to 7% FAME called DF) and six categories of residual fuel (RM grades). There are differences between them with regards to the specified minimum and maximum limits. The most common distillate is DMA marine gas oil (MGO), followed by DMB marine diesel oil (MDO).

The six categories in ISO 8217:2017 - Table 2 Residual marine fuels range from very high density/high viscosity RMK, to fuel grades that are close to distillates such as RMA. The most commonly sold fuel grade prior to 2020 was HSFOs with maximum 3.50% sulphur classified as RMG 380 (max. 380 cSt at 50°C RM fuels), followed by RMG 180 (max. 180 cSt at 50°C RM fuels) and RMK 500 (max 500 cSt at 50°C) RM fuels.

Price reporting services, prior to 2020, typically reported bunker prices as IFO 380, IFO 180, MDO and MGO, differentiating between regular (high sulphur) and low sulphur products meeting regulatory limits such as 0.10% for emission control area (ECA) fuels.

Unfortunately, with the advent of the 0.50% sulphur limit, fuels are now lumped together as just one category, either VLSFO or 0.50%S fuels, in price reporting. Also, a lot of bunker delivery notes (BDNs) say just "VLSFO" instead of specifying the ISO 8217 grade it conforms to. It is easy to see how this has contributed to the idea that there is no specification for VLSFO, which – after all – is simply a description of either a distillate (VLSFO-DM) or residual (VLSFO-RM) fuel grade that conforms to a maximum 0.50% sulphur limit.

VLSFOs typically have lower density and viscosity than HSFOs because to reduce the sulphur content, more light and less viscous blend stocks are required. There are, however, wide variations depending on which blend components have been used (more on that later).

Bunker fuel purchase contracts still require fuels to meet ISO 8217 specifications, mostly RMG 380, so VLSFOs will have to meet RMG 380 specifications in order to be placed on the market, or other specifications (e.g. RMG 180) as required by purchasers.

It would help if all BDNs specified a grade, e.g. RMG 380/RMG 180/RMD 80, to better describe the fuels provided. Meanwhile, unless the BDN specifies that the product is a high density/high viscosity grade such as RMK 700 or RMG 500, the default assumption is that VLSFOs meet RMG 380 specifications. This sets maximum limits for density, viscosity, catalyst fines (Al+Si), sediments, pour point, acid number etc. but the fuel may have density and viscosity well below the upper limits, which has a significant impact on how the fuel should be handled once onboard the ship.

In September 2019, "ISO/PAS 23263:2019 Petroleum products — Fuels (class F) — Considerations for fuel suppliers and users regarding marine fuel quality in view of the implementation of maximum 0,50 % sulphur in 2020" was published. It confirms that ISO 8217 specifications apply to fuels meeting the 0.50% sulphur limit, and provides technical advice on fuel characteristics that might apply to particular fuels for kinematic viscosity, cold flow properties, stability, ignition characteristic and catalyst fines. In addition, it provides information on how to consider compatibility between fuels, including test methods for checking whether fuels are compatible.

Addressing VLSFO safety concerns

Prior to 2020, the prevailing fears were that compliant fuels would not be safe to use due to instability, incompatibility, non-compliance with the SOLAS and ISO 8217 flashpoint limit of minimum 60°C, excessive cat fines, poor ignition and cold flow properties, high acid number as well as contaminants which are not specified in the ISO 8217 standard.

The fact is that IMO 2020 compliant fuels still have to be blended to meet ISO 8217 specifications, which address all of those issues apart from compatibility, which is a fuel management issue. Unspecified contaminants are covered under Clause 5, "General requirements". The latest edition, ISO 8217:2017, says fuels shall be made from hydrocarbons and not contain any additive, added substance or chemical waste at a concentration that jeopardizes the safety of the ship or adversely affects the performance of the machinery, is harmful to personnel or contributes overall to additional air pollution.

There was no shortage of guidance to help stakeholders prepare for safe management of VLSFO. IBIA was a major contributor to the IMO's work in this area, as we are one of the NGOs with consultative status that bring relevant expertise through submissions and discussions in working groups and meetings. IBIA also took part in producing the "Joint Industry Guidance on the supply and use of 0.50% – sulphur marine fuel" to give stakeholders tools to prepare for safe supply and use of IMO 2020 compliant fuels. This publication was developed by experts from across shipping, refining, supply and testing of marine fuels and made available to all in August 2019.

Thanks to the industry's preparations and efforts to raise awareness, the transition from HSFO to mainly VLSFO, but also some MGO, went more smoothly than most had anticipated. Managing VLSFO puts demands on ships' crew due to wide variations in key handling characteristics like viscosity and cold flow behaviour in VLSFOs provided to the market. They also need to pay close attention to avoiding co-mingling of different batches of fuel onboard due to the risk of incompatibility. These challenges are not new. The industry has known about them for decades as they also apply to the well-known HSFOs, but the VLSFOs are more variable. 

There have been some incidents of VLSFOs causing operational problems, but nothing like the operational nightmares that had been predicted prior to 2020. VLSFOs exceeding the ISO 8217 limit of max. 0,10% for sediment, an indicator of fuel stability, has been higher than what was seen for HSFOs pre-2020, but numbers are still low at no more than 1.5% of all samples tested during the first half (H1) of 2020, according to data collected by the International Organization for Standardization (ISO).

VLSFOs often have higher pour point temperatures, but as long as the temperature is known, it can be managed, ensuring the fuels are sufficiently heated to stay liquid and maintain optimum flow characteristics.

The 'Frankenstein fuel' allegory

In order to meet the lower sulphur limit, the blend recipes for VLSFO are different from HSFO. There has been an element of secrecy about VLSFO production methods and blend formulas among companies that were working on achieving well-performing fuels in preparation for IMO 2020, and some sought to patent their methods.

Maybe it was the secrecy, combined with ignorance about how fuels are produced and/or limited initial knowledge of which blend components would be used, that led some quarters to refer to VLSFO as "Frankenstein fuels". Presumably, this moniker was meant to refer to creating "monster" fuels due to an experiment gone wrong.

In the novel by Mary Shelley, a young scientist, Victor Frankenstein, undertakes a mysterious laboratory experiment to create a sentient being out of human body parts and chemicals. Frankenstein's creation started out as a kind and gentle giant, but his looks scared anyone who saw him, and the way humans treated him turned him into a monster.

Let's be clear: all oil-based marine fuels are blends of various refinery streams, and the blending process has two main targets: to meet ISO 8217 specifications (including the minimum 60°C flashpoint limit and General Requirements), and a specific sulphur limit in accordance with MARPOL Annex VI or local regulatory requirements. HSFOs and VLSFOs are created in the same way, but the components vary.

Some VLSFO blends have been problematic, but the same applies to HSFO. Judging all VLSFOs, or HSFOs for that matter, on the basis of a few bad examples is as meaningless as judging all cyclists or drivers on the basis of a minority that behaves badly.

Referring to VLSFOs as "Frankenstein fuels" is scaremongering, as it implies that all VLSFOs are experiments gone wrong.  After more than a year when the majority of the global fleet has been using VLSFOs without incident, it is time to put the Frankenstein allegory to rest.

Quality concerns aside, another reason VLSFO was referred to as a "super-pollutant Frankenstein fuel" was the theory that the shift from HSFO to VLSFO would lead to a massive increase in black carbon emissions. Let's look at where that came from.

VLSFO and black carbon emissions

In January 2020, VLSFO came under attack amid claims these blends would cause an increase in emissions of black carbon (BC) due to being more aromatic than the HSFO they were replacing. IBIA and others in the industry were baffled, as the expectation was that VLSFOs would generally be less aromatic and more paraffinic in nature than HSFOs.

These claims originated from conclusions drawn from a measurement study submitted to the IMO in mid-November 2019, investigating the potential link between fuel specimens with high aromatic content and the formation of black carbon. The study, submitted by Germany and Finland to the seventh session of IMO's Sub-Committee on Pollution Prevention and Response (document PPR 7/8), said the tested 0.50% sulphur fuels were ordered as "possible sample mixtures from refinery-streams most likely to be used in 2020" and that "high aromatic content in future low sulphur marine fuels after 2020 is expected."

The three ordered VLSFO specimens used in the measurement study had aromatic content ranging from 70% to 95%. By contrast, the study used HSFO with 50% and MGO with 20% aromatic content.

The subject was thoroughly discussed at PPR 7 in February 2020, where it was made clear that the VLSFO specimens used in the measurement study were not representative of the VLSFOs actually in the market. Suggesting, therefore, that VLSFOs would cause an increase in black carbon emissions was based on flawed assumptions about the nature of the fuels that were expected to come on the market.

Data available in February 2020 suggested that VLSFOs in the market until then on average were more paraffinic in nature than the HSFOs they have replaced.

Papers submitted to PPR 8, scheduled to take place virtually from 22 to 26 March this year (2021), provide further comment and evidence as to why linking VLSFO to an increase in BC emissions is flawed, as the majority of VLSFOs that have actually been supplied to ships appear to be less aromatic than HSFOs, as documented by fuel testing data. It should also not be overlooked that the operational pattern of the engines, as well as maintenance and general condition are equally important factors - if not more so - in the tendency to emit BC.

VLSFO vs HSFO test data

ISO/ TC28/SC4/WG6, the committee in charge of ISO 8217, has analysed fuel testing data from fuels actually delivered to ships, gathered from most of the major testing agencies for the first half (H1) of 2020, and compared these with HSFO data for 2018.

"This collected data shows that 2020 RM VLSFOs have lower viscosity, lower density, lower MCR and lower CCAI, higher net specific energy and along with the percentage of VLSFOs having higher pour points point to VLSFOs in general tending to be more paraffinic in nature. As a result, VLSFOs, in general, are proving to have enhanced ignition and combustion properties over that of HSFOs and would be expected to reduce the tendency to form BC emissions in comparison to HSFO," says a paper submitted by ISO/ TC28/SC4/WG6 to PPR 8.

Apart from demonstrating that VLSFOs, at least those supplied during H1 2020, are likely to emit less black carbon than HSFOs, the data also suggest that VLSFOs generally are better fuels than HSFOs in terms of energy content and how well they burn.

ISO/ TC28/SC4/WG6 has submitted a more detailed review of marine fuel quality of bunkers supplied in H1 2020 to the 76th session of the IMO's Marine Environment Protection Committee, looking at both DM marine fuels and RM VLSFO, drawing comparisons with HSFO data for 2018.

The most notable change is the broader spread of viscosity of VLSFOs to that of HSFO, requiring increased attention to fuel management practices. 95% of RM HSFO samples in 2018 had a viscosity at 50°C above 180 cSt, compared with just 13-14% of RM VLSFO samples in the first half of 2020. The majority (80%) of RM VLSFO samples had a viscosity at 50°C between 80 and 180 cSt and 6.5% were below 20 cSt – with the average at 105 cSt compared to 355 cSt for HSFO in 2018.

There is good news regarding cat fines, as only 0.2% of H1 2020 VLSFO samples had Al+Si exceeding 60 mg/kg compared to 1.5% of 2018 HSFO samples. 60 mg/kg is the upper limit for RMG, the most common fuel grade, in ISO 8217:2017. Moreover, the lower density and viscosity of most VLSFOs mean that cat fines are easier to remove during normal onboard fuel treatment prior to engine injection.

Flashpoint off-specs always get a lot of attention, as a flashpoint below 60°C is not only outside the ISO 8217 specification, it is also a breach of SOLAS regulations. Looking at the H1 2020 data, ISO noted there had been a small increase in DM samples with a flashpoint below 60°C compared to the 2018 DM samples, but still below 1% of all samples. It found that 99.9% of RM VLSFO samples had a flash point at or above 60°C and 0.08% had a flash point between 55°C and 60°C. In both 2018 and 2020, more than 99.5% of HSFO samples had a flash point at or above 60°C. Overall, then, it seems VLSFOs have been no more prone to off-spec flashpoint than HSFOs, while the share of DM samples below the limit showed a small increase.

The most noticeable quality issue from a fuel safety perspective is an increase in the percentage of samples exceeding the Total Sediment (TSA) specification limit of max. 0.10%, indicating a fuel that is either prone to asphaltene precipitation (unstable) or contains extraneous dirt – both of which result in sediments that affect separators and filters. The ISO review found that 0.7% of the H1 2020 RM VLSFO samples showed TSA ranging from 0.10 up to 0.15%, and 0.8% had TSA exceeding 0.15% in comparison to 0.09% and 0.14%, respectively, for the RM 2018 HSFO samples. That means 1.5% of H1 2020 VLSFOs samples tested above the specification limit for TSA, compared to 0.23% of HSFO samples in 2018.

Sludging caused by unstable fuels is one of the most serious operational concerns. Further complicating the picture is the fact that problems have been reported on some ships not only for VLSFO exceeding the TSA/TSP specification limit, but also for VLSFO having TSA/TSP well below the maximum specification limit.

The root cause for a ship experiencing sludging can be hard to determine. It can be an inherent stability problem in the fuel which was not discovered during routine testing; some fuels have limited reserve stability causing them to deteriorate faster. It can be due to comingling, as two fuels that are stable in themselves may be incompatible, meaning the mix becomes unstable (e.g. if a new fuel is loaded on top of a previous fuel in the bunker tanks or when fuels are mixed in the fuel system - including settling and service tanks - during change over). Another possible factor is too high temperature during storage and treatment of the fuel onboard the ship.

Further investigation is ongoing to better understand the sediment formation tendency of VLSFOs. We need ships, suppliers and fuel testing agencies to work together on this and share information to try to get to the root of these problems. By identifying the factors behind these problems, they can be avoided or mitigated.

Where does the bad reputation come from?

The study referred to above (PPR7/8) caused a reputation for VLSFO as a more polluting fuel than HSFO by linking it to high aromatic content and an increase in black carbon emissions. This has been hard to shake, despite all the evidence to the contrary. But where did the assumption come from that VLSFOs would have high aromatic content?

PPR 7/8 makes reference to a 2018 research paper which suggested that 0.50% sulphur fuels were expected to be highly aromatic. The objective of the research was to look into the combustion of fuels that have caused operating difficulties in marine engines and the paper postulated that 0.50% sulphur fuel blends could lead to more fuels with poor ignition and combustion characteristics, as the authors identified refinery streams that typically have high levels of aromatics as potential blend components for lower sulphur fuels.

Indeed, prior to 0.50% sulphur fuels coming into the market, there was speculation that blenders would increase the use of by-products from the fluid catalytic cracker (FCC) process in refineries, including slurry oil, or clarified slurry oil, heavy cycle oils and light cycle oils, all of which typically have high aromatic content.

FCCs use specialised aluminium and silicon particles as catalysts. Some of these particles, the cat fines or Al+Si, end up in the slurry oil and when used as a blend component, it therefore introduces them to bunker fuels. The previous 1.00% sulphur limit in emission control areas saw a marked increase in cat fines in RM fuels produced to meet this limit compared to HSFOs, largely attributed to increased use of slurry oil as a blend component to reduce the sulphur content of RM fuels. Some thought this would get even worse for RM fuels with the 0.50% limit, but it doesn't seem to have been the case. Indeed, the test data compiled by ISO/TC28/SC4/WG described above show that VLSFOs have, on average, less Al+Si than HSFOs.

Another blend component that appears to be used extensively in VLSFOs is vacuum gas oil (VGO). This is a heavy distillate most commonly processed in FCCs to produce gasoline. It makes excellent marine fuel with a high energy content, but because it is highly paraffinic, mixing it with mainly aromatic blend components could create unstable fuels. Aromatics have an important role to play in the stability of RM fuels because they help to keep asphaltenes in suspension; introducing too high a proportion of paraffinic components into the blend can upset this balance and cause asphaltenes to precipitate, causing heavy sludging.

This has caused fears of unstable fuels coming into the market, and increased the onus on ship's crew to ensure segregation of fuels as each new batch can be materially different and hence incompatible with other fuels onboard.

The prevalence of mainly paraffinic fuel with high pour point temperatures indicates that a lot of VGO or other distillates has entered the marine fuel pool, but thanks to good practices, sludging caused by mixing incompatible fuels has largely been avoided. For any ship operator concerned about being able to manage potentially incompatible fuels, they have the option of running on distillates, as they have no asphaltenes and hence no risk of incompatibility causing asphaltenic sludge. It will cost a bit more, but the choice is there.

Conclusions about VLSFO so far

VLSFOs have been the main answer to the need for ships to meet IMO 2020 requirements, accounting for a bigger share of total marine fuel use in 2020 than marine distillates, exhaust gas cleaning systems with HSFO and alternative low emission fuels like LNG or methanol combined.

It has led to a 70% cut in total sulphur oxide emissions from shipping, according to the IMO. This is good news for air quality and hence human health, the protection of which was the key objective behind the reduced sulphur limits under MARPOL Annex VI.

Apart from a small share of VLSFOs being prone to sludging, overall, the quality of VLSFOs has so far been better than HSFOs, with higher energy and better ignition and combustion properties.

Overall, around 3% of all VLSFO samples tested conclusively outside ISO 8217 specification limits in 2020 globally, which is no worse than during preceding years. Some fuel testing agencies report a higher percentage of off-specs, as they do not consider the inherent variability in test results and disregard the 95% confidence limit of the test methods.

The most prevalent off-specs seen in 2020 were for sulphur and sediment, but on average, RM VLSFO sulphur content during H1 2020 was 0.45% versus 2.61% for HSFOs tested in 2018, according to the review by ISO/ TC28/SC4/WG6.

VLSFO has some challenges, especially due to the huge variations in its composition and key characteristic, which requires operators to pay close attention to fuel management. Suppliers can help by providing more detailed relevant information to buyers about the fuels they supply, beyond just putting "VLSFO" on the BDN, and declaring the sulphur content and density as required under MARPOL Annex VI. VLSFOs could, for example, be described more accurately by applying ISO 8217 grade names to various products that reflect their composition more accurately, so we are not comparing RMB 30 (maximum 30 cSt at 50°C) with RMG 380 (maximum 380 cSt at 50°C), for example.

There will always be those who will seek to give VLSFOs a bad reputation for their own reasons, whether it relates to protecting the environment or promoting specific business interests. VLSFOs have provided an effective response to IMO 2020 and are the preferred option for most ship operators. We should not let ulterior motives or misconceptions cloud our judgement about VLSFO, but of course also not ignore -- and try to resolve -- any real issues that arise. Let's get the facts and put them into context to ensure a more balanced view.