LOW SULPHUR FUEL OILS (LSFOs): What Every Environmentalist, Team Responder Should Know.
It is estimated that the daily sulphur and nitrous oxide emission of the world’s 200 biggest ships is more than the entire global car fleet combined. These findings reinforced the high usage of sulphur fuel in vessels compared to other modes of transportation. Worried by this, the International Maritime Organisation (IMO) has implemented standards to reduce sulphur pollution from ships. These standards require a reduction in sulphur contents in fuel oils from a maximum of 3.50 to 0.50% (m/m) in other parts of the world, and to as low as 0.1% (m/m) within the Emission Control Areas (ECAs). The ECAs comprise the Baltic Sea area, the North Sea area, the North American area and the United States Caribbean Sea area. The ultimate goal of this new regulation is to limit the amount of pollutants released into the atmosphere, protect the environment and people living close to ports and the coast.
The change in IMO regulations has resulted in a switch to a new generation of Low Sulphur Fuel Oils (LSFOs). The LSFOs that have been developed specifically to meet up with the new requirements. However, the introduction of these new blends of fuels has some properties that need to be understood. These include how it weathers in order to determine the appropriate response options and strategy as well as the toxicity effects on various marine life. While this new innovation present significant benefits, little is known about its behaviour in the aquatic environment. For example, the July 2020 Mauritius oil spill was the first reported spill involving LSFO, hence, this new generation of fuel oils need to be understood. This is because the more a product is known, the more effective environmentalist and response staff will be in protecting sensitive environmental receptors and cleaning up the spills.
So, what do we know about LSFOs, what is the fate and behaviour, dispersibility, ignitability, the viscosity of spilt LSFO in the marine environment, what is the toxicity of the water-soluble fraction of LSFO in the marine environment?
This article hopes to answer some of these questions and more.
WHAT DO WE KNOW ABOUT LSFOs?
LSFOs are a range of new fuels that entered the market to meet the IMO 0.5% global and 0.1% ECA sulphur requirements. LSFO is used mainly as marine fuel oil. The quality of the fuel will depend on the refinery type, feedstock as well as the upgrading of the different conversion process in order to reduce the amount of sulphur and residual materials (hydro-desulfurization, catalytic cracking, vis-breaking).
According to Total, LSFO is a dark brown viscous complex mixture of paraffinic, cyclic and polycyclic aromatic hydrocarbons with a carbon number in the range of C15-C50 and boiling point of between 160 -7500C. LSFO is defined either by a density of 840–1100 kg/m3 at 150C or a kinematic viscosity of 30–700 mm2/s at 500C. It is insoluble in water but very toxic to aquatic life with long-lasting effects. This product is also incompatible with strong oxidizing agents, acids as well as halogens. It is also volatile, thus, changing properties in weeks rather than months.
A key differentiator of LSFOs is their SOx content. The following main classes with regards to sulphur content can be distinguished.
(a) Ultra-Low Sulphur Fuel Oil (ULSFO): Maximum 0.1% SOx to meet ECA requirements. It is composed of neat distillates that could be hybrids of gas oil blended with residual oil.
(b) Very Low Sulphur Fuel Oil (VLSO): Maximum 0.5% SOx that is made up of a blend of suitable residual products with low sulphur distillates.
LSFO: WHAT EVERY RESPONDER SHOULD KNOW
This section aims to provide responders better knowledge and preparedness for spills involving this new generation of fuel oils and touch on weathering, dispersibility, emulsifying properties, ignitability and toxicity.
1. Weathering: when oil is spilt into the marine environment, it undergoes physical and chemical changes. These processes are termed weathering and determine the fate and behaviour of the oil as well as the effectiveness of the response operations. The weathering process is dependent on type and quantity of oil spilt as well as environmental and hydrodynamic conditions.
Available data shows that LSFOs have a very low evaporative loss in the range of <2–8%. The low evaporative rate may be attributed to the low amount of volatiles in the oils. This means that a higher proportion of LSFO will persist in the marine environment, hence, making response operations very difficult. Despite the low evaporative rate of LSFOs, it is important for responders to wear breathing apparatus. This is because mists and vapours from LSFOs have been found to be irritating to the mucus membrane and the eyes.
2. Dispersibility: The essence of dispersants is to enhance the natural dispersion of surface oil as small droplets into the water column and enhance biodegradation.
Analysis of available LSFOs in the market shows that fresh oils, emulsified and fresh weathered residues have limited dispersibility. The effectiveness of dispersants may be limited due to high viscosities and pour point of some of the LSFOs available in the market. However, at a higher temperature (13 degrees Celcius), presence of breaking waves (>5 m/s) wind and a high dispersant dosage, dispersants showed a high potential to break up surface oil slick into smaller patches. This means that the window of opportunity must be utilized, and the above-stated factors must be taken into consideration before the application of dispersants. It is important to state that among the available dispersants used to test for dispersibility of LSFOs, the popularly known Corexit 9500A showed a higher potential to break up an oil slick into patches compared to others.
3. Emulsifying Properties: Emulsification is the entrainment of water in oil thereby increasing the volume of spilt oil to about five times its original volume, thus, slowing down evaporation and other weathering processes. Oils with asphaltene content of 0.5% tend to form a stable emulsion and persist in the marine environment. The wax and resin contents also play a critical role in emulsion formation. It is well known that the emulsification of spilt oil into stable water-in-oil emulsions (chocolate mousse) has numerous detrimental effects upon clean-up operations. Available LSFOs in the market have exhibited emulsifying properties, that is to say, they can incorporate water (up to 30–60 vol%) upon weathering at sea. The LSFOs expressed lower emulsification at lower temperatures compared to higher temperatures. Despite this, the rate of emulsification was slow at both temperatures. Furthermore, fresh LSFOs have higher emulsification rate than weathered residues at both temperatures. At both temperatures, the emulsion formed was stable and the addition of emulsion breakers had no effect. It is, therefore, safe to say that the low rate of evaporation of LSFOs may be attributed to the emulsifying properties of the oils. Furthermore, some of the oils have high asphaltene and resin contents, thus, promoting the formation of stable emulsions.
The response team have to take all of these into consideration when carrying out mechanical recovery by selecting the right equipment and making adequate provision for the high volume of waste to be evacuated. Every minute and second count for specific countermeasures to be used.
4. Ignitability: ignitability refers to the time needed to ignite the oils by using a progressive ignition strategy. Non emulsified LSFOs were ignitable, however, this takes a long time for the oil to ignite (varies between 3–18 minutes) depending on the brand of fuel oil. The burning effectiveness for non-emulsified fuel oils is between 35–45% while for emulsified fuel oil is 15–25%.
The long time it takes to ignite the fuel may be attributed to the low amount of volatiles (light compounds) and how easily the oil gets emulsified. On the other hand, emulsified fuel oils were not ignitable except a significant amount of diesel (1mm and 3mm) is added to the top of the emulsion. The findings from ignitability tests indicate that even low content of water incorporation (w/o-emulsification) at sea for these new generations of marine residual fuel oils are exceedingly difficult to ignite by use of present operative ignition methodology (i.e., gelled gasoline/diesel) without application of a significant amount of primer (e.g. diesel) on the emulsified oil.
This means that, if in-situ burning is being considered as a response strategy, it has to be swift in order to utilize the window of opportunity before the fuel oil is emulsified.
CONCLUSION
With the new IMO regulation in force, different kinds of fuel oils are in the market. However, these oils have exhibited different physio-chemical and weathering properties.
Basically, these oils have low evaporative, dispersion and ignitibility rate, they also possess high viscosities and pour points. Hence, can persist in the marine environment, thus, making response operations difficult. It is therefore important for an oil spill responder to know the type of fuel oil spilt and the weathering properties for a swift, effective and adequate cleanup.
REFERENCES
IMO, I. (2020) Sulphur 2020 — Cutting Sulphur Oxide Emissions [online] Available from <https://www.imo.org/en/MediaCentre/HotTopics/Pages/Sulphur-2020.aspx> [31 December 2020]
Sørheim, K., Daling, P., Cooper, D., Bust, I., Faksness, L., Altin, D., Petterson, T. and Bakken, O. (2020) Characterization Of Low Sulfur Fuel Oils (LSFO) — A New Generation Of Marine Fuel Oils. Trondheim: SINTEF
LOW SULFUR FUEL OIL (UN 3082) (2020) available from <https://www.marinefuels.total.com/sites/g/files/wompnd516/f/atoms/files/low_sulfur_fuel_oil_un_3082_mtr_eu_en.pdf> [31 December 2020]
Bobra, M. (1991) “Water-In-Oil Emulsification: A Physicochemical Study”. International Oil Spill Conference Proceedings [online] 1991 (1), 483–488. available from <https://www.bsee.gov/sites/bsee.gov/files/osrr-oil-spill-response-research//120az.pdf>
Hellstrøm, K.C (2017): Weathering Properties and Toxicity of Marine Fuel oils. Summary report. SINTEF report OC2017-A124.
