During an oil spill, oil behaves differently in water depending on whether it is heavy or light: the pollution which has affected Russia and Crimea in the Black Sea since mid-December involves “heavy fuel oil” type fuel. , difficult to clean.
Heavy fuel oil involved
The Kerch Strait, between Russia and the Ukrainian Crimean peninsula which it annexed in 2014, has been polluted since mid-December by the sinking of two Russian oil tankers during a storm, and this oil spill continues to grow. ‘extend.
The two tankers contained 9,200 tonnes of fuel oil and at least a quarter (26%) of the cargo escaped at sea, according to the latest estimate by Russian authorities.
This is “the first accident in the world involving “heavy” fuel oil of M100 quality,” declared the Russian sea rescue service Morspassloujba.
This type of fuel oil “does not float on the surface” and “there is no proven technology in the world to eliminate it in water”, according to the same source and “this is why the main method is collection on the coast.”
““Heavy fuel oil” (M100, Editor’s note) is a trade name for a particular type of “heavy fuel oil” (Heavy fuel oil, HFO in English, Editor’s note) produced in Russia and Kazakhstan,” explains Rob James to AFP , Senior Vice President Europe/Asia at Lamor, an oil and chemical pollution control company.
Heavy fuel oils are low-cost residual fuels from the distillation of crude oil in refineries, “generally used as fuel for large ships and industrial boilers,” he says.
Heavy or light oil, what’s the difference?
There are two types of oil: heavy fuel oils with almost tarry consistencies, and so-called “light” oils including diesel, gasoline or kerosene.
The first, very polluting, are characterized by high viscosity and density. They can be as heavy or heavier than water, sink or be suspended, and persist longer in the aquatic environment.
The latter, with low viscosity and density, degrade quickly.
Due to its characteristics, “heavy fuel oil (HFO) does not evaporate and dispersants have little effect on it”. It is described “as ‘persistent’ because the climatic and biological processes that can naturally reduce the impact of a crude oil spill have little impact on heavy fuel oil,” emphasizes Mr. James.
“Any heavy fuel oil is generally more difficult to clean up than a spill of crude oil or other refined petroleum products,” he adds. Cleaning requires “a mechanical or manual process which takes time and labor resources”, like the sinking of the Erika in December 1999 in Brittany which released 20,000 tonnes of fuel oil. heavy.
How does an oil spill evolve?
The type of oil as well as weather and sea conditions are determining factors for its fate in water.
Once spilled, petroleum products can undergo eight main chemical and physical modification processes including: surface propagation, evaporation, accentuated by strong winds and high temperatures, dispersion into droplets under the effect of waves, emulsification, which increases the volume of the oil as it absorbs water, sedimentation which sees the oil interact with sediment and sink.
“Spreading, evaporation, dispersion and emulsification are important in the early stages of the spill, while photo-oxidation, sedimentation and biodegradation are long-term processes that determine the final fate of the oil” , indicates a technical note from the International Federation of Oil Shipowners Against Pollution (ITOPF).
“The speed at which these processes occur depends on weather conditions and oil characteristics,” including density, volatility and viscosity, according to this memo.
According to ITOPF, “a small number of residual oils are dense enough to sink in the event of a spill. However, most oils float and only sink when mixed with denser sediments.”
