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Marine Fuels:
What is Heavy Fuel Oil?

4 minute read

Efforts to reduce emissions from ships – including stricter regulations about marine fuels’ allowable level of sulphur – are curbing the use of heavy fuel oil (HFO) in the marine shipping industry.

Until recently, most ocean-going ships used HFO to power their engines. The fuel was so popular that, according to the International Maritime Organization’s (IMO) Third Greenhouse Gas Study, HFO made up 86% of international ship fuel used. Since the mid-19th century, HFO has been a logical choice for ships because it is very high in energy — so a little takes a ship a long way.

And it was inexpensive: HFO is cheaper than other fuels because it is the leftover or residual product from the oil refining process. Refining removes other fuels such as gasoline and diesel, called distillates, for use in cars, trucks, planes and smaller vessels, leaving the HFO behind.

Why is marine fuel called bunker fuel?

The term bunker fuel dates back to the age of steamships when the coal used to power the steam engines was stored in coal bunkers and shovelled on board. Today, “bunker” refers to liquid marine fuels and “bunkering” means refueling a ship.

HFO and sulphur content

Unlike other fuels, HFO is thick and has to be warmed up to flow freely for use in the ship’s engines. And unfortunately, the leftovers that form HFO have many impurities, including sulphur. The sulphur in the fuel helps to lubricate the engine, but once burned, it becomes air pollution – sulphur oxide or SOx – one of the contaminants resulting from incomplete combustion. Although not the only source, shipping is estimated to contribute 13% of the world’s total sulphur oxide emissions. These air pollutants from ships can cause serious health and ecological harm.

The IMO is working with the marine shipping industry to implement measures to reduce sulphur oxide pollution. The most far-reaching measure to date is the IMO 2020 regulation, which limits the sulphur content of marine fuel to 0.5% by mass since January 2020.

What about exhaust gas cleaning systems (scrubbers)?

To meet the 0.5% sulphur limit of IMO 2020, ships can burn heavy fuel oil with a reduced sulphur content or switch to a low-sulphur marine gas oil or liquefied natural gas. Alternatively, ships can continue to use HFO if they have installed an exhaust gas cleaning system to scrub (hence the term scrubbers) the excess sulphur from the exhaust before it is released into the atmosphere.

Although scrubbers are approved by the IMO as a means of compliance and are expected to meet international guidelines, scrubbers are a source of controversy due to the waste they produce and the potential impact this waste could have on the ocean. Clear Seas is studying the environmental impact of scrubbers and will release its report in 2020.

Black carbon and climate change

Another pollutant created through imcomplete combustion of HFO is a black soot called particulate matter. Some of the soot is called “black carbon”, particles that absorb sunlight while airborne and darken ice and snow when they fall to earth, contributing to global warming by decreasing the amount of solar energy reflected into space (the albedo effect) and increasing the rate of ice melt in polar regions.

Most black carbon comes from natural sources such as forest fires and volcanic activity and other human sources such as vehicle emissions and industrial output. Black carbon is estimated to have the greatest impact on global climate warming, after carbon dioxide emissions.

HFO ban in the Arctic

With the growing availability of other fuel options and with melting ice opening new Arctic shipping routes, pressure is building to ban HFO in this remote and fragile ecosystem. If spilled in the Arctic, HFO would be challenging to clean up due to the nature of the oil and a lack of spill response infrastructure and resources. HFO has been banned in the Antarctic since 2011.

Banning HFO in the Arctic would reduce environmental harm from the creation of black carbon when HFO is burned as well as eliminate the risk of spills. However, the environmental benefits must be weighed against the potential economic and social impacts to those who rely on ships to bring food and supplies into the Arctic.

A ban of the use and carriage for use of HFO as fuel in the Arctic to enter into force on July 1, 2024 has been proposed to the IMO. If approved, the process to enter into force would begin in late 2020. Following consultation with Northern communities and completion of an impact assessment, Canada supports this ban.

Will ships still use HFO in the future?

Since the mid-19th century, HFO has been the mainstay fuel of the shipping industry. Today, that position is changing following stricter regulations about marine fuel’s allowable levels of sulphur. Fuel manufacturers are finding ways to reduce the level of sulphur in HFO either by blending it with low-sulphur distillate fuels or by removing the sulphur during refining.

The manufacture and supply of marine fuels is a complex and volatile situation especially as a result of the COVID-19 pandemic and the associated economic slowdown. HFO is not expected to completely disappear – especially for those ships equipped with scrubbers. However, scrubbers may not be an attractive alternative if the price of very low-sulphur fuels continues to drop, reducing the price advantage that HFO used to hold.

Further, efforts by the IMO and the shipping industry to cut greenhouse gas emissions by the year 2050 to 50% of their 2008 levels will bring further pressure to use alternative lower-carbon fuels. The industry is exploring other energy sources such as fuel cells, batteries, solar and wind power either as a sole source of power or in combination with other systems.

As a research body focused on sustainable marine shipping, Clear Seas is conducting research in this evolving area including undertaking a comprehensive literature analysis of the climate change impacts of a range of marine fuels. Learn more here.

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