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In the bulk shipping sector, the search for sustainable solutions faces technical and economic challenges. Currently, the burning of heavy fuel oil combined with the use of scrubbers is seen as the most viable alternative
New scientific research challenges long-held ideas about pollution caused by bulk carriers. The study, published in the journal Environmental Science and Technology, shows that burning heavy fuel oil with scrubbers can be as or more environmentally friendly than using low-sulfur marine fuels.
The data comes from a detailed analysis by scientists at the MIT, from Georgia Tech and other institutions, in partnership with the company Oldendorff Carriers.
The conclusion surprises some in the maritime industry and environmental policy makers.
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Since 2020, the burning of fuels with high sulfur content has been limited internationally.
It was then expected that the options less polluting would be more expensive and refined fuels. But the numbers showed something else.
The choice after the 2020 rule
In 2020 the International Maritime Organization (IMO) imposed a limit on the sulfur content of marine fuels.
The goal was to reduce harm to human health and the environment. The new ceiling was 0,5% for most seas and 0,1% for regions close to large cities or sensitive ecosystems.
As a result, companies in the maritime sector were faced with three main options: adopt low-sulfur fuels, such as marine gas oil; install scrubbers to continue using heavy fuel oil; or try alternatives such as biofuels — which are not widely available.
The most practical solution turned out to be the installation of scrubbers. Before the rule change, less than a thousand ships used this system.
Today, there are more than 5.800 vessels with scrubbers in operation. Most have open-circuit technology, which uses seawater to clean exhaust gases.
How the debugger works
The scrubber is a giant metal cylinder, installed in the ship's chimney.
Seawater is drawn in, sprayed and thrown over the hot gases coming out of the engine. This triggers a chemical reaction: the sulfur dioxide turns into sulfate, a soluble substance that already exists naturally in the ocean.
The clean gas is released into the atmosphere, and the wash water, now acidic, is returned to the sea. This has raised doubts. Could this water, mixed with combustion byproducts, be just as polluting as sulfur?
The study and the data
The researchers decided to investigate further. They conducted a complete life cycle analysis of the fuels and scrubbers.
This included everything from the production and transportation of fuel to the installation and use of equipment on board.
There were also real measurements, taken inside a bulk carrier operating in China.
Scientists compared the combustion of heavy fuel oil with scrubbers and low-sulfur fuels. The sea and engine operating conditions were the same.
Air and wash water samples were collected. Gas emissions and the concentration of more than 60 chemical substances in the water used for the process were also measured.
Surprising results
The findings were clear. The scrubbers reduced by up to 97% sulfur dioxide emissions.
In practice, this would put heavy fuel oil on a par with low-sulfur fuels in this specific respect.
Other pollutants, such as carbon monoxide and nitrogen oxides, were also analyzed, with similar results.
Wash water samples showed very low levels of chemical compounds.
All were below the limits established by International Maritime Organization. And even by stricter standards, such as those of the European Union and the US Environmental Protection Agency, levels were generally well below.
Furthermore, as this water is released slowly into the open sea, and the ship is always moving, natural dilution further reduces any risk.
Comparing the entire impact chain
One of the strengths of the study was to consider the complete impact, from the origin of the fuels to their use at sea.
Producing low-sulfur fuels requires more steps in refineries, which generates more pollution in the form of gases and particles.
Heavy fuel oil, because it is less processed, has less impact even before it reaches the ship. And when you add the use of scrubbers, with a useful life of around 20 years, the scenario changes in a surprising way.
The construction and installation of the scrubbers has a small environmental impact when diluted over two decades.
Thus, overall, the option of burning heavy oil with scrubbers proved to be the least harmful in almost all 10 impact factors analyzed.
These include greenhouse gas emissions, soil acidification, ozone formation and use of natural resources.
A study done on the high seas
Scientist Patricia Stathatou, the lead author of the study, boarded a ship to collect the data. She spent a week at sea, dealing with the noise of the engines, the heat and the safety equipment.
This was, she says, the most difficult part of the entire research. But the data obtained on board was crucial.
They helped validate theoretical models and confirm that, in practice, debuggers work as expected—and perhaps even better than imagined.
"This study shows that we need to look at the whole cycle. We can't make decisions based solely on what comes out of the chimney.“, said Patricia.
The future of research
For the authors, the results reinforce the importance of basing environmental policies on comprehensive scientific studies.
Decisions about fuels and technologies must consider real data and all stages of the process.
Scott Bergeron, director of Oldendorff Carriers and co-author of the study, highlighted that the work helps to clarify many doubts and myths about scrubbers. “Now we have real data. That's what we need to make the right choices.“He said.
Thomas Klenum, from the Liberian Registry, believes that this type of study should guide the International Maritime Organization's decisions in the coming years.
New paths and questions
Despite the progress, there are still challenges. The transition to alternative fuels — such as ammonia or hydrogen — is under debate, but there are still no definitive answers about its real environmental impact.
"We need to compare new options with existing solutions. Sometimes what looks new and clean can hide bigger impacts elsewhere in the process.“, warned Patricia.
The research offers a fresh perspective on an old question. Instead of relying solely on what looks cleanest, the scientists suggest looking at the whole picture.
This includes what happens before, during and after each fuel is burned.
The study showed that, when considering the entire life cycle of the fuel and technology, the combination of heavy fuel oil with scrubbers not only meets international limits, but also stands out as the option with the lowest environmental impact in several categories.
This data could change the course of political and technological decisions in the global maritime sector in the coming years.
