Researchers from MIT and Georgia Tech in a novel lifecycle assessment, found that burning heavy fuel oil with scrubbers in the open ocean can match or surpass using low-sulfur fuels.
Installing exhaust gas cleaning systems, or scrubbers, is considered the most feasible and cost-effective option for reducing emissions. However, there has been significant uncertainty among firms, policymakers, and scientists about how environmentally friendly these scrubbers truly are.
To address this, researchers combined data on the production and operation of scrubbers and fuels with emissions measurements taken onboard an oceangoing cargo ship.
They found that, when the entire supply chain is considered, burning heavy fuel oil with scrubbers was the least harmful option in terms of nearly all 10 environmental impact factors they studied, such as greenhouse gas emissions, terrestrial acidification, and ozone formation.
In our collaboration with Oldendorff Carriers to broadly explore reducing the environmental impact of shipping, this study of scrubbers turned out to be an unexpectedly deep and important transitional issue.
…commented Neil Gershenfeld, MIT professor, Director of the Center for Bits and Atoms (CBA), and senior author of the study.
Furthermore, in 2018, fewer than 1,000 vessels employed scrubbers. After the cap went into place, higher prices of low-sulfur fossil fuels and limited availability of alternative fuels led many firms to install scrubbers so they could keep burning heavy fuel oil.
Today, more than 5,800 vessels utilize scrubbers, the majority of which are wet, open-loop scrubbers. A wet, open-loop marine scrubber is a metal tank in a ship’s exhaust stack that uses seawater to wash exhaust gases, converting sulfur dioxide into harmless sulfates.
The cleaned exhaust is released into the air, while the washwater is returned to the ocean. However, the washwater can contain harmful byproducts, raising concerns about whether scrubbers are as environmentally effective as using low-sulfur fuels.
A “well-to-wake” analysis
The team conducted a lifecycle assessment using a global environmental database on production and transport of fossil fuels, such as heavy fuel oil, marine gas oil, and very-low sulfur fuel oil.
Moreover, the researchers also collaborated with a scrubber manufacturer to obtain detailed information on all materials, production processes, and transportation steps involved in marine scrubber fabrication and installation.
If you consider that the scrubber has a lifetime of about 20 years, the environmental impacts of producing the scrubber over its lifetime are negligible compared to producing heavy fuel oil.
…said Patricia Stathatou, lead author of the study and Assistant Professor at Georgia Tech.
Stathatou spent a week onboard a bulk carrier vessel in China to measure emissions and gather seawater and washwater samples. The ship burned heavy fuel oil with a scrubber and low-sulfur fuels under similar ocean conditions and engine settings.
The study found that scrubbers reduce sulfur dioxide emissions by 97%, making heavy fuel oil comparable to low-sulfur fuels. Similar trends were observed for other pollutants like carbon monoxide and nitrous oxide. Washwater samples were tested for over 60 chemicals, including metals and hydrocarbons.
The concentrations of regulated chemicals were well below IMO requirements, and unregulated chemicals were much lower than U.S. and EU industrial limits. Given the dilution of washwater in the ocean, these findings suggest that using scrubbers with heavy fuel oil may be as environmentally friendly as, or more so than, low-sulfur fuels.
In addition, since washwater is diluted thousands of times as it is dispersed by a moving vessel, the concentrations of such chemicals would be even lower in the open ocean.
The findings of the research suggest that the use of scrubbers with heavy fuel oil can be considered as equal to or more environmentally friendly than low-sulfur fuels across many of the impact categories the researchers studied.
“This first-of-its-kind study on a well-to-wake basis provides very valuable input to ongoing discussion at the IMO” said Thomas Klenum, Executive Vice President of Innovation and Regulatory Affairs at the Liberian Registry, emphasizing the need “for regulatory decisions to be made based on scientific studies providing factual data and conclusions.”
