Well-to-Wake: Scrubbers Beat HFO on Environmental Performance

Researchers from MIT and Georgia Tech have concluded that burning heavy fuel oil with scrubbers in the open ocean can match or surpass using low-sulfur fuels when a wide variety of environmental factors is considered.

The scientists combined data on the production and operation of scrubbers and fuels with emissions measurements taken onboard a bulk carrier owned by Oldendorff Carriers. Gaseous and particulate matter (PM) emissions data were collected while the bulk carrier  was burning 3%S HFO, 0.1%S marine gas oil (MGO), and 0.5%S very low-S fuel oil (VLSFO)

The researcherrs 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.

“Claims about environmental hazards and policies to mitigate them should be backed by science. You need to see the data, be objective, and design studies that take into account the full picture to be able to compare different options from an apples-to-apples perspective,” said lead author Patricia Stathatou, an assistant professor at Georgia Tech.

Today, more than 5,800 vessels utilize scrubbers, the majority of which are wet, open-loop scrubbers. The seawater used in the scrubber interacts with sulfur dioxide in the engine exhaust gas, converting it to sulfates — water-soluble, environmentally benign compounds that naturally occur in seawater. The washwater is released back into the ocean even though it can contain other combustion byproducts like heavy metals.

The team conducted a lifecycle assessment using a global environmental database on production and transport of fossil fuels. Considering the entire lifecycle of each fuel is key, since producing low-sulfur fuel requires extra processing steps in the refinery, causing additional emissions of greenhouse gases and particulate matter.

“If we just look at everything that happens before the fuel is bunkered onboard the vessel, heavy fuel oil is significantly more low-impact, environmentally, than low-sulfur fuels,” Stathatou says.

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,” she adds.

Stathatou spent a week onboard a bulk carrier vessel in China to measure emissions and gather seawater and washwater samples. The results showed that scrubbers reduce sulfur dioxide emissions by 97%, putting heavy fuel oil on par with low-sulfur fuels according to that measure.

The researchers saw similar trends for emissions of other pollutants like carbon monoxide and nitrous oxide. In addition, they tested washwater samples for more than 60 chemical parameters, including nitrogen, phosphorus, polycyclic aromatic hydrocarbons and 23 metals.

The concentrations of chemicals regulated by the IMO were far below the organization’s requirements. For unregulated chemicals, the researchers compared the concentrations to the strictest limits for industrial effluents from the U.S. Environmental Protection Agency and European Union. Most chemical concentrations were at least an order of magnitude below these requirements.

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.

“This study demonstrates the scientific complexity of the waste stream of scrubbers. Having finally conducted a multiyear, comprehensive, and peer-reviewed study, commonly held fears and assumptions are now put to rest,” says Scott Bergeron, managing director at Oldendorff Carriers and co-author of the study.

“This first-of-its-kind study on a well-to-wake basis provides very valuable input to ongoing discussion at the IMO,” adds 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.”

This study was supported, in part, by Oldendorff Carriers.