Researchers from the National Renewable Energy Laboratory (NREL) and other Department of Energy laboratories are looking at the use of marine biofuels as part of a global initiative to minimize sulfur and greenhouse gas (GHG) pollution from ships.
"Biofuels turned out to be very good choices because they have zero or very, very low sulfur relative to fossil fuels," said Eric Tan, NREL's senior research engineer and lead author of a recent paper published in the journal Environmental Science and Technology.
Ling Tao, also from NREL, and scientists from Argonne National Laboratory, Pacific Northwest National Laboratory, and the US Department of Transportation's Maritime Administration are co-authors of "Biofuel Options for Marine Applications: Techno-Economic and Life-Cycle Analyses."
Reduced Volumes of Sulfur Oxide
After 2005, the International Marine Organization (IMO) has gradually reduced the volume of sulfur oxides that ships are permitted to emit. The sulfur content of ships' fuel oil was lowered to 0.5 percent from 3.5 percent under the most recent upper cap, which went into operation at the start of 2020. According to the IMO, the reduction would benefit the atmosphere and people's health, especially those who live near ports and coasts. Furthermore, the IMO has set ambitious goals to decarbonize marine transport, aiming for a 50% decrease in GHG emissions from international shipping by 2050, compared to 2008 levels.
Individual countries are responsible for enforcing the new legislation, which necessitates modifications to carry ships into compliance. To mitigate emissions, shipowners may either add sulfur scrubbers or switch to a low-sulfur diesel. All options come with a price tag.
The NREL-funded study is a good starting point for determining whether ships will run on biofuels. Fuel costs already make up a large portion of the cost of operating a freight line, so the researchers looked at both rates and pollution.
The costs of burning heavy fuel oil (HFO), which accounts for roughly three-quarters of the fuel used by ships, are measured against the economics. Low-sulfur HFO is marginally more expensive per gallon than regular HFO. The low-sulfur HFO levels will be the highest ship owners can pay for biofuels for a one-to-one substitution. The biofuels are seen as possible drop-in fuels for marine engines, but further research must validate the compatibility.
Other Fuel Sources
When the researchers looked at various types of fuels for their potential to mitigate greenhouse gas and air pollution emissions, they discovered that biofuels made solely from biomass had much lower life-cycle greenhouse gas emissions, ranging from 67 percent to 93 percent less than HFO. Biomass-derived oils are also largely sulfur-free and have lower criteria for air pollutant emissions, including particulate matter.
According to Tan's report, the United States has a vast supply of bio-feedstocks for processing vast quantities of marine biofuels to replace fossil fuels if shipping has little competition. For ships consuming 400 million metric tons of fuel per year, a biofuel mix of 5% equals around 5 billion gallons.
The study was financed by the Bioenergy Technologies Office of the US Department of Energy and the Maritime Administration of the US Department of Transportation.
The National Renewable Energy Laboratory (NREL) is the official national laboratory for renewable energy and energy conservation research and development for the US Department of Energy. The Alliance for Sustainable Energy, LLC manages NREL on behalf of the Energy Department.
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