Researchers from the National Renewable Energy Laboratory (NREL) and other Department of Energy facilities are investigating the potential use of marine biofuels as part of a global effort to reduce sulfur and greenhouse gas (GHG) emissions from ships.
“Biofuels turned out to be very good options because they have zero or very, very low sulfur compared to fossil fuels,” said Eric Tan, an NREL senior research engineer and lead author of a new article 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 U.S. Department of Transportation’s Maritime Administration are his co-authors on “Biofuel Options for Marine Applications: Techno-Economic and Life-Cycle Analyses.”
A global effort to reduce sulfur and greenhouse gas (GHG) emissions from ships has researchers investigating the potential use of marine biofuels.
Since 2005, the International Maritime Organization (IMO) has been gradually reducing the allowable amount of sulfur oxide emissions from ships. The most recent upper limit, which went into effect at the beginning of 2020, reduced the sulfur content of ship fuel oil from 3.5 percent to 0.5 percent. According to the IMO, the reduction should have a significant impact on the environment and people’s health, particularly those who live near ports and along coasts. Furthermore, the IMO has set aggressive targets for decarbonizing marine shipping, aiming for a 50% reduction in GHG emissions from international shipping by 2050, compared to 2008 levels.
Individual countries must enforce the new regulation, which necessitates changes to bring ships into compliance. Shipowners can either install sulfur scrubbers to reduce emissions or use low-sulfur fuel. Both options come at an extra cost.
The NREL-directed research serves as a starting point for determining the viability of ships powered by biofuels. Fuel costs are already a significant part of the cost of running a shipping line, so the researchers looked at both prices and emissions.
The economics are weighed against the cost of burning heavy fuel oil (HFO), which accounts for roughly three-quarters of ship fuel. A gallon of low-sulfur HFO costs slightly more than a gallon of traditional HFO. Low-sulfur HFO prices would be the most ship owners would be willing to pay for biofuels as a one-to-one replacement. Biofuels are thought to be potential drop-in fuels for marine engines, but more research is needed to confirm that compatibility.
The fossil fuels currently used in shipping have a number of negative effects, including pollution of the environment, large oil spills, and the production of greenhouse gases, in addition to their rising cost. Biofuels such as algal-derived methanol, ethanol, methane, and butenol can replace marine diesel, but marine engines must be remodeled and improved to accommodate their use.
When the researchers examined different types of fuels for their ability to reduce greenhouse gas emissions and air pollutants, they discovered that biofuels made entirely from biomass offer much higher reductions in life-cycle greenhouse gas emissions – from 67 percent to 93 percent less than HFO. Biomass-derived fuels are also mostly sulfur-free and have lower levels of criteria air pollutant emissions such as particulate matter.
Tan’s research concluded that, if shipping had no competition, the US has a large supply of bio-feedstocks for producing significant amounts of marine biofuels to replace fossil fuels. With ships consuming 400 million metric tons of fuel per year, a 5 percent biofuel blend equates to approximately 5 billion gallons.
The research was supported by the Bioenergy Technologies Office of the United States Department of Energy and the Maritime Administration of the United States Department of Transportation. The National Renewable Energy Laboratory (NREL) is the primary national laboratory of the United States Department of Energy for renewable energy and energy efficiency research and development. The Alliance for Sustainable Energy, LLC manages NREL on behalf of the Energy Department.