Charting a Course toward Cleaner Shipping

by Christina Nunez (Industry Today) Research suggests that swapping heavy fuel with fuel made from wood waste, waste fats, oils and greases could cut planet-warming emissions. ... Using batteries instead of heavy fuel oil to propel gigantic cargo ships, which annually move more than 10 billion tons of goods, isn’t yet feasible.

So what will fuel the commercial fleet of the future? Scientists at U.S. Department of Energy (DOE) national laboratories are exploring a raft of biofuel options and the results are promising. A recent analysis found that compared to conventional fuel, biofuels could cut greenhouse gas emissions between 40 and 93 percent, depending on the feedstocks and conversion processes. Even better, the study—conducted by researchers from DOE and the Department of Transportation—found cleaner biofuels could also be cost-effective after considering credits such as those offered by California’s Low Carbon Fuel Standard.

The viscous, tar-like fuel most commercial fleets run on today is relatively cheap and energy dense, but a replacement is needed for the maritime sector to play a role in curbing planet-warming pollution and other air pollutants.

To conduct their research, Hawkins (Troy Hawkins, a scientist at DOE’s Argonne National Laboratory) and team relied on Argonne’s Greenhouse gases, Regulated Emissions, and Energy use in Technologies model (GREET ®). The analytical tool helps determine the energy and environmental impacts of different fuels—not just the impacts of burning them, but also of producing/procuring and transporting them, and converting the feedstocks and transporting fuel to users. Long used to evaluate the impact of transportation technologies, GREET’s marine transportation module has been significantly expanded recently to include new alternative fuel pathways for seagoing vessels.

Beyond lowering carbon emissions, biobased feedstocks could also reduce the release of harmful sulfur oxides by 97 percent or more, the researchers found. Particulate matter emissions fell between 84 and 90 percent. The study’s datasets are publicly available and could also support the evaluation of fuels to meet California’s Low Carbon Fuel Standard, which takes a similar life-cycle view to encourage options with the lowest carbon intensity.

Many Possibilities, Complex Decisions

Another recently published study by Hawkins and colleagues at Argonne and NREL affirmed the potential for biofuels to keep ships moving with fewer emissions. However, it also highlighted the complexity of the decisions involved for investors and the industry.

Potential feedstocks for shipping biofuels include wastes from wood products and agriculture operations; used cooking oil; wastewater sludge; manure; soybean and corn crops; or energy crops like switchgrass or miscanthus. Each biofuel type comes with its own set of considerations, including cost, energy density, where and how it can be stored, and whether additional infrastructure or engine retrofits are needed.

DOE announced a partnership among the governments of the United States, Denmark and Norway to develop technologies for zero-emission shipping as part of Mission Innovation, a global initiative to accelerate affordable, accessible clean energy solutions.

Many of the biofuels Hawkins and colleagues analyzed are drop-in fuels that can be used on their own or mixed with conventional heavy fuel oil. Biofuel blends could be used in existing ships to help lower carbon intensity in the short term.

“It may also turn out that new ships using different fuels, such as ammonia, hydrogen, or methanol, are needed to achieve decarbonization goals—and those may have a higher cost. READ MORE

Excerpt from Environ. Sci. Technol.: This study performed technoeconomic and life-cycle analyses to assess the economic feasibility and emission benefits and tradeoffs of various biofuel production pathways as an alternative to conventional marine fuels.

(1) Fischer–Tropsch diesel from biomass and cofeeding biomass with natural gas or coal,

(2) renewable diesel via hydroprocessed esters and fatty acids from yellow grease and cofeeding yellow grease with heavy oil, and

We also developed a new version of the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) marine fuel module for the estimation of life-cycle greenhouse gas (GHG) and criteria air pollutant (CAP) emissions of conventional and biobased marine fuels.

The alternative fuels considered have a minimum fuel selling price between 2.36 and 4.58 $/heavy fuel oil gallon equivalent (HFOGE), and all exhibit improved life-cycle GHG emissions compared to heavy fuel oil (HFO), with reductions ranging from 40 to 93%.

The alternative fuels also exhibit reductions in sulfur oxides and particulate matter emissions. Additionally, when compared with marine gas oil and liquified natural gas, they perform favorably across most emission categories except for cases where carbon and sulfur emissions are increased by the cofed fossil feedstocks.

The pyrolysis bio-oil offers the most promising marginal CO₂ abatement cost at less than $100/tonne CO₂e for HFO prices >$1.09/HFOGE followed by Fischer–Tropsch diesel from biomass and natural gas pathways, which fall below $100/tonne CO₂e for HFO prices >$2.25/HFOGE. Pathways that cofeed fossil feedstocks with biomass do not perform as well for marginal CO₂ abatement cost, particularly at low HFO prices.

This study indicates that biofuels could be a cost-effective means of reducing GHG, sulfur oxide, and particulate matter emissions from the maritime shipping industry and that cofeeding biomass with natural gas could be a practical approach to smooth a transition to biofuels by reducing alternative fuel costs while still lowering GHG emissions, although marginal CO₂ abatement costs are less favorable for the fossil cofeed pathways. READ MORE