U.S. MARAD released a study that evaluates total fuel cycle emissions for natural gas versus conventional marine fuels.

Thes study was conducted as a part of MARAD's Maritime Environmental & Technology Assistance program, which focuses efforts on emerging marine transportation and environmental issues.

Results of the study showed that the use of natural gas as a propulsion fuel can reduce air quality pollutants and reduce major greenhouse gas emissions when compared to conventional fuels. The information provided by this study is important as marine transportation stakeholders evaluate the use of natural gas as aviable alternative propulsion fuel for reducing air polluting emissions. The research was conducted through a cooperative partnership with the Maritime Administration, the University of Delaware and The Rochester Institute of Technology.

American Marine Highways Network

Marine cargo in the US transits one of five main routes: i) calling on ports along the East Coast (in regional and trans-Atlantic service); ii) moving barges up and down the Mississippi River and other inland rivers; iii) transiting the Great Lakes; iv) calling on ports along the Gulf Coast; or v) calling on ports on the West Coast (in regional and trans-Pacific service to Asia/Australia). The U.S. Department of Transportation (USDOT) has begun to designate certain routes as part of the American Marine Highway system, encouraging shippers to use marine routes in domestic service to ease congestion on land routes. Two domestic routes examined in this report are a part of this system, while the other two transit the ocean, and there is no equivalent land-based route in the US.

Cases describing several potential routes were included in the scope of this report, with the understanding that these provide sufficient insight to consider the maritime sector as part of the US natural gas picture. The first two routes analyzed leave from the Port of LA/LB. Ships from there transit to Shanghai, China, or Honolulu, HI. The inland route transits the Mississippi River between Peoria, IL and New Orleans, LA. On the East Coast route ships transit between PANYNJ and Jacksonville, FL. The last two routes are formally identified within the US DOT-designated American Marine Highways Network.

Consideration of Natural Gas Fuels for Marine Vessels

The emissions signature of natural gas meets all current, pending, and proposed standards for marine vessel operations, and the current price differential favoring natural gas suggests an economic advantage may exist. Recently, the shipping industry has joined other sectors in considering the merits of gaseous fuels as a feasible, economical, and low-emitting alternative to traditional petroleum fuels. For these reasons, natural gas is emerging as an attractive fuel, with many newly constructed vessels powered either by natural gas exclusively or by a combination of conventional diesel and natural gas (MarineLink, 2013; Posplech, 2013; Walls & Abrahamsen, 2012).

Historical wellhead price of crude oil and natural gas showing the increasing price differential between these two fuels that has emerged since 2005.

The emergence of market-ready reciprocating internal combustion engines capable of natural gas and/or dual fuel operation in maritime service makes studies such as this one more important for industry leaders and policy decision makers. Multiple firms are building or are planning to build vessels using these engines, making this work extremely relevant to current investment decisions (Germanischer Lloyd, 2011; Rolls Royce, 2013).

Of course, existence of the technology is not the only thing considered when deciding whether or not to switch to alternative fuels.

Operators are looking at cost and technical feasibility issues, including:
  • the ability to operate within and beyond emission control areas, without the need for aftertreatment of exhaust gases for traditional pollutants;
  • the price differentials for LNG/CNG versus other marine fuels, including residual heavy fuel oil; the existence of infrastructure networks for obtaining LNG/CNG fuel; and,
  • attractive financing of LNG/CNG vessels in fleet modernization/replacement strategies.

Regarding the second point above, recent trends in the prices of crude oil and natural gas are making natural gas a more attractive marine fuel. In addition, natural gas infrastructure is growing, making it more plausible to fuel ships with natural gas in the future.

Fuel Pathways

A “fuel pathway” represents the series of processes that are necessary for fuel production and use. There are various steps in the process in which decisions can be made. Consequently, there are multiple fuel pathways for a given fuel. In the study, 28 possible fuel pathways for natural gas fuels get explored.

Generic Pathways for Getting Fuel from Wellhead to Ship

Two distillate fuels are also examined in the report, namely ECA-compliant distillate fuels meeting 2012 and 2015 sulfur standards (that is, 10,000 ppm S and 1,000 ppm S, respectively). Unlike the natural gas market, where different upstream pathways are being examined for economic and environmental criteria, the distillate fuel market is mature, with established upstream pathways. Therefore different pathways were not analyzed. Instead, it is used default GREET 2013 pathways for all upstream distillate processes.

Overall Results and Discussion

Two observations relate to the vessel and route (operational phase). The first observation should be stated for completeness – the farther a shipping vessel goes, the more fuel is needs to get it there and the longer the engines need to run, so resulting energy demand and emissions will be higher. Second, vessel operations are important – more efficient engines and engines that technologically control for pollutant formation produced fewer emissions.

With regard to the fuel pathways, the pathway’s effect on total emissions depended on the pollutant in question. Methane emissions for natural gas fuel are highly affected by the way the natural gas is obtained, the amount of time (e.g., distance) in the natural gas pipeline, and the amount of time in storage. Using conventional wells and minimizing pipeline distance and storage time would both reduce methane emissions. For the other pollutants analyzed, the upstream processes did not affect the overall results.

Natural gas is considered by many to be a win-win-win marine fuel: i) economically attractive; ii) low-emitting for key air quality pollutants; and iii) lower GHGs (primarily lower CO2). However, natural gas may achieve some goals better than others. Other studies have found that switching to natural gas does not improve GHG emissions, especially considering methane leakage impacts on global warming potential (Brynolf, Magnusson, Fridell, & Andersson, 2013; Lowell et al., 2013; Meyer et al., 2011).

Source and Image Credit: U.S. MARAD


For more information please read the report by clicking below:


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