Last Updated: Apr 2012
Biofuels are currently in a developmental phase. For shipping, the International Maritime Organization (IMO) notes that not all biofuels have a carbon dioxide (CO2) reduction benefit. The benefit will also depend on whether the complete fuel cycle is taken into account (producing the fuel) rather than just combustion. So-called second-generation fuels are regarded as being more sustainable over the long term. The focus so far in 2011 has been on the benefits of algae as a sustainable biofuel.
The combustion characteristics of biofuels and the emissions produced depend on the type of biofuel. Some biofuel companies have claimed substantial CO2 reductions. The IMO warns that some tests have led to increased nitrogen oxides (NOx) emissions by 7-10%, although it expected that this could be reduced with optimised engine configurations. There are also technical issues for the storage of fuel on vessels, and modifications to allow the fuel to be burnt in the engine.
LNG offers substantial potential emissions benefits. It contains no sulphur, so sulphur oxides (SOx) emissions would be eliminated. NOx emissions are reduced by around 90% due to the high temperatures in combustion. CO2 emissions are also reduced, although methane emissions are higher, so the overall greenhouse gas (GHG) benefit is equivalent to a 15% reduction, according to IMO figures.
LNG requires larger storage tanks as its volume is 1.8-times larger than diesel for the energy content. Conversion of engines to LNG is possible, but it is better suited to newbuilds. Bunkering options for LNG are currently limited, but the price is currently below that of distillate fuels. The IMO concludes that LNG propulsion might be better suited to short sea operations in coastal areas where SOx and NOx limits are particularly strict.
The International Maritime Organization (IMO) is being urged to finalise regulations for ships using liquefied natural gas (LNG) as fuel to remove uncertainties currently holding up developments. The plan is to have the regulations in place ahead of the introduction of a 0.10% sulphur limit in Emission Control Areas (ECAs) that will enter into force in 2015.