As the shipping industry fights to reduce both sulphur oxide emissions and carbon footprint, methanol and ethanol have been identified as good potential fuel alternatives in achieving this goal, according to a study published by the European Maritime Safety Agency (EMSA).
The use of alternative fuels in the shipping industry has been receiving increasing attention as a method of complying with low sulphur requirements for fuels and reduced emissions of sulphur oxides. As methanol and ethanol are sulphur-free, they would ensure compliance with the European Commission Sulphur Directive.
Both methanol and ethanol are very attractive fuel choices from an environmental perspective because they are clean-burning, contain no sulphur, and can be produced from renewable feedstocks, the study said. Emissions of both methanol and ethanol from combustion in diesel engines are low compared to conventional fuel oils with no aftertreatment.
Regarding engine technology, both have been shown to work well in heavy duty diesel engines, but there is limited experience with marine applications.
Methanol has been used in a full scale ferry installation in 2015 on the Stena Germanica and is being installed in new build chemical tankers for delivery in 2016. No projects have been identified for ethanol on ships, but it has been used in diesel engines in road transport for many years.
“More projects and experience with different ship applications would be beneficial for demonstrating the potential of the fuels,” according to the study.
Considering availability and supply, methanol and ethanol are both widely available globally but no specific infrastructure for marine fuel is in place, however, the costs for developing this are considered low in comparison to the equivalent LNG infrastructure and it can be done economically on a small scale.
Retrofit and new build investment costs for methanol are similar to those for exhaust gas after treatment and below investments required for LNG.
Both methanol and ethanol have about half of the energy density of conventional fossil fuels, which means that more fuel storage space would be required on board a vessel as compared to conventional fuels. The study also noted that they can be corrosive to some materials, so materials selection for tank coatings, piping, seals and other components must consider compatibility.
The behaviour of these fuels when spilled to the aquatic environment is also important from an environmental performance perspective as ship accidents such as collisions, groundings and foundering may result in fuel and cargo spills. Both fuels dissolve readily in water, are biodegradable, and do not bioaccumulate. They are not rated as toxic to aquatic organisms.