Scientists are experimenting with a growing number oftechniques to cut the volume of greenhouse gases emitted into the atmosphere by human activities. These cover principally carbon dioxide, but not only.
The shipping industry has been devising policies for SOx and NOx emissions for more than two decades, and emissions are now regulated by both IMO and the national authorities.
In June 2021, IMO announced a series of medium-term measures to reduce the carbon intensity of international shipping. The aim is to cut carbon dioxide emissions per transport work (CO2/tonne-nautical mile) by 40% in 2030 versus 2008. A second target will seek to cut carbon dioxide emissions per transport work by 70% in 2050 versus 2008.
IMO is also aiming to reduce total annual GHG emissions from international shipping by at least 50% by 2050 compared to 2008.
In parallel, the need to protect local coastal communities is pushing many ports to introduce policies to reduce and eliminate emissions from ships and yachts in harbour.
Battery-based zero emission propulsion systems have been developed in recent years for use on board both ships and yachts. These enable emissionfree manoeuvring in port, and also permit extended periods in dock without the use of internal combustion engines:propulsion and electrical
services are powered by large battery installations. Meanwhile, connection to an onshore electrical grid removes emissions from yachts when moored in marinas.
Alternative solutions are also being tested by shipyards. These range from the use of hydrogen and fuel cells to supply the vessel’s electric load, to hybrid or electric propulsion for short navigation and manoeuvring time, to the use of LNG or methanol with reformers and fuel cells, or as part of dual fuel internal combustion engines.
These solutions are particularly useful when the battery installation is insufficient to meet all the vessel’s energy needs. Instead, the installation can support the vessel for a reduced period, depending on the system’s storage capacity.
Studies have shown that hydrogen can either be stored at high pressure (compressed form), or at low pressure using metal hydrades that absorbs hydrogen, or in liquid form at very low temperature (-253°C).
Methanol also offers a serious alternative. Methanol does not completely decarbonise vessel emissions, but can reduce the carbon dioxide in emissions generated by marine diesel oil or marine gasoil, especially when bio-methanol is used. The advantage of methanol is that it is liquid at ambient temperatures and atmospheric pressures.
Both methanol and hydrogen have a low flash point, which must be addressed both by applying existing safety rules and by carrying out detailed risk analysis. This ensures a reduction in emissions but also an equivalent or superior level of safety versus traditional oil-based solutions.