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Ammonia Breakthroughs Could Turn the Tide for Green Shipping

Maritime transport is vital to the world’s economy, enabling international trade, commerce and facilitating the movement of goods and resources across the whole globe. However, the shipping sector is  estimated to be the source of 3% of the carbon dioxide (CO2) emitted worldwide since it is still based on the exploitation of cheap and low-grade fossil fuels such as heavy fuel oil (HFO) and marine diesel oil (MDO).  Nowadays, the marine industry is facing challenges in adopting new technologies and operational practices  to comply with the increasingly strict environmental regulations and to achieve the GHG reduction targets set for the 2050 by the International Maritime Organization (IMO).

Among the broad spectrum of technology and fuel solution pathways in front of ship designers, operators  and owners, ammonia (NH3) has been identified as potential marine fuel that could enter the global market  fairly quickly and drive the sector’s sustainable transition.

Ammonia: a promising marine fuel  
Ammonia is already well-known to the maritime field since it is widely transported as cargo in gas carriers  to be used as fertilizer in the food industry. Currently, NH3 is large-scale produced in the Haber-Bosch  process by combining gaseous hydrogen and nitrogen (N2+3H2=>2NH3), accelerated by the presence of a  metal catalyst.

At atmospheric pressure and ambient temperature, it is a clear and colorless gas, lighter than air with a  distinctive pungent smell. At -33°C under atmospheric pressure or if pressurized to 8.6 bar at ambient  temperature, NH3 becomes a liquid, making transport and storage onboard vessel easier.  In this regard, the main advantages that make liquefied ammonia a suitable energy vector to lead the  decarbonization of the maritime industry include:

❖ Carbon free. The key advantage is its status as a zero-carbon fuel when produced renewably,  enabling ships to eliminate CO2 emissions;

❖ Availability. The atmospheric nitrogen (N2), one of its molecule’s precursors, is widely and freely  available;

❖ Storage. As a chemical commonly traded commodity, NH3 can be transported at practical pressure  and temperature, gaining benefits from its well-developed terminal network;

❖ Improving technology. Ammonia can be burnt directly in Internal Combustion (IC) engine which are  closer to scale-development and to a higher readiness steps than other alternative fuel’s solutions. Ammonia or Hydrogen: what to choose?

Since the ammonia is produced from the same process as hydrogen, it is reasonable to question whether H2 can be used directly as a marine fuel instead of NH3.

In order to exploit hydrogen’s fuel potential and minimise the space required onboard a vessel, it would be  necessary to high compress (from 250-700 bar) or liquefy (at -253°C) it.

There is a near consensus that ammonia is a preferred energy carrier compared to hydrogen due to its  higher volumetric energy density and boiling temperature. Indeed, even in its liquid state, the storage of  hydrogen would require five times more volume compared to petroleum-based fuels (MDO) while liquefied  ammonia is just around 2.9, carrying the same energy content.

 

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