Sustainability in the marine industry is lately mostly associated with the issue of using fossil fuels. Different global research and development projects are working on switching vessel's propulsion systems to units that run on renewable energy. The latest target set by the International Maritime Organization includes the reduction of emissions by 50% until 2050, in comparison to the emissions in 2008. The marine transport emissions of NOx and SOx represent 15 and 13% of the global total.
In our last post we discussed the different efforts, while today we are going to touch more upon hydrogen, ammonia and methanol as fuel. Alongside ship design, switching to renewable fuels is the most disruptive way to cut CO2 emissions.
HYDROGEN
The first fuel we will touch upon is hydrogen. We covered some of the main characteristics of hydrogen in our previous post, but how is hydrogen produced? The most common way is electrolysis, but it is not the most commercialized way. Current methods of hydrogen production rely on the use of fossil fuels as starting material. However, it is possible to use water and excess renewable energy as starting material (Turner, 2004).
The main problem regarding the use of hydrogen as fuel includes hydrogen storage. The storage methods currently deployed include compressed hydrogen, liquid hydrogen, ammonia, Fischer–Tropsch diesels, synthetic natural gas, methanol, formic acid, aromatic liquid organic hydrogen carriers and several solid-state hydrogen carriers (Van Hoecke et al., 2020).
The currently most developed and widely used method to store hydrogen is by compression. Five different types of storage tanks have been developed and are used to store hydrogen at increased pressure, from 10–20 to 70 Mpa.
AMMONIA
The second fuel we will touch upon is ammonia.
Ammonia can serve both as a hydrogen carrier molecule and as a fuel. Ammonia is a carbon free chemical, but the current production of hydrogen from ammonia comes from steam reforming methane. This process is associated with greenhouse gases, since methane is a hydrocarbon and by producing hydrogen, CO2 is emitted as well.
On the contrary, ammonia can be produced by electrolysis powered by renewables or nuclear energy. DNV states that then it is an excellent source of zero-emission fuel. However, this type of ammonia production is not yet commercially viable.
METHANOL
Methanol is one of the most produced chemicals in the world. In 2015 more than 70 million tons of methanol were produced globally.
Storing methanol has several benefits over ammonia and hydrogen. Methanol has low toxicity to marine life and it can be stored inside the double hulls of ships. The lower toxicity is definitely a benefit for the overall environment, since the spill of methanol would not cause as extensive harm as fossil fuel leaks. However, an obstacle is that methanol is characterized as a low flashpoint fuel according to the IMO. The flashpoint is a point at which compounds become volatile and explosive in reaction with air.
An additional feature of methanol is that it only requires minor modifications to existing terminal infrastructure, according to Methanex.
CONCLUSION
It can be concluded how all of the three molecules as fuel have their benefits. However, they are only as sustainable as their production stems from renewables and low toxicity compounds. It will be interesting in a few years to see which fuel will have the best quality vs sustainability vs price ratio!
References
1. Turner, J. A. (2004) Sustainable Hydrogen Production. Science, 305, 972-974.
2. Van Hoecke, L., Laffineur, L., Campe, R., Perreault, P., Verbruggen, S. W., & Lenaerts, S. (2021). Challenges in the use of hydrogen for maritime applications. Energy & Environmental Science, 14(2), 815-843. https://doi.org/10.1039/d0ee01545h