According to a study from Chalmers University of Technology in Sweden, switching to ammonia as a marine fuel, with the goal of decarbonisation, can instead create entirely new problems.
Researchers from the university carried out life cycle analyses for batteries and for three electrofuels including ammonia. They found that eutrophication and acidification are some of the environmental problems that can be traced to the use of ammonia – as well as emissions of laughing gas (N2O), which is a very potent greenhouse gas.
In the search for viable fossil-free marine fuels, ammonia has been on the agenda for several years as one of the strongest alternatives. Ammonia (NH3) is a carbon-free fuel and has the advantage of a higher energy density than, for example, hydrogen. It can be liquefied fairly easily although it is a gas at standard conditions. However, a significant disadvantage is that the production of electro-ammonia – which requires electricity – is very energy intensive. Moreover, the new study shows that an eagerness to rid the shipping sector of carbon emissions, by using ammonia, might create entirely new problems instead.
Selma Brynolf, Chalmers researcher and co-author of the paper, said: “Although ammonia is carbon-free, its combustion in engines is not free from greenhouse gas emissions. Engine tests have shown varying degrees of emissions of laughing gas, which is a very potent greenhouse gas with more than 200 times the global warming impact than carbon dioxide.”
Fayas Malik Kanchiralla, PhD student at the Department of Mechanics and Maritime Sciences at Chalmers and lead author of the paper added: “There is simply a lack of deeper risk analyses of what a switch to ammonia could mean.”
The researchers used life cycle assessment and life cycle cost to evaluate technical viability, environmental impacts, and economic feasibility for four types of renewable energy carriers, for three different types of ships. The energy carriers examined included electricity via batteries, and three electrofuels: hydrogen, methanol, and ammonia. The energy carriers were in turn used in combination with both engines and fuel cells.
The study shows that ammonia and methanol have the lowest cost of the alternatives studied.
Kanchiralla said: “The market is usually drawn by costs, and since electro-ammonia has the lowest cost, the market is aiming towards it. There is a hype around this fuel in shipping today. But if, and when, we make a shift to ammonia, it is to solve the problem of using fossil fuels, and at the moment it seems like we might end up creating more problems instead.”
This is because ammonia comes with a set of environmental disadvantages. Its use as a fuel can affect air and water quality due to ammonia leakage and emissions of NOx, such as N2O. It will be important to control this for ships operating in areas with emission controls, for example a sensitive marine area such as the Baltic Sea.
Electrofuels are defined as ‘green’ when they are produced with renewable electricity. But the study shows that all three green electrofuels have a higher environmental impact than traditional fuels in terms of human toxicity, use of resources such as minerals and metals, and water use.
The use of ammonia is associated with substantial toxicity challenges and risks, which are manageable, but would increase the complexity of the safety systems required. This would potentially limit the use of the fuel to only deep-sea cargo ships.
Kanchiralla said: “Among the environmental problems that can be traced to use of ammonia are eutrophication and acidification. To sum up; even though green ammonia is a fossil-free and relatively clean fuel, it is probably not green enough for the environment as a whole. More risk assessments on the emissions of ammonia, and the related nitrogen compounds, need to be done before adopting this fuel for shipping.”
The study shows the difficulty of finding a simple non-fossil fuel solution that works for all types of ships and is able to meet the goal of reducing GHG emissions in shipping. Assessing the environmental and economic aspects of different fuel options for the shipping sector is complex, and several factors need to be considered when developing climate strategies for various types of ships and modes of operation.
Kanchiralla concluded: “From a life cycle perspective, one needs to find different types of solutions for decarbonisation for different kinds of ships. There is no silver bullet. More research and more life cycle analyses need to be done.”
Image: Effects of NH3 as ship fuel (credit: Chalmers University of Technology/Petra Persson)
