The use of ammonia as a ship fuel could contribute to eutrophication and acidification, due to ammonia leakage and emissions of nitrogen oxides. One of the possible emissions is laughing gas, which is also a greenhouse gas with a much higher warming impact than carbon dioxide. Credit: Illustration: Chalmers University of Technology/Petra Persson
As climate change continues to worsen, researchers everywhere are working to find greener solutions to some of earth’s biggest problems. Society’s reliance on fossil fuels is one of those problems.
The automative industry has addressed this with the introduction of electric and hybrid cars, although the technology underlying electric cars is still a work in progress. Meanwhile, the aviation industry has gone in on sustainable aviation fuel (SAF), which is made from non-petroleum feedstocks.
Worldwide, the shipping industry is responsible for 3% of all human-driven CO2 emissions each year—more than cars and planes. Some estimates even say, at current growth rates, shipping could represent 10% of all global greenhouse gas emissions by 2050. Container shipping lines, which carry the bulk of global trade, are indeed betting on greener technologies, but there are still reasons those wagers could fail.
A new study by researchers at Chalmers University of Technology (Sweden) has shown that not only are there risks to switching to ammonia—the “greener” frontrunner—but there also may not be a one-size-fits-all solution for alternative marine fuel.
For the study, published in Applied Energy, the researchers used life cycle assessment and life cycle cost to evaluate technical viability, environmental impacts, and economic feasibility of four types of renewable energy carriers—electricity via batteries, hydrogen, methanol and ammonia—across three different types of ships. The results show that ammonia and methanol have the lowest cost of the alternatives studied.
“The market is usually drawn by costs, and since electro-ammonia has the lowest cost, the market is aiming toward it. There is a hype around this fuel in shipping today,” says lead author Fayas Malik Kanchiralla.
While ammonia is a carbon-free fuel, Kanchiralla and his team warn that its use could create an entirely new set of problems.
“Although it is carbon-free, its combustion in engines is not free from greenhouse gas emissions,” said co-author Selma Brynolf, a Chalmers researcher on Kanchiralla’s team. “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.”
Additionally, ammonia has been linked to acidification and eutrophication, or the growth of microorganisms in a body of water so excessive that animal life dies from lack of oxygen.
In their paper, Kanchiralla and his colleagues stress the importance of controlling ammonia’s affect on air and water quality, especially for ships operating in areas with emission controls—for example, a sensitive marine area such as the Baltic Sea.
“Even though green ammonia is a fossil-free and relatively clean fuel, it is probably not green enough for the environment as a whole,” said Kanchiralla.
Electrofuels—such as hydrogen, methanol and ammonia—are synthetic fuels that are produced with electricity, in a process where energy-rich molecules are made from other molecules. These fuels are defined as “green” when they are produced with renewable electricity. But this study shows that all three green electrofuels have a higher environmental impact than traditional fuels in terms of human toxicity, use of resources like minerals and metals, and water use.
“If and when we make a shift to ammonia, it is to solve the problem of using fossil fuels, but at the moment it seems like we might end up creating more problems instead,” said Kanchiralla.
The study also shows that it is very difficult to find a simple non-fossil fuel solution that both works for all types of ships and is able to meet the goal of reducing greenhouse gas emissions in shipping.
“From a life cycle perspective, one needs to find different types of solutions for decarbonization for different kinds of ships,” said Kanchiralla. “There is no silver bullet. More research and more life cycle analyses need to be done.”