Aluminium as a fossil-free marine fuel? Yes, it actually works. The metal also has several advantages compared with other alternative fuels such as hydrogen and ammonia. This is shown in a new scientific article from Lund University.

In the search for future fossil-free fuels for shipping, favored candidates such as ammonia and hydrogen may face competition from an unexpected source. Aluminium, which in shipping is best known as a lightweight material used in ship structures and containers, is in fact a potentially suitable energy carrier with the capacity to fundamentally change the industry's climate footprint.

This conclusion is drawn by Joakim Haraldsson, a researcher at Lund University. In an article published in Energy Conversion and Management, he highlights aluminium’s potential, while also noting that the idea did not originate from his own previous research on aluminium.

“I was contacted by someone from Ideon Science Park in Lund who had heard that aluminium could be used as a fuel. It wasn’t something I had thought about before, and it was something of an aha moment for me as well. But after reading up on it, I discovered that there is a certain logic to it,” he says.

Aluminium can be used in two ways in a fuel process. Either it can be oxidized with oxygen—for example in powder or molten form—releasing large amounts of heat. Or it can be oxidized with water, producing both heat and hydrogen.

“The heat can be used to drive a turbine that propels the ship forward, while the hydrogen can either be burned or used in fuel cells. One advantage of hydrogen is that it can also be used to generate electricity for other onboard systems, not just propulsion. In this way, hydrogen can be produced directly on board without the need for storage,” says Joakim Haraldsson.

This represents a clear advantage, as aluminium has a significantly higher energy density than hydrogen. In addition, it is considered safer to store than both hydrogen and ammonia.

“Another important advantage is that the combustion of aluminium produces aluminium oxide, which can be reused to produce new aluminium. This creates opportunities for a circular flow with both economic and environmental benefits compared with, for example, e-fuels.”

There are, of course, also some major challenges associated with aluminium. First of all, the technology is not yet developed, and there is limited knowledge about how economically viable aluminium would be compared with other fuels.

“Aluminium production today has a fairly high environmental impact. It must become green to be a sustainable alternative. Infrastructure for handling in ports and other related systems also needs to be developed.”

Even though the potential is significant, Joakim Haraldsson believes it will take decades before aluminium can be used as a fuel in shipping. Until then, extensive research is required.

“I am currently working on two articles that build on this research. In one, I am investigating whether there are specific segments within shipping where aluminium is more suitable. As mentioned, the high energy density is a clear advantage, making it particularly interesting for ocean-going vessels. In the other article, I am conducting a life cycle analysis to calculate aluminium’s total environmental impact as a fuel. I will also attempt to make comparisons with other fuels,” says Joakim Haraldsson.

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