Sailing on iron

Approximately 10% of the CO2 caused by the transport sector worldwide comes from shipping. Large container ships and mega cruise ships naturally attract the most attention.

We regularly hear about the considerable pollution caused by these ships, especially because they are allowed to burn heavy fuel oil. Incidentally, this is increasingly restricted the closer they sail to shore. But on the high seas, we apparently don’t care much if there are a lot of sulfur and nitrogen oxides. So the justifiable question is: can this transport ever become sustainable?

A large container ship uses as much as 250,000 liters of fuel oil a day. Iron powder can be an alternative.

A large ship can carry around 15,000 containers, and has a diesel engine on board with a capacity of 100,000 hp. If such a ship sails for forty days, it can use as much as ten million liters of fuel oil. That’s 250,000 liters a day. In forty days the ship uses one hundred million kilowatt hours (kWh) of energy.

That 10 million liters of oil on board weighs about eight million kilos. Modern batteries with this volume and weight provide approximately two million kWh of electrical energy. Assuming that electric motors are three times as efficient as a diesel ship’s engine, we can sail for two days with those batteries. That’s not very practical.

Researchers at Eindhoven University of Technology are now looking at an alternative: the use of metal powder. A special engine allows you to burn this powder on a ship and convert it into kinetic energy. Back in the harbor, you can dispose of the residual product – iron oxide – to a power station, which uses green hydrogen to convert it back into iron powder. This makes a sustainable CO2-free cycle possible.

One million liters of iron powder weighs as much as ten million liters of fuel oil: eight million kilos. This amount of powder provides (assuming combustion is as efficient as diesel) 20 million kWh of energy. Enough foreight days of sailing. If we take along five million liters of iron powder, we can sail for another forty days. As long as with fuel oil, but with half the volume and another five times its weight. In a sustainable way, without harmful emissions. It’s an interesting option to explore further, I think.

Maarten Steinbuch