Could ammonia be shipping and aviation’s green fuel of the future?
Industries may have no other option in order to cut emissions, say experts. Hasan Chowdhury reports
On the high seas off the coast of Scandinavia, cargo ships are a familiar sight ferrying supplies to the region’s oil platforms. If scientists have their way, a new type of vessel could soon appear on the horizon, powered not by polluting hydrocarbons but by something else: ammonia.
Wärtsilä, the world’s biggest ship engine manufacturer, announced this month that it was working on the first ever full-scale test of ammonia as a green fuel in ships.
The goal? The Finnish group aims to find better ways to comply with global efforts to tackle climate change as the International Maritime Organisation pushes the sector to cut its emissions in half by 2050.
“It is a huge undertaking to change the shipping industry,” says Egil Hystad of Wärtsilä. “Shipping is emitting carbon dioxide corresponding to 40m personal cars every year. That’s 1bn tons of carbon dioxide.”
At one level, ammonia is just a gaseous mix of nitrogen and hydrogen, better known for its use as a fertiliser.
But like Wärtsilä, many see ammonia’s potential to serve as a sustainable fuel by carrying hydrogen, helping to decarbonise operations.
Earlier this year, companies including British engineering firm Lloyd’s Register and Samsung’s shipbuilding division signed on for a project to build an ammonia-fuelled tanker. So has its time arrived?
For the shipping industry, there is little choice but to give it a try. Hydrogen alone, tabled as an alternative, falls flat as a fuel given its rapid boil-off rate.
Any hopes of electrifying ships are likely to fail too, given the batteries required would simply be too large, says Dr Tristan Davenne, engineer on a green ammonia project in Harwell. “They’re certainly not scalable up to that level at the moment.”
One challenge for sectors such as shipping looking to ammonia is to find a way of producing it that doesn’t generate harmful emissions.
Typically, ammonia is made in a process known as steam reforming. Hydrogen is generated from a reaction involving methane, water and air, and then combined with nitrogen in a process known as the Haber method. However, carbon dioxide is produced as a by-product – undermining its use to tackle climate change.
Dr John Constable, director of the New Energy Foundation, sees one fix for this that banks on carbon capture and storage, a relatively unproven technology that sucks carbon dioxide from the air and stores it deep underground. “If you can capture the carbon from steam methane reforming, it may be clean at the point of consumption,” he says.
Another method picking up traction from Wärtsilä involves the use of electricity generated by wind farms to split water into its components of hydrogen and oxygen through a process known as electrolysis.
That hydrogen can then be combined with nitrogen pulled from the atmosphere to create ammonia in a way that has cut carbon emissions altogether. For years, the method has proved too costly, but Hystad claims 400 gigawatts of wind turbines are due to be installed in the North Sea between now and 2050, more than 20 times the current output.
With clean options of generating ammonia emerging, the next challenge involves turning it into a form that can be used as fuel. Wärtsilä is exploring the possibility of pumping ammonia 70m below sea level where high pressure can turn it into a liquid, while another option involves cooling the gas to -40C to liquefy it.
Once in a liquid form, ammonia can be used in a retrofitted internal combustion engine, or can generate electricity in a reaction driven by a device known as a fuel cell.
The ability to create green ammonia is opening up potential applications far beyond the high seas too. A study led by Davenne’s team has been investigating the potential for ammonia to replace kerosene as the go-to fuel in the aviation industry.
At a cruising altitude, ammonia could sit in the wings of a plane as a liquid, and the engine would need few changes.
But there are some real hurdles to overcome.
In planes, ammonia could struggle as its energy density is a lot lower than kerosene, meaning much more fuel will be needed on-board. For shipping, the corrosiveness of ammonia presents “a real problem for the integrity of the engine”, according to Constable, and could pose safety threats to operators.
Both processes of generating ammonia require large amounts of fresh water too.
“Bear in mind it won’t be returned to the water table because when it’s burned it obviously goes off as water vapour,” Constable says.
However, seafarers may have no choice but to accept ammonia’s time has come. “It’s the only way of decarbonising 100pc for transport,” he says.
‘Shipping is emitting carbon dioxide corresponding to 40m personal cars every year’