Fuel for thought: Charting a course towards the ammonia economy

Most people have heard of the hydrogen economy, where renewable electricity creates hydrogen fuel from water – but an ammonia economy is emerging as a more viable possibility.

In the ammonia economy, ships, trucks, buses, power generators and even jets would run on ammonia. In the words of chemist Doug MacFarlane, by 2050 ammonia could replace fossil fuels “in almost any application”.

“We're talking about energy that we can generate in one place and move to another place,” he says. Australian solar and wind power cannot be loaded onto ships, as petroleum and diesel can, for example.

Sustainably-produced ammonia meets this requirement. And, it has other practical advantages over green hydrogen, says Professor Macfarlane, the lead author of a paper, “A Road Map to the Ammonia Economy”, recently published in the sustainable energy journal Joule.

He wrote the paper to explain ammonia’s potential for people “who have never thought of ammonia as a fuel”.

Some 175 million tonnes of ammonia is already produced annually, mostly for use as synthetic fertiliser (the market value is US$70 billion). The technology of shipping and transferring ammonia by pipeline is well-established. Liquid hydrogen is more expensive. It’s also highly combustible, and therefore difficult to transport.

A brief history of ammonia

Ammonia has been produced in bulk for more than a century, using a process first developed during WWI by two Germans, industrial chemist Fritz Haber and chemical engineer Carl Bosch.

The Haber-Bosch process makes ammonia by converting nitrogen (N2) from the atmosphere – nitrogen is the most abundant element in the air we breathe – and combining it with hydrogen (H). The chemical formula for ammonia is NH3.

Haber and Bosch patented their technique in 1910. Germany employed the process at an industrial scale during WWI after the allies blocked their access to nitrogen-rich guano that was mined in Chile, and imported to improve crop yields.

Over the next century, the advent of cheap synthetic fertiliser transformed global food production – without Haber-Bosch ammonia, only two-thirds of the food grown today would be produced, and the present population of the world could not be sustained. Haber and Bosch both received Nobel prizes.

But the Haber-Bosch method is energy-intensive, contributing to 1.4 per cent of global carbon emissions. In recent years, research began into producing ammonia sustainably.

Using ammonia as a fuel

Researchers initially believed that sustainable ammonia could not only be used as fertiliser, but as a means of transporting hydrogen – which would be separated from the ammonia at the point of delivery, and used as a fuel.

But using ammonia directly is more efficient, with researchers making giant strides over the past 18 months or so. Last August, a green ammonia conference was organised by the Monash-based Australian chapter of the Ammonia Energy Association and held at the CSIRO in Melbourne. Delegates from the Singapore Port Authority and MAN, a German engine manufacturer, both spoke of the urgent need to develop ammonia as a replacement fuel for the heavy diesel used in ships.

“It’s not something that most of us had given much thought to,” Professor MacFarlane says. “Singapore Port Authority was there, because they’re one of the biggest trans-shipping ports in the world, and they have to hold massive qualities of bunker fuel, which is marine diesel for ships to refuel as they pass through. The future is mandated already, by the International Marine Organisation, a very powerful body that has far more muscle than the UN, because they run the international waters.”

“People are starting to realise they need a solution, and it needs to come along soon if the IMO’s target is going to be reached,” Professor MacFarlane says. “There’s only one answer – it’s ammonia.”

The IMO has ruled that marine-generated carbon emissions must be cut by half by 2050. This effectively means that all new ships must be carbon-free – because ships have a long life, and global shipping is forecast to expand substantially by 2050.

“People are starting to realise they need a solution, and it needs to come along soon if the IMO’s target is going to be reached,” Professor MacFarlane says. “There’s only one answer – it’s ammonia.”

Marine and diesel engines that can run on ammonia already exist, Professor Macfarlane says. MAN Energy is developing a prototype for large ships now, to be launched as a demonstration model for the international shipping market. Buses and trucks could also be adapted to run on ammonia, he says, with jet turbines a future possibility.

The roadmap to green ammonia

Professor MacFarlane says he wrote the paper for Joule to set out the three-step process for manufacturing sustainable ammonia at scale, as a way of demonstrating how an ammonia economy could be established by 2050.

Most ammonia sold today is what he calls “black ammonia”, because fossil fuels are used to make it.

Generation One ammonia on his roadmap is today’s ammonia, but with carbon capture and storage used to deal with the emissions. “It’s likely to represent only a transitional solution, helping to establish a market for ammonia beyond the fertiliser and chemical industries,” he writes.

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Generation Two ammonia is still made by the Haber-Bosch process, but powered by renewable energy. Siemens established a small demonstration plant of this type in Oxfordshire, England, in 2018. The Norwegian fertiliser company Yara, which operates one of the largest ammonia plants in the world from the Pilbara in WA, has also been investigating the feasibility of solar-powered ammonia.

“I think we could forecast Gen Two supplying a very significant fuel market in the world by 2030,” Professor MacFarlane says. “The shipping industry will ensure that it becomes a major reality. Just how major is the next question.”

Generation Three ammonia bypasses the Haber-Bosch process. Monash A  led by Professor MacFarlane, funded by the Australian Renewable Energy Agency (ARENA), is investigating how to convert atmospheric nitrogen into ammonia, in an electrochemical process involving high-performing electrodes. The ammonia project is running in tandem with Monash research into how to split hydrogen from water more cheaply and efficiently. The two research teams learn from each other’s advances, he says, but the economics are still challenged by the low cost of fossil fuels.

What could go wrong?

We understand the carbon cycle, which explains how burning fossil fuels contributes to global warming. But the nitrogen cycle is less well-understood. The intensive use of synthetic fertilisers over the past 100 years has vastly increased the planet’s exposure to nitrogen compounds. “It’s approximately double what it would have been, say, 200 years ago,” Professor MacFarlane says.

NOx is a generic term for the nitrogen oxides that cause atmospheric pollution. Fertiliser run-off, in the form of nitrates, are pollutants in rivers and seas.

“They go through a number of processes in the ocean, and eventually get emitted back to the atmosphere as N2 [nitrogen],” Professor MacFarlane says. “But some of those cycles, some of the intermediate materials involving nitrogen in the ocean, have very long half-lives, of more than 100 years.”

This means their long-term effects remain unknown. “So, we're not remotely at any kind of steady state, where we can honestly say, yes, the planetary systems are coping ... Nobody could rightly say that.”

More research into the nitrogen cycle is essential, Professor MacFarlane says. In his roadmap, he expressed his concerns this way: “It’s obviously important that humankind doesn’t avoid one crisis revolving around CO2 emissions by creating another crisis involving ammonia and NOx emissions.”