Is Ammonia the Carbon-Free Fuel of the Future?

Could a compound listed by the federal government as an Extremely Hazardous Substance be a clean-fuel solution for ships? Maybe. Ammonia, the world’s second most common industrial chemical, is suddenly getting a lot of attention as a possible power source—and as a storage and delivery medium for another carbon-free fuel: hydrogen.

Instantly recognizable by its pungent odor, ammonia consists of nitrogen and hydrogen. When burned, it emits no carbon—because it has none to emit. (There are other problematic emissions, but ammonia itself can neutralize them. More on that in a moment.)

The world produces 260 million tons of ammonia a year. More than 80% becomes fertilizer, mostly for agricultural crops. Ammonia is also an industrial refrigerant and a curing agent for leather. It’s used in household cleaners, and in the manufacturing of dyes, pharmaceuticals, cosmetics, vitamins, textiles, and other products.

It’s corrosive and can be toxic for fish and animals, including humans. Still, the chemical industry long ago learned to handle it safely.

Ammonia’s utility as a fuel remains almost entirely theoretical. “It doesn’t ignite very well, and it burns slowly,” said Kaj Portin, general manager, fuel and operational flexibility, for the Finnish maritime and energy company Wärtsilä Marine (quoted in a company blog post). “You have to be careful with the temperatures and pressures to get it to work.”

Huge Potential Market

So why is Wärtsilä testing ways of using ammonia to power ships? Because the potential market is huge. The world has 56,000 oceangoing merchant ships, and that doesn’t count freshwater vessels such as the massive freighters that ply the Great Lakes. Shipping contributes 3% of the world’s carbon dioxide emissions. The International Maritime Organization—the United Nations agency that regulates shipping—has announced a 2050 goal of reducing greenhouse gas emissions by 50% compared with 2008 levels.

Most ships use diesel engines; a few still burn notoriously dirty heavy bunker fuel. Newer ships operate on liquified natural gas, or LNG. That’s significantly cleaner than diesel, but not clean enough to achieve the IMO’s emissions goal.

Ammonia might be. Wärtsilä and Man Energy Solutions of Germany are working on ammonia engines. The idea isn’t crazy. During World War II, fuel shortages led Belgium to power about 100 public buses with an ammonia-coal gas mixture. Wärtsilä is testing the possibility of mixing ammonia with LNG and diesel.

The company is also exploring another ammonia technology: fuel cells, which would power electric propulsion motors. Ammonia fuel cells emit only nitrogen (which makes up 78% of the atmosphere) and water.

MS Viking Energy, a Norwegian oil platform supply ship launched in 2003, is scheduled to get refitted in 2024 with a 2-megawatt ammonia fuel cell system, with LNG as a backup fuel. Wärtsilä is a partner on the project. Yara, a top multinational ammonia producer, will supply “green” ammonia via an electrolysis process using hydroelectricity.

“We are really excited about the opportunity ammonia as a fuel provides,” said Cato Esperø, sales director for Wärtsilä Norway. “In the near future, engines will be running with zero carbon emissions. It will happen fast. We are doing something good for the future, and this will be great news for the whole world.”

A Couple of Hurdles to Overcome

Before that wondrous future arrives, a couple of issues need to be solved. Burning ammonia may not emit carbon, but it does produce nitrogen oxides, a group of potent greenhouse gases.

Fortunately, ammonia can clean up its own NO_x emissions. In a process called selective catalytic reduction, it converts the NO_x in exhaust gases to nitrogen and water.

Ammonia cannot, however, clean up its own manufacturing. Remember when we mentioned “green ammonia”? Nearly all ammonia today derives from nonrenewable fossil fuels, and its production is far from green.

The chemical is common in nature, but usually in trace amounts. In 1909 and 1910, German chemists Fritz Haber and Carl Bosch developed a way to synthesize it on an industrial scale. The process requires a lot of hydrogen, usually from natural gas (again, nonreneweable), and a lot of energy.

“The current way we make ammonia via the Haber-Bosch method produces more CO₂ than any other chemical-making reaction,” said Emma Lovell, PhD, a chemical engineering lecturer at the University of New South Wales Sydney in Australia, as quoted in a university news release.

“In fact,” she said, “making ammonia consumes about 2% of the world’s energy and makes 1% of its CO₂—which is a huge amount if you think of all the industrial processes that occur around the globe.”

Working on Ways to Go Green

The most common green alternative technique is electrolysis using clean, renewable sources like hydro, wind, or solar. Running electricity through water breaks it down into hydrogen and oxygen. The hydrogen is then combined with nitrogen to form ammonia. CF Industries, another giant ammonia manufacturer, plans a pilot electrolysis project at its flagship plant in Donaldsonville, Louisiana.

Lovell and other chemical engineers at UNSW Sydney and the University of Sydney are trying a different approach involving air, water, and renewable electricity. They published a paper about it on January 19 in the journal Energy & Environmental Science.

“The way that we did it does not rely on fossil fuel resources nor emit CO₂,” Lovell said. “And once it becomes available commercially, the technology could be used to produce ammonia directly on-site and on demand. Farmers could even do this on location using our technology to make fertilizer. Which means we negate the need for storage and transport.”

Those and other new technologies need a lot of work. “To make [green] ammonia is not hard,” said Grigorii Soloveichik, who works for a US Department of Energy renewable-fuels program. “Making it economically on a large scale is hard.”

A Surplus of Clean, Renewable Energy

At least the clean, renewable electricity may be available. Some parts of the world already have a surplus. During sunny spring and summer days, for example, California produces more solar power than needed. Electrical grid operators “curtail” the excess by reducing solar output.

What if that wasted electricity got diverted to produce ammonia? The ammonia could even replace coal or natural gas at conventional power plants. JERA, the largest power generation company in Japan, has announced plans to “co-fire” coal plants with small amounts of ammonia. It hopes to gradually increase the percentage until, sometime in the 2040s, the plants run on 100% ammonia.

Each ammonia molecule consists of 1 nitrogen atom and 3 hydrogen atoms. Hydrogen itself could fuel everything from electric power plants and cargo ships to buses, trucks, trains, and airplanes. Toyota just announced the second generation of its hydrogen fuel cell car, the Mirai, which debuted in 2016.

When hydrogen burns, it emits just water and, usually, small amounts of nitrogen oxides. When used in a fuel cell, it emits only water.

However, hydrogen is usually made from nonrenewable fossil fuels. Producing green hydrogen from water suffers from the same problems as producing green ammonia: it’s expensive and not (yet) practical at industrial scales.

Hydrogen is also tricky to store. It’s usually either liquefied at temperatures below -252.8°C (-487°F) or highly compressed. Committing to a hydrogen economy might require a huge investment in storage and transportation.

Ammonia to the Rescue

“The bane for hydrogen fuel cells has been the lack of delivery infrastructure,” said Sossina Haile, a professor of materials science and engineering at Northwestern University’s McCormick School of Engineering, as quoted in a university news release. “It’s difficult and expensive to transport hydrogen, but an extensive ammonia delivery system already exists. There are pipelines for it. We deliver lots of ammonia all over the world for fertilizer.”

Haile led a team of researchers that developed an efficient, environmentally friendly way of converting ammonia into hydrogen. “If you give us ammonia, the electrochemical systems we developed can convert that ammonia to fuel cell-ready clean hydrogen on-site at any scale.”

That could eliminate the problem of long battery recharge times for electric vehicles. “Converting ammonia to hydrogen on-site and in a distributed way would allow you to drive into a fueling station and get pressurized hydrogen for your car,” Haile said. You would simply fill up a tank, as you do with gasoline vehicles.

“There’s also a growing interest for hydrogen fuel cells for the aviation industry because batteries are so heavy,” Haile said.

In other words, as far as the fuel-related future of ammonia concerned, the sky is literally the limit.