Fuels such as liquefied natural gas, methanol and hydrogen are being considered to decarbonize the shipping industry. But some experts believe green ammonia also has potential due to its unique makeup.
Green ammonia, or e-ammonia, is produced by combining nitrogen from the air with green hydrogen, which is produced using renewable electricity-powered electrolyzers that split water into hydrogen and oxygen.
Unlike e-methanol and LNG, ammonia contains no carbon molecules, so if ammonia is produced using renewable electricity, it does not result in carbon emissions.
“Other than crude oil and crude oil products, ammonia is one of the most produced chemicals in the world,” Torben Nørgaard, head of energy and fuels at Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping, told FreightWaves. So the global supply chain and infrastructure for ammonia are in place already, unlike hydrogen.
Ammonia is considered a hydrogen carrier. Hydrogen is not being widely considered as a fuel for long-distance shipping because it is very expensive to store at cryogenic temperatures and is much less energy dense than ammonia.
But there is not currently an ammonia-powered engine for shipping on the market, and the fuel raises safety concerns.
Designing an ammonia-powered engine
Augsburg, Germany-based Marine propulsion and engine designer Man Energy Solutions is developing a dual-fuel ammonia engine for marine use.
“There’s no precedent for running big engines on ammonia. … It’s the fuel itself and the combustion process that is simply unknown,” Peter Kirkeby, promotion manager and business development of dual fuel engines at Man Energy Solutions, told FreightWaves.
The company is conducting its first full-scale two-stroke dual-fuel ammonia engine test at its headquarters for development of two-stroke engines in Copenhagen, Denmark, this summer. After the testing is complete, Man Energy will design engine iterations. This should lead to delivery of the first ammonia engine to a shipyard by the end of 2024.
Other stakeholders working on designing new-build ammonia-powered vessels “are looking at us because without the engine, designing other parts of the ship for ammonia doesn’t make a whole lot of sense,” Kirkeby said.
Considering how quickly the industry has to change and lower emissions, focusing solely on new vessel builds is not enough to meet the targets set by some organizations and companies.
Man Energy is using a modular design that does not drastically change the layout of the propulsion system, which could make it easier to retrofit existing vessels to run on ammonia and potentially speed up the green ammonia adoption process in shipping.
“By not making any fundamental changes to the propulsion layout of these ships, it actually allows shipping to adopt new fuels without having to rethink entire ship designs in an easy way and in a short period,” Kirkeby said.
Marine fuels emit a mixture of air pollutants and greenhouse gases. Compared to marine gas oil (MGO) and other fuels, ammonia emits much less particulate matter. It also emits zero sulfur dioxide, carbon monoxide, heavy metals and hydrocarbons, which can harm human health, according to a 2020 International Conference on Energy, Environment and Storage of Energy paper.
One air pollutant that is not eliminated when combusting ammonia is nitrogen oxides (NOx). NOx GHG emissions are prevalent in the transport sector, but vessels can use selective catalytic reduction equipment to reduce those emissions, the paper said.
Because ammonia contains no carbon molecules, it theoretically could be produced and combusted without any carbon emissions.
“If you want to burn something without emitting carbon dioxide, ammonia’s the answer,” Nørgaard said. “Provided that we can manage potential NOx emissions, it’s very effective in terms of decarbonizing as a fuel and as an energy carrier.”
However, Kirkeby said Man Energy’s first ammonia dual-fuel engines will reduce GHG emissions by about 95% from tank to propeller compared to engines that run on MGO.
The 5% of emissions that will remain at least in the short term are due to using a small pilot flame to ignite the ammonia. The company is currently targeting conventional diesel oil as the pilot fuel.
Kirkeby said the planned ratio of ammonia to diesel and the resulting emissions are “significantly better” than anything else that has been done or planned.
Using a reliable fuel that is well known, inexpensive and widely available such as diesel for the backup fuel in an ammonia-powered dual fuel engine is the “cheapest way to make ship propulsion redundant on board,” Kirkeby said.
Ammonia is typically stored as a liquid in a pressurized tank, a refrigerated tank or a hybrid tank. When stored in refrigerated tanks, it is cooled to a temperature of minus 28 degrees Fahrenheit, whereas hydrogen requires cryogenic storage at minus 423 degrees F, according to a paper on green ammonia by the Environmental Defense Fund (EDF).
Therefore, ammonia requires much less money and energy to liquefy and store than hydrogen.
Hydrogen requires 7.6 times more storage space than MGO, whereas ammonia requires 4.1 times more storage space, according to the EDF paper. Methanol and LNG require 2.3 times more storage space than MGO, even less than ammonia and hydrogen.
Because many sustainable alternative marine fuels have lower energy densities than MGO, sacrificing cargo space to store more fuel is a common trade-off. To accommodate increasing emissions regulations by adopting lower-emission fuels, shippers may have to choose between dedicating more space to fuel storage and shortening their shipping routes.
One of the biggest safety technologies for ammonia is use of double-walled pipes, which are used for other fuels such as LNG. They allow space between the inner and outer layers of the pipes for a ventilation air system, which can detect leaks easily, Kirkeby said.
Double-walled pipes and other safety procedures could be crucial to preventing what Steve Crolius, president of Carbon Neutral Consulting, called an “ammonia slip,” in which ammonia escapes into the atmosphere during production, transportation or storage.
“The safety risks associated with ammonia are well understood and manageable,” the EDF paper noted. “It is less flammable than other fuels, so it poses a lower fire risk, and risks from cryogenic burns are lower than for liquid hydrogen or LNG.”
Another safety mechanism the Man Energy team is using for its ammonia engine project is a “double block and bleed.” It separates systems and has the capability to purge areas with nitrogen that previously held ammonia. As ammonia is purged from certain areas, Man Energy’s concept captures that ammonia and prevents it from going into the atmosphere, only emitting nitrogen, Kirkeby said.
For engines and other equipment, this is important because crews will need to be able to safely troubleshoot and do maintenance.
“We take responsibility for our engine,” Kirkeby said. “We go through all of the different scenarios that might cause a dangerous situation.”
While working with manufacturers and creators of equipment that interfaces with theirs to address potential dangerous scenarios, if any safety concerns are raised, they will put a countermeasure in place for that situation.
Crolius said: “Ammonia as a chemical substance is acutely hazardous. It is not to be taken lightly at all.”
Ammonia can cause eye damage, severe skin burns and acute respiratory symptoms. It is dangerous to animals and plants as well.
Ammonia leaked from a pressurized tank could create a large cloud of toxic ammonia quickly and kill “pretty much all forms of life in close proximity,” Crolius said. It would eventually rise farther into the atmosphere and disperse since it is less dense than air.
Refrigerated ammonia would have similar impacts on marine life if it were spilled into the ocean. But in contrast to ammonia stored in pressurized tanks, it would release slower in the event of a leak and could be more easily contained, according to Crolius. He said that would give emergency responders a greater chance of limiting the harm, and he predicted that nearly all ammonia on board a ship will be in a refrigerated or hybrid tank.
Nørgaard said several safety standards and procedures are in place for producing and handling ammonia, but operating with it and combusting it on a vessel with a crew and minimal evacuation space is completely different. Safe design and operation is something that “needs to be demonstrated,” he said.
Cost of production, implementation
The cost to produce ammonia using renewable electricity is about three or four times more expensive than MGO today, Nørgaard said. Like most sustainable solutions, improving the economies of scale helps bring down costs.
Crolius said one exercise estimated the cost of green ammonia to be nearly twice the cost of gray ammonia to produce. Gray ammonia is produced using natural gas instead of renewable electricity.
An EDF financial analysis estimated that up to $6 trillion in green ammonia and renewable energy plants would be required to decarbonize about 40% of international shipping between now and 2050.
“Of the fuels available to decarbonize the maritime transport sector, green ammonia is one of the most technically feasible in the short term,” the paper noted.
Nørgaard said that some models show green ammonia adoption picking up in the mid-2030s, but it is very sensitive to the cost of renewable electricity.
Scaling and timeline
Nørgaard said decarbonizing the entire maritime industry using green ammonia would take about 500 million tons of ammonia per year, which is two and a half times more than the 180 million tons of ammonia the world currently produces annually. Therefore, one single fuel such as ammonia will “unlikely be able to decarbonize the whole sector.”
“One of the challenges related to e-ammonia, or any e-fuel, is the scale and the implementation rate,” Nørgaard said. “The scaling of this is so tremendous, it’s so significant, that it’s not done overnight.”
Scaling of green ammonia, like many e-fuels and green fuels, relies on economies of scale and the cost and availability of renewable electricity. An implemented carbon price would also help close the gap between fossil fuels and more sustainable fuels.
Crolius said shippers like Ikea and members of the Cargo Owners for Zero Emission Vessels are expressing increasing interest in green fuels. They understand how important their role is in demanding green fuels from suppliers, he said.
“It doesn’t matter whether they have any awareness of ammonia,” Crolius said. “They need to put on the pressure, and the carriers are going to find the ways to meet their customers’ demands.”
One positive impact of scaling green ammonia production is that it “presents an opportunity for developing countries around the world to attract investment in sustainable industrial growth,” the EDF paper said. It could create jobs, spur economic growth and support supply chains.
Select countries — including some developing countries — have huge potential when it comes to renewable electricity production. Nørgaard said that regions such as the Middle East, Australia and Chile, “areas where we expect the cost of electricity to come down first and dramatically,” are looking into green ammonia.
The EDF paper said, “Demand for green ammonia as a marine fuel could provide a dependable long-term revenue stream — supported by long-term supply agreements — to justify investment in large-scale renewable plants in developing nations.”
It said adoption of green ammonia would need to begin in the 2020s to reduce absolute shipping-related emissions by at least 50% by 2050, compared to 2008 levels, which is the International Maritime Organization’s current emission-reduction target.