From fertilizer to fuel: carbon-free shipping on the horizon?

As the world strives to decarbonize, the maritime transport and shipping industry is pushing ahead with cleaner solutions and trying to find alternatives to heavy fuel oil — which has powered ships for the past century. A promising alternative is sustainably sourced ammonia, since it could offer zero or near-zero carbon solutions for maritime transport.

Shipping is currently responsible for 3% of global greenhouse-gas emissions. But growing demand could see that figure reach 10–13% within a few decades if nothing was done to mitigate emissions.

In response to calls to reduce emissions, the United Nations’ International Maritime Organization revised its clean shipping targets, which commits the industry to uptake of zero and near-zero fuels by 2030, and net-zero greenhouse-gas emissions by 2050. The organization has also set goals to cut emissions by at least 20% by 2030 and 70% by 2040 compared to 2008 levels.

Achieving these goals is a complex undertaking. Since no single fuel can be a complete solution, ship owners and designers are investing in various new fuels as alternatives to heavy fuel oil. Among these alternative fuels, ammonia is particularly promising.

The long-term goal is to use to develop commercially viable, zero-carbon methods to produce ‘green ammonia’. An attractive way is to use sunlight to split water and then combine the resulting hydrogen with nitrogen. But it is also critical to design ships that can run on ammonia — a focus of engineers at Nippon Yusen Kaisha Line (NYK Line).

Benefits of ammonia

Ammonia is used in a wide range of applications, by far the largest of which is as a fertilizer for agriculture. Consequently, a large industry has developed surrounding the production and distribution of ammonia. Many countries with low renewable energy sources are also looking at using ammonia to generate thermal power.

It has other merits too. “Ammonia doesn’t emit carbon when it burns,” says Tetsuya Kakinuma, Manager of the Green Technology Team, in NYK Line’s Technical Group, which is based in Tokyo. “Compared with hydrogen — another fuel with the potential for zero emissions — ammonia is easier to handle in terms of its boiling point and volume per calorific value.”

NYK Line is focusing on developing ammonia as a fuel for ships plying seas and coastal waters. While there is a long history of using ammonia on land, it has never been used as a maritime fuel.

In a 12.3-billion-yen (US$82.4 million) project supported by the Japanese government’s Green Innovation Fund, NYK Line is now leading a consortium to look into the adoption of ammonia in this context. This consortium includes shipbuilder Nihon Shipyard, ship classification society ClassNK, marine-engine licensor IHI Power Systems Co. and Japan Engine Corp.

The consortium’s first goal is to develop a commercial tugboat that runs on ammonia. Called A-Tug, it will enter service in the harbour of Yokohama city in 2024, where it will service commercial vessels.

Following this, the group hopes to take the technology to the high seas with the development of a new ‘ammonia-fueled ammonia-gas carrier’ (AFAGC) that will begin operation in 2026. The ambitious project aims to demonstrate that ammonia can be a safe and practical fuel for ships.

“The A-Tug will have an output of 3 megawatts, and to achieve that kind of power within the limited space on a tugboat requires an internal combustion engine,” says Kakinuma. “It will be the first of its kind in the world amid a global race to produce ammonia-powered vessels.”

Addressing challenges

Developing ammonia as a sustainable fuel is not without its challenges. For one thing, making ammonia using traditional non-renewable methods without carbon dioxide capture and storage produces significant greenhouse gases because nitrogen from the air must be combined with hydrogen from natural gas or coal.

However, green ammonia made through solar- or wind-powered electrolysis of water can be produced without emission of greenhouse gases. It can then be used to store and ship renewable energy much like traditional fossil fuels, and benefitting from the existing global energy infrastructure.

An additional challenge is that low amounts of nitrous oxide may be produced when ammonia is burned. The main combustion products of ammonia are nitrogen and hydrogen, but under certain conditions nitrous oxide can be produced in small amounts. This is a problem because, per weight, nitrous oxide contributes 265 times more to global warming than carbon dioxide. New combustion technology is thus needed to minimize these emissions and make ammonia truly clean.

“Our partner Japan Engine has patented technology that allows ammonia to burn properly and minimizes the release of nitrous oxide and nitrogen oxides,” says Takuya Matsumoto, deputy general manager of the Technical Group at NYK Line.

There is also the problem of ammonia’s toxicity. Exposure to even small amounts of ammonia can be poisonous or fatal, so NYK is working with its partners to rethink the design of ammonia engines and engine rooms, and the approach to operations and maintenance. For instance, engineers routinely enter engine rooms to monitor conditions, but with an ammonia-powered vessel, engineers will have to enter the engine room only when necessary and with appropriate protective equipment. The engine rooms will be equipped with escape routes.

“Toxicity is the one of the most challenging aspects of ammonia, so we’re focusing on safety first on board,” says Yasushi Yamamoto, general manager of the Technical Group at NYK Line. “We’re now collaborating with ClassNK, and having detailed discussions about how to develop safe ammonia-powered vessels.”

Moving forward

The development of the two vessels is proceeding. In April 2023, IHI Power Systems Company tested a four-stroke ammonia engine with 80% ammonia co-firing, the first achievement of its kind in the world. In October 2023, NYK Line subsidiary Keihin Dock Co. began modifications to the liquefied-natural-gas tugboat, which will be refashioned as A-Tug. Meanwhile for the AFAGC, Japan Engine Corporation has begun test combustion of ammonia in a large, low-speed, two-stroke engine, also the first of its kind. ClassNK approved both vessels in principle in 2022.

The synthesis of ammonia just over a century ago sparked an agricultural revolution that helped feed the planet and increase the human population. Ammonia now stands at the threshold of a similar transformation. If it can be harnessed as a green fuel for shipping, it could help significantly reduce global greenhouse-gas emissions. The A-Tug and AFAGC are two major steps towards realizing that goal.