Ammonia as a marine fuel: scientific publications
Ammonia as a marine fuel has increasingly become a focal point of scientific research, driven by an urgent need for sustainable and low-carbon alternative fuels within the maritime industry. Over the past decade, there has been a significant rise in publications exploring the potential of ammonia, reflecting its growing importance in the global push toward decarbonization. This surge in research is not only widespread across multiple countries, but also gaining momentum, as indicated by the substantial increase in the number of studies, particularly within the last few years.
Figure B62 presents the number of scientific publications related to ammonia as a marine fuel from 2010 to 2024. Data reveal a steady increase in research activity over time, with a significant rise starting around 2018. This upward trend likely reflects growing interest and urgency in finding alternative, sustainable marine fuels as the maritime industry faces increasing pressure to decarbonize. The peak in 2023, with over 200 documents, marks the highest level of research output in this field. However, there was a notable decline in 2024, which could indicate either a temporary dip in research activity or a shift toward application and implementation phases after intensive initial research.
The geographical distribution of scientific publications reveals that major industrialized nations like the United States, China, Japan and the United Kingdom are leading the way, underscoring the global recognition of ammonia’s potential to transform maritime fuel systems (Figure B63). This expanding body of literature highlights both the challenges and opportunities associated with ammonia as a marine fuel, positioning it as a key player in the future of sustainable maritime transport.
China and the United States are leading contributors, each with close to 225 documents, indicating their strong focus on this emerging technology. The United Kingdom and Japan follow, showing substantial research efforts as well. The Republic of Korea, Germany and Italy are also notable contributors, reflecting a widespread global interest in this technology. The presence of other countries like Canada, India and the Kingdom of the Netherlands, although with fewer publications, underscores the global recognition of ammonia as a marine fuel's potential.
Ammonia as a marine fuel: patent data
Patenting activity in the field of ammonia as a marine fuel has recently picked up speed. From only 33 patent family publications in 2020, the number of patent publications jumped to 223 in 2023 (Figure B64).
At the country level, most patent families were published by inventors from the Republic of Korea and China (Figure B65).
Ammonia as a marine fuel: patent examples
Interest in green ammonia, especially, has increased over the past years. Yara, a global leader in crop nutrition and industrial solutions, is heavily involved in the development and production of green ammonia. The company has made significant investment in green ammonia production, using renewable electricity to produce hydrogen through electrolysis, which is then combined with nitrogen to create green ammonia.
The company’s patent EP4211076A1 from 2020 describes a dual pressure plant for the production of nitric acid that integrates advanced components to enhance efficiency and sustainability. The process begins with air being compressed to a low pressure, which is then mixed with ammonia and oxidized to produce a low-pressure mixture of nitrogen oxides (NOx) and steam. This mixture is then compressed to a higher pressure, where it reacts with water in an absorber unit to produce nitric acid and dissolved nitrogen oxides. A high-pressure bleacher unit strips these nitrogen oxides from the nitric acid using an oxygen-rich gas provided by a high-pressure water electrolyzer. The gas, now loaded with NOx, is recycled back into the system, optimizing efficiency and reducing energy consumption.
The inclusion of a high-pressure water electrolyzer is particularly significant as it generates the oxygen-rich gas used in the stripping process, potentially lowering the energy requirements of the entire plant. Additionally, the plant may include a flash vessel to further enhance gas recovery and recycling, making the overall process more economical and environmentally friendly.
Vessel designs play a vital role in respect to the leakage and toxicity concerns associated with ammonia. Nihon Shipyard Co., Ltd., a prominent Japanese shipbuilding company, is actively involved in the development of ammonia-powered ships as part of its efforts to contribute to the global transition toward greener maritime transport. Nihon Shipyard's patent WO2023210390A1 from 2023 for an ammonia-fueled ship is a significant innovation that addresses the critical safety challenges associated with using ammonia as a marine fuel, particularly its toxicity and corrosiveness. The design features an advanced engine room layout that is divided into several distinct areas, according to the risk of ammonia gas leakage. These areas are separated by specially designed partitions that prevent the spread of ammonia gas, effectively containing any potential leakage within specific zones and minimizing the risk to other parts of the ship.
The partitions can be configured to either completely seal off areas or to only partition the upper spaces, depending on the level of risk and operational requirements. Additionally, in an emergency, these partitions are designed to allow water to pass through, providing a means of controling or neutralizing leakages.
The engine room is thoughtfully divided into specific regions; for example, there is one that houses the generator using ammonia as fuel and another that contains the engine. A key safety feature is the inclusion of a designated area through which ammonia fuel does not pass, thereby further reducing the risk of critical components being exposed to ammonia.
To further mitigate the risk of ammonia leakage, the patent proposes that areas with a higher likelihood of leakages be maintained at a lower internal pressure compared to those at a lower risk. This pressure differential helps contain any ammonia gas within high-risk zones, preventing it from spreading. Each region is also equipped with an independent ventilation system designed to effectively remove ammonia from the air. Ventilation systems are optimized with exhaust ports positioned higher than air supply ports, so as to ensure the efficient removal of lighter ammonia gas, complemented by ventilation fans that actively manage air circulation.
This patent plays a crucial role in advancing the use of green ammonia as a marine fuel by addressing the significant safety concerns that have been a barrier to its adoption. By implementing these advanced safety features, Nihon Shipyard is making it feasible to safely operate ammonia-fueled ships, thereby supporting the broader transition to this zero-carbon fuel. As the maritime industry seeks to reduce its carbon footprint, innovations like this patent are essential for making ammonia a viable and safe alternative to traditional fossil fuels, facilitating the industry's shift toward sustainable energy sources.