The decarbonization of maritime transport is a key challenge in the transition toward a more sustainable sector. As international regulations become stricter, the shipping industry is seeking alternative fuels that can drastically reduce greenhouse gas emissions. In this context, DNV, one of the leading classification societies and technical consultancies in the maritime industry, has recently conducted a comprehensive analysis on the use of ammonia and hydrogen as marine fuels.
Therefore, we will conduct a detailed assessment of the feasibility of these fuels, addressing their advantages, disadvantages, technical implications, and impact on port infrastructure. DNV has developed this report based on safety studies, technical tests, and its expertise in certifying the first vessels powered by these types of fuels. Additionally, critical regulatory and safety aspects have been considered to ensure the efficient and safe implementation of these technologies in the shipping industry.
We will review the key findings of this renowned company’s study, highlighting the challenges and opportunities that ammonia and hydrogen present as future fuels, while also introducing LNG into the equation.
ALTERNATIVE FUELS
Both ammonia (NH₃) and hydrogen (H₂) have been identified as viable options for reducing emissions in the maritime sector. These alternatives can be used in fuel cells or adapted internal combustion engines. Despite their benefits and recent advancements, they still pose challenges in terms of safety, storage, and operational efficiency.
HYDROGEN
The first element of the periodic table, hydrogen, is the lightest chemical element and exists stably in diatomic molecular form (H₂). Under normal conditions, it is a colorless, odorless, and tasteless gas.
On Earth, hydrogen is highly abundant, making up approximately 75% of the universe’s matter. However, it is usually found combined with other elements, such as oxygen in water molecules or carbon in organic compounds. Therefore, it is not a fuel that can be directly extracted from nature but rather an energy carrier that must be produced.
Advantages:
- Zero CO₂ and SOₓ emissions during combustion.
- Compatible with fuel cell technology.
- Can be produced from renewable energy sources.
Disadvantages:
- Complex and bulky storage, reducing cargo space on ships.
- Liquid hydrogen requires operating temperatures of -253°C, making handling extremely challenging and imposing structural constraints on vessels.
- Due to its small molecular size, it is difficult to store and easily leaks.
- Highly flammable, with low density and high ignition potential, requiring strict safety controls.
- Very high production costs.
Currently, the first small hydrogen-fueled ships using fuel cells are in the testing phase. Hydrogen internal combustion engines are also under development.
AMMONIA
Ammonia is a chemical compound whose molecule consists of one nitrogen (N) atom and three hydrogen (H) atoms, with the formula NH₃. It is a colorless gas with a very strong odor, highly soluble in water, and easily evaporates in its liquid state.
Its storage is significantly easier than hydrogen, as it remains liquid at -33°C, whereas hydrogen requires -253°C and LNG -160°C. This represents a major difference in storage complexity. Ammonia has a higher energy density than hydrogen, facilitating operations for larger vessels. It also significantly reduces CO₂ and SOₓ emissions.
The main disadvantage is its high toxicity, making it hazardous for crews and the marine ecosystem. It emits toxic NOₓ gases, which require additional treatment. It also requires specialized port infrastructure for safe supply and handling, which is currently lacking on a global scale.
Tests with two-stroke engines using direct injection technology are still in the experimental phase. Ships with dual-fuel diesel-ammonia engines are beginning to be used.
LNG (Liquefied Natural Gas)
Liquefied Natural Gas (LNG) is natural gas in a liquid state at a temperature of -160°C, making it a cryogenic liquid. The advantage of the liquid state is its reduced volume—each liter of LNG produces approximately 570 liters of gaseous natural gas at ambient temperature. LNG is composed of about 95% methane (CH₄) and smaller proportions of ethane, propane, butane, nitrogen, and carbon dioxide. It is an odorless, colorless fuel that is non-toxic and non-corrosive. Natural gas is currently the purest and cleanest fossil fuel, thanks to its high hydrogen-to-carbon ratio, making it a viable transition solution.
LNG has been the preferred alternative fuel over the past decade due to its lower carbon footprint compared to traditional fossil fuels. However, it still emits CO₂ and methane, meaning it is not a definitive solution for decarbonization.
Nevertheless, it offers improvements over conventional fossil fuels by reducing CO₂ emissions by 20-30% compared to traditional fuel oil. It benefits from well-developed port infrastructure with wide availability. Additionally, LNG has lower flammability and higher operational safety compared to hydrogen.
IMPLICATIONS FOR PORT INFRASTRUCTURE
The use of these fuels entails a significant transformation of port infrastructure.
From a safety perspective, handling hydrogen and ammonia requires strict protocols to prevent leaks and explosions. Storage tanks must be cryogenic for hydrogen and pressurized for ammonia. For bunkering services involving these fuels, international regulations still need to be established to ensure safe refueling procedures.
REGULATORY CHALLENGES
The lack of specific regulations for these fuels remains a significant issue. The current International Maritime Organization (IMO) regulations are not yet fully adapted to accommodate these alternative fuels.
Additionally, their use requires specialized training, meaning that crews must undergo specific instruction to handle these fuels safely. Therefore, new design and operational regulations are needed to minimize toxicity and explosion risks.
CONCLUSIONS
Ammonia and hydrogen represent viable alternatives for the decarbonization of maritime transport, although their full adoption will require overcoming significant technical, safety, and regulatory challenges.
While hydrogen stands out for its zero-emission potential, ammonia offers advantages in storage and energy density. Port infrastructure and international regulations must evolve to ensure a safe and efficient transition to these alternative fuels.
However, shipowners continue to face growing pressure to reduce emissions, while technical solutions, regulations, Emissions Trading Systems (ETS), and specialized port infrastructures are not progressing at a pace aligned with regulatory deadlines.
Looking at current new ship orders in shipyards, a high percentage of them are equipped with dual-fuel propulsion systems using LNG. Within the industry, there is a widespread commitment to reducing emissions, but achieving this goal is neither as easy nor as fast as desired to meet the imposed deadlines. This represents a significant challenge for shipping companies and shipowners, who are striving to keep up with the future.
