Natural gas, the primary feedstock for blue ammonia, is produced on a large scale across various regions. Methane in natural gas is processed in a reforming process that converts methane into hydrogen and CO₂. The hydrogen is separated from CO₂ and combined with nitrogen (from air) to produce ammonia. To make the ammonia ‘blue’, the CO₂ produced must be captured and stored. The current energy supply and infrastructure are sufficient for producing blue ammonia. The nitrogen found in air is abundant and replenishable, and air separation technology is industrially applied, mature, and scalable. 

Ensuring low fugitive methane emissions from the natural gas supply chain is critical for blue ammonia to have a beneficial climate impact. While natural gas can be extracted with minimal fugitive emissions, there are examples of careless practices leading to excessive emissions. Countries like Norway demonstrate effective regulation of fugitive methane emissions through schemes such as MIQ, leading to more than 5% of global liquefied natural gas (LNG) being certified. Best practices must be established and enforced to ensure credible certification of feedstocks and control of emissions. 

The feasibility of CO₂ storage is confirmed, with sufficient capacity identified. However, certification and mobilization of infrastructure for permanent CO₂ storage must be more widely deployed (see also the fuel production tile for blue ammonia). Thus, the scale-up of global CO₂  storage infrastructure is another key enabler for the blue ammonia fuel pathway. 

Blue ammonia is produced by combining nitrogen from air with hydrogen sourced from natural gas. While ammonia synthesis using natural gas is a mature technology, blue ammonia production additionally requires capture and storage of the CO₂ generated during the separation of hydrogen from natural gas (reforming). With current best-practice technology, 85-95% of these emissions can be captured. For example, autothermal reforming (ATR) generates a single, concentrated CO₂ stream that can be captured effectively, with capture rates often exceeding 90%. Several existing projects have reached a final investment decision (FID) for either transitioning from conventional ‘gray’ to blue ammonia by adding carbon capture and storage to the installed process or newbuild facilities using ATR.

Currently, permanent CO₂ storage has been identified as sufficient to support the scale required for widespread maritime use of ammonia. However, certification and mobilization of infrastructure for permanent CO₂ storage must be deployed more widely; thus, advancement of global CO₂ storage infrastructure is another key enabler for the blue ammonia fuel pathway. We do not consider the conventional use of CO₂ for enhanced oil recovery as a method for permanent CO₂ storage, as additional activities are needed to qualify/certify a complete and secure sequestration of this CO₂.

The air separation unit technology used to obtain nitrogen from air is both scalable and effective, while the Haber-Bosch process used to produce ammonia from nitrogen and hydrogen has been industrialized and scaled for over a century.

For blue ammonia to achieve a beneficial climate impact as a low-emissions fuel, three key areas must be addressed: (1) certifying the reduction of fugitive methane emissions (see also the feedstock availability tile for blue ammonia); (2) fully capturing CO₂ emissions from reforming; and (3) certifying the permanent storage of these emissions over the production facility’s operational lifetime (see also the regulation and certification tile for blue ammonia).

Overall, certifying reductions in blue ammonia’s carbon footprint toward near-zero levels compared with fossil fuels will be necessary for blue ammonia to be a viable fuel pathway.

Ammonia is handled globally as a commodity today and several ammonia bunker vessel design concepts have been developed. However, there are still gaps to be closed in developing standard processes for safe handling, storage, and bunkering of ammonia as a maritime fuel.

Development of main and auxiliary ammonia engines, as well as ammonia-powered fuel cell technologies, is still ongoing. The first dual-fuel ammonia engines, both two- and four-stroke, are commercially available, but there is no operational experience from first movers using ammonia as a fuel on ships.

Fuel cells and catalytic ammonia crackers are also under development for marine applications. Systems for ammonia emissions abatement and ammonia release management are commercially available. While solutions for managing nitrous oxide (N₂O) emissions from engines using low-pressure fuel injection still need to be developed, ammonia-fired boilers are not yet commercially available. However, ammonia-fired burners are currently used in emission control systems to help mitigate ammonia releases.

The MMMCZCS, together with partners, has released several studies and concept ship designs relating to ammonia as fuel.

Industry must address the potential safety hazards which correspond with using ammonia as an alternative fuel. Because ammonia is highly toxic, onboard safety and operations present a crucial challenge for this fuel pathway. Accordingly, risk assessments and their impact on vessel design and cost are key areas of investigation to enable maturation of this pathway. Onboard safety and operations are crucial for a successful adoption of ammonia-fueled vessels.

Currently, liquefied petroleum gas (LPG) carriers handle the safe management of ammonia as a cargo; however, a vessel fueled by ammonia will introduce different risks, including crew exposure to ammonia leakages or emissions. Understanding risks to crew and the safeguards that can be implemented to reduce these risks is therefore paramount.

To protect the crew against safety risks, comprehensive and regular training must be developed and rolled out. The maritime industry must ensure that operating procedures, safety management arrangements, and crew training keep pace with innovation. In the coming years, crew need to be trained in how to handle, store, and manage ammonia safely and in how to operate technically advanced propulsion systems.

Precautions including inherently safer ship design and increased automation will further help to maintain safety risks within tolerable limits. Risk assessments and accompanying impacts on vessel design and cost are also key areas for investigation.

As ammonia contains no carbon, its combustion does not produce CO₂ emissions. However, ammonia-fueled engines require a small quantity of pilot fuel, which may produce some CO₂ if the pilot fuel is carbon-based.

Ammonia-fueled internal combustion engines are a relatively new technology, and therefore, we have limited access to robust information about the emissions produced by these engines. Potential emissions include the greenhouse gas nitrous oxide (N₂O), toxic uncombusted nitrogen oxides (NO_x), and ammonia slip.

Recent results from trials of an ammonia-fueled two-stroke engine with high-pressure liquid injection suggest that emissions can be managed using engine tuning and a selective catalytic reduction (SCR) system. Meanwhile, a four-stroke engine with low-pressure gas injection will achieve a 70% net reduction in greenhouse gas emissions, due to formation of N₂O and higher consumption of pilot fuel oil. Emissions from ammonia-fed boilers and fuel cells are currently unknown.

The regulatory environment for ammonia as a maritime fuel still requires considerable development. For instance, there is no ammonia fuel standard (e.g., on purity), which is needed to allow the use of this fuel. Detailed prescriptive rules for ammonia as a fuel are not incorporated into the International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels (IGF Code), meaning that ammonia-fueled vessel design projects currently must undergo an alternative process for design approval by the flag state. Several classification societies have released guidelines for ammonia-fueled vessels; however, these guidelines are not unified in their approaches and requirements. The International Maritime Organization (IMO) has recently approved draft interim guidelines for the safety of ships using ammonia as fuel, but these guidelines should be considered high-level and still under review. Changes to the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) have also recently been introduced to accommodate ammonia as a fuel.

At the same time, the IMO is advancing its development of well-to-wake-based regulations to promote the use of sustainable fuels, including e-ammonia. Regulating the climate impact of fuel use from a life-cycle (tank-to-wake) perspective offers the industry the opportunity to establish sustainable fuel production and consumption patterns. Such regulation can help mitigate the risk of shifting climate impact from the downstream (tank-to-wake) segment of the value chain to the upstream (well-to-tank). This is a crucial consideration for alternative marine fuels, as a significant portion of their climate impact is associated with upstream activities.

However, many elements of these IMO regulations remain to be discussed and finalized, including certification and sustainability criteria applicable to blue ammonia. In addition, criteria concerning eligibility of captured and stored CO2 from blue ammonia’s production phase must be further evaluated.

The European Union (EU) has made progress with the introduction of the EU Emissions Trading Scheme (ETS) and the FuelEU Maritime regulation, which may promote the uptake of blue ammonia. With that said, some aspects relating to the certification of blue ammonia remain to be resolved. Also in the EU, the development of secondary legislation for producing blue ammonia is in progress, with finalization expected by end of 2024.