Ammonia Fuel Ship Looks Near, But a Bit Far Further Ahead

Hu Keyi, CSSC Jiangnan Shipbuilding

It is not an easy task for ammonia fuel powered ship to truly achieve engineering approach and commercialization, as there is still a lot of work to be done around the research and development and application of ammonia fuel power units, the innovation of containment systems, and the revision of regulations for ammonia as a marine fuel.

At present, shipyards and ship design institutes, including Jiangnan Shipbuilding, a subsidiary of China State Shipbuilding Corporation, conform to the general trend of the transformation of the shipping industry to zero carbon, launched the conceptual design of ammonia fuel ships and obtained the approval in principle (AIP) of the classification society. However, it is by no means easy for the ammonia fuel powered ships to truly achieve engineering approach and commercialization. There is still a lot of work to be done, and there is still a long way to go in ammonia fuel power device R&D application, the innovation of the containment system, and the revision of ammonia as a marine fuel regulations, etc..

Ammonia fuel ships coming soon?

Ammonia fuel is a clean energy source that emits zero carbon dioxide and sulfur oxides when ammonia is burned, excluding guide oils or other carbon-containing combustion agents. From a supply-side perspective, there is currently about 243 million tons of annual production capacity of usable ammonia in the world, while the annual production of ammonia is 180 million tons, and only about 75% of the capacity is used. China is the largest producer of ammonia, with a total of 56 million tons of synthetic ammonia in 2020.

Last November, 22 countries, including Australia, the United Kingdom and the United States, signed the Clydebank Declaration, working to promote the implementation of green corridors, committing to establish at least six two- or moreport green shipping corridors around the world by 2025. The establishment of green shipping corridors may play a demonstration role for the use of environmentally friendly fuels such as ammonia and methanol, and "open the door" for their marine use. Studies have shown that green ammonia and green methanol are the most likely zeroemission fuels to be deployed on the Asia-Europe container shipping route, one of the candidate green shipping corridors. However, although methanol engine technology is currently available, chloroamine will have a more cost advantage in this transport route.

In order to meet the changes and meet the demand, China's shipbuilding industry has carried out a lot of work in the research and development of ammonia fuel ships. For example, based on the positioning of the two mainstream ship types currently under construction, liquefied gas ships and large container ships, as well as the design and construction experience of various types of cryogenic containment systems, Jiangnan Shipbuilding has achieved results in the R&D of ammonia fuel liquefied gas ships and ammonia fuel large container ships.

In terms of liquefied gas vessels, the company upgraded the liquid ammonia-capable medium liquefied gas carrier (MGC) to ammonia fuel propulsion, and its 40,000 m3 ammonia-powered MGC ship type scheme has now received AIP certification from the classification society; and will upgrade its mainstream ship type VLGC to ammonia fuel propulsion; develop very large liquid ammonia carrier (VLAC) using ammonia-powered propulsion. In terms of large container ships, in order to cooperate with the construction of the Green Corridor for Container Transport in Asia and Europe, the company has developed a 15,000 TEU ammonia fuel very large container ship, and the midship is equipped with fuel tank that can provide Type B LNG compatible with ammonia fuel in the full range. In addition, the company's self-developed "AmmoCELL" unit combined ammonia fuel tank can be provided as an ammonia power extender, which can realize the full range application of ammonia fuel.

In the development of ammonia fuel vessels, the shipyard pays special attention to how to deploy ammonia fuel engines and gas supply system on board, and how to innovate the containment system for storing ammonia fuel, etc., and the Technical Readiness Level (TRL) of the technologies determines the commercialization process of ammonia fuel ships.

Patience required for power supply source

From the perspective of the working mechanism of the diesel engine, the main power source of the ship, whether it is the Diesel cycle or the Otto cycle, ammonia can be used as fuel, but the combustion temperature range of ammonia is relatively narrow, and a higher proportion of guide oil or combustion improver is required. Moreover, compared with other fuels, ammonia fuels have problems such as higher nitrogen oxide emissions, stronger corrosion and toxicity in addition to poor combustion. At present, some major diesel engine manufacturers have included ammonia fuel engines in their research and development plans and formulated corresponding schedules, and commercial order intentions exist for two-stroke highpressure low-speed machines. Some radical low-carbon shipping promoters have even explicitly included ammoniafueled engines in the "confirmed items" of green corridors and zero-carbon shipping implementations.

At the same time, due to the opaque R&D process and TRL of diesel engine manufacturers, the high proportion of guide oil for ammonia fuel four-stroke engines, the stress corrosion of ammonia on the cylinder block and the need for additional treatment of nitrogen oxides of ammonia, some rational shipbuilding players will inevitably have some concerns about the application of ammonia fuel on ships. As of now, LNG, LPG and liquefied ethylene (LEG) dual-fuel main engine as well as LNG dual-fuel generators have many embarkation performances, for ship designers and builders, the arrangement of ammonia fuel propulsion machinery and gas supply system and the aforementioned alternative fuel is not fundamentally different, nor is there any special difficulty, therefore, for shipyards, waiting for the development readiness level of ammonia fuel power source may be something most time-consuming.

Change expected for containment system

Liquid ammonia fuel has a specific gravity of about 0.6 tons / cubic meter, must be stored at a low temperature of minus 33 degrees Celsius or stored in the containment system at room temperature of 9 bar pressure. In order to ensure that no leakage occurs during the storage process, it is necessary to be equipped with the corresponding leakage emergency treatment device. Containment systems for liquid ammonia fuel storage must be designed within existing regulatory frameworks in accordance with the International Safety Code for Ships Using Gas or Other Low Flash Point Fuels (IGF Code) and the International Bulk Transport of Liquefied Gas Vessel Construction and Equipment Code (IGC Code). Type A, Type B and Type C tanks and membrane tanks defined in the IGC Code can theoretically be loaded with liquid ammonia.

In the application scenario of ammonia fueled large container ship, Type B tank made of aluminum alloy as an ammonia fuel containment system has great comparative advantages in terms of weight reduction, space utilization and sway resistance, especially in the case of LNG fuel tank while taking into account ammonia fuel loading, it is even more suitable than the membrane tank.

In terms of the characteristics of liquid ammonia, polymer materials that are corrosion resistant and have certain thermal insulation properties seem to be optional materials for liquid ammonia containment systems, and the combined containers of standardized units can provide safety protection for ammonia fuels. The research and development of this innovative containment system needs to be promoted through cross-industry, cross-discipline and cross-value chain mechanisms, and it is necessary to create a more friendly industrial ecosystem for innovation advocates, and this is not achieved overnight.

Laws and regulations must be changed

For the safety protection of ammonia fuel, the toxicity of ammonia fuel should also be considered. Low concentrations of ammonia can irritate people's eyes, lungs and skin, and direct contact with high concentrations of ammonia can be immediately lifethreatening. In view of the circumstances, existing regulations do not allow liquid ammonia to be used as a fuel.

Liquid ammonia is currently transported on semi-cold and fully cold LGCs and unloaded in a dedicated chemical storage area or ammonia storage and transport facility at the receiving port. Under the framework of the IGC Code, liquid ammonia carriers cannot use cargo as fuel, and the IGF Code does not have safety technical provisions for ammonia fuels and no clear development plans. It is worth noting that the cryogenic containment system defined in the IGC Code and the IGF Code requires a secondary divisional bulkhead for Type A and Type B independent tanks, the original intention of which is to prevent the failure and damage of the hull structure by low temperature leaks. However, the protective effect of this measure on ammonia toxicity after ammonia leakage is not obvious.

At present, some international classification societies have formulated guidelines for the application of ammonia fuel for ships, and it is expected that the revision of the IGC Code and the IGF Code will be on the agenda as ammonia plays an increasingly important role in the zero-carbon transformation and green corridor promotion of the shipping industry. Objectively speaking, it is not difficult to revise the regulations on the application of ammonia as fuel, but the choice faced by the maritime community is whether to carry out a comprehensive upgrade covering the innovation of tank type, breakthroughs in materials for containment systems, toxicity protection, etc., or a simple upgrade based on the provisions of the LNG dual fuel rule. These need to be clarified as soon as possible.