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Nitrogen+Syngas 390 Jul-Aug 2024

Ammonia safety at sea


AMMONIA

Ammonia safety at sea

A look at the safety challenges that face developers of ammonia-powered shipping vessels before it can become used more widely as a low carbon fuel.

As the nitrogen industry begins to slowly turn its output towards lower carbon ammonia production so the interest in using it as a relatively clean fuel increases, mainly from the shipping industry. As we noted in our editorial in the previous issue, the Det Norske Veritas (DNV) count of orders for new ammonia-powered ships this year reached four in April 2024, bringing the total currently under order to nine; much smaller than methanol, LNG or conventional powered vessels, but still significant. Current projections foresee that demand from the power sector and bunkering for ammonia will account for up to 4% of total ammonia demand in 2030, and possibly to as high as 29% in 2050.

The interest from ship builders and operators is due to International Maritime Organisation (IMO) targets which aim to reduce the total greenhouse gas (GHG) emissions from international shipping by at least 50% by 2050, compared to 2008 levels. In addition, a target has been set to reduce the carbon intensity of shipping by 40% by 2030, thus emphasising the need for the rapid introduction of existing and new low carbon technologies. Ammonia has a number of characteristics which make it attractive as an alternative fuel, from producing no carbon emissions when burned, to a relatively high octane rating of 110–130, and a small flammability range, making it relatively safe in terms of explosion risk. It also has a relatively high power-to-fuel-to-power efficiency, and there is already a large scale global distribution network in place.

It has required some re-engineering to make it feasible, however. Development of an ammonia powered ship engine has taken some time, but Finnish marine engine manufacturer Wärtsilä now commercially offers its new Ammonia 25 four stroke engine, and while MAN Energy Solutions has put back the date for the launch of its own two-stroke ammonia marine engine from 2024 to 2027, it remains confident that it will be able to offer retrofit conversions to existing two-stroke engines from that date. Itochu and Vopak are looking at ammonia bunker fuel infrastructure for Singapore, and Japanese shipping company NYK Line, shipbuilder Japan Marine United Corporation (JMU), and ClassNK are developing an ammonia-fuelled gas carrier, in addition to an ammonia floating storage and regasification barge.

Challenges

But ammonia does face several challenges before it becomes more widely taken up by the shipping industry, however. On a technical level, ammonia combustion generates nitrous oxides which must be scrubbed from exhausts, and it must be stored as a refrigerated and/or pressurised liquid. Green ammonia also remains extremely costly, although if some of the large carbon capture and storage projects currently under development come to fruition, large volumes of blue ammonia should be available at a relatively competitive cost with conventional shipping fuels like diesel. But the largest concern for ship owners, operators and ports, is safety.

Ammonia safety at sea

Ammonia chiefly presents three main hazards; toxicity, fire risk, and corrosion risk. Corrosiveness is perhaps the least immediately concerning from a safety perspective, but complicates ammonia operations. Ammonia reacts with water to form ammonium hydroxide, which is strongly alkaline and which can corrode metals and cause embrittlement of plastics or rubber, damaging components and possibly leading to failures. This necessitates proper storage and handling procedures, as well as the use of protective coatings and materials that are resistant to alkaline substances.

Flammability

Ammonia burns – that is the whole point of using it as a fuel. However, the autoignition temperature of ammonia under atmospheric conditions is 651°C, and it requires considerable energy to auto-ignite. The main flammability hazard comes from dispersions of ammonia vapour in air. Ammonia is lighter than air and diffuses relatively quickly, especially if released at high pressure. Without ignition, ammonia dissipates by vaporisation and forms a vapour cloud that disperses in the air. However, in the event of ignition, there are four potential risk scenarios for ammonia, including a vapour cloud flash fire, jet fire, pool fire, and vapour cloud explosion. Compared to LNG and LPG, ammonia has a lower risk of fire due to its lower burning rate; liquid ammonia does not burn continuously, as the heat emitted from the flames is not sufficient to reach the liquid, but if an external heat source is present, enough ammonia can vaporise to keep the fire burning.

The use of water spray, fog, or foam can be effective in extinguishing large ammonia flames, while dry chemicals or CO2 are more appropriate for small ammonia fires. However, it is important to avoid directing a water jet directly towards a leak or liquid ammonia source as this may cause a hazardous reaction. Responders must wear protective equipment with an oxygen supply.

Toxicity

The main concern of an ammonia release is its toxicity. Ammonia concentrations above 1700 ppm (0.17%) cause coughing and oedema, and concentrations of 25004500 ppm (0.25-0.45%) can be fatal in approximately 30 minutes. Above 0.5% concentration usually produces rapid respiratory arrest. The concentration at which the gas is immediately harmful to life or health (IDLH) is 300 ppm. The human nose can detect ammonia concentrations as low as 5ppm. This means that a low level threat can be readily identified and action taken to withdraw from the ammonia contaminated area. However, the danger can be higher on a ship due to the number of small compartments where ammonia could build up without dispersing.

Shipboard operation

Lloyd’s Register Maritime Decarbonisation Hub and the Maersk Mc-Kinney-Møller Center for Zero Carbon Shipping (MMMCZS) have produced a multi-disciplinary assessment of the design challenges and risks to seafaring personnel from the use of ammonia as a marine fuel. The analysts chose three ammonia-fuelled reference ship designs to model, including a 3,500 TEU feeder container ship with a liquid ammonia tank at ambient pressure and a temperature of minus 33°C; an 80-100,000 dwt bulk carrier with a fully pressurised ammonia fuel tank at ambient temperature and a pressure of 18 bar; and a 50,000 dwt medium-range tanker with a semi-refrigerated tank on deck at a pressure of 4 bar.

The recommendations from the report were that;

  • Lower storage temperatures and pressures both reduce the safety risk from ammonia fuel. This has been borne out by other studies which show that releases from high pressure storage (>12 bar) lead to the formation of a visible, aerosol gas cloud which is heavier than air with ammonia concentrations >20,000 ppm (2%). Ship fuel storage is likely to be lower pressure (ca 4 bar), at which the risk of gas cloud formation does exist but at a far reduced level. Conversely, a release of fully refrigerated ammonia presents a more benign scenario, where a slowly-evaporating pool produces a fast-dissipating, lighter-than-air cloud, although at sea there is the risk that release onto the sea surface will result in vigorous evaporation, as it reacts both chemically and thermally with the water.
  • The fuel preparation room should be divided into two or more separate spaces containing different groups of equipment that could leak ammonia.
  • Access to and length of time spent in spaces containing ammonia equipment should be minimised, monitored, and controlled.
  • Ventilation outlets from spaces containing ammonia equipment should be placed in a safe location adequately separated from areas accessed by crew to avoid accidental release of toxic concentrations of ammonia affecting personnel
  • Multiple sensors of different types should be installed to detect ammonia.
The Advario Gas Terminal at the Port of Antwerp, soon to be the site of an ammonia transfer terminal.

Containing ammonia releases is important. Secondary containment mechanisms, such as double-walled piping, used for ammonia-related equipment outside of already-restricted areas, have been proven to significantly reduce risk.

Where ammonia does leak, good ventilation of spaces containing ammonia equipment can provide mitigation of toxic effects for many smaller, but not all, potential ammonia leaks, and particularly for smaller leaks. Small ammonia concentrations or leaks will likely drive workers out of the confined space because of ammonia’s pungent smell. Due consideration should be given to additional precautions for personnel entering these spaces.

Ventilation of spaces containing ammonia equipment also reduces the risk of SOURCE: ADVARIO ammonia concentrations reaching a flammable level. Ammonia leak alarms should be installed in both controlled areas (for example, the fuel preparation room) and near potential leak sources, and the fuel system should be subject to rapid and reliable manual and automated shutdown in the event of an ammonia leak.

In its work on ammonia engines, Wärtsilä identified ammonia leak risk zones in and around ammonia engines, including: the gas inlet or liquid fuel injection system, which is mitigated by use of ventilated double wall piping, and a low pressure return line for the liquid system. Another vector for exposure was unburnt ammonia in the exhaust at very low levels, which can be removed along with NOx in the catalytic absorber. Wärtsilä is developing PPE use profiles for working with and near marine ammonia engines. Ammonia handling PPE is already well-defined, both in regulatory terms and in commercial availability. ASTI details levels of protection from A to C, with the minimum level being an “ASTI vest”, including a detector, goggles and respiratory mask, likely to be worn in an engine room under normal operating conditions.

Bunkering

Outside of day to day ship operation, the other major area subject to hazards is storage and transfer of ammonia fuel. Compared to conventional liquid fuels, ammonia bunkering is associated with possible risks related to cryogenic liquid/high-pressure liquid transfer and vapour return. It is relatively easy to imagine an ammonia fuel line becoming disconnected during fuel transfer, resulting in potentially lethal concentrations of ammonia at the dockside, and the potential for ignition.

A Korean joint study by the Korea Maritime Transportation Safety Authority and research partners looked at safety in ammonia bunkering based on an analysis of 118 research papers and 50 regulations and guidelines. It considered experience gathered from ammonia’s prior use in chemical plants, large refrigeration units, and at farms. According to US statistics, from 1985 to 2019, there were approximately 71 fatal accidents involving anhydrous ammonia. The primary causes of deaths and injuries were identified as either fire or inhalation. Accidents involving ammonia release are generally due to human error, operational mistakes, and maintenance and inspection failures during storage tank operations, the bunkering process, and pipeline operations.

One of the chief mitigation steps against accidents during bunkering is the imposition of a safety zone; a designated area surrounding the bunkering operation where access is restricted and the necessary safety measures are implemented. However, the study found delineating such a zone problematic due to the number of factors which can influence an ammonia release, including the proximity of other vessels or structures, weather conditions, and potential environmental impacts, and factors such as the direction of a leak, leak area configuration, wind direction, ship structure, and cargo state all affect the determination of a safe zone. Because ammonia bunkering is a fairly new thing, there are currently no well-defined industry guidelines, regulations, or standards in place regarding safety zones.

Weighing up deterministic and risk-based methods in delineating the area of a safety zone, the study concluded that a hybrid approach yielded a more consistent safety zone design compared to the deterministic approach across various bunkering situations, and highlighted the usefulness of combining deterministic and risk-based elements in safety zone planning to create a more adaptable and robust approach.

Overall, their safety assessment of the ammonia bunkering process had the following recommendations;

  • Strict safety regulations must be followed for the storage and handling of ammonia due to its hazardous nature. Storage containers for ammonia must be specifically designed and certified for this purpose. Trained personnel who wear suitable protective gear are responsible for handling and transferring ammonia. Appropriate personal protective equipment (PPE) and safety equipment, such as gas detectors, respirators, protective clothing, and eye and face protection, should be used.
  • It is crucial to plan and carry out the bunkering process meticulously with trained personnel. The crew of the receiving vessel should be notified about the procedure and any necessary safety precautions. The process should be monitored closely to ensure it is executed safely.
  • A safety zone should be established. To prevent unauthorized access, it is necessary to place clear signs and barriers.
  • Proper ventilation is essential during the bunkering process to avoid the accumulation of ammonia vapours. The area where the bunkering is carried out must have adequate ventilation to disperse any leaks or spills swiftly.
  • In the event of an accident or spill during bunkering, there must be emergency response plans in place. The crew should be trained to handle an ammonia spill, and necessary equipment, such as personal protective gear and spill containment equipment, should be easily accessible.
  • Additionally, all equipment, pipelines, and storage tanks used during bunkering should be properly maintained and inspected.

Fuel quality specifications

A final area for consideration is the development of fuel quality specifications for ammonia. These relate particularly to its water content. Ammonia absorbs water easily, and although a small amount of water in ammonia (up to 0.5%) is needed to improve the safety of storage by reducing the risk of stress corrosion cracking (SCC). Too much water will lead to poor combustion. Commercial ammonia is available at range from 99.5% to 99.995% purity, with most bulk chemical/agricultural grade ammonia at 99.5% purity – sufficient for fuel use, but bunkering will need to control water ingress into ammonia storage.

MAN Energy Solutions has developed its own preliminary guidance for ammonia going into its dual-fuel ammonia engines once these reach the market. It notes that particles in the fuel could come from particles breaking free from catalyst used in ammonia production and from transportation of the ammonia. This raises a consideration about the need for the ammonia fuel standard to control particulate matter, and possible requirements for onboard fuel filtering between fuel tank and engine.

Evolving regulations

While ammonia has been carried safely as freight for many years, the shipping industry is still adjusting to its use as a fuel. The International Maritime Organisation has been playing its part, and has reported “significant progress” on the development of draft interim guidelines for the safety of ships using ammonia as fuel. The Sub-Committee on Carriage of Cargoes and Containers (CCC) has agreed to convene a working group from 9 -13 September 2024, which will aim to finalise these guidelines for approval by the IMO’s Maritime Safety Committee in December 2024.

The IMO’s International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (‘IGC Code’) currently states that toxic cargoes shall not be used as fuels on gas-carrying vessels, which prevents the use of ammonia. However, last September the CCC agreed to develop guidelines to ensure ships using ammonia and other toxic cargoes as fuel are designed and operated to the same level of safety as a ship carrying and using natural gas as fuel. As for ships not carrying ammonia, Lloyd’s Register published rules for ammonia-fuelled non-gas carrier vessels in July 2023, based on the alternative risk-based design pathway allowed for under the IGF Code, and hopes to publish Rules for Ammonia Gas Carriers consuming its own cargo in July 2024. Rules for gas carriers using ammonia as fuel will be published once IMO requirements and any interim prescriptive requirements become clear.

In general, none of the barriers to ammonia’s commercialisation as a bunker fuel – technical/engineering, cost, or regulatory – appear to be insuperable, and there is considerable will to overcome them in the industry. However, developing a new regulatory structure is not a fast process, and it remains to be seen whether this will impede the uptake of this promising use for ammonia. n

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