AMF #14 - Ammonia as a Marine Fuel: Technical Considerations

1. Introduction

Ammonia (NH3) has emerged as a promising alternative fuel for the maritime industry due to its potential to reduce greenhouse gas emissions. However, its adoption as a marine fuel requires addressing several technical challenges and considerations, including:

1. Development of ammonia-compatible engines or retrofitting existing engines to handle the unique combustion characteristics of ammonia, such as its low flame speed and temperature.
2. Implementation of robust leak detection, ventilation, and safety systems to mitigate the risks associated with ammonia's toxicity and potential for forming explosive atmospheres.
3. Training and education of crew members on the safe handling, storage, and use of ammonia as a marine fuel, including emergency response procedures.
4. Establishment of a comprehensive supply chain and bunkering infrastructure for ammonia, including production, transportation, and storage facilities.

Ammonia (NH3) is a gaseous compound at atmospheric pressure and temperatures above -33.3°C. Its equilibrium points between gas and liquid phases occur at specific pressure and temperature combinations, such as 10.25 bar at 25°C, 11.67 bar at 30°C, 15.56 bar at 40°C, and 20.34 bar at 50°C. This means that ammonia can be stored in a liquefied form by either cooling, pressurization, or a combination of both methods. Gaseous ammonia is significantly lighter than air, with a density of 0.696 g/m3 compared to 1.225 kg/m3 for air.

To store ammonia as a marine fuel, specialized refrigerated tanks or pressurized tanks are required. Refrigerated tanks maintain ammonia in a liquid state at around -33°C and slightly above atmospheric pressure, while pressurized tanks store ammonia as a liquefied gas at ambient temperatures but under high pressure, typically around 10-20 bar. Both storage methods present challenges in terms of insulation, material compatibility, and safety considerations.

Ammonia is highly soluble in water, with a solubility of 340 g/l at 25°C, creating an alkaline solution with a pH of 11.3 for a 1M solution (approximately 17 g ammonia per liter of water).

Ammonia is challenging to ignite, with a minimum ignition energy generally estimated to be in the range of 12-50 mJ, compared to hydrogen's 0.016 mJ. It has a low flame speed of 0.07 m/s and a low flame temperature. These properties, combined with the potential dependence of the flashpoint on the method used to determine it (e.g., ISO 1523, ISO 2719, ISO 2592, ISO 3679, ISO 13736), have introduced uncertainty in determining its flashpoint, with reported values ranging from 11°C to 650°C.

2. Risks and Hazards of Ammonia as a Marine Fuel

The use of ammonia as a marine fuel presents several risks and hazards that must be carefully addressed to ensure safe operations these include:

2.1 Toxicity

Ammonia is highly toxic to humans and marine life. In case of a release, it can pose severe health risks to both shipboard personnel and nearby populations. According to the National Institute for Occupational Safety and Health (NIOSH), the Recommended Exposure Limit (REL) for ammonia is 25 ppm averaged over an 8-hour workday, with a maximum allowable Short Term Exposure Level (STEL) of 35 ppm during any 15-minute period, and an Immediately Dangerous to Life and Health (IDLH) value of 300 ppm.

For more information refer to AMF #03 - Understanding Ammonia's Toxicity as Marine Fuel .

2.2 Explosion Hazard

Despite the uncertainty surrounding its flashpoint, it is well-established that ammonia can create an explosive atmosphere when its concentration in the air is between 15% (Lower Explosive Limit, LEL) and 28% (Upper Explosive Limit, UEL). Therefore, precautions should be taken to prevent the formation of both toxic and explosive atmospheres for its safe use as a fuel, regardless of the definition of a low flashpoint fuel given in SOLAS regulation II-1/2.30.

2.3 Low Temperature and Frostbite Hazards

For marine applications, ammonia is typically stored as a liquefied gas at a cryogenic temperature of around -33°C (-27.4°F) under atmospheric pressure. While not as extremely low as some other cryogenic fluids, this temperature still poses a risk of frostbite and cold burns to personnel handling the ammonia fuel systems. Appropriate personal protective equipment (PPE), such as insulated gloves and face shields, must be worn when working with cryogenic ammonia storage tanks, piping, and transfer lines.

The insulated storage tanks and piping systems are designed with specialized materials like polyurethane foam, aluminum cladding, and load-bearing foam glass to maintain the required temperature and prevent heat ingress.

2.4 Corrosion

Ammonia is corrosive to certain materials, especially copper and its alloys, which necessitates careful material selection and compatibility considerations for storage tanks, piping systems, and engine components. Stainless steel, aluminum, and certain types of plastics are generally considered suitable for handling ammonia, but compatibility testing and proper material selection are crucial to ensure the safe and reliable operation of ammonia-fueled systems.

2.5 Invisible Flame Characteristics

Pure ammonia-air flames have a faint blue color that is visible to the naked eye. The blue color in ammonia flames is attributed to the chemiluminescence emission from NH2 radicals reacting with water to produce visible light around 630 nm.

However, ammonia flames are less luminous and have a weaker visible signature compared to hydrocarbon flames, which exhibit brighter yellow and orange colors due to soot radiation and CH radicals.

When ammonia is blended with hydrogen, the resulting ammonia-hydrogen-air flames become nearly invisible in the visible spectrum, as hydrogen combustion itself does not produce significant visible emissions.

3. Safety Considerations, Risks and Hazards

The use of ammonia as a marine fuel presents various risks and hazards across different areas of a vessel's operations, including:

1. Strict adherence to safety protocols and procedures for handling, storage, and bunkering operations, drawing from experience with existing ammonia carriers (IGC Code ships).
2. Development of ammonia-compatible engines and fuel systems, with ongoing efforts by engine manufacturers to deliver ammonia-capable engines by the end of 2024.
3. Implementation of robust leak detection, ventilation, and safety systems to mitigate the risks associated with ammonia's toxicity and potential for forming explosive atmospheres.
4. Training and education of crew members on the safe handling, storage, and use of ammonia as a marine fuel, including emergency response procedures.
5. Establishment of a comprehensive regulatory framework and guidelines for the use of ammonia as a marine fuel, addressing areas such as bunkering operations, ship design, and crew competency requirements.

Here's a breakdown of the potential hazards in each area:

3.1 Chemical Hazards

• Toxicity: Ammonia is highly toxic, posing a significant risk to human health in case of exposure.
• Corrosiveness and stress corrosion cracking (SCC): Ammonia can cause corrosion and stress corrosion cracking, particularly in carbon steels and copper-zinc alloys, which may lead to structural failures and leaks.
• Explosivity and flammability: Ammonia is flammable and can create an explosive atmosphere when its concentration in the air is between 15% (Lower Explosive Limit, LEL) and 28% (Upper Explosive Limit, UEL).

3.2 Bunkering Hazards:

• Ammonia vapor leak: Leaks of ammonia vapor during bunkering operations can pose a toxic hazard to personnel and the surrounding environment.
• Liquid ammonia leak – hose failure/loading arm: Failures in bunkering equipment, such as hoses or loading arms, can result in liquid ammonia leaks, posing a significant risk of exposure and environmental contamination.

3.3 Navigation Hazards

• Vessel collision leading to NH3 leak and fuel tank damage: In the event of a collision, ammonia fuel tanks may be damaged, leading to leaks and potential explosions or fires.
• Grounding leading to NH3 leak and fuel tank damage: Grounding incidents can also result in damage to ammonia fuel tanks, posing similar risks as collisions.

3.4 Fuel Storage Hazards

• Ammonia vapor leak: Leaks of ammonia vapor from fuel storage tanks can create toxic and potentially explosive atmospheres.
• Liquid ammonia leak: Leaks of liquid ammonia from storage tanks can lead to environmental contamination and exposure risks.

3.5 Fuel Preparation/Handling System Hazards

• Liquid ammonia leak: Leaks of liquid ammonia from fuel preparation or handling systems can pose exposure risks and environmental hazards.
• Structure damage: Failures or leaks in fuel preparation/handling systems can potentially cause structural damage to the vessel.

3.6 Fuel Management System Hazards

• Over-pressurization of tank: Improper fuel management can lead to over-pressurization of ammonia storage tanks, increasing the risk of leaks or explosions.
• Overfilling of tank: Overfilling of ammonia storage tanks can also result in leaks or other hazardous situations.

3.7 Engine Room Hazards

• Ammonia leak: Leaks of ammonia in the engine room can create toxic and potentially explosive atmospheres, posing risks to personnel and equipment.
• Exhaust explosion: Improper combustion or leaks in the exhaust system can lead to explosions or fires.
• Ammonia vapor release in secondary systems: Ammonia vapor leaks in secondary systems, such as cooling or lubrication systems, can pose exposure risks and potential equipment failures.

3.8 Accommodation Hazards

• Internal fire: Fires within the accommodation areas can pose risks to personnel and potentially lead to ammonia leaks or explosions.
• External fire: External fires near the accommodation areas can also pose similar risks.
• Ammonia leakage in accommodation: Leaks of ammonia in the accommodation areas can create toxic atmospheres and pose severe health risks to personnel.

3.9 External Risks

• Dropped objects: Dropped objects from external sources, such as cranes or other vessels, can potentially damage ammonia storage tanks or piping systems, leading to leaks or explosions.
• Cargo fire: Fires involving other cargo on board or nearby vessels can potentially impact ammonia storage or handling systems, posing risks of leaks or explosions.

4. Guidance Documents and Standards for Ammonia as a Marine Fuel

The use of ammonia as a marine fuel is a relatively new concept, and the existing regulatory framework and standards are still in the process of being developed and updated to address the unique challenges and requirements associated with this alternative fuel.

4.1 Regulatory Readiness Level

The International Convention for the Safety of Life at Sea (SOLAS) Chapter II regulates low-flashpoint fuels (< 60°C) through the following provisions:

• SOLAS Chapter II-1 Part G (low-flashpoint liquid fuel or gas) and the International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels (IGF Code); or
• SOLAS Chapter II-1 Part F (Alternative design and arrangement) – MSC.1/Circ.1212/Rev.1 and MSC.1/Circ.1455

However, the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) identifies ammonia as a toxic product and prohibits its use as a fuel.

Currently, the IGF Code does not cover ammonia as a fuel, but draft interim guidelines for the safety of ships using ammonia as fuel are under development by the International Maritime Organization (IMO).

4.2 New IACS Unified Requirement H1: Control of Ammonia Release in Ammonia-Fueled Vessels

The IACS Unified Requirement H1 (URH1) addresses the control of ammonia releases on ammonia-fueled vessels, reflecting growing interest in ammonia as an alternative marine fuel. URH1 is aligned with recommendations from the U.S. National Institute for Occupational Safety and Health (NIOSH), emphasizing the need to limit ammonia concentrations on ships to ensure safety. This requirement mandates risk assessments and gas dispersion analyses to manage potential ammonia releases effectively. The development of URH1 demonstrates the proactive approach of the IACS in addressing the specific hazards associated with ammonia, such as its high toxicity and potential for creating explosive atmospheres. Engineering Background for Technical Basis of URH1 consists of the following considerations:

• Toxicity of Ammonia: Ammonia is recognized as highly toxic to both human and aquatic life. To mitigate risks, it is crucial to design containment systems that prevent the release of ammonia under normal conditions. Exposure to ammonia vapors and the discharge of ammonia-containing effluents must be avoided.
• Special Cases of Ammonia Release: In normal conditions, there are instances where ammonia cannot be entirely contained, such as the minor vapors released during the disconnection of bunkering hoses. These cases should be identified through risk assessments. Systems should be arranged to ensure that any released ammonia in accessible areas remains below a concentration of 25 ppm, which is the NIOSH Recommended Exposure Level for long-term exposure (Time Weighted Average).
• Gas Dispersion Analysis: Currently, predicting the behavior of ammonia vapor plumes is challenging due to variable factors like quantity released, wind speed, and area obstructions. Expected concentrations in accessible areas should be demonstrated through gas dispersion analysis. Future experience may allow for standard separation distances to replace individual analyses, with revisions to the Unified Requirement (UR) as necessary.
• Abnormal and Emergency Scenarios: Ammonia is stored as a liquefied gas, either by refrigeration, compression, or both. Scenarios where ammonia cannot be contained (e.g., equipment malfunctions, collisions, fires) must be identified through risk assessments and analyzed using gas dispersion studies. Measures must be implemented to prevent exposure to dangerous concentrations (300 ppm or more) during these scenarios. Potential measures include the use of personal protective equipment (PPE), ammonia treatment systems, and designated safe zones with
• Alarm Systems: Points where ammonia is typically released, such as vent masts, must have gas detectors that trigger audible and visual alarms if ammonia concentrations exceed 300 ppm. This allows personnel to avoid or evacuate toxic areas and take refuge promptly.
• Monitoring and Safety Actions: Areas prone to ammonia leaks, like secondary enclosures and fuel preparation rooms, should be equipped with gas detection, monitoring, and alarm systems. These typically unmanned spaces should prevent releases, but if concentrations reach 300 ppm, automatic shutdown procedures (e.g., closing tank valves) should be enacted to prevent escalation.

4.3 Existing Standards

While there are no dedicated marine standards available for ammonia as a fuel, several ISO standards related to ammonia from land-based industries can provide guidance and best practices:

• ISO 5771:2008: Rubber hoses and hose assemblies for transferring anhydrous ammonia
• ISO 7103:1982: Liquefied anhydrous ammonia for industrial use – Sampling – Taking a laboratory sample
• ISO 7105:1985: Liquefied anhydrous ammonia for industrial use – Determination of water content – Karl Fischer method
• ISO 7106:1985: Liquefied anhydrous ammonia for industrial use – Determination of oil content – Gravimetric and infra-red spectrometric methods
• ISO 7108:1985: Ammonia solution for industrial use – Determination of ammonia content – Titrimetric method
• ISO 6957:1988: Copper alloys – Ammonia test for stress corrosion resistance
• ISO 7179:2016: Stationary source emissions – Determination of the mass concentration of ammonia in flue gas – Performance characteristics of automated measuring systems
• ISO 1877:2019: Stationary source emissions – Determination of the mass concentration of ammonia – Manual method

These standards cover various aspects of ammonia handling, storage, testing, and analysis, which can be adapted and applied to the maritime industry as appropriate.

5. Final Thoughts

In conclusion, ammonia's role as a marine fuel holds significant promise for reducing greenhouse gas emissions and advancing sustainable shipping practices. However, its implementation comes with substantial safety challenges due to its high toxicity and potential fire hazards. The IACS Unified Requirement H1 marks a crucial step forward, outlining comprehensive measures to manage ammonia releases on vessels. These measures emphasize the importance of designing containment systems to prevent ammonia leakage under normal conditions, and implementing risk assessments to manage unavoidable releases, ensuring they stay below hazardous concentrations.

Further safety protocols include the use of advanced gas detection systems and alarm mechanisms to promptly alert crew members of any dangerous ammonia levels, particularly in areas prone to leaks. Additionally, gas dispersion analyses are essential to predict the behavior of ammonia vapors and determine safe separation distances, with ongoing revisions expected as more operational data becomes available.

Ammonia's storage in liquefied form, either through refrigeration or compression, introduces both normal and emergency scenarios where containment might fail. Such cases require robust risk assessments and tailored safety measures, including personal protective equipment (PPE), ammonia treatment systems, and the establishment of safe zones on ships.

The widespread adoption of ammonia as a marine fuel will involve continuous improvement of safety protocols, design innovations, regulatory updates and development of Ammonia specific requirements. Collaboration among industry stakeholders, regulatory bodies, and research institutions is essential in addressing safety concerns and realizing the full potential of ammonia as a sustainable and safe marine fuel.

Disclaimer: The opinions and views expressed in this article are solely those of the author and do not necessarily reflect the official position or policies of ABS. This article is not endorsed by ABS and should not be construed as an official communication from the company. While the author is an employee of ABS, this article is written in a personal capacity and does not represent ABS in any official manner. The content provided herein is for informational purposes only and should not be interpreted as professional or legal advice from ABS.