Decarbonizing shipping is an environmental imperative and an emerging area of innovation, reflecting the industry’s shift toward alternative fuels, sources Britannia.
Risk Assessment
As part of their decision-making, shipowners must perform due diligence, including a thorough risk identification and assessment when choosing an alternative fuel. As part of this assessment, several stakeholders will need to be consulted, for example, the engine maker, fuel supplier, classification society, hull & machinery insurers, and the ship’s flag state.
The considerations to be taken include
- SUITABILITY AND IMPACT ON THE ON-BOARD ENGINES
The engine maker should be consulted to determine whether the onboard engines are suitable for consuming the selected alternative fuel or whether the engine will require any retrofitting.
- FUEL MANAGEMENT
Handling alternative fuel on board will likely present different operational hazards compared to other fuels. Therefore, it is essential to train the crew properly in handling these new fuels.
- HEALTH, SAFETY, AND ENVIRONMENT (HSE)
While alternative fuels may have their obvious environmental benefits, they may come with some increased safety risks. Therefore, any alternative fuel should be accompanied by a thorough assessment of its HSE risks, and this should form the basis of the onboard safety measures for handling the fuel.
- QUALITY
With the current lack of international standardization, a clear and detailed bunker specification needs to be developed by the shipowner to ensure suitable fuel is delivered. Britannia’s loss prevention department has collaborated with Waves Group to provide practical advice on the widely discussed alternative fuels: Biofuels, Liquefied Natural Gas, Methanol, Ammonia, and Hydrogen. The examination for each of these alternative fuel types will focus on good practices in storage, handling, bunkering, safety, and emergency response.
Storage
If a type A tank system is used, a reliquefication system must be fitted to the ship to contain the boil-off gas (BOG) and return it as liquid back to the storage tank. Ammonia boils at -33 °C when at atmospheric pressure. Alternatively, the BOG could be managed using the ships engines, auxiliary engines, and boilers. BOG will still need to be managed when the ship is not sailing, so the design must be able to handle the boil-off expected when only the auxiliary engines and/or boilers are in use.
Type C tanks have a pressure vessel design, and the design pressure can be as high as 18 bar, which corresponds to an ammonia vapor pressure at 45 °C. Both tank types will require material that can withstand the low, -33 °C, temperatures for ammonia. Arrangements will need to be made available to purge and vent the storage tanks. The storage tanks will need to be inert before admitting liquid ammonia into them. The location of the fuel tanks will need to be selected carefully and if the fuel tanks are type C, then they could be placed on the open deck. Independent fuel tanks, of type C design could also be placed in Tank Connection Spaces (TCS) and from there connected to the ship’s piping systems via approved flexible hoses.
Bunkering
Given the highly toxic nature of ammonia, the correct PPE should be worn by operators involved with the connection/ disconnection of the bunkering hose. Further points to consider are:
- Plan each bunkering operation individually, collaborating closely with the bunker supplier. This planning includes: a. Conducting a combined risk assessment b. Performing a compatibility assessment c. Developing a joint plan of operations d. Creating a separate plan and risk assessment for any simultaneous operations (SIMOPs) e. Confirming the methods of communication
- Install an Emergency Shutdown System (ESD) on the vessel, connecting it to the bunkering sources ESD system during the bunkering operations
- Test the ESD system after connecting the bunkering hose and before ammonia transfer
- Fit a filter/strainer at the bunkering source to prevent the ingress of foreign objects
- Purge bunker hoses and lines with nitrogen before starting bunkering, ensuring it is below the Lower Explosion Limit (LEL) of ammonia
- Pressure test the manifold connection with nitrogen before commencing ammonia transfer to confirm there are no leaks
- Agree on maximum transfer rates with the supplier
- Continuously monitor the fuel tank levels and pressures, considering the tank pressure relief valve capacity
- Drain and purge bunker hoses and lines upon completing bunkering and before disconnection
- Constantly monitor the vessel’s moorings throughout the transfer operation to avoid a breakout situation
Handling
To prevent toxic vapors from entering areas on the ship where personnel might be exposed, the ammonia fuel line should be double-skinned. Areas such as the tank connection space and the fuel preparation room have the correct ventilation and gas detection systems so double-skinned piping may not be required. The annular space in the double-skinned pipe should be mechanically ventilated to a safe area in the open air, normally the ship’s vent mast.
The piping in the engine room will be required to be double-skinned. Selection of the material for the fuel pipe and secondary skin must be chosen to ensure resistance to corrosion and low temperatures. To avoid unnecessary operational discharges of ammonia from the fuel system, the system should be designed with a minimum operating pressure of 18 bar. This corresponds to the vapor pressure of ammonia at 45 °C.
This is the temperature the International Association of Classification Societies specify as the highest temperature in the temperature range that all machinery in the fuel system shall be designed to operate. Every effort shall be made to minimise the time that personnel spends in spaces containing ammonia equipment, with access to these spaces strictly controlled.
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Source: Britanniapandi
