Benefits and drawbacks of emerging fuels for shipping

As Standard Club reminds, the IMO has set international shipping decarbonization goals, as its “IMO-2030” targets a minimum 40% reduction in carbon intensity by 2030 while pursuing efforts towards 70% by 2050, compared to 2008 levels.

What is more, “IMO-2050” sets a 50% reduction in annual greenhouse gas (GHG) emissions by 2050, while working towards phasing them out by the end of this century.

These targets may get even tougher – a strategy review planned for 2023 is expected to bring forward this net-zero requirement to 2050

Examining emerging fuels

#1 Methanol

Methanol has several benefits, including:

• Liquid at ambient temperatures, so no need to heat or cool.
• Relatively easier to store and handle than cryogenic fuels.
• Possible to convert existing engines from conventional fuel to methanol.
• Relatively minor modifications needed to existing storage and bunkering facilities.
• Already widely traded, well-understood and readily available in some ports for bunkering.
• Water-soluble and biodegradable, with a lower impact on the environment if a spill happens.
• Comparatively more energy-dense than hydrogen and ammonia.
• Clean burning fuel with low levels of sulphur oxide (SOx), nitrous oxide (NOx) and particulate matter.

However, it also presents a number of challenges:

• Production is still currently mainly via processing natural gas (grey methanol) or coal (brown methanol), limiting the reduction of CO2 emissions.
• Only when methanol is produced using renewable sources like biomass, and if the power used to produce it comes from renewable energy, it is considered to be green methanol.
• Lower energy density than conventional fuel oil.
• Large fuel volume is almost 2.5 times fuel oil, so requires larger storage tanks and/or more frequent bunkering.
• Low flash point of well below 60°C is a fire risk, requiring extra fire prevention measures when handled and stored.
• Toxic if inhaled, ingested or handled.
• Increased corrosion risks Apart from larger volume of fuel tanks, additional cofferdams will be needed to prevent any potential leak into machinery spaces.

#2 Ammonia

Benefits of ammonia include:

• Since ammonia doesn’t contain any molecular carbon, during its combustion there are no CO2 emissions.
• ‘Green’ production, using green hydrogen and renewable power for the conversion process, is possible. However, this process may influence its cost competitiveness.
• Currently produced in substantial volumes for the chemical industry and distributable using existing infrastructure.
• Commonly transported as cargo, so issues around handling and carriage are already understood.
• Compared to hydrogen or LNG, ammonia is relatively easier to handle in terms of temperature, as it is stored at around -33oC.
• Low fire risk due to its relatively narrow flammability range, as compared to other fuels.

However, it also poses a variety of challenges, such as:

• Its toxicity. Being extremely soluble, even at extremely low concentrations, ammonia can be absorbed by body fluids (sweat, tears, saliva) and may cause severe chemical burns. Therefore, using ammonia fuel will require additional safety systems.
• Ammonia also poses enhanced corrosion risk of certain metals such as copper, brass and zinc and various alloys.
• Although ammonia is commonly carried as a cargo, it is still in the early stages of development as a fuel the regulatory frameworks are still being worked out.
• The IGF Code currently does not provide prescriptive requirements to cover toxic fuels like ammonia.
• Ammonia’s lower volumetric efficiency and energy density means much more storage capacity will be required on board. The additional space for fuel may require larger vessel sizes, decreased cargo space or more frequent bunkering.
• Tanks will need to be designed for temperature and/or pressure control if ammonia is stored in a refrigerated condition, as ammonia continuously evaporates and generates boil-off gas due to heat gain, which increases pressure in tanks if not managed. This storage at low temperatures will require energy.
• Ammonia burns much more slowly than other fuels and has higher autoignition temperature than conventional fuel oil. This means that sustaining combustion once it gets started is going to be more difficult with ammonia than with other fuels. It will require an initiator/ igniter (combustion promoter) to enhance the burn, and this may cause difficulties in increasing engine output.
• While carbon-free, ammonia contains nitrogen, and burning it will result in nitrogen oxide (NOx) and nitrous oxide (N2O) emissions. GHG impact of N2O emissions is nearly 300x greater than CO2.