Maersk Mc-Kinney Moller Center: Emission risks won’t be a showstopper for ammonia-based fuels

The toxicity of ammonia as potential zero-emission fuel of the future for the shipping industry might be solvable after all despite all the hype over its likely impact on the safety of seafarers.

There have been a lot of discussions about the dangers of potential releases of ammonia on board during a combustion process or handling or storage.

Ammonia is a highly toxic gas, and exposure to it can cause severe health hazards. High concentrations of ammonia can cause chemical burns, severe lung damage, and even death.

In addition to safety risks for crew and passengers on board a vessel, NO_X formed by incomplete ammonia combustion presents a health risk to local communities where vessels operate and must be managed to maintain regulatory compliance.

What is more, it is possible for some nitrous oxide to be produced as a byproduct of the combustion of ammonia if the combustion conditions are not ideal or if there are impurities in the ammonia or the air used for combustion. N₂O is a potent greenhouse gas (GHG) impacting the global climate (1 gram of N₂O is equivalent to 265 grams of CO₂).

The emissions profile for ammonia fuels is currently unknown, as ammonia engines are still under development. Due to poor ammonia combustion characteristics, secondary or pilot fuel will be required. However, while ammonia combustion presents emission risks that are not fully known today, a combination of emission management technologies is already available or under development.

According to the findings of a dedicated working group of Maersk Mc-Kinney Moller Center for Zero Carbon Shipping (MMMCZCS), managing ammonia emissions is possible and management technology development timelines are expected to align with ammonia internal combustion engines (ICEs) development.

The group studied three potential emission scenarios for ammonia ICEs and technologies that can reduce emissions to acceptable levels. As explained, all scenarios required 3-4 different treatment technologies to achieve acceptable emissions levels.

These include emission management technologies to treat ammonia boil-off gas (BOG) from fuel tanks, ammonia mixtures from purging and venting operations, and combustion emissions from the engine(s).

“While such combinations would enable significant emissions reduction, they would also increase the cost and complexity of vessel design compared with vessels operating on conventional fuels,” the group said.

“Some emission management technologies are already commercially available for maritime use, including reliquefication and selective catalytic reduction (SCR). Others are based on existing maritime or shore-based concepts that need to be adapted for ammonia as a fuel, including engines, gas combustion units (GCU)/ boilers, catalysts, and water catchers/chemical absorbers.”

The group pointed out that an industry-wide collaboration during engine and emission management technology development is needed to optimize ammonia-fueled vessel designs.

“All stakeholders, including engine manufacturers and emission management technology suppliers, must work together to develop ammonia-fueled vessel designs and optimize the use of materials, costs, and overall system efficacy. Without collaboration, specific parts of the vessel design will be developed in isolation, and interconnected systems and technologies could end up unnecessarily oversized, inefficient, or costly. Regulators should follow upcoming tests and technology development closely to ensure that practical, effective, and realistic targets and goals are set from the beginning,” the group’s findings show.

Nevertheless, since acceptable ammonia emission levels are not yet clearly defined, and given the lack of knowledge on ammonia as a fuel for the maritime sector, there is a need to be conservative when defining guidelines as an additional safeguard.

Thus, low limits are generally included in Classification Society (Class) guidelines, ahead of mandatory International Maritime Organization (IMO) instruments in response to the industry’s interest in ammonia as a fuel.

As a result, the operational ammonia limits defined in existing class guidelines vary, and there is a need for a coordinated alignment on thresholds for adequate risk management to secure standardization and industry guidance.

“Our analysis showed that, with industry-wide collaboration across ammonia engine development, emission management, and vessel design, emission risks will not be a showstopper for ammonia-based fuel pathways. However, well-to-tank (WTT) emissions from ammonia fuels still need to be better understood to assess the overall viability of ammonia-based alternative fuel pathways,” the group concluded.