Study looks into managing emissions from ammonia-fueled vessels

8 March 2023

The Maersk McKinney Moller Center for Zero Carbon Shipping (MMMCZCS) released a new study that examined the potential emission scenarios for ammonia-fueled internal combustion engines (ICE), and technologies that could reduce emissions to acceptable levels [5728]. The work is focused on emissions from ammonia dual-fueled (DF) ICEs, which are currently under development, with the first commercially available engine expected in 2024.

The key emissions of concern from ammonia-fueled engines include ammonia, nitrous oxide, and NOx. NH₃ emissions are a concern from a toxicity perspective, N₂O is a powerful greenhouse gas, while NOx is an air pollutant.

The GWP₁₀₀ potential of N₂O is 265 (i.e., 1 g of N₂O is equivalent to 265 g of CO₂). Consequently, small quantities of N₂O may invalidate the case for ammonia as a low-emission fuel. The study analyzed the emission impact at four N₂O emission levels: 0.06 g/kWh, 0.47 g/kWh, 0.95 g/kWh, and 1.9 g/kWh. The respective GHG emission contribution from N₂O relative to VLSFO propulsion were found to be 3%, 25%, 50%, and 100% (i.e., 1.9 g/kWh of N₂O would have the same climate warming effect as CO₂ emissions from diesel combustion).

Considering GHG emissions, safety issues with ammonia and other criteria, the study proposed the following emission reduction target levels:

• NH₃: 10-30 ppm
• N₂O: 0.06 g/kWh
• NOx: IMO Tier III (≈2 g/kWh)

The study analyzed a number of emission control technologies, including engine optimization, exhaust gas recirculation (EGR), catalysts, and plasma treatment. One potentially feasible approach to control all three of the above emissions involves an SCR catalyst—optimized to reduce both NOx and N₂O—followed by an NH₃ slip catalyst.

Ammonia emissions can also be released onboard ships from other sources than the combustion engine. These include ammonia boil-off gas (BOG) from fuel tanks and ammonia mixtures from purging and venting operations in the fuel system. These emissions could be controlled using such technologies as gas combustion units, reliquefaction, and water catcher and adsorber systems.

The Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping will present the conclusions of the study at a webinar scheduled for March 23, 2023.

Source: Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping