Reducing Methane Emissions Onboard Vessels – A Report

Reducing methane emissions onboard vessels – A report by the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping, this paper is the second in the Onboard Vessel Solutions series: Vessel Emission Reduction Technologies & Solutions

The paper series covers the impact and role of vessel greenhouse gas and air pollutant emission reduction in maturing alternative fuel pathways. Onboard impact is defined in terms of tank-to-wake global warming potential with the role of onboard emission reduction either being for regulatory compliance or as an option to reduce emissions. Fuel pathway maturity is an assessment of solution readiness across the entire value chain.

Based on identified vessel emission risks, the paper series deep dives into specific emissions that need to be addressed to increase alternative fuel pathway maturity. The objective of these deep dives is to understand current or potential emission levels, set reduction targets, and identify and map applicable technologies and solutions. Emission reduction potential is then determined, and recommendations given to mature the selected fuel pathways. Finally, areas or concepts for further research and development are identified including recommended future project topics.

Papers are based on work completed as part of Center projects and working groups consisting of Center partners and external participants and contributors. Working groups provide a collaborative framework facilitated by the Center to jointly engage partners and external experts and companies on specific topics to deliver clear and impactful results.

Executive Summary

Liquefied electro- and bio-methane have been identified by the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping (MMMCZCS) as potential low-emission alternative fuel pathways. In addition, given the rapid expansion of the liquified natural gas (LNG)-fueled vessel fleet and industry projections, the use of LNG as a fuel for the maritime industry will continue well into the future. The use of these methane-based fuels, however, present both a regulatory compliance and climate risk related to onboard vessel methane emissions, in particular methane slip from internal combustion engines, that increases a vessel’s overall CO2-equalivent (CO2-eq) emissions.

Potential and upcoming regulation of onboard vessel methane emissions presents a risk for methane-based fueled vessel owners, operators, and charterers. Currently, there are no international regulations on methane emissions from vessels, however, ongoing initiatives and regional guidelines indicate that regulations are highly likely to appear soon. The FuelEU for Maritime regulation, for example, will include methane slip in its CO2-eq methodology.

While CO2 is the main source of shipping’s climate impact with over 90% of total greenhouse gas (GHG) emissions, methane has a higher climate impact in terms of global warming potential (GWP). As a result, methane emission reduction can be an efficient way to reduce a vessel’s overall CO2-eq emissions, allowing compliance with upcoming regulations and increasing the viability and competitiveness of methane-based alternative fuel pathways.

A dedicated MMMCZCS working group was established to study reducing methane emissions onboard vessels, which is one vessel specific emission-related consideration for methane-based alternative fuel pathways. Based on its results, the following conclusions have been made:

• A vessel’s total methane emissions should be considered: While the main source of onboard vessel methane emissions is methane slip from main and auxiliary internal combustion engines, total methane emissions of a vessel is highly dependent on a vessel’s operations, system dimensioning, machinery configurations and connected technologies. In addition to selecting baseline engine and potential after-treatment technologies, system solutions can significantly reduce onboard vessel methane emissions.
• Cost-efficient onboard vessel methane emission reduction is possible but limited for existing vessels: For the vessels studied, onboard methane emissions can be cost-efficiently reduced by 40-80% for a newbuild and 20-50% for an existing vessel through the selection of baseline engine technologies and the use of after-treatment technologies and system solutions. These reductions translate to onboard methane emissions being reduced from 7-14% of total tank-to-wake (TTW) GHG emissions to 2-8% for a newbuild and 4-12% for an existing vessel. Cost efficiency is considered as being less than the forecasted cost of bio-methane and is associated with CO₂-eq abatement cost of less than about $200/tonCO₂-eq. Ship owners should carefully consider onboard methane emission reduction at the newbuild phase to avoid potential costly modifications later in the vessel’s lifetime. While it is technically feasible to further reduce onboard vessel methane emissions beyond these levels, utilizing other options like the use of low-emission fuels could be more cost-efficient if further GHG emission reductions are required.
• Reducing onboard vessel methane emissions are needed to increase viability of electro- and bio-methane fuel pathways: Reducing onboard vessel methane emissions to these cost-efficient levels increases the longer-term viability of the electro- and bio-methane fuel pathways, however, it is still unclear if upstream well-to-tank fugitive emissions can be reduced to acceptable levels. Using the FuelEU methodology and cost-efficient onboard methane emission reduction measures, GHG WTW emissions can be reduced to 5-9 gCO₂eq/MJ using 100% electro-methane and hydrothermal liquefaction (HTL) Oil as a pilot fuel (a 90-95% decrease relative to heavy fuel oil).
• Proposed FuelEU for Maritime limits are not strict enough to activate onboard vessel methane emission reduction: For the vessels studied, GHG emission levels are already compliant with the 2025 and 2030 FuelEU GHG intensity index limits without introducing any onboard vessel methane emission reduction measures. This is due to LNG’s lower CO₂ emission factor used within its 100-year GWP methodology. If a CO₂-eq regulation with the proposed FuelEU limits is introduced, no emission reduction actions would be needed until 2035.
• Regulation is required for widespread adoption of onboard vessel methane emission reduction technologies and solutions: Without strong incentives or regulatory requirements to reduce methane emissions, there is limited commitment from ship owners to adopt methane emission reduction technologies and solutions. There are ongoing discussions at the IMO to include methane into its LCA methodology, a CO₂-eq approach like FuelEU. There is also the possibility that methane is regulated in a more direct way using a vessel’s Technical File like NO_X emissions. This type of regulation could more directly target methane slip levels and the need to reduce them onboard the vessel either for newbuilds or existing vessels if retroactive.

To properly assess the viability of methane-based alternative fuel pathways like electro- and bio-methane, the ability to reduce upstream well-to-tank fugitive emissions needs to be fully understood. Upstream fugitive emissions are not covered in this paper but are currently being studied at the MMMCZCS to enable a complete viability assessment of the methane-based fuel pathways. The MMMCZCS also plans to study onboard vessel emissions in operation where factors like dynamics engine loads and sea states can influence methane emission levels.

Despite the slow progress to incentivize or require LNG-fuelled vessels to limit their methane emissions, there is significant international social pressure to reduce emissions of GHGs, particularly methane. From the Global Methane Pledge (COP26) to the US’ Inflation Reduction Act of 2022, growing worldwide concern is strongly pushing for GHG reductions to limit the increase in the global average temperature to well below 2°C above pre-industrial levels. It is expected that this social pressure will lead to definitive action by stakeholders across all industries.

A Report by Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping – MMMCZCS

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