Tackling Methane Slip in Shipping

Published — June 20, 2024

Insights into options for regulation and quantification

Liquefied natural gas (LNG) has increased in popularity as a maritime fuel due to its associated environmental benefits. While the tank-to-wake (TTW) carbon dioxide (CO2) emissions from the complete combustion of methane are nearly 30% lower* than those from diesel for the same energy, methane slip emissions during combustion and fuel production may pose an obstacle for methane-based pathways to reach zero emissions. To make methane-based fuel pathways a viable solution for net-zero shipping, methane emissions during the whole life cycle need to be addressed.

Looking to the coming decades, the growing methane-fueled fleet will drive up the consumption of LNG and other methane-based fuels, while the expected switch to sustainable bio- and e-methane will reduce this fleet’s overall CO2-equivalent greenhouse gas (GHG) emissions on a well-to-wake (WTW) basis. At the same time, if no mitigation actions are taken, methane slip will remain and even increase as the methane-fueled fleet grows. Therefore, methane slip from shipping will continue to contribute to global warming if not controlled. As such, this paper focuses on TTW methane slip emissions from engine combustion.

Past research at the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping (MMMCZCS) ​has demonstrated that current regulations that include methane, such as CO2-equivalent fuel standards (e.g., FuelEU Maritime), will have a limited effect on reducing onboard methane emissions in the short- to mid-term. Furthermore, the default methane slip value concept does not provide a direct incentive to engine makers, ship owners or operators to proactively reduce methane slip.

Our research has indicated that, considering the expected growth trajectory for the methane-fueled fleet, methane slip will contribute significantly to GHG emissions from shipping. The industry needs effective and relevant regulations that will drive the implementation of solutions that effectively minimize methane slip. To support the development of effective regulation of methane slip, this report summarizes analysis and insights into two key areas:

1) Impact of possible regulatory measures on methane emissions from LNG as a shipping fuel towards 2050

In this analysis, we modeled eight different scenarios to assess methane slip mitigation strategies based on different ambition levels, incorporating various regulatory and technological measures. This section aims to inform regulators on the potential effectiveness of various approaches to reducing methane slip and, consequently, decreasing overall emissions from the marine fleet.

Notably, our analysis reveals that the early implementation of methane slip regulations for newbuild vessels could achieve reductions in methane slip similar to those from retroactive measures. We therefore highlight the early regulation of newbuilds as a cost-effective method for meaningful reduction of methane slip, emphasizing the urgency and economic efficiency of early regulatory action to ensure the qualification of the sustainable methane-based fuel pathway with a near-term uptake.

2) Quantifying methane slip from engines on a ship level

We applied four different quantification approaches to calculate methane slip using real operational data from vessels in different shipping segments. Our analysis indicates that a test cycle average quantification approach based on the IMO NOx Technical Code can provide a relatively accurate estimate of real-life methane slip without requiring overly burdensome data collection. Further, unlike the default value approach (e.g. as currently applied in the FuelEU Maritime regulation), this quantification approach would incentivize engine manufacturers to strive for slip reduction and thereby contribute to the need for prompt reduction of GHG emissions in the shipping industry.

Based on these insights, we conclude this report with a set of recommendations and guiding actions by regulators, equipment manufacturers, and shipowners and operators, as well as some suggestions for further technical research. Specifically, we propose that the regulatory community consider measures targeting onboard methane slip at a ship level in the short term. This should ideally be achieved through the adoption of the test cycle average quantification method outlined in this report. Furthermore, we encourage equipment manufacturers to standardize the integration of methane slip reduction technologies in their product designs, while also focusing on the adaptability of these technologies for retrofitting on existing vessels. For shipowners and operators, actively selecting fuel and engine technology with emphasis on methane emissions mitigation is critical. Such proactive measures will contribute to the reduction of methane emissions, and at the same time mitigate the risk of incurring significant costs due to future regulations.

*Calculation based on the formula 1 ÷ LHV x Cf. For methane: 1 ÷ (50 MJ/kg) × 2.75 = 0.055; for MGO: 1 ÷ (42.7 MJ/kg ) × 3,206 = 0.075 ; 1 − 0.055 ÷ 0.075 = 27%.

Learn more — read the full report here

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