(96g) Marine Scrubbers Vs. Low-Sulfur Fuels: A Comprehensive Well-to-Wake Life Cycle Assessment Supported By Measurements Aboard an Ocean-Going Vessel

Maritime transport serves as the backbone of the global economy, with ocean-going vessels transporting more than 80% of the total volume of internationally traded goods¹. The shipping sector currently contributes around 3% of the world's annual greenhouse gas (GHG) emissions, alongside sulfur dioxide (SO₂), nitrogen oxides (NO_x), and particulate matter (PM) emissions, which can cause air pollution and climate change, while elevating ozone levels impacting human health². Efforts to mitigate environmental pollution from maritime transport have been prioritized recently, leading to the implementation of stricter regulations. The International Maritime Organization (IMO), among other measures, established the Emission Control Areas (ECAs), where NO_x and SO_x emissions are more rigorously controlled, and set upper limits for the sulfur content of marine fuels under the Annex VI of the International Convention for the Prevention of Marine Pollution from Ships (MARPOL). Since January 1, 2020, this maximum allowable sulfur content has been reduced to 0.1% m/m inside ECAs and 0.5% m/m outside ECAs, aiming to further limit the global SO_x emissions^3,4.

To abide by these regulations, ocean-going bulk carrier vessels, which have been traditionally burning heavy fuel oil (HFO) with higher sulfur contents (1-3%), have three options: i) switch to low sulfur fossil fuels, such as marine gas oil (MGO) and very low-sulfur fuel oil (VLSFO); ii) burn biofuels, such as biodiesel, which have significantly low sulfur contents; iii) implement exhaust gas cleaning systems or scrubbers to remove SO_x emissions while continuing burning HFO. The first two options are considerably more expensive, while the current availability of biofuels is very low to accommodate demand. Due to the economic feasibility of installing marine scrubbers that would allow for continuing burning less expensive HFO, the third option is the most widely used, with over 4,000 vessels being fitted with scrubbers in 2023 compared to less than 800 in 2018⁵. The most prevalent scrubber type is the wet, open-loop one, which uses sea water to neutralize SO_x in the exhaust gases, discharging the generated washwater from this process to the sea without treatment.

While the widespread adoption of marine scrubbers is a positive step towards SO_x emission reduction, growing concerns are being raised regarding the release of washwater into the sea and its potential impact on marine life and biogeochemical processes. The acidic nature of washwater, combined with the presence of various organic and inorganic contaminants, such as heavy metals, Polycyclic Aromatic Hydrocarbons (PAHs), and eutrophication agents, may pose potential threats to marine ecosystems. Yet, there is no conclusive scientific evidence demonstrating significant harm to aquatic life from scrubber washwater. Additionally, comprehensive comparisons accounting for the environmental impacts of HFO/scrubber production and operation, versus the production and combustion of low sulfur fuels are lacking. Therefore, we conducted a first-of-its-kind, holistic, Well-to-Wake life cycle assessment (LCA) comparing climate change, air pollution, acidification, eutrophication and ecotoxicity impacts associated with the production of a marine scrubber as well as the production, bunkering and combustion of HFO, MGO and VLSFO under similar operating conditions, informed by real-time, air and washwater emission data collected aboard an ocean-going bulk carrier vessel.

In this talk, the results of this comprehensive, measurement-informed LCA study will be presented. Scrubber production emissions were found to be negligible throughout its lifetime compared to fuel emissions. Scrubber/HFO had significantly lower Well-to-Tank impacts than MGO and VLSFO across all the considered LCA impact categories. For the Tank-to-Wake assessment, CO₂, CO, NO_x, SO₂ and PM_2.5 emission data were collected for all three fuels aboard the Hedwig Oldendorff vessel, following the ISO 8178 standard⁶. In parallel, during scrubber operation, seawater and washwater samples were collected and analyzed for over 60 quality parameters. Fuel and lubricant samples were also collected to close the mass balance. The Tank-to-Wake results demonstrated notable reductions in almost all air-related impact categories for scrubber/HFO compared to low-sulfur fuels, with lower emissions observed, except for PM formation. Specifically, HFO released on average approximately 10% less g PM_2.5-Eq/MJ after the scrubber compared to VLSFO, but 26% more compared to MGO. With regards to washwater emissions, all the analyzed parameters were significantly below the IMO thresholds. The Tank-to-Wake marine eutrophication and ecotoxity LCA impact indicators were higher for scrubber/HFO due to lack of washwater generation in case of low-sulfur fuels. However, the measured, net concentrations of all organic and inorganic pollutants released through washwater into the sea were below the US EPA Aquatic life criteria for toxic chemicals, suggesting no likely adverse impacts on receiving water bodies and ecosystems. Overall, the presented study will challenge the notion that "end-of-pipe" solutions outperform "start-of-pipe" ones, emphasizing the need for holistic, measurement-informed LCA approaches. The adoption of such cradle-to-grave approaches by policy makers, supported by robust data while accounting for a variety of impacts and not just focusing on particular emissions or parts of the considered supply chains, would enable the effective assessment of different fuel systems, pollution abatement and decarbonization technologies avoiding perverse incentives and expediting maritime decarbonization. The implications of these findings for the scientific community, the shipping industry, and policy makers will be also discussed, paving the way for adopting the LCA rationale in other transportation sectors.

References

1. UNCTAD, Review of Maritime Transport: Towards a Green and Just Transition. 2023.
2. IMO 4th GHG Study
3. IMO: International Maritime Organization, Prevention of Air Pollution from Ships, https://www.imo.org/en/OurWork/Environment/Pages/Air-Pollution.aspx, accessed August 9, 2021.
4. https://www.imo.org/en/MediaCentre/HotTopics/Pages/Cutting-GHG-emission…
5. https://www.statista.com/statistics/1099286/number-of-scrubbers-in-vessels/
6. ISO: International Organization for Standardization INTERNATIONAL STANDARD ISO 8178-2: Reciprocating Internal Combustion Engines: Exhaust Emission Measurement. Part 2: Measurement of Gaseous and Particulate Exhaust Emissions under Field Conditions , Geneva, Switzerland, 2008.