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Study: Marine scrubbers are cost-effective but environmentally damaging

10 May 2024

A new analysis led by Sweden’s Chalmers University of Technology shows that more than 95% of ships with a scrubber systems reach break even within five years after scrubber installation. However, the marine ecotoxicity damage cost from scrubber water discharge is much higher than the economic benefit for ship operators, “showing that private economic interests come at the expense of marine environmental damage,” the study concludes [6163].

In January 2020, the International Maritime Organization (IMO) implemented global regulations that reduce the allowable sulfur content of marine fuels from a maximum of 3.5% to 0.5%. Even stricter limits apply for ships operating in designated sulfur emission control areas (SECA), where a maximum sulfur content of 0.1% is allowed. To meet sulfur regulations, most ships have switched to the more expensive low-sulfur fuels such as distillate marine gas oils (MGO) or hybrid fuels such as very low-sulfur fuel oils (VLSFO). Another option is to install exhaust gas cleaning systems (EGCS), a.k.a. scrubbers, and continue to use the less-expensive heavy fuel oil (HFO) with high sulfur content while still being compliant with the IMO regulations.

A key measure of the profitability of scrubbers is the so-called scrubber spread-the global average price difference between VLSFO and HFO fuels. It is generally believed that VLSFO fuels need to maintain a premium of at least $100 per tonne over HFO to make the economics of installing a scrubber on a vessel viable.

Between January and August 2023, the VLSFO − HFO fuel price difference ranged between $70 and $240 per tonne, whereas the MGO − HFO price difference was between $280 and $600 per tonne of fuel. Based on an analysis of historical fuel prices, the Chalmers study found that within five years from the time of installation, more than 95% of the scrubber systems have reached economic break even. By the end of 2022, 51% of the global scrubber-fitted fleet reached break even, with a surplus of €4.7 billion due to the lower fuel costs as compared with running the ships on the more expensive low-sulfur fuels.

These economic benefits for ship operators come at the expense of marine ecotoxicity damage due to the toxicity potential of several metals and polyaromatic hydrocarbons (PAH) that are commonly found in scrubber water discharge. The study analyzed scrubber water discharge in the Baltic Sea Area during the period of 2014–2022 and estimated the related societal damages at more than €680 million. These findings question the overall benefit of scrubber installation on marine vessels.

High-sulfur HFO that is allowed in scrubber-equipped ships amounts to approximately 25% of the total marine fuel demand, according to the study. While not discussed in the paper, this level of HFO usage does not seem consistent with the size of the global marine fleet. There are around 100,000 marine vessels in the world, including about 60,000 large ocean going vessels that constitute the core of the global merchant marine fleet. It is hard to see how the 5,000 scrubber-equipped vessels alone can consume 25% of marine fuel, suggesting that quantities of HFO are consumed by ships that are not equipped with scrubbers.

Source: Nature Sustainability