Phase out scrubbers on ships

A new 36-page report from the International Council on Clean Transportation (ICCT), urges governments and the International Maritime Organization (IMO) to phase out all scrubbers. The study includes a comparison of the emissions associated with ships equipped with scrubbers using 2.6% sulphur heavy fuel oil (HFO) to ships without scrubbers using 0.7% sulphur marine gas oil (MGO).

Regarding air emissions, the results show that:

  • SO₂ emissions from ships using HFO and scrubbers are on average 31% lower than from ships using MGO.
  • PM emissions are nearly 70% higher using HFO with a scrubber compared with MGO.
  • Black carbon emissions are 81% higher using HFO with a scrubber than using MGO in a medium-speed diesel engine and more than 4.5 times higher than using MGO in a slow-speed diesel engine.

The authors conclude that scrubbers are not equivalently effective at reducing total air pollution emissions compared to using MGO. Moreover, direct CO₂ emissions are 4% higher using HFO with a scrubber compared to MGO, and even though HFO has lower upstream emissions than MGO, the extra fuel consumption associated with powering the scrubber results in 1.1% higher CO₂ emissions on a life-cycle basis when using HFO.

Regarding water emissions, the study finds that:

  • Scrubber discharges typically comply with IMO guidelines, but all scrubbers – open-loop, closed-loop, and hybrid – discharge water that is more acidic and turbid than the surrounding water. This contributes to ocean acidification and worsens water quality.
  • All scrubbers emit nitrates, PAHs, and heavy metals that accumulate in the environment and food web and can negatively affect both water quality and marine life.

Given these findings, the ICCT recommends that individual governments continue to take unilateral action to restrict or prohibit scrubber discharges from both open-loop and closed-loop systems. This could include an immediate prohibition on scrubber discharges in ports, internal waters, and territorial seas. Internationally, the IMO should consider prohibiting the use of scrubbers on newbuild ships and phasing out scrubbers on existing ships, because scrubbers are not equivalently effective at reducing air pollution compared to using lower-sulphur fuels.


Source: ICCT, 24 November 2020.

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