Comparison of CO2 and air pollutant emissions of MARPOL Annex VI compliance options in 2020

MARPOL, the main international convention preventing pollution from ocean-going vessels, sets limits on the sulphur content of the fuel oil they burn. Under Regulation 14 of MARPOL Annex VI, as of January 1st, 2020 the maximum permitted sulphur content of fuel oils used outside Emissions Control Areas (ECAs) is 0.50% m/m. Inside ECAs, the limit has been 0.10% m/m since 2015.

In practice, there are two options for compliance with this regulation:

  1. using an Exhaust Gas Cleaning System (EGCS) in combination with fuel oils with a sulphur content over 0.50% or 0.10%, respectively
  2. using fuel oil with a maximum sulphur content of 0.50% (VLSFO) or 0.10% (ULSFO).

These reports, commissioned by three major EGCS suppliers, quantify and compare the environmental impacts two options. The first report focusses on the carbon footprint, the second on emissions of PM, metals and PAHs to the air.

For the first option, use of an EGCS, It is found that this results in a 1.5-3% increase of CO2 emissions for a range of representative ships. This is because an EGCS needs to be powered by an engine running on fuel oil and thus emitting CO2. In addition, there are emissions associated with scrubber manufacture as well as emissions from the seawater.

While desulphurisation in a refinery inevitably leads to improved fuel quality in terms of aromatics content and viscosity, the desulphurisation process itself increases CO2 emissions by over 1% and often a multiple of that figure, depending on the degree of fuel quality improvement, refinery layout and the crude used. In addition, the process requires hydrogen, which is generally produced from methane, emitting CO2 in the process, on top of the emissions due to energy use.

The conclusion of the first study is therefore that well-to-wake CO2 emissions increase in both options.

The second study shows that PM emissions of ships using an EGCS are higher than those of ships using compliant fuels, whereas metal emissions are lower.

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