The CO2-emissions associated with using an Exhaust Gas Cleaning System (EGCS, or scrubber) are lower than the emissions caused by producing low-sulphur fuels for these ships. This is the main conclusion from the new study “Comparison of CO2 emissions of MARPOL Annex VI compliance options in 2020” issued by CE Delft.

The researchers found that the CO2-emissions of scrubbers vary between 1.5 and 3 per cent for a number of representative ships. In many cases, the emissions caused by producing low-sulphur fuels for these ships are higher, depending on the quality of the low-sulphur fuel, the refinery and the crude oil slate.

MARPOL sets limits for the sulphur content of fuel oil. As of January 1st, 2020, the sulphur content of fuel oils used outside Emissions Control Areas (ECAs) is 0.50 per cent m/m. Inside ECAs, the limit has been 0.10 per cent m/m since 2015.

In practice, there are two options to comply with the MARPOL Annex VI Regulation 14:

  1. using an EGCS in combination with fuel oils with a sulphur content that is higher than 0.50 or 0.10 per cent; and;
  2. using fuel oil with a sulphur content of 0.50 per cent (VLSFO), respectively 0.10 per cent or less (ULSFO).

Both options result in an increase of well-to-wake CO2 emissions:

  1. an EGCS requires energy which is generated by engines running on fuel oil and thus generate CO2. In addition there are emissions associated with manufacturing scrubbers and emissions from the seawater;
  2. desulphurisation in a refinery requires hydrogen which is generally produced from methane, emitting CO2 in the process, as well as energy.

This report quantifies and compares the CO2 footprint of both options. The use of an EGCS results in an increase of CO2 emissions by between 1.5 and 3 per cent for a range of representative ships. Desulphurisation inevitably leads to an improvement of the fuel quality in terms of aromatics content and viscosity. The increase of emissions associated with desulphurisation in a refinery are higher than 1 per cent and in many cases multiple times higher, depending on the quality improvement of the fuel, the refinery layout and the crude used.

‘This study provides a comprehensive overview of the climate impacts of different options to reduce sulphur emissions,’ says Jasper Faber, Aviation and maritime specialist and manager Mobility & Transport at CE Delft. ‘It shows that in many cases, the carbon footprint of using a scrubber is lower than low-sulphur fuels.’

The study has been commissioned by three major EGCS suppliers.