Study shows the well-to-wake CO2 impact of SOx scrubbers is less than that of compliant fuels

In the run-up to the 2020 global sulphur cap, the marine industry was firmly focused on fuel sulphur and SOx emissions. As IMO now strives to slash greenhouse gas emissions by 2050, CO2 has also entered the spotlight. According to a new study from CE Delft, using a scrubber to control SOx adds less CO2 to the atmosphere than operating on sulphur-compliant fuels.

An assessment of climate implications 

The CE Delft study was commissioned by Alfa Laval and two other major suppliers of exhaust gas cleaning systems. It evaluates CO2 emissions on a well-to-wake basis, using HFO operation without a scrubber as a reference for comparison. In other words, it accounts for the total CO2 impact of each compliance optionnot only on board but also during fuel refining. The results of the study indicate that the carbon footprint of SOx scrubbers is significantly smaller than that of compliant fuels.   

It’s important for customers to have a complete picture of their compliance options, and it matters for Alfa Laval as a supplier of equipment supporting all fuel choices,” says Rene Diks, Head of Exhaust Gas Cleaning Systems. “From a carbon perspective, the study shows the impact of a scrubber like Alfa Laval PureSOx is likely many times less than that of low-sulphur fuels.” 

Scrubbing adds far less CO2 than refining 

According to the CE Delft study, the use of a SOx scrubber increases carbon output by 1.5% to 3%. This is due to the fuel oil burned by the engine in order to power the exhaust gas cleaning system, as well as the CO2 released in manufacturing the scrubber itself. 

The refining of compliant low-sulphur fuel, on the other hand, may put many times more CO2 into the atmosphereRefining emits CO2 not only through energy consumption, but also because it uses hydrogen that is generally produced from methane, releasing CO2 in the process. The exact CO2 increase depends on the level of desulphurization and the quality of fuel produced, but the study places it somewhere between 1% and 25%.  

“Both extremes for refining compliant fuel are theoretical,” says Diks. “Removing the bare minimum of sulphur to meet regulations would increase CO2 by 1%, but doing so is not technically feasible. Refining all fuel products down to a sulphur-compliant level would mean an increase closer to 25%, but most of those products would be too pure for marine use. The reality is somewhere between, but it is clearly far higher than the 1.5% to 3% associated with a SOx scrubber. 

Jasper Faber, Project Manager at CE Delft, confirms, This study provides a comprehensive overview of the climate impacts of different options to reduce sulphur emissions. It shows that in many cases, the carbon footprint of using a scrubber is lower than low-sulphur fuels.”  



CO2 emissions associated with the production of low-sulphur marine fuels will be between these extreme values. Source: CE Delft 


Download the full study from CE Delft here.

To learn more about Alfa Laval PureSOx and Alfa Laval’s approach to exhaust gas cleaning, please visit: 



Rene Diks

Director, Exhaust Gas Cleaning Systems

+31 24 352 3180


Geertje van Duijne

Marketing Communications Manager, Business Unit Gas Systems, Alfa Laval Marine Division

+31 24 352 3239