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Our impact – emissions to air


This article covers NOx IMO annex VI, SOx – IMO 2020, Exhaust gas cleaning, CO2 – Green House Gasses

Exhaust gas cleaning

An alternative way to change to a low sulphur fuel is to install an exhaust gas cleaning system called seawater scrubber. The system has been used since the 1930s ashore. This is a preferred way to remove pollutants from exhaust in coal or oil-fueled power stations and other industry with seawater available.

The extra fuel consumption from running an exhaust gas cleaning system is approximately 2-3 percent. This means removing emissions from an HFO-fuelled ship will increase the total CO2 emissions, either by 10-15 percent if HFO is cracked in a refinery, or by 2-3 percent if done by an on-board scrubber.

A seawater exhaust cleaning system (scrubber) normally has an efficiency ratio exceeding 98 percent, limiting the SOx emissions to the air to a comparable fuel with sulphure content less than 0,1 % S. It also removes a considerable part of the soot and other particles, the exact ratio depending on the technical system.

Given a total evaluation including environmental performance, cost, flexibility, operational complexity and safety, HFO together with exhaust gas cleaning has so far been the  best solution for us in Solvang. Heavy fuel oil is available all over the world, it is a safe and technically excellent fuel for deep sea shipping, and it also gives maximum fuel capacity and operational flexibility.  At the moment, Solvang has 15 of 27 vessels equipped with exhaust gas cleaning systems.

NOx IMO annex VI

The NOx control requirements of IMO Annex VI apply to installed marine diesel engines of over 130 kW output power, other than those used solely for emergency purposes irrespective of the tonnage of the ship onto which such engines are installed.

The Tier III controls apply only to the specific ships while operating in Emission Control Areas (ECA) established to limit NOx emissions. Outside such areas the Tier II controls apply. In accordance with regulation 13.5.2, certain small ships would not be required to install Tier III engines. 

A marine diesel engine that is installed on a ship constructed on or after the following dates and operating in the following ECAs shall comply with the Tier III NOx standard:

- January 1st 2016 and operating in the North American ECA and the United States Caribbean Sea ECA; 

- January 1st 2021 and operating in the Baltic Sea ECA or the North Sea ECA.


SOx - IMO 2020

1. January 2020, a new limit on the sulphur content in the fuel oil used in ships came into force, marking a milestone to improve air quality, preserve the environment and protect human health.

Known as “IMO 2020”, the rule limits the sulphur in the fuel oil used in ships operating outside designated emission control areas to 0.50% m/m (mass by mass) - a significant reduction from the previous limit of 3.5%. Within specific designated emission control areas the limits were already stricter (0.10%). This new limit was made compulsory following an amendment to Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL).

The resulting reduction in sulphur oxide (SOx) emissions from ships gives major health and environmental benefits to the world, particularly for populations living close to ports and coasts. Sulphur oxides are harmful to human health, causing respiratory, cardiovascular and lung disease. Once released in the atmosphere, SOx  can lead to acid rain, which impacts crops, forests and aquatic species and contributes to the acidification of the oceans.


What does the initial IMO GHG strategy say?

The initial IMO strategy’s goal is a reduction in greenhouse gas emmissons of international shipping:

  • Reduce emissions per DWT per nautical mile on average by at least 40% by 2030, compared to 2008.
  • Reduce emissions per DWT per nautical mile on average by at least 70% by 2050, compared to 2008.

Total annual tonnes GHG emissions released from international shipping should be reduced by at least 50% by 2050 compared to 2008.

The strategy includes a specific reference to “A pathway of CO2 emissions reduction consistent with the Paris Agreement temperature goals”.


Reducing greenhouse gas emissions from ships

CO2 is the only greenhouse gas that is given directly from the amount of fuel and the fuel’s carbon factor. Solvang’s approach is to design and operate our vessels to use as little fuel as possible. This reduces our CO2 emissions and all other emissions to air.

Greenhouse gasses are a global challenge and not a local problem. The logical approach must therefore require an assessment of the complete energy cycle, from well to wake.

Taking a fuel life-cycle approach to reach the ambitious IMO goals, we find that the potential reduction of GHG gases from fossil fuels are minor, around 10-15% in total. The IMO goals are 50-70%.

If we include methane slip (very potent GHG) we find that the total GHG emissions from low carbon fuels are in many cases higher than conventional fuels. Methane is a very potent gas, and it must be included in the full picture of GHG emissions. See figure below.

Well-to-wake categorisation of the fuels is under development. Standards for including other types of climate gases into the GHG calculation, especially methane slip and N2O, are under development.   

Global man-made GHG emissions in 2010


We have to look at the full picture of GHG to make a real difference, and not only comply with regulations. Methane has a different weight as GHG depending on the time horizon for decomposition. The figure above shows the difference between 20 and 100 years.


IMO is developing new life-cycle carbon-equivalent factors (LCCF) covering well-to-wake to replace the conventional categorisation of the fuels. The factors strongly support our philosophy that scrubber installations are effective in limiting the total GHG emissions instead of changing to LSFO (0,5%S).

Hull design/engine type and fuel are given during the construction of the vessel, but operation and maintenance will decide the environmental footprint during the lifetime of the vessel.