As discussed in our previous article (Nox Emission), one of the major global environmental concerns today is the air pollution from maritime transportation. The main elements of pollution are NOx and SOx. Sulphur oxides emission is mainly due to the presence and burning of sulphur compound in the fuel.
Causes and Effects of SOx Emission
The sulphur oxides emission is due to the presence of sulphur compound in the marine fuels used in marine engines on board vessel. Better the grade, lower will be the sulphur content as it is removed by refining of the fuel.
The smoke containing sulphur oxides emitted by the combustion of marine fuel will further oxidise and in presence of catalyst like NO2, will form sulphuric acid which is a major cause of acid rain.
It has also been recognised that the emission of SOx contributes in formation of secondary inorganic aerosol gases, fine particles which are harmful to humans.
Maritime industry consumes mostly low grade of fuel oil i.e. heavy oil and diesel oil with high sulphur content as compared to any other transportation medium. But due to MARPOL Annex VI stringent norms, marine engines are now using better grade of marine fuel like marine gas oil.
Limits for SOx Emission from a Merchant Vessel
When the ship is out of emission controlled area
- The sulphur content of any oil used onboard ship must not exceed 3.5% m/m.
When the ship is within emission controlled area
- The sulphur content of any fuel oil used on board ships must not exceed 0.1% m/m.
- An exhaust gas cleaning system or other technological methods to be used onboard to reduce total sulphur emission from ships including auxiliary and main propulsion engine to less then or equal to 6.0g SOx/kwh.