NO x is a generic term for the nitrogen oxides that are most relevant for air pollution, namely nitric oxide (NO) and nitrogen dioxide (NO 2 ).These gases contribute to the formation of smog and acid rain, as well as tropospheric ozone.

NOx Formation Formed at elevated temperatures during combustion of fuel in the presence of air. Approximately 90 to 95% of the nitrogen oxides generated in combustion processes are in the form of nitric oxide (NO). (Remember this for later on!) Once in the atmosphere, the NO reacts in a variety of photochemical and thermal reactions to form NO 2.

NOx Emission Standards NOx emission limits are set for diesel engines depending on the engine maximum operating speed (n, rpm), as shown in Table. Tier I and Tier II limits are global, while the Tier III standards apply only in NOx Emission Control Areas.

methods to reduce NOx emission from ship Humid Air Method: water vapour is mixed in the combustion air before supplying it to the cylinder. Exhaust Gas Re circulation (EGR): some amount of engine exhaust gases are send back to the scavenge space to mix up with the air to be supplied to cylinder for combustion. Water Injection and Water emulsion: water is added to reduce the temperature of combustion leading to low NOx emission. High Scavenge Pressure and Compression Ratio: large amount of air can be introduced inside the cylinder to lower combustion temperature and NOx emission. Two Stage Turbocharger: ABB’s latest two stage turbocharger can reduce the exhaust temperature in the intercoolers and also the NOx content in the emitted exhaust.

Selective Catalytic Reduction: The SCR is the most efficient method to reduce NOx emissions from ships (up to 90-95% of reduction). In this method the exhaust gas is mixed by water solution of urea and then it is passed through catalytic reactor.

What is Sulphur Oxides or Sox? 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.

Effects Human Health (as well as animals):  Lung and throat irritation  Worse symptoms for those with bronchitis  Weakening of the immune system Plants Corrosion Acid Rain

fuel sulfur limits

Reducing SOx Emission Use of Low sulphur fuel oil: It is expensive but most commonly used method to comply with Annex VI of MARPOL while entering emission controlled Area or ECA. Exhaust Gas Scrubber Technology: The exhaust gas from the engine is passed through the scrubber tower where a liquid is showered over it. Fresh water blended with caustic soda (NaOH) is used as a scrubbing liquid which reduces the SOx to 95%. The scrubbing water is then sent to a water treatment effluent emulsion breaking plant after which it can be discharged overboard. Cylinder Lubrication: Good quality cylinder lubrication along with efficient control systems such as Pulse or Alpha lubrication systems can neutralize the sulphur in the fuel and reduce SOx emissions from the engine

Exhaust Gas Scrubber Technology

Co2 emissions Maritime shipping is the world's most carbon-efficient form of transporting goods - far more efficient than road or air transport. Yet, the industry seeks to further improve the fuel efficiency and carbon footprint of its vessels. Today's container ships and vehicle carriers enable the movement of tremendous volumes of goods across the world, which has fueled global economic growth in a manner considered implausible only 50 or 60 years ago.