EMISSIONS

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A draft protocol has been compiled by the IMO organisation to reduce the effects of vessel emissions on overall air pollution. This protocol forms Annex VI of the MARPOL 73/78 Regulations. Applies to every ship of 400 gross tons and above. Entered into force 19^th May 2005. The main parts of the protocol which affect vessel operation are regulations 12 to 18, namely:

Regulation 12           Ozone Depleting Substances

Regulation 13           Nitrogen Oxides

Regulation 14           Sulphur Oxides

Regulation 15           Volatile Organic Compounds

Regulation 16           Shipboard Incinerators

Regulation 17           Reception Facilities

Regulation 18           Fuel Oil Quality

The vessel complying with these new regulations will be issued with an IAPP certificate, similar to the present IOPP for oil pollution.

Regulation 13  Nitrogen Oxides

The main thrust of this regulation is to reduce and control NO_x emissions from diesel engines. The regulation is for new or converted engines of over 130kW built after 1/1/2000. Although the type of fuel plays a major part in the composition of the emissions, the major factor that determines the amount of No_x is engine speed. For the engines that fall under this criterion, the engine must have limits of NO₂ from the engine of:-

            17                    g/kWh for engines under 130 rpm

            45n^-0.2             g/kWh for engines between 130 and 2000 rpm (where n = rpm)

            9.8                   g/kWh for engines over 2000 rpm

These emissions contribute to `smog' formation by increasing ozone concentrations in highly inhabited areas, affecting the respiration of humans and plants, and as NO₂ is soluble in water it will be absorbed by rain to produce acidic precipitation.

These oxides are formed during the combustion process when the normally inert nitrogen reacts with the plentiful oxygen present, to form nitrogen oxides. The initial reaction is the formation of Nitric Oxide (NO), which is later converted to form Nitrogen Dioxide (NO₂, visible as a yellow/brown gas) and Nitrus Oxide (N₂O), typically 5% and 1% of the original NO quantity.

The nitrogen comes from:-

a)            the fuel (fuel NO_x, which is totally converted),

b)            the air (thermal NO_x, the amount converted depends on how long and at what temperature the reactants are held at).

Large bore slow speed engines inherently produce larger quantities of NO_x emissions, as the slower speeds and larger bores both result in higher gas temperatures.

The controlling factors of how much NO_x will be produced depends upon the concentration of oxygen, and the temperature and duration of combustion (increases x3 for every 100°c),

To reduce NO_x emissions we can use:-

Primary methods – denitration of fuel, alternative fuels (LPG) or affecting combustion,

Secondary methods – during exhaust.