Page 70: of Maritime Reporter Magazine (June 2003)

QUEENS HIGHWAY, FREEPORT HARBOUR • P.O. BOX F-44867

FREEPORT, GRAND BAHAMA • BAHAMAS • 242-352-7711 • FAX: 242-352-7695

WEB: www.bradford-grand-bahama.com • EMAIL: [email protected]

NOx than MGO or MDO. Total NOx emissions in 2001, again including the emissions produced by the auxiliary engines onboard, was estimated to be 22 mil- lion tons, again more than twice of the NOx emission level reported in the literature so far.

This result shows that the introduction of more and more ships with modern low-emission engines is mandatory. Since every year more vessels with NOx- optimized engines enter the fleet and older ships with unregulated engines are being-laid off, annual NOx emissions from shipping will decrease, however in a slow process especially in times when the newbuilding business is down.

All diesel engines for new ships with keel-laying since January 2000 comply with the IMO NOx limit.

For a typical four-stroke engine in the 5 MW power range with a speed of some 400 rpm, the allowable upper NOx emission is 13.5 g/kWh (cycle value). But the engine industry already has developed NOx reduc- tion technologies, for instance by introduction of water into the combustion space, to reach emissions of as low as 6-8 g/kWh. Even lower emissions than that, i.e. 4 g/kWh, is achievable today by humidifying the com- pressed intake air. The lowest possible NOx emissions, approx. 2 g/kWh, are possible by selective reduction technologies (SCR).

Needless to say that such equipment will increase the price tag of a marine engine and also operation and maintenance costs as well as the necessary machine room volume.

For more information from the Author

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Sources 1.) Koehler, Horst W., "How much NOx do ships actu- ally emit? The Martime Environment." Luebeck,

Germany: (June 2002). 2.) Koehler. Horst W., "NOx emissions from oceango- ing ships: calculation and evaluation." Spring 2003

Technical Conference of the ASME International

Combustion Engine Division. Salzburg, Austria: (May 2003). *Corbett, James J., and Koehler, Horst W., "Improving the Accuracy of Ship Emissions Inventories." Marine

Environmental Engineering Technical Symposium,

MEETS 2003. (August 2003): Arlington, Va. *(in preparation). 70 Circle 239 on Reader Service Card Maritime Reporter & Engineering News