Lately, emissions of nitrogen oxides (NOx) from large ships and other marine vessels are getting worldwide attention. Oceangoing vessels are reportedly responsible for 36% of NOx emissions at the Ports of Long Beach and Los Angeles in the United States, thus of great concern to those living in the San Pedro Bay port area. At 37%, ships are reported as the largest source of NOx emissions in Norway. The European Commission estimates that without appropriate policy measures, maritime NOx emissions are projected to grow higher than all landbased sources combined by 2020.

NOx emissions are regulated under the Gothenburg protocol, which binds participating nations to reduce or stabi lize the amount they release at ceiling values. At 195 000 tons, Norway’s NOx emissions in 2006 were 25% above the level that the country is committed to reaching in 2010 under the Gothenburg protocol.

Shown is the schematic of an SCR system installation as it would be used on a diesel engine complete with Yarwill’s products.

Norway-based Yara International and Wilhelmsen Maritime Services have formed a 50-50 joint venture called Yarwil to supply deNOx nitrogen oxides reduction technology to the maritime market. Yarwil plans to expand its emissions control marketing to include additional products for reducing other maritime emissions such as sulphur oxides. Yara is one of the world’s largest producers of urea, which is a commonly used nitrogen fertilizer. The company already upplies ammonia- and urea-based chemicals for both selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR) emission control systems for power plants, incinerators, cement kilns, refineries and heavyduty vehicles.

Yarwill’s deNOx process involves SCR catalytic technology already widely used for cleaning up land-based power generation, industrial and mobile application NOx emissions. The technology involves introducing a urea solution to the hot exhaust fumes from the ship’s engines, where it is cracked to ammonia. As the mix passes through the catalytic converter, the ammonia reacts with the NOx in the exhaust to yield clean water and nitrogen that already comprises about 79% of the atmosphere.While both ammonia and urea are suitable for NOx reduction, urea is the most suitable for shipboard use.

A urea solution is a nonhazardous, nontoxic, nonflammable, non-explosive fluid and is, therefore, very safe to use. No special safety measures must be taken for storage, handling and use of a urea solution. SCR systems using urea solutions are already widely used to meet NOx emission reductions from diesel engines powering cars and trucks. AdBlue, a urea solution widely available throughout Europe, allows diesel cars and heavy trucks to meet stringent emission standards. In addition, its use will now allow Mercedes-Benz, BMW, Audi, VW and others to sell diesel-powered cars that meet emission requirements in all 50 U.S. states.

The Bourbon Mistralshown here is equipped with the Yarwill deNOxtechnology.

When urea is used, it must be converted to ammonia prior to reaction. This conversion occurs by thermolysis as an integrated part of both SCR and SNCR processes. Yara’s urea solutions consist of pure urea in demineralized water and it is available in two concentrations,32.5 and 40% urea. Yarwil’s deNOx technology marketing will initially cover that part of the maritime market in which NOx emissions are governed by official regulations. For example, Norway now imposes a tax of one Norwegian krone per 15 kg of NOx emitted from engines larger than 750 kW, including ships under foreign flags sailing between two or more Norwegian ports.

Thus,the initial marketing of the technology will be for vessels operating close to land. This would include ferries, fishing vessels and supply ships.It will also be used on Norway’s large cruise ship fleet.Unlike greenhouse gases such as carbon dioxide, NOx is primarily a local pollution problem. While it is currently possible to remove NOx emissions from diesel generators on large oceangoing vessels, the adaptation of the technology of this type is still being developed. According to Yara, its deNOx product could cut such emissions from ships by 95%.

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