28 March 2011
MAN Diesel & Turbo has launched the world’s first marine engine that meets the IMO’s strictest Tier III emission standards. The Tier III NOx emission limit of 3.4 g/kWh—an almost 80% reduction from Tier II levels—was met using urea-SCR technology.
The engine, a two-stroke MAN B&W 6S46MC-C8 type with a maximum output of nearly 7 MW, was constructed in the Fall 2010 by Hitachi Zosen Corporation at its Ariake works in southern Japan. The first engine start took place in January 2011. The engine is bound for a general cargo carrier, to be built at the Nakai shipyard and scheduled to enter active service later this year. The vessel was ordered by Japanese customer, BOT Lease Co. Ltd., and is operated by Nissho Shipping Co. Ltd.
The SCR system features:
- more than 80% NOx reduction based on the load cycle
- more than 70% NOx reduction on each load point in the load cycle
- easy switching between on/off modes for optimal emission performance on high seas and coastal waters.
MAN confirmed that the engine—as the world’s first—meets all emission requirements as stipulated by the International Maritime Organization’s Tier III legislation. Effective from 2016, Tier III NOx emissions will be required in waters designated by the IMO as emission control areas (ECA). The North American ECA, adopted in March 2010, extends up to 200 nautical miles along most of the US and Canadian coasts. Outside of ECA waters, ships must meet Tier II NOx emissions.
MAN considered both SCR and EGR technologies for reaching the Tier III NOx emissions. Based on a general evaluation of two-stroke MAN B&W engines, a high-pressure, urea-based SCR system was chosen as the optimal solution.
Low exhaust temperatures are one of the major challenges in applying SCR technology on two-stroke engines. To expose the catalyst to the highest possible temperatures, the SCR reactor has been placed upstream of the turbocharger. Additionally, a number of engine control methods developed and patented by MAN have been implemented to ensure the required exhaust temperatures.
Source: MAN Diesel & Turbo