30 December 2011
Japanese classification society ClassNK has issued its first IMO Tier III emission certification for a marine diesel engine, according to a report by Motorship. The certification, issued on November 1, 2011, confirms that the engine meets the IMO MARPOL Annex VI Tier III NOx emission limits.
The engine is fitted with a selective catalytic reduction (SCR) system—developed by Hitachi Zosen—installed in a pre-turbo location. The unit is the main propulsion engine for the Santa Vista, a 37,800 dwt general cargo ship built by Naikai Zosen for Nissho Shipping, which entered service on October 31, 2011.
The pre-turbo location exposes the SCR catalyst to the highest possible exhaust temperatures, which is very important in installations on cool running, large two-stroke engines. However, due to the thermal mass of the SCR reactor, the pre-turbo location creates challenges for transient turbocharger response and requires a more refined design of the turbocharger system.
The Tier III NOx emission limits become effective from 2016 and are applicable for vessels within IMO Emission Control Areas (ECA). The Tier III standards require an approximately 75% NOx emission reduction from the current, global IMO Tier II levels. The absolute Tier III limits range from 3.4 to 1.96 g/kWh, depending on the engine maximum operating speed.
ClassNK recently issued “Guideline for SCR (Selective Catalytic Reduction) Systems and Reductant Agent Supply Systems” to assist manufacturers in installing SCR systems on commercial vessels.