NOx buster for MAN

MAN B&W has seen the first installation of a selective catalytic NOx reduction system on one of its 6S35MC diesels. The ship has now passed its test trials and begun reduced-emission operations. The SCR option for cutting NOx output on a two-stroke was achieved aboard the Navion Dania, a 7,500m3 LPG carrier owned and operated by Norwegian companies Navion Shipping and Rasmussen Maritime Services. When built in 2000 by Hyundai Ulsan in Korea, the ship was prepared for later fitting of the SCR system. The shipyard and MAN B&W licensee Hyundai Engine Machinery installed urea tanks and a loading system, added an extra flange on the engine exhaust gas receiver and provided larger electric motors for the auxiliary blowers. A Haldor Topsoe SCR system was installed in just six days this spring. Subsequent trials were undertaken successfully during the summer. The SCR reactor is installed before the turbocharger, as the temperature level there allows the use of normal heavy fuel oil; this would not be possible if the SCR system were behind the turbocharger, as there would be problems with condensation of ammonia sulphate. The heat capacity of the catalytic elements is compensated for during transient load by the installed SCR bypass valve, turbocharger bypass valve and auxiliary blowers. When temperature equilibrium is reached, and the SCR bypass valve is fully closed, urea injection begins. All valves, blowers and urea supply is automated. The amount of injected urea is based on a pre-set level of NOx emissions and the engine load curve. The curve is adjusted based on data from a feedback NOx measurement in the stack. On the 6S35C, the system works at between 40 and 100% engine load, when running on HFO with a sulphur content of up to 2.4%. Below about 40% engine load the injection of urea is stopped due to low exhaust gas temperatures; this avoids the condensation of ammonia sulphates.