11 September 2009
A sulfur oxides (SOx) scrubber for marine engines developed by Wärtsilä has been granted a Sulphur Emission Control Area (SECA) Compliance Certificate by the classification societies Det Norske Veritas and Germanisher Lloyd. The Wärtsilä scrubber—an aftertreatment device for removing of sulfur oxides from the exhaust gas—is the first ever marine scrubber to be awarded this certification.
A full size SOx scrubber test plant was installed on board the ‘MS Suula’, and was used to clean the exhaust gases from the ship’s 4-cylinder in-line Wärtsilä 20 auxiliary diesel engine. This Neste Oil owned, Finnish registered product tanker operates mainly in the IMO SECA Baltic Sea area. Tests performed with both high sulfur (3.4%) and low sulfur (1.5%) heavy fuel oil verified that the scrubber system efficiently removed SOx from the exhaust gas. The measurements, which were part of the certification process, demonstrated an SO2 removal efficiency of 99% throughout the load range and with both fuels. The efficiency of NOx removal was 3-7%. The removal of PM was in the range of 30-60%.
The Wärtsilä technology is a closed-loop fresh water scrubber, where SOx is neutralized using NaOH. The closed-loop system features cleaning of a small bleed-off extracted from the loop. Clean effluents can be safely discharged overboard. If operation in zero discharge mode is requested, the effluent can be collected in a holding tank for scheduled, periodical discharge.
The International Maritime Organization (IMO) gradually limits the allowable sulfur content in marine fuels, but allows SOx aftertreatment in lieu of switching to low sulfur fuels. The most common fuels used in marine diesel engines today are heavy fuel oils (HFO) with a typical sulfur content of 1.5 to 3.5%. With more stringent fuel sulfur regulations, SOx scrubbing is a potentially attractive way of minimizing operational costs by continuing the use of HFO. Wärtsilä estimates that in 2015, when the final IMO sulfur limit of 0.1% becomes effective in SECA areas, the return on investment from using the scrubber with the less expensive HFO fuel can be less than one year.
The Wärtsilä SOx scrubber system complies with the new IMO Guidelines, adopted in July 2009, for cleaning the exhaust emissions from all 2- and 4-stroke engines, including main and auxiliary engines, as well as from oil-fired boilers, in retrofits and newly built ships (IMO Resolution MEPC.184(59)).