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Two Ro-Ro vessels owned and operated by Stena Line, the Swedish transport and ferry company, are to be retrofitted with Wärtsilä in-line closed-loop scrubber systems.

The scrubbers are scheduled to be installed on the Stena Transit and Stena Transporter ferries operating between Hoek van Holland in the Netherlands and Killingholme in the U.K. The order was placed with Wärtsilä in December 2014 and the retrofitting is due to take place in the fourth quarter of 2015 and the first quarter of 2016.

By installing the scrubber systems, Wärtsilä asserts that the ferries will comply with the regulations covering emissions of sulphur oxides (SOx) while using conventional residual marine fuel. The operating routes of these two ferries fall within the North Sea's Sulphur Emission Control Area (SECA).

"This is the first ever order for an in-line closed-loop scrubber system, as the in-line option has earlier only been available with open-loop systems. The compact design of the inline system saves space and it also facilitates easier and faster installation, thereby reducing the length of time that the vessel needs to be out of service for retrofitting," Wärtsilä said in a statement.

The Wärtsilä closed-loop scrubber system operates so that the wash water is being circulated within the scrubber. Exhaust gas enters the scrubber and is sprayed with fresh water that has been mixed with caustic soda (NaOH). The sulphur oxides in the exhaust react with this mixture and are thereby neutralised. The cleaned effluents can be safely discharged overboard without causing harm to the environment.

"Wärtsilä was the first company to be awarded certification for marine scrubber technology, and we are the clear market leaders in this field. Our in-house know-how of engines, scrubber systems and marine applications is backed by our extensive resources and global reach. Furthermore, our extensive experience in retrofitting projects added considerable value to our engineering preparations for the project, and has thus helped the customer in their discussions with the yard. With the latest restrictions to sulphur emissions affecting more and more of the global fleet, our scrubber systems offer a competitive alternative to low sulphur fuels," commented Juha Kytölä, Vice President, Environmental Solutions, Wärtsilä Ship Power.

"Stena Line takes environmental issues very seriously and the retrofitting of Wärtsilä scrubber systems to these vessels will significantly lower their environmental footprint. We are also, in cooperation with Wärtsilä and other partners, converting the Stena Germanica on the route Göteborg-Kiel to be run on Methanol, another step in our strive to achieve sustainable shipping. In the scrubber retrofit we are especially happy with the in-line option, which means that the retrofitting will take less time and allow the ships to be back in service with a minimum of delay," remarked Bjarne Koitrand, Technical Director, Stena Line.

In addition to the scrubbers, Wärtsilä has also agreed to supply engineering support, technical advisor services, and commissioning of the systems.