JAnUARy/FEbRUARy 2010
Positively Promising
THE MARITIME EXECUTIVE
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Positively Promising: Pressure on Propulsion The urgency to achieve a cleaner carbon footprint is perhaps felt more strongly in the highly visible passenger vessel sector than anywhere else. Fortunately, it turns out there’s more than one way to reach the Promised Land. Baseline
Compliance with the International Maritime Organization’s (IMO) new standards governing SOx emissions from ships affects both ship design and operation. The IMO isn’t the only regulator in the game, of course. Local Emission Control Areas (ECAs) also muddy the waters. Meeting SOx emission regulations is, therefore, no longer a lofty goal to strive for; it’s the law. Shipowners do have options. Compliance can be achieved by using low-sulfur fuel, utilizing more efficient engines or by cleaning exhaust gases using SOx scrubbers. Beyond this, regulatory compliance is only one part of the puzzle. Proving that a particular power system meets emissions standards will be quite another.
the Case for scrubbers
SOx scrubbers have been used, with great success, for shoreside power plants for
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many decades. Now – and in response to growing pressure from environmental regulations – these devices are being specifically designed for the requirements of ship’s power. And where engine design and lowering sulfur content for marine fuels prove insufficient to meet global and local emission standards, scrubbers can be the ticket to compliance. Simply stated, a scrubber is an aftertreatment technology for cleaning exhaust gases of sulfuric oxides. SOx scrubbers can be installed both for newbuildings and as a retrofit to existing ships. Combustion units can be diesel engines of any make, type, or application, 2-stroke or 4-stroke. The working principle of freshwater scrubbers is based on a closed loop system. Within the process sulfur oxides in the exhaust gas stream are captured and neutralized by scrubbing water. The scrubbing water is based on freshwater
By marEx staff boosted with alkali, typically sodium hydroxide (NaOH). As a result of the chemical process, sulfur oxides from the exhaust gas are neutralized to sulfates in the scrubbing water. The IMO and other regulators will gradually limit the sulfur content in marine fuels. The most common fuels used in marine diesel engines are heavy fuel oils with sulfur contents typically of 1.5 to 3.5 percent. Such engines can readily burn low-sulfur fuel oils as well, though the associated problems are known and suitable operating guidance is available. Scrubbing exhaust gases is an environmentally friendly and cost-effective alternative for reducing SOx emissions down to 0.1 percent. A list of current SOx ECAs includes the Baltic Sea, North Sea and English Channel. In the future, this will expand to North America and most likely to other sensitive areas. Beyond this, the IMO Marine Environmental Protection Committee adopted “Guidelines for Exhaust Gas Cleaning Systems,” IMO Resolution MEPC.184(59), in July 2009. The guidelines include rules for certification, verification and documentation of scrubbers and regulations for monitoring and discharge of washwater.
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