As our largest ecosystem, oceans provide more than half the oxygen we breathe and most of the fish we eat. They are also waterways for transportation. Healthy oceans are essential to our survival. As we become more mindful of the need to reduce our environmental imprint, the marine industry has increased its focus on ways to regulate its impact, including minimising the release of harmful emissions.
The release of sulphur in the atmosphere from marine vessels has caused considerable concern. The International Maritime Organisation (IMO) is introducing new environmental requirements to reduce the level of atmospheric sulphur from marine vessels. With the new regulation, substantial growth is anticipated for nickel-containing marine diesel exhaust scrubbers.
One design of scrubber, shown below, reduces emissions of sulphur oxides (SOX) by passing the exhaust gas stream produced by the engine through several chambers that contain a carefully generated “scrubbing cloud” of sea water. Scrubbing hot exhaust with seawater produces a corrosive environment that includes chlorides, high temperatures, and acidic conditions and as a result requires the use of corrosion-resistant alloys (CRA). CRA’s considered for this application include 6%Mo super austenitic stainless steels, such as AL-6XN™ (UNS N08367), to C-Type nickel alloys, such as Alloy 276 (UNS N10276) and Alloy 59 (UNS N06059).
The International Convention for the Prevention of Pollution from Ships (MARPOL) has established several Emission Control Areas (ECAs), which currently restrict allowable sulphur in the ship’s fuel to 0.10 wt%. These areas include the Baltic Sea, the North Sea, North America (covering designated coastal areas off the United States and Canada) and the United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands).
Currently, outside of the ECAs the global sulphur cap is 3.50 wt% falling to 0.50 wt% on January 1, 2020. The 2020 date is subject to a review of the availability of low-sulphur fuel oil and could be deferred to 2025 depending on the outcome. The review is expected to be completed by 2018.
Options to meet the regulations are to burn more expensive low sulphur fuel, switch to natural gas, or install an exhaust scrubber system, which is quickly becoming the preferred choice for the marine vessel industry.