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Press Release - Source: Alfa Laval Tumba AB, Sweden

Searching for alternatives to heavy fuel oil to meet the revised International Maritime Organization Marpol Annex VI convention? There is a less expensive way to tackle the challenge than switching to distillate fuels. Consider Alfa Laval PureSOx to scrub diesel exhaust gas clean.

Full steam ahead

Alfa Laval PureSOx is a unique marine exhaust gas cleaning system. PureSOx is the only hybrid seawater/freshwater system that has proven its worth through 4,000+ hours in operation. It is also the largest system in operation today, capable of handling 200,000 kg of exhaust gas per hour.

The system was installed on the Ficaria Seaways [pictured], one of the RoRo vessels of the shipping company DFDS. It removes virtually all of the sulphur oxide (SOx) emissions and also partially removes other particulate matter - basically soot - from ship exhaust gases, enabling the release of clean steam from the vessel's large 10-metre high funnel.

PureSOx enables continued use of HFO

Fitted with this exhaust gas cleaning system from Alfa Laval, the Ficaria Seaways now meets IMO regulations that come into force in Emission Control Areas (ECAs) in 2015 and worldwide in 2020. But instead of using more expensive low-sulphur fuel, the vessel continues to use heavy fuel oil.

A 21-MW MAN B&W two-stroke main engine propels the Ficaria Seaways using heavy fuel oil with a sulphur content of 2.2 percent, and emits 200,000 kilograms of exhaust gas per hour. PureSOx washes the exhaust gas, reducing the SOx content to the 0.1 percent level demanded by IMO regulations that take effect in 2015.

"With this system we can carry on running with high-sulphur fuel oil on some of the ships. If we don't have a system like this, then we have to start using low-sulphur fuel on all ships in 2015, and that will be very expensive," says Søren Pedersen, the Ficaria Seaways chief engineer.

Quick return on investment

René Diks, Manager Marketing & Sales Exhaust Gas Cleaning at Alfa Laval, says that, in general, ships sailing through ECAs for 50% of their time or more can realize payback on investment in a PureSOx system in one to two years. Actual payback time will vary, depending on various factors, such as running hours, fuel prices and engine size. Diks notes that, for ships with larger engines, the payback time is quicker than for vessels with smaller engines because the payback time has a direct correlation to annual fuel consumption.

Save up to $1.8 million before 2015

According to Diks, the savings can add up to between $40-50,000 per month before 2015. Currently the ECA legislation requires the use of fuel with a sulphur content of 1%. Let's assume, for instance, that the difference in price between heavy fuel oil and lowsulphur fuel oil with 1% sulphur content is about $40 per tonne and that the vessel uses about 1,200 tons of fuel per month.

Based on these assumptions, the use of a PureSOx system can help realize a potential savings of up to $1.8 million in fuel costs alone over the next three years.

From 2015 onwards, these savings will increase significantly. Forecasts indicate a drastic rise in the price of low sulphur fuel oil. However, even when using current prices of heavy fuel oil and low-sulphur MGO with 0.1% sulphur, the price difference is approximately $300 per tonne. This means potential savings from installing a PureSOx system can amount to $3.6 million per year.

Strips more than 99% of sulphur from exhaust gas

The PureSOx hybrid system can use either seawater or freshwater to clean ship exhaust gas. When operating in seawater mode, it can clean more than 98 percent of sulphur out of the exhaust gases.

When operating in fresh water mode, it can clean more than 99 percent. The system is also able to trap up to 80 percent of particulate matter.

Operating the system in seawater mode drastically reduces the consumption of caustic soda and fresh water, thereby providing additional savings. In sensitive areas where overboard discharge of system water is not allowed, the system switches to freshwater mode. In this mode, the water used for cleaning the exhaust gas circulates in a closed system with zero discharge to the environment. Alfa Laval highspeed separation technology helps clean the effluent to ensure compliance with water criteria.

"Otherwise we would have to change water every eight or nine hours," says Pedersen. "We don't have enough fresh water on board to change it so often." The residue cleaned out of the water is collected for safe disposal onshore."

Just a big shower

So just how does the Alfa Laval Aalborg scrubber work? The scrubber sprays the hot exhaust gases rising through the ship funnel with water, washing away soot and other particles from the hot diesel exhaust gases and enabling clean steam to leave the funnel.

"It can be simply described as a big shower cabinet placed in the funnel of the ship," explains Olav Knudsen, head of R&D Exhaust Gas Cleaning at Alfa Laval. "Using water, either seawater or freshwater mixed with caustic soda, scrubbers wash the exhaust gas from the ship's engines."

First retrofit order signed

While the Ficaria Seaways is the first-ever RoRo vessel to install a single inlet PureSOx system, Diks says that other shipowners are signing up. Alfa Laval recently signed its first order for a multiple inlet PureSOx system with Spliethoff, a leading Dutch transport and logistics company. The system will handle exhaust from the vessel's main and auxiliary engines that have a combined rate output of 28 MW.