A cold shower for SOx emissions

Could scrubbers be a way to lower SOx in the exhaust gas? Read more about the first test installation on Maersk Tukang.

A Belco scrubber was installed on one auxiliary engine on Maersk Tukang in 2013-2014 and has been running since May 2014 in open loop.
The first test ever run on a scrubber on a Maersk vessel has just come to an end and the results are rather promising. What started as an innovation project in 2010 could now be a viable technology to bring down SOx emissions to meet the IMO requirements that entered into force in January 2015.

Why is SOx undesirable?

SOx, or sulphur oxides, are, besides NOx (nitrogen oxides), one of the two main causes of acid rain. Acid rain is known to have adverse impacts on forests, freshwaters and soils, killing insects and aquatic life-forms as well as causing damage to buildings and having negative impacts on human health.
SOx emissions from ships correspond to the sulphur content in the fuel, currently 3,5 %, and 1 % in Emission Control Areas (ECAs).

Relevant regulations
In 2012, the International Maritime Organisation (IMO) revised the MARPOL Annex VI to reduce the global sulphur cap from 4.5 % to 3.50 %. The limits applicable in ECAs for SOx and particulate matter were further reduced to 0.10 %, effective from 1 January 2015. It goes without saying that Maersk has to comply with these regulations, which is why Maersk Maritime Technology is closely monitoring the regulatory developments as well as testing technical solutions to meet them. 

But how do we comply with such a drastic cap in SOx emissions? The most obvious solution would be to turn to low sulphur fuel. However, only Diesel oil has a low enough sulphur content to be able to meet the future 0.10 % regulations in ECAs - and Diesel oil is for the time 50% more expensive than regular heavy fuel oil (HFO).

For vessels that operate in ECA areas the majority of their trading time, it can be beneficial to use a scrubber instead of low sulphur fuel, depending on the price spread between heavy fuel oil and low sulphur oil.
This project is exciting because it could potentially provide us with a solution to meet one of the biggest regulatory and environmental challenges – SOx. It is exciting to test out brandnew technical solutions that really can make a difference and at the same time challenge me in my field of expertise.
Per Hother Rasmussen, Propulsion & Automation systems in MMT

When MMT was approached by scrubber manufacturer Belco who offered a free scrubber for testing on one of our vessels, as long as we paid the installation cost, we accepted in the light of the upcoming regulatory pressure. The Belco scrubber was installed on one auxiliary engine on Maersk Tukang in 2013-2014 and has been running since May 2014 in open loop. 

A scrubber works in many ways like a shower. By sprinkling the exhaust gas with salt water in a pipe, it removes the SOx almost entirely and the exhaust gas can be released from the ship. The water with the washed off sulphur can be released into the ocean when certain limits are maintained according to ISO Guidelines.

The project is expected to be concluded officially in April 2015 when the closed loop is tested as well. So far there are positive results: SOx emissions were not only reduced to the required 0.1 %, but down to 0.01 %. Good results however rarely come without a cost: in this case energy. A scrubber obviously requires energy to be operated – the more the exhaust gas is cleaned, the more energy, i.e. fuel, is required. This situation causes some complexity in the calculation as it needs to be taken into consideration how much the vessel operates in ECAs. One way to alleviate this problem was a recent modification: the scrubber has now been modified with smaller nozzles allowing for less water consumption and thereby less power consumption.


Scrubbers are costly to install as precious metals or special materials are needed for the installation to avoid corrosion. Further, a scrubber takes up a lot of space in the casing and in engine room for pumps, tanks and scrubber body itself - space you may not have readily available on a ship. In such case the casing can be extended, or a completely new casing can be made where the components are arranged in a more optimal way with available space. The Belco scrubber we are testing is 11 meters high and 1,6 meters wide.
Which solution, or combination of solutions the Maersk business units will go for is not sure yet, but scrubbers seem to be a workable and functional one for certain vessels.