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Case: Wärtsilä SOx Reducer

Fresh water SOx scrubber

The Wärtsilä SOx reducer is a fresh water and sodium hydroxide (NaOH) based closed loop exhaust gas scrubber, designed to remove SOx from the exhaust gas stream of ships. The Wärtsilä SOx reducer scrubber system is an efficient and cost-effective alternative to the use of low sulphur fuel for reducing SOx emissions. Wärtsilä is the first manufacturer to have been awarded a marine SOx scrubber certificate issued by Det Norske Veritas and Germanischer Lloyd.


As a default, the scrubber system is designed for fuel having a maximum sulphur content of 3.5%. The SOx reduction efficiency is 97.15%, corresponding to a reduction of fuel sulphur content from 3.5% to 0.1%. This is the typical guaranteed performance of the system.


The SOx scrubber system is available in two different configurations:

  • Main stream scrubber
  • Integrated scrubber

The main stream scrubber is designed to be installed in the main exhaust gas stream of an individual diesel engine. The exhaust gas pressure loss over the main stream scrubber at full gas flow is typically approximately 800 Pa.

The integrated scrubber is designed to clean the exhaust gases of several main and auxiliary engines, as well as onboard oil-fired boilers, with a single scrubber unit. The integrated scrubber system does not increase the exhaust gas back pressure, thus making it particularly suitable also for oil-fired boilers and all diesel engines.

Test and testing results onboard MT Suula

A Wärtsilä fresh water testing unit was installed onboard the Neste oil tanker MT "Suula". Testing of the unit was started in 2008 and completed in 2010. The MT "Suula" sailed mainly around the Baltic Sea, but also visited North Sea harbours. Normal ship operations were not interrupted or limited during the tests. Test data was recorded in many ways, including a tamper-proof recording device. Gas and liquid samples were taken. Classification societies surveyed the certification process.

The test results were very positive. The measured sulphur reduction was excellent, and well within the International Maritime Organisation's (IMO) most stringent limits. Furthermore, other measured exhaust and effluent parameters were favourable. The effluent was very clean, and the sludge produced by the water cleaning unit was found suitable for normal disposal at port reception facilities. The scrubber and its auxiliary systems worked with a good level of reliability. Sea conditions did not affect or limit the scrubber's use.

Sulphur removal efficiency during certification tests

Test 12345678
Engine test load % 8 40 70 100 8 40 70 100
Fuel sulphur content % m/m 1.5 1.5 1.5 1.5 3.4 3.4 3.4 3.5
SO2 after scrubber * ppm-v 0 0 0 0 0 0 0 0
CO2 after scrubber %-v 4.7 6.1 6.5 6.6 4.6 6.0 6.4 6.7
SO2 / CO2 ratio ppm/% 0 0 0 0 0 0 0 0
* A ‘0' value indicates the result was below measurable limits (~2 ppm).
Measurement equipment from a 3rd party accredited company has an accuracy of
±2 ppm. For reference 0.1 % sulphur corresponds to 20...30 ppm.

As a part of the certification test, the effluent quality was demonstrated to classification societies. The Wärtsilä scrubber fulfils all the effluent quality requirements thanks to the efficiency of the Wärtsilä water treatment unit. The IMO resolution MEPC.184 (59) defines limits for pH, turbidity, PAHphe and nitrate content. Metals in the effluent were also measured. The tests showed that after the water treatment unit, PAHphe concentration and turbidity are clearly below the IMO limits. The pH of the effluent was over 6.5, which is the IMO limit for effluent pH. Certification tests also proved that nitrate concentration in the effluent is below the IMO limits.

Reduction in concentration of chemical components in the bleed-off
treatment unit with a fuel sulphur content of 3.4% m/m.

More information can be found in Wärtsilä's public test report.