Hybrid Scrubber Test Plan

Abstract

During recent years, increasing attention has been directed towards ship emissions and their reduction. The United Nations specialized agency, IMO, is in charge of creating and setting regulations for ship emissions. Particularly, sulphur dioxide emissions from ships are subject of being tightened. For instance, starting from 1.1.2015, in SECA area which covers almost the entire northern European seas, the permitted sulphur dioxide emission corresponds to the usage of fuel oil containing only 0.1 % of sulphur.

Sulphur dioxide emissions can be reduced by using two different methods. The first and more expensive one is the use of low sulphur fuel oil. The second and more attractive method is to use high sulphur fuel oil and remove sulphur dioxide from the exhaust gas by washing it. For this purpose there are scrubbers which operate typically either by us-ing sea water, or fresh water + alkali solution. The same cleaning result can be achieved by using any of the methods. Sulphur dioxide is soluble in water and is converted fur-ther to environmentally harmless substances, to sulphites and sulphates.

The purpose of this study was to create a test plan for a hybrid scrubber which can util-ise both sea water and fresh water simultaneously in the same process chain. By using this method, an effective cleaning result can be achieved regardless of levels of critical values of the sea water scrubber, water alkalinity and temperature. In practice, the sea water stage removes as much sulphur dioxide as its capacity allows, and the fresh water part finalises the cleaning result.

The test program includes more than 200 different tests. This is due to the fact that the sea water scrubber stage, and therefore the total cleaning performance of the hybrid scrubber, is substantially affected by ambient conditions such as seawater temperature and alkalinity. The most effective cleaning result is anticipated to be reached in a geo-graphical area where sea water alkalinity is high and temperature low.