What happens to sulphur oxides in an exhaust gas cleaning system using seawater?
Seawater scrubbing requires the exhaust gases to be intimately mixed with seawater in order to dissolve the sulphur oxides. Manufacturers use various techniques to achieve mixing without unduly obstructing the passage of exhaust gas, as this could result in a “back pressure” outside of the engine builder’s limits and adversely affect engine operation. The sulphur oxides of shipping exhausts typically consist of ~95% sulphur dioxide, SO2 and the remaining ~5% of sulphur trioxide, SO3. When dissolved, a reaction occurs whereby the sulphur dioxide is ionised to bisulphite and sulphite, which is then readily oxidized to sulphate in seawater containing oxygen [1].
