What happens to sulphur oxides in an exhaust gas cleaning system using fresh water with a chemical additive such as sodium hydroxide?
In a freshwater scrubber using caustic soda, the simplified chemical reactions with sulphur oxides are shown below. A mixture of sodium sulphite, sulphate and bisulphite is produced. The proportion of each depends on the pH and amount of oxidation [22]
Relevant Chemistry
Caustic Soda
NaOH(s) + H2O > Na+(aq) + OH–(aq) + H2O
Sulphur Dioxide
2Na+ + 2OH– + SO2 > Na2SO3 (aq sodium sulphite) + H2O
2Na+ + 2OH– + SO2 + ½ O2 > Na2SO4 (aq sodium sulphate) + H2O
Na+ + OH– + SO2 > NaHSO3 (aq sodium bisulphite)
Sulphur Trioxide
SO3 + H2O > H2SO4 (sulphuric acid)
2.NaOH + H2SO4 > Na2SO4 (aq sodium sulphate) + 2.H2O
