Enhancement Mechanism on Removal of NO in Shipping Desulphurization System Using NaOH Solution

Abstract

The NO removal characteristic of sodium-alkali solutions was studied in a counter current packed column in continuous flow mode. The effect mechanism of pH, S(IV), H₂O and UV oxidation was discussed in the paper. When S(IV) did not exist in the absorbent, pH was not effect on removal of NO. When there was S(IV) in the absorbent, the NO removal was high and pH was also effect on NO removal. The essence of reaction was that the high pH value could increase the concentration of S(IV) and the redox reactions of NO were stronger than hydrolysis reactions. The mechanism of UV oxidation on NO removal was also deduced. The active molecules such as O₃ derived from UV-photocatalytic were the main ingredient enhancing the conversion of NO to NO₂ and the oxidation ratio was associated with the oxygen content in exhaust. The presence of H₂O in exhaust could enhance NO removal, but the presence of SO₂ could reduce this enhancement on NO removal. The reaction showed that SO₂ could react with the OH radical and it could reduce the NO oxidation ratio. The experimental results show that the NO_x removal in desulfurization process is available under proper operation conditions and the NO_x removal efficiency can satisfy the stringent emissions regulations of International Maritime Organization.