Wet oxidation of NO with NaClO2 in alkaline conditions: effects of acidic components in flue gas

Abstract

Excessive ClO₂ tends to be produced and escape, causing secondary pollution when wet oxidation of NO with NaClO₂ is conducted under acidic conditions. NaClO₂ alkaline oxidation has accordingly received a wide attention. In this work, NaClO₂ alkaline oxidation of NO has been systematically studied in a self-built spray tower. Focus has been placed on the effects of acidic components contained in flue gas such as CO₂, HCl and SO₂. ClO₂ and HClO₂ are considered more effective for NO oxidation, which tend to be produced in an acidic environment. HCO₃⁻ has a relatively higher hydrolysis coefficient than ClO₂⁻, leading to more HClO₂ formation. Similarity is found with HCl although the effect is not as significant as CO₂ due to its low concentration in flue gas. SO₂ exhibits a negative effect on NO removal since HClO₂ can be consumed by SO₂. Nearly 100 % NO removal efficiency can be achieved although there is an initial time delay necessary for the neutralization of alkaline environment. A similar performance has been observed for HCl. On the contrary, SO₂ exhibits a negative effect on NO removal due to the competition with NO in the consumption of NaClO₂. Additives such as NaClO and CTAC were also used to enhance NaClO₂ alkaline oxidation performance. Interesting to note that CTAC can nearly eliminate the time delay by intensifying the gas-liquid mass transfer.