Quick vaporization of sprayed sodium hypochlorite (NaCIO_((aq))) for simultaneous removal of nitrogen oxides (NO_x), sulfur dioxide (SO_2), and mercury (Hg°)

摘要

Sodium hypochlorite (NaClO) has been widely used as a chemical additive for enhancing nitrogen oxide (NOx; NO + NO2), sulfur dioxide (SO2), and mercury (Hg-0) removals in a wet scrubber. However, they are each uniquely dependent on NaClO(aq) pH, hence making the simultaneous control difficult. In order to overcome this weakness, we sprayed low liquid-to-gas (L/G) ratio (0.1L/Nm(3)) of NaClO(aq) to vaporize quickly at 165 degrees C. Results have shown that the maximized NOx, SO2, and Hg-0 removals can be achieved at the pH range between 4.0 and 6.0. When NOx and Hg-0 coexist with SO2, in addition, their removals are significantly enhanced by reactions with solid and gaseous by-products such as NaClO(s), NaClO2(s), OClO, ClO, and Cl species, originated from the reaction between SO2 and NaClO(aq). We have also demonstrated the feasibility of this approach in the real flue gases of a combustion plant and observed 50%, 80%, and 60% of NOx, SO2, and Hg-0 removals, respectively. These findings led us to conclude that the spray of NaClO(aq) at a relatively high temperature at which the sprayed solution can vaporize quickly makes the simultaneous control of NOx, SO2, and Hg-0 possible.Implications: The simple spray of NaClO(aq) at temperatures above 165 degrees C can cause the simultaneous removal of gaseous NOx, SO2, and Hg-0 by its quick vaporization. Their maximized removals are achieved at the pH range between 4.0 and 6.0. NOx and Hg-0 removals are also enhanced by gaseous and solid intermediate products generated from the reaction of SO2 with NaClO(aq). The feasibility of this approach has been demonstrated in the real flue gases of a combustion plant.