Simultaneous Multi-Pollutants Removal with Ozone and Wet Scrubber - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 80

Fig. 4.9 Concentration of ions at different pH values with the existence of S(IV)

4.4.3 Effect of the Initial NO 2 Concentration

Experiments were carried out with typical solution parameters (i.e., a pH value of
5.5 with 0.01 mol/L tetravalent-S existence) that are usually used in desulfurizers.
Fig. 4.10 shows the removal efficiency variation with the initial concentration of
NO 2 . The removal efficiency decreases a little from 74 to 68% as the initial NO 2
concentration increases from 100 to 400 ppm. The variation behavior of the
concentration ratio of NO 2 /NO 3 can also be analyzed from this figure. The
NO 2 /NO 3 concentration ratio actually represents the comparison between the
redox reactions and NO 2 hydrolysis. It is concluded that advancing the two
reactions in Eqs. (4.10) and (4.11) can increase the ratio, while strengthening the
NO 2 hydrolysis, on the contrary, decreases the ratio value. The figure shows that
the NO 2 /NO 3 ratio decreases from 220 to 78 as the initial NO 2 concentration
increases from 100 to 400 ppm; this means that the proportion of the redox
reactions decreases. The reaction rates in Eqs. (4.10) and (4.11) can be expressed
as k=k o ×[S(IV)]×[NO 2 ]. With increasing the NO 2 concentration and maintaining
the total tetravalent-S (denoted by S(IV) here) concentration, both the first order
reaction rate constant remain constant, while the

absorbed NO 2 increases, thus increasing the S(IV) depletion in the solution.
Accordingly, the concentration of H + generated from reactions in Eqs. (4.10) and
(4.11) increases. These circumstances favor the occurrence of the reverse reactions
listed in Eqs. (4.8) and (4.9), thereby decreasing the NO 2 consumption in the
redox reactions. Consequently, the ratio of NO 2 /NO 3 decreases clearly with the

k o × [S(IV)] of NO 2 and