Environmental Engineering Reference
In-Depth Information
with NO
2
, the slightly higher NO
3
concentration at low pH levels is attributed to
two reactions: (i) a part of the generated HNO
2
participates in its ionization
reaction (as shown in Eq. (4.6)), where HNO
2
is a product of the NO
2
hydrolysate
reaction presented in Eq. (4.4); (ii) the left unionized HNO
2
transforms into HNO
3
,
following the reaction shown in Eq. (4.7). A low pH facilitates the reaction
balance in Eq. (4.6) to moves toward the left and thus increases the HNO
2
concentration. As a result, these circumstances accelerate the reaction in Eq. (4.7).
HNO
2
=
H
+
+NO
2
(4.6)
3HNO
2
=
HNO
3
+2NO+H
2
O (4.7)
Fig. 4.4
Concentration of NO
2
and NO
3
in the solution at different pH values
Additional attention is needed to determine the effect of the reaction in Eq.
(4.7) during the removal process. The aforementioned results have already
uncovered that the NO concentration of remains around the initial value of 11 ppm
at different pH values (Fig. 4.3); this indicates that the NO generated through the
reaction in Eq. (4.7) is not considerable enough. The essentially low NO
x
concentrations in the simulated flue gas actually develop a low HNO
2
concentration (usually around 10
5
) in the absorption solution, which can
decreases further because of the occurrence the reaction in Eq. (4.6). Obviously,
the resulted decomposition reaction in Eq. (4.7) is negligible
[21]
, without affecting
considerably the final removal efficiency.
In consequence, a relatively strong
HNO
2
decomposition process (finally resulting in a little higher NO
3
concentration than that of NO
2
) during a full experiment test should occur in the
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