Environmental Engineering Reference
In-Depth Information
3.4.2 Reaction Competition Between NO and Hg
0
with Ozone
Both NO and Hg
0
, existing in coal-fired flue gas, can be effectively oxidized by
ozone or O radical. Therefore, the competition between NO and Hg
0
with ozone
needs to be clarified. Hg
0
can also be oxidized by high-order nitrogen species,
such as NO
2
, and NO
3
, as shown in the following reactions:
NO
2
+Hg
=
HgO+NO (3.21)
NO
3
+Hg
=
HgO+NO
2
(3.22)
Fig. 3.18 indicates the reactions between the ozone and a mixture of NO/Hg at
423 K. Apparently, the NO oxidation is easier than that of Hg
0
. Almost all NO can
be converted into higher order nitrogen species when the O
3
/NO stoichiometric
ratio is larger than 1.0. On the contrary, only a limited increase (from 12% to
39.7%) appears in the oxidation rate of Hg with increasing continuously the ozone
concentration. These observations suggest that NO is prior to elemental mercury
in the ozone oxidizing reaction competition. Apart from the direct oxidation of NO
into NO
2
, further NO oxidation reactions (such as the formation of NO
3
and N
2
O
5
)
consume parts of the excessive ozone, which counteracts the Hg
0
oxidation to
some extent.
Fig. 3.18
Reaction competition between NO and Hg
0
with ozone,
T
= 423 K
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