Environmental Engineering Reference
In-Depth Information
It is quite common for denitration to adopt the typical alkali chemicals to
absorb NO
x
in the tail alkali absorption. The typical alkali chemicals comprise
KOH, NaOH, Ca(OH)
2
, Na
2
CO
3
, NaHCO
3
, and so on. Nevertheless, the
absorption efficiency is quite low because of the comparatively low reaction
activity indexes (definitely shown in Table 5.1) of these alkali chemicals.
Considering that NO is hardly soluble in water while its oxidized form of NO
2
has
a strong water solubility, NO should be transformed into NO
2
initially and
effectively absorbed by alkali solution afterwards.
Ta b l e 5. 1
Relative value of the reaction activity of
various alkali chemicals that absorb NO
x
Alkali chemicals
Relative value
KOH
1
NaOH
0.84
Ca(OH)
2
0.8
Na
2
CO
3
0.78
K
2
CO
3
0.63
Ba(OH)
2
0.56
NaHCO
3
0.51
MgCO
3
0.41
BaCO
3
0.4
CaCO
3
0.39
Nowadays, the WFGD technology is globally adopted, in which a
lime/limestone slurry washing is the most matures and widely used for the
coal-fired flue gas desulfurization because of its advantages cost-effective,
high-efficient, and abundant raw materials. The simultaneous removal
multi-pollutants through ozone oxidation and an alkali solution adsorption can be
easily obtained if NO
x
, SO
2
, H
2
S, Hg, and VOCs are sufficiently oxidized. If the
FGD system has already been installed in the power plants, the ozone oxidation
equipment can be installed before the desulfurization system. The oxidation
products and acids in flue gas can be absorbed by a CaCO
3
solution. If there is no
FGD existing, the ozone oxidation and chemical absorption equipments can be
installed after the dust collecting system. To evaluate the simultaneous
multi-pollutants removal performance, a pilot-scale ozone oxidation and chemical
absorption system has been established with a maximal 300 Nm
3
/h flue gas
processing capacity, as shown in Fig. 5.2.
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