Environmental Engineering Reference
In-Depth Information
When NO 2 was added to the simulated flue gas, Hg 0 adsorption by AC(XK)
increased substantially. On the other hand, the concentration of NO increased more
than that of NO 2 (Fig. 5.27). Based on the concentration changes of Hg 0 , NO 2 and
NO, Hg 0 was oxidized by NO 2 with the catalysis of surface carbon, which can be
expressed as the following reaction: Hg+NO 2 HgO+NO. When NO and HCl were
added, respectively, both did not affect Hg 0 adsorption by AC(XK) in this experi-
ment.
As confirmed in subsection 5.4.4.1, the impact of simulated flue gas compo-
nents on the changing speciation of Hg 0 was limited. When simulated flue gas was
switched to bypass in the middle of experiment, the concentration of Hg 0 reverted to
the initial concentration of the Hg 0 source (Fig. 5.27). This is similar to the con-
clusions obtained in subsection 5.4.4.1.
When the simulate flue gas switched back through the adsorption bed, Hg 0 was
again immediately adsorbed by AC(XK) in the simulated flue gas. When the si-
mulated flue gas components were added one by one, NO 2 was one of the best
components in terms of the promotion of Hg 0 adsorption by AC(XK).
In addition, NO 2 was first subtracted from the simulated flue gas components.
The subtraction of NO 2 from simulated flue gas did not have a great influence on
Hg 0 adsorption by AC(XK). This result can be attributed to the fact that the sub-
traction of NO 2 did not obviously change the concentration of NO 2 and merely
induced a slight decrease in NO concentration (Fig. 5.26). Moreover, NO 2 was
easily produced through the reaction between the O 2 and NO.
In the next stage, O 2 was removed from the simulated flue gas, which resulted in
a significant increase in NO concentration and a rapid decrease in NO 2 concentra-
tion. As a result, the outlet Hg 0 concentration of the adsorption bed increased. As
NO was consumed, the Hg 0 adsorption capability of AC(XK) was further reduced.
Among the other simulated flue gas components, HCl also had a greater influence
on Hg 0 adsorption by AC(XK), as shown in Fig. 5.27.
Prior to the individual removal of simulated flue gas components, AC(XK) had
already adsorbed the Hg 0 from simulated flue gas for nearly 3 h. This reaction
changed the composition on the surface of AC(XK) (see the discussion in subsec-
tion 5.4.4.2), which induced differences in the Hg 0 adsorption dynamic curves
between the process of adding simulated flue gas components and that of sub-
tracting simulated flue gas components. However, both Hg 0 adsorption dynamic
curves were generally symmetrical, indicating chemical adsorption. Moreover, Hg 0
adsorption by AC, which was produced using the physical method in simulated flue
gas, was a complicated chemical adsorption process relying on the both acidic
simulated flue gas components and surface carbon. In this experiment, NO 2 played
a major role in Hg 0 chemical adsorption by AC.
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