Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 123

cific active element apart from possible hydrogen and oxygen elements, according
to the steam activation method. However, it was obvious that the oxygen functional
groups did not work in the process of Hg 0 adsorption by ACs in the N 2 environment
in this study. Hence, steam activation was not a good choice for preparing ACs to
capture Hg 0 .
In contrast to the steam activation methods of AC(XK)/AC(YK)/AC(MJ),
AC(MZ) was prepared through a chemical method using ZnCl 2 . Then, some ZnCl 2
was left in the AC(MZ). Previous studies have shown that the Cl element can fa-
cilitate the adsorption of AC to Hg 0 . Table 5.10 shows the results of the analysis of
the surface chemical element of AC(MZ) and treated-AC(MZ). The percentage of
Cl was 0.31% (weight) or 0.11% (atom), whereas the percentage of S was 0.24%
(weight) or 0.09% (atom) on AC(MZ). The proportions of Cl and S were lower than
those of other elements in AC(MZ), but the amounts of Cl and S were greater than
those of Hg 0 in the N 2 environment. For the purpose of proving the importance of
the chemical elements (e.g., Cl and S) in the Hg 0 adsorption by AC, a high tem-
perature treatment system was utilized to remove SFGs from the surface of
AC(MZ). The treated AC(MZ) was labeled as AC(MZ-T). Furthermore, there was
nothing on the surface of AC(MZ-T) except for C.

Ta b l e 5. 1 0 Percentage of elements in AC(MZ) and AC(MZ-T)

ACs Element Peak value Weight (%) Atom (%)

C 33474 96.66 97.68

O 1179 2.79 2.12

AC(MZ)

S 195 0.24 0.09

Cl 248 0.31 0.11

AC(MZ-T) C 1759 100 100

Fig. 5.22 shows the Hg 0 adsorption curves of AC(MZ-T) in the N 2 environment.
When the gas flow was switched to adsorption, there were noticeable decreases for
both the outlet Hg 0 concentrations with initial Hg 0 concentrations of 16.9 and 13.7
g/(N·m 3 ), respectively. The decreases were around 30% of the initial Hg 0 con-
centrations. The adsorption curves quickly rose back to the initial Hg 0 concentra-
tions at about 5 min (Fig. 5.22). Thus, AC(MZ-T) only had limited adsorption
capability of Hg 0 in the N 2 environment, which could be the result of incomplete
surface cleaning (Fig. 5.22). In other words, if it did not have the chemical element
on its surface, the Hg 0 adsorption capability of AC(MZ) in the N 2 environment
would have been similar to those of AC(XK), AC(YK), and AC(MJ).
The results of determining by Autosorb/1/C indicated that the surface physical
structure of AC(MZ-T) was almost the same as that of AC(MZ). Compared with
AC(MZ), there was a decrease of approximately 20% in the specific surface area
and pore volume of AC(MZ-T) (Table 5.8). However, the 20% loss in porosity
resulting from high temperature treatment did not cause the observed elimination of
the Hg 0 adsorption capacity of the treated sample.