Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 125

5.4.4 Hg 0 Adsorption by ACs in Simulated Flue Gas Environment

The Hg 0 adsorption by AC is a chemical process in the N 2 environment. This
chemical force may be attributed to elements on the surface of AC as well as to the
adsorption environment. During the process of adsorbing Hg 0 from coal-fired flue
gas, AC confronted many kinds of flue gas components, such as SO 2 , NO 2 , O 2 , H 2 O,
HCl and so on, except for mercury.
Here, Hg 0 adsorption by AC(YK), AC(XK), and AC(MZ-T) in the simulated flue
gas was conducted, following the work conditions shown in Table 5.11. The ex-
periment was divided into three stages: first, the stabilization of the Hg 0 source in
the balance of N 2 gas through bypass; second, the adsorption of Hg 0 in the N 2 at-
mosphere by ACs; and third, the adsorption of Hg 0 in the simulated flue gas at-
mosphere by ACs.

Ta b l e 5. 11 Work conditions of Hg 0 adsorption using ACs in the simulated flue gas
Work
condition

Hg 0
(g/(N·m 3 ))

Flow
(L/min)

Sorbent
(g)

Thickness of
fixed bed (mm)

Temperature
(°C)

AC

No.1 YK-AC 1 19.4 0.0505 About 2 130

No.2 XK-AC 1.3 14.1 0.0505 About 2 130

No.3 MZ(sm)-AC 1.3 13.7 0.0507 About 2 130

When the absorption atmosphere was switched from N 2 to simulated flue gas,
AC(YK), AC(XK), and AC(MZ-T) showed good Hg 0 adsorption capacities and had
an initial Hg 0 adsorption efficiency of 80% (Fig. 5.23). This result showed that
simulated flue gas composition promoted Hg 0 chemical adsorption by ACs. How
was the chemical adsorption formed? Was Hg 0 first oxidized into Hg 2+ in the
simulated flue gas and then adsorbed by ACs? Was Hg 0 chemically adsorbed di-
rectly by ACs? This section focuses on the influence of flue gas composition, Hg 0 ,
and activated carbon surface on Hg 0 adsorption by ACs in a simulated flue gas
environment.

5.4.4.1 Influence of Simulated Flue Gas Components on Hg 0 Speciation

The influence of the simulated flue gas component on Hg 0 speciation was studied at
the temperature of a flue tail. In this experiment, the mercury speciation was
monitored in real-time when simulated flue gas components were changed step by
step. The simulated flue gas components were changed in four phases described
below.
In the first phase, the amount of carried Hg 0 gas was 300 ml/min, the balance gas
of N 2 was 966 ml/min, and total flow of simulated flue gas was 1266 ml/min. As a
result, the concentration of Hg 0 was 14.1 g/(N·m 3 ) and that of Hg 2+ was 0.7
g/(N·m 3 ). In the second phase, simulated flue gas components were added (except
for H 2 O): O 2 /CO 2 /SO 2 / NO 2 /NO/HCl. In the third phase, H 2 O was added based on