Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 131

When Step 2 was finished, the simulated flue gas components were introduced
into the gas flow one by one. Meanwhile, the total flow was kept constant by ad-
justing the N 2 balance gas. The effect of different flue gas components on Hg 0
adsorption was evaluated in this step.
Once all the gas components were added, the adsorption of Hg 0 by AC in the
complete simulated flue gas started. The adsorption time in the Step 4 was quite
long at approximately 41 h and 22 min. The effect of flue gas components on Hg 0
adsorption and the mechanism of Hg 0 adsorption by AC were studied.
Fig. 5.28 shows the outlet Hg concentration on the fixed adsorption bed. Ini-
tially, the rate of Hg 0 adsorption by AC was very high. As the experiment pro-
ceeded, Hg 0 was detected 4 h later, and its concentration reached 14.2 g/(N·m 3 ) at
the 16 th hour; Hg 2+ never emerged during the entire process. The above-mentioned
Hg 0 adsorption phenomenon seemed to indicate that the Hg 0 adsorption by AC in
N 2 may be a physical adsorption. When the Hg 0 adsorption by AC was a physical
adsorption, the saturated adsorption of the AC was reached at the 16 th hour (Fig.
5.28). Then, more Hg 0 would no longer be adsorbed by AC because all the pores in
the surface of AC were filled by Hg 0 when the AC had reached the saturated ad-
sorption. However, the following adsorption in the simulated coal-fired flue gas
provided interesting and important results.
When the gas flow into the reactor was switched from N 2 to simulated gas
components one by one, the concentration of Hg 0 dropped (Fig. 5.28) (Step 3). The
influence of different gas components on Hg 0 adsorption was observed during
switching from N 2 gas to the simulated flue gas from 15:59:50 to 19:29:50 (Fig.
5.29). Excluding CO 2 , almost all other gas components, especially NO, enhanced
Hg 0 adsorption by AC.
Fig. 5.29 Concentrations of Hg 0 and Hg 2+ during switching from N 2 gas to simulated flue gas
Competitive adsorption also existed between CO 2 and Hg 0 on AC. Accordingly,
Hg 0 concentration increased because surface conditions of AC favored CO 2 ad-
sorption when CO 2 was added at 15:59:50.