Mercury Speciation Transformation During Coal Combustion - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 94

employing the occurrence of an oxidizing reaction with Hg 0 . Cl component con-
centration varied with residence time as shown in Fig. 4.87. Free radical Cl had a
peak value of 0.4 ppm at the beginning of the reaction, whereas it was fast reduced.
Cl 2 gradually generated 1 s of residence time later, the highest concentration 0.1
ppm appeared by undergoing stable steps of 1 5 s. Consequently,

HgCl 2 generated was due to the existence of Cl 2 . The influence of HCl concentra-
tion on Hg oxidization was very little (Fig. 4.88), although its concentration had a
high value of 25 ppm. HCl concentration had a fluctuation trend at an earlier stage.
Moreover, there was little obvious concentration variety at 2

1.7 s and 2.5

5 s reaction stage.
Definitely, Cl 2 was the key active component participating in Hg oxidizing reaction
in the rear flue instead of other chlorine compounds, as the model indicated, which
was in good accordance with the literature [7] . Nevertheless, the oxidation was go-
verned primarily by HCl concentration, quench rate and background gas composi-
tion [6] . The mercury oxidation mechanism bears further investigation.

1.2

1.0

Hg 0
HgCl
HgCl 2
HgO

0.8

×

0.6

0.4

0.2

0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Resident time (s)

Fig. 4.85 Hg transformation in rear flue

1600

9

1400

8

7

1200

6

1000

5

800

Hg 0
Hg 2+
HgCl 2
HgO
Rear temperature

4

600

3

400

2

200

1

0 0

0 1 2 3 4 5

Resident time (s)

Fig. 4.86 Hg distribution proportion in rear flue