Mercury Speciation Transformation During Coal Combustion - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 60

namics analysis on mercury transformation is to be performed if possible, if the
typical gas components, initial concentration of mercury and reaction condition
(pressure, temperature) are input into the Equilib module.
Table 4.12 shows mercury compound included in the model, which comprises the
mercury chemical species in gas/liquid/solid phases when specified elements or
compounds react or partially react to reach a state of chemical equilibrium. In fact,
most of them are intermediate products which are unstable, liable to decompose
with a temperature increase.

Table 4.12 Mercury compound included in the model

Gas phase Hg, Hg[+], Hg 2 , HgH, HgCl, HgCl 2 , Hg(CH 3 ) 2 , HgO, HgS

Liquid phase Hg, HgCl 2 , Hg(CH 3 ) 2

HgO, HgS, HgSO 4 , Hg 2 SO 4 , Hg 2 CO 3 , Hg 2 C 2 O 4 , Hg 2 (N 3 ) 2 , Hg 2 (N 3 ) 2 ,
Hg 2 (CNS) 2 , Hg 2 (C*N*S) 2

Solid phase

During calculation, four cases with various initial conditions are given here
(Table 4.13). A typical coal-fired flue gas such as O 2 (0 - 7%), CO 2 (fixed at 13%),
N 2 as balance gas (80% - 87%), were considered firstly. Other cases involved 4%
O 2 , 13% CO 2 , 83% N 2, HCl (0 - 1000 ppm), NO (0 - 900 ppm), SO 2 (0 - 1200 ppm)
simultaneously. The initial mercury concentration in the flue gas was 18.75 g/m 3 ,
equivalent to 9.3E - 08 by mole fraction. The flue gas temperature was arranged at
300 900 K, ambient pressure. In general, mercury tended to be oxidized with the
assistance of an oxidizing agent, such as chlorine, oxygen, nitrogen oxide, sulfur
oxide. The mercury transformation was defined as mercury oxidization, as

mercury transformation
mass of mercury oxide in the flue gas

ˁ

(4-28)

˙ *100%

ˇ

mass of mercury oxide mass of elemental mercury

Table 4.13 Initial condition during the calculation
Case 1 Case 2 Case 3 Case 4

O 2 N 2 CO 2 4%O 2 -13%CO 2 -83%N 2

O 2
(%)

Mole
fraction

N 2
(%)

Mole
fraction

CO 2
(%)

Mole
fraction

HCl
(ppm)

NO
(ppm)

SO 2
(ppm)

0 0 87 1.214 13 0.181 0 0 0

0.2 0.002 86.8 1.212 13 0.181 20 100 100

0.5 0.007 86.5 1.207 13 0.181 50 300 500

1 0.014 86 1.200 13 0.181 100 600 1200

2 0.028 85 1.186 13 0.181 150 900 -

4 0.056 83 1.158 13 0.181 500 - -

7 0.098 80 1.117 13 0.181 1000 - -