Environmental Engineering Reference
In-Depth Information
During Coal Combustion
with the temperature decrease along the rear heating surface, and Hg 0 dropped
dramatically after 3.4 s, especially at the exit of the downdraft economizer. Whereas
the mercury oxide such as HgCl 2 , HgCl and HgO appeared and increased a little
with the resident time increase, the amount of HgCl 2 appearing was dominant,
fitting in well with Hg 2+ production. Definitely, HgCl 2 speeded up greatly after a
residence time of 3.4s corresponding to the area between downdraft air preheaters
and the electrostatic precipitator (temperature 540 - 383 K).
1 200
platen superheater
1 000
high temperature superheater
high temperature reheater
800
steering rooom
600
up economizer
up air preheater
400
down economizer
down air preheater
200
electrostatic precipitator
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Fig. 4.84 Rear heating surface temperature distribution and its residence time
Resident time (s)
Table 4.18 Simulation input component parameter (mole fraction)
N 2
2
CO 2
2 O
CO
SO 2
NO
H 2 S
HCl
0.74
0.03
0.17
0.06
5.23E-04
3.00E-04
3.00E-04 5.84E-05 2.51E-05
Cl 2
Cl
H 2
H
OH
Hg
HgCl 2
HgO
1.80E-07 1.70E-10 1.52E-04 1.71E-04
1.20E-04
9.54E-10
3.90E-11 7.02E-11
Note: All parameters derive from integral value calculated in three-dimensional furnace outlet surface
From Fig. 4.86, Hg 0 concentration at the furnace outlet was about 8.52 g/m 3 ,
and Hg 2+ content was 1.15 g/m 3 . HgO and HgCl 2 were 0.68 and 0.47 g/m 3 indi-
vidually. Hg 0 concentration reduced with rear flue temperature decrease. Mean-
while, Hg 2+ concentration was constantly enhanced due to a great deal of HgCl 2
generation instead of HgO. However, the rear temperature hardly had an effect on
HgO production, so HgO concentration continuously remained constant with the
resident time going up. That was because the low temperature helped HgCl 2 pro-
duction with the existence of Cl 2 . Sometimes Cl 2 was actively superior to oxygen,
and HgO was oxidized to HgCl 2 possibly. Furthermore, intermediate production
HgCl slightly increased with an Hg 0 concentration decrease and Hg 2+ concentration
enhancement by comparison between Figs. 4.85 and 4.86.
Hg 2+ content rose to 4.3 g/m 3 in flue gas at the outlet of the electrostatic pre-
cipitator. Fig. 4.87 illustrated that the temperature decrease induced Cl 2 generation
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