Mercury Speciation Transformation During Coal Combustion - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 65

Transformation After Coal Combustion

of HCl concentration on T ts and T te in mercury transition. The higher the concen-
tration of HCl gas, the higher the initial and cut-off temperature of mercury con-
version. Without HCl, T ts and T te were 900 K and 300 K, respectively. With the
assistance of a small amount of hydrogen chloride gas, T ts and T te in mercury con-
version were significantly higher. When the HCl concentration was 100 ppm, both
temperatures were 1,350 K and 800 K, respectively. Musmarra et al . [27] reported
that when the HCl concentration increased from 10 to 1,000 ppm in the incinerator
flue gas, the compounds of mercury had the same distribution. Sliger et al . [28] re-
ported 50% equilibrium conversion to HgCl 2 occurred at approximately 950 K in
the presence of 500 ppm HCl. Some equilibrium calculations declared that the 50%
conversion point depended on chlorine content in the flue gas [1] . Other investigators
proposed conversion points in the same general 800 900 K range [29] .

The existence of HCI could effectively improve the mercury transition tem-
perature, and the oxidation of mercury worked easily within a wide temperature
range. The calculation suggested that a higher concentration of HCl gas in the flue
would help Hg 0 convert to Hg 2+ at a higher temperature.

1600

1400

T ts
T te

1200

1000

800

600

400

0 200 400 600 800 1000

HCl concentration (ppm)

Fig. 4.67 Effect of HCl on the initial and cut-off temperature of mercury conversion

4.4.3.4 Influence of NO

In consideration of the actual coal-fired boiler flue gas components generally con-
taining NO of 300 600 ppm, case 3 (Table 4.11) was employed to analyze the

influence of NO on the transformation of mercury species by changing the con-
centration of NO. The simulation results are shown in Fig. 4.68.
By comparing Fig. 4.64(a) and Fig. 4.68(a), it could be seen that the reaction of
mercury trends and reaction products were the same with or without NO in flue gas.
That means the components of NO were insensitive to the homogenous conversion
to mercury. There was not any change happening even with an increase or decrease
in the concentration of NO. It was deduced by the simulation results that NO neither
promotes nor hinders the conversion of mercury, which plays a neutral role in the
homogenous reaction.