Chemical Kinetics and Oxidation Mechanisms Between O and NO/SO/Hg - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 63

Hg 0 +O 3 = HgO+O 2 (3.19)
Hg 0 +O = HgO (3.20)
Fig. 3.15 shows the experimental results of O 3 oxidizing Hg 0 at temperatures
ranging from 423 to 573 K. Apparently, the elemental mercury can be efficiently
converted into oxidized mercury by adding 50 - 100 ppm ozone (equaling to an
O 3 /Hg stoichiometric ratio of approximately 8900 - 17900). Thereafter, the
oxidation rate increases slowly with the ozone concentration. From 423 K to 473
K, an approximately 25% increase can be observed in the mercury oxidation rate.
The oxidation rate decreases a little as the temperature increases from 473 to 523
K. However, increasing further the temperature to 573 K decreases considerably
the oxidation rate. Around 80% of Hg 0 can be oxidized with 80 ppm ozone
(equaling to the stoichiometric ratio of approximately 14300) at 473 K. In contrast,
relatively lower conversion rates nearby 55% appear at 423 and 573 K.
Consequently, the optimal temperature range for Hg 0 oxidation should be 473 -
523 K, which is slightly different from that for NO oxidation. The above
observations suggest that the Hg 0 oxidation rate initially increases but then
decreases with the temperature. An explanation may rely on the decomposition of
O 3 and HgO at higher temperatures, which counteracts the oxidation reaction.
Fig. 3.15 Mercury oxidation properties by ozone at different temperatures
To uncover more clearly the causes of the changing trend of Hg 0 oxidation
with respect to the temperature, Fig. 3.16 shows the equilibrium analysis of the
HgO thermal decomposition property by FACTsage (a well-known software of