Development of Pollution Control Technology During Coal Combustion - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 12

fabric filter), NO x -control equipment (SCR). In view of the high water-solubility
of oxidized mercury compounds (such as HgCl 2 ), the WFGD system can remove
80% - 95% of Hg 2+ [41] . Hg 0 is very difficult to be removed because of its high
volatility and particularly low water-solubility. However, Hg 0 in flue gas can be
oxidized into Hg 2+ by the SCR catalysts in the existing denitration equipment.
This enables the Hg 0 abatement to be achieved in coal-fired power plants. The
mercury removal efficiency of such an equipment depends on the mercury
speciation distribution in flue gas, which is ultimately affected by the coal type.

1.2.3.4 Corona Discharge Plasma Technology

As a new mercury removal method, the corona discharge plasma technology is
keeping developed. Using a narrow pulsed-corona discharge method, Wu and
Urabe [42] conducted an industrial test to remove the Hg vapor in the 10 m 3 /h flue
gas of a waste incinerator. It was found that the removal efficiency deceased with
the gas temperature and related with the gas residence time in the electric field,
pulse voltage frequency, and corona power. When the initial Hg vapor
concentration reached 2 mg/m 3 , the removal efficiency achieved 100% under
certain conditions. The existing HCl gas could also improve the removal efficiency.
The removal principles relied on that the Hg vapor was oxidized by O atoms and
O 3 in the corona discharge field. The related oxidation reactions are as follows.

Hg+O HgO (1.3)

Hg+O 3 = HgO+O 2 (1.4)
Hg+2Cl

=

= HgCl 2 (1.5)

Since the mercury concentration in typical coal-fired flue gas is very low, the
absorption of oxidized mercury is not easy. Again, considering the high cost and
running fee, the corona discharge plasma technology is still not put into
commercial application in coal-fired boilers to remove mercury.

1.2.3.5 Semi-Dry Based Hg Removal Technology

A more-effective semi-dry mercury removal technology specially for coal-fired flue
gas has been proposed recently by the Institute for Thermal Power Engineering,
Zhejiang University. This technology, designed to remove mercury together with
SO 2 emission [43-46] , comprises several steps. At the beginning, the absorbent is