Development of Pollution Control Technology During Coal Combustion - Simultaneous Multi-Pollutants Removal in Flue Gas by Ozone - page 11

combustion methods and developing additives; and (iii) mercury control
technologies after combustion, i.e. utilizing various absorbents, the existing
pollution control devices, and de-Hg technologies to achieve the mercury removal.
Typical de-Hg technologies contain the corona discharge plasma technology and
multi-pollutants removal technology by ozone oxidation.
1.2.3.1 Absorbent
Currently, more and more studies have focused on adopting activated carbon and
other adsorbents for mercury removal [33] . However, the mercury absorption
mechanism by using activated carbon remains unclear. Absorbents and the related
adsorption performance have been extensively reported in the literature, which
mainly include activated carbon [34] , fly ash [35] , calcium-based absorbent [36] ,
mineral substance-based absorbent [37] , zeolite-based catalytic adsorbent [38] , and
precious metal-based adsorbent [39] .
1.2.3.2 Coal-Washing or Coal Drying Technology
Coal washing and drying are effective methods for eliminating mercury before
combustion [40] . Generally, coal washing is divided into two categories. One is
based on the different specific gravity to separate impurities, such as
dense-medium separators and cyclones. The other utilizes different physical and
chemical properties of coal surface, involving the coal-flotation and oil-
flocculation technologies. The mercury removal rate of the flotation technology,
with a mean value ranging from 21% - 37%, depends on the coal type, method of
washing, and mercury concentration in coal. Generally, a coal drying technology
can obtain a higher mercury removal of about 70%. Actually, both coal washing
and drying are out-of-dated technologies and therefore are hardly to be taken into
practice in industry, despite a considerable mercury removal accomplished.
1.2.3.3 Conventional Pollution Control Device
Mercury control technologies after combustion refer to mercury removal from the
coal-fired flue gas. Besides the absorbent method in flue gas, using the existing
conventional flue gas pollution control devices to reduce mercury emission is
considered as a cost-effective alternative way. Currently, the existing flue gas
pollution control devices contain the FGD, particle-control equipment (ESP or