Mercury Control and Mercury Stability in Byproducts - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 103

5
Mercury Control and Mercury Stability in
Byproducts
5.1 Introduction
As stated previously, coal burning is one of the major sources of mercury pollution
in China. Here, Hg 0 and Hg 2+ are main mercury speciation in flue gas from
coal-fired power plants. Generally, water-soluble Hg 2+ is relatively easy to remove
by water scrubber. However, Hg 0 is very difficult to control [1,2] . Currently, more
studies have focused on using activated carbon or other sorbents to remove Hg (g)
from coal-fired flue gas.
Powdered carbon has been used for removing mercury from flue gas from in-
cinerator plants [3] . According to previous studies, powdered carbon can adsorb Hg (g)
with high efficiency [4,5,6,7] . Activated carbon, which is usually modified by adding
iodine, chlorine, sulfur compounds, etc., can enhance the adsorption of Hg 0 .
However, modified activated carbon can increase production costs. Many factors,
including the characteristic of activated carbon, the running condition of adsorption,
etc., influence the adsorption efficiency of mercury; thus, the adsorption mechanism
of mercury using activated carbon remains unclear [8,9] .
Mercury removal using activated carbon can be conducted in two ways: through
the injection of powdered activated carbon (PAC) before a particle removal de-
vice [5] , and through the utilization of the adsorption bed of granular activated carbon
(GAC) [10] . Other types of sorbents, which mainly include fly ash, calcium-based
sorbents, precious metals, etc., are not very efficient in mercury adsorption [11,12,13] .
Zhejiang University and several other domestic universities and research in-
stitutions have been engaged in various projects on coal-fired mercury control
technology for over 20 years, and the researchers have achieved some results during
these years. This section introduces the findings of Zhejiang University on the
adsorbent control of mercury emissions in flue gas, including the adsorption per-
formance of different mercury sorbents, the development of new adsorbents, the
mechanism of activated carbon adsorption of mercury in flue gas, and the stability
of mercury in the adsorption product.