Mercury Sampling and Measurement in Coal-Fired Power Plants - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 17

Table 2.8 Hg removal efficiency of three main particulate control devices

Streets
(2005)

US EPA
(2002)

US EPA
(1997)

Wang et al .
(2000)

Zhu et al .
(2002)

Type

ESP 30.6 36.0 30.4 25.7 30.3

Wet dust removal 6.5 8.7 4.3 ˉ ˉ

ˉ ˉ

Cyclone dust removal 0.1 0.1 0.0

The 6 particulate control devices chosen in this study were all ESPs. Based on
the test results, Table 2.9 shows the calculated Hg emission factor (EMF) of ESP in
6 typical coal-fired power plants in China.
As shown in Table 2.9, the average EMF based on test results of 6 ESPs was
0.875, which was higher than that evaluated by other scholars. For example, Streets
et al . [5] estimated that the EMF of ESP was 0.694 in coal-fired power plants in
China. Wang et al . [4] believed it was 0.743, whereas Zhu et al . [6] believed it was
0.697.

Table 2.9 Hg EMF of 4 ESPs in China

Total Hg before
ESP (g/h)

Total Hg after
ESP (g/h)

Hg removal
efficiency (%)

Location EMF

Zhejiang 15.52 15.39 0.8 0.992

Zhejiang 34.10 33.16 2.7 0.973

Jiangsu 37.53 22.11 41.1 0.589

Fujian 18.02 17.03 5.5 0.945

2.6.3 Mercury Removal by WFGD

The limestone-gypsum wet desulphurization process, is a kind of WFGD technol-
ogy, which is widely used in China. WFGD can reduce SO 2 emissions as well as
remove most of the gaseous Hg 2+ in flue gas. However, WFGD does not work with
Hg 0 ; it can even increase Hg 0 emissions because it can cause the Hg 2+ adsorbed into
sulphite to be released again.
Chlorine concentration in coal can affect seriously the speciation of Hg (g) , which
is one of the important factors for mercury removal with WFGD. When chlorine
concentration in coal ranges from 50 to 100 ppm, the flue gas Hg removal efficiency
of ESP+WFGD could range within 30% 60%, with an average mercury removal
efficiency of about 49%. At the same level of chlorine concentration, mercury
removal efficiency of FF+WFGD could reach 88% [7] .
Table 2.10 shows the mercury removal efficiency of the WFGD bench-scale
experiments [8] . The range of mercury removal efficiency in the present work ranged
from 0 to 61.7%, and the average mercury removal efficiency was about 31%.