Mercury Sampling and Measurement in Coal-Fired Power Plants - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 18

Table 2.10 Hg removal efficiency of WFGD in bench-scale experiment
Type of WFGD/ Hg
concentration in flue gas (g/(N·m 3 ))

Hg removal
efficiency (%)

References

Limestone / 9.9 10.87 Radian, 1993a (EPRI)

Limestone 0.00 Radian, 1993b (EPRI)

Limestone / 8.1 22.63 Interpoll, 1990a (NSP)

Limestone / 11.6 59.3 Interpoll, 1991 (NSP)

Lime / 6.0 45.91 EPRI, 1993a

Limestone / 10.0 12.05 Battelle, 1993a (DOE)

Limestone / 12.5 20.15 Radian, 1994b (EPRI)

Lime / 5.6 61.67 Radian, 1994c (EPRI)

Southern Research Ins.,
1995a

Limestone / 9.5 45.10

Average 30.85 ˉ

When the boiler was burning the lignite, the mercury removal efficiency of the
WFGD reached less than 5%. This occurred because Hg 0 showed the most speci-
ation in the lignite flue gas, which prevented WFGD from removing the mercury.
When the boiler was burning high-Cl coal, the proportion of gaseous Hg 2+ rose in
the flue gas, which allowed WFGD to easily capture mercury. This indicated that
the mercury removal capacity of WFGD was decided mainly by the characteristics
of the coal being burned.
Based on the test results, the calculated mercury removal efficiency and mer-
cury emission factor of WFGD are presented in Table 2.11.

Ta b l e 2. 11 Hg removal efficiency and EMF of 3 WFGDs in China

Total gaseous Hg
before WFGD (g/h)

Total gaseous Hg
after WFGD (g/h)

Hg removal
efficiency (%)

Location WFGD Type EMF

Beijing Limestone-gypsum 4.36 1.25 71.4 0.286

Anhui Limestone-gypsum 13.59 2.95 78.3 0.217

Fujian * Sea-water 15.05 0.86 94.3 0.057

Note: * SCR was equipped before the WFGD

2.7 Summary

Accurate measurement of flue gas mercury is the key factor in the study of mercury
control technology. In this section, the tests of 6 typical coal-fired power plants in
China were described in detail. Through data analysis, mercury speciation in power
plants, as well as the impact and the performance of air pollution control devices on
demercuration, have been mainly discussed.
Mercury emissions from 6 coal-fired power plants came mainly in the form of
Hg (g) , accounting for about 87% to 98% of the total mercury concentration, whereas
the Hg p occupied a small proportion, accounting for only 2% to 13%. When there
was only ESP as a cleaning device, the ratio of gaseous Hg 0 was almost the same as
that of gaseous Hg 2+ in the flue gas after the ESP. On the basis of ESP, when WFGD