Mercury Speciation Transformation During Coal Combustion - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 95

28

0.4

Cl
Cl 2
ClO
ClO 2

HCl

27

0.3

26

0.2

25

24

0.1

23

0.0

22

0 1 2 3 4 5

0 1 2 3 4 5

Resident time (s)

Resident time (s)

Fig. 4.88 HCl concentration transformation

Fig. 4.87 Cl component transformation

The comparative result between the field test results on the 410 tons/h station
boiler and the calculation results were identified here. The field test data came from
CEM in-situ measurement on line at the outlet of the electrostatic precipitator
(ESP). The results data derived from the gaseous Hg 0 and gaseous Hg 2+ content
were 51.63% and 48.37% by field test, respectively, while those of content of
gaseous Hg 0 and gaseous Hg 2+ were denoted as 59.18% and 40.82% by simulation
calculation. Usually, the field testing of mercury could not be precisely enough
conducted owing to mercury being absorbed by flying ash, low residue, heating
surfaces and mercury oxidation or catalyzed by mineral substances in fly ash during
the practical boiler operation.
Although a small deviation occurred between them, the simulation data was
satisfactory, fitting well with CEM in-situ measurement data of mercury species
concentrations. Therefore, this kind of CFD model was validated to do the model-
ing of mercury distribution during the combustion process, and even the 1-D dy-
namic model for the rear flue worked as well. But of course, it needs to be inves-
tigated further.

4.6 Summary

In this chapter, the mercury speciation transformation during coal combustion was
discussed completely using different research methods.
In the research of mercury emissions from coal of different combustion types,
the behavior of mercury emissions was checked by heating coal in a fixed quartz
tube furnace, a pulverized coal boiler and circulating fluidized-bed bench tests,
respectively. From the experimental results of coal burning in a fixed bed and a state
of suspension, the ratios of Hg (g) and Hg p were found to be similar. The ratio of
Hg (g) , Hg p in the flue gas from the three different combustion methods indicated that
Hg (g) was the main speciation emission when coal was fired. Given the conditions of
the three different combustion methods, the speciation distributions of Hg 2+ and Hg 0
were similar. Coal burning in a fixed bed increased the Hg 0 concentration, which