Mercury Speciation Transformation During Coal Combustion - Mercury Emission and its Control in Chinese Coal-Fired Power Plants - page 71

During Coal Combustion

platforms, from blood flow to semiconductor manufacturing, and from clean room
design to wastewater treatment plants. Special models that give the software the
ability to model in-cylinder combustion, aeroacoustics, turbo machinery and mul-
tiphase systems have served to broaden its reach.
Although FLUENT6.2 code was quite successful in respect of simulating flow,
heat transfer, combustion and so on, it was incapable of modelling trace elements in
the furnace, such as Hg. To model Hg reaction and distribution in a furnace, there
are a series of challenges: first, it is very difficult to accurately describe the reaction
process between Hg and various gas species; second, the devolatilization process of
Hg accompanied by carbon has not been deeply understood; finally, because the
magnitude of Hg concentration is very low, normally in the order of parts per bil-
lion, the numerical error in the computational process can largely degrade the ac-
curacy of results. Additionally, currently the species database of FLUENT6.2 does
not include the relevant species parameters of Hg. All these factors should be con-
sidered in the simulation work.
The calculation steps mainly include grid meshing, turbulence model choice,
combustion model choice, particle phase treatment, boundary condition setting, Hg
computational model treatment, iteration solving and simulation results treatment.

4.5.1.2 Furnace Introduction

Nowadays, the tangentially fired pulverized coal boiler is popular, specifically
accounting for 95% of the total of utility boilers in China. A CFD investigation has
been applied to the performance of a typical 410 tons/h tangentially coal-fired
boiler with high volatility coal, at full load. Combined bituminous coals of 70%
Shenhua coal and 30% Zhungeer coal were used here and the composition inputs
were determined using proximate and ultimate analysis data (dry basis) provided in
Table 4.14. Concentrations of mercury and chlorine in coal were given as well,
mercury was 0.077 g/g, chlorine was 0.02 g/g, respectively.

Table 4.14 Proximate and ultimate analysis of coal

Q ar, dw
(kJ/kg)

C ar H ar O ar N ar S ar M ar A ar V ar FC ar

54.57% 3.43% 9.62% 0.8% 0.36% 18.21% 12.71% 23.53% 45.55% 20993

The boiler was made by Haerbin Boiler Co. Ltd., and was a single drum natural
circulation, solid slag, square spray combustion, high-pressure pulverized coal
boiler, and an intermediate warehouse ball mill pulverizing system was adopted.
As designed here, the furnace is square, 9980 mm×9980 mm, arranged as sin-
gle-chamber, -type, 39 m high from the platform, 42.6 m high from the drum
centerline, with membrane wall all around, super-heaters in the flue and two-stage
super-heaters in the stack flue, well-decorated as well. The two-stage economizer