Environmental Engineering Reference
In-Depth Information
During Coal Combustion
The power grid distortion performed well. All the grid distortions were lower
than 0.9, less than 0.5 in general, except for the specific areas such as furnace
hopper and arch.
●
Mathematical models
Pulverized coal combustion is very complex process, including water evaporation,
coal devolatilization, homogenous combustion of volatiles and heterogenous
combustion of char. A lot of physical and chemical models are needed to simulate
the combustion of pulverized coal. Gas phase flow, gas-solid two-phase flow,
gas-solid heat transfer, devolatilization, char combustion, radiative heat transfer,
etc. should be taken into account. The following models were chosen in this simu-
lation work: Κ-ε standard turbulence flow model for gas flow, DPM (Discrete Phase
Model) for char combustion, single rate devolatilization model for coal devolatili-
zation, non-premixed combustion model for volatile combustion and kinet-
ic/diffusion limited model for char combustion, P-1 radiation model, Langrange
discrete phase model for particle traces in the furnace, stochastic trajectory model
for particle turbulent diffusion and PDF (Probability Density Function Model) for
turbulent and chemical interactivity.
●
Governing equation
The mathematical model used here was based on the commercial CFD code,
FLUENT6.2, where gas flow was described by the time averaged equations of
global mass, momentum, enthalpy and species mass fraction. The base gas phase
conservation equations for mass, momentum, energy, turbulence, quantities and
species concentration can be expressed, in an Eulerian rectangular framework, as
()
(
u
)
(
)
S
(4-38)
t
In the above equation,
Φ
stands for general dependent variables expressed as a
physical quantity per unit mass.
ρ
, Γ
,
S
stand for density, diffusion coefficient and
source term corresponding to
Φ
, respectively.
●
Equation of motion
The equation of motion obeys following equations:
2
d
u
d
v
w
p
p
p
(
uu
),
(
vv
)
,
(4-39)
g
p
g
p
d
t
d
t
r
p
d
w
w v
p
p
p
(
ww
)
...
(4-40)
g
p
d
t
r
p
18
C
Re
gD
p
where
.
2
24
d
pp
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