Environmental Engineering Reference
In-Depth Information
4. Numerical Simulations
The power plant of CERCS is situated inside a very narrow valley in the west part
of Spain 100 km far from Barcellona inside the Pirenaic Mountains.
The modeling system consists in a coupled model based on the regional
atmospheric model RAMS 6.0 and the Lagrangian particle model SPRAY. The
two models are interfaced by MIRS code, which uses the RAMS outputs to
calculate the boundary layer and turbulence parameters for the Lagrangian
dispersion model SPRAY not directly provided by the circulation model. The
forecast of the hourly 3D wind and turbulence fields for the 2 day simulation
period (6-7 February 2006) has been carried out by RAMS-MIRS using three
nested grids driven by the ECMWF global model analysis fields as boundary
condition. The dispersion simulations were performed by SPRAY on a domain
corresponding to the smallest RAMS grid of 22 × 22 km
2
centered on the stack
(120 m high) with a horizontal resolution of 500 m. A variable time step scheme
has been used for the Lagrangian particles displacement while the chemical reactions
time step was set equal to 30 s. The cells for the concentrations computation have
been set equal to 100 × 100 × 50 m
3
and constant all over the domain. The
reaction rates
k
and
J
were computed every hour using the following equations
(IUPAC 2005 and Parrish et al., 1983):
3
k
=
3
⋅
10
⋅
exp(
−
1450
/
T
)
J
=
0
.
01305
⋅
exp(
−
0
.
36
/
cos(
α
))
;
,
where T is the air temperature, computed by RAMS, and α is the complementary
of the solar elevation angle. The ozone background concentration have been set
variable, equal to the hourly O
3
concentration measured by an EMEP (http://
tarantula.nilu.no/projects/ccc/emepdata.html) background station located 50 km
far from CERCS plant. An air quality station located 1 km far from the stack
measures the NO and NO
2
hourly average concentrations used for the comparison
with the model results. For sake of comparison two kinds of simulations have been
carried out activating (“segr”) or not (“no segr”) the segregation parameterization.
350.00
300.00
250.00
NOx measurements
NOx Spray segr
NO2 measurements
NO2 Spray segr
200.00
150.00
100.00
50.00
0.00
1
3
5
7
9
11 13
15
17 19
21 23
25 27
29
31 33
35 37
39
41 43
45 47
time
Fig. 1.
NO
2
, NOx hourly average concentrations measured and simulated by Spray (segr)
simulation during the period 6-7 February 2006
