Page 301 - Materials Chemistry, Second Edition

L1644_C07.fm Page 273 Monday, October 20, 2003 12:10 PM

sensitive to the ambient air temperature. The mixing height is calculated as a function
of the stability class (VDI, 1992). An equal distribution of wind directions is
assumed. Therefore, as derived by Nigge (2000), the combined frequency distribu-
tion of wind speed and stability class is independent of the wind direction.
The remaining task is to determine a statistical distribution of wind speed, u,
and stability class, s, for each class of meteorological conditions in the region under
study. If the distribution parameters of the Weibull distribution are known, an hourly
wind speed file can be generated from the average annual wind speed. Manier (1972)
states that the distribution of stability class and that of wind speed classes are
correlated. As a consequence, the only parameter required as additional input for
using the impact indicator is the mean annual wind speed of the considered district.
Mass flow, volume flow and exit velocity determine the outcome of the concen-
tration calculations of ISCST-3. However, unlike in EcoSense, the concentration
increment calculated by BEEST does not change linearly by changing certain param-
eters of source characteristics. Therefore, statistical values for these parameters
(volume flow and mass flow) must be defined.
A set of nine different industrial processes with stack heights ranging from 10
to 250 m were evaluated for the example with respect to their volume flows. The
correlation between volume flow and stack height has a trend line that can be
described with the potential approach in Expression 7.10, where V ˙ is the volume
3
flow in (Nm /h) and h stack the stack height in (m), and the regression coefficient r 2
equals 0.799. Expression 7.10 is only a rough approximation to calculate the volume
flow. Nine processes is not at all a representative statistical number that allows
making general conclusions.
The mass flow of each pollutant is obtained from the volume flow and the
˙
respective threshold of each pollutant according to Expression 7.11, where M is
p
the mass flow of pollutant, p, and c threshold,p is the legal threshold concentration of
pollutant p in flue gas. The threshold values for municipal waste incinerators are
taken from the regulations valid for the region under study (in the example, the
Catalan District 323/1994 that includes the European Guideline 89/369/EEC). In
order to apply the correct threshold for the organic substances considered, the share
of total organic carbon (TOC) of every pollutant is calculated and in this way the
threshold of TOC is adapted to each single organic substance considered.
The use of a threshold at this stage is probably not the best solution; in further
works, basing the mass flow also on statistical reasoning according to industry types
should be attempted. An alternative would be to use the mean average emission
value of the respective industry.
As a matter of fact, for dispersion, the decisive parameter relating to the release
height is not the stack height, but the effective stack height, h , which also takes
eff
into account the momentum rise and the buoyancy rise of the plume and is auto-
matically calculated by BEEST. In order to make the results of this work comparable
to other studies that relate the impact indicators to the h (e.g., Nigge [2000]), the
eff
effective stack height is calculated for the indicators derived in this study (Table
7.2). The calculation of h is carried out according to Israel (1994). The comparison
eff
of the results from different studies must be done with care, thoroughly checking
the congruence of the applied algorithms for h eff.

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