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Dispersion Modeling

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Dispersion Modeling Powered By Docstoc
					  Introduction to SCREEN3



                       Marti Blad
NAU College of Engineering and Technology

   smokestacks image from Univ. of Waterloo Environmental Sciences
           Dispersion Models
   Repetitious solution of dispersion
    equations
       Computer solves over and over again
   Based on principles of transport,
    diffusion
       Complex mathematical equations
   Computer-aided simulation of
    atmosphere based on inputs
       Best models need good quality and site-
        specific data
                                                  2
  Historically




Image from collection of Pittsburgh
Photographic Library, Carnegie
Library of Pittsburgh

                                 3
    Types of Dispersion Models
   Gaussian Plume
       Analytical approximation of dispersion
   Numerical or CFDs
       Transport & diffusional flow fields
   Statistical & Empirical
       Based on experimental or field data
   Physical
       Flow visualization in wind tunnels, etc.


                                                   4
Computational Fluid
Dynamics Modeling
         image from MAGNUM Technologies, Inc




                                               5
CFD Building Effects




                       6
              Gaussian Dispersion
         z


                                        Dh = plume rise

    Dh                                    h = stack height
                                         H = effective stack
             H = h + Dh                      height
H
    h                                x

                          C(x,y,z) Downwind at (x,y,z) ?
                          y
                                                           7
Gaussian Plume




                 8
    SCREEN3 Model Assumptions
   Continuous pollutant emissions
   Conservation of mass in atmosphere
   Steady-state meteorological conditions
   Concentration profiles are represented by
    Gaussian distribution—bell curve shape




                                             9
     SCREEN3 designed for…
   Single source, short-term calculations
      Estimate maximum ground level
        concentrations
      Distance to max. concentration from source
      Concentrations at user defined distances
      Simple downwash algorithm
           Max. concentrations in near & far wake
       Estimate concentrations in cavity
        recirculation zone
   Source types
       All options for point & flare
                                                     10
    SCREEN3 designed for…(cont.)
   Full range of meteorological conditions accepted
       Stability classes
       Wind speeds
       Inversion break up
       Shoreline fumigation
   Determine plume rise for flare releases
   Includes effects of BID
       Buoyancy induced dispersion
   Simple area & volume sources

                                                 11
Source Options




                 12
Dispersion Model Structure
         INPUT DATA: Operator
             experience
                 EMISSIONS
    METEROLOGY               RECEPTORS




         Model does calculations


     Model Output: Estimates of
     Concentrations at Receptors



                                         13
    Model Input Considerations
   Source type
        Point, area, volume, flare
   Stack or source emission data
        Pollutant emission data
        Stack- or source-specific data
        Temperature in stack
        Velocity out of stack
   Receptor data
                                          14
Input screen 1




                 15
          Input Considerations
   Actual pattern of dispersion depends on
    atmospheric conditions prevailing during
    release
   Major meteorological factors that influence
    dispersion of pollutants
       Atmospheric stability (& temperature)
       Mixing height
       Wind speed & direction

                                                  16
           Meteorological inputs
   Appropriate meteorological
    conditions
       Appropriate for location
       Appropriate for averaging time period
       Wind stability and speed
   Flat terrain or complex terrain
   Distances to points of interest
       Receptors
                                                17
Input screen: met data




                         18
Discrete Distance input




                          19
Automated Distances input




                            20
Model Inputs not Covered Today
   Height of plume rise calculated
       Momentum and buoyancy
       Can significantly alter dispersion & location of
        downwind maximum ground-level concentration
   Effects of nearby buildings estimated
       Downwash wake effects
       Can significantly alter dispersion & location of
        downwind maximum ground-level concentration



                                                           21
Building downwash option




                           22
Run: screen update




                     23
Model results: graphs




                        24
View text results: editor




                            25
Editor information




                     26
                     Review
   Dispersion = expand & diffuse
       Picture
   Gaussian = even spreading directions
       Highest along axis
   Input data quality critical
   Screen3 limitation for reactive chemicals
       No reactions assumed to create or destroy



                                                    27
   SCREEN3
DEMONSTRATION

Software provided courtesy of




  a division of Lakes Environmental Consultants Inc.   28
Exercise 1 input 1




                     29
Exercise 1 input 2




                     30
Run: Exercise 1




                  31
Results exercise 1: graph




                            32
Editor view1




               33
Editor: Model Summary




                        34
Exercise 2 input 1




                     35
Exercise 2 input 2




                     36
Run: Exercise 2




                  37
Exercise 2 results




                     38
Editor: Exercise 2




                     39
Editor: Model summary




                        40
Exercise 3 input 1




                     41
Exercise 3 results: graph




                            42
Exercise 3: Model summary




                            43
Model summary




                44
Input screen




               45
Editor: exercise 3




                     46

				
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