Environmental Modeling in Industrial Application Models for Supporting Incident Evolution: Release of Dense-than-air Pollutants
Содержание
- 2. CONTENTS INTRODUCTION PREVISION MODELS SLAB THEORETICAL DESCRIPTION MODEL ORGANIZATION GOVERNING EQUATIONS TIME AVERAGED CONCENTRATIONS SLAB USER
- 3. INTRODUCTION Emission of polluting substances can come from: Vehicular traffic Industrial plants Thermo-electric plants Natural sources
- 4. INTRODUCTION The spatial and temporal distribution of the concentration of the polluting substance can help to
- 5. INTRODUCTION The dense gases The importance of the problem is very high when dealing with: toxic
- 6. INTRODUCTION The dense gases Example: SO2 Molecular weight (SO2) = 64 kg/kmol Molecular weight (air) =
- 7. /24 Airborne chemical pollution Attention must be paid to: accurately determine the types of pollutants taking
- 8. /24 Airborne chemical pollution Pollutants are gaseous mixtures or aerosols, i.e. suspensions of solid or liquid
- 9. /24 Airborne chemical pollution In general, toxic pollutants can penetrate in the organism through: the respiratory
- 10. /24 Airborne chemical pollution An important reference are the tables published and periodically updated by the
- 11. /24 Airborne chemical pollution The following indications about TLV can be adopted: If the limit TVL
- 12. /24 Airborne chemical pollution The limits shown in the ACGIH TVL tables refer to the absorption
- 13. /24 Airborne chemical pollution The asphyxiating agents do not have a predetermined limit value for each
- 14. /24 Airborne chemical pollution The experimental measurements for the determination of the concentration of a pollutant
- 15. /24 Impact on the environment By law, the Chemical Safety Assessment (CSA) and the compiling of
- 16. /24 Impact on the environment The risk evaluation for the environment based on the intrinsic features
- 17. /24 Impact on the environment PBT Criteria: Persistency half life in sea water >60 days half
- 18. /24 Impact on the environment vPvB Criteria: Very persistent substance (vP) half life in water >60
- 19. /24 Impact on the environment PNEC determination PNEC is determined for each environmental compartment on the
- 20. /24 Impact on the environment Evaluation of environmental exposure Determination of the PEC (Prevented Environmental Concentrations)
- 21. /24 Impact on the environment
- 22. Impact on the environment Regional PEC Point-shaped releases diffused over a wide area have an effect
- 23. Impact on the environment Characterization of the hazard Comparison between prevented environmental concentrations (PEC) and prevented
- 24. Impact on the environment Characterization of the hazard Hazards adequately controlled if PEC If the condition
- 25. Phenomenology Phenomenology of the phases of dense gases dispersion: Source term; Falling and gravitational slumping Stratified
- 26. Phenomenology Source term: Mass of substance released (puff) or flow rate of the continuous release (plume).
- 27. Phenomenology Gravitational slumping of the cloud: The cloud formed by a denser than air release continues
- 28. Phenomenology Stratified dispersion: The cloud concentration reduces further for dilution with air, until its density becomes
- 29. PREVISION MODELS To evaluate and quantify the dispersion of a pollutant emission in the atmosphere, it
- 30. PREVISION MODELS Gaussian models These are very simple analytical codes which require a modest metereologic input
- 31. PREVISION MODELS 3D Lagrangian models They simulate the dispersion of a pollutant through computational particles displaced
- 32. MODELS FOR DENSE GAS RELEASES EVALUATION Open source models DEGADIS SLAB Proprietary models AIRTOX CHARM FOCUS
- 33. MODELS FOR DENSE GAS RELEASES EVALUATION DEGADIS DEGADIS was originally developed for the US Coast Guard
- 34. MODELS FOR DENSE GAS RELEASES EVALUATION SLAB SLAB was developed by Lawrence Livermore National Lab to
- 35. MODELS FOR DENSE GAS RELEASES EVALUATION AIRTOX AIRTOX has been developed by ENSR Consulting and Engineering
- 36. MODELS FOR DENSE GAS RELEASES EVALUATION CHARM CHARM is a Gaussian puff model created by Radian
- 37. MODELS FOR DENSE GAS RELEASES EVALUATION FOCUS FOCUS is a hazards analysis software package designed by
- 38. MODELS FOR DENSE GAS RELEASES EVALUATION SAFEMODE SAFEMODE was developed by Technology and Management Systems Inc.
- 39. MODELS FOR DENSE GAS RELEASES EVALUATION TRACE TRACE was developed by EI Dupont De Nemours Company.
- 40. SLAB
- 41. INTRODUCTION SLAB is a computer code that simulates the atmospheric dispersion of denser than air releases.
- 42. INTRODUCTION Atmospheric dispersion of the release is calculated by solving the conservation equations of Mass Momentum
- 43. INTRODUCTION The cloud can be modeled as a steady-state plume or as a puff, as visible
- 44. INTRODUCTION A continuous release (very long emission duration) is treated as a plume. In the case
- 45. INTRODUCTION Solution of the spatially-averaged conservation equations in either dispersion mode yields the spatially-averaged cloud properties.
- 46. INTRODUCTION The time averaged concentration is obtained in a two step process: The effect of the
- 47. MODEL ORGANIZATION Cloud meander effect
- 48. THEORETICAL DESCRIPTION The atmospheric dispersion of a large denser than air release is affected by phenomena
- 49. THEORETICAL DESCRIPTION In combustible gas releases one can be concerned with the instantaneous concentration. In toxic
- 50. THEORETICAL DESCRIPTION To meet these requirements, the SLAB model is built upon a theoretical framework that
- 51. THEORETICAL DESCRIPTION
- 52. THEORETICAL DESCRIPTION The conservation equations are different for the two modes, plume and puff. The steady
- 53. THEORETICAL DESCRIPTION Figure 3
- 54. THEORETICAL DESCRIPTION The theoretical framework of the SLAB model is completed by the inclusion of the
- 55. THEORETICAL DESCRIPTION To solve the basic set of equations, additional submodels are required. These submodels describe
- 56. THEORETICAL DESCRIPTION The turbulent mixing with surrounding air, is treated by using the entrainment concept which
- 57. THEORETICAL DESCRIPTION In the steady state plume mode the conservation equations are averaged over the cross
- 58. THEORETICAL DESCRIPTION The 3D concentration distribution of the cloud is determined from the average concentration and
- 59. MODEL ORGANIZATION The calculational flow within the SLAB code is reported in Figure below
- 60. MODEL ORGANIZATION There are three stages in a typical simulation: Source identification and initialization for dispersion;
- 61. MODEL ORGANIZATION Dispersion from an evaporating pool and a horizontal jet both begin in the steady
- 62. MODEL ORGANIZATION The situation for the vertical jet is similar to that of the horizontal jet;
- 63. MODEL ORGANIZATION The dispersion calculation for a continuous but limited release of duration t_sd is initially
- 64. MODEL ORGANIZATION The puff center of mass is set equal to Xt, so that the emitted
- 65. MODEL ORGANIZATION Figure 4
- 66. MODEL ORGANIZATION An exception to this procedure is taken when an evaporating pool release fails to
- 67. MODEL ORGANIZATION Completion of the dispersion calculations in either mode, yields the instantaneous spatially averaged cloud
- 68. MODEL ORGANIZATION The calculation of the time-averaged concentration is conducted in 2 steps: The effective cloud
- 69. MODEL ORGANIZATION Cloud meander effect
- 70. GOVERNING EQUATIONS Steady state plume mode The steady state plume mode of SLAB is based on
- 71. GOVERNING EQUATIONS Steady state plume mode
- 72. GOVERNING EQUATIONS Steady state plume mode Conservation of species (only one species of pollutant is considered)
- 73. GOVERNING EQUATIONS Steady state plume mode Conservation of mass Variation in the x direction of the
- 74. GOVERNING EQUATIONS Steady state plume mode Conservation of energy Variation in the x direction of the
- 75. GOVERNING EQUATIONS Steady state plume mode Conservation of momentum Variation of the control volume momentum in
- 76. GOVERNING EQUATIONS Steady state plume mode Conservation of momentum Variation of the control volume momentum in
- 77. GOVERNING EQUATIONS Steady state plume mode Conservation of momentum Variation of the control volume momentum in
- 78. GOVERNING EQUATIONS Steady state plume mode In a horizontal jet release, the source velocity term Ws
- 79. GOVERNING EQUATIONS Steady state plume mode The solution of the governing equations is divided into two
- 80. GOVERNING EQUATIONS Transient puff mode The transient puff mode of SLAB is based upon the volume-averaged
- 81. GOVERNING EQUATIONS Transient puff mode
- 82. GOVERNING EQUATIONS Transient puff mode
- 83. GOVERNING EQUATIONS Transient puff mode The equations for the puff mode differ from those in the
- 84. GOVERNING EQUATIONS Transition from plume to puff mode The puff dispersion mode can be entered: at
- 85. GOVERNING EQUATIONS Transition from plume to puff mode To begin the puff mode calculation it is
- 86. GOVERNING EQUATIONS Cloud length and time dependence in the plume mode The approach taken in the
- 87. GOVERNING EQUATIONS Solution of the dispersion equations The basic model equations can be solved by direct
- 88. GOVERNING EQUATIONS Ambient velocity profile The ambient wind velocity profile is derived from the following assumed
- 89. GOVERNING EQUATIONS Entrainment rates The vertical entrainment rate includes the effects of surface friction, differential motion
- 90. GOVERNING EQUATIONS Heat and momentum flux terms The flux terms are adapted from Zeman (1982). The
- 91. GOVERNING EQUATIONS Thermodynamic model Liquid droplets formation and evaporation is governed by an equilibrium thermodynamic model
- 92. GOVERNING EQUATIONS Plume rise The plume from a vertical jet or stack release initially rises until
- 93. TIME AVERAGED CONCENTRATIONS All of the SLAB results (concentration, cloud width …) represent ensemble averages. An
- 94. TIME AVERAGED CONCENTRATIONS
- 95. TIME AVERAGED CONCENTRATIONS in addition to the ensemble average, SLAB uses two other average types: Spatial
- 96. Cloud meander Cloud meander is the random oscillation of the cloud centerline about the mean wind
- 97. Cloud meander When the cloud concentration os averaged over time, the effective width of the cloud
- 98. Cloud meander In SLAB code solution to the dispersion equations, the cloud meander is ignored and
- 99. Time averaged volume concentration With the determination of the effective cloud half width for the concentration
- 100. SLAB User’s guide
- 101. General information SLAB is implemented in the Fortran 77 language. SLAB operates by acquiring an input
- 102. Input file There are 30 possible input parameters required to run in SLAB. Such parameters include
- 103. Input file
- 104. Source type and numerical substep parameter IDSPL – Spill source type SLAB has 4 types of
- 105. Source type and numerical substep parameter Figure 5
- 106. Source type and numerical substep parameter The evaporating pool is a ground level area source of
- 107. Source type and numerical substep parameter The vertical jet release is an area source with source
- 108. Source type and numerical substep parameter In SLAB the pressure within the cloud is always 101325
- 109. Source type and numerical substep parameter The parameter NCALC is an integer substep multiplier that specifies
- 110. Source properties WMS = molecular weight of the source material [kg] CPS = vapor heat capacity
- 111. Source properties DHE = heat of vaporization at the boiling point temperature[J/kg] CPSL = liquid specific
- 112. Source properties Some examples of substances are here provided
- 113. Spill parameters TS = temperature of the source material When the release is an evaporating pool,
- 114. Spill parameters QS = mass source rate [kg/s]4 For an instantaneous release, the QS value should
- 115. Spill parameters TSD = continuous source duration [s] This parameter specifies the duration of the release
- 116. Field parameters TAV = concentration averaging time [s] The concentration averaging time is the appropriate averaging
- 117. Field parameters XFFM=maximum downwind distance [m] This is the maximum downwind (x) distance for which the
- 118. Meteo parameters ZO = surface roughness height [m] Is generally estimated in two ways: The first
- 119. Meteo parameters ZA = ambient measurement height [m] This is the height at which ambient windspeed
- 120. Meteo parameters STAB = stability class values The whole numbers from 1 to 6 are used
- 121. Meteo parameters The classes of atmospheric stability are an method of classification of the atmospheric stability,
- 122. Meteo parameters ALA = inverse Monin-Obukhov length [1/m] This is a stability parameter used to describe
- 123. Meteo parameters The Obukhov length is used to describe the effects of buoyancy on turbulent flows,
- 124. Input file closure After the code has read the input and executed a run, it returns
- 125. CALCULATIONAL FLOW A SLAB model simulation can be viewed as occurring in three sequential phases: initialization,
- 126. CALCULATIONAL FLOW Initialization The initialization begins with the specification of the source type. There is one
- 127. CALCULATIONAL FLOW Dispersion calculation The dispersion phase contains the bulk of the calculation. It is here
- 128. CALCULATIONAL FLOW Dispersion calculation The steady state plume mode is used for the finite duration releases
- 129. CALCULATIONAL FLOW Dispersion calculation In the steady state plume mode the conservation equations are spatially averaged
- 130. CALCULATIONAL FLOW Dispersion calculation In the transient puff mode the conservation equations are averaged over the
- 131. CALCULATIONAL FLOW Dispersion calculation In the transient puff mode the conservation equations are averaged over the
- 132. CALCULATIONAL FLOW Time averaged concentration calculation After the spatially-averaged cloud properties are calculated at all downwind
- 133. CALCULATIONAL FLOW Time averaged concentration calculation The calculation of the time averaged volume fraction C_tav(x,y,z,t) from
- 134. CALCULATIONAL FLOW Time averaged concentration calculation The time available for cloud meander at the downwind location
- 135. OUTPUT FILE The output file contains several types of information which can be grouped in 3
- 136. OUTPUT FILE Problem description The Problem description output lists the various input parameters used by the
- 137. OUTPUT FILE Instantaneous spatially averaged cloud properties The instantaneous spatially averaged cloud properties output gives the
- 138. OUTPUT FILE Instantaneous spatially averaged cloud properties The table below lists the instantaneous spatially averaged parameters
- 139. OUTPUT FILE Instantaneous spatially averaged cloud properties The cloud properties listed before, are described as “instantaneous”
- 140. OUTPUT FILE Instantaneous spatially averaged cloud properties The “spatial” averaging in SLAB is of 2 types:
- 141. OUTPUT FILE Time averaged volume fraction In SLAB the time averaged concentration is expressed as the
- 142. OUTPUT FILE Time averaged volume fraction The concentration contour parameters output lists a number of parameters
- 143. OUTPUT FILE Time averaged volume fraction The concentration in the Z=ZP(I) plane gives the the time
- 144. OUTPUT FILE Time averaged volume fraction The final result is the maximum centerline concentration. Here the
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