API 4628 : 1996

A GUIDANCE MANUAL FOR MODELING HYPOTHETICAL ACCIDENTAL RELEASES TO THE ATMOSPHERE

American Petroleum Institute

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NOMENCLATURE
CHAPTER ONE: Introduction
  Manual Organization
  Quick References
  Conventions
  Terminology
  Subject Indexes Development
CHAPTER TWO: Overview of Release/Dispersion Processes
and Demonstration Scenarios
  The Overall Modeling Process
  Near vs Far Field Modeling
  Release-to-Dispersion Phenomena
  Demonstration Scenarios
CHAPTER THREE: Source Modeling
  Overview
  Phase Equilibria
  Fluid Properties
  Thermodynamics of Fluid Depressurization
  Flow Rate Estimation
  Initial Jet Expansion
  Example Calculations
  Evaporation
CHAPTER FOUR: METEOROLOGY
  Modeling Parameters
  Release Duration
  Plume Buoyancy Criteria
CHAPTER FIVE: Mitigation Countermeasure Modeling
  Introduction
  Review of Plume Mitigation Methods
  Estimation of Plume Modification Parameters
CHAPTER SIX: Analysis and Simulation of Release Scenarios
  Introduction
  1: Hydrogen Sulfide from Unlit Flare Stack
  2: Hydrogen Sulfide and Carbon Dioxide from a Safety
     Relief Stack
  3: Supercritical Propane Pipe Hole Release
  4: Oil Well Blowout
  5: Liquified Chlorine Tank Truck Accident
  6: Ammonia Hose or Pipe Break
  7: Hydrogen Chloride Pipe Break
  8: Evaporating Pool of Liquid Benzene
REFERENCES
APPENDIX 1: Recommended Default/Starting Values for
              Modeling Parameters
Appendix II: Overview of Scenario Modeling Programs
  Submodels
  Time Dependent Modeling
  Thermodynamic and Physical Properties
  Program Output
  New Version of HGSYSTEM
APPENDIX III: HGSYSTEM File Listings for Scenario 7
INDEX
I. Figures
Chapter 2: Overview of Release/Dispersion Processes and
Demonstration Scenarios
1 Paths to Air Dispersion Near the Release Point
2 Release Paths for Scenarios 1, 2 and 3
3 Release Paths for Scenarios 4, 6 and 7
4 Release Paths for Scenario 5
5 Release Path for Scenario 8
Chapter 3: Source Modeling
1 Equilibrium Vapor Pressures
2 Binary VLE Diagram
3 Control Volume Example
4 Critical Pressure Ratio Definitions
5 Flashing Choked Flow Methods
6 High and Low Subcooling: Leung
7 Non-Flashing and Flashing Flow: Leung
8 Expanding Jet Force Balance
9 Evaporating Pool Mass and Energy Flows
10 Heat Conduction Model
Chapter 4: Meteorology
1 Incident Wind Profile Diagram
2 Roughness Length vs. Site Classification
3 Stability Class and Plume Height
4 Pressure and Temperature vs Height
5 Humidity Effect of Air Density
6 Concentration Time Series
Chapter 5: Mitigation Countermeasure Modeling
1 Dilution-only Mitigation by a Spray Barrier: Meroney
2 ICHMPA HF Water Spray Study
3 Spray Curtain Removal: Meroney
4 Spray Curtain Removal with Entrainment: Meroney
5 Steady-state Concentration Correction Factors for
   Constant Rate, Finite Duration Releases
6 Overhead View of Intercepted Plume
Chapter 6: Scenario 1
1 Plume Centerline Paths
2 SLAB H2S Concentrations
Chapter 6: Scenario 2
1 Initial DEGADIS Distance
2 Search for Acceptable Stack Height
3 Final Centerline Ground Level Concentrations
4 Final Plume Centerline Elevations
Chapter 6: Scenario 3
1 Propane Choked Flow Rates
2 Turbulent Jet Centerline Concentrations
Chapter 6: Scenario 4
1 Downwind H2S Concentrations
2 SLAB Cloud Half-widths
3 Downwind H2S Concentrations
Chapter 6: Scenario 5
1 Centerline Concentrations, E Stability,3 m/s Wind,293 K
2 Centerline Concentrations, C Stability 4 m/s Wind,303 K
3 1 ppm Chlorine Isopleths, E Stability, 3 m/s Wind,293 K
4 1 ppm Chlorine Isopleths, C Stability, 4 m/s Wind,303 K
Chapter 6: Scenario 6
1 Vapor Pressure of Ammonia
2 Molal volume of Liquid Ammonia
3 Vapor Enthalpy of Saturated Ammonia
4 Enthalpy of Liquid Ammonia
5 Maximum Centerline Concentrations, Horizontel Jet, 10 s
   Averagine Time
6 Times to Maximum Concentrations
7 Maximum Centerline Concentrations, Horizontal Jet, 60 s
   Averaging Time
8 Vertical Jet Release
Chapter 6: Scenario 7
HCI Release Water Spray Mitigation
1 Steady State and Finite Duration Centerline
   Concentrations
2 Time Dependent Simulations
3 Time Dependent and Steady State (corrected)
   Simulations, instantaneous averaging
4 Time Dependent and Steady State (corrected)
   Simulations, averaging time = 300 s
Chapter 6: Scenario 8
1 Downwind Centerline Concentrations, Evaporating Benzene
   Pool
2 Concentration Isopleths, 1 ppm Benzene
3 Concentration Isopleths, 50 ppm Benzene
II. Tables
Chapter 2: Overview of Release/Dispersion Processes and
Demonstration Scenarios
1 Summary of Senario Attributes
Chapter 3: Source Modeling
1 STN Databases
2 Minimum rs, Ratios of Liquid Chlorine Heads, vs.
   Stagnation Temperatures
3 Summary of Evaporation Model Features
4 Thermal Properties of Natural Materials
Chapter 4: Meteorology
1 Definition os Pasquill-Gifford Stability Classes
2 Typical Values of p in Equation 3
Chapter 6: Scenario 1
1 Stack Gas Composition
2 Summary of SLAB Results for Scenario 1
Chapter 6: Scenario 2
1 Stack Diameter Sizing Parameters
2 Source/Release Parameters
3 H2S Ground Level Centerline Concentrations
Chapter 6: Scenario 3
1 Propane Properties at 7.0 Mpa
2 Source Parameters and Modeling Results
Chapter 6: Scenario 4
1 Crude Oil Flash Results - Two-Phase Summary
2 Summary of Results for Scenario 4
Chapter 6: Scenario 6
1 Base Case Input for SLAB
Chapter 6: Scenario 7
1 Release Parameters
2 Development of Spray Curtain Plume Mitigation
   Parameters
3 Parameter Symbols and Conversion Factors from PLUME
   to HEADAGAS
4 Vapor Cloud Characterization Parameters for Spray
   Curtain Barrier Mitigation Simulations
Chapter 6: Scenario 8
1 Benzene Properties
2 Storage Tank Parameters
Appendix II: Overview of Scenario Modeling Programs
1 Comparison of Modeling System Features
III Example Boxes
Chapter 3: Source Modeling
Phase Rule Examples
Heat of Vaporization Example
Multicomponent Vapor-Liquid Equilibrium Calculation
Examples
Example Calculation of Pseudo-Pure component Properties
Example for Instantaneous Flashing Release
Example Gas Flow Rate Calculations
Example: Expanded Jet Diameter for Chloring Vapor Choked
Flow
Example: Expanded Jet Diameter for Flashing Liquid
Chlorine Choked Flow
Example Rate Calculations for Evaporation

Abstract

Gives methods for modeling hypothetical accidental releases of fluids and gases into the atmosphere from process operations. Given a particular type of release and the chemicals or petroleum fractions involved, methods for modeling the release and subsequent dispersion phenomena are treated in a step-wise, comprehensive manner. Detailed simulation of eight hypothetical release scenarios are presented to demonstrate how the modeling procedures can be implemented.