API PUBL 4636:1995

EXECUTIVE SUMMARY 1. Historical background As a result of many years in-house research, the gas dispersion group at Shell Research Ltd. Thornton (United Kingdom) has developed a package of mathematical models, called HGSYSTEM, to study the atmospheric dispersion of accidental pollutant releases with emphasis on denser-than-air materials. HGSYSTEM can be simulate different dispersion scenarios (jet dispersion, heavy gas dispersion, passive dispersion). The first version of HGSYSTEM was made freely available for use in November 1990. This version, called NOV90 or version 1.0, was prepared by Shell Research Ltd. for The Industry Cooperative HF Mitigation/Assessment Program, Ambient Impact Assessment Subcommittee as one component of a wider programme aimed at a better understanding of atmospheric dispersion, including hydrogen fluoride (HF) releases. HGSYSTEM can model the full HF chemistry and thermodynamics. Most of the modules in the HGSYSTEM package can also be used for more general, non-reactive (ideal gas) releases as well. Validation of the HF-related simulations has been done with the well-known Goldfish Test Series. Full documentation to the 1.0 version was given in the HGSYSTEM Technical Reference Manual and User's Manual. After release of the 1.0 (NOV90) version, a version 1.1 was made available which contained minor changes to solve some program bugs. Several internal versions were also developed. 2. HGSYSTEM 3.0 HGSYSTEM is in wide use for simulation of atmospheric dispersion scenarios for HF and other pollutant releases. It has been assessed against other models and found to rank amongst the best available atmospheric dispersion models in the world. HGSYSTEM sets the standard for HF dispersion calculations. However, a number of topics were open for improvement and generalisation. With financial support of the American Petroleum Institute, Air Modelling Task Force, Shell Research has upgraded and updated the existing HGSYSTEM package, resulting in a new release called HGSYSTEM version 3.0. The following major changes have been made to HGSYSTEM 1.0 to obtain HGSYSTEM 3.0: -- The thermodynamical models available in HGSYSTEM have been extended. The full HF chemistry and thermodynamical model is now suitable for mixtures of HF, water and an inert ideal gas. The non-reactive ideal gas description has been extended to multi-compound liquid-vapour mixtures (aerosols). -- A database containing physical properties for some 30 compounds has been added to HGSYSTEM. This database is needed when using the new two-phase multi-compound thermodynamical model. -- The PLUME model for pressurised releases has been extended to model jet dispersion of multi-compound, two-phase mixtures and is now called AEROPLUME. -- A new model describing the initial phase of instantaneous releases, HEGABOX, has been added to HGSYSTEM. -- A new model to calculate release rates from pressurised vessels, SPILL, is now available in HGSYSTEM version 3.0. -- The existing evaporating pool model EVAP has been replaced by a better model, LPOOL, for boiling and non-boiling pools and land and water. LPOOL is based on a model developed by Exxon Research and Engineering Company. -- The formulation of the lateral spreading in the heavy gas dispersion model HEGADAS has been reviewed and improved. -- Several options have been added to the time-dependent version of the heavy gas model HEGADAS making it easier to use and to evaluate the results. -- HGSYSTEM now contains three post-processors to generate data for graphical output after a pressurised jet release, steady state heavy gas release and a time-dependent heavy gas release respectively. These post-processors will improve the ease of use of the HGSYSTEM modules. -- Five additional options resulting from work done on HGSYSTEM as sponsored by Martin Marietta Energy Systems Inc (USA) are available to all HGSYSTEM users. -- A new HGSYSTEM 3.0 User's Manual and Technical Reference Manual have been written. These are now up-to-date and their format allows for easy future updating. 3. Modules available in HGSYSTEM 3.0 The following models are available in HGSYSTEM version 3.0: Database program DATAPROP generates physical properties used in other HGSYSTEM models Source term models SPILL transient liquid release from a pressurised vessel HFSPILL SPILL version specifically for hydrogen fluoride (HF) LPOOL evaporating multi-compound liquid pool model (unpressurised release) Near-field dispersion models AEROPLUME high-momentum jet and elevated plume model HFPLUME AEROPLUME version specifically for hydrogen fluoride (HF) HEGABOX dispersion of instantaneous heavy gas releases Far-field dispersion models HEGADAS heavy gas dispersion (steady-state and transient version) PGPLUME passive Gaussian plume dispersion Utility programs HFFLASH flashing of hydrogen fluoride (HF) from pressurised vessel POSTHS/POSTHT post-processing of HEGADAS results (steady state and time-dependent version) PROFILE post-processor for concentration contours of air borne plumes GET2COL utility for data retrieval 4. Documentation HGSYSTEM version 3.0 is documented in the following two manuals: HGSYSTEM 3.0 User's Manual L. Post Shell Research Limited, Thornton Research Centre, TNER.94.058 1994 HGSYSTEM 3.0 Technical Reference Manual L. Post (editor) Shell Research Limited, Thornton Research Centre. TNER.94.059 1994 The User's Manual is thought to be the main reference document for normal us of the HGSYSTEM modules. It contains all information necessary to run the models and interpret the generated results. The Technical Reference Manual is intended as a source of background information for users who want to know more about the technical/scientific contents of the HGSYSTEM modules. HGSYSTEM 3.0 Course Notes (TNER.94.060) are also available for use during possible HGSYSTEM training sessions.