| Kinds of toxic gases and liquids are produced, stored and used in different modern petrochemical industry and other related fields. Once leaked due to some reasons, e.g. human, equipment, production control and environment, those substance may release large quantity of toxic gases into the atmosphere. Gas and air compound into the formation of vapor clouds, and lead the people near the leakage sources to be toxiced. Thence, it's much important to study the emergency response of chemical accidents. This paper carries out the study on numerical simulation on gas dispersion based on CFD, which may provide theoretical base for the establishment and implementation of emergency response plan and evacuation procedure.In this paper, a transient heavy gas dispersion model is presented, in which a k-εtwo-equation turbulence model modified with buoyancy effect, a control volume method and the SIMPLE procedure are adopted. Based on it, a self-compiled three-dimensional program is developed for the numerical simulation.For validation purpose, the test data from the Thorney Island Phase I Trial No. 8, which is specially an instantaneous release of large quantity of heavy gas, are adopted to verify the accuracy of the model and the correctness of the simulation. The numerical simulation of this trial can visually show the phenomena observed in the experiments, such as gravity driven slumping, entrainment of air, formation and evolution of vortex etc., and provide the distribution and evolution of the concentration and velocity profiles at different moments after the release.The model and the simulation algorithm are further extended to simulate the circumstances of the leakage of chlorine and sulfur dioxide and extracted a method to identify the dangerous areas by RMP, which directs to the preview of dangerous areas and the adoption of immediate emergency response actions.
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