화학물질 누출에 따른 초기 피해영향 범위 산정을 위한 분산모델 연구

Abstract

Most factories deal with toxic or flammable chemicals in the industrial process and the hazardous substances are always at risk of leak by various accidents such as fire and explosion. When the accident occurs, the hazardous chemical spreads not only inside the industrial facilities but also to nearby areas, which may result in massive casualties and property damages. Therefore, it is necessary to assess their risk quantitatively to design and operate the facility and the dispersion model of leakage must be the core of the consequence analysis. Even there are a few methods to evaluate the chemical dispersion in the atmosphere, most analysis has used the neutral dispersion models assumed that the density difference is same as that of ambient air and hence can be rule out the buoyancy effect of the leaked hazardous chemicals. However the model is valid only after a long time to release or away from the source because it is assumed the perfect mixing between leaked gas and the surrounding fluid basically. Generally most dangerous region due to the diffusion of actual hazardous chemicals might be nearby place from a leak source, which means initial stage of dispersion in the event of chemical leak. Therefore initial dispersion model is required to assess risk quantitatively and predict the extent of damage. In this study, the dispersion model for initial consequence analysis was developed with three dimensional unsteady advective diffusion equation, where instantaneous leakage is assumed as puff and wind velocity is considered as coordinate transform in the solution. Ethane was used as leaked fuel to minimize the buoyance force and two different diffusion coefficients were introduced. The calculated concentration field with molecular diffusion coefficient shows a moving circular iso-line in the horizontal plane and the maximum concentration decreases with increasing time and distance. In the case of turbulent diffusion coefficient, the diffusion along a wind velocity is enhanced and hence elliptic iso-contour line is found. The mostly used ALOHA commercial program was introduced and compared with the end point of lower explosion limit. In the future, we plan to build a more accurate and general initial risk assessment model by considering a turbulence diffusion and a buoyancy effect on the dispersion.