Desenvolvimento e aperfeiçoamento de modelos matemáticos na previsão de liberações bifásicas em atmosferas explosivas.

Abstract

Continuous releases of flammable chemicals can result in the formation of explosive atmospheres in process plants, which can lead to incidents of high proportions. Calculating the extent of these risk areas is therefore of paramount importance. For this purpose, currently, many organizations make use of the existing normative prescriptions, which employ the use of standardized or pre-defined figures as a method for classifying areas. However, several authors argue that this strategy has numerous uncertainties that can generate errors and incurring in risky situations. In this sense, this work presents a more reliable alternative to prescriptive models. Since many accidents involve two-phase releases of flammables or toxics into the atmosphere, a systematic methodology, based on previous studies, is proposed to map the explosive areas generated in this context. The method includes the use of analytical source models to estimate the amount of product released and the behavior of the jet after expansion. Mass, momentum and energy balances were used to predict the dispersion of the jet and the droplets present in it. The effects of the component's vapor phase and the interaction between droplets and gas (air + vapor) are accounted. A new normalization ratio for the centerline temperature, based on pre-existing concepts, was developed for application in the two-phase region. To avoid discontinuities in the velocity, concentration and temperature profiles calculated on the centerline, an alternative was developed for determining the decay constants. The Matlab® software was used as a simulation tool to analyze the methodology, validating it with experimental data available in the literature for liquids stored under saturation and subcooling conditions. The results showed that the degree of subcooling influences the amount of air drawn into the gas cloud. Furthermore, it was found that the greater this degree, the greater the distance required for the complete evaporation of the drops. A correlation for the calculation of the drag coefficient in hypotheses involving releases with a high degree of subcooling is proposed. The temperature profiles obtained showed a good agreement with the experimental points, being better than the predictions obtained by other authors. The other results showed the expected behavior for each process variable. Finally, the applicability of the model to situations considering other flammable substances and different inclination angles was verified.