The study of emergency venting of multiphase vapor-liquid mixtures and the thermodynamics of multi-component systems has become an integral part of industrial practice. The prediction of venting conditions and the use of different sizing methods for two-phase vapor-liquid flashing flow is important when designing emergency relief systems for runaway reactions.

It is well known that, when selecting an appropriate model, a number of factors such as flow patterns, phase distribution, flow conditions and fluid properties must be considered with respect to the nature of the fluid. A wide variety of theoretical models which apply to two-phase flow have been published, however, each model has limitations and while a particular model may work well under certain conditions it may not be applicable in others.

There are several commercially available software packages available on the market capable of accounting for the complexities of multiphase flow, multi-component thermodynamics, and chemical reactions under unsteady state conditions for emergency relief system evaluation. However, these software packages are usually expensive and are cumbersome to use for the casual user. In addition, due to their general nature, these software packages usually use large amounts of computing time to solve problems that include all of the complexities described above.

The purpose of this contribution is to demonstrate the use of spreadsheet applications with visual basic (VBA) code to carry out multicomponent multiphase dynamic system calculations. However, multicomponent multiphase thermophysical properties are not easily calculated in this computational environment Therefore a CAPE OPEN compliant interface or a thermodynamic modeling package like Aspen Plus can be used to generate the thermophysical properties of the pure component and the mixtures as a function of temperature, pressure, and composition. Once the spreadsheet is set up to do the calculations, data acquisition from thermodynamic modeling package to spreadsheet can be automated using VBA to rerun the calculations that require solving a series of differential energy and mass balances.

Different container disengagement models, ideal nozzle models in the case of relief valves and flow through various piping configurations in the case of a rupture disk place in a piping system were considered. The work was extended further by considering two situations: one where the energy input was derived from an internal uncontrolled exothermic reaction, and the second where the energy input is from an uncontrolled external source such as fire. The calculations are presented with classical examples along with comparisons against other calculations done with more sophisticated tools and against available literature.

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