186p Developing a Simple Spreadsheet Application for Multi-Component Two-Phase Flow Calculations Utilizing An Interface to a Thermodynamic Property Package

Subin Hada¹, Robert N. D'Alessandro², Srinivas Palanki¹, and Jeffrey R. Seay³. (1) Department of Chemical Engineering, University of South Alabama, North University Blvd., Mobile, AL 36688, (2) Process Engineering Department, Evonik Degussa Corporation, 4301 Degussa Road, PO Box 868, Theodore, AL 36590-0606, (3) Department of Chemical and Materials Engineering, University of Kentucky, Paducah, KY 42002

One of the primary objectives in the safety concept of any chemical process is to protect personnel from the dangers of overpressurizing equipment. In addition to protecting personnel, minimizing major release of toxic or flammable chemicals to the environment and avoid damage to equipment is also paramount.

In order to safely handle the material discharge from pressurized vessels during an emergency, a Safety Relief Valve (SRV) is often used. 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.

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.

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.

Two different vessel conditions were considered: 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. These two conditions were further analyzed for fluids exhibiting churn-turbulent flow and bubbly flow fluid behaviors. The calculations are presented with classical examples along with comparisons with more rigorous calculation methods and against available literature.