Desenvolvimento do aplicativo EPT-LK para estimativas de propriedades termodinâmicas via equação de Lee-Kesler

Abstract

The Lee-Kesler Equation of State is widely used in the prediction of volumetric, residual and thermodynamic properties of pure substances and mixtures generally used in fluid processing of petrochemical and natural gas industries. The Lee-Kesler formulation uses two fluids (simple fluid and reference fluid) and the Taylor Series ́s expansion around the properties of the simple fluid (spherical) truncated in linear terms and with geometric correction estimated by finite differences of the two fluids. The compressibility factors of simple and reference fluids are predicted through modifications of the BWR equation of state (Benedict-Webb-Rubin).Since this is a transcendental equation, calculations require the use of numerical methods to solve nonlinear equations. From the volumetric properties, the residual and thermodynamic properties are determined. Given the importance of this equation in Chemical Engineering, it was proposed to develop an app in Fortran 90 programming language for Windows capable of providing reliable property predictions, with only truncation and conversion errors (rounding). The app proposed was divided into eight modules: 1) vapor pressure; 2) acentric factor; 3) functions of simple fluid, reference fluid and geometric correction; 4) compressibility factor curves (intermolecular forces ́s nature and intensity) as a function of pressure; 5) volumetric and residual properties of pure substances; 6) volumetric and residual properties of mixtures; 7) thermodynamic properties between two states and 8) fugacity of species i in the mixture. In addition, a database was created containing the physical properties of pure species (hydrocarbons, organic and inorganic compounds). The final app contains 68 forms (UserForm) and 81 subprograms. Validations of the app modules were conducted after the construction stage, comparing, under the same conditions, the results provided by the app with those reported in world literature. From the validations made, it was observed that the Fortran 90 subprograms were coded quite efficiently, providing reliable results with only numerical computation errors (truncation and conversion-rounding) from the volumetric, residual and thermodynamic properties. The research ́s final result is a friendly interface app which is easy to use and manipulate throughout the various modules. The acquisition cost is symbolic and can be used by undergraduate and/or graduate students, as well as professionals in the chemical and petrochemical industry.