STUDY OF VAPOR – LIQUID EQUILIBRIA OF PETROLEUM FRACTIONS

The calculations of vapor – liquid equilibria for petroleum fractions are important in design and operation of petroleum processing equipment. The most important vapor – liquid calculation for petroleum fractions is well known as the equilibrium flash vaporization curve (EFV). The EFV curve can be predicted from the true boiling point curve (TBP) by using two methods: The graphical methods and the pseudo – components (computer) methods.The purposes of the present work were divided into two parts: First part has two folds: First one graphical method and various pseudo – components methods were selected and tested to decide which method showed the greatest promise.Secondly, various attempts for improving the accuracy of existing methods were investigated. The selected flash method for part one were, the Raizi – Daubert
graphical method (RD graph) and five pseudo – components flash methods including the Soave – Redlich, Kowng (SRK) and Peng – Robinson (PR) equations of state flash methods, activity coefficients flash methods in which the SRK and PR equations of state used for vapor phase and the van – Laar activity coefficients model used for liquid phase (SRK + Van and PR + Van) and finally the ideal solution K – values flash method (Ideal K) also used. To perform the purpose of part one, the data for 18 petroleum stocks were selected from literature including the TBP, EFV and the specific gravity data or curves. As a results of part one investigations, it was concluded that the modified Ideal K flash method based on the present work of new suggested vapor pressure correlation was the most accurate and reliable flash method for estimation the EFV curves. The expression of the new suggested vapor pressure correlation is as follows: