This method (SRKKD) is a modification of the Soave-Redlich-Kwong method to improve the prediction of vapor-liquid-liquid phase equilibria for hydrocarbon systems with water. To achieve this, Kabadi and Danner proposed a two parameter mixing rule for calculation of the "a(T)" term in the SRK equation. They also developed a means to provide estimates for water-hydrocarbon equilibria when no data are available.
The SRKKD method in PRO/II uses an improved alpha correlation developed by SimSci. The improved correlation provides more accurate vapor pressure predictions than the original SRK formulation for a wide variety of components.
In addition to K-values, the SRKKD equation may be used to predict the enthalpies, entropies and densities for the liquid and vapor phases. The predicted liquid phase densities are not very
accurate and the API method is selected by default when this system is chosen.
See "Soave-Redlich-Kwong Kadabi-Danner (SRKKD)" under "Equations of State" in Chapter 2, Volume 1, of the PRO/II Reference Manual for more information.
Application Guidelines
Natural gas systems at high pressures which contain water. Hydrocarbon systems with water where prediction of the hydrocarbons dissolved in the water is important. This method is poor at predicting the solubility of hydrogen in the aqueous phase.