The Sour package (SOUR) uses the SWEQ (Sour Water Equilibrium) method developed by Grant Wilson for a joint API/ EPA project. A modified van Krevelen method is used to predict the phase equilibria for CO2, NH3, H2S and H2O.
The SWEQ model uses Henry's law constants for each component in solution as a function of temperature and the composition of the undissociated molecular species in the liquid phase. The Henry's law constants for H2S and CO2 were obtained from data published by Kent and Eisenberg. The Henry's law constant for water was obtained by correlating water vapor pressures from the steam tables. Henry's law data for NH3 was taken from a publication of Edwards, et. al.
The chemical equilibria of all of the main reactions in the liquid phase due to the dissociation of the sour gas molecules are considered in the model. The reaction equilibrium constants are correlated as functions of temperature, composition of undissociated sour gas molecules and ionic strength. Vapor phase corrections for non-idealities are applied in PRO/II, extending the applicable pressure to 1500 psia.
Liquid and vapor entropies and vapor enthalpies and densities are computed using the SRK-Modified Panagiotopoulos-Reid (SRKM) method. Liquid enthalpies and densities are computed with the Ideal method.
See "Sour Package (SOUR)" in Chapter 2, Volume 1, of the PRO/II Reference Manual for more information.
Application Guidelines
Sour systems in which both NH3 and H2O are present. Other sour gas components are also usually present. Temperatures in the range 68 - 300 degrees F and pressures up to 1500 psia may be considered.
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