Wilson K-values ยท SBV Mixing ยท GPSA 14th Ed
Understand phase diagrams, retrograde condensation, and EOS modeling
A phase envelope is a pressure-temperature diagram showing the boundary between single-phase and two-phase regions for a gas mixture. It defines the dew point curve (first liquid forms), bubble point curve (first vapor forms), cricondenbar (maximum two-phase pressure), and cricondentherm (maximum two-phase temperature).
Retrograde condensation occurs when a gas mixture forms liquid as pressure decreases, which is opposite to normal behavior. This happens between the cricondentherm and the critical point on the phase envelope, and is a key concern for pipeline operations and separator design.
Wilson K-values are equilibrium ratios that estimate vapor-liquid distribution of each component based on its critical properties and acentric factor. They provide a rapid approximation of dew and bubble points without requiring a full equation of state calculation.
Wilson K-value correlations with SBV mixing rules provide ยฑ5-10% accuracy for typical natural gas compositions. For detailed design, a process simulator with a tuned equation of state such as Peng-Robinson or SRK should be used.