GPSA Method · Rachford-Rice · Wilson Correlation
Solves the Rachford-Rice equation iteratively:
β = vapor fraction (V/F), zi = feed composition
Understand flash calculations principles, calculations, and industry applications
Component Tc, Pc, and ω values from NIST Chemistry WebBook and DIPPR database, validated against GPSA Table 23-3.
| Wilson: | P < 500 psia, Tr < 0.9 |
| Raoult: | P < 100 psia, ideal mixtures |
| Components: | C₁ through nC₄ paraffins |
For higher pressures or near-critical conditions, use equation of state methods (SRK, PR).
| Comp | Tc (°R) | Pc (psia) | ω |
|---|---|---|---|
| C₁ | 343.0 | 667.8 | 0.012 |
| C₂ | 549.8 | 708.3 | 0.100 |
| C₃ | 665.7 | 617.4 | 0.152 |
| nC₄ | 765.3 | 551.1 | 0.200 |
Source: NIST/DIPPR, verified against GPSA Table 23-3
It performs vapor-liquid equilibrium flash calculations using the Rachford-Rice method and Wilson K-value correlation per GPSA standards.
The calculator uses the Rachford-Rice method for solving flash equations and Wilson K-value correlations for equilibrium constants.
A VLE (vapor-liquid equilibrium) flash calculation determines how a multi-component mixture splits into vapor and liquid phases at given temperature and pressure conditions.
The Rachford-Rice method solves vapor-liquid equilibrium by iteratively finding the vapor fraction (β) that satisfies the equation f(β) = Σ zi(Ki-1)/[1+β(Ki-1)] = 0. It uses Newton-Raphson iteration and is the industry-standard algorithm for isothermal flash calculations.
Wilson correlation is recommended for pressures below 500 psia and accounts for molecular shape through the acentric factor. Raoult's Law (ideal) is only valid for ideal mixtures at low pressures below 100 psia.
Wellhead separators typically operate at 200-1000 psia, production separators at 50-300 psia, and flash tanks at 15-100 psia. The calculator determines phase split, equilibrium K-values, and compositions at any specified temperature and pressure.