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Expanded Gas and Isomer PR Flash Calculator

Calculate PR phase equilibrium for C1-C6, iC4/iC5, N2, CO2 and H2S with pinned ChemSep PR pairs and explicit missing-pair assumptions.

Inputs

Results

Calculate to view linked results. Default values are examples, not recommended operating inputs.

Calculation sequence

  1. Enter eleven feed mole fractions on one molar basis and make their sum one. Include isomers in their own slots; do not add iC4 to nC4 or confuse nitrogen/CO2/H2S with a gas-gravity approximation. This dry mixture tool searches vapor plus one liquid only; water is not an accepted feed species.
  2. Use the pinned ChemSep PR kij wherever that exact pair has an entry. A missing entry is not a verified zero: the calculation lists each active missing pair and applies the common user coefficient explicitly. This common assumption is a sensitivity input, not a substitute for pair-specific laboratory fitting. Available coefficients are not overwritten by the missing-pair setting.
  3. Inspect vapor and liquid compositions, component allocations and mass versus mole fractions. CO2/H2S/N2 change mixture behavior through real species parameters and the disclosed interactions, rather than through a universal sour-gas correction. H2S inclusion is a property calculation, never a sour-service handling or safety judgment.
  4. At every returned state independently re-evaluate classical PR pressure, log fugacity and residual enthalpy/entropy. Require component balance <=2e-7, log-fugacity mismatch <=2e-5 and relative pressure residual <=2e-6. Reject vanishing phase fractions below 1e-6 and density separation below 1.1 for ordinary splits. These are numerical checks, not measured-PVT validation.
  5. Calculations run locally in a dedicated WebAssembly worker. The advanced Python/scientific engine is a roughly 33 MB first download, separate from ordinary calculators; it is self-hosted and version pinned. No composition or measurements are sent to a calculation server. Save and file backups retain canonical inputs, while CSV/PDF include returned tables and source notes. The worker is released after idle time and failures never return partial results.

Worked check

At 300 K and 2 MPa the synthetic eleven-species feed gives vapor mole fraction about 0.749351 and bulk density 41.024947 kg/m3. Database interactions are used where available and missing dry pairs use the explicit zero assumption. The example demonstrates composition and interaction handling, not a calibrated sour-gas PVT test.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

  • Classical PR, no volume translation, at most one vapor and one liquid phase, 180-450 K, 0.1-10 MPa(a). Fixed component list only. No heavy ends, reactions, ionic species, adsorption, wax or hydrates. Numerical stability search is not proof of stability against arbitrary additional phases.
  • Database kij values are constant and are not guaranteed accurate across the software envelope. Missing dry pairs use k_missing; missing water pairs use k_water. Both are common symmetric assumptions, not pair-specific fits. No default coefficient is represented as measured calibration for this feed.
  • No second-liquid stability search in this dry tool. A converged two-phase solution can still be inadequate for mixtures that form additional phases. At least two present components, each >=0.001. Use measured phase/density data to assess the physical model; passing closure cannot establish such accuracy.

Implemented equations

PR attraction with a disclosed interaction matrix

a=∑i∑jxixjaiaj(1−kij)kij=kji,kii=0\begin{aligned}a&=\sum_i\sum_j x_ix_j\sqrt{a_ia_j}(1-k_{ij})\\k_{ij}&=k_{ji},\quad k_{ii}=0\end{aligned}

Multiphase component and molar-volume balances

zi=∑αβαxi,α∑αβα=1vˉ=∑αβαvαxi,αφi,α=xi,γφi,γ\begin{aligned}z_i&=\sum_\alpha\beta_\alpha x_{i,\alpha}\\\sum_\alpha\beta_\alpha&=1\\\bar v&=\sum_\alpha\beta_\alpha v_\alpha\\x_{i,\alpha}\varphi_{i,\alpha}&=x_{i,\gamma}\varphi_{i,\gamma}\end{aligned}

Sources and maintenance

Published by PetroCalcHub Team. Implementation and source checks: . This does not claim independent expert review.

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