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Four-Cut C7+ Heat-Duty and Isenthalpic Flash Calculator

Solve a heavy-mixture pressure-drop energy flash using an explicitly supplied heavy ideal-gas heat-capacity fit and four characterized C7+ cuts.

Inputs

Results

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

Calculation sequence

  1. Use the same conditional gamma inputs as the PT tool, then supply an independently justified ideal-gas C7+ heat-capacity fit valid over the entire 180-450 K calculation interval. A measured liquid Cp is not interchangeable with ideal-gas Cp. The default linear fit is synthetic. Molecular-weight scaling assumes equal mass-specific ideal-gas Cp across all four cuts.
  2. Evaluate the fully audited inlet PT equilibrium, then form the molar enthalpy target from prescribed specific heat and feed molecular weight. The six real species use pinned native ideal-gas functions; heavy cuts use the supplied fit. Add each phase's PR departure enthalpy and apply the phase lever rule. Species reference offsets cancel because the total feed composition is unchanged.
  3. At the lower or equal outlet pressure, require an increasing enthalpy bracket on a 25-point 180-450 K grid. Use a bounded Brent root and enforce an absolute energy residual below 0.0001 J/mol. Zero q is isenthalpic, not isothermal; heating and cooling can change both temperature and the phase split.
  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

For the synthetic four-cut feed at 5 MPa and 330 K, expanding to 1 MPa with q=0 and C7+ Cp0(300 K)=300 J/(mol.K), slope=0.6 J/(mol.K^2), gives outlet T about 302.352656 K and vapor mole fraction 0.764602. These outputs depend on that explicit synthetic caloric assumption; they are not properties inferred from SG and MW alone.

Synthetic examples for reproducibility, not measured field results.

Assumptions and limitations

  • A deliberately bounded four-cut approximation over 100-300 g/mol, not a complete Whitson C7-to-C80 assay. Every cut uses the same supplied 60/60 F SG. Reject an unbracketed mean, retained gamma probability below 1e-6, Tb>=Tc or omega outside 0-1. Shape does not determine aromaticity or a measured carbon-number distribution.
  • MW=100-300 g/mol, SG=0.65-0.90, shape=0.5-10; the conditional mean must also be achievable at that shape. At least two feed fractions >=0.001; C7+ is 0.004-0.99. T=180-450 K and p=0.1-10 MPa(a) are software bounds, not a validated accuracy envelope. No water, N2, CO2, H2S, solids, multiple liquids, volume shifts or density matching.
  • Only methane/heavy-cut pairs share the user k_heavy (-0.2 to 0.4). All other pairs are zero. Properties use the pinned NeqSim Riazi-Daubert MW-SG variant plus explicit Edmister omega, not a silent Pedersen or Kesler-Lee fallback. Neither a solved flash nor a fitted parameter is proof of physical accuracy.
  • The supplied ideal-gas Cp fit must give positive Cv for every cut across the full trial envelope; passing this gate is not caloric-data validation. No shaft work, kinetic/potential energy, fitted formation heat transfer, compression or pressure traverse. Reject unbracketed/nonmonotone energy targets rather than extrapolating a Cp fit.

Implemented equations

Conditional gamma moments and four equal-probability cuts

f(M)∝g(M)e−(M−100)/bg(M)=(M−100)α−1100≤M≤300Mˉj=∫ajaj+1Mf(M) dM∫ajaj+1f(M) dM∫ajaj+1f(M) dM=1/4\begin{aligned}f(M)&\propto g(M)e^{-(M-100)/b}\\g(M)&=(M-100)^{\alpha-1}\\100&\le M\le300\\\bar M_j&=\frac{\int_{a_j}^{a_{j+1}}M f(M)\,dM}{\int_{a_j}^{a_{j+1}}f(M)\,dM}\\\int_{a_j}^{a_{j+1}}f(M)\,dM&=1/4\end{aligned}

Supplied heavy ideal-gas caloric fit

Cp,j0(T)=MjMˉ[A+B(T−300)]hˉo=hˉi+1000qMz\begin{aligned}C_{p,j}^0(T)&=\frac{M_j}{\bar M}[A+B(T-300)]\\\bar h_o&=\bar h_i+1000qM_z\end{aligned}

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}

Sources and maintenance

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

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