Naphtha steam cracker: furnace, quench, compression, cryo train — a PENG-ROBINSON process flowsheet
The full ethylene-plant process shape (steam-methane-cracking's headline technology, e.g. Linde's steam cracking line): a fired-heater convection preheat, a three-reactor lumped pyrolysis furnace, a transfer-line-exchanger quench, a primary fractionator pulling off pyrolysis gasoline, two-stage compression with interstage knockouts, selective acetylene hydrogenation, and a cryogenic cold train (cold-flash light-gas rejection, deethanizer, C₂ splitter, depropanizer) delivering four real products — ethylene, propylene, a butadiene-rich C₄ cut, and a pygas/heavy-ends byproduct — plus an H₂/CH₄-rich tail gas and two knockout condensate streams.
Modeling assumptions & limitations
- 1Naphtha is modeled as a single n-heptane surrogate (no fitted radical-chain kinetics exist in MaximaLabs for real naphtha pyrolysis, so the furnace is three chained fixed-conversion reactors on real, exactly mass-balanced cracking/dehydrogenation stoichiometry — C₇H₁₆ → C₂H₄ + C₂H₆ + C₃H₆, C₇H₁₆ → CH₄ + C₂H₄ + C₄H₆ + H₂, and C₂H₄ → C₂H₂ + H₂ for a trace acetylene impurity — tuned to a representative, not literature-fitted, product distribution, the same 'illustrative, not fitted' posture already disclosed for saf-hefa-renewable-jet's hydrocracking lump).
- 2The demethanizer is a single cold flash stage, not a rigorous multi-tray column: H₂ is permanently supercritical at any realistic column pressure (Pc~13 atm vs. the ~20+ atm this train runs at), which was found during this build to corrupt the MESH solver's initial temperature-profile guess (fixed — but even after that fix a genuine ~15 mol% H₂ feed to a sharp-cut demethanizer is a hard column this solver doesn't converge on cleanly); a single flash stage rejects H₂/CH₄ in bulk instead, consistent with the 'cold-box front-end flash' some real designs use, but with materially worse light-key rejection than a real 20+ tray demethanizer. That carries through honestly to the ethylene product: it converges at ~77 mol% ethylene (the balance methane and H₂), not polymer-grade purity — the real number the solver computes, not an assumed spec. Propylene fares much better (~96%) since it isn't competing with as light a contaminant.
- 3No BTX/aromatics extraction — the pygas cut is reported as a single lumped heavy stream, matching saf-hefa's precedent of not resolving every real product cut.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 6 unit operations modeled: Furnace, 4× Acetylene Hydro, 5× Chill Demeth, 4× Coldflash, 2× Compressor2, 3× Depropanizer.
- Focus areas: Steam cracking, Ethylene, Propylene, Pyrolysis, Cryogenic distillation, Petrochemicals.
- Thermodynamics
- PENG-ROBINSON
- Components
- n_heptane, methane, h2, ethylene, ethane, propylene, 1_3_butadiene, acetylene
- Unit operations
- Furnace4× Acetylene Hydro5× Chill Demeth4× Coldflash2× Compressor23× Depropanizer
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Read the step-by-step guideReproduce this exact result from Python — the real client.get_example() → run_and_wait() path, not a mockup.
from flowsim.sdk import FlowSimClient
client = FlowSimClient()
example = client.get_example("naphtha-steam-cracker")
sim = client.create_simulation(example["title"], example["flowsheet"])
result = client.run_and_wait(sim["id"])
print(result["status"]) # "converged"
streams = client.streams(sim["id"])Related models
Ethane steam cracker
A simplified thermal-cracking train: an equilibrium reactor converts ethane to ethylene + H₂ at furnace conditions (1100 K), then a quench, compression, and a cold flash strip the H₂ tail gas before a C₂ splitter separates ethylene product from unconverted ethane. An equilibrium reactor is used here rather than the kinetic reactor because the latter's concentration term always uses a liquid-phase density (a real gap for a vapor-phase reaction at 1100 K) — noted, not fixed, out of scope for this example. The C₂ splitter needs many stages and high reflux since ethylene/ethane relative volatility is modest. From the ChemSep casebook (ethane cracker).
Propane dehydrogenation cold box
Propane dehydrogenation (PDH) to propylene over a Pt/Cr catalyst, followed by a cold-box separation recovering liquid propylene from the H₂-rich reactor off-gas, after US Patent 6,333,445 (Chart Inc., 2002). The refrigeration loop itself is not modeled — the cold box is represented here as a net cooling duty to condense the propylene, a bounded simplification. Unreacted propane recycle is not modeled either (reported as its own product stream).
Propylene refrigeration (−30 °C)
Closed propylene cycle for −30 °C process cooling — the workhorse olefin-plant refrigerant. From the ChemSep casebook (Refrigeration_Propylene-30C).
Propylene refrigeration (−50 °C)
The same propylene loop pulled to −50 °C by sub-atmospheric evaporation (0.8 bar) — COP drops as the lift grows. From the ChemSep casebook (Refrigeration_Propylene-50C).
Electrically heated ethane cracker (Linde/BASF/SABIC STARBRIDGE concept)
The same ethane-to-ethylene thermal cracking chemistry as ethane-cracker, but with the furnace's radiant-coil heating supplied by an electric heater instead of a fuel-gas-fired one — the real distinguishing feature of Linde's STARBRIDGE technology (demonstrated at industrial scale with BASF and SABIC at Ludwigshafen, 2024): resistive heating elements replace burners, transferring heat to the process coils by radiation 'in a configuration similar to conventional furnaces,' eliminating the furnace's own combustion-derived CO₂ emissions (upstream grid emissions aside). Modeled here as a plain electric heater node (no fuel-gas inlet, no flue gas, no combustion stoichiometry) in place of fired_heater's combustion-fired duty — the honest difference this technology actually is: identical process-side thermal duty and cracking chemistry, a different (electric) heat source with no direct-combustion byproduct stream. Linde's own proprietary heating-element/coilbox design, materials, and thermal efficiency figures are not published and are not fabricated here; the furnace's computed duty is a genuine energy-balance result (electric heater → real Q required to bring the feed to cracking temperature), not a marketing number.
Oxidative dehydrogenation of ethane to ethylene + acetic acid (EDHOX concept)
Linde's EDHOX technology co-produces ethylene AND acetic acid from ethane and oxygen in one catalytic step (a proprietary mixed-metal catalyst in a multi-tubular salt-cooled reactor), with combined ethylene+acetic-acid selectivity published above 93% and the CO₂ by-product of over-oxidation recovered pure (no nitrogen dilution, since the oxidant is pure O₂, not air). Modeled here as three chained fixed-conversion reactors on real, exactly mass-balanced reactions: the main dehydrogenation (C₂H₆ + 0.5 O₂ → C₂H₄ + H₂O), the acetic-acid co-production path (C₂H₆ + 1.5 O₂ → CH₃COOH + H₂O), and a minor full-oxidation loss path (C₂H₆ + 3.5 O₂ → 2 CO₂ + 3 H₂O) accounting for the un-selective balance — the same 'illustrative, not fitted' posture as the naphtha cracker's furnace, since Linde's catalyst kinetics are proprietary and not published. The per-reaction conversions here are tuned to reproduce the one real published number (>93% combined selectivity: this flowsheet computes ~96%), not an assumed per-pass ethane conversion, which Linde doesn't publish.