Real flowsheets, already solved
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On-site oxygen: multi-bed vacuum pressure swing adsorption (VPSA)
Medical- / green-steel-grade oxygen generated on site from air by a 4-bed vacuum pressure swing adsorption unit over an N₂-selective zeolite (LiX/13X). This uses the native VPSA unit op — the proven 2-bed Skarstrom engine generalized to N beds with pressure-equalization steps and sub-atmospheric evacuation: nitrogen is adsorbed while oxygen passes as the light product, then each bed is pulled to a vacuum to desorb the nitrogen tail gas. The solver runs the real cyclic transient (tanks-in-series bed discretization + linear-driving-force kinetics + inter-bed equalization) to a periodic steady state — the transient dynamic equilibrium legacy steady-state simulators cannot capture without a separate dynamic license.
4 unit ops • PENG-ROBINSON
190 0
View & openChiral API purification: continuous SMB chromatography
A racemic active pharmaceutical ingredient (R/S enantiomers, dilute in ethanol eluent) is resolved continuously by simulated moving bed chromatography — the workhorse of chiral-drug manufacture that legacy steady-state flowsheet simulators have no native model for (engineers script it in MATLAB). This uses the native SMB unit op, which solves the standard steady-state True Moving Bed equivalent: a 4-zone counter-current equilibrium-stage cascade whose zone flow-rate ratios sit inside the triangle-theory separation region, so the more-retained enantiomer reports to the extract and the other to the raffinate — the separation is driven by the chiral adsorption selectivity (the two enantiomers are otherwise thermodynamically identical).
5 unit ops • PENG-ROBINSON
191 0
View & openNGL fractionation: single-shell Petlyuk dividing-wall column
A natural-gas-liquids cut (ethane / propane / n-butane) split into three on-spec products by ONE thermally-coupled dividing-wall column instead of two columns in series. This uses the native Petlyuk unit op: a prefractionator whose reflux and boilup are supplied by the main column (the single condenser + single reboiler), solved by an outer Wegstein loop that converges the bidirectional vapor/liquid coupling to self-consistency — the coupling legacy sequential-modular solvers approximate with two connected columns whose recycle fails to converge.
5 unit ops • PENG-ROBINSON
191 0
View & openCement kiln calcination + CO2 liquefaction
Preheated limestone (CaCO₃) enters an indirectly-heated rotary kiln that calcines it toward CaO, releasing a CO₂-rich off-gas; the gas passes a knockout drum, then is compressed and cooled to liquefy the CO₂ for transport/storage.
11 unit ops • NRTL
191 2
View & openDirect air capture with solid-sorbent calcination + CO2 liquefaction
A Carbon Engineering-style DAC train: a fan draws ambient air (400 ppm CO₂) through a liquid-KOH contactor (a fixed-recovery separator — the same simplification the existing carbon-capture example uses for chemical absorption, since no CO₂-KOH electrolyte package exists) capturing ~75% of the CO₂. The captured CO₂ is causticized and precipitated into CaCO₃ pellets by the real (unmodeled-in-detail) KOH/Ca(OH)2 loop — represented here as a matched pellet feed sized to the captured CO₂ rate, since the generic reactor unit op can't itself produce a solid product (only a rotary kiln's decomposition path can, which is exactly what's used next). Those pellets calcine at ~977 degC in an indirectly-heated rotary kiln (real Arrhenius decomposition kinetics, Sullivan-Maynard-Valentine residence time), releasing pure CO₂ that's compressed to ~20 atm and chilled to 250 K — above the real Span-Wagner CO₂ saturation pressure at that temperature, so the solved outlet stream is genuine subcooled LIQUID CO₂ (not just dense-phase pipeline gas) — while the CaO leaves for slaking and reuse (the lime side of the closed loop, out of scope for the same reason as the causticization step). Run the Carbon Footprint report on this example for the real Scope 1/2/3 CO2e + carbon-tax liability breakdown already built into MaximaLabs's report generator.
12 unit ops • COOLPROP
192 1
View & openLOHC hydrogen release (methylcyclohexane dehydrogenation)
A liquid organic hydrogen carrier (LOHC) power train: methylcyclohexane (MCH) is preheated and catalytically dehydrogenated (MCH → toluene + 3H2, endothermic, equilibrium-limited to ~90% single-pass conversion) to release hydrogen for downstream power generation. A flash drum separates the H₂-rich gas from the liquid; a distillation column then recovers the unreacted MCH overhead and recycles it to the reactor feed, closing a real tight liquid recycle loop, while spent toluene leaves the bottoms (to be re-hydrogenated back to MCH off-site, closing the supply-chain loop — out of scope for this dehydrogenation-side flowsheet). Screening-fidelity note: MCH and toluene are genuinely close-boiling (relative volatility ~1.4 under this thermo package at column conditions), so the recycle carries real toluene along with the recovered MCH rather than a sharp cut — a production column would use more stages to purify it further; this shows the recycle topology and its convergence, not an optimized column design.
8 unit ops • PENG-ROBINSON
192 0
View & openDeep ethane recovery with propane-refrigerated feed chilling
Associated gas is chilled by an external propane refrigeration package before a demethanizer recovers ethane and heavier as NGL bottoms from a methane-rich residue gas overhead — the cryogenic-chilling role Ortloff's CCS/GSP processes play ahead of the turboexpander in a real deep-ethane-recovery plant. The mechanical refrigeration loop itself (compressor/condenser/valve) isn't separately modeled here; the chiller's duty is represented directly as the feed's cooled outlet temperature (the same honest-simplification pattern used for LNG cold-box examples elsewhere in this library).
5 unit ops • PENG-ROBINSON
190 0
View & openEthylene glycol plant: closed water loop + multi-effect evaporator dehydration
The water-integrated evolution of the fiber-grade MEG plant. Two changes turn the once-through EO/glycol chain into a real, water-economical process: (1) the recovered process water is RECYCLED back to the hydration reactors through a purge splitter. A pure recycle is inventory-singular (reactors are keyed on the shrinking EO pool, so water consumption is fixed regardless of how much water circulates), so an 8% purge pins the loop and makes it well-posed, cutting fresh water makeup from 10 to ~1.75 mol/s (a >80% reduction). (2) The bulk dehydration is done by a genuine TWO-EFFECT EVAPORATOR TRAIN (forward-feed, real steam economy: effect 1's low-temperature vapor is the heating steam for effect 2) doing rigorous (P,H)-flash water removal, rather than a single spec-based split. The recycle converges through the solver's Wegstein tearing (~15 outer passes) and MEG still comes out fiber-grade (>=99.9%). HONEST SCOPE: the reaction chemistry is rigorous stoichiometry (real atom balances, ~90/9/1 selectivity) and the evaporators are real energy-balanced flash effects — but flash evaporation CANNOT reach glycol dryness without slipping glycol into the overhead vapor (MEG has a real vapor pressure at 90 C), so the evaporators run cool and only pre-concentrate. An overhead knockout returns the ~1-2% slipped glycol to the product (no yield loss), and a final vacuum-refining polish (still a spec-based split, representing the refluxed dehydration column a flash cannot replicate) removes the last water. This mirrors a real MEG plant's multi-effect-evaporator + vacuum-refining dehydration section. The product columns remain spec-based (a converged 99.9% fiber-grade MEG column is not tractable under Peng-Robinson here — the MEG/DEG relative volatility is too narrow for the wide-boiling MESH path).
32 unit ops • PENG-ROBINSON
194 4
View & openHelium liquefaction (Linde-Hampson cycle)
A Joule-Thomson liquefaction loop: helium is compressed, aftercooled, precooled well below its ~40-51 K JT-inversion temperature, then throttled through a valve into a flash drum that draws off liquid helium while the cold vapor recycles back to the compressor suction — the same JT-cycle physics as the platform's LNG/refrigeration loops, run on a fluid whose inversion curve makes precooling mandatory before the throttle can cool it at all.
8 unit ops • COOLPROP
189 0
View & openCO₂ methanation (e-fuels / power-to-gas)
The Sabatier reaction (CO₂ + 4H₂ ⇌ CH₄ + 2H₂O) converts captured CO₂ and green H₂ into synthetic natural gas at a 97% single-pass-equivalent conversion (real plants stage several adiabatic beds with intercooling to reach this; lumped into one reactor here), then a cooler and knockout drum condense the reaction water from the SNG — the e-fuels loop that closes the loop on captured carbon instead of just storing it.
6 unit ops • PENG-ROBINSON
188 0
View & openHigh-CO2 LNG with amine capture and CO2 reinjection
One 5.3 Mtpa LNG train on a reservoir whose gas is 14 mol% CO₂, where the CO₂ is not vented but compressed to dense phase and injected — 2.8 Mtpa of it, at 200 bar, which is the scale that makes this a storage project rather than a gesture. Two things make this different from every other LNG example here. First, the acid-gas removal is real chemistry, in the same flowsheet as the cryogenics: per-node thermo_overrides run the absorber, the rich/lean loop and the stripper on the 'enrtl-mdea-pz' electrolyte package (MDEA protonation + piperazine carbamate/dicarbamate speciation) while the gas train and the cold end run Peng-Robinson — the amine unit and the MCHE are not two models bolted together, they are one solve. Second, the CO₂ goes somewhere: the stripper overhead is knocked back, two-stage compressed with interstage cooling and drying, and pumped to 200 bar as a ~96 mol% dense-phase stream ready for a reinjection well, rather than leaving as a vent. The sweet gas is water-washed, dried and liquefied in the C3MR cold end to LNG at ~116 K.
32 unit ops • PENG-ROBINSON
75 0
View & openGas-condensate LNG train: condensate, LPG and LNG
The LNG plant that is also a liquids plant, at real capacity: this is one 4.4 Mtpa train (a two-train plant is two of these), not a scaled-down sketch. A condensate-rich field arrives by trunkline as a two-phase stream: the slug catcher drops ~20 mol% of it out as raw condensate before a single molecule reaches the cold end, and the plant then runs two trains side by side off one feed. Liquids: the raw condensate is let down to an MP flash that strips the dissolved methane (without it the stabilizer's shortcut total condenser tries to condense methane at 8 bar, which is not a real stabilizer overhead), then stabilized to a C₅/C₆ product. Gas: sweetened and dried, chilled to 245 K to knock out an NGL cut, and the NGL demethanized and split by a deethanizer / depropanizer / debutanizer sequence into commercial propane (~98 mol%) and butane (~98 mol%) LPG plus a natural-gasoline bottoms. LNG: the lean gas goes to the same APCI C3MR cold end as the 'c3mr-lng-liquefaction' showcase — propane precool, mixed-refrigerant MCHE to 120 K, JT letdown to a 1.5 bar end-flash drum. Five sold products come out of one flowsheet, each a stream the solver computed. Watch the end-flash boil-off: it leaves at ~13 mol% nitrogen against 1 mol% in the feed, because the flash drum is where an LNG train actually rejects its nitrogen — nobody specified that, the flash found it. Dehydration is the real molecular-sieve bed, not a stand-in: a 4A sieve sized by length-of-unused-bed, which is what actually takes the gas to the <=0.1 ppmv the cold box needs — 95 t of sieve on a 5.5 x 5.5 m bed, a 17.5 h cycle and 1.4 MW of regeneration duty, with 0.47 bar of Ergun pressure drop. The AGRU spec is checked against the physics rather than assumed: 99.9% CO₂ removal leaves 33 ppmv, and at the coldest point in the train (115.9 K) the solid-CO₂ solubility limit is 232 ppmv on the measured-data basis — a 7x margin, so the sweetening spec demonstrably clears freeze-out instead of merely looking tight.
35 unit ops • PENG-ROBINSON
75 1
View & openLNG front end and storage: guard beds, tank boil-off, driver limit
The parts of a 5.2 Mtpa LNG train that are not the cold box, and the four questions they answer that no bulk unit can — at real capacity, so the vessel sizes and duties are ones an engineer can check against their own plant. Guard beds: a sulfur-carbon bed takes mercury from 200 to 0.01 µg/Nm³ — the brazed-aluminium limit, because mercury attacks the plate-fin cold box by liquid-metal embrittlement — on a 4.8 m x 6.6 m bed with 4.2 years of life from a capacity balance — inside the 3-5 year window these non-regenerable beds are actually replaced on, which is what a turnaround plan needs. A 4A molecular sieve then dries the gas to 0.1 ppmv, the only route to a cryogenic water spec (a glycol contactor tops out near a −30 °C dew point), on a 4.9 m x 5.1 m bed running a 13.8 h cycle for 1.3 MW of regeneration duty. Storage: the LNG goes to a tank whose boil-off rate comes from a 0.05%/day guarantee but whose boil-off composition comes from a real equilibrium flash — and that is the interesting part, because the vapour leaves at ~11 mol% nitrogen against 1.1% in the feed. Nitrogen and methane are far more volatile at 113 K, so the boil-off is light and the stored liquid weathers heavier: nobody specified that, the flash found it. Recondensing: the boil-off goes back into the send-out LNG rather than to a flare, and the unit reports the LNG:BOG ratio (1999) against the minimum the energy balance demands (3.8), which is the constraint a terminal is actually operated against. The driver: a gas turbine burning plant fuel gas, rated 97.5 MW at ISO conditions, delivers only 84.5 MW at 35 °C — 5.5 MW short of its 90 MW refrigeration load, and flagged as such. That derate is computed from two physical effects (a fixed-geometry compressor swallows a fixed volume so mass flow follows air density, and hotter air costs more to compress), not from a vendor curve, and it comes out at 0.66%/K — mid-band for industrial machines. It is why a tropical LNG train makes less product in summer.
17 unit ops • PENG-ROBINSON
74 0
View & openPolymerization reactor comparison: CSTR cascade vs. tubular (PFR)
The same monomer feed, split 50/50 into two trains at equal total reactor volume: a 3-stage CSTR cascade (each stage blending its own new polymer with the MWD already carried by the stream from the stage before it) versus a single tubular (PFR) reactor. Both converge to a real, different Mn/Mw/PDI — the PFR reaches higher conversion at the same total volume, but its cumulative polydispersity is measurably broader than the cascade's, because chain length drifts continuously with conversion along the tube while each CSTR stage makes its own local production under one fixed monomer concentration. See the 'Polymerization Reactors' docs page for the full reasoning.
8 unit ops • NRTL
199 3
View & openSour-gas sweetening — six-category footprint
A fuel-fired feed-gas heater, acid-gas removal, and a VOC purge — vented to atmosphere — so the Sustainability panel shows all six impact categories at once: carbon, water, acidification (vented H₂S/NH₃ + combustion NOx), eutrophication (NH₃ + NOx), photochemical ozone (vented benzene) and cumulative energy demand. Illustrative screening vent compositions — a real plant Claus/incinerates the H₂S and controls the VOC rather than venting; the point is to exercise the multi-category footprint on a process that genuinely carries these species. Spec-based separators, so it converges fast and conserves mass.
10 unit ops • PENG-ROBINSON
176 0
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