Feed-effluent preheater — duty from the flowsheet, geometry from EDR — a PENG-ROBINSON process flowsheet
A feed/effluent preheater, built so the shell-and-tube rating in the Analysis panel has a real duty to rate. The flowsheet answers how much heat; the rating answers whether this exchanger can move it — the split Aspen sells as EDR, and it had no curated example.
From the flowsheet. Hot reactor effluent (130 mol/s at 420 K) preheats 120 mol/s of cold feed to 360 K, transferring 1.53 MW and leaving the hot side at 373 K, against an LMTD of 66.4 K. Those are the numbers you carry into the rating.
The rating (Analysis > HX design). Put a candidate bundle against that duty — a 0.6 m shell, 320 tubes of 19 mm OD on a 4.88 m length, two tube passes, 0.25 m baffle spacing — and the Bell-Delaware method returns U = 681 W/m2K, 93.2 m2 available against 53.6 m2 required: 74% over-surface, adequate. It also exposes the correction factors that actually decide the shell-side coefficient (segmental-cut j_c = 0.91, leakage j_l = 0.67, bypass j_b = 0.54, combined 0.33), which is where a real rating lives — most of the difference between an ideal bank and the bundle you can buy is leakage and bypass.
Reading the margin. 74% over-surface is generous, not automatically right: it buys fouling allowance and turndown, and costs capital and residence time. The rating is the tool for trading those off — shrink the bundle and watch the margin close.
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Modeling assumptions & limitations
- 1** Shell-side characterization (Reynolds, Prandtl, conductivity, tube-side coefficient) is supplied as screening input rather than derived from the stream, so this sizes and checks a bundle, it does not replace a vendor's thermal design. The exchanger in the flowsheet is specified by outlet temperature; its own `u_a` rating mode is the alternative when you want the duty to fall out of the geometry instead.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 1 unit operations modeled: FEED Preheater.
- Focus areas: Heat exchanger rating, Bell-Delaware, EDR, Shell and tube.
- Thermodynamics
- PENG-ROBINSON
- Components
- n_hexane, n_heptane
- Unit operations
- FEED Preheater
Opens in a new tab, loaded straight into the app — no setup.
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("feed-effluent-preheater-rating")
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
LNG 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.
Gas-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.
Deep 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).
Gas compressor air-cooled aftercooler (fin-fan)
A natural-gas booster compressor followed by an air-cooled (fin-fan) aftercooler — the standard way to reject compression heat where no cooling water is available. The compressor raises the gas from 8 to 24 atm (hot discharge ~150 °C); the air cooler then rejects that heat to ambient air, cooling the gas back to 49 °C. Unlike a plain cooler, the air_cooler op closes the air side: from the process duty and the 35 °C design ambient it solves the air mass flow (a 15 °C air rise) and reports the fan power from the given fan static pressure. Honest scope: screening air-side model (fixed cp_air, ideal-gas air density, no fin/row geometry rating); an air cooler cannot cool below ambient, so the 49 °C target sits safely above the 35 °C air inlet.
Hydrocracking reaction section
A refinery hydrocracker: heavy VGO (modeled as n-dodecane) plus excess H₂ is cracked over catalyst into lighter products via a discrete lumped first-order kinetic network, then flashed to knock out recycle H₂/light gas from the liquid product (Peng-Robinson). Conversion is set by reactor temperature and LHSV.
Hydrocracking fractionation train
The standard downstream train a hydrocracker reaction section feeds into: a high-pressure separator knocks the H₂-rich recycle gas off the reactor effluent, a letdown valve drops the liquid to low pressure for a second flash (LPG-range off-gas), then a fractionator (crude_distillation, one side draw) splits what remains into light naphtha, a kerosene/diesel cut, and unconverted oil bottoms. A textbook train topology (Gary & Handwerk-style HP-sep → letdown → LP-sep → fractionator), not a replication of any specific published paper's numbers — the reaction lumps/kinetics are the same illustrative n-paraffin network as the 'hydrocracker-unit' example, not a real assay.