Blending header — one model, three solve modes — a NRTL process flowsheet
A solvent blending and distribution header, built to demonstrate the capability AVEVA sells SimCentral on and Aspen splits across separate products: one flowsheet that solves steady-state, pressure-driven, and dynamically — no re-modelling between them. A water-rich supply and an ethanol-rich additive each pass a control valve into a common header, down a trunk line, and split at a tee to two consumers.
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Steady-state (Solver menu > Steady-state). You specify the flows (100 and 25 mol/s) and each valve's outlet pressure; the solver reports the blend — 22 mol% ethanol — and the pressure profile down the header. This is the design question: what pressures do I need to move this flow?
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Pressure-driven (Solver menu > Pressure-driven). Now the feeds specify pressure (9 bar) instead of flow, the consumers are pinned at 2 bar, and each valve's cv becomes a resistance law. Flow is a solved unknown, closed by mass balance against every element's resistance. This is the rating question: what flow do I actually get? The valves here are sized for the design duty, so the answer comes back at the same 125 mol/s and the same 6.0 bar header — the two modes agree because they describe one plant. The tee is where it gets interesting: in pressure-driven mode the 60/40 split is not read from split_fractions (that parameter is ignored) — it is solved from the two consumer valves' Cv against the downstream pressures. Halve HCV_UNIT2's cv and the split moves and the total flow drops; do the same in steady-state mode and nothing budges, because there the split is something you asserted rather than something the network decided.
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Dynamic (Solver menu > Dynamic). Initialized from the steady-state solution, step the additive feed to 98 mol% ethanol and watch the blend move: the header responds first, then each consumer lags it by its own holdup, all settling at 23.6 mol% — the value a hand mass balance gives, ((100x0.05) + (25x0.98))/125.
Modeling assumptions & limitations
- 1The dynamic mode is composition dynamics at fixed hydraulics (a standard simplification — the flows stay at their steady-state values, so this is not a pressure transient); the pressure-driven nodal solver uses a representative composition for pipe density inside a split, exact for the single-fluid case here and screening-level for a genuinely multi-fluid ΔP. Neither is a limitation of the flowsheet — both are documented bounds of the engines, stated so the demo is not read as more than it is.
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- Rigorous NRTL thermodynamics, solved by the same engine every simulation runs on.
- 4 unit operations modeled: 4× HCV Unit2, Header, Trunk, TEE.
- Focus areas: Pressure-driven, Dynamic, One model, Hydraulics, Valve Cv.
- Thermodynamics
- NRTL
- Components
- water, ethanol
- Unit operations
- 4× HCV Unit2HeaderTrunkTEE
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("three-mode-blending-header")
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
Pumped transfer — where the pump curve meets the system
Water pumped from an atmospheric tank through a control valve and a 150 m line into a tank held at 3 bar — the everyday hydraulic question every plant asks of a centrifugal pump: at what flow does it actually run? The pump is given the way a vendor gives it, as three points off the datasheet curve (45 m at shut-off, 39 m at 2 L/s, 21 m at 4 L/s), not as a flow or an outlet pressure. Design (Steady State). The flow is specified (150 mol/s, about 9.7 m³/h) along with each block's outlet pressure; the solver reports the pump's 1.25 kW shaft duty and the pressure profile down the line. Rating (Run Mode > Pressure Driven). Now nothing specifies the flow. The pump follows its curve, the valve its Cv law, the pipe Darcy-Weisbach friction, and the flow is wherever the pump's head equals what the valve, the line and the 2 bar lift into the receiving tank take away — the operating point on a pump-and-system-curve chart. The valve is sized so that point is the design duty: 150 mol/s, 34 m of head, 4.32 bar at the discharge. Throttle it. Set FCV₁₀₁'s opening to 0.5 on its Input sheet and re-run: the flow falls to 93 mol/s and the discharge pressure rises to 4.98 bar, because a pump delivers more head at less flow and rides back up its curve. That is the behaviour the curve encodes and a fixed pressure rise cannot show.
Long-distance phosphate concentrate slurry pipeline (gravity line)
A phosphate concentrate slurry carried 187 km downhill from a mine plateau to a coastal fertilizer complex, the shape of OCP's Khouribga to Jorf Lasfar line, rated segment by segment as a Bingham plastic. The publicly stated figures used are: the 187 km length (Rusconi, Lakhouaja & Kopuz, 'The Design and Engineering of the 187 km Khouribga to Jorf Lasfar Phosphate Slurry Pipeline', Procedia Engineering 138 (2016) 142-150), that the line is gravity powered (Wikipedia, 'OCP Group'), Khouribga at 786 m above sea level (Wikipedia, 'Khouribga'; the same article's text says 820 m) and Jorf Lasfar on the Atlantic coast, taken here at sea level. Everything else is REPRESENTATIVE, not OCP data: the 0.75 m bore, the 1.6 m/s velocity (about 2,580 t/h of solids), 60 wt% solids, the five-segment profile with a 30 m ridge, the 5 bar head station pressure, and the rheology. Solid density 3150 kg/m3 is fluorapatite's specific gravity of 3.1-3.2 (Wikipedia, 'Fluorapatite'); its molar mass 0.5043 kg/mol is Ca₅(PO₄)3F from IUPAC 2021 atomic weights. The Bingham yield stress (5 Pa) and plastic viscosity (15 mPa s) are illustrative values chosen by us: no published rheology for this concentrate was reachable, and a real design uses the measured flow curve of the slurry it will carry. What the line shows, solved: the slurry is 1,690 kg/m3 and 32 vol% solids; it runs turbulent (Bingham Reynolds 1.35e5 against Hanks' transition at 4.4e4, Hedstrom 2.1e7, Darby-Mun-Boger friction), 85% above its laminar-turbulent transition velocity of 0.86 m/s, which is the operating limit a non-settling slurry is held to. Friction costs 52 kPa per km, 9.8 MPa over the line, against 13.0 MPa of static head gained on the mixture density, so the line needs no pumps, consistent with the gravity-powered description; the 37.6 bar left at the terminal is the excess head a real gravity line throttles in choke stations. The pressure dips to 10 bar at the top of the ridge, the point that would fall first if the flow rose. Each segment's Hedstrom and Reynolds numbers, regime, friction factor, static head and margin are in the pipe's Results tab. Honest scope: steady state only (no slack flow in the descending legs, no startup or shutdown transient, no water-hammer); the rheology is a constant Bingham fit at one temperature; no heat transfer; the profile is five straight segments, not a survey; and this example is not validated against OCP operating data.
Ethylene 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).
Pressure-swing ethanol dehydration (Gᴱ mixing rule)
Ethanol–water is the classic azeotrope, and pressure-swing distillation breaks it without an entrainer: the azeotrope moves with pressure, so a low-pressure column and a high-pressure column pass each other's azeotropic distillate and each recovers a pure product. The whole process only works if the property package tracks that shift — which is exactly where a conventional package choice falls between two chairs. This flowsheet runs the high-pressure column at 15 bar on pr-mhv1: Peng-Robinson with an MHV1 excess-Gibbs mixing rule, so the cubic equation of state gets its attraction parameter from NRTL's excess Gibbs energy instead of from a single binary interaction constant. Switch the thermo package (Solver menu) and compare the predicted azeotrope: | package | 1 atm | 15 bar | valid at 15 bar? | |---|---|---|---| | NRTL | 0.891 | 0.802 | no — γ-φ is a low-pressure formulation (~10 bar) | | Peng-Robinson (kij) | 0.586 | 0.613 | yes, but a kij cannot represent this azeotrope | | pr-mhv1 | 0.949 | 0.798 | yes | (mole fraction ethanol; the repo's DECHEMA-validated 1 atm anchor is 0.894.) At 15 bar pr-mhv1 lands within 0.005 of NRTL while remaining a genuine equation of state, whereas plain Peng-Robinson is off by ~0.19 and puts the azeotrope in the wrong place entirely. Selecting nrtl here also trips the applicability guard, which warns that the activity model is past its pressure ceiling and names the fix. The flowsheet demonstrates the mechanism on itself. Drop the column pressure to 1 atm and re-run, changing nothing else: the solve fails with SPEC_THERMODYNAMICALLY_IMPOSSIBLE, because at atmospheric pressure the requested bottoms purity sits beyond the azeotrope and no column can reach it. At 15 bar the same specification converges and the bottoms leaves at x_EtOH ≈ 0.924 — past the atmospheric azeotrope of 0.894, which is precisely the composition an atmospheric column cannot cross.
Phosphoric acid concentration: steam evaporator baseline (29 → 54% P2O5)
The conventional wet-process step, at the scale of one Jorf Lasfar concentration line: 138 t/h of 29% P₂O₅ acid, heated by 3.5 bar LP steam in a graphite exchanger and flashed under vacuum (0.12 bar) to 54% P₂O₅, evaporating 64.0 t/h of water. The steam feed is tuned so the concentrate lands on 54.0 wt% P₂O₅ (the user variable p2o5_wt_product), which takes 73.6 t/h of steam — 1.84 t steam per tonne of P₂O₅, 44.5 MW of condensing duty. That is the single-effect ideal; the published plant benchmark of ~2.8 t/t carries exchanger approach, losses and off-design operation on top. The point of the number here is what it costs the site: at Jorf Lasfar this steam is a co-product of the exothermic sulfuric-acid plants, which is the fact any electric alternative has to beat. Compare the two sibling examples, phosphoric-acid-concentration-microwave and -hybrid. Model scope, stated up front. The acid runs on the brine package, which carries phosphoric acid as a non-volatile molecular solute with its CRC liquid heat capacity (145 J/mol/K) — the streams show the real H₃PO₄/water compositions and the acid's sensible heat is in the balance — and a water activity fitted to measured data: binary boiling points (Li 2017, NIST TRC ThermoML Archive) and 20 °C vapour pressures up to 85 wt% (Kirk-Othmer), with a held-out error of 2% in water activity. The boiling-point elevation is therefore the fitted one, 23.5 K at 54% P₂O₅ and 0.12 bar (the ideal, Raoult's-law activity this replaced gave 9 K). Checked against a boiling point the fit never saw, it puts 85 wt% acid at 164 °C at atmospheric pressure against a measured 158 °C. Above 18 mol% acid the temperature dependence rests on one coefficient and that single check, so read the concentrate temperature to within a few kelvin. No heat of dilution is carried (about 1.5% of the latent duty at 54% P₂O₅). The 320 K feed stands in for a hotter plant feed. The acid heated at 1 atm here partly boils in the exchanger (the model's fitted boiling point at 1 atm); the real acid is kept liquid under static head and flashes in the chamber.
Phosphoric acid concentration: microwave heating (29 → 54% P2O5)
The same duty with the steam exchanger replaced by volumetric microwave heating: 44.5 MW absorbed in the acid, then the same vacuum flash to 54.0 wt% P₂O₅ and the same 64.0 t/h of water removed — the microwave does not remove water, it supplies the latent heat. At a 65% wall-plug magnetron efficiency (915 MHz industrial units reach ~85%) that is 68.5 MW of electricity, 1,710 kWh per tonne of P₂O₅ (1,310 at 85%). The comparison that decides it is the energy carrier, not the heating mechanism: at Jorf Lasfar the baseline's 1.84 t/t of steam is a co-product of the sulfuric-acid plants, and the site turns that steam into electricity at roughly 30%. Sending it through a turbine, a magnetron and back into the acid delivers about a fifth of the heat the exchanger delivers directly (0.30 × 0.65 ≈ 0.2), so on this site the microwave route needs roughly five times the primary steam energy of the baseline. Where microwaves do earn their place is not here but at the superphosphoric end (>70% P₂O₅, viscous, fouling, where the recent literature targets them), and an electric route for the 29-54 step should be compared against mechanical vapour recompression, which reuses the latent heat at a coefficient of performance of 10-30. Sweep the absorbed duty to see the product concentration and the electricity follow it. Model scope, stated up front. The acid runs on the brine package, which carries phosphoric acid as a non-volatile molecular solute with its CRC liquid heat capacity (145 J/mol/K) — the streams show the real H₃PO₄/water compositions and the acid's sensible heat is in the balance — and a water activity fitted to measured data: binary boiling points (Li 2017, NIST TRC ThermoML Archive) and 20 °C vapour pressures up to 85 wt% (Kirk-Othmer), with a held-out error of 2% in water activity. The boiling-point elevation is therefore the fitted one, 23.5 K at 54% P₂O₅ and 0.12 bar (the ideal, Raoult's-law activity this replaced gave 9 K). Checked against a boiling point the fit never saw, it puts 85 wt% acid at 164 °C at atmospheric pressure against a measured 158 °C. Above 18 mol% acid the temperature dependence rests on one coefficient and that single check, so read the concentrate temperature to within a few kelvin. No heat of dilution is carried (about 1.5% of the latent duty at 54% P₂O₅). The 320 K feed stands in for a hotter plant feed. Microwave penetration depth (about a centimetre in a conductive acid at 2.45 GHz) and the HF attack on quartz windows are equipment questions this model does not carry.