Quench-converter ammonia synthesis loop — a PENG-ROBINSON process flowsheet
The multi-bed quench converter BASF first installed in 1942, which displaced the tube-cooled converters before it, running inside a complete 200 bar synthesis loop. Ammonia synthesis is equilibrium-limited and exothermic, so the catalyst wants to run hot for rate and cool for equilibrium, and no single adiabatic bed can do both. The quench converter's answer is mechanical: split the loop gas, send 55% through the interchanger into bed 1 and inject the other 45% as cold shots between the beds, so each bed heats up adiabatically and each quench pulls it back down. What it computes: the sawtooth, 673 → 766 K in bed 1, quenched to 689 K and out at 760 K, quenched to 712 K and out at 766 K; 12.5 mol% ammonia at the converter exit, in the 12-18% band real quench converters deliver, at 20.9% nitrogen conversion per pass; 44.6 mol/s of 97.8% liquid ammonia off the 250 K separator; and argon and methane held at 3.3% and 4.2% in the loop by a 3% purge, with the recycle closed by a Wegstein tear. The acid test is the counterfactual: one adiabatic bed producing that same 12.51 mol% ammonia exit ends at 834.7 K — 562 C, past the sintering limit of promoted-magnetite catalyst — while the three-bed quench converter delivers the identical duty with a 766 K (493 C) peak.
Modeling assumptions & limitations
- 1Each bed is a specified-conversion adiabatic reactor, so the model computes the THERMAL consequence of a given quench split faithfully but does not predict the conversion itself — the equilibrium ceiling that motivates the design is an input to the story here, not an output of it, and a kinetic or equilibrium bed model is the next increment
- 2The feed/effluent interchanger is represented by two specified-temperature heaters rather than a coupled exchanger, so its area and approach are not checked
- 3No catalyst kinetics, bed pressure drop, or converter sizing
- 4The 2.2% dissolved hydrogen, nitrogen and argon in the liquid ammonia is a real separator result, not an artifact — a plant recovers it in a letdown flash that is not modeled here
- 5This is the converter class BASF pioneered, not a reproduction of a specific BASF converter. Closed loop balances of this kind are what an acceptance test under VDI 2048 reconciles plant measurements against.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 5 unit operations modeled: 3× Qmix2, 3× Chill, 2× Purgesplit, 3× BED3, SEP.
- Focus areas: Ammonia, Haber-Bosch, Quench converter, Adiabatic beds, Recycle convergence, VDI 2048.
- Thermodynamics
- PENG-ROBINSON
- Components
- n2, h2, ammonia, argon, methane
- Unit operations
- 3× Qmix23× Chill2× Purgesplit3× BED3SEP
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("quench-converter-ammonia-loop")
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
High-recycle ammonia loop (equation-oriented)
A tight, high-recycle ammonia synthesis loop built to show why a modern simulator solves recycles the way legacy sequential-modular tools can't. Fresh syngas (N₂ + 3H2, with argon inert) mixes with a large recycle, reacts to only ~10% per pass, chills so ammonia condenses out as product, and the unreacted gas recycles — a recycle-to-fresh ratio of ~5:1, with argon building up until a small purge balances it. Run this in Equation-Oriented mode (Solver menu > Mode > Equation-oriented). In the default sequential-modular mode the solver tears the recycle and iterates Wegstein ~78 times to close the loop; the equation-oriented solver instead makes every inter-unit stream a global unknown and closes all ~35 of them in one simultaneous Newton solve — the same simultaneous approach AVEVA SimCentral / gPROMS / IDAES use, and the reason tightly coupled recycles that crawl (or stall) in sequential-modular converge cleanly here.
aMDEA closed solvent loop (activated-MDEA acid-gas removal)
The activated-MDEA (aMDEA) acid-gas removal process BASF developed at Ludwigshafen — methyldiethanolamine promoted with piperazine — run as a genuinely CLOSED solvent loop: the regenerated lean amine is cooled, pumped back to absorber pressure and returned to the absorber, with a small side bleed and a demin-water/amine makeup. The companion 'mixed-amine-acid-gas-treating' showcase deliberately leaves that loop open (the regenerated solvent is a product); closing it is what this example adds, and it changes what the model can tell you. Sour gas at 50 bar (5% CO₂, 3% H₂S in methane) is contacted with lean solvent; the rich amine is heated, let down to 1.8 bar and stripped; the lean solvent returns through a cooler and a pump; a 3% bleed purges degradation products; makeup replaces what leaves. One Wegstein tear on the lean stream closes it. The headline result is one no open-loop model can produce: the lean-solvent composition is not specified anywhere in the flowsheet — it is the fixed point of the loop's own water and amine balance — and it converges to 87.7 mol% water / 10.2% MDEA / 2.0% piperazine, which is 41 wt% MDEA and 5.9 wt% PZ (about 3.6 and 0.7 mol/L at a typical 1.04 g/cm3 solvent density), inside the concentration window BASF's own aMDEA patents claim. Also computed: 114 mol/s of circulating solvent for 100 mol/s of sour gas, a rich loading of 0.36 mol CO₂ + 0.21 mol H₂S per mole of amine, treated gas that is pure methane, a 39 mol/s acid-gas overhead, and 0.23% hydrocarbon slip into it. Sweeping the stripping steam traces the loop's water balance: more steam carries more water overhead, so the circulating inventory shrinks from 225 to 53 mol/s across the sweep — a closed-loop coupling that simply does not exist in an open-loop model. Balance closure is the precondition for an acceptance test under VDI 2048 (control and quality improvement of process data by correction calculation, for operation and acceptance tests in energy technology and the chemical industry); the same variance-weighted least-squares correction that standard is built on is available on solved results through the data-reconciliation tool.
Jet loop reactor: nitrobenzene to aniline
A circulating loop reactor of the kind BASF and Buss built for strongly exothermic three-phase hydrogenations — here nitrobenzene to aniline (C₆H₅NO₂ + 3 H₂ → C₆H₅NH₂ + 2 H₂O, -443 kJ/mol). Fresh nitrobenzene and hydrogen are injected into a large circulating liquid stream; the reactor itself runs adiabatic and the reaction heat is taken out by a heat exchanger in the EXTERNAL loop, which is the whole architectural point — the exchanger area is set independently of the reactor, and the circulation rate, not a cooling jacket, is what holds the temperature. A gas separator vents the excess hydrogen, 5% of the liquid is taken off as crude aniline, and the rest is pumped back. What it computes: a 19:1 recycle-to-product ratio holds the adiabatic reactor to 429.7 K in / 494.3 K out, a 64.6 K rise, with the loop cooler removing 4.66 MW; overall nitrobenzene conversion is 99.98% (99.70% per pass) and the crude leaves at 34.7% aniline / 64.9% water. Counting the vent as well as the crude, one aniline is made per two water, which is the stoichiometric mass-balance check on the whole loop — the crude by itself runs slightly water-lean because the vent carries water vapour off with the excess hydrogen. The acid test is what happens without the loop: the same feed in one adiabatic once-through reactor is already at 627 K by 30% conversion and runs off the top of the model's temperature range well before full conversion. That gap is the reason the architecture exists.
Ammonia refrigeration cycle
A single-stage vapor-compression refrigeration loop using ammonia — the classic industrial (rather than HFC) refrigerant — condensed to subcooled liquid, throttled through a valve, and superheated back to vapor in the evaporator before recycling (inspired by ChemSep's Refrigeration_Ammonia-30C reference case).
Green ammonia synthesis
An equilibrium reactor runs N₂ + 3H₂ ⇌ 2NH₃ on green-hydrogen syngas (Keq illustrative) — the new-energy leapfrog workflow.
Refinery sour water stripper (NH₃ + H₂S)
The standard refinery sour water stripper: sour water carrying ammonia and hydrogen sulfide is steam-stripped in a 10-stage column, sending both overhead as sour gas and returning stripped water fit for reuse. Runs on the new sour-water weak-electrolyte package, which is what makes the result meaningful — ammonia and H₂S suppress each other's volatility (ammonia raises pH and holds sulfide down as HS⁻; H₂S lowers pH and holds ammonia down as NH₄⁺), and heat reverses both, which is precisely why a stripper works. The two removals come out asymmetric for the real reason: H₂S strips essentially completely while ammonia, five orders of magnitude more soluble, is the duty that sets the steam rate.